A new perspective on tetrapod phylogeny

Chapter 2 A New Perspective on Tetrapod Phylogeny Michel Laurin Robert r. Reisz introduction The origin of amniotes has always attracted much attention, and early studies proposed several potential close relatives of amniotes. Most notable among these are the articles by Carroll, who, following Romer (1950), proposed that anthracosaurs, such as gephyrostegids and Solenodonsaurus, were the most plausable ancestors of amniotes (Carroll, 1969, 1970a). Recent discussions largely agreed with Carroll and focused almost exclusively on diadectomorphs and seymouriamorphs (Gauthier et ai, 1988; Laurin and Reisz, 1995). Similarly, several potential relatives of modern amphibians have been suggested (Parsons and Williams, 1963; Carroll and Currie, 1975; Carroll and Holmes, 1980) but most studies have only dealt with temnospondyls (Bolt, 1979; Trueb and Cloutier, 1991). Milner (1993) was one of the first to compare hypotheses on the origin of lissamphibians in which temnospondyls and lepospondyls were considered. Amniote Origins Copyright© 1997 by Academic Press, Inc. All rights of reproduction in any form reserved. 9 10 M. Laurin and R. Reisz Relatively few large-scale phylogenetic studies on early tetrapods have been performed, and the origin of amniotes has generally been studied separately from the origin of lissamphibians. Studies on the origin of amniotes usually only dealt with anthracosaurs (Carroll, 1970a; Gauthier et al, 1988) because these have been presumed to be the closest relatives of amniotes. A consensus emerged that Diadectomorpha is the sister-group of Amniota whereas seymouriamorphs are among the next closest relatives of amniotes (Panchen and Smithson, 1988; Laurin and Reisz, 1995). Research on the origins of lissamphibians concluded that "dissorophoids" were the closest relatives of lissamphibians (Trueb and Cloutier, 1991). The latest and most comprehensive study on the origin of amniotes was performed by Carroll (1995) and was consulted extensively for the present study. Most of the characters used in this study (Appendix 1) were taken from or modified from Carroll's insightful manuscript and from other phylogenetic studies (Gauthier et al, 1988; Milner, 1988; Panchen and Smithson, 1988; Trueb and Cloutier, 1991), but all were recoded from specimens or the descriptive literature. In addition to including early amniotes and anthracosaurs, Carroll (1995) considered lepospondyls and temnospondyls. This inclusive and judicious choice of taxa yielded new insights into the origin of amniotes, such as the hypothesis that lepospondyls are closely related to diadectomorphs and amniotes. If this is accurate, seymouriamorphs are not as closely related to amniotes as previously believed. This conclusion is relevant to studies on the origin and early evolution of amniotes because using lepospondyls instead of seymouriamorphs as a second outgroup could affect the polarity of several characters. Few phylogenetic studies considered the origin of amniotes and lissamphibians in the context of a global analysis of tetrapod relationships. However, this approach is necessary in order to Figure 1. Most parsimonious tree. The nodes are numbered in alphabetical order from the in-group node up. When a name is given, the letter designating the node is omitted but it is still reserved for this node. Several clades are named in the text but could not be labeled on the figure. These include the following clades: K (Embolomeri), N (Seymouriamorpha), Y (Apoda), Z (Gymnophiona), AA (Salientia), AB (Anura) and AD (Diadectomorpha). + New Perspective on Tetrapod Phytogeny 11 3 3) ~ CD B) ~ Osteolepiformes Panderichthyidae Acanthostega Ichthyostega Crassigyrinus Loxommatidae Colosteidae Dendrerpeton Ecolsonia Tersomius Amphibamus Proterogyrinus Archeria Gephyrostegidae Kotlassia Seymouria Ariekanerpeton ATstopoda Adelogyrinidae Nectridea Pantylus Rhynchonkos Brachystelechidae Lysorophia Eocaecilia Rhinatrematidae Ichthyophiidae Hynobiidae Proteidae Sirenidae Triadobatrachus Discoglossidae Pipidae Limnoscelis Diadectes Synapsida Captorhinidae Procolophonidae 12 M. Laurin and R. Reisz determine which early terrestrial choanates are relatives of amniotes,which are relatives of lissamphibians, and which are relatives of the crown group that has been called Tetrapoda (Gauthier et al, 1989). The first large-scale phylogenetic study of tetrapods based on a data matrix (Fracasso, 1983) did not gain general acceptance and only a condensed tree without a supporting matrix was published (Fracasso, 1987). Panchen and Smithson (1988) published the first discussion of tetrapod phylogeny that was extensively supported by polarized characters. Panchen and Smithson concluded that lissamphibians are part of Temnospondyli. According to them, successively more remote relatives of this clade include Microsauria, Colosteidae, Nectridea, and Ichthyostegidae. They considered Diadectomorpha to be the sister group of Amniota, and that Seymouriamorpha, Anthracosauroideae, Crassigyrinus, and Loxommatoidea were related to this clade. Therefore, all known terrestrial Paleozoic choanates except ichthyostegids were part of the crown group defined by lissamphibians and amniotes, according to Panchen and Smithson. This implied that the evolutionary lineage leading to amniotes had diverged from the amphibian lineage in the Devonian. Panchen and Smithson's phylogeny was probably the best supported phylogeny of tetrapods, but it was not based on a data matrix (or the matrix was not published). The present study is the first discussion of tetrapod evolution based on a computer-assisted phylogenetic analysis of a data matrix including both amniotes and lissamphibians. methods Representative taxa of all the major groups of Paleozoic choanates and modern amphibians were selected (Appendix 2). The terminal taxa are restricted to small, well-defined groups whose monophyly is well established. This procedure allows the monophyly of large taxa to be tested and avoids the problematic reconstruction of the primitive condition of relatively diverse taxa. Therefore, taxa such as Seymouriamorpha and Microsauria are not included as terminal taxa but are represented by a sample of genera (Fig. 1). Thirty-eight taxa (including two outgroups) and 157 characters (Appendix 1) were used in this study. Polymorphism within terminal taxa was coded when the primitive condition for a taxon could not be reconstructed New Perspective on Tetrapod Phylogeny 13 with confidence. Partial uncertainty (when a taxon can possess a subset of the states only) was also coded. PAUP 3.1.1 and MacClade 3.0 were used to analyze the data. Because MacClade allows partial uncertainty and polymorphism in a matrix but PAUP does not, the tree lengths reconstructed by these two programs do not coincide and the numbers given below were obtained from MacClade (Maddison and Maddison, 1992). In PAUP, multistate taxa were interpreted as polymorphism (rather than uncertainty). Interpreting the multi state taxa as uncertainty yields the same phylogeny. All characters were equally weighted and unordered. Characters were optimized by the DELTRAN algorithm of PAUP 3.1.1 (Swofford, 1993). Alternate reconstructions (when the optimization is ambiguous) were examined using MacClade 3.0. All the polytomies present in the consensus trees discussed are interpreted as soft. Therefore, character optimizations close to Lissamphibia were examined in MacClade 3.0 and differ somewhat from the optimizations given by PAUP 3.1.1 because the latter supports only hard polytomies. MacClade was also used to examine character optimization at the base of the tree. Therefore, the list of autapomorphies of nodes A-C (Appendix 3) do not follow exactly the PAUP output. The heuristic search algorithm was used with the following parameters: seven trees were kept in the stepwise addition sequence, 20 iterations were done using the random addition sequence, the tree bisection-reconnection swapping algorithm was chosen, zero- length branches were collapsed, and all the most parsimonious trees were saved. Because of time limitations and the extensive amount of time required to analyze large data matrices, some taxa are only represented by a few members when many more would have been required to illustrate the full range of morphological variations present in a taxon. This is especially true of temnospondyls, amniotes, microsaurs, and lissamphibians. Temnospondyls are extremely speciose and morphologically diverse (Milner, 1990). Two early, basal temnospondyl taxa (Colosteidae and Dendrerpetori) are included to allow determination of the affinities of temnospondyls to other groups of Paleozoic choanates (Fig. 2), whereas three dissorophoids are included to test the 14 M. Laurin and R. Reisz hypothesis that temnospondyls gave rise to lissamphibians (Figs. 3 and 4). Three dissorophoids were required because Amphibamus and Tersomius have been extensively compared to lissamphibians but are relatively poorly known (Carroll, 1964), whereas Ecolsonia has not been compared as frequently but is a much better known genus (Berman et al, 1985). No branchiosaur was included in this study because they are probably based on immature specimens (Schoch, 1992). Amniotes are also very diverse and speciose, and their phylogeny and anatomy have been studied in detail (Laurin and Reisz, 1995). Therefore, this analysis will only consider three taxa (synapsids, procolophonids, and captorhinids) representing the main groups of early amniotes (synapsids, anapsids, and romeriids in the terminology of Gauthier et al, 1988). Eleven families and two suborders of microsaurs were recognized by Carroll and Gaskill (1978). Three of the best known families and both suborders are represented in this analysis. Pantylus and Rhynchonkos (the sole representatives of Pantylidae and Rhynchonkidae, respectively) represent the Tuditanomorpha (which includes 7 families) whereas Brachystelechidae represent the Microbrachomorpha (known by 4 families). These taxa were chosen Figure 2. Skulls of terrestrial choanates in dorsal view. A, Ichthyostega sp.; B, Megalocephalus pachycephalus (Loxommatidae); C, Greererpeton burkemorani (Colosteidae); D, Tersomius texensis; E, Proterogyrinus scheelei; F, Seymouria baylorensis; G, Limnoscelis paludis; H, Captorhinus laticeps (Captorhinidae). Most of the illustrations were redrawn from the following sources: A, Carroll (1988); B, Beaumont (1977); C, Smithson (1982); D, Carroll (1964); E, Holmes (1984); G, Fracasso (1983); H Heaton (1979). In this figure and all the following, the skulls were drawn at various scales to make their lengths comparable. Scale bar equals 1 cm. Abbreviations used in Figs. 2-4: apf, anterior palatal fenestra; at, anterior tectal; be, braincase; bo, basioccipital; ch, choana; ep, epipterygoid; ex, exoccipital; f, frontal; fo, fenestra ovalis; fp, frontoparietal; in, internasal; it, intertemporal; j, jugal; 1, lacrimal; m, maxilla; mp, maxillopalatine; n, nasal; nc, nasal capsule; o, orbit; ob, os basale; oc, otic capsule; op, opisthotic; os, orbitosphenoid, p, parietal; pal, palatine; pf, postfrontal; pi, pleurosphenoid; pm, premaxilla; po, postorbital; pop, preopercular; pp, postparietal; prf, prefrontal; pro, pro-otic; ps, parasphenoid; pt, pterygoid; q, quadrate; qj, quadratojugal; s, stapes; sm, septomaxilla; so, supraoccipital; sph, sphenethmoid; sq, squamosal; st, supratemporal; t, tabular; tf, tentacular fossa; v, vomer. ^ 16 M. Laurin and R. Reisz because they are relatively well known and because Rhynchonkos has been closely allied to apodans (Carroll and Currie, 1975). The three orders of lissamphibians are represented by three terminal taxa each. Eocaecilia, the newly described Jurassic apodan, was included because it retains several primitive characters lost in all other known apodans (Jenkins and Walsh, 1993). Rhinatrematidae and Ichthyophiidae represent gymnophiones because these two families are believed to have diverged early from other caecilians (Duellman and Trueb, 1986). Urodeles have a poor fossil record and are represented by three extant families: Hynobiidae, Sirenidae, and Proteidae. The first two families were included because they are believed to have diverged early from other urodeles, whereas proteids are well known (Duellman and Trueb, 1986). Salientia is represented by Triadobatrachus (the oldest known salientian) and two basal, extant families (Discoglossidae and Pipidae). Much of the data come from descriptive literature, but specimens of many taxa were examined, including Amphibamus, Lysorophia, Diplocaulus (Nectridea), Seymouria, Ariekanerpeton, Alytes (Discoglossidae), Pipa, Xenopus (Pipidae), Hynobius (Hynobiidae), Necturus (Proteidae), Siren, Pseudobranchus (Sirenidae), Epicrionops (Rhinatrematidae), Ichthyophis (Ichthyophiidae), Diadectes, Synapsida, Captorhinidae, and Procolophonidae. Space limitations prevent us from listing all the primary literature used to gather the anatomical data used in the analysis, but many of these references can be found in Carroll and Gaskill (1978), Duellman and Trueb (1986), Reisz (1986), Carroll (1988), Gauthier et al. (1988), Trueb and Cloutier (1991), Clack (1994), and Laurin and Reisz (1995). Some characters were problematic because of the wide morphological diversity of the taxa. For instance, all lepospondyls except for some aistopods and some nectrideans have lost a temporal bone (Fig. 3). We have considered the remaining element to be a tabular because this is how it has usually been interpreted in microsaurs and in lysorophians (Carroll and Gaskill, 1978; Wellstead, 1991). Therefore, we assumed the loss of a temporal element in lepospondyls to be homologous. We have also assumed that the New Perspective on Tetrapod Phylogeny 17 tabular-squamosal element of adelogyrinids was a squamosal because the tabular has been lost more frequently in various tetrapods than the squamosal. The composition of the centrum (character 102 in the appendices) of lepospondyls and lissamphibians has been debated (Wake and Lawson, 1973) and partial uncertainty was coded when a single element was present throughout the column. Therefore, two conditions were entered for such taxa: centrum composed of a large, circular intercentrum (1), and centrum composed of a large pleurocentrum (5). This was done in an attempt to determine the composition of the centrum in these taxa by looking at the optimization of this character on the most parsimonious tree. The robustness of the clades was established by determining how many extra steps were required to collapse the nodes. A similar procedure has occasionally been used in paleontological studies (Laurin and Reisz, 1995), but it has been first and most often employed by botanists, who called it "decay analysis", "decay index", or "Bremer support" (Mishler, 1994). results Only three most parsimonious tree were found. They require 654 steps and have a consistency index of 0.52. The character optimizations and discussions below are all based on the strict consensus tree (Fig. 1). The consensus tree differs substantially from the commonly accepted phylogeny of tetrapods and has important implications for hypotheses of amniote origins. For instance, Lepospondyli includes Lissamphibia and is closely related to diadectomorphs and amniotes. Previously, seymouriamorphs were considered to be among the closest known relatives of amniotes (Gauthier et al, 1988). In the new phylogeny, Diadectomorpha, Amniota and Lepospondyli form the crown group of terrestrial choanates. Gauthier et al. (1989) defined Tetrapoda as the crown-group of terrestrial choanates. According to Gauthier et al. (1989), Tetrapoda included temnospondyls, embolomeres, seymouriamorphs, diadectomorphs, and amniotes because temnospondyls were thought to have given rise to modern amphibians, whereas embolomeres and seymouriamorphs were thought to be closely related to amniotes. 18 M. Laurin and R. Reisz The new phylogeny changes drastically the composition of this crown group, but the taxonomic implications of this fact will be dealt with elsewhere. In this study, the crown group of terrestrial choanates will simply be called "crown batrachomorphs". Batrachomorpha Save-Soderbergh, 1934, is here defined as all choanates sharing a more recent ancestry with amniotes than with embolomeres. This taxon resembles superficially Batrachosauria as defined by Gauthier et al. (1988), but it is distinct because Batrachomorpha is not part of Anthracosauria as defined by Gauthier et al. (1988), whereas Batrachosauria is. Under the phylogeny presented by Gauthier et al (1988), Batrachomorpha would be a junior synonym of Batrachosauria, but under the new phylogeny Batrachosauria is a junior synonym of Anthracosauria and it cannot be used. Seymouriamorphs, gephyrostegids, Embolomeri, Temnospondyli, loxommatids, Crassigyrinus, and the Devonian choanates Ichthyostega and Acanthostega are successive sister groups of crown batrachomorphs. The phylogenetic analysis allows a new list of autapomorphies of the included taxa to be given (Appendix 3). The new phylogeny also warrants a new taxonomy of tetrapods, but this will be done elsewhere. Most nodes in the tree are designated by one or two letters (Fig. 1), but previously defined taxa are labeled whenever possible. discussion Comparisons with Previous Phytogenies The close relationships between amniotes and lissamphibians is probably the most unorthodox result of this analysis. However, close relationships between some lepospondyls and amniotes have been postulated in the past. Vaughn (1962) suggested that "microsaurs" (probably a paraphyletic group) were closely related to "captorhinomorphs" (another paraphyletic group including early relatives of diapsids). Carroll (1995) produced a phylogeny in which lepospondyls were closely related to amniotes. Lepospondyls have repeatedly been argued to be a paraphyletic group (Carroll and Gaskill, 1978; Milner, 1993; Panchen and Smithson, 1988). However, these arguments were based more on suspected convergence between New Perspective on Tetrapod Phylogeny 19 various lepospondyls than on similarities between some lepospondyls and other terrestrial vertebrates. The only study to which the present phylogeny can be easily compared is Carroll's (1995) phylogenetic analysis of Paleozoic choanates. Most of the eighteen taxa studied by Carroll are also included in the present study, and thus the results are readily compared. Carroll found four equally most parsimonious trees but did not give a consensus tree of these. We produced a strict consensus of Carroll's trees (Fig. 5). Its topology is very similar to the shortest tree found in this study. Indeed, most of the clades found by Carroll have also been found in this study. The only exception consists in the clade including lysorophids, adelogyrinids, and ai'stopods found by Carroll (1995). In this study, nectrideans and various microsaurs seem to share more synapomorphies with lysorophids than with adelogyrinids and ai'stopods. Of course, these results are difficult to compare because the present study includes three clades of microsaurs instead of Microsauria as a terminal taxon, and Carroll omitted lissamphibians from his study. Otherwise, the agreement between these two studies is remarkable and may result partly from a similar choice of characters. The inclusion of lissamphibians in the matrix was essential to this analysis. Without modern amphibians, the phylogeny could have been interpreted as suggesting that lepospondyls were early "reptiliomorphs." Such a conclusion would have been erroneous, even if it had been based on an accurate phylogeny. Therefore, studies of the origin of amniotes should not ignore the position of modern amphibians. Decay Index and Robustness of the Clades In most previous phylogenetic studies of tetrapods, the strength of various clades was assessed by counting the number of synapomorphies linking its members (Gardiner, 1982; Gauthier et al, 1988; Panchen and Smithson, 1988). However, such an approach is fundamentally incomplete in that it does not consider how many characters support alternative clades. Such homoplasy can seriously weaken the strength of a clade and only a few extra steps may be required to collapse a clade supported by several characters. This has been recently recognized and some studies have discussed 20 M. Laurin and R. Reisz characters supporting alternative clades to provide a more realistic assessment of the support for various taxa (Milner, 1993). However, even such an approach is insufficient because it may not give a global assessment of the parsimony of the alternatives. For instance, Milner (1993) listed the characters thought to support close affinities between dissorophoids and lissamphibians, and the characters supporting close affinities between some lepospondyls and lissamphibians. In the present study, an equivalent procedure would have consisted in listing the characters supporting the Lepospondyli or one of its subgroups (as redefined here) and comparing this to a list of synapomorphies linking dissorophoids to lissamphibians. Such an approach only considers the autapomorphies of one node without considering the optimization of all the other characters on the rest of the tree. An even more rigorous approach is to determine exactly how many extra steps are required to collapse the nodes in a phylogeny (Laurin and Reisz, 1995) This number has often been called the decay index (Mishler, 1994). The higher the decay index, the more robust is the node. This method takes into consideration homoplasy and even characters whose optimization is ambiguous. This approach was applied here for selected clades. Several clades in the new phylogeny are only weakly supported and require only one extra step to collapse (nodes B, I, S, V, Y, and Diadectomorpha). The small amount of support for some of these nodes probably results from the lack of available anatomical data. For instance, nectrideans are a fairly diverse group, but no genus is well known. Diploceraspis is represented by well-preserved cranial remains (Beerbower, 1963) but few postcranial remains. Urocordylids are known from several skeletons, but their skulls are poorly preserved and the braincase is often cartilaginous (Bossy, 1976). Figure 3. Skulls of lepospondyls in dorsal view. A, Sauropleura pectinata (Nectridea); B, Pantylus cordatus; C, Rhynchonkos stovalli; D, Brachydectes elongatus (Lysorophia); E, Epicrionops petersi (Rhinatrematidae); F, Siren lacertina (Sirenidae); and G, Pipa pipa (Pipidae). Cartilage is stippled. Some of the illustrations were redrawn from the following sources: A, Bossy (1976); B, Romer (1969); C, Carroll and Currie (1975); D, Wellstead (1991); E, Nussbaum (1977). Scale bar = 1 cm unless otherwise indicated. See the legend to figure 2 for abbreviations. 22 M. Laurin and R. Reisz The apparent paraphyly (or polyphyly) of urodeles is surprising. Urodeles are perhaps not usually perceived as poorly known, but relatively few descriptions of the osteology of the basal families are available, and specimens of these families are not widely available (Duellman and Trueb, 1986). Furthermore, the affinities of urodeles and their phylogeny have often been discussed, but their monophyly has seldom been rigorously tested. Some soft anatomical, biochemical, or behavioral autapomorphies of urodeles may be known, but such characters could not be incorporated into the present study because most of the included taxa are extinct. Therefore, the apparent paraphyly of urodeles is probably an artifact and it is hoped that the present study will stimulate the search for more osteological diagnostic characters of urodeles and publications of osteological descriptions. We do not believe urodeles to be paraphyletic, although this is a remote possibility. Furthermore, the main reason for including lissamphibians in this analysis was to evaluate their relationships to amniotes rather than to study the phylogeny within Lissamphibia. In order to deal adequately with the last topic, many more representatives of extant amphibians should be included. Several clades are strongly supported. Among the most robust are Seymouriamorpha (node N, seven extra steps), node P (crown batrachomorphs, eight extra steps), Lepospondyli (seven extra steps), node U (five extra steps), node W (five extra steps), and Lissamphibia (five extra steps). Fortunately, these nodes are also among the most important clades in this phylogeny. The strength of these nodes is not surprising considering that the origin of all these clades appears to be associated with a radical shift in morphology. Figure 4. Skulls of terrestrial choanates in occipital view. A, Megalocephalus pachycephalus (Loxommatidae); B, Greererpeton burkemorani (Colosteidae); C, Tersomius texensis; D, Proterogyrinus scheelei; E, Seymouria baylorensis; F, Limnoscelis paludis; G, Captorhinus laticeps (Captorhinidae); H, Pantylus cordatus; I, Rhynchonkos stovalli; J, Brachydectes elongatus (Lysorophia); K, Siren lacertina (Sirenidae); L, Pipa pipa (Pipidae). For credits, see the legends to Figures 2 and 3, except for F, redrawn from Fracasso (1983). Scale bar = 1 cm unless otherwise indicated. See the legend to Figure 2 for abbreviations. 