May 31, 2016

I tried to google “crocodiles are living fossils,” to see just how commonly that expression was used in popular articles. There were indeed a few articles that referenced this idea, suggesting that croc fossils from 80 million years ago would look identical the skeletons they have today. However, most were news stories reporting various discoveries in the fossil history of crocodiles and their relatives; in these, paleontologists repeatedly debunked the notion of the “living fossil,” each describing some of the strange twists and weird turns taken by crocs over the past 250 million years.

I wouldn’t argue that croc history is fraught with more twists than an M. Night Shymalan movie, but there’s ONE place where I think the “living fossil” statement can be used. The body plan of crocodiles, the overall construction of the various parts of the animal, has been maintained for at least 190 million years since the Jurassic Period. The long, flat snout; the low slung body with a sprawled posture; and the coat of armor have held true for all that time. Now, as I note in the episode, the individual species and families of crocodile-relatives that have explored this sit-and-wait aquatic ambush predator role have varied greatly through time. There is a constant pattern of competition, extinction, and dynamic change in the fossil record. But, if we are to use “living fossil” to describe the basic “shape” of the modern croc, I think that is pretty appropriate.

The creatures featured in this episode of Past Time are members of the extinct croc-relative family Allodaposuchidae: the short-snouted, big-toothed Lohuecosuchus and the alligator-like Agaresuchus. These two animals co-existed in a single ecosystem in the Late Cretaceous Period of Spain. As illustrated above by Carlos de Miguel (deviant art link below), the two were roughly the same size despite their dramatic differences in anatomy. It is unlikely that these two aquatic predators did not occasionally come to blows (bites?) over the body of a hapless dinosaur plucked from the riverbank. But, we know from today’s crocodile-dominated regions that multiple croc species can coexist just fine, suggesting that they don’t completely overlap in their ecological roles. The major anatomical differences between the new species suggests that they too were doing things slightly differently in the waters of the Lo Hueco ecosystem over 70 million years ago.
Dig Deeper (Links and References):

For more on this discovery, check out the original research papers by Iván Narváez of the Grupo de Biología Evolutiva, Universidad Nacional de Educación a Distancia in Madrid, Spain and his colleagues:

Lohuecosuchus was described in the journal PLoS One (http://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0140679).

Agaresuchus was described in the journal Cretaceous Research. This paper also talks about the high diversity and distribution of other allodaposuchids across the Cretaceous of Europe.
(http://www.sciencedirect.com/science/article/pii/S019566711630088X)

More paleoart by Carlos de Miguel can be found here: https://carlosdino.deviantart.com/

There haven’t been many books written about the storied history of crocodiles and their fossil relatives. My personal favorite is probably King of the Crocodylians by Dr. David Schwimmer, which is mostly focused on the gigantic Cretaceous North American animal Deinosuchus (http://www.amazon.com/King-Crocodylians-Paleobiology-Deinosuchus-Life/dp/025334087X/ref=sr_1_5?ie=UTF8&qid=1463549829&sr=8-5&keywords=Deinosuchus).

Perhaps I should get writing on that…