Ichnology

An ancient feature resembling a shod human footprint was recently discovered adjacent to a buried prehistoric housepit dating to ~1840 cal yr BP at the Swan Point site in central Alaska. Recovery of footprints in this context is rare, prompting us to question if the impression was indeed the result of human activity. We tested if the feature's morphometrics fell within the mean biometrics of a shod human footprint using photogrammetric modeling techniques and classic landmark analyses. The feature was extensively photographed throughout the excavation, and the photos were used to produce three-dimensional photogrammetric digital models from which to obtain landmark biometrics. The results suggest that the feature falls within the expected mean parameters of a prehistoric human footprint. We characterized the footprint as belonging to a healthy, non-obese 9-12-year-old child. The presence of a child and well-constructed house in associated context suggests a healthy prehistoric family. The footprint represents the first of its kind from the subarctic, and the first described from Alaska.

Based on the integration of laser scans, sedimentology, geochemistry, archeobotany, geometric morphometrics and photogrammetry, here we present evidence testifying that a Palaeolithic group of people explored a deep cave in northern Italy about 14 ky cal. BP. Ichnological data enable us to shed light on individual and group level behavior, social relationship, and mode of exploration of the uneven terrain. Five individuals, two adults, an adolescent and two children, entered the cave barefoot and illuminated the way with a bunch of wooden sticks. Traces of crawling locomotion are documented for the first time in the global human ichnological record. Anatomical details recognizable in the crawling traces show that no clothing was present between limbs and the trampled sediments. Our study demonstrates that very young children (the youngest about three years old) were active members of the Upper Palaeolithic populations, even in apparently dangerous and social activities.

The morphology of fossil footprints is the basis of vertebrate footprint ichnology. However, the processes acting
during and after trace fossil registration which are responsible for the final morphology have never been precisely
defined, resulting in a dearth of nomenclature. Therefore, we discuss the concepts of ichnotaphonomy,
ichnostratinomy, taphonomy, biostratinomy, registration and diagenesis and describe the processes acting on
footprint morphology. In order to evaluate the morphological quality of tetrapod footprints, we introduce the
concept of morphological preservation, which is related to the morphological quality of footprints (M-preservation,
acronym MP), and distinguish it from physical preservation (P-preservation, acronym PP), which
characterizes whether or not a track is eliminated by taphonomic and diagenetic processes. M-preservation
includes all the morphological features produced during and after track registration prior to its study, and may
be divided into substages (ichnostratinomic, registrational, taphonomic, stratinomic, diagenetic). Moreover, we
propose an updated numerical preservation scale for M-preservation. It ranges from 0.0 (worst preservation) to
3.0 (best preservation); intermediate values may be used and specific features may be indicated by letters. In
vertebrate footprint ichnotaxonomy, we regard the anatomy-consistent morphology and to a lesser extent the
trackway pattern as the only acceptable ichnotaxobases. Only footprints showing a good morphological preservation
(grade 2.0–3.0) are useful in ichnotaxonomy, whereas ichnotaxa based on poor morphological preservation
(grade 0.0–1.5) are considered ichnotaphotaxa (nomina dubia) characterized by extramorphologies. We
applied the preservation scale on examples from the Palaeozoic to the present time, including three ichnotaphotaxa
and 18 anatomy-consistent ichnotaxa/morphotypes attributed to several vertebrate footprint producers.
Results indicate the utility, feasibility and suitability of this method for the entire vertebrate footprint record in
any lithofacies, strongly recommending its use in future ichnotaxonomic studies.

