Garudimimus: Beast of the Week

This week we're checking out a feathered dinosaur that helps us understand the evolution of the "bird mimic" family of dinosaurs.  Enter Garudimimus brevipes!

Garudimimus was a theropod dinosaur that lived in what is now Mongolia during the Cretaceous period, between 96 and 89 million years ago.  From beak to tail it would have measured about 11.5 feet (3.5 meters) long and it likely would have been an omnivore when alive.  The genus name translates to "Garuda Mimic", in reference to Garuda, the half bird half human Hindu deity.  The species name, brevipes, translates to "short foot".

Watercolor life reconstruction of Garudimimus by Christopher DiPiazza.

Garudimimus was a member of the ornithomimosaur family of theropod dinosaurs that are famous for resembling ostriches while not being directly related to them, rather evolving a similar body plan independently millions of years prior.  Garudamimus is interesting because it can be considered a transition fossil, possessing characteristics of both older and more recent relatives of this family, and thus helping us understand how this group evolved.  Earlier members of the ornithomimosaur family, like Harpymimus, are known for having teeth and still possessing four toes on each foot, the first of which was very short and probably had no purpose, like the dewclaw on a dog.  Later living members, like Ornithomimus and Struthiomimus, had much longer, more slender limbs, with only three toes per foot and toothless beaks.  Garudimimus possesses a mix of these traits, having a stockier build with the vestigial fourth toe on each foot, but also a toothless beak.  Many paleontologists currently believe that Garudimimus is actually more closely related to the extremely large and unusual member of the ornithomimosaur family, Deinocheirus.    

Skull of Garudimimus on display at the Mongolian Natural History Museum.

Garudimimus' skull had a relatively narrow beak with a weak bite force, even compared to other ornithomimosaurs, suggesting it was more specialized to eating plants.  The sides of its beak had a sharper edge which may have helped it cut bite-sized pieces of leaves as it ate.  Its eye sockets were proportionally huge and round, implying it had a strong sense of sight and its neck would have been long and flexible, which would have been helpful for looking out for potential predators.  Some experts have suggested Garudimimus would have been active at night, but having large eyes doesn't always reflect a nocturnal lifestyle. (modern ostriches are a good example of this)

Garudimimus' legs were proportionally shorter and stockier than those of its later relatives, but it still would have been comparably fast, especially compared to other dinosaurs in its environment, likely relying on speed to avoid predation.  Like all members of its family it likely would have had feathers in life, which would have aided in regulating its body temperature, caring for eggs and young, and possibly for display within its species.  

References

Barrett, P. M. (2005). "The diet of ostrich dinosaurs (Theropoda: Ornithomimosauria)". Palaeontology. 48 (2): 347−358.

Hughes, G. M.; Finarelli, J. A. (2019). "Olfactory receptor repertoire size in dinosaurs". Proceedings of the Royal Society B. 286 (1904) 20190909.

Kobayashi, Y.; Barsbold, R. (2005). "Reexamination of a primitive ornithomimosaur, Garudimimus brevipes Barsbold, 1981 (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia" (PDF). Canadian Journal of Earth Sciences. 42 (9): 1501−1521.

Kurumada, Y.; Aoki, S.; Aoki, K.; Kato, D.; Saneyoshi, M.; Tsogtbaatar, K.; Windley, B. F.; Ishigaki, S. (2020). "Calcite U–Pb age of the Cretaceous vertebrate-bearing Bayn Shire Formation in the Eastern Gobi Desert of Mongolia: usefulness of caliche for age determination". Terra Nova. 32 (4): 246−252.

Schmitz, L.; Motani, R. (2011). "Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology". Science. 332 (6030): 705−708.