Ben Creisler
Some recent early tetrapod papers:
AodhÃn à GogÃin and Patrick N. Wyse Jackson (2021)
Microcomputed tomography of the holotype of the early tetrapod Ichthyerpeton bradleyae (Huxley in Wright and Huxley, 1866) from the Pennsylvanian of Ireland.
Journal of Paleontology (advance online publication)
DOI:
https://doi.org/10.1017/jpa.2021.31 https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/microcomputed-tomography-of-the-holotype-of-the-early-tetrapod-ichthyerpeton-bradleyae-huxley-in-wright-and-huxley-1866-from-the-pennsylvanian-of-ireland/D75A5D64496AB8CDEC9A4BA17A8E4F19Ichthyerpeton bradleyae (Huxley in Wright and Huxley, 1866) is one of the seven tetrapods originally described by Huxley from the Jarrow Assemblage (Pennsylvanian, Langsettian Regional Substage equated with the Bashkirian International Stage) in south-eastern Ireland. The holotype, one of only two specimens considered to represent the taxon, consists of the postcranial skeleton, which has been highly compressed and has undergone extensive replacement of bone by carbonaceous material. The holotype is studied using microcomputed tomography, which reveals that the vertebral column has at least 25 diplospondylous vertebrae with cylindrical centra. Neural arches and a haemal arch are described for the first time. Neural arches in the caudal region are paired and neural spines only contact one another dorsally. The hemal arch is fused and wraps around the ventral margin of the centrum. A stout femur and tibia are described. The morphology of the femur is unique for early tetrapods, with fibular and tibial condyles of similar length and lacking an adductor crest. The morphology of the femur, and its length relative to the tibia, suggests that the holotype of I. bradleyae preserves an immature individual. The tibia is a flat bone characteristic of stem tetrapods. Phalanges from the right and left pes are present. Because the phalanges are disarticulated, a phalangeal count cannot be determined. Despite the new anatomical information, the systematic position of I. bradleyae is still difficult to establish; however, it does not belong within the colosteids, temnospondyls, or embolomeres, to which it has previously been assigned.
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Free pdf:
Among amniote and non-amniote tetrapod trackways from late Carboniferous to early Permian deposits, certain trackway measures vary notably. Some of this variability can be attributed to evolutionary changes in trackmaker anatomy and locomotion style close to the origin of amniotes. Here we demonstrate that steps in early amniote locomotion evolution can be addressed by applying methods of ancestral state reconstruction on trackway data â a novel approach in tetrapod ichnology. Based on (a) measurements of 186 trackways referred to the Carboniferous and early Permian ichnogenera Batrachichnus, Limnopus, Hylopus, Amphisauropus, Matthewichnus, Ichniotherium, Dimetropus, Tambachichnium, Erpetopus, Varanopus, Hyloidichnus, Notalacerta and Dromopus, (b) correlation of these ichnotaxa with specific groups of amphibian, reptiliomorph, synapsid, and reptilian trackmakers based on imprint morphology and (c) known skeletal-morphology-based phylogenies of the supposed trackmakers, we infer ancestral states for functionally controlled trackway measures in a maximum likelihood approach. The most notable finding of our analysis is a concordant change in trackway parameters within a series of ancestral amniote trackmakers, which reflects an evolutionary change in locomotion: In the ancestors of amniotes and diadectomorphs, an increase in body size was accompanied by a decrease in (normalized) gauge width and glenoacetabular length and by a change in imprint orientation toward a more trackway-parallel and forward-pointing condition. In the subsequent evolution of diadectomorph, synapsid and reptilian trackmakers after the diversification of the clades Cotylosauria (Amniota + Diadectomorpha) and Amniota, stride length increased whereas gauges decreased further or remained relatively narrow within most lineages. In accordance with this conspicuous pattern of evolutionary change in trackway measures, we interpret the body size increase as an underlying factor that triggered the reorganization of the locomotion apparatus. The secondary increase in stride length, which occurred convergently within distinct groups, is interpreted as an increase in locomotion capability when the benefits of reorganization came into effect. The track-trackmaker pair of Ichniotherium sphaerodactylum and Orobates pabsti from the early Permian Bromacker locality of the Thuringian Forest, proposed in earlier studies as a suitable ancestral amniote track-trackmaker model, fits relatively well with our modeled last common ancestor of amniotes â with the caveat that the Bromacker material is younger and some of the similarities appear to be due to convergence.