Archive for February, 2011

CSI: Pleistocene Alaska

February 24, 2011

“Science” programs on cable networks are often idiotic.  I suppose the television producers want to boost ratings and make their presentation dramatic for entertainment value.  But for those of us who know a good bit more about the subject than the average couch potato, these programs are laughable.  I think it was the History Channel that featured a special about the Pleistocene megafauna that concluded the beasts became extinct because of global warming.  The imbecilic producers actually showed computer images of the beasts dropping dead due to a heat wave.  They made no mention of overhunting by humans which is a much more plausible cause of extinction.  Instead, they wanted to jump on the bandwagon of global warming phobia, unware that all of these “Ice Age” species survived the Sangamonian Interglacial which was on average warmer than present day temperatures.

Another program about megafauna extinction (either on Discovery or PBS) did give equal time to overkill, climate change, hyperdisease, and comet impact.  The latter two, in my opinion, are crackpot theories.  While it is clear that an extraterrestrial impact probably led to the extinction of the dinosaurs, the evidence that a comet caused the recent megafauna extinction event is not at all convincing.  Supposedly, the comet hit a glacier–explaining why there’s no impact crater.  The theory is on shaky legs to start, if it’s proponents have to make an excuse for the lack of a smoking gun.  Other independent scientists have been unable to replicate their findings, perhaps relegating the comet impact theory to the trash can of illogical ideas.  When interviewed for the above mentioned program, one of the comet impact proponents made an astoundingly illogical comment.  He stated that the overkill theory didn’t make sense to him because he couldn’t believe humans could kill every last individual of a species.

His statement demonstrates a remarkable ignorance of basic ecology.  Humans would not have to kill every last individual of a species to render it extinct.  All wild species of animals already have high rates of natural mortality.  Let’s take the mastodon for example.  Mastodons had a long lifespan and low birthrate.  Saber-tooths and scimitar-toothed cats caused a certain amount of mortality.  Diseases, such as tuberculosis, took a percentage more.  Accidents (falling into quagmires, males killing each other in battles for mates, etc.) took a toll as well.  But this was mortality the mastodon birthrate could keep up with, and they maintained their existence for millions of years.  However, the addition of human hunting was a variable that increased a mortality rate that exceeded their birthrate.   So man + natural mortality = extinction.  Remove man from the equation and it would be natural mortality = a still extant species.

In my opinion overhunting by man is the only cause of the demise of the Pleistocene megafauna.  There is no other logical solution to this mystery. But I don’t agree with Paul Martin’s blitzkrieg model of extinction.  I believe the process took thousands of years rather than hundreds.  A recent study supports my belief in a protracted overkill scenario.

Researchers taking cores of permafrost in Alaska’s north slope.  There is forensic evidence of extinct Pleistocene megafauna in some of these cores.  This forensic evidence dates thousands of years later than the most recent dated fossil evidence of these species.  That means these animals lived more recently than previously thought.  Photo from google images.

A group of scientists led by James Halle examined cores of permafrost found in Alaska.  They were looking for megafauna DNA.    The cores were dated using carbon dating and optically stimulated luminescence (see  http://crustal.usgs.gov/laboratories/luminescence_dating/technique.htmlxplanation for an explanation of OSL dating).  The dates of the cores with the megafauna DNA ranged from 11,000 to 8,000 years old.  This sediment is more recent than the youngest known dated megafauna fossils from the interior of Alaska.  (A population of dwarf mammoths is known to have survived on the Pribiloff Islands until ~4000 BP.)  These cores harbored DNA from mammoth, horse, bison, moose, and snowshoe hare.  This DNA is referred to as sedaDNA and comes from hair, feces, and urine.  It proves the existence of these species in the environment, even though they left no fossil evidence from this time period.  The mammoth DNA is 2600 years younger than the youngest known mammoth fossil from the interior of Alaska; the horse DNA is 3700 years younger than the youngest known horse fossil from this region.  Using sedaDNA is uniquely possible in Alaska, thanks to permafrost conditions, and it’s a technique probably not possible anywhere else. 

The scientists concluded that the continued existence of megafauna until ~7500 BP rules out climate change, the blitzkrieg model of overhunting, comet impact, