Cretaceous ichthyosaurs: dwindling diversity or the empire strikes back?
by Maria Zammit
published in 'Geosciences' 2012
Recent descriptions of new taxa and recognition of survivorship of Jurassic genera across the Jurassic–Cretaceous... more Recent descriptions of new taxa and recognition of survivorship of Jurassic genera across the Jurassic–Cretaceous boundary bring the total number of Cretaceous ichthyosaur genera to eight. Taxa currently known from the Cretaceous include Ophthalmosaurus, Caypullisaurus, Aegirosaurus, Platypterygius, Maiaspondylus, Athabascasaurus, Sveltonectes, and Acamptonectes. This review summarizes the occurrence of all Cretaceous genera. A discussion of morphological diversity demonstrates the different, though overlapping, ecological niches occupied by the different taxa, while the comparison of phylogenetic hypotheses shows the problems inherent in understanding the evolutionary relationships between Cretaceous genera. The Late Jurassic radiation indicated in the competing phylogenetic hypotheses may correlate with the opening of the Atlantic Ocean or additional dispersal routes established by the breakup of Gondwana. Inclusion of the stratigraphically oldest Platypterygius species may aid in resolving these evolutionary relationships.
The Australian Cretaceous ichthyosaur 'Platypterygius australis': a description and review of postcranial remains
by Maria Zammit
co-authored with Rachel M. Norris and Benjamin P. Kear
published in 'Journal of Vertebrate Paleontology' 2010
Australian Cretaceous ichthyosaur material is amongst the most complete in the world. This study describes postcranial... more Australian Cretaceous ichthyosaur material is amongst the most complete in the world. This study describes postcranial remains referred to the upper Albian species Platypterygius australis, including the first record of pelvic and hind limb elements for this taxon. A combination of phylogenetically significant traits such as lack of fusion between the atlas-axis complex and third cervical centrum, the presence of three distal facets on both the humerus/femur for accommodation of the anterior zeugopodial elements plus the radius/tibia and ulna/fibula, concave preaxial accessory facet surfaces on both the humerus and the femur, and complete fusion of the ischiopubis with closure of the obturator foramen, are considered diagnostic for the species and (in conjunction with other previously identified cranial/postcranial features) may serve to distinguish P. australis from the other paleogeographically disparate Platypterygius spp.
A review of Australasian ichthyosaurs
by Maria Zammit
published in 'Alcheringa' 2010
Ichthyosaur fossils have been recorded from four landmasses in the Australasian region—Australia, New Zealand, New... more Ichthyosaur fossils have been recorded from four landmasses in the Australasian region—Australia, New Zealand, New Caledonia and Timor—and occur in all three systems of the Mesozoic. Most of the remains are non-diagnostic, but at least three genera have been identified: Mixosaurus, from the Middle Triassic of Timor; Shonisaurus, from the Upper Triassic of New Caledonia; and Platypterygius, from the Lower Cretaceous of Australia and New Zealand. Of these, Platypterygius contains the only material that can be diagnosed to species level. However, current taxonomy of the specimens is controversial, with two synonyms, P. australis and P. longmani, persisting in the literature. An examination of cranial traits in the ‘quasi-holotype’ of P. australis vs P. longmani demonstrates that they represent the same taxon. Thus, P. longmani should be regarded as the junior synonym. A neotype is also here designated for P. australis to replace the original, which is presumed lost.
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TURNER, S., & BURROW, C.J., 1999. Micropaleontology, vertebrate. Pp. 740-749. In R. SINGER (ed.), Encyclopedia of Paleontology. Fitzroy Dearborn Publishers. vol. 2; Chicago.
by Susan Turner
Co-authored with Dr Carole Burrow
Consideration of vertebrate microfossils, especially early vertebrates, agnathans and fish Consideration of vertebrate microfossils, especially early vertebrates, agnathans and fish
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TURNER, S. 1999. Westoll, Thomas Stanley, English 1912-1995. Pp. 1338-1341. In R. SINGER (ed.), Encyclopedia of Paleontology. Fitzroy Dearborn Publishers. vol 2; Chicago.
