The Co-existence of the Rice Rat (Orzomys palustris) and the Florida Muskrat (Neofiber alleni)

Water-loving rodents of many different sizes abounded in Pleistocene marshes and swamps.  It’s likely man overhunted giant beavers (Castoroides ohioensis) and capybaras (Hydrochoreus and Neochoreus) into extinction, but several medium and small species remain.  Beavers (Castor canadensis) and muskrats (Ondatra zibethicus) are still common throughout the southeast, except in Florida where both are completely absent.  However, the presence of round-tailed or Florida muskrats (Neofiber alleni) proves that an aquatic rodent can survive in environments that host significant numbers of alligators. 

The Pleistocene range of the Florida muskrat is a curious example of Ice Age mammal distributions and how they differed from those of the present.  Today, the round-tailed muskrat is restricted to Florida, but during warm climate phases, they use to have a range that extended north.

Range map of the Florida muskrat.  During warm climatic phases of the Pleistocene, it was more widespread living as far north as Pennsylvania and Kansas where it shared the range with common muskrats (Ondatra).

Fossils of Florida muskrats were among those excavated from Ladds stone quarry in northwest Georgia.  These likely date to the Sangamonian Interglacial.  Their fossils have also been found in Texas, Kansas, and Pennsylvania and in many of these fossil sites their bones were associated with common muskrat (Ondatra) bones.  This is evidence that the 2 species of muskrats used to co-exist but presently they do not.  Because Florida muskrats are thought to be maladapted to cold climates, they must have only co-occurred with Ondatra zibethicus during extremly warm interglacials when winters were warmer than those of today. 

Florida or round-tailed muskrat (Neofiber alleni)

Round-tailed muskrat nest in Putnam County, Florida.  Photo by Alan Cressler.

Florida muskrats still share habitat with another aquatic rodent–the rice rat (Orzomys palustris).  The latter, though restricted to the south, is more widespread.

Rice rat range map

Rice rat (Orzomys palustris)

The rice rat feeds upon many of the same foods and utilizes Florida muskrat runways and feeding platforms.  They even occasionally build their nests on the roofs of muskrat nests.  Muskrat nests generaly consist of 12-25 inch grass mounds that are accessed by 2 tunnels saturated with groundwater.  Rice rats construct globular nests 6-18 inches in diameter and are located about 6 inches above the flood line.  The preferred habitat of both is a grassy marsh where bamboo cane, sawgrass, cattails, arrowhead, and pickerel weed grow.  Rice rats are omnivorous, feeding on succulent plants, mushrooms, seeds including those of iris and rice, insects, fiddler crabs, snails, fish, and carrion.  Florida muskrats are more vegetarian, eating mainly the stems of water plants and the roots of ferns, but Frances Harper reported that they ate crayfish as well.  Unlike muskrats, rice rats are not specifically adapted to aquatic life–they do not have waterproof fur and webbed toes and they can live in grassy meadows away from water.  But they are good swimmers and divers.

Florida muskrats are members of the vole family.  Most voles are small mouse-sized rodents, and muskrats are just big overgrown voles.  Florida muskrats are gregarious and share feeding platforms with other muskrats.  This behavior is not like that of other vole species including Ondatra which are territorial.  Rice rats are distantly related to white-footed or field mice.  Only 1 species of rice rat lives in North America, but many more occur in South America.  The North American species probably is descended from rodents that colonized the continent when a landbridge formed between the two.

I’ve never seen a rice rat, but I have seen common muskrats (Ondatra) quite often in and around Augusta, Georgia.  I took a boat ride on the Augusta canal a few years ago and saw a score of them.  I see their sign in Woodbridge Lake in Evans, and once I witnessed a hawk carrying a muskrat away.  I’ve seen a Florida muskrat on 1 occasion.  When I was about 10 years old, my grandparents lived on a canal in Inverness, Florida.  As I walked along the bank of the canal in the morning, a round-tailed muskrat swam along beside me and barked at me the whole time.

Frances Harper surveyed the Okefenokee Swamp circa 1920.  He estimated 10,000 Florida muskrats inhabited the swamp but none lived north of it.  However, fossil remains of Florida muskrats, dating to the Boling-Alerod interstadial (~14,000 BP) were found at Clarks Quarry, near Brunswick, which is slightly north of their modern day range limit.  Curiously, their fossils were found with woodchuck fossils (along with mammoth, long-horned bison, etc.).  The climate must have suddenly become much warmer, because woodchucks (which are a cool climate species) were still present in the region, though eventually they would disappear here.  It may be that the Boling-Alerod interstadial was a climate phase with warm winters but cool summers, so both species of rodent were able to live in the same geographic range.

George Leonard Herter writes in his classic Bull Cook and Authentic Recipes and Practices that muskrat is a delicious animal formerly popular to eat among pioneers of Swedish descent who settled in Minnesota.  His method of cooking muskrat was to a) remove the fat, b) boil the hind legs and hams for about an hour, c) season with salt, pepper, and nutmeg, d) sautee in butter and smother in onions and celery.  I assume removing the fat and boiling gets rid of the musky odor.

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.