A walk in the maze: Variation in Late Jurassic tridactyl dinosaur tracks - A case study from the Late Jurassic of the Swiss Jura Mountains (NW Switzerland)
- Published
- Accepted
- Subject Areas
- Paleontology
- Keywords
- Dinosaur ichnology, Theropods, Kimmeridgian, Reuchenette Formation
- Copyright
- © 2018 Castanera 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. A walk in the maze: Variation in Late Jurassic tridactyl dinosaur tracks - A case study from the Late Jurassic of the Swiss Jura Mountains (NW Switzerland) PeerJ Preprints 6:e3506v1 https://doi.org/10.7287/peerj.preprints.3506v1
Abstract
Background. Minute to medium-sized (FL less than 30 cm) tridactyl dinosaur tracks are the most abundant in the Late Jurassic tracksites of Highway A16 (Reuchenette Formation, Kimmeridgian) in the Jura Mountains (NW Switzerland). During excavations, two morphotypes, one gracile and one robust, were identified in the field. Furthermore, two large-sized theropod ichnospecies (Megalosauripus transjuranicus and Jurabrontes curtedulensis) and an ornithopod-like morphotype (Morphotype II) have recently been described at these sites. Methods. The quality of preservation (preservation grade), the depth of the footprint, the shape variation and the footprint proportions (FL/FW ratio and mesaxony) along the trackways have been analysed using 3D models and false-colour depth maps in order to determine the exact number of morphotypes present in the tracksites. Results. The study of the footprints (n = 93) collected during the excavations has made it possible to identify and characterize the two morphotypes distinguished in the field. The gracile morphotype is mainly characterized by a high footprint length/width ratio, high mesaxony, low divarication angles and clear, sharp claw marks and phalangeal pads (2-3-4). By contrast, the robust morphotype is characterized by a lower footprint length/width ratio, weaker mesaxony, slightly higher divarication angles and clear, sharp claw marks (when preserved), whereas the phalangeal pads are not clearly preserved although they might be present. Discussion. The analysis does not allow the two morphotypes to be associated within a morphological continuum. Thus, they cannot be a consequence of extramorphological variations on similar tracks produced by a similar/single trackmaker. Comparison of the two morphotypes with the larger morphotypes described in the formation (Megalosauripus transjuranicus, Jurabrontes curtedulensis and Morphotype II) and the spatio-temporal relationships of the trackways suggest that the smaller morphotypes cannot reliably be considered small individuals of the larger morphotypes. The morphometric data of some specimens of the robust morphotype (even lower values for the length/width ratio and mesaxony) suggest that more than one ichnotaxon might be represented within the robust morphotype. The features of the gracile morphotype (cf. Kalohipus) are typical of “grallatorid” ichnotaxa with low mesaxony whereas those of the robust morphotype (cf. Therangospodus and ?Therangospodus) are reminiscent of Therangospodus pandemicus. This work sheds new light on combining an analysis of variations in footprint morphology through 3D models and false-colour depth maps, with the study of possible ontogenetic variations and the identification of small-sized tridactyl ichnotaxa for the description of new dinosaur tracks.
Author Comment
This is a submission to PeerJ for review.
Supplemental Information
List of the specimens analysed, their quality of preservation (preservation grade) and the maximum depth
Those with preservation grade 0-0.5 are not included in the figshare file. The tracks where the variation along the trackway has been analysed are in red.
Map of the Courtedoux—Béchat Bovais tracksite, level 500 (BEB500)
In red (gracile) and blue (robust) the minute to medium-sized tridactyl tracks and in green, the larger morphtoype (Morphotype II).
Map of the Courtedoux—Tchâfouè tracksite, level 1065 (TCH1065)
In red (gracile) and blue (robust) the minute to medium-sized tridactyl tracks and in green, the larger morphtoype (Jurabrontes curtedulensis see Marty et al., 2017).
Map of the Chevenez—Combe Ronde, level 500 (CRO500)
In red (gracile) and blue (robust) the minute to medium-sized tridactyl tracks and in green, the larger morphtoype (Morphotype II).