A Very Cool Ancient Crocodile

I have never actually seen a snake eat a crocodile or a crocodile eat a snake, but I am pretty sure I've seen a snake planning to eat a Nile Croc. And that was in the geological present.

In the geological past, about 60 million years ago (during the "Eocene" a.k.a. "dawn age") there was a rain forest that is sort of the ancestor to modern rain forests, which is now a coal deposit (and thus, eventually, will be part of our air) in Columbia. It has yielded interesting materials, and the latest report, just published, is of a fossil dyrosaurid crocodyliform (ancient croc ancestor). It is African.

Dyrosauridae is a family of crocodiles that emerged prior to the K-T Boundary, in the Late Cretaceous, and that are mainly found through the Eocene. They are found in Arica, Eurasia, North America and South America. This makes sense because during much of that period of time, the Atlantic Ocean either didn't exist or was just forming and thus did not present a great barrier. One thing that is notable about the Dyrosauridae is that they survived the Great Extinction at the K-T Boundary. It has been suggested that organisms that lived in low wet spots had a better chance of surviving the initial rather dramatic heat waves that came off the impact site, but in this case, it may also have helped to have lived across a very large geographical region.

Fossils crocodyliforms are not too common in South America with a mere three previously identified types previously found. The paper just published reports "three partial mandibles, maxillary fragments, teeth, and referred postcrania." This new crock is placed in a new genus, Acherontisuchus. The mandible has characteristics of Dyrosauridae, and the new species, Acherontisuchus guajiraensis, is different from other dyrosaurids two main ways: Various esoteric details of the head bones which I will not bore you with here, and a body that would have been adapted to a "...more placid, fluvial habitat than most known Old-World dyrosaurids."

This new fossil was placed in the data set of previously known form to generate a cladistic analysis, to determine what is related to what on the family tree of the Dyrosauridae. The result of this indicates that the Dyrosauridae arose first in Africa, and then dispursed from there to what is now the New World multiple times. Also, the study indicates that the original Dyrosauridae ancestors lived in marine habitats and some of the more derived groups secondarily adapted to riverine habitats. Today, of course, most crocs live in fresh water rivers or fresh or alkaline lakes, and only some in marine environments.

But what about the snakes and crocs in this ancient forest, how did they get along?

First of all, did I mention that the new croc would have been about 20 feet long. In the same region at the same time, there was a snake called Titanoboa, that was rather larger, perhaps 40 to 50 feet in length. That is believed to have been the world's largest species of snake, though I'm confident other snakes of that size range will eventually be found (just a gut feeling at this point).

According to the paper's lead author, Alex Hastings, "The younger [crocs] were definitely not safe from Titanoboa, but the biggest of these species would have been a bit much for the 42-foot snake to handle."

The snake and the croc would also have likely competed for food.

The most significant part of this find with respect to evolutionary theory is this: When we see a diversity of animals living at the same time, and one form (living or reconstructed) seems to be the basal, primitive, less specialized one, it is easy to assume that this is most like the ancestor to all the other forms. In other words, a generalized form gives rise to many different species, some or many of which are specialize. However, the reconstruction of dyrosaurid evolution prompted by this find suggests that a diversity of specialized forms could arise from a prior also-specialized form. This, of course, could relate to the fact that the dyrosaurids diversified after the K-T boundary extinction event, probably in a world with many empty niches previous occupied by other crocodiles that were wiped out during that event.

Hastings, A.K., Bloch, J. I., & Jaramillo, C.A. (2011). A new longirostrine dyrosaurid (Crocodylomorpha, Mesoeucrocodylia) from the Paleocene of north-eastern Colombia: biogeographic and behavioural implications for New-World Dyrosauridae
Palaeontology, 54 (5), 1095-1116 : 10.1111/j.1475-4983.2011.01092.x