24 M. Laurin and R. Reisz Origin of Lissamphibians One of the most surprising results of this analysis is that Lissamphibia seems to be only remotely related to dissorophoids. Most of the discussions during the past quarter century on the origins of modern amphibians have focused on temnospondyls, especially dissorophoids (Bolt, 1969, 1977, 1979; Bolt and Lombard, 1985; Milner, 1988; Trueb and Cloutier, 1991). The results of our analysis suggest that lissamphibians are lepospondyls. Indeed, Lepospondyli, as redefined here, is one of the most robust nodes and requires seven extra steps to collapse. Lepospondyl affinities for lissamphibians have been suggested before (Gregory, 1965), but such views never gained much popularity. Carroll and Currie (1975) suggested that Rhynchonkos was closely related to apodans, whereas Carroll and Holmes (1980) argued that urodeles evolved from microsaurs. Milner (1993) compared support for the hypothesis that all lissamphibians were derived from temnospondyls with the evidence favoring an origin of gymnophiones from microsaurs and an origin of batrachians from temnospondyls. He concluded that only slightly more evidence supported a monophyletic origin of all lissamphibians from temnospondyls than separate origins of gymnophiones from microsaurs and batrachians from temnospondyls. None of these earlier studies were based on a data matrix, and the number of taxa considered was low. Consequently, only a small subset of all the possible hypotheses were considered. The results of the present study differ from these earlier hypotheses in that modern amphibians seem to form a monophyletic group excluding all the known groups of Paleozoic terrestrial vertebrates. Furthermore, Rhynchonkos does not appear to be the closest relative of lissamphibians. Lysorophians share several synapomorphies with lissamphibians, but they have never been considered seriously as close relatives of extant amphibians. Indeed, Wellstead (1991) only discussed affinities between lysorophians and apodans (rather than lissamphibians) and concluded that "there is no Figure 5. Strict consensus of the four equally most parsimonious trees found by Carroll (1995). This tree is identical to the majority-rule consensus of the four most parsimonious trees. The nodes that are also found in Figure 1 have been labeled on this tree; they do not follow the terminology used in Carroll (1995). New Perspective on Tetrapod Phytogeny 25 Eusthenopteron Panderichthys Acanthostega Ichthyostega Crassigyrinus Loxommatids Colosteids Temnospondyls Anthracosaurs Seymouriamorphs Westlothiania Diadectomorphs Amniotes Nectrideans Microsaurs Lysorophids Adelogyrinids ATstopods 26 M. Laurin and R. Reisz autapomorphy linking apodans and lysorophoids." Nevertheless, five extra steps are required to collapse the clade that includes lysorophoids and lissamphibians (node W). The shortest tree in which lissamphibians are closely related to dissorophoid temnospondyls was searched to determine how many extra steps this hypothesis requires. Surprisingly, the shortest tree in which dissorophoids and lissamphibians form a clade requires 33 extra steps (687 steps). This high number of extra steps is unexpected, considering that few studies have argued for lepospondyl origin of lissamphibians, but is readily explained by the sum of autapomorphies of the taxa that include Lissamphibia but not Temnospondyli (nodes W, V, U, T, S, Lepospondyli, nodes P, M, Batrachomorpha, and node J). Most of the characters supporting these nested clades are convergent in the trees in which lissamphibians are closely related to temnospondyls. Therefore, the hypothesis that lissamphibians are derived from temnospondyls can be rejected with confidence. Some readers might object that some of the temnospondyls believed by Trueb and Cloutier (1991) to be the closest relatives of lissamphibians were not included in this analysis. The authors excluded these taxa because they are too poorly known, because some of them may be represented by juvenile postmetamorphic specimens, and because their morphology did not seem to be distinct enough from the dissorophoids already included. Status of Anthracosaurs The paraphyly of anthracosaurs as they were previously understood is unexpected. Our ideas about the phylogeny and relationships of Anthracosauria have varied, but this taxon typically included embolomeres, gephyrostegids, seymouriamorphs, and sometimes diadectomorphs and amniotes (Carroll, 1988; Lombard and Sumida, 1992). Some may be surprised that gephyrostegids do not form a clade with embolomeres, but it takes three extra steps to obtain this topology and only one unambiguous synapomorphy links gephyrostegids to embolomeres in such a tree (the potentially mobile joint between the skull table and the cheek). Seymouriamorphs have been compared to diadectomorphs and amniotes because they were believed to be closely related to them (Heaton, 1980; White, 1939). Indeed, seymouriamorphs were once New Perspective on Tetrapod Phylogeny 27 believed to be an early group of reptiles (White, 1939). Instead, seymouriamorphs now seem relatively remote from amniotes in that they are as closely related to lissamphibians as they are to amniotes. Status of the Crown Group of Terrestrial Choanates The crown group of terrestrial choanates was previously believed to include most known terrestrial choanates as temnospondyls were assumed to be closely related to lissamphibians and anthracosaurs were thought to have given rise to amniotes (Gaffney, 1980; Panchen and Smithson, 1988). Only Devonian taxa, such as Ichthyostega, Acanthostega, Tulerpeton, and the Mississippian choanate Crassigyrinus, were thought to be excluded from this crown-group (Panchen and Smithson, 1988; Gauthier et al, 1989). The position of lepospondyls was problematic and there was no consensus on whether or not they were monophyletic (Carroll and Gaskill, 1978; Carroll, 1988; Panchen and Smithson, 1988). Therefore, most groups of early terrestrial choanates were compared either with modern amphibians (Bolt, 1977) or with amniotes (Carroll, 1970a) to document the origin of these groups of tetrapods. The present phylogeny suggests that these efforts were largely misdirected because only diadectomorphs and lepospondyls are more closely related to one of the two extant clades of tetrapods (Amniota and Lissamphibia) than to the other. A crown group of a similar composition has been suggested by Gardiner (1982). Gardiner's (1982) phylogeny is similar to the new phylogeny, but Gardiner only considered a few taxa. The terminal taxa included in his crown group were Anura, Urodela, Apoda, Aistopoda, Nectridea, and Amniota. Therefore, he did not consider diadectomorphs, "microsaurs", adelogyrinids, or lysorophians. Gardiner believed that ai'stopods and nectrideans formed a clade that was the sister-group of Lissamphibia. Therefore, his monophyletic Lepospondyli excluded Lissamphibia. Nevertheless, his phylogeny agrees with ours in most other details and he believed temnospondyls and loxommatids to be successive sister groups of the crown group of terrestrial choanates. The new phylogeny suggests that amniotes and lissamphibians are more closely related and that they share a longer evolutionary history than previously believed. Previous phylogenies (Panchen and Smithson, 1988) suggested that the evolutionary lineage leading to 28 M. Laurin and R. Reisz amniotes had diverged from the lineage leading to lissamphibians soon after the first terrestrial choanate appeared, in the Devonian. However, the present phylogeny suggests that a diverse terrestrial vertebrate fauna (represented by Ichthyostega, Acanthostega, Crassigyrinus, loxommatids, temnospondyls, embolomeres, gephyrostegids, and seymouriamorphs) existed for several million years prior to the divergence of the amniote and lissamphibian lineages. Therefore, the evolutionary lineage that led to amniotes diverged from the lineage leading to lissamphibians in the Mississippian at the latest. Previous phylogenies (Panchen and Smithson, 1988) suggested that this divergence had occurred in the Upper Devonian, if not earlier. Evolution of Selected Characters The new phylogeny has interesting implications for the evolution of four characters frequently used in considerations of amniote relationships. Tabular-Parietal Contact The tabular-parietal contact has usually been considered to unite embolomeres and seymouriamorphs to diadectomorphs and amniotes (Gauthier et al, 1988), but this character is also present in all lepospondyl groups that have a tabular (Figs. 2 and 3). Therefore, this character is diagnostic of node J (embolomeres and batrachomorphs). Of course, the identity of the temporal element in most lepospondyls is difficult to determine and it has been assumed to be a tabular in this analysis, but even if this element were a supratemporal the presence of a tabular-parietal contact would be an autapomorphy of node J. Some nectrideans also have a supratemporal and the tabular-parietal contact is definitely present in this group (Fig. 3). Transverse Flange of the Pterygoid The transverse flange of the pterygoid has been usually considered to be diagnostic of amniotes and diadectomorphs (Gauthier et al, 1988; Panchen and Smithson, 1988), but it is a synapomorphy of seymouriamorphs, gephyrostegids, diadectomorphs, and amniotes and also appeared convergently in dissorophoids. The transverse flange was lost in lepospondyls (see Appendix 3). New Perspective on Tetrapod Phylogeny 29 Supraoccipital The supraoccipital has often been considered to be a synapomorphy of amniotes and diadectomorphs (Gauthier et al, 1988) and its presence in some lepospondyls (Fig. 4) was often assumed to result from convergence, but it seems to be a synapomorphy of all these taxa. Among the lepospondyls included in this analysis, a supraoccipital is present in Pantylus, Rhynchonkos, brachystelechids, and lysorophians. Nectrideans and lissamphibians appear to have lost this element (this character could not be coded in a'istopods and in adelogyrinids). Parasternal Process of the Interclavicle The parasternal process (long posterior stem) of the interclavicle has been thought to be a synapomorphy of amniotes, diadectomorphs, and seymouriamorphs (Carroll, 1968), but this character seems to be an autapomorphy of the clade that includes all these taxa and lepospondyls. A parasternal process may have been present primitively in lepospondyls because it is present in Pantylus, brachystelechids, and some lysorophians. However, the optimization of this character at the base of Lepospondyli is ambiguous because the interclavicle of adelogyrinids and nectrideans lacks a parasternal process (this character could not be coded in a'istopods). Lissamphibians have lost the interclavicle. Origin of Amniotes The significance of this new phylogeny to the origin of amniotes lies in the recognition of an entirely new set of outgroups beyond diadectomorphs. The new phylogeny indicates that future phylogenetic studies of amniote phylogeny will have to include lepospondyls as outgroups. This has not been a common practice, but it will be necessary if the phylogeny presented here is accepted. Using lepospondyls could certainly help to polarize several characters used in phylogenetic studies of amniotes because they are very different from the seymouriamorphs that were previously used as outgroups. Carroll (1970b, 1991) suggested that early amniotes showed evidence of having passed through a phase in which their skull was reorganized to be adapted to small size (snout-vent length 100 mm). 30 M. Laurin and R. Reisz Carroll's is the most explicit functional scenario on the origin of amniotes and needs to be summarized before it is discussed. Carroll suggested that amniotes evolved from anamniote tetrapods that had direct development and laid their eggs on land, like plethodontid salamanders. According to Carroll, the size of an anamniotic egg is limited by the absence of extraembryonic membranes and by the absence of a mineralized shell because support and gas exchange would be problematic beyond a certain size (10 mm in diameter). Caecilians have large eggs, but this may be possible because of the elastic fibers in the egg capsule and the large filamentous gills of the embryos. Carroll suggests that external gills would not have been present in the embryos of the ancestors of amniotes because the gas exchange is performed by the allantois. These constraints on the egg size of the ancestors of amniotes, together with the correlation between egg size and adult size found in modern amniotes and plethodontids, suggests that our anamniotic ancestors would have been small and that their size could have increased only after the acquisition of the amniotic egg (according to Carroll, extant amphibians can only reach large adult sizes through a long growth period in a larval stage). This apparently explained why the groups suggested by Carroll as the earliest amniotes and their sister groups were generally small. Furthermore, the extensive ossification found in the vertebrae, carpus, and tarsus of early amniotes suggests that the adults were small, like plethodontids in which precocious ossification appears to result in small adult size (growth stops when all the cartilage is replaced by bone). Therefore, there were theoretical reasons to expect the earliest amniotes to be small (Carroll 1970b, 1991), and there was some support in favor of this scenario (such as the small size and extensive ossification of the earliest amniotes). One problem with this scenario is that factors other than egg size may constrain plethodontids. The most obvious of these is the absence of lungs. Without lungs, plethodontids are restricted to small adult size because the surface/volume ratio of the animal must remain high enough to allow the animal's needs in oxygen to be accommodated by cutaneous respiration. Therefore, the small size of terrestrial plethodontids does not necessarily result from the small size of their eggs and from their direct development. Indeed, the polarity New Perspective on Tetrapod Phytogeny 31 of this argument may be reversed. Direct development and terrestrial eggs are also found in some gymnophiones (Duellman and Trueb, 1986). The small size of many gymnophiones may yield further support for Carroll's scenario, but again, other factors may constrain the size of many gymnophiones. The fossorial existence of most of these tetrapods may select for a small size. Furthermore, the correlation between egg size and adult size claimed by Carroll (1991) for most tetrapods is not strong among lissamphibians (Duellman and Trueb, 1986). The suggestion that lepospondyls are close relatives of amniotes may at first appear to lend support to Carroll's scenario because most lepospondyls are small. However, optimization of size on the tetrapod phylogeny indicates that lepospondyls are the only small relatives of amniotes and that small size (snout-vent length 100 mm) does not appear to be primitive for Amniota or larger clades that also include diadectomorphs and lepospondyls. Diadectomorphs, embolomeres, and some, if not all, seymouriamorphs are large. Utegenia, Ariekanerpeton, and Discosauriscus, the only small seymouriamorphs, seem to be only represented by incomplete growth series in which the adults are missing. It is possible that the relatively small size of the earliest amniotes may simply be coincidental or result from taphonomic biases. For instance, most amniotes found at Joggins and Florence, Nova Scotia (two of the localities in which the earliest amniotes were found) were preserved in hollow tree stumps. As the largest stumps had a diameter of only about 30-60 cm, the vertebrates preserved in them were necessarily relatively small. Even here, some of the amniote remains found at Joggins and Florence (Reisz, 1972) were only moderately small (centrum length 5-9 mm), with an estimated snout-vent length of up to 350 mm. In fact, the smallest presumed amniote from Joggins, Archerpeton with an estimated snout- vent length of 60 mm (Carroll, 1964, 1970b), is a tiny microsaur (R. Reisz, personal observation). A survey of Middle Pennsylvanian amniote bearing localities indicates that the size of amniotes found in these sites ranges from 130 to 300 mm in snout-vent length. Furthermore, Carroll's scenario was predicated on the assumption that the earliest known amniotes were basal, an assumption that is not supported by the most recent phylogeny (Laurin and Reisz, 1995). 32 M. Laurin and R. Reisz Figure 6. Evolutionary history of egg retention in extant choanates. This cladogram indicates that the primitive state for egg retention cannot be determined for amniotes or their extant sister taxon on the basis of the available evidence. Therefore, the hypothesis that the origin of amniotes included an intermediate stage in which anamniotic eggs were laid on land is not more parsimonious than the suggestion that the extraembryonic membranes evolved to facilitate extended egg retention. New Perspective on Tetrapod Phytogeny 33 Therefore, very small size is probably not a primitive character for amniotes and this aspect of the scenario proposed by Carroll (1970b, 1991) is not supported by the fossil record. Carroll's hypothesis of transformation from the presumed basal amphibian to the amniotes includes a number of evolutionary modifications of the reproductive process. These involve internalfertilization, abbreviation and elimination of larval stages, laying of eggs in terrestrial locations; and development of extraembryonic membranes and shell. According to Carroll, all of these changes are more or less interdependent and must have occurred concurrently. However, he assumed that the evolution of the amniote reproductive pattern proceeded via an intermediate stage in which anamniotic eggs were laid in damp places on land. We are convinced that this assumption cannot be made because the evolutionary innovation of internal fertilization immediately raises the possibility of embryo retention and embryo-mother interaction (Lombardi, 1994). This is supported by the development of placentation in extant synapsids and frequent placentation in squamates, regardless of whether they lay eggs or not. It is quite reasonable to suggest (Lombardi, 1994) that some of the extraembryonic membranes evolved in an embryo-retaining form, as a pathway for fetal-maternal interaction, rather than a protection from the harsh external environment. Carroll's hypothesis of amniote origins also assumes that the primitive amniote condition involves the laying of eggs on land. Unfortunately, we cannot deduce the reproductive pattern of diadectomorphs, the nearest sister taxon of amniotes. We also have no evidence on the reproductive strategies of the numerous fossil members of the amniote clade because neither embryo-retaining specimens nor nests of Paleozoic or Early Mesozoic amniotes have been found. If we use a cladogram of extant tetrapods, with Latimeria and Dipnoi as outgroups, and investigate the evolutionary history of embryo retention among amniotes, we see the following ambiguous distribution pattern of the two character states (extensive embryo retention absent or present): The nearest relatives of tetrapods have both conditions, with Latimeria showing extensive embryo retention, whereas extant Dipnoi lay eggs at an early developmental stage. Lissamphibia have both conditions. Among extant squamates 34 M. Laurin and R. Reisz we see a bewildering array of reproductive strategies, with frequent placentation as well as extended embryo retention (Blackburn, 1992), but egg laying without extended embryo retention appears to be primitive for sauropsids because all other extant members of this clade crocodiles, birds, and turtles lack extended embryo retention. All extant synapsids (including monotremes and therians) show extended embryo retention. The resultant pattern does not allow us to determine the primitive condition for amniotes (Fig. 6). Therefore, the scenario that the evolution of the amniotic condition involved the intermediate stage of anamniotic eggs being laid on land is not more parsimonious than the alternative suggested here (that extraembryonic membranes appeared to facilitate extensive embryo retention). It is obvious that this aspect of the origin of amniotes needs further study. The fossil record does not support the thesis that the earliest amniotes and their ancestors were small. If the evolutionary innovation of the amniotic egg permitted an increase in the size of the adult, as suggested by Carroll, the fossil record should provide a test for this hypothesis. However, the fossil record indicates that the adult size of amniotes does not show a significant increase in size from the earliest appearance of amniotes in the lower part of the Middle Pennsylvanian until the upper part of the Late Pennsylvanian. Therefore, the main adaptive advantage of the amniotic egg was probably not to allow increase in the size of the adults in the absence of extended larval stages but rather increased chances of survival of the hatchling by reducing the probability of starvation or predation. It is generally assumed that tetrapods primitively practiced a reproductive strategy involving large numbers of eggs laid in water, with little parental investment per egg. This is the presumed reproductive strategy of lepospondyls and seymouriamorphs. In contrast, the assumed primitive condition for amniotes involves a reproductive strategy of producing fewer eggs than their anamniotic relatives with greater parental investment in each egg, including nourishment and possibly parental care. Perhaps the origin of amniotes includes a shift between these two reproductive strategies. Therefore, though the origin of amniotes is probably associated with terrestrial reproduction, it may also be associated with a shift toward increased parental investment in each egg. Early amniotes may have New Perspective on Tetrapod Phytogeny 35 laid larger eggs than their distant ancestors, and they may have laid them later if they had extensive embryo retention. Their hatchlings may have been larger and vulnerable to predators to a lesser degree or for a shorter period than the eggs and hatchlings of groups that laid smaller eggs and that lacked embryo retention. By investing energy into parental care, early amniotes would have ensured high survival chances to their offspring. The new phylogeny and the scenario of the origin of amniotes associated with a shift in reproductive strategies do not specify when the amniotic egg appeared. However, according to the new phylogeny, the amniotic egg can only have appeared in the lineage that led to Amniota, no sooner than the divergence of this lineage from the lineage that led to lissamphibians, and at least slightly before the divergence between synapsids and sauropsids. Determining more accurately the timing of the appearance of the amniotic egg requires knowledge of the type of egg laid by diadectomorphs (or Westlothiania, if it is a close relative of amniotes). Unfortunately, fossil eggs are rare in the Paleozoic (and amniote eggs have not been discovered) and only indirect arguments may allow us to solve this question. Aquatic larvae are known in temnospondyls and seymouriamorphs, and lateral-line canal grooves are known in several groups of early terrestrial choanates. Therefore, the status of diadectomorphs may one day be established using such