Morrosaurus antarcticus

Right hind limb of Morrosaurus antarcticus, viewed front-on. The scaling of the limb bones was based on the Australian ornithopod specimen NMV P186047 ('Junior'), which might be referable to Leaellynasaura.

Dinosaurs reign supreme in Antarctica today. Sounds weird, doesn't it? But it’s true! The reason? Every bird braving the frigid southern continent, be it a waddling penguin or a wandering albatross, is a living, breathing, highly derived theropod dinosaur. You might then wonder: Are the birds of modern day Antarctica continuing an ancient legacy? Did dinosaurs reign supreme in Antarctica during the Mesozoic Era? The answer to both questions, as has become clear in the last three decades or so, is emphatically yes.

To date, Antarctica has only produced evidence of dinosaurs from the Jurassic and Cretaceous periods. All of the Jurassic specimens (of which I am aware) are held in institutions in the USA. However, fortunately for me, almost all of the Cretaceous-aged dinosaur specimens collected from Antarctica are housed here in Argentina. Next week, at Museo de La Plata, I will have the opportunity to study two of these. Earlier this week, however, I was privileged to be able to study the most recently named dinosaur from Antarctica — Morrosaurus antarcticus.

In the last two blog posts, I was able to provide a fair bit of information about the collection history of the other dinosaurs I studied at the Museo Argentino de Ciencias Naturales — Loncosaurus argentinus and Chubutisaurus insignis. This was largely possible because such details were published as part of the papers in which these specimens were described. Frustratingly, a similar level of information was not easily available for Morrosaurus! All I found out is that it was collected by geologists Juan M. Lirio and Héctor Nuñez during 2002 (or perhaps a year or two prior), based on an abstract published in Ameghiniana by them — in conjunction with Fernando Novas and Andrea Cambiaso — that year.

The type specimen of Morrosaurus (MACN 19777) comprises bits and pieces of a right hind leg. The shafts of the femur (thighbone) and the tibia and fibula (shinbones) are missing, but at least their top and bottom ends are preserved (only one end in the case of the fibula). By contrast, the metatarsals (the upper toe bones in the foot bound in flesh) are almost complete. In fact, I suspect that the only reason that they are incomplete is because of repeated freezing and thawing of the specimen: the part of Antarctica from which Morrosaurus derives is, in the modern day, covered by ice in winter but not summer. The metatarsals are quite distinctive: the middle one was evidently massive, whereas the flanking metatarsals are distinctly compressed, meaning that the metatarsus as a whole would have comprised a tightly-packed bundle of bones. Whether Morrosaurus possessed a rudimentary first and/or fifth toe is unknown based on the available material.

The first description of MACN 19777 was produced by Andrea Cambiaso and included as part of her 2007 Ph.D. dissertation. However, Cambiaso never published on this specimen, and evidently did not consider it worthy of a name since she did not give it one. Finally, in 2016, Sebastian Rozadilla and colleagues (including Novas and Lirio) decided that it was worth naming MACN 19777, and they dubbed it Morrosaurus antarcticus.

When I first saw the type specimen of Morrosaurus, I was struck by how large it was (well, relatively speaking; large for a small ornithopod, if you will). In fact, the same was true of Loncosaurus — both it and Morrosaurus were evidently quite a bit larger than even the largest of the known Cretaceous ornithopods from Victoria (Leaellynasaura, Atlascopcosaurus, Qantassaurus and Diluvicursor were quite titchy by comparison). Once I have seen Talenkauen and Macrogryphosaurus — both of which are larger still — I might ponder the significance of that size discrepancy further… for now though, I’ll press on.

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Metatarsals of Morrosaurus antarcticus viewed from behind. Note the small bivalve preserved near the bottom end of metatarsal IV.

​Morrosaurus lived during the Maastrichtian stage (72–66 Ma), the last phase of the Cretaceous Period. At that time, Antarctica was in much the same position on the planet as it is today, but both Australia and South America were situated further south and at least intermittently connected to Antarctica. Critically, Earth as a whole was far warmer than it is today, so much so that even the southernmost continent was evidently ice-free all year round — at least as far as the geological record tells us. Instead, it was covered in forest, and was clearly quite suitable for dinosaurs — remains of ornithopods, ankylosaurs, sauropods and theropods (including birds) have all been found in the López de Bertodano Formation, the rock unit from which Morrosaurus derives. Specifically, Morrosaurus itself was found at a locality called “The Naze”, more properly known as Península el Morro (from which its name derives), on James Ross Island. 

Finally, it should be noted that Morrosaurus is not the only ornithopod dinosaur to have been found in Antarctica, nor was it the first to be discovered there. That honour goes to a presently undescribed ornithopod, held in the United Kingdom, which was first reported on in 1991 but remains undescribed. The only other ornithopod specimens from Antarctica are a few hadrosaur fragments, and another small ornithopod — which is one of the two Antarctic dinosaurs I shall see at La Plata next week! More on both of them then.

References

Barrett, P., Milner, A. & Hooker, J., 2014. A new ornithopod dinosaur from the latest Cretaceous of the Antarctic Peninsula. Journal of Vertebrate Paleontology, Abstracts of Papers, Seventy-fourth Annual Meeting 34, 85A–86A.

Cambiaso, A.V., 2007. Los ornitópodos e iguanodontes basales (Dinosauria, Ornithischia) del Cretácico de Argentina y Antártida. Ph.D. thesis. Universidad de Buenos Aires, Buenos Aires, Argentina, 410 pp. (unpublished).

Case, J.A., Martin, J.E., Chaney, D.S., Reguero, M., Marenssi, S.A., Santillana, S.M. & Woodburne, M.O., 2000. The first duck-billed dinosaur (family Hadrosauridae) from Antarctica. Journal of Vertebrate Paleontology 20, 612–614.

Hooker, J.J., Milner, A.C. & Sequeira, S.E.K., 1991. An ornithopod dinosaur from the Late Cretaceous of West Antarctica. Antarctic Science 3, 331–332.

Novas, F. E., Cambiaso, A. V., Lirio, J. M., & Nuñez, H. J. (2002). Paleobiogeografía de los dinosaurios polares de Gondwana. Ameghiniana, 39, 15R.

Rich, T.H., Vickers-Rich, P., Fernández, M. & Santillana, S., 1999. A probable hadrosaur from Seymour Island, Antarctica Peninsula. In Proceedings of the Second Gondwanan Dinosaur Symposium: National Science Museum Monograph, 15. Tomida, Y., Rich, T.H. & Vickers-Rich, P., eds, Tokyo, 219–222.

Rozadilla, S., Agnolin, F.L., Novas, F.E., Aranciaga Rolando, A.M., Motta, M.J., Lirio, J.M. & Isasi, M.P., 2016. A new ornithopod (Dinosauria, Ornithischia) from the Upper Cretaceous of Antarctica and its palaeobiogeographical implications. Cretaceous Research 57, 311–324.