Armadillosuchus: One bad crocodyliform



Life restoration of the head of Armadillosuchus. From Marinho and Carvalho (2009).

ResearchBlogging.org When I was trying to come up with a title for this post I almost went with “Armadillosuchus: An armored crocodyliform you wouldn’t want to mess with.” Obviously I changed my mind. Not only was the title too long, but it was redundant to boot. All crocodyliformes (which includes living crocodylians) are “armored” in that they have little bony plates called osteoderms (primarily on the dorsal, or top, side of their bodies) beneath their scales, which in turn overlay a layer of bony plates called osteoscutes. Crocodyliformes are tough!

The newly-described crocodyliform Armadillosuchus from the Late Cretaceous deposits of Brazil, however, was carrying a more bizarre complement of armor. Right behind its head was an armored dome of hexagonal plates. This bony buckler was rigid, but could be moved independently of the head so that the neck was not always locked in one position. Now comes the really interesting part. Behind this “cervical shield” was a series of about seven mobile armored bands. (What the researchers call “mobile-banded body armor.”) This is very similar to what is seen in living armadillos, hence the croc’s name Armadillosuchus. This crocodyliform had “armadillo-like” armor even before the mammals did!



Armadillosuchus. The head is to the left, followed by the cervical shield and mobile-banded body armor. From Marinho and Carvalho (2009).

Yet Armadillosuchus was even stranger still. Despite the claim that crocodiles have persisted “unchanged for millions of years” there was a greater past diversity of crocodyliform types than is represented today. Armadillosuchus is a fine example of this. In addition to the armor bands it had large hand claws, a shortened snout, and teeth that differed throughout its mouth (contrary to the “homodont” condition I was taught to associate with reptiles in elementary school).



The partial upper and lower jaws of Armadillosuchus. The front is to the right. From Marinho and Carvalho (2009).

Indeed, Armadillosuchus had what looked like large, curved “canine” teeth, shorter teeth that stuck out straight forward at the front of the lower jaw, and stubby conical teeth with shearing ridges. The paleontologists who described it were not sure what it ate, but based upon this dental toolkit it may very well have been an omnivore. The large hand claws also suggest that it was a digger, possibly rooting about in the ground after food (again like modern armadillos).

But why all that armor? Was Armadillosuchus at risk of becoming prey to a bigger, badder crocodyliform? Possibly. The area in which it was found, the Bauru Basin, was chock-full of strange crocodyliformes during the Late Cretaceous (including the terrestrial species Montealtosuchus arrudacamposi I wrote about last year). Then again there might be another reason why this crocodyliform had mobile-banded body armor, so we should be careful when asking why it evolved this particular feature. Even so, it is still fascinating that during the Late Cretaceous this part of what is now Brazil was the land of the crocodyliformes; numerous forms have been found there that are unlike anything seen today.

I apologize if this entry seems a little breathless, but it is difficult not to get excited about such a wonderful new species! Who would have guessed that, sometime between 99 and 65 million years ago, there was a short-snouted crocodyliform with “tusks” in its mouth and armadillo-like armor on its back? I never would have imagined it, but the fact that such a form evolved has set my mind reeling. This is why I love paleontology!

Marinho, T., & Carvalho, I. (2009). An armadillo-like sphagesaurid crocodyliform from the Late Cretaceous of Brazil Journal of South American Earth Sciences, 27 (1), 36-41 DOI: 10.1016/j.jsames.2008.11.005