by Susan Turner
Life and work of British geologist and vertebrate palaeontologist
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Seen by: TURNER, S. 1995h. Professor Thomas Stanley Westoll Ph.D., D.Sc., F.R.S., F.R.S.E. 1912-1995. A memorial. Ichthyolith Issues 16, Dec. 1995,16-17.
by Susan Turner
brief memorial to important British vertebrate palaeontologist
Rinconsaurus caudamirus gen. et sp. nov., a new titanosaurid (Dinosauria, Sauropoda) from the Late Cretaceous of Patagonia, Argentina
Calvo, J.O. y González Riga, B.J. 2003. Rinconsaurus caudamirus gen. et sp. nov., a new titanosaurid (Dinosauria, Sauropoda) from the Late Cretaceous of Patagonia, Argentina. Revista Geológica de Chile 30 (2): 333-353.
The predatory ecology of Deinonychus and the origin of flapping in birds
FOWLER, D.W., FREEDMAN, E.A., SCANNELLA, J.B., & KAMBIC, R.E. (2011) PLoS One 6(12): e28964. doi:10.1371/journal.pone.0028964
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Most non-avian theropod dinosaurs are characterized by fearsome serrated teeth and sharp recurved claws.... more Most non-avian theropod dinosaurs are characterized by fearsome serrated teeth and sharp recurved claws. Interpretation of theropod predatory ecology is typically based on functional morphological analysis of these and other physical features. The notorious hypertrophied ‘killing claw’ on pedal digit (D) II of the maniraptoran theropod Deinonychus (Paraves: Dromaeosauridae) is hypothesized to have been a predatory adaptation for slashing or climbing, leading to the suggestion that Deinonychus and other dromaeosaurids were cursorial predators specialized for actively attacking and killing prey several times larger than themselves. However, this hypothesis is problematic as extant animals that possess similarly hypertrophied claws do not use them to slash or climb up prey. Here we offer an alternative interpretation: that the hypertrophied D-II claw of dromaeosaurids was functionally analogous to the enlarged talon also found on D-II of extant Accipitridae (hawks and eagles; one family of the birds commonly known as “raptors”). Here, the talon is used to maintain grip on prey of subequal body size to the predator, while the victim is pinned down by the body weight of the raptor and dismembered by the beak. The foot of Deinonychus exhibits morphology consistent with a grasping function, supportive of the prey immobilisation behavior model. Opposite morphological trends within Deinonychosauria (Dromaeosauridae + Troodontidae) are indicative of ecological separation. Placed in context of avian evolution, the grasping foot of Deinonychus and other terrestrial predatory paravians is hypothesized to have been an exaptation for the grasping foot of arboreal perching birds. Here we also describe “stability flapping”, a novel behaviour executed for positioning and stability during the initial stages of prey immobilisation, which may have been pivotal to the evolution of the flapping stroke. These findings overhaul our perception of predatory dinosaurs and highlight the role of exaptation in the evolution of novel structures and behaviours.
The first giant titanosaurian sauropod from the Upper Cretaceous of North America
FOWLER, D.W., & SULLIVAN. R.M. (in press; 2011) The first giant titanosaurian sauropod from the Upper Cretaceous of North America, Acta Palaeontologica Polonica 56(4): 685-690
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Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the largest dinosaur so far discovered and is... more Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the largest dinosaur so far discovered and is one of several giant titanosaurian sauropods known from the Upper Cretaceous of South America and Asia, but surprisingly not from North America. Here we present the first evidence of giant titanosaurian sauropods from the Upper Cretaceous of North America: two enormous vertebrae and a partial femur, from the Naashoibito Member of the Ojo Alamo Formation, New Mexico, and referred to Alamosaurus sanjuanensis. One of the new vertebrae, a posterior cervical, is comparable in size to a posterior cervical described for Puertasaurus: an Argentinosaurus-sized titanosaurian from the Maastrichtian of Argentina. This makes A. sanjuanensis the largest dinosaur from North America, and among the largest in the world. These findings indicate that A. sanjuanensis is diagnosed based on immature remains, which may have implications for cladistic analyses.
