Testing for a facultative locomotor mode in the acquisition of archosaur bipedality

Grinham, Luke R. and VanBuren, Collin S. and Norman, David B. (2019) Testing for a facultative locomotor mode in the acquisition of archosaur bipedality. Royal Society Open Science, 6 (7). p. 190569. ISSN 2054-5703 DOI https://doi.org/10.1098/rsos.190569

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Official URL: https://doi.org/10.1098/rsos.190569


Bipedal locomotion is a defining characteristic of humans and birds and has a profound effect on how these groups interact with their environment. Results from extensive hominin research indicate that there exists an intermediate stage in hominin evolution—facultative bipedality—between obligate quadrupedality and obligate bipedality that uses both forms of locomotion. It is assumed that archosaur locomotor evolution followed this sequence of functional and hence character-state evolution. However, this assumption has never been tested in a broad phylogenetic context. We test whether facultative bipedality is a transitionary state of locomotor mode evolution in the most recent early archosaur phylogenies using maximum-likelihood ancestral state reconstructions for the first time. Across a total of seven independent transitions from quadrupedality to a state of obligate bipedality, we find that facultative bipedality exists as an intermediary mode only once, despite being acquired a total of 14 times. We also report more independent acquisitions of obligate bipedality in archosaurs than previously hypothesized, suggesting that locomotor mode is more evolutionarily fluid than expected and more readily experimented with in these reptiles.

Item Type: Article
Uncontrolled Keywords: 2019AREP; IA76
Subjects: 04 - Palaeobiology
Divisions: 04 - Palaeobiology
07 - Gold Open Access
12 - PhD
Journal or Publication Title: Royal Society Open Science
Volume: 6
Page Range: p. 190569
Identification Number: https://doi.org/10.1098/rsos.190569
Depositing User: Sarah Humbert
Date Deposited: 13 Mar 2020 14:20
Last Modified: 13 Mar 2020 14:20
URI: http://eprints.esc.cam.ac.uk/id/eprint/4655

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