Ornithopod locomotion evolution from femur morphology (free pdf)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Free pdf:

Romain Pintore, Alexandra Houssaye & John R. Hutchinson (2025)
How femoral morphology informs our understanding of the evolution of ornithopod locomotion and body size
Palaeontology 68(4): e70016
doi: https://doi.org/10.1111/pala.70016
https://onlinelibrary.wiley.com/doi/10.1111/pala.70016

Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/pala.70016


Ornithopoda is one of the three main ornithischian dinosaur clades in which secondary quadrupedality is represented. However, when it evolved from obligate bipedality remains controversial. Indeed, the ability to alternate between the two habits was inferred in some ornithopods based on ichnological observations and a mosaic of bipedal and quadrupedal skeletal features. Yet a straightforward inference of such ability is complicated by the concomitant evolution of enlarged body mass, hence confusing the interpretation of skeletal features as related to quadrupedality or weight support. Previous 3D geometric morphometrics studies distinguished locomotor specializations from enlarged body mass in various archosaur femora (e.g. Triassic pseudosuchians and avemetatarsalians and giant Jurassic–Cretaceous theropods). Our study better characterizes ornithopod specializations by analysing 41 femora using 3D geometric morphometrics and comparing the results with those of the aforementioned studies. Whereas hadrosaur femora possessed quadrupedal archosaurian features (e.g. anteroposteriorly straight shaft, a symmetric fourth trochanter and a more obtuse angle between the lateral condyle and the crista tibiofibularis), femora from ornithopods with indeterminate locomotion were distinct from those of the obligate bipedal ones by having a laterally-bowed shaft (i.e. oblique femur). Oblique femora seem associated with a wider-gauge stance, previously inferred as indicating static bipedal abilities in a quadrupedal dinosaur clade (Titanosauria). Our study disambiguated femoral specializations to locomotor habit and weight support in heavy ornithopods with indeterminate locomotion, adding evidence that hadrosaurs were obligate quadrupeds and suggesting that non-hadrosaurian ankylopollexians and Rhabdodontidae may have had some facultative static bipedal abilities, which remain to be investigated biomechanically.

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