Reanalysis of "Raptorex kriegsteini": a juvenile tyrannosaurid dinosaur from Mongolia
FOWLER, D.W., WOODWARD, H.N., FREEDMAN, E.A., LARSON, P.L., & HORNER, J.R. (2011) PLoS One 6(6): e21376. doi:10.1371/journal.pone.0021376
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The carnivorous Tyrannosauridae are among the most iconic dinosaurs: typified by large body size, tiny forelimbs, and... more The carnivorous Tyrannosauridae are among the most iconic dinosaurs: typified by large body size, tiny forelimbs, and massive robust skulls with laterally thickened teeth. The recently described small-bodied tyrannosaurid Raptorex kreigsteini is exceptional as its discovery proposes that many of the distinctive anatomical traits of derived tyrannosaurids were acquired in the Early Cretaceous, before the evolution of large body size. This inference depends on two core interpretations: that the holotype (LH PV18) derives from the Lower Cretaceous of China, and that despite its small size, it is a subadult or young adult. Here we show that the published data is equivocal regarding stratigraphic position and that ontogenetic reanalysis shows there is no reason to conclude that LH PV18 has reached this level of maturity. The probable juvenile status of LH PV18 makes its use as a holotype unreliable, since diagnostic features of Raptorex may be symptomatic of its immature status, rather than its actual phylogenetic position. These findings are consistent with the original sale description of LH PV18 as a juvenile Tarbosaurus from the Upper Cretaceous of Mongolia. Consequently, we suggest that there is currently no evidence to support the conclusion that tyrannosaurid skeletal design first evolved in the Early Cretaceous at small body size.
Predatory functional morphology in raptors: Interdigital variation in talon size is related to prey restraint and immobilisation technique
FOWLER, D.W., FREEDMAN, E.A., & SCANNELLA, J.B. (2009) PLoS One 4(11)
Despite the ubiquity of raptors in terrestrial ecosystems, many aspects of their predatory behaviour remain poorly... more
Despite the ubiquity of raptors in terrestrial ecosystems, many aspects of their predatory behaviour remain poorly understood. Surprisingly little is known about the morphology of raptor talons and how they are employed during feeding behaviour.
Talon size variation among digits can be used to distinguish families of raptors and is related to different techniques of prey restraint and immobilisation. The hypertrophied talons on digits (D) I and II in Accipitridae have evolved primarily to restrain large struggling prey while they are immobilised by dismemberment. Falconidae have only modest talons on each digit and only slightly enlarged D-I and II. For immobilisation, Falconini rely more strongly on strike impact and breaking the necks of their prey, having evolved a ‘tooth’ on the beak to aid in doing so. Pandionidae have enlarged, highly recurved talons on each digit, an adaptation for piscivory, convergently seen to a lesser extent in fishing eagles. Strigiformes bear enlarged talons with comparatively low curvature on each digit, part of a suite of adaptations to increase constriction efficiency by maximising grip strength, indicative of specialisation on small prey. Restraint and immobilisation strategy change as prey increase in size. Small prey are restrained by containment within the foot and immobilised by constriction and beak attacks. Large prey are restrained by pinning under the bodyweight of the raptor, maintaining grip with the talons, and immobilised by dismemberment (Accipitridae), or severing the spinal cord (Falconini).
Within all raptors, physical attributes of the feet trade off against each other to attain great strength, but it is the variable means by which this is achieved that distinguishes them ecologically. Our findings show that interdigital talon morphology varies consistently among raptor families, and that this is directly correlative with variation in their typical prey capture and restraint strategy.
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New sauropod material from the Late Jurassic part of the Shishugou Formation (Junggar Basin, Xinjiang, NW China)
WINGS, O., SCHWARZ-WINGS, D. & FOWLER, D.W. (2011) Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. DOI: 10.1127/0077-7749/2011/0183
In April 2006, three new dinosaur localities were discovered in the upper part of the Middle to Late Jurassic... more In April 2006, three new dinosaur localities were discovered in the upper part of the Middle to Late Jurassic Shishugou Formation within “Dinosaur Valley”, a classic Junggar Basin locality for Jurassic vertebrates. Recovered bones comprise cervical vertebrae of an adult and a juvenile sauropod and several sauropod forelimb elements. The vertebrae show several affinities to Mamenchisaurus , but a generic assignment cannot be undertaken considering the fragmentary nature of the material and the uncertain status of taxa assigned to the genus Mamenchisaurus . Comparisons make it likely that they are more closely related to Mamenchisaurus and Omeisaurus than to other eusauropods and Euhelopus . All vertebrae expose an accessory lamina at the vertebral centrum, which might also be present but remained undescribed in species of Mamenchisaurus . Indications in the forelimb elements, such as humerus, ulna, and pollex claw, do not allow a determination of the taxa, although there are no distinct differences to Mamenchisaurus . The remains are important because of their extreme size, including potentially the first recognized juvenile remains of a Mamenchisaurus relative, and demonstrate further evidence for the occurrence of non-neosauropod eusauropods in the Junggar Basin.
