[Reflections of SICB] S2: Walking with Dinosaurs

We asked students to revisit some of the sessions/authors showcased at SICB/SICB+ 2022 as part of our Reflections of SICB, of which S2 is showcased here.

Eudibamus cursoris, a species of bolosaur, one of the first known bipeds (photo courtesy of N. Tamura)

Peyton McCain, Florida Southern College

When thinking about how animals developed bipedalism, most people would think back to early mammals: great apes that walked on two legs in order to better provide for their offspring (as explained by this PBS NOVA article). However, bipedalism was seen as early as the Permian period, 290 million years ago. Most of these first bipeds, the bolosaurs, were wiped out in the Permian-Triassic extinction event, but bipedalism continued to be seen after. Dinosaurs, as we know them, were first seen during the Triassic period, appearing after the mass extinction event. As a group, dinosaurs persisted over a period of 165 million years, outlasting huge groups of other animals that roamed the Earth at the same time. The Triassic-Jurassic extinction was the cause of death for a lot of these species, including the “crocodile line” animals (excluding the direct ancestors of the crocodilians we see today). What is unknown, however, is what caused the downfall of the previously dominant crocodile line, and what allowed for the dinosaur line to take over their place of dominance.

What is the Locomotor Superiority Hypothesis?

Dr. John Hutchinson, Professor of Evolutionary Biomechanics at The Royal Veterinary College, noticed this gap in knowledge, and wanted to look more into what allowed the dinosaurs to succeed. Dr. Hutchinson, an American/UK double citizen, performs his research through The Royal Veterinary College. He was awarded a European Research Council grant, through which he funded his recently completed DAWNDINOS project. DAWNDINOS was a five-year-long research project intended to investigate the question of “Why did the dinosaurs succeed?”

Using the locomotor superiority hypothesis (LSH), Dr. Hutchinson and his colleagues investigated why the dinosaurs were successful, while the crocodilians weren’t. The LSH states that dinosaurs – mostly bipedal, light, agile animals – were able to outcompete the quadrupedal, heavier, armored crocodilians because they were able to run faster, and therefore get more food and avoid being eaten themselves.

DAWNDINOS takes this hypothesis and puts it to the test, first studying locomotion in living birds (descendants of the dinosaurs) and crocodiles (descendants of pseudosuchians, the extinct crocodilians). They used this information to program computer simulations of extinct dinosaurs and pseudosuchians, comparing the possible locomotion. Their continued efforts in this area aim to use this information to determine whether or not the LSH is a plausible explanation for the success of the dinosaurs over the crocodilians. Although funding has been completed for this project, Dr. Hutchinson and his crew will continue to address what made dinosaurs different from other archosaurs – a reptilian group including dinos, birds, and crocodilians – and what (if anything) their bipedalism had to do with it.

Prestosuchus chiniquensis (left) and Eoraptor lunensis (right), an example of pseudosuchus and bipedal dinosaurs, respectively. Both lived during the Late Triassic period. (photos courtesy of DiBgd & N. Tamura)

Meet the Archosaurs!

The species of archosaur that this project focused on included two living species and many different extinct species. The two living species being directly observed are the Nile crocodile (Crocodylus niloticus) and the Tinamous (Eudromia elegans). The Nile crocodile was used as a model for the extinct pseudosuchidae and relatives. Nile crocodiles most commonly walk on all four legs in a low stance, and also swim with their legs tucked against their bodies. Smaller crocodiles can also run in a “gallop,” similar to how Dr. Hutchinson and the DAWNDINOS team expect pseudosuchidae to have moved. Tinamous most closely match the anatomy of the most recent common ancestors of current birds, and will be used for comparison to the early dinosaurs.

The extinct species are a mix of pseudosuchidae, dinosaurs, and various close relatives. The DAWNDINOS team has chosen four pseudosuchians, three dinosaurs, two rauisuchians, one sphenosuchian, one archosauriform, and two dinosauriforms. As evidenced by this variegated list, the DAWNDINOS team plans to model a wide variety of groups. Other than the pseudosuchians and dinosaurs themselves, the team has isolated members of dinosauriforms (direct dinosaur ancestors), rauisuchians (a rare, under-researched variety of pseudosuchian), archosauriforms (direct archosaur ancestors), and sphenosuchians (ancestral crocodilians). Using this variety of species, the team aims to identify differences and possible ancestral links between the different modes of locomotion.

The archosaur family tree, under which crocodilians, dinosaurs, and avians fall. Dinosaurs have their own lineage within, in which non-avian dinosaurs and birds diverge into their own branches. (image courtesy of John Conway)

The DAWNDINOS Team

The DAWNDINO team was headed by Dr. Hutchinson and made up of six scientists, with a wide array of backgrounds.

Dr. Delyle Polet, works with the methods used to model the dinosaur and pseudosuchus locomotion. Dr. Polet is a postdoc with DAWNDINO, and has previously done research with conceptual locomotion models for mammals.

Louise Kermode is the research administrator, having previous experience working in project management. She has also worked in the Royal Veterinary College’s pathobiology and population sciences department.

Oliver Demuth works as an illustrator and 3D modeler for the project. Demuth also has experience working in the paleontological field, working directly with various museums around the world.

Dr. Philip Morris has experience in archaeology, paleontology, and skeletal anatomy evolution. He uses lots of 3D virtual reconstruction for his work, having done his postdoc at the University of South Florida on the anatomy and biomechanics of bird jaws.

Dr. James Charles completed his doctorate at the Royal Veterinary College, working with skeletal modelling of mice. He then completed postdoctoral positions researching human functional anatomy, specifically the metabolic cost of walking.

The last member of the DAWNDINO team, Dr. François Clarac, did his doctorate specifically on the bone structure and evolution of the crocodilian lineage, and has worked in many scientific fields. He will be working with DAWNDINO to assist in determining the locomotion methods of early crocodilian species.

Additionally, DAWNDINOS has a long list of collaborators, who are working with the team to assist in modelling, XROMM (x-ray reconstruction of moving morphology), and fossil analysis.

Dr. Hutchinson was able to share some results evaluating LSH at the 2022 SICB Annual Meeting in Phoenix, AZ. The results of which are now available in the Integrative and Comparative Biology journal: Walking—and Running and Jumping—with Dinosaurs and their Cousins, Viewed Through the Lens of Evolutionary Biomechanics.

Just like the non-avian dinosaurs themselves, DAWNDINOS (funding) has come to an end (but only after 5.5 years vs. 165 million). This doesn’t mean the extinction of the LSH or the DAWNDINO teams efforts though. Future studies established by this collaborative team will continue to evaluate the success archosaurs as it relates to their overall biomechanics, alongside other potentially advantageous features.

Research methods and related studies by the DINODAWN team is outlined further at www.dawndinos.com

Author: Jason Macrander

I am an evolutionary biologist using comparative ‘omics approaches in sea anemones and other venomous animals to address questions concerning venom evolution, protein function, and the physiology of symbiosis. In my research, I use sea anemones as a model to understand how evolutionary and ecological factors influence biological interactions and molecular diversity from a phylogenetic perspective. I am currently an Assistant Professor of Marine Biology at Florida Southern College.

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