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Sharks! Welcome Back to School

Welcome back to the new school year. Some of you will be excited to be back, seeing old friends, making new ones, and learning new things. Some of you will be sad to see summer end. Many of you will be doing both at once. Others of you of course aren’t in school and don’t care about it, but if you are here, you are nevertheless interested in learning cool new stuff. So it is a time for a celebration of the natural world.

Shark Week is a big summer event on the Discover Channel. It is probably their biggest viewer draw all year. Who doesn’t like learning about sharks and seeing them in all their awe-inspiring glory? Additionally, if one is keeping up with the weather, southern Louisiana is currently being deluged, with Baton Rouge and surrounding areas practically getting washed away.

So I thought this would be a good time for Paleoaerie to hold its own version of Shark Week. I can’t do a series of tv specials, so I am going to extend my Paleo Shark week over two full weeks. All this week I will be putting up short posts on marine creatures that swam in the oceans of southern Arkansas during the Cretaceous. Every day will be a new post on something that would make your swim…interesting. Next week will truly be Paleo Shark Week. Every day next week will be highlighting a different shark that would be swimming in the Cretaceous waters of southern Arkansas.

To kick things off, I will start with this creature.

goniopholisAR

This is a crocodylomorph, meaning that it is in the same group that includes crocodiles and alligators. Specifically, it is a member of the family Goniopholididae. Species in this group were, at least superficially, similar to modern crocodilians. They were semi-aquatic hunters living in marsh and swamp lands. They wouldn’t look out of place with the modern alligators swimming around Arkansas today, except that they probably couldn’t compete effectively with alligators, who are better adapted for the lifestyle than they were. They lived throughout much of the Mesozoic, from the early Jurassic to the Late Cretaceous, when the more modern forms replaced them.

Goniopholids are what is known as mesosuchians, which means “middle crocodiles”. Mesosuchians, as the name suggests, were more derived than the earliest crocodyliforms, such as the protosuchians, although less derived than modern-day crocodilians. Mesosuchians is not a formal name, but an informal and decidedly paraphyletic (i.e. not a valid cladistic grouping because it leaves out some descendants) name to designate those crocodyliform species showing the early characteristics and those that show the characteristics of the modern crocodilians. Here is a phylogenetic tree put out by Chris Brochu in 2001, showing the general relationships within the crocodylomorphs. The names on the left side of the long main line include everything from that point on, e.g. Crocodymorpha includes “sphenosuchians” and everything below it, but not the Aetosauria and above. Mesosuchians plus Eusuchia (which does include all modern groups) can correctly be called Mesoeucrocodylia, but that hardly helps us specify the group.

crocbrochu2

Simosuchus_clarki,_ROM.jpg

Simosuchus, Royal Ontario Museum.  Photo by Gordon E. Robertson.

 

Mesosuchians include a wide variety of animals with a large number of species. They include terrestrial  animals like the carnivorous boar croc Kaprosuchus and the herbivorous Simosuchus, as well as the more typical semi-aquatic pholidosaurs, which include the super croc Sarcosuchus, one of the largest crocodylomorphs ever, reaching almost 40 feet.

Sarcosuchus may not have been quite as big as Deinosuchus though. Deinosuchus was an alligatoroid (within the larger alligator family, but not a modern alligator), which potentially reached upwards of 40 feet, but may have been heavier set. Sarcosuchus lived in the early Cretaceous at the same time as Goniopholis in Arkansas, but lived in Africa and South America. Deinosuchus, on the other hand, lived int he Late Cretaceous right here in Arkansas. While we have no bones to prove this, we do know they lived in Texas and Mississippi, as well as many other places in the United States. The environment would have been suitable for them, so there is no reason to think they did not live here as well.

2002-01-16 15.40.23

Sarcosuchus life size model “attacking” my family.

 


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