The fossil record ofmid to late Permian terrestrial vertebrates in the South African Karoo Basin is regarded as the
most abundant and diverse in the world. Despite the extensive research on body fossils, to-date the vertebrate
footprint sites have not been subjected to an anatomy-consistent ichnotaxonomic investigation. Here we present
a comprehensive ichnotaxonomic revision of Permian-Early Triassic tracksites in the main Karoo Basin of South
Africa. Furthermore, a track-trackmaker correlation for all Permian synapsid groups is provided for the first time,
based on the analysis of the functionalmorphology of potential producers. The following ichnotaxa and their proposed
trackmakers are recognized: Brontopus giganteus (dinocephalians), cf. Capitosauroides isp.
(therocephalians), cf. Dicynodontipus isp. (cynodonts), Dolomitipes accordii (small dicynodonts), Dolomitipes icelsi
n. comb. (large dicynodonts), Karoopes gansfonteinensis n. igen. n. isp. (gorgonopsids), Procolophonichnium
nopcsai (procolophonids) and Rhynchosauroides isp. (non-archosauriformdiapsids). Three different footprint assemblages
(FA I–III) are proposed for footprint biostratigraphy: FA I (lower Tapinocephalus AZ), a Guadalupian
assemblage dominated by dinocephalian tracks; FA II (topmost Tapinocephalus-Cistecephalus AZ), a latest
Guadalupian-Wuchiapingian assemblage dominated by gorgonopsid and dicynodont tracks in association with
subordinate therocephalian tracks and FA III (lower Lystrosaurus AZ), an Induan assemblage with dicynodont,
cynodont, procolophonid and diapsid tracks. The lower FA II includes the earliest ichnofauna with Lopingian affinity
all over the world (topmost Tapinocephalus-Pristerognathus AZ, ~260–259Ma) and could indicate an early
recovery phase after the end-Guadalupian mass extinction, because of the high abundance of large gorgonopsid
tracks and absence of dinocephalian tracks. This footprint recordmay also predate the body fossil record, suggesting
an earlier gorgonopsid radiation. FA III represents the earliest and most complete post end-Permian extinction
ichnofauna, which includes an early phase of abundant small dicynodont tracks, potentially indicating a
stressed post-event community. Nevertheless, this ichnofauna looks very similar to pre-extinction ichnofaunas
from Europe, in agreement with the skeletal record at the Daptocephalus-Lystrosaurus AZ transition.

The tetrapod footprint record of Permian eolian environments has long been underestimated because of overall
poor preservation and its apparent monospecifity. The best known and most abundant Cisuralian record of
tetrapod footprints is from the Coconino and De Chelly formations of Arizona, which, however, thus far encompassed
only the ichnogenera Chelichnus and Dromopus. We revised the locomotion and taphonomy of these
footprints and propose a new model, basing it on: 1) trackways changing direction, 2) trackways heading in
different directions on the same surface, 3) trackways in situ, and 4) laboratory experiments with common wall
lizards, Podarcis muralis. In all cases, the Chelichnus-like appearance of footprints is due to digit tip sliding on
inclined depositional surfaces, masking the original footprint shape and orientation. Also, the trackway pattern
and body position are largely influenced by the angle of inclination (dip) of the substrate being walked on. Based
on an anatomy-consistent ichnotaxonomy, Chelichnus and Laoporus are here considered nomina dubia, and the
footprints from the Coconino and De Chelly formations are revised and assigned to: parareptiles/captorhinomorph
eureptiles (Erpetopus, Varanopus curvidactylus), bolosaurid parareptiles/ diapsid eureptiles (cf. Dromopus),
varanopid synapsid (cf. Tambachichnium) and reptiliomorph amphibians (Amphisauropus, Ichniotherium sphaerodactylum).
The ichnoassociation is dominated by parareptile/captorhinomorph tracks, similarly to all the late
Cisuralian marginal marine, floodplain, alluvial fan and ephemeral lacustrine tetrapod ichnoassociations of
North America, Europe and North Africa. A review of all the available data including the new results suggests a
facies-crossing transition between an early-Cisuralian amphibian- and synapsid-dominated ichnofauna
(Dromopus track biochron) and a late Cisuralian parareptile/captorhinomorph-dominated ichnofauna (Erpetopus
track biochron) at low latitudes of Pangea.