Shit-eating Sharks and Fish of the Cretaceous

To keep abreast of the latest paleontological finds in Georgia, I often check the Georgia Journal of Science.  The March 2010 volume has a couple of fascinating articles.  The first is “Coprolites of Deinosuchus: Late Cretaceous Estuarine Crocodylian Feces from West Georgia,” by Samantha Harrell and David Schwimmer.

Deinosuchus rugosus may have been the most powerful predator to ever live in what’s now Georgia.  This monstrous crocodylian grew to 36 feet long, weighed 12,000 pounds, and had a bite force of 13,000 newtons, perhaps the hardest bite of any land animal to ever live.  It dominated the salt marshes of Cretaceous North America (salt marshes were the most widespread ecotone of its time) even seizing and killing dinosaurs such as hadrosaurs and tyrannosaurs.  Its most common prey, however, were turtles that it crushed in its deadly jaws.  It survived as a species from 84 million to 77 million years BP, and left many fossils on the West Georgia/East Alabama border along Hanahatchee Creek near Columbus.  It was neither alligator nor crocodile but is thought to be related to an ancestor of the former.  Dr. Schwimmer, a professor from Columbus College, has been studying dinosaurs in Georgia for almost 30 years, and he wrote an excellent book devoted to the ecology of this fearsome creature.

Part of the dust cover of Dr. Schwimmer’s excellent book about Deinosuchus.

Dr. Schwimmer and Samantha Harrell now believe they’ve identified coprolites originally excreted by Deinosuchus which they found associated with its fossils in west Georgia. 

Picture of Deinosuchus coprolites from Dr. Schwimmer’s book.

Surprisingly, fossil shark and fish teeth are occasionally found on the outside of these coprolites.  These are not interpeted to have been prey of Deinosuchus.  Instead, the scientists believe it’s evidence that the sharks and fish were feeding on its feces.  It’s thought that the strong digestive juices would’ve destroyed and rendered unrecognizable the shark’s teeth, if they had been eaten by Deinosuchus, but the ones they found are identifiable as those from crow sharks (Squalicorax) http://www.oceansofkansas.com/sharks/Kansas/s-kaup1.jpg , an extinct scavenging species.  See the link for a picture of a crow shark’s tooth.  Other crocodylian coprolites discovered in Georgia are thought to belong to another extinct crocodylian–Borealosuchus.

Coprophagy, or the eating of feces, is not that unusual in the animal world.  Box turtles eat deer feces.  Crows and ravens eat crap of all kinds.  Dogs fed dry dog food crave their own feces.  Rabbits and rats must reconsume their own feces for nutrient extraction.  Foals must consume the mama horse’s feces in order to obtain the bacteria they need to digest the plants they will eat as adults.  Some snails depend entirely on fish feces.  And many insects such as butterflies and dung beetles are all attracted to shit…like flies, as the old cliche` goes.

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The second interesting article from the March volume of the GJS is a “Preliminary Description of Pleistocene Rodents from Clark Quarry, Brunswick, Georgia,” by Ray Cornay and A.J. Mead who is from Georgia College in Milledgeville.  Clark Quarry is a productive fossil site, yielding adult and juvenile mammoth skeletons, the complete skull of a long-horned bison which I discussed in an earlier blog entry, and many other large and small mammal, bird, reptile, amphibian, and fish fossils.  Here’s the list of rodents found at this fossil site:

Woodchuck–Marmota monax

Bog lemming–Synaptomys cooperi

Capybara–Hydrochoeris holmesi

Florida or round-tailed muskrat–Neofiber alleni

Rice rat–Oryzomys palustris

Cotton rat–Sigmodon hispidus

Harvest mouse–Reithrodontomys

The first two species on this list no longer range this far south.

Current range of the woodchuck.  This map is a little off.  I’ve seen woodchucks in Lafayette, Georgia.  Notice how far south Clark Quarry is compared to this species’ present range.

Current range of the bog lemming.

The Florida muskrat ranges just a little south of Brunswick today by only a few miles.  This species was more widespread during the Pleistocene, but today is restricted to Florida and extreme south Georgia.  Rice rats, cotton rats, and harvest mice still live in the region.  The species of capybara found as fossil specimens here is, of course, extinct.

The presence of woodchucks and bog lemmings is evidence of much cooler summers than those of today’s south Georgia, but the other species indicate winters at least as mild as those of today.  Scientists believe a warm thermal enclave existed near the south Atlantic coast during the Ice Age, and many believe temperatures were more equable.  I think temperatures were more equable during some climate phases of the Ice Age, but not all the time.

Woodchucks and bog lemmings both prefer to inhabit meadow/forest edge habitat which was probably a predominant ecotone of the late Pleistocene southeastern coastal plain where a mixture of open forests, prairie and wetlands existed rather unlike the closed canopy forests of today.  Fire, megafauna grazing, passenger pigeon mast consumption, locust infestations, and rapid climate fluctuations created a dynamic habitat where the ratio of woodlands to grasslands waxed and waned.  Florida muskrats (which aren’t closely related to the common muskrat–Ondatra) like open marshes, and capybaras thrive in flooded grasslands, so I believe wet prairies must have been one of the common environments in this region during the late Pleistocene.

Tags: bog lemmings, Clark Quarry, Coprophagy, Cretaceous, crow sharks, David Schwimmer, Deinosuchus rugosus, harvest mice, long-horned bison, mammoth, round-tailed muskrat, Squalicorax, woodchucks