The early Mesozoic saurischian trackways Evazoum and Otozoum: implications for ‘prosauropod’ (basal sauropodomorph) gaits

ABSTRACT

Trackways of bipeds and quadrupeds attributed to Late Triassic and Early Jurassic basal sauropodomorphs (‘prosauropods’) fall into several ichnogenera. Four of these – Otozoum, Pseudotetrasauropus, Evazoum and Kalosauropus – are conceptually subsumed into the OPEK plexus, where the former two represent large facultative quadrupeds, and the latter two represent bipeds. In revaluating ~53 measurable Evazoum tracks from 13 Upper Triassic sites in the Northern Hemisphere, we found a consistently enlarged proximal pad on digit II, which together with digit I show highly variable registration. These suggest that the trackmakers tended to preferentially carry weight on digits III and IV. Furthermore, over a dozen Evazoum trackways also indicate notable variations in trackway width, consistent with previous inferences about the ‘prosauropodian’ gait. Comparisons to five Kalosauropus trackways from the Lower Jurassic of the Southern Hemisphere show that these two more closely related track types were likely made by basal sauropodomorphs (prosauropods) that were more fully adapted to obligatory bipedalism. The much larger Otozoum, reported from 16 trackways globally from both the Upper Triassic and Lower Jurassic, has trackway patterns that indicate changes in trackway width and shifts between bipedal and quadrupedal progression.

KEYWORDS:

• Dinosaur trackway
• OPEK plexus palaeogeography
• Otozoum
• Evazoum
• bipeds
• quadrupeds

Acknowledgments

We thank the reviewers Christian Meyer, University of Basel and Spencer G. Lucas, New Mexico Museum of Natural History and Science, for contributing with their insightful comments to the overall quality of this study. Christian Meyer also kindly provided a photograph of a manus-pes set of Otozoum-like tracks originally illustrated with only a line drawing by Ishigaki (1988). Opinions expressed and conclusions reached are those of the authors and are not necessarily to be attributed to the funders or anybody else.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.

Additional information

Funding

The work was supported by the Offices of the Dinosaur Trackers Research Group, University of Colorado Denver to MGL; German Research Foundation (DFG grant LA 4611/2-10 to JNL); Swiss National Science Foundation (SNF grant 200021_192036 for the Jurassic Globetrotters Project) to LS and National Research Foundation of South Africa GENUS DST-NRF Centre of Excellence in Palaeosciences (grant numbers CoE PAL 2019EB, 2020EB & 2021EB) to EM; National Research Foundation of South Africa GENUS (DST-NRF Centre of Excellence in Palaeosciences)National Research Foundation of South Africa GENUS (DST-NRF Centre of Excellence in Palaeosciences) [CoE PAL 2019EB, 2020EB & 2021EB];