evidence. No diadectomorph larva is known, and as far as we know diadectomorphs lacked lateral-line canal grooves. These facts, as well as the large size of diadectomorphs, do not preclude the possibility that diadectomorphs may have laid amniotic eggs, but the fossil record is currently insufficient to safely settle this question. The new phylogeny presented here is of course incomplete and more detailed phylogenies will no doubt appear in the future, but it is hoped that the present study will stimulate research on the anatomy and phylogeny of early choanates. The large amount of missing and partially uncertain data present in the matrix (Appendix 2) clearly illustrates that progress in this field will require more anatomical data. 36 M. Laurin and R. Reisz SUMMARY A phylogenetic analysis based on a data matrix of 38 taxa and 157 osteological characters has produced a dramatically new hypothesis of tetrapod phylogeny. Amniota and diadectomorphs are closely related, as previously reported, but this clade is closely related to a monophyletic Lepospondyli that includes Lissamphibia. In contrast to previous hypotheses, diadectomorphs, amniotes, and Lepospondyli include all extant tetrapods and constitute the crown group of terrestrial choanates. This crown group is much smaller that previously suggested. Seymouriamorpha, long considered closely related to diadectomorphs and amniotes, is the sister group of tetrapods according to this analysis. Gephyrostegids, embolomeres, temnospondyls, loxommatids, and Crassigyrinus are more distant relatives of the crown group. ACKNOWLEDGMENTS We thank Ms. Diane Scott for drawing the reconstructions of the skulls. We sincerely thank all the curators and other personnel who lent us specimens for this study. The people include (in alphabetical order) Dr. David S Berman (Carnegie Museum), Dr. John R. Bolt (Field Museum of Natural History), Dr. Richard S. Laub (Buffalo Museum of Science), Dr. Robert Murphy (Royal Ontario Museum), Dr. Timothy B. Rowe (Texas Memorial Museum), Dr. B. Sanchiz, (National Museum of Natural Sciences, Madrid) Mr. C. R. Schaff (Museum of Comparative Zoology), and Mr. William F. Simpson (Field Museum of Natural History). We are grateful to Dr. Robert L. Carroll (Redpath Museum, McGill University) for sending us a manuscript of his unpublished phylogenetic study of choanates and some articles that were unavailable at Toronto. We thank Dr. D. Wake and Dr. M. Wake for reading the manuscript, for stimulating conversations on lissamphibian anatomy, and for letting one of us (M. L.) study the extensive collection of lissamphibian dried skeletons and cleared and stained specimens in the Museum of Vertebrate Zoology and in the Marvalee Wake Collection. Personal communications were obtained from David S Berman on Ecolsonia and from Mr. Michael deBraga on Procolophonidae. We thank Dr. J. Gauthier for New Perspective on Tetrapod Phylogeny 37 stimulating conversations on systematics. We thank Dr. K. Padian for interesting conversations on systematics and for his hospitality. We also thank the staff of the document delivery and interlibrary loan services of the Erindale Campus (especially Mrs. Pamela King, Mrs. Andrea Pillo, and Mrs. Patricia Lai) for their help. We are indebted to Mr. Xu Jianping for translating parts of a Chinese article on hynobiid salamanders into English. This research was funded by Natural Sciences and Engineering Research Council of Canada (NSERC), Fonds pour la Formation de Chercheurs et l'Aide a la Recherche (FCAR), the Fondation Desjardins, the University of Toronto, and a grant to Robert R. Reisz. This is UCMP Contribution 1648. APPENDIX 1 List of Characters Used in this Study 1 Lateral-line canals location in adults: surrounded by bone (0); in grooves at the surface (1); in soft tissues or absent (2). 2 Lateral-line canal grooves in ontogeny: always present (0); in larvae only, lost in adults (1); never present (2). 3 Dermal sculpturing: high ridges and pits, "temnospondyl pattern" (0); cosmine (1); shallow, widely spaced pits, "anthracosaur pattern" (2); low rugosities, pustules (3); none, smooth bone (4). 4 Rostrum: absent (0); short, high (1); long (2). 5 Orbit: elliptical, surrounded by bone (0); with large anterior fenestra (1); expanded posteriorly (2). 6 Jaw joint position relative to occiput (i.e., the occipital condyle): behind occiput (0) ; close to level of occiput (1); in front of occiput (2). 7 Frontal and parietal: distinct, with at least three large ossifications (0); both present as paired ossifications (1); fused into a frontoparietal (2); paired parietal and median frontal (3). 8 Frontal: excluded from orbit (0); contacts orbit between prefrontal and postfrontal (1); contacts orbit, postfrontal absent (2). 9 External naris: marginal, reaches ventral skull margin (0); well above skull margin (1). 10 Anterior tectal: present (0); absent (1). 11 Skull table-cheek joint: sutured (0); potentially mobile, smooth joint present (1) ; potentially mobile, slit or fenestra present (2). 12 Parietal: restricted to skull table (0); with superficial occipital flange (1). 13 Parietal-squamosal contact: absent (0); present (1). 14 Postorbital-supratemporal contact: present (0); absent (1). 15 Pineal foramen: present (0); absent (1). 16 Intertemporal: present (0); absent (1). 38 M. Laurin and R. Reisz 17 Supratemporal: present (0); absent (1). 18 Tabular: present (0); absent (1). 19 Tabular occipital flange: absent (0); single, extends ventromedially from posterolateral corner of skull table (1); two broad, low laminae or a lamina and a tabular horn (2); long, curved flange with ventromedial expansion (3); single, broadly attached to posterior edge of dorsal flange (4); single, overlapped by postparietal posteriorly (5). 20 Subdermal tabular horn: absent (0); present (1). 21 Ventrally bent, sculptured tabular horn: absent (0); present (1). 22 Postparietal number: two (0); one (1); absent (2). 23 Postparietal position: on skull table or on skull table and on occiput (0); only on occiput (1). 24 Tabular-parietal contact: absent (0); present (1). 25 Prefrontal: present (0); absent (1). 26 Prefrontal anterior contacts: anterior tectal and lacrimal, minimally (0); nasal and lacrimal only (1); external naris and/or septomaxilla, in addition to other elements (2). 27 Postfrontal: reaches orbit (0); excluded from orbit (1); absent (2). 28 Postorbital: reaches orbit (0); excluded from orbit (1); absent (2). 29 Lacrimal: reaches orbit (0); excluded from orbit (1); absent (2). 30 Jugal: reaches orbit (0); excluded from orbit (1); absent (2). 31 Temporal emargination: absent, temporal area covered by postspiracular and opercular series (0); present between squamosal, tabular, and supratemporal (1) ; absent, squamosal, tabular and supratemporal occupy temporal area (2) ; present behind quadrate (3); present behind squamosal (4). 32 Maxilla-quadratojugal contact: present (0); absent (1). 33 Palatal shelf of maxilla : absent (0); present (1). 34 Tentacular foramen in maxilla: absent (0); present (1). 35 Quadratojugal: present (0); absent (1). 36 Pterygoid-squamosal contact: absent (0); present (1). 37 Occipital flange of squamosal: absent (0); present, convex (1); present, concave, in notch (2). 38 Quadrate dorsal process: long, high (0); short, low (1). 39 Lateral palatal tooth row: present, uninterrupted (0); interrupted (1); absent (2). 40 Posteromedial transverse vomerine tooth row: absent (0); present (1). 41 Palatal recess: present (0); divided medially (1); covered by bone (2). 42 Vomerine fangs: present (0); absent (1). 43 Vomerine shagreen of denticles: absent (0); present (1). 44 Palatine: discrete (0); fused or absent (1). 45 Lateral exposure of palatine: absent (0); present (1). 46 Palatine fangs: present (0); absent (1). 47 Palatine shagreen of denticles: absent (0); present (1). 48 Ectopterygoid: discrete (0); fused or absent (1). 49 Ectopterygoid fangs: present (0); absent (1). 50 Ectopterygoid shagreen of denticles: absent (0); present (1). New Perspective on Tetrapod Phytogeny 39 51 Transverse flange of pterygoid: absent (0); present, extends into adductor chamber (1); present, extends transversely to ectopterygoid (2). 52 Transverse vertical flange of pterygoid: absent (0); present (1). 53 Pterygoid shagreen of denticles: present (0); absent (1). 54 Pterygoid-maxilla contact: absent (0); present (1). 55 Parasphenoid: contacts vomer (contact visible on palate) (0); does not reach vomer (1). 56 Interpterygoid vacuity: narrow (0); broad (1); absent (2). 57 Palatine position: excluded from interpterygoid vacuity (0); contacts vacuity (1). 58 Maxilla: excluded from interpterygoid vacuity (0); contacts vacuity (1). 59 Parasphenoid morphology: narrow cultriform process, body moderately broad (0); broad cultriform process merging into broad body (1); narrow cultriform process, body expanded into lateral wings (2). 60 Parasphenoid denticles: present (0); absent (1). 61 Parasphenoid posterior edge: transverse or indented (0); forms a posteromedial process (1). 62 Ventral cranial fissure: exposed on the palate (0); covered by the parasphenoid (!)• 63 Posttemporal fenestra: large (0); reduced to a foramen or absent (1). 64 Paroccipital process: absent (0); present (1). 65 Otic tube: absent (0); present (1). 66 Exoccipital contact with dermatocranium: absent (0); with postparietal (1); with parietal (2). 67 Braincase endochondral roof: ossified as a unit (0); unossified (no supraoccipital is present) (1); discrete supraoccipital present (2). 68 Basioccipital condyle: deeply concave, with notochord extension into braincase (0); concave condyle with shallow notochordal pit (1); paired (2); median, broad, convex (3); narrow, convex (4). 69 Basioccipital and exoccipital: indistinguishably fused in the adult (0); suturally distinct throughout ontogeny (1); basioccipital never distinct (2). 70 Basioccipital position: reaches edge of foramen magnum (0); excluded from edge of foramen magnum (1). 7' Parasphenoid and endochondral braincase elements (other than basisphenoid): suturally distinct in adults (0); indistinguishably fused in adults (1). 72 Gap between sphenethmoid and oticooccipital portions of braincase: absent (0) ; present (1). 73 Preopercular: present (0); absent (1). 74 Subopercular: present (0); absent (1). 75 Epipterygoid ossification: present (0); absent (1). 76 Epipterygoid and pterygoid: fused (0); suturally distinct or epipterygoid absent (1) . '7 Basicranial articulation: not fused (0); sutured (1). 78 Stapes position: links braincase to quadrate (0); without bony contact distally (!)• 40 M. Laurin and R. Reisz 79 Stapes: without a dorsal process (0); with a dorsal process confluent with the footplate (1); with a dorsal process distinctly set off from the footplate by the notch (2). 80 Proximal stapedial footplate: absent (0); present, discrete (1); represented by a gentle proximal swelling (2). 81 Stapedial foramen: present (0); absent (1). 82 Mandibular fenestra: absent (0); some small fenestrae in splenial, postsplenial, and angular (1); between angular, postsplenial, splenial, and prearticular (2). 83 Anterior coronoid: present (0); fused or absent (1). 84 Central coronoid: present (0); fused or absent (1). 85 Posterior coronoid: present (0); fused or absent (1). 86 Anterior splenial: present (0); fused or absent (1). 87 Postsplenial: present (0); fused or absent (1). 88 Prearticular: present (0); fused or absent (1). 89 Angular: present (0); fused or absent (1). 90 Surangular: present (0); fused or absent (1). 91 Parasymphysial fangs: present (0); absent (1). 92 Coronoid fangs: present (0); absent (1). 93 Coronoid denticles: absent (0); present (1). 94 Dentary: dentigerous (0); edentulous (1). 95 Retroarticular process: small to mid-sized, extends posteriorly (0); very large (1) ; medium sized, extends posteroventrally (2). 96 Medial mandibular tooth row: present (0); absent (1). 97 Crowns of marginal teeth: monocuspid (0); bicuspid (1); tricuspid (2); bulbous with a labially convex cutting edge and a lingual cavity (3). 98 Marginal teeth: nonpedicellate (0); pedicellate (1). 99 Maxillary tooth size: at least as large as dentary teeth (0); much smaller than dentary teeth (1). 