On the morphological variability of Ichniotherium tracks and evolution of locomotion in the sistergroup of amniotes
- Published
- Accepted
- Subject Areas
- Evolutionary Studies, Paleontology, Taxonomy, Zoology
- Keywords
- vertebrate tracks, locomotion, Diadectomorpha, Carboniferous, Permian, pace angulation, step cycle, ichnology, multivariate statistics
- Copyright
- © 2018 Buchwitz et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2018. On the morphological variability of Ichniotherium tracks and evolution of locomotion in the sistergroup of amniotes. PeerJ Preprints 6:e26460v1 https://doi.org/10.7287/peerj.preprints.26460v1
Abstract
Ichniotherium tracks with a relatively short pedal digit V (digit length ratio V/IV < 0.6) form the majority of yet described Late Carboniferous to Early Permian diadectomorph tracks and can be related to a certain diadectid clade with corresponding phalangeal reduction that includes Diadectes and its close relatives. Here we document the variation of digit proportions and trackway parameters in 25 trackways (69 step cycles) from nine localities and seven further specimens with incomplete step cycles from the type locality of Ichniotherium cottae (Gottlob quarry) in order to find out whether this type of Ichniotherium tracks represents a homogeneous group or an assemblage of distinct morphotypes and includes variability indicative for evolutionary change in trackmaker locomotion. According to our results, the largest sample of tracks from three Lower Permian sites of the Thuringian Forest, commonly referred to Ichniotherium cottae, is not homogeneous but shows a clear distinction in pace length, pace angulation, apparent trunk length and toe proportions between tracks from Bromacker quarry and those from the stratigraphically older sites Birkheide and Gottlob quarry. Three Late Carboniferous trackways of Ichniotherium with relatively short pedal digit V from Haine's Farm, Ohio, and Alveley near Birmingham, United Kingdom, that have been referred to the ichnotaxa "Baropus hainesi", "Megabaropus hainesi" and "Ichniotherium willsi", respectively, share a marked outward rotation of foot imprints with respect to walking direction. Apart from this feature they are in many aspects similar to the Birkheide and Gottlob records of Ichniotherium cottae. With the possible exception of the Maroon Formation (Early Permian, Colorado) sample, Early Permian Ichniotherium trackways with a relatively short pedal digit V fall into the morphological spectrum of the three well defined 'Hainesi-Willsi', 'Birkheide-Gottlob' and 'Bromacker' morphotypes. With their more obtuse pace angulations and higher body-size-normalized pace and stride lengths the Bromacker type tracks imply higher walking speeds of their trackmakers compared to all other Ichniotherium tracks. More generally, a trend towards higher locomotion capability from the last common ancestor of all Ichniotherium producers to the last common ancestor of all "Ichniotherium with relatively short pedal digit V" and from the latter to the trackmakers of the mid-Early Permian Bromacker type can be deduced – with the reservation that overall sample size is relatively small, making this scenario a preliminary assessment. Whether the presumed advancements represent a more general pattern within diadectomorphs, remains open until the non-European Ichniotherium trackway record improves. Ichnotaxonomic implications are discussed.
Author Comment
This is a submission to PeerJ for review.
Supplemental Information
Table of average pedal digit IV and V toe lengths for all Ichniotherium specimens considered in Figure 1A
Metadata and specimen averages for the complete short pV Ichniotherium sample
Table of toe lengths and toe length ratios for the complete short pV Ichniotherium sample
Table of trackway measurement data for the complete short pV Ichniotherium sample
Variable plots illustrating the correlation of pedal and manual digit length IV with other imprint measures
A-B, manus length vs. pedal digit length IV. C-D, pes length vs. pedal digit length IV. E-F, arithmetic mean of all other toe lengths vs. pedal digit length IV. G-H, arithmetic mean of all other toe lengths vs. manual digit length IV. Plots on the right side represent ln-ln plots of the same variable pairs depicted on the left side.
PCA results based on logarithmized length ratios
The variable combinations and samples of the six depicted PCA results correspond to diagrams depicted in the manuscript: A, Biplot (PC1 vs. 2) for a PCA of four logarithmized manual toe ratios, corresponds to Fig. 12B. B, PCA result for the same data as in A but based on the correlation matrix. C, Biplot (PC1 vs. 2) for a PCA of four logarithmized pedal toe ratios, corresponds to Fig. 12A. D, PCA result for the same data as in C but based on the correlation matrix. E, Biplot (PC1 vs. 2) for a PCA of two logarithmizedlength ratios and four angle measures, corresponds to Fig. 13A. F, Biplot (PC1 vs. 2) for a PCA of two logarithmized length ratios and four angle measures, corresponds to Fig. 14C.