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.

Muttaburrasaurus: Beast of the Week

 This week we will be checking out a mysterious plant-eating dinosaur that called what was once Australia home.  Enter Muttaburrasaurus langdoni!

Muttaburrasaurus was a plant-eating dinosaur that lived in what is now Northern Australia during the early to middle Cretaceous period, between 103 and 113 million years ago.  From snout to tail it measured about 23 feet (7m) long.  Its name translates to "Muttaburra Reptile/Lizard" in reference to the part of Queensland in Australia where its fossils were first found. 

Muttaburrasaurus life reconstrucion in watercolors by Christopher DiPiazza.

Muttaburrasaurus would have stood on powerful hind legs, and possessed short but strong arms. It likely normally walked on two legs but would have been capable of dropping down to all fours at times if it wanted.  Scientists were able to predict this not only based on the proportions of its limbs, but also the shape of it's inner ear bones, which often can indicate an animal's posture and preferred head orientation.  

Skeletal mount of Muttaburrasaurus on display at the National Museum of Australia.

Muttaburrasaurus had a relatively long neck and proportionally small head with a snout was originally thought to have ended in a tall crest, similar to those of some hadrosaurs, but it was more recently found, thanks to finding additional missing parts of its skull, that it actually had a rather pointed, narrow snout with a bony bulge midway up the nose, making it much more unique looking.  We still don't know the exact purpose of this feature.  It probably had something to do with display within the species.  Others have suggested it perhaps had something to do with the dinosaur possessing salt glands to help it eat plants that grew in ocean water near where it lived.

Remember putting a plastic cup over your mouth as a kid?  It looks like that.

The back of Muttaburrasaurus' jaws were lined with leaf-shaped teeth for slicing through plants.  Unlike its distant relatives, the hadrosaurs, these teeth were arranged in a single row in each jaw with the new replacement teeth growing directly from below.  Muttaburrasaurus also possessed teeth at the very front of its snout, which is actually rare among ornithopod dinosaurs, notably also present in Thescelosaurus. (which it was also maybe closely related to?)  Like all ornithopods, the tip of its snout was a beak, which would have been for clipping vegetation. 

Skull of Muttaburrasaurus (missing the tip of the snout) (Photo courtesy of Alcharinga Journal of Paleontology.)

The environment Muttaburrasaurus would have lived in was near an ocean coast and would have been seasonally cold.  This is because during that part of the Cretaceous, Australia was much further south and still attached to Antarctica.  Some experts suggest Muttaburrasaurus may have even been adapted to eat plants and algae that grew in salt water, possibly as a food source during the colder months when other plants were more scarce.

Muttaburrasaurus was a member of the ornithopod group of dinosaurs, most famous for including distant relatives like Iguanodon and the "duck-billed" hadrosaurs.  Its identity within this group has proven to be more difficult to pin down.  It was originally considered a close relative of Iguanodon and was even reconstructed with thumb spikes to reflect this. Other experts have since suggested  it was more closely related to dinosaurs like Camptosaurus, and others more to the big-headed rhabdodontid family, like Zalmoxes. (The taxonomy of ornithopod dinosaurs is currently very complicated and tends to change as we discover more fossils.)

References

Bartholomai, Alan and Molnar, R.E. (1981). "Muttaburrasaurus: a new Iguanodontid (Ornithischia:Ornithopoda) dinosaur from the Lower Cretaceous of Queensland". Memoirs of the Queensland Museum. 20 (2): 319–349.

Herne, M. C.; Bevitt, J. J.; Milan, L.; Hocknull, S. A.; Tait, A. M.; Allen, C. M.; Rozefelds, A. C.; Molnar, R. E.; Weisbecker, V.; Bell, P. R. (2026). "Cranial anatomy, palaeoneurology, palaeobiology and stratigraphic age of the large-bodied ornithopod, Muttaburrasaurus langdoni Bartholomai and Molnar, 1981, from the mid-Cretaceous of Australia". PeerJ. 14 e20794.

Molnar, Ralph E. (1996). "Observations on the Australian ornithopod dinosaur, Muttaburrasaurus"". Memoirs of the Queensland Museum. 39 (3): 639–652.