100 Labyrinthine infolding: present (0); absent (1). 101 Zygapophyses: absent from most of the tail (0); present almost to the tip of the tail (1). 102 Presacral centra: large, crescentic intercentrum, small, paired pleurocentrum (0); large, circular intercentra, no pleurocentra (1); large, crescentic intercentrum, no pleurocentrum (2); circular pleurocentrum, crescentic intercentrum (3); circular intercentrum and pleurocentrum (4); large pleurocentrum, no intercentrum (5). 103 Neural arches and spines: all paired or fused only at tip of spine (0); fused in at least some segments (1); separated by a thin layer of cartilage (2). 104 Neural arches and centra: discrete elements (0); fused in adults, traces of a neurocentral suture may remain (1); indistinguishably fused early in ontogeny (2) . 105 Canal for supraneural ligament: present in at least some arches (0); absent (1). 106 Large foramina in centrum or pedicle: absent (0); present in centrum (1); in pedicle (2). 107 Anterior dorsal neural arches: flat or concave (0); swollen (1). New Perspective on Tetrapod Phytogeny 41 108 Atlantal arch: paired (0); fused (median) (1). 109 Distinct odontoid process: absent (0); present as a convex median process medial to two concave articular surfaces (1); formed by the apex of two angled articular surfaces (2). 110 Anterior articular surface of atlantal centrum: no broader than posterior surface of centrum (0); broader than posterior surface (1). 111 Anterior process of axial intercentrum-atlantal pleurocentrum complex: absent (0) ; present (1). 112 Atlantal pleurocentrum and axial intercentrum: discrete elements (0); fused (1). 113 Atlantal intercentrum: present (0); absent (1). 114 Atlantal pleurocentrum: paired (0); median (1). 115 Transverse processes in mid-presacral vertebrae: absent (0); short, robust (1) ; long (2). 116 Parapophyses: short (0); almost as long as the diapophyses (1); absent or not distinct from the diapophyses (2). 117 Capitulum articulation in mid-presacral vertebrae: with the intercentrum of its segment (0); intercentrum and pleurocentrum of its segment (1); pleurocentrum of its segment (2); pleurocentrum of segment in front (3); transverse process (4). 118 Number of presacral vertebrae: 23-32 (0); fewer than 23 (1); 33-60 (2); more than 60 (3). 119 Number of sacral vertebrae: none (0); one (1); two or more (2). 120 Ribs: short, straight (0); long, curved (1). 121 Discrete dorsal fin: present (0); absent (1). 122 Radials for caudal fin: present (0); absent (1). 123 Uncinate processes: absent (0); present (1). 124 Interclavicle: without a parasternal process (0); with a parasternal process (1); absent (2). 125 Clavicle: present (0); absent (1). 126 Clavicle shape: with a distinctly expanded ventral plate (0); without a ventral plate, or with narrow ventral plate (1). 127 Cleithrum: broad dorsally (0); slender (1); broad ventrally (2); absent (3). 128 Anocleifhrum: present (0); absent (1). 129 Lateral extrascapular: present (0); absent (1). 130 Median extrascapular: present (0); absent (1). 131 Number of scapulocoracoid ossifications: one (0); two (1); three (2). 132 Humerus: present (0); absent (1). 133 Supinator process: absent, shaft with rounded anterior edge (0); absent, anterior ridge present on shaft (1); present (2). 134 Ectepicondyle: low, indistinct, or absent (0); high, distinct (1). 135 Deltopectoral crest: distinct from proximal articular surface (0); confluent with proximal articular surface (1). 136 Entepicondyle: not greatly expanded (0); greatly expanded (1). 137 Ectepicondylar foramen: present (0); absent (1). 138 Entepicondylar foramen: present (0); absent (1). 139 Radius and ulna: discrete elements (0); fused to each other (1); absent (2). 42 M. Laurin and R. Reisz 140 Olecranon process in adult: absent or cartilaginous (0); ossified (1). 141 Number of manual digits: none (0); eight (1); five (2); four (3). 142 Number of pelvic ossifications: one (0); three (1); two (2). 143 Iliac blade: very short (0); consists of dorsal and posterior flanges (1); posterodorsal flange only (2); dorsal flange (3); long anterodorsal flange (4). 144 Internal trochanter: absent (0); present and separated from articular surface by periosteal bone (1); confluent with proximal articular surface (2). 145 Intertrochanteric fossa: present, proximal head of femur concave ventrally (0) ; absent, proximal head convex ventrally (1). 146 Adductor crest: absent (0); present (1). 147 Tibia and fibula: discrete elements (0); fused into tibiofibula (1). 148 Astragalus: absent, discrete tibiale, intermedium, and proximal centrale are present (0); present (1). 149 Tibiale and fibulare: short (0); long (1). 150 Number of pedal digits: none (0); seven (1); five (2); four (3). 151 Number of phalanges in second toe: two (0); three (1). 152 Number of phalanges in third toe: three (0); four (1). 153 Number of phalanges in fourth toe: four (0); five (1); three (2). 154 Number of phalanges in fifth tow: four (0); five (1); three (2); two (3). 155 Dorsal scales: rhombic or ovoid (0); circular (1); absent (2); sculptured osteoderms (3); long and slender (4); quadrangular with rounded corners (5). 156 Ventral scales: quadrangular, long, and slender (0); sculptured osteoderms (1) ; mosaic of polygonal plates (2); elliptical (3); absent (4). 157 Lepidotrichia: present (0); absent (1). appendix 2 Data matrix. On pages 43-53 taxa, characters, and character-states utilized in discussion of results and hypotheses of relationships in this chapter. Polymorphism and partially uncertain data are indicated by two or more states separated by the symbols "&" and "/," respectively. Unknown condition is indicated by "?". New Perspective on Tetrapod Phytogeny 43 Taxa\*-naracier» 7 L c j a U 7 i o o « y in 11 11 11 IZ 1J Id If Osteoiepiioriiics q VOL I o o o u A V 1 q 1 o 0 o Panacricninyiude o n V z A 9 A U u \j n A u A A u A cciTithostegQ o o o o o o q o 1 o o o o Ichthyostega u A n u A W A A U A VJ o \j n u A U A u A u CrCtSSlgyrinuA ] o o o o o 9 o 1 o o 9 Loxommatidae 1 1 n u A 1 1 A U A V n u A U A u A u L-OlOaLCiUaC 1 o o o o o Q o o o q Dendretpeton z I/Z n u A U A u A U A u n u A U A V A u Tersomius z l/Z A U A u 1 1 1 1 f\ \j A U A u A U Afftphibcifttus 9 9 A A w A A n \j A U A u A u Ecolsonia z ill u A U A u A U 1 1 1 1 1 A U A U A A u Proterogyrinus i l (\Xt 1 Uocl z A U A u A U >' A u i 1 1 A u A U 9 Archer ia i 0 2 0 0 0 0 1 0 0 7 Gephyrostegidae i 1 l/Z T j A A i i 1 1 1 1 1 1 1 A A 0 A U Kotlassia z l/Z n U A U A U i l 1 A U 1 1 A U A U A 1 1 Seymouria ") z 1/z A U A A U l A A u A u A u 1 1 Ariekanerpeton z 1 1 A u A U A U i l A U A V A u A 1 1 Aistopoda 9 9 9 A A U 1&2 HP, 1 1 1 A A u A u Adelogyrinidae i 1 A u U u f\ V 1 1 0 1 1 0 A u 1 Nectridea 1&2 0&1 0 0 0 0&1 &2 1&3 0&1 1 1 0&1 0 0&1 0 Pantylus 2 1/2 0 1 0 1 1 0 1 1 0 0 0 ryi__... „ i j Khyncnonkos 2 1/2 4 1/2 0 2 1 0 1 1 0 0 0 Brachystelechida 2 1/2 4 1/2 0 2 1 1 1 1 0 1 1 Lysorophia ^ z 1/2 4 0 2 2 1 0 1 0 0 1 Triadobatrachus 2 1/2 3 0 2 1 2 2 1 0 0 1 l» i o Lug i o a a i uae z Z AjPr/1 A u i z i i 1 1 1 1 0 A u 0 Pipidae 2 2 4 0 2 1 2 2 1 1 0 0 0 i viiuDiiuae i z 2 4 0 2 2 1 2 1 1 0 1 I ■JliCIllUdC z 2 4 0 2 2 1 2 1 0 1 0&1 Prr\t/»i Ana z 2 4 7 2 2 1 2 1 0 1 0 Eocaecilia 2 2 4 0 0 2 0 0 1 Rhinatrematidae 2 2 4 0 0 2 0 2 0 Ichthyophiidae 2 2 4 0 0 2 0 2 1 Limnoscelis 2 1/2 3 1 0 1 0 0 0 0 0 Diadectes 2 1/2 3 0 0 1 0 0 0 0 0 Synapsida 2 2 3&4 0&1 0 1 1 0 0 0 0 Captorhinidae 2 2 0 0&1 0 1 1 0 0 1 1 Procolophonidae 2 2 4 1 0 2 1 0 1 0 0 44 M. Laurin and R. Reisz Taxa\Characters 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Osteolepiformes 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Panderichthyidae 0 O&l 0 0 0 0 0 0 0 0 0 0 O&l 0 Acanthostega 0 1 0 0 0 0 0 0 0 0 0 1 0 0 Ichthyostega 0 1 0 0 1/2 0 0 1 0 0 0 1 0 0 Crassigyrinus 0 0 0 0 1 1 0 0 0 0 0 0 0 Loxommatidae 0 O&l 0 0 1 0 0 0 0 0 0 1 0 0 Colosteidae 0 O&l 0 0 1 0 0 0 0 0 0 0 O&l Dendrerpeton 0 0 0 0 7 0 1 0 0 0 0 1 0 0 Tersomius 0 1 0 0 1 7 7 0 0 0 0 1 0 0 Amphibamus 0 1 0 0 7 7 7 0 0 0 0 1 0 0 Ecolsonia 0 1 0 0 2 0 1 0 0 0 0 0 0 Proterogyrinus 0 0 0 0 2 1 0 0 0 0 \ 0 0 Archeria 0 0 0 0 2 1 0 0 0 1 0 1 0 0 Gephyrostegidae 0 0 0 0 7 7 7 0 0 1 0 1 0 0 Kotlassia 0 0 0 0 2 0 0 0 0 0 0 0 Seymouria 0 0 0 0 2 0 1 0 0 1 0 1 0 0 Ariekanerpelon 0 0 0 0 2 0 0 0 0 1 0 1 0 0 Aistopoda 0 I O&l O&l ? 0 0 O&l &2 0 7 0 1 0&2 O&l Adelogyrinidae 0 1 1 1 - - - 0 0 - 0 7 0 1 Nectridea 0 1 O&l 0 0&3 &4 0 0 0 0 1 0 2 0 O&l &2 Pantylus 1 1 1 0 3 0 0 0 0 1 0 1 0 0 Rhynchonkos 0 1 1 0 3 0 0 0 0 1 0 1 0 0 Brachystelechida 0 1 1 O&l 0 0 0 2 - 1 0 1&2 0 0 Lysorophia 1 1 1 0 0 0 0 0 1 1 0 2 2 2 Triadobatrachus 0 1 1 1 - - - 2 - - 0 7 2 2 Discoglossidae 1 1 1 1 - - - 2 - - 1 - 2 2 Pipidae O&l 1 1 1 - - - 2 - - 1 - 2 2 Hynobiidae 1 1 1 1 - - - 2 - - 1 2 2 Sirenidae 1 1 1 1 - - - 2 - - 1 - 2 2 Proteidae 1 1 1 1 - - - 2 - - 1 - 2 2 Eocaecilia 1 1 1 1 - - - 2 - - 2 0 0 Rhinatrematidae 1 2 2 2 Ichthyophiidae 1 2 2 2 Limnoscelis 0 0 0 5 0 0 1 1 1 0 0 0 Diadectes 0 0 0 5 0 0 1 1 0 0 0 0 Synapsida 0 0 0 5 0 0 0 1 1 0 0 0 Captorhinidae 0 0 1 0 1 0 0 0 Procolophonidae 0 0 1 2 0 0 0 New Perspective on Tetrapod Phytogeny Taxa\Characters 29 30 31 32 33 34 35 36 37 38 39 40 41 4 Osteolepiformes 0 0 0 0 0 0 0 0 0 - 0 0 0 0 Panderichthyidae 0 O&l 0 0 0 0 0 0 0 7 0 0 0 0 Acanthostega 1 0 1 0 0 0 0 1 0 0 0 0 1 0 Ichthyostega 1 0 1 0 0 0 0 1 0 7 0 0 0 0 Crassigyrinus 1 0 1 0 0 0 0 1 0 0 0 0 1 ? Loxommatidae 0 0 1 O&l 0 0 0 1 0 0 2 0 0&2 0 Colosteidae 0 0 0 0 0 0 1 1 1 0 0 1 0 Dendrerpeton 0 0 1 0 0 0 0 1 0 7 2 0 2 0 Tersomius 0 0 1 0 0 0 0 1 0 0 2 0 2 0 Amphibamus 0 0 1 7 0 0 0 7 0 7 1 0 2 0 Ecolsonia 0 0 1 0 0 0 0 7 0 0 2 0 2 0 Proterogyrinus 0 0 1 1 0 7 0 1 0 0 1 7 7 7 Archeria 1 0 1 1 0 0 0 1 0 0 1 7 7 7 Gephyrostegidae 0 0 1 O&l 0 0 0 7 0 0 2 0 2 0 Kotlassia 0 0 1 7 0 0 0 1 0 0 0 0 2 7 Seymouria 0 0 1 1 0 0 0 1 0 0 2 0 2 0 Ariekanerpeton 0 0 1 7 0 0 0 1 0 ? 2 0 2 0 Aistopoda 0 0&2 2 O&l 0 0 0 0 7 7 1 7 2 1 Adelogyrinidae 7 0 4 O&l 0 0 0 0 2 7 2 7 ? 1 Nectridea 0 0 2 O&l 0 0 0 7 O&l 0 0 0 2 1 Pantylus 0 0 2 1 0 0 0 0 1 0 2 0 2 1 Rhynchonkos 0 0 2 7 0 0 7 0 7 1 0 0 2 1 Brachystelechida 0 0 2 7 0 0 1 0 1 0 7 0 2 Lysorophia 0 2 2 - 0 0 1 0 1 0 1 0 2 1 Triadobatrachus 7 2 4 7 0 7 7 7 0 7 1/2 7 7 Discoglossidae 2 2 4 0 0 0 0 0 0 1 2 1 0 1 Pipidae 2 2 4 - 0 0 1 0 0 1 2 0 0 1 Hynobiidae 0 2 2 - 0 0 1 0 0 0 2 1 0 1 Sirenidae 2 2 2 - 0 0 1 - 0 0 1 0 O&l 1 Proteidae 2 2 2 - - - 1 0 0 0 0 0 0&2 1 Eocaecilia 0 0 2 1 0 1 0 7 0 0 0 0 2 1 Rhinatrematidae 2 2 2 1 1 1 0 0 0 0 0 2 Ichthyophiidae 2 2 2 1 1 1 0 0 0 0 0 2 Limnoscelis 0 0 2 1 0 0 0 0 0 0 2 0 2 Diadectes 0 0 3 1 0 0 0 0 0 0 2 0 2 Synapsida 0 0 2 0 0 0 0 0 1 0 2 0 2 Captorhinidae 0 0 2 1 0 0 0 0 1 0 2 0 2 Procolophonidae 0 0 3 1 0 0 0 1 2 0 2 0 2 46 M. Laurin and R. Reisz New Perspective on Tetrapod Phytogeny 47 Taxa\Characters 43 44 45 46 47 48 49 50 51 Osteolepiformes 0 0 0 0 0 0 0 0 0 Panderichthyidae ? 0 0 0 ? 0 0 0 ? Acanthostega 1 0 0 0 1 0 1 0 2 Ichthyostega ? 0 0 1 7 0 1 7 2 Crassigyrinus ? 0 0 0 0 0 0 ? 0 Loxommatidae 9 0 0 0 7 0 0 9 0 Colosteidae 0 0 0 0 0 0 0 0 0 Dendrerpeton 1 0 0 0 1 0 0 1 ? Tersomius 0 0 1 0 0 0 0 0 1 Amphibamus 1 0 7 0 1 0 0 ? 1 Ecolsonia 1 0 1 0 1 0 0 0 1 Prolerogyrinus 7 0 0 0 1 0 0 1 ? Archeria 7 7 0 7 ? 0 9 0 0 Gephyrostegidae 1 0 0 0 1 0 0 1 1 Kotlassia ? 0 0 7 1 0 7 7 1 Seymouria 1 0 0 0 1 0 1 1 1 Ariekanerpelon 1 0 0 0 1 0 1 1 1 Aistopoda ? 0 0 1 7 9 7 0 Adelogyrinidae 1 0 0 1 1 0 1 0 0 Nectridea O&l 0 0 1 O&l O&l 1 0 0&2 Pantylus 1 0 0 1 1 1 - 0 Rhynchonkos 0 0 0 1 0 0 1 - 0 Brachystelechida 0 0 0 0 0 1 0 0 Lysorophia 0 0 - 1 0 1 - - 0 Triadobatrachus 7 0 0 1 0 1 - 9 0 Discoglossidae 0 1 - - 1 - - 0 Pipidae 0 1 - 1 - 1 - - 0 Hynobiidae 0 1 - - 1 - - 0 Sirenidae O&l 0 - 1 1 1 - - - Proteidae 0 1 - - 1 - - 0 Eocaecilia 0 0 0 0 0 Rhinatrematidae 0 1 1 lchthyophiidae 0 1 0 Limnoscelis 1 0 0 0 1 0 Diadectes 1 0 0 0 1 0 Synapsida 1 0 0 0 1 0 Captorhinidae 0 0 0 1 Procolophonidae 1 0 0 0 1 0 52 53 54 55 56 TaxaVCharacters 57 0 0 0 0 0 Osteolepiformes 0 0 ? 0 0 0/2 Panderichthyidae 0 0 0 0 ! 0 Acanthostega 0 0 ? 0 1 0 Ichthyostega 0 0 0 0 ? 0 Crassigyrinus 0 0 0 0 1 0 Loxommatidae 0 0 0 0 1 1 Colosteidae 0 ? 0 0 0 1 Dendrerpeton 0 0 1 0 0 1 Tersomius 1 0 0 ? 0 1 Amphibamus 1 ? 