Navajodactylus boerei, n.gen., n.sp. (Pterosauria, ?Azhdarchidae) from the Upper Cretaceous Kirtland Formation (Upper Campanian) of New Mexico
SULLIVAN, R.M., & FOWLER, D.W. (2011) In: Sullivan et al. (eds.). "Fossil Record 3": New Mexico Museum of Natural History and Science Bulletin 53: 393-404.
Navajodactylus boerei gen. et sp. nov. is a new ?azhdarchid pterosaur from the Upper Cretaceous Kirtland Formation... more
Navajodactylus boerei gen. et sp. nov. is a new ?azhdarchid pterosaur from the Upper Cretaceous Kirtland Formation (Hunter Wash Member), San Juan Basin, New Mexico. The holotype consists of the proximal portion of a right 1st wing phalanx with a fused extensor tendon process. Comparison to other named and unnamed pterosaurs indicates that the morphology of the extensor tendon process can be used to differentiate pterosaur taxa. Navajodactylus boerei is characterized by having a well-developed extensor tendon process that covers 75% of the proximal articulation surface of the 1st wing phalanx, with a pronounced dorsal boss on the superior margin of the dorsal cotyle, and it has a shallow, open extensor tendon process saddle. The arc of metacarpal IV is large and occupies more than 50% of the proximal area of the dorsal cotyle on the extensor tendon process.
Navajodactylus boerei is a component of the Hunter Wash local fauna (Kirtlandian land-vertebrate age [LVA]), which is approximately 75 Ma (late Campanian). This age date is based on the stratigraphic position of the type locality which lies below ash 2, dated at 74.44 Ma, and above ash DEP, dated at 75.56 Ma. Navajodactylus boerei is also identified among the pterosaur material recovered from the the Dinosaur Park Formation, Dinosaur Provincial Park, Alberta, Canada. This material is late Judithian LVA and is dated approximately 76-75.3 Ma, an age slightly older than the age of the holotype.
Burrow, C.J. & Turner, S. 2012. Fish stew: fossil fish taphonomy and the contribution of microfossils in documenting Devonian vertebrate history In: J.A. Talent ed. Global biodiversity, extinction intervals and biogeographic perturbations through time. UNESCO/International Year of Planet 'Earth and Life' theme. Springer.
by Susan Turner
Co-author to Dr Carole J. Burrow on invited chapter to International Year of Planet Earth book; Earth and Life
Global Biodiversity, Extinction Intervals and Biogeographic Perturbations Through Time
Series: International Year of Planet Earth
Talent, John A. (Ed.)
2012, 2012, XXXII, 1107 p. 620 illus., 429 in color.
Hardcover, ISBN 978-90-481-3427-4
Taphonomic studies provide new insights into palaeoenvironmental reconstruction and direct palaeobiological... more Taphonomic studies provide new insights into palaeoenvironmental reconstruction and direct palaeobiological significance including evolutionary novelty, ontoge-netic development, population composition, and post-mortem processes. A com-parative taphonomic analysis is applied to the different groups within vertebrate assemblages from a range of environments reflecting different tectonic settings and climatic regimes, with a particular emphasis on the Australian Devonian re-cord. Detailed descriptive studies in recent decades of fossil assemblages including their taphonomy from 'Konzentrat' bonebed deposits in the Devonian, notably in East Gondwana especially Australia, have given ‘added value’ to work on complete remains. Analysis of Australian bonebed and other rich fish-bearing deposits has expanded temporal resolution in the mid-Palaeozoic fossil record (sample acuity, stratigraphic completeness), and contributed to solutions of broad-scale problems in evolution, biogeography, and biostratigraphy.