A new Cretaceous terrestrial crocodylian, Montealtosuchus arrudacamposi


The new crocodylian Montealtosuchus arrudacamposi. [Image source].

ResearchBlogging.orgLiving crocodylians have often been referred to as "living fossils," creatures that have survived "virtually unchanged" for hundreds of millions of years. In truth, crocodylians as we recognize them today (i.e. aquatic ambush predators) first appear in the fossil record during the Jurassic (see comment below), but there was a much wider diversity of crocodylians during past epochs that were just as interesting (and even terrifying) as any dinosaur.* In the Bauru Basin of Brazil, for instance, the remains of at least five different groups of ancient crocodylians have been found, representatives of the notosuchids, sphagesaurids, baurusuchids, trematochampsids and peirosaurids all being found there. The latest addition to the Cretaceous crocodylian fauna of what is now Brazil is the terrestrial form Montealtosuchus arrudacamposi, recently described in the journal Zootaxa.

*A small, terrestrial crocodile dubbed Mekosuchus inexpectatus existed on some islands in the Pacific until very recently, perhaps around 1,700 years ago. Darren has more on this species and its relatives over at iteration 1 of Tetrapod Zoology.

Montealtosuchus was a peirosaurid, a group of crocodylians that (according to the paper of Carvalho, et al.) occurred only in South America, African, and Madagascar, essentially being restricted to Gondwanaland during the Cretaceous (remains of peirosaurids, across deposits in which they have been found, appear to have existed between 125 and 65 million years ago). Montealtosuchus lived during the Late Cretaceous, between 93 and 83 million years ago (Turonian-Santonian), in an area that was prone to floods by a river and had plenty of ephemeral ponds.

How can we say Montealtosuchus was probably terrestrial? I'm sure there are a number of traits (especially in the post-cranial skeleton) that would bear this out, but the placement of the eyes is important. Rather than having the eyes on the top of the head for the classic modern crocodylian profile, Montealtosuchus had eyes on the sides of its head that were oriented slightly forward, an arrangement differing from its relatives that were aquatic ambush predators. Montealtosuchus also exhibits a small degree of heterodonty in the maxilla region of the tooth row, two large and more conical teeth being followed by a set of smaller, more finely-serrated teeth that gives the skull an almost mammalian appearance. This sort of condition is not unknown in ancient crocodylians and is even more exaggerated in some species; in 1989 Clark, et al. described the existence of mammal-like dentition in a Cretaceous crocodylian from Malawi in Africa (Louis Jacobs describes the puzzle this fossil presented in Quest for the African Dinosaurs).

Unfortunately the paper does not offer much more illumination about this new species outside of the description of the skull and its significance in increasing the temporal range through which the peirosaurids are known in the Bauru Basin, but it is still an impressive find. I'm sure someone who is better versed in the diversity and evolution of ancient crocodylians could do a better job than I could describing the significance of this fossil and the habits of Montealtosuchus, but if nothing else the discovery of such a wonderfully preserved specimen is certainly exciting.

[Hat-tip to Jerry Harris for passing along the paper.]

CARVALHOCARVALHO, I., DE VASCONCELLOS, F., TAVARES, S. (2008). Montealtosuchus arrudacamposi, a new peirosaurid crocodile (Mesoeucrocodylia)
from the Late Cretaceous Adamantina Formation of Brazil. Zootaxa, 1607, 35-46.

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Crocs as aquatic ambush predators date back at least to theLlate Jurassic. Goniopholis, a genus present in the Early Cretaceous Bernissart deposit, is also present in the Morrison of western NA. Goniopholis' limbs are a little lanky in comparison to modern crocs, but the orbits are on the top of the skull, which would be particularly useless for a terrestrial carnivore. To be fair, most NA Goniopholis specimens are pretty pathetic -- just teeth, usually. Still, the Morrison was also home to Eutretauranosuchus, which is known from the more-or-less complete holotype at the Cleveland Musuem of Natural History. I got a chance to look it over as part of my master's thesis research. Larry Witmer down at OU had the skull at the time (so he could C-T scan it), so I can't testify as to the position of the orbits, but the critter was pretty stubby-limbed. However, Mook's 1967 paper on the critter focused entirely on the skull -- if anyone can track it down, I'd lay any (small) amount of money that the orbits face upwards. Given that the Metriorhynchus/Eutretauranosuchus clade contains all aquatic marine predators with the exception of Eutretauranosuchus (see the Crocodyliformes chapter in "In the Shadow of the Dinosaurs"), I would be surprised to find that Eutretauranosuchus was not itself at least a semi-aquatic predator.

Oh. Well, while cool by itself, it sounds like this croc isn't the big hullabaloo the press is making it out to be (duh!). And that's a really beautiful fossil skull.

I am fascinated by the skull and structure - eye placement and so forth, but with the somewhat mammalian structure, not to mention the existence of current species of non croc reptiles I am uncertain as to how this can be clearly placed in that class. Obviously I am no expert, but I also have a hard time understanding any of this when all I can see related to the creature is its skull (great find) along with what appears to be neck and back bone structure. How does the creature pictured in the back come from that? Except that there are creatures today who somewhat resemble type of structure, although without that type of head. I'd appreciate any clarification.

By Craig Spofford (not verified) on 13 Feb 2008 #permalink