0 0 0 1 Ecolsonia 0 0 0 0 1 0 Prolerogyrinus 0 0 0 0 1 0 Archeria 0 0 0 0 ? 0 Gephyrostegidae 0 1 0 0 1 0 Kotlassia 0 1 0 0 1 2 Seymouria - 1 0 0 1 2 Ariekanerpelon - 0 7 0 ? 0 Aistopoda 0 0 0 0 ? 0 Adelogyrinidae 0 0 O&l 0 O&l O&l Nectridea O&l 0 0 0 1 0 Pantylus 0 0 1 0 7 1 Rhynchonkos 0 0 1 0 1 1 Brachystelechida 0 0 1 0 0 0 I ysorophia 0 0 1 1 ? 1 Triadobatrachus 1 0 1 1 1 1 Discoglossidae _ 0 1 1 7 1 Pipidae _ 0 1 0 0 1 Hynobiidae _ 0 - - 0 - Sirenidae _ 0 1 - 0 0 Proteidae _ 0 0 0 1 Eocaecilia 1 0 1 0 1 Rhinatrematidae 1 0 1 0 1 lchthyophiidae 1 0 0 0 0 Limnoscelis 0 0 1 0 0 Diadectes 0 0 0 0 0 Synapsida 0 0 0 0 0 Captorhinidae 0 0 0 0 0 Procolophonidae 0 58 59 60 61 62 63 64 65 66 67 68 69 70 0 0 0 0 0 0 0 o 0 o 0 0 ? o 7 o 7 ? ? ? ? ? 7 9 7 7 0 0 O&l 0 1 9 1 0 ? 9 o I ? 0 0 1 0 0 ? 1 0 7 ? 0 ? 7 0 0 7 0 ? ? ? ? ? 1 ? ? 0 0 ? 0 , 0 1 0 0 0 1 1 9 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 j ? 7 ? 1 ? ? ? 7 0 0 0 0 0 1 0 1 1 2 0 0 ? 0 0 0 ? ? ? 7 ? ? ? ? 0 0 1 0 1 1 0 1 1 2 ? 0 0 0 0 0 0 0 0 1 1 1 0 0 0 1 0 0 0 0 1 1 1 0 0 0 0 ? ? ? 0 7 ? ? 7 o 0 0 ? 1 , 1 1 1 1 1 1 ? ? 2 1 1 x 1 1 1 1 1 1 1 0 2 ? 1 j 1 1 1 ? ? 1 1 ? 0 0 9 7 , 0 0 0/2 1 0/2 7 0 0 1 0 ? ? o 1 ? 1 ? ? 0 0 1 1 0 1 0 1 1 2 1 0 0 2 1 1 0 1 o 0 2 2 1 o 0 0 0 O&l 1 0 o 1 2 2 1 o 0 0 1 O&l 1 o o 2 2 o o 0 1 1 0 1 0 o 1 2 2 1 o 1 2 1 0 ? o 1 ? ? 2 7 1 2 1 1 j 1 0 1 1 2 2 1 1&2 1 1 , 1 0 1 1 2 2 1 1 1 j 1 0 0 1 2 2 1 O&l j 1 0 0 1 2 2 j o ] n f) z t "j X 0 0 0 1 0 0 ? 2 0/2 0 1 1 1 0 0 1 2 2 0 1 1 0 0 1 2 2 0 0 0 0 ? 0 0 0 2 3 1 ? 0 0 1 0 1 1 0 0 0/2 3 1 1 0 0 O&l 0 0& 1 0 0 0/2 4 0&1 1 0 0 1 1 0 1 0 0 2 4 0 ? 0 0 1 0 0 1 0 0 2 4 1 ? 48 M. Laurin and R. Reisz Taxa\Characters 71 72 Osteolepiformes 0 0 Panderichthyidae 7 7 Acanthostega 0 0 Ichthyostega 0 7 Crassigyrinus 0 ? Loxommatidae 0 0 Colosteidae 0 1 Dendrerpeton 7 7 Tersomius 0 1 Amphibamus 0 7 Ecolsonia 0 7 Proterogyrinus 0 1 Archeria 0 0 Gephyrostegidae 0 7 Kotlassia 0 1 Seymouria 0 1 Ariekanerpeton 0 9 Aistopoda 7 0 Adelogyrinidae 7 7 Nectridea 0 7 Pantylus 0 0 Rhynchonkos 0 0 Brachystelechida O&l 0 Lysorophia 0 1 Triadobatrachus 0 1 Discoglossidae 0 1 Pipidae 0 1 Hynobiidae 0 1 Sirenidae 0 1 Proteidae 0 7 Eocaecilia 1 7 Rhinatrematidae 0 0 Ichthyophiidae 1 0 Limnoscelis 0 1 Diadectes 0 1 Synapsida 0 1 Captorhinidae 0 I Procolophonidae 0 1 73 74 75 76 77 78 79 80 81 82 83 84 85 0 0 0 0 0 0 0 0 0 ? 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 ? 0 0 0 0 1 1 0 ? ? ? ? 0 0 0 0 7 7 ? ? ? 0 0 0 0 0 1 0 0 0 7 ? 7 ? 0 0 0 0 1 1 0 0 0 7 ? 7 ? 1 0 0 0 i i 0 0 0 0 0 1 0 2 0 0 ? 1 1 ? 7 0 7 7 7 0 2 ? 7 ? 1 I 0 1 1 7 ? ? ? 2 0 0 0 1 1 0 7 7 7 7 1 0 2 7 7 0 i i 7 0 0 1 ? ? ? 2 0 0 0 1 J 0 1 0 ? ? ? ? 2 0 0 0 1 i 0 0 0 ? ? ? ? 2 0 0 0 1 i 7 ? 0 ? ? ? ? 2 ? ? 0 1 i 0 7 0 1 0 2 0 2 0 0 0 1 i 0 1 0 1 0 2 1 0 0 0 0 1 i 0 1 0 ? ? ? 7 2 0 0 0 1 i 0 0 1 0 1 1 0 1 1 1 1 i 7 ? 7 ? ? ? ? 7 1 i 7 1 O&l ? ? 7 2 1 1 O&l I i 0 I 0 ? 7 1 2 0 7 1 i 0 1 0 0 0 I O&l 2 x 0 0 1 i 0 1 0 0 0 I O&l 2 x 1 I 1 i 1 1 0 0 0 I x 0 x 1 x 1 i 1 I 7 1 0 1 x 0 , 1 \ i 1 I 1 1 0 x 0 1 x X 1 1 X 1 1 0 x x 0 1 I 1 1 1 1 0 0 0 x x 0 x 1 x 1 1 1 1 _ 0 0 x 0 x 1 x ! ! ! ! 0 0 0 ! 0 0 J 7 0 0 0 0 7 1 1 0 0 0 0 0 1 1 0 0 0 1 0 1 0 0 ? ? 7 2 0 0 7 1 ? 2 0 2 0 ? 0 0 0 2 0 0&2 0 0 0 7 0 2 0 2 1 0 0 0 1 0 1 2 1 0 New Perspective on Tetrapod Phytogeny Taxa\Characters 86 87 88 89 90 91 92 93 94 95 96 97 98 99 Osteolepiformes 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Panderichthyidae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Acanthostega 7 7 0 7 0 0 7 ? 0 0 ? 0 0 0 Ichthyostega 0 0 0 0 0 0 ? ? 0 0 ? 0 0 0 Crassigyrinus 0 0 0 0 0 0 0 1 0 0 1 0 0 0 Loxommatidae 0 0 0 0 0 0 1 1 0 0 1 0 0 0 Colosteidae 0 0 0 0 0 0 0 1 0 0 1 0 0 1 Dendrerpeton 0 0 0 0 0 0 1 1 0 0 1 0 0 0 Tersomius 0 0 0 0 0 0 1 0 0 0 1 O&l 1 0 Amphibamus 0 0 0 0 0 7 1 ? 0 0 1 1 1 7 Ecolsonia 0 0 0 0 0 7 1 1 0 0 1 0 0 0 Proterogyrinus 0 0 0 0 0 0 0 1 0 0 1 0 0 0 Archeria 0 0 0 0 0 O&l 1 1 0 0 1 0 0 0 Gephyrostegidae 0 0 0 0 0 0 1 1 0 0 1 0 0 0 Kotlassia 0 0 0 0 0 1 1 0 0 0 0 ? Seymouria 0 0 0 0 0 .' 1 1 0 0 ! 0 0 0 Ariekanerpeton 0 0 0 0 0 1 1 1 0 0 0 0 0 Aistopoda 1 1 1 0 1 1 " - 0 0 1 0 0 0 Adelogyrinidae 0 0 0 0 0 1 7 ? 0 0 1 0 0 0 Nectridea 0 1 0 0 0 1 1 O&l 0 0 O&l 0 0 0 Pantylus 0 0 0 0 0 1 1 1 0 0 1 0 0 0 Rhynchonkos 0 0 0 0 0 1 1 0 0 0 0 0 0 Brachystelechida 0 ? 0 0 ? 1 - - 0 0 1 O&l &2 0 0 Lysorophia 0 1 0 0 0 1 - - 0 0 1 0 0 0 Triadobatrachus 1 1 0 1 1 - - 1 7 ? ? ? Discoglossidae 1 1 0 1 1 1 - - 1 0 1 1 1 0 Pipidae 1 1 0 1 1 1 - - 1 0 1 0 0 0 Hynobiidae 1 1 0 1 1 - - 0 0 1 0 1 0 Sirenidae 1 1 0 1 1 1 1 1 1 2 1 3 O&l 0 Proteidae 1 1 0 1 1 1 - - 0 0 1 1 1 - Eocaecilia 0 0 1 0 1 1 ? Rhinatrematidae 0 0 1 0 0 1 0 Ichthyophiidae 0 0 1 O&l 0 1 0 Limnoscelis 0 0 0 0 1 1 0 0 1 0 0 0 Diadectes 0 0 0 0 7 ? 0 0 ? 0&2 0 0 Synapsida 0 0 0 0 1 0 0 0 1 0 0 0 Captorhinidae 0 0 0 0 1 0 0 0 1 0 0 0 Procolophonidae 0 0 0 0 1 0 0 0 1 O&l 0 0 50 M. Laurin and R. Reisz Taxa\Characters 99 100 101 102 103 104 105 106 107 108 109 110 111 112 1 Osteolepiformes 0 0 0 0&1 0 0 0 0 0 7 0 0 0 0 0 Panderichthyidae 0 0 0 1 0 ? ? 0 ? 0 7 7 ? - ? Acanthostega 0 0 7 ? 7 ? ? ? ? ? ? ? ? ? ? Ichthyostega 0 0 0 0 7 0 0 0 ? ? 7 ? ? ? ? Crassigyrinus 0 0 0 2 0 0 _ 0 0 0 0 0 0 _ 0 Loxommatidae 0 0 ? ? 9 ? 7 ? ? ? 7 ? ? ? ? Colosteidae 1 0 1 0 i 0 0 0 0 0 ? ? ? 0 0 Dendrerpeton 0 0 7 0 i 0 7 0 0 ? ? ? 7 ? 7 Tersomius 0 7 ? 0&3 i 0 ? 0 ? ? ? ? ? ? 7 Amphibamus 7 7 1 0&3 i 0 7 0 0 ? ? ? ? ? ? Ecolsonia 0 0 1 0 i 0 1 0 0 ? ? ? ? 7 7 Proterogyrinus 0 0 1 3 i 0 0 0 0 0 0 0 0 0 0 Archer ia 0 0 1 4 i 0 0 0 0 0 0 0 0 0 0 Gephyrostegidae 0 0 3 i 0 1 0 0 0 0 0 0 0 0 Kotlassia 7 0 1 3 l 1/2 1 0 1 0 ? 9 7 0 0 Seymouria 0 0 1 3 l 1 1 0 1 0 0 0 0 0 0 Ariekanerpeton 0 ? 1 3 i 0/1 1 0 1 0 ? ? ? 7 ? Aistopoda 0 1 1 1/5 i 2 1 2 0 0 0 0 0 1 Adelogyrinidae 0 1 5 i 0 1 1 0 0 7 0 0 - 1 Nectridea 0 1 1 1/5 i 2 1 0 0 1 1 1 0 - 1 Pantylus 0 1 1 5 i 2 1 0 ? 1 1 1 0 - 1 Rhynchonkos 0 1 1 3 i 2 1 0 0 1 1 1 0 0 1 Brachystelechida 0 1 1 5 i 2 1 0 7 ? 1 1 0 _ x Lysorophia 0 1 1 1/5 0 ! 1 0 0 1 1 0 _ I Triadobatrachus 7 ? 1/5 i 2 1 0 0 1 0 1 0 1 Discoglossidae 0 1 1/5 i 2 1 0 0 1 0/2 1 0 _ i Pipidae 0 1 - 1/5 i 2 1 0 0 1 0/2 1 0 1 Hynobiidae 0 1 1 1/5 i 2 1 2 0 1 1 1 0 - 1 Sirenidae 0 1 1 1/5 i 2 1 2 0 1 1 1 0 - 1 Proteidae - 1 1 1/5 i 2 1 2 0 1 1 1 0 1 Eocaecilia 7 3 ? 2 0 1 1 0 0 Rhinatrematidae 0 1/5 2 ? 0 1 2 0 Ichthyophiidae 0 1/5 2 ? 0 1 2 0 Limnoscelis 0 3 1/2 0 1 0 ? ? 1 1 0 Diadectes 0 3 1/2 0 1 0 ? 0 1 1 0 Synapsida 0 3 1 0 0 0 0 0 0 0& 0 Captorhinidae 0 3 1/2 0 1 0 0 0 0 1 0 Procoiophonidae 0 3 1/2 ? 1 0 0 0 0 1 0 New Perspective on Tetrapod Phytogeny si Taxa\Characters 114 115 116 117 118 119 120 121 122 123 124 1 7< 11*7 127 Osteolepiformes 0 0 0 0 0 0 0 0 0 0 o q u 0 Panderichthyidae ? 0 0 0 ? ? 0 1 0 0 o o 7 o Acanthostega ? 7 ? ? ? ? ? ? ? ? o o o o Ichthyostega ? 1 0 0 0 1 1 1 0 1 1 o o o Crassigyrinus . 1 0 0 7 7 1 1 1 0 0 o 0 o Loxommatidae ? 7 ? ? ? ? 7 7 ? ? ? 7 7 7 Colosteidae 0 2 0 0 2 1 0 1 1 1 o o o o Dendrerpeton ? 7 0 0 0 ? 0 1 1 ? o o o o Tersomius ? ? ? ? ? ? 0 1 1 0 ? ? 7 ? Amphibamus ? 7 0 0 1 1 0 1 1 0 o o 7 1 Ecolsonia ? 2 0 0 ? ? 0 1 1 1 o o o o Proterogyrinus 0 I 0 1 0 1 1 0 o o o n Archeria 1 ! 0 1 2 1 , J 1 0 o o q Gephyrostegidae ? ! 0 7 0 7 , J 1 1 1 o n i Kotlassia ? I 0 0/1 0 1/2 J { 1 1 1 o o o Seymouria 0 ! 0 1 0 1&2 ] j 1 0 1 o o ] Ariekanerpeton ? ! 0 0/1 0 1 J J o 1 1 n V u 1 1 Aistopoda 0 2 3 7 0 1 1 0/1 1 -5 J Adelogyrinidae 0 3 3 0 1 1 o o 0 fi \J Nectridea 1&2 0&1 2 0&1 1 0 1 o o o A yj 1 1 Pantylus 0 3 0 1 1 1 o 1 o i l 1 1 Rhynchonkos ! ? ? 2 2 0 1 o 7 o 0 7 Brachystelechida ! 0 3 1 1 1 1 o I n u l 1 1 Lysorophia 1 0 3 3 1 0 1 1 0&1 0&1 o 1 i 1 1 Triadobatrachus 2 2 2 1 1 0 1 1 o 7 o 7 1 l Discoglossidae 2 2 4 1 1 0 1 1 o 2 o 1 9 Pipidae 2 2 _ 1 1 2 o 1 X Hynobiidae 2 1 2 1 1 0 1 1 o 2 1 •2 J Sirenidae 2 1 2 2 0 1 1 0 2 1 3 Proteidae 2 1 2 1 1 0 1 1 0 2 1 3 Eocaecilia 0 ? 2 7 0 1 1 0 ? 7 7 ? Rhinatrematidae 0 2 3 0 1 1 0 2 1 3 Ichthyophiidae 0 2 3 0 1 1 0 2 1 3 Limnoscelis 0 1/2 0 2 0 ? 0 0 0/1 Diadectes 0 2 0 2 1 1 0 0 0 Synapsida 1&2 0 2 0 2 0 1 0 0 0 Captorhinidae 1&2 0 2 0 2 0 1 0 0 1&3 Procoiophonidae 0 2 0 2 0 1 0 1 3 52 M. Laurin and R. Reisz Taxa\Characters 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 Osteolepiformes 0 0 0 0 0 0 0 0 0 0 0 0 0 o 0 Panderichthyidae 0 0 0 ? 0 0 0 7 0 7 ? 0 0 0 ? Acanthostega 0 1 1 0 0 1 0 7 1 0 0 0 0 1 ? lchlhyostega 1 0 0 1 0 0 1 0 0 0 1 7 0 Crassigyrinus J x 1 ? 0 1 1 1 0 0 0 0 0 7 1/2 Loxommatidae ? 1 1 ? 0 7 7 7 7 7 7 0 7 7 7 Colosteidae ! ] 1 0 0 1 0&1 1 1 J 0 0 [ 3 j Dendrerpeton , [ I 0 0 0 I 7 0 [ 0 0 ? Tersomius ? 1 1 ? 0 7 ? 7 ? 7 0 ? Amphibamus ! J 1 0 0 7 ? 0 , 1 0 3 Ecolsonia 1 | 1 0 0 2 ! 0 0 1 0 ! 7 Proterogyrinus , ( 1 0 0 1 0 { 0 0 ! 2 Archeria , , 1 0 0 1 0 ! 0 0 , 2 j Gephyrostegidae i ] 1 0 0 1 j 7 ! ! 0 0 I 2 ! Kotlassia ! i 1 ? 0 2 7 ! 1 0 I 7 ] Seymouria \ I 1 1 0 2 I 0 j ! 0 0 0 2 ! Ariekanerpeton ! ! 1 1 0 0/2 1 ? ! 0 0 7 2 j Aistopoda , | 1 2 0 Adelogyrinidae [ 1 2 0 Nectridea 1 0 0 2 ! ? 1 0&1 0 7 3 Pantylus ! j 1 0 0 0 0 0 0 0 0 1 3 Rhynchonkos 9 1 1 ? 0 0 0 0 0 1 0 1 ? Brachystelechida ! j 1 0 0 0 7 0 0 0 o 1 7 Lysorophia j j 1 0 0 0 0 1 0 0 0 3 1/2 Triadobatrachus 1 ? 0 ? 7 7 0 j J 0 1 7 Discoglossidae I 1 0 0 0 7 0 , , 1 1 3 Pipidae 1 1 0 0 0 1 0 j J 1 1 3 Hynobiidae ! , 1 0 0 0 0 1 0 j J 0 0 3 Sirenidae ! , 1 0&1 0 0 0 1 0 , ! 0 0 3 Proteidae , j 1 0 0 0 0 1 0 j j o o 3 2 Eocaecilia 1 ? 0 7 7 ? 0 0 7 ? ? Rhinatrematidae 1 2 Ichthyophiidae 1 2 Limnoscelis 1 1 0 2 1 0 0 0 1 2 Diadectes 1 1 0 2 1 ? 0 0 1 2 Synapsida 1 2 0 2 1 0 0 0 1 2 Captorhinidae 1 2 0 0 1 0 0 0 1 2 Procolophonidae 1 2 0 2 0 0 0 0 0 2 ./VeH> Perspective on Tetrapod Phytogeny 53 Taxa\Characters 143 144 145 146 147 148 149 150 151 152 153 154 155 156 1 Osteolepiformes 0 0 0 0 0 0 ? 0 - - - - 0&1 0 0 Panderichthyidae ? ? ? ? ? 0 ? 0 - - - - 0 0 0 Acanthostega ? ? ? ? ? ? ? ? 7 7 7 ? 0 0 0 lchlhyostega 1 0 0 1 0 0 0 1 7 7 7 7 I 0 0 Crassigyrinus 1 ? ? ? 0 ? ? ? ? 7 7 7 7 0 Loxommatidae ? ? ? ? ? ? ? ? 7 7 7 7 7 7 Colosteidae 2 1 0 1 0 0 0 2 0 0 0 7 0 0 Dendrerpeton 2 1 0 1 0 0 0 9 7 7 7 7 0 0 Tersomius ? ? ? ? 0 ? ? ? 7 7 7 7 2 7 Amphibamus 3 ? ? 1 0 0 0 2 0 0 0 0 7 0 Ecolsonia ? 1 0 1 0 ? 0 ? 7 7 7 7 3 1 Proterogyrinus 1 2 0 1 0 0 0 2 1 7 7 1 2 0 Archeria 1 2 0 1 0 0 0 2 7 7 7 7 7 0 Gephyrostegidae 1 ? ? 1 0 0&1 - 2 1 1 7 1 1 0 Kotlassia 1 1 0 1 0 0 0 ? 7 7 7 7 7 7 Seymouria 1 2 0 1 0 0 0 2 7 7 7 7 7 7 Ariekanerpeton 3 ? ? ? 0 ? ? 2 1 1 1 2 1 3 Aistopoda - - - - - - - 7 - - - - 1 0 Adelogyrinidae 0 0 Nectridea 2 ? ? 1 0 1 ? 2 1 1 0 2 2 0 Pantylus 2 1 0 1 0 0 0 2 7 7 7 ? 2 2 Rhynchonkos 2/3 1 0 1 0 0 0 2/3 1 0 7 7 2 7 Brachystelechida 3 1 0 1 0 1 - 2 1 0&1 0&1 0&2 2 0 Lysorophia 3 2 0 1 0 ? ? 2 1 0 2 2 2 4 Triadobatrachus 4 0 1 0 0 0 1 7 7 7 7 7 2 4 Discoglossidae 4 0 1 0 1 0 1 2 0 0 0 3 2 4 Pipidae 4 0 1 0 1 0 1 2 0 0 0 3 2 4 Hynobiidae 3 1 1 0 0 0 0 2&3 0 0&1 2 2 2 4 Sirenidae - - - - - - - 0 - - - - 2 4 Proteidae 3 1 0 0 0 0 3 0 0 2 2 4 Eocaecilia ? ? ? 0 ? ? 7 7 7 ? 7 7 7 Rhinatrematidae 0 7 5 3 Ichthyophiidae 0 7 5 3 Limnoscelis 1 0 0 0 0 2 1 1 1 0 7 7 Diadectes 2 0 0 ? ? 7 7 7 7 7 7 7 Synapsida 2&3 0 0 1 2 1 1 1 0 2 0 Captorhinidae 2 0 0 1 2 1 1 1 0 4 0 Procolophonidae 3 0 0 0 1 2 1 1 1 0 2&3 0 54 M. Laurin and R. Reisz Appendix 3 The following is a list of autapomorphies of the clades and terminal taxa. In this list, ambiguous characters are indicated by an asterisk and the state of the character is indicated in parentheses when it is not "1." Reversals (any transition to a state of lower numerical value than the state present at the next more inclusive node) are indicated by a "minus" and by a number in parentheses when the reversal is not to the state "0". Node A: -6*, 31, 36, 43*, 55, 64*, 69*, 80, 115, 119*, 120, 129, 130, 133, 143*, 146*. Node B: 16, 26*, 29*, 49, 51(2), 136*. Acanthostega: 10, 41*, 47*, 141*. Ichthyostega: 19*(l/2), 22, 46, 60*, 123*, 124, 128*, 140, 150*, 155. Node C: 1, 9*, 19*, 62*, 68, 74, 93*, 96*, 122, 128*, 134, 142, 157. Crassigyrinus: 11, 20, 29*, 41*, 102(2), 135. Node D: 10, 26*, 39(2), 73,92. Loxommatidae: 5, 82*. NodeE:41*(2), 67, 72, 82*(2), 101*, 103*, 137*, 140*, 144*, 150*(2). Temnospondyli: 56, 66*, -69, 115(2), -120, 141*(3), 143(2). Colosteidae: -9, 26(2), 31(2), 37, 38*, -39, -41(1), -43, 79*, -92, 99, 118(2), 123*, 135, 136*. Node G: 1(2), 2(1/2), 21, 47*, -55. Dendrerpeton: 50,-133*. Node H: 16, 45, 51*, 68*(2), 138. Ecolsonia: 8*, 19(2), 26(2), 60, 63, 78*, 105*, 123*, 133*(2), 155*(3), 156. Node I: 57, 98. Tersomius: 6, 8*, -43, -47, 53, 76*, 77*, -93*, 155*(2). Amphibamus: -39(1), 97*, 118*, 127*, 143*(3). Node J: 19(2), 24, 32,47*, 102(3), 117, 136*, 141*(2), 151*, 154*. Embolomeri: 3(2), -9, 11*, 20, -39(1), -64, 144(2). Proterogyrinus: 50*, 76*, -92, 155*(2). Archeria: 29, 60, -72, 102(4), 114, 118(2). Batrachomorpha: 6, 51, 105, 124, 152*, 155*. Gephyrostegidae: 2*(l/2), 3(3), 8, 11*, 50*, 123, 127. Node M: 1(2), 49, 60, 76*, 91, 104, 133(2), 154(2). Seymouriamorpha: 2*, 14, 52, 61, 63, 65, 66*, 78, 80(2), 107*. Kotlassia: -39, 123, 138. Node O: 50*, 56(2), 59(2), 127, 131*. Seymouria: 21,81*, -82, -140*, 144*(2). Ariekanerpeton: -134, 135, 143(2), 156*(3). Node P: 16, 31(2), -36, 42, 46, 67(2), 83, 100, 114, 117(2), 143(2). New Perspective on Tetrapod Phytogeny 55 Lepospondyli: 17, -51, 66*, -72, 81, 102(5), 104(2), 113, -120. Node R: 118(3), 123, 132, 139(2),-141*. Aistopoda: -39(1), -64*, 69*(0/2), 78*, -82*, 84*, 85*, 86, 87*, 88, 90, 106*(2), 125, 127(3). Adelogyrinidae: -1*(1), 13, 18*, 28*, 31(4), 37*(2), -104, 106*, 117(3), -124*, - 155*. Node S: 19*(3), 68(2), 108, 110, 127, 141*(3), 155*(2). Nectridea: 26(2), -39*, 61*, -67(1), 84*, 87*, 109*(2), -124*, 148. Node T: 2*(2), 4, 37*, 109*, 117(3), -133, -134, -136. Pantylus: 15, 48, 59(2), 61*, -66, 120, 126*, 156(2). Node U: 3(4), 6(2), -43, -47, 53, 56*, 63, -64, -152*. Rhynchonkos: 38, -39*, -60, -93, -96, -102(3), 118*(2), 119(2), 138*. Node V: 13, -19, 35*, 84*, 85*, 118*, 126*, 143*(3). Brachystelechidae: 8, 12, 22*(2), -69, 120, 148. Node W: -4, 5*(2), 15, 27(2), 28(2), 30(2), 48, -55*, 59, 72*, 75, -82, 87*, 135, 138*,-140*, 153*(2), 156(4). Lysorophia: -9, 23*, 26*(2), -39(1), -56*, 103(2), -104, 106, -108, 118*(3), 144(2). Lissamphibia: 8*(2), 12*, 18, 22*(2), 29*(2), -37, 57*, -67(1), 69(2), 86, 89*, 90, 98*, 106*(2), 115*(2),-117(2), 124(2), 125*, 127*(3), 145*, 146*,-151*. Hynobiidae: -29*, 40*, -41*, 44*, 58*, 61*, -89*, 116*. Sirenidae: 25*, 39*, 47, 94, 95(2), 97*(3), 116*, 118*(2), -150*. Proteidae: -13*, 25*, -39*, 44*, -56*, 66*(2), -84, 97*, 116*, 142*(2), 150*(3). Apoda: -5*, -8*, 34, -39*, 95, -96, -115*(1), 118*(2). Eocaecilia: 26*(2), -27, -28, -29*, -30, -35, -53, -60, 71*, -81*, 97*, -102*(3). Gymnophiona: 11(2), 25*, 33, 44*, 54*, -72*, 109(2), 118*(3), 132, 139(2), -150*, 155*(5), 156*(3). Rhinatrematidae: -13, 51, 61*, -81*. Ichthyophiidae: 71*. Salientia: -6(1), 7(2), -12*, 31(4), 54*, 58*, 59(2), 65, 78, 94*, -109, 116(2), -125*, 140*, 143*(4),-144*, 149*. Triadobatrachus: -3(3), -15, -127*(1), 142*(2). Anura: -13*, 25*, 38*, -41*, 44*, 61*, 77*, 127(2), 131*, 139, 147, -153*, 154*(3). Discoglossidae: -32*, -35, 40*, 55*, 97*, 117*(4). Pipidae: -98*. Node AC: 2*(2), 19*(5), 23, 70, 79(2), 87*, 112, 119(2), 153*, -154. Diadectomorpha: 3*(3), 22, 68*(3), 107*, 111, 131*. Limnoscelis: 4*, -60, -64, -91, -100, 115(2), -143(1). Diadectes: -24, 31(3), 53, 63*, 77, 123. Amniota: 8, 37*, 68*(4), -93, 131*(2), 148, 155*(2). Synapsida: 3*(3/4), -32. Reptilia: 18, 84, 107*, 127(3). Captorhinidae: 13, 14, -43, 48, 61, -69, -133, 155(4). Procolophonidae: 3*(4), 4*, 6(2), 12, 22(2), 31(3), 36, 37(2), 78, -79, 81, 126, -134, -140, 143(3), -146. 56 M. Laurin and R. Reisz LITERATURE CITED Beaumont, E. H. 1977. Cranial morphology of the Loxommatidae (Amphibia: Labyrinthodontia). Philosophical Transactions of the Royal Society of London, B280: 29-101. Beerbower, J. R. 1963. Morphology, paleoecology, and phylogeny of the Permo- Pennsylvanian amphibian Diploceraspis. Bulletin of the Museum of Comparative Zoology, 130:33-108. Berman, D. S, R. R. Reisz, and D. A. Eberth. 1985. Ecolsonia cutlerensis, an Early Permian dissorophid amphibian from the Cutler Formation of north-central New Mexico. Circular of the New Mexico Bureau of Mines and Mineral Resources, 191:1-31. Blackburn, D. G. 1992. Convergent evolution of viviparity, matrotrophy, and specializations for fetal nutrition in reptiles and other vertebrates. American Zoologist, 32:313-321. Bolt, J. R. 1969. Lissamphibian origins: possible protolissamphibian from the Lower Permian of Oklahoma. Science, 166:888-891. Bolt, J. R. 1977. Dissorophoid relationships and ontogeny, and the origin of the Lissamphibia. Journal of Paleontology, 51:235-249. Bolt, J. R. 1979. Amphibamus grandiceps as a juvenile dissorophid: evidence and implications. Pages 529-563 in: Mazon Creek Fossils (M. H. Nitecki, ed.). London: Academic Press. Bolt, J. R. and R. E. Lombard. 1985. Evolution of the amphibian tympanic ear and the origin of frogs. Zoological Journal of the Linnean Society, 24:83-99. Bossy, K. V. H. 1976. Morphology, paleoecology, and evolutionary relationships of the Pennsylvanian urocordylid nectrideans (subclass Lepospondyli, class Amphibia), pp. 370, Unpublished Ph.D. dissertation, Yale University, New Haven, Connecticut. Carroll, R. L. 1964. Early evolution of the dissorophid amphibians. Bulletin of the Museum of Comparative Zoology, 131:161-250. Carroll, R. L. 1968. The postcranial skeleton of the Permian microsaur Pantylus. Canadian Journal of Zoology, 46:1175-1192. Carroll, R. L. 1969. Problems of the origin of reptiles. Biological Reviews of the Cambridge Philosophical Society, 44:393-432. Carroll, R. L. 1970a. The ancestry of reptiles. Philosophical Transactions of the Royal Society, B257:267-308. Carroll, R. L. 1970b. Quantitative aspects of the amphibian-reptilian transition. Forma et Functio, 3:165-178. Carroll, R. L. 1988. Vertebrate Paleontology and Evolution. New York: W. H. Freeman and Company. Carroll, R. L. 1991. The origin of reptiles. Pages 331-353 in: Origins of the Higher Groups of Tetrapods—Controversy and Consensus, (H.-P. Schultze and L. Trueb eds.). Ithaca: Comstock Publishing Associates. Carroll, R. L. 1995. Phylogenetic analysis of Paleozoic choanates. Bulletin du Museum National d'Histoire naturelle de Paris, 4 serie, 17:389-445. New Perspective on Tetrapod Phylogeny 57 Carroll, R. L. and P. J. Currie. 1975. Microsaurs as possible apodan ancestors. Zoological Journal of the Linnean Society, 57:229-247'. Carroll, R. L. and P. Gaskill. 1978. The Order Microsauria. Memoirs of the American Philosophical Society, 210 pages, Philadelphia: American Philosophical Society. Carroll, R. L. and R. Holmes. 1980. The skull and jaw musculature as guides to the ancestry of salamanders. Zoological Journal of the Linnean Society, 68:1- 40. Clack, J. A. 1994. Acanthostega gunnari, a Devonian tetrapod from Greenland; the snout, palate and ventral parts of the braincase, with a discussion of their significance. Meddelelser om GrOnland, Geoscience, 31:1-24. Duellman, W. E. and L. Trueb. 1986. Biology of Amphibians. New York: McGraw-Hill. Fracasso, M. A. 1983. Cranial osteology, functional morphology, systematics and paleoenvironment of Limnoscelis paludis Williston. pp. 624 Unpublished Ph.D. dissertation, Yale University, New Haven, Connecticut. Fracasso, M. A. 1987. Braincase of Limnoscelis paludis Williston. Postilla, 201:1- 22. Gaffney, E. S. 1980. Phylogenetic relationships of the major groups of amniotes. Pages 593-610 in: The Terrestrial Environment and the Origin of Land Vertebrates (A. L. Panchen, ed.). London: Academic Press. Gardiner, B. G. 1982. Tetrapod classification. Zoological Journal of the Linnean Society, 74:207-232. Gauthier, J., D. C. Cannatella, K. De Queiroz, A. G. Kluge, and T. Rowe. 1989. Tetrapod phylogeny. Pages 337-353 in: The Hierarchy of Life (B. Fernholm, K. Bremer, and H. Jornvall, eds.). New York: Elsevier Science Publishers B. V. (Biomedical Division). Gauthier, J., A. G. Kluge, and T. Rowe. 1988. The early evolution of the Amniota. Pages 103-155 in: The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds (M. J. Benton, ed.). Oxford: Clarendon Press. Gregory, J. T. 1965. Microsaurs and the origin of captorhinomorph reptiles. American Zoologist, 5:277-286. Heaton, M. J. 1979. Cranial anatomy of primitive captorhinid reptiles from the Late Pennsylvanian and Early Permian Oklahoma and Texas. Bulletin of the Oklahoma Geological Survey, 127:1-84. Heaton, M. J. 1980. The Cotylosauria: A Reconsideration of a Group of Archaic Tetrapods. Pages 497-551 The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds (M. J. Benton, ed.). Oxford: Clarendon Press. Holmes, R. 1984. The Carboniferous amphibian Proterogyrinus scheelei Romer, and the early evolution of tetrapods. Philosophical Transactions of the Royal Society, B306:431-527. Jenkins, F. A., Jr. and D. M. Walsh. 1993. An Early Jurassic caecilian with limbs. Nature, 365:246-249. 58 M. Laurin and R. Reisz Laurin, M. and R. R. Reisz. 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society, 113:165-223. Lombard, R. E. and S. S. Sumida. 1992. Recent progress in understanding early tetrapods. American Zoologist, 32:609-622. Lombardi, J. 1994. Embryo retention and evolution of the amniote condition. Journal of Morphology, 220 (3):368. Maddison, W. P. and D. R. Maddison. 1992. MacClade: Analysis of phylogeny and character evolution. Sunderland, Massachusetts: Sinauer Associates. Milner, A. R. 1988. The relationships and origin of living amphibians. Pages 59- 102 in: The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds (M. J. Benton, ed.). Oxford: Clarendon Press. Milner, A. R. 1990. The radiations of temnospondyl amphibians. Pages 321-349 in: Major Evolutionary Radiations (P. D. Taylor and G. P. Larwood, eds.). Oxford: Clarendon Press. Milner, A. R. 1993. The Paleozoic relatives of lissamphibians. Herpetological Monographs, 7:8-27. Mishler, B. D. 1994. Cladistic analysis of molecular and morphological data. American Journal of Physical Anthropology, 94:143-156. Nussbaum, R. A. 1977. Rhinatrematidae: A new family of caecilians (Amphibia: Gymnophiona). Occasional Papers of the Museum of Zoology, University of Michigan, 682:1-30. Panchen, A. L. and T. R. Smithson. 1988. The relationships of the earliest tetrapods. Pages 1-32 in: The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds (M. J. Benton, ed.). Oxford: Clarendon Press. Parsons, T. S. and E. E. Williams. 1963. The relationships of the modern Amphibia: A re-examination. Quarterly Review of Biology, 38:26-53. Reisz, R. R. 1972. Pelycosaurian reptiles from the Middle Pennsylvanian of North America. Bulletin of the Museum of Comparative Zoology, 144:27-62. Reisz, R. R. 1986. Pelycosauria. Encyclopedia of Paleoherpetology, 17A: 1-102. Romer, A. S. 1950. The nature and relationships of the Paleozoic microsaurs. American Journal of Science, 248:628-654. Romer, A. S. 1969. The cranial anatomy of the Permian amphibian Pantylus. Breviora, 314:1-37. Schoch, R. R. 1992. Comparative ontogeny of Early Permian branchiosaurid amphibians from Southwestern Germany. Palaeontographica. Abteilung A. Palaeozoologie-Stratigraphie, 222:43-83. Smithson, T. R. 1982. The cranial morphology of Greererpeton burkemorani Romer (Amphibia: Temnospondyli). Zoological Journal of the Linnean Society, 76:29-90. Swofford, D. L. 1993. PAUP: Phylogenetic Analysis Using Parsimony. Champaign, Illinois: Illinois Natural History Survey. Trueb, L. and R. Cloutier. 1991. A phylogenetic investigation of the inter- and intrarelationships of the Lissamphibia (Amphibia: Temnospondyli). Pages 223-313 in:, Origins of the Higher Groups of Tetrapods—Controversy and New Perspective on Tetrapod Phylogeny Consensus (H.-P. Schultze and L. Trueb, eds.). Ithaca: Cornell University Press. Vaughn, P. P. 1962. The Paleozoic microsaurs as close relatives of reptiles, again. American Midland Naturalist, 67:79-84. Wake, D. B. and R. Lawson. 1973. Developmental and adult morphology of the vertebral column in the plethodontid salamander Eurycea bislineata, with comments on vertebral evolution in the Amphibia. Journal of Morphology, 139:251-300. Wellstead, C. F. 1991. Taxonomic revision of the Lysorophia, Permo-Carboniferous lepospondyl amphibians. Bulletin of the American Museum of Natural History, 209:1-90. White, T. E. 1939. Osteology of Seymouria baylorensis Broili. Bulletin of the Museum of Comparative Zoology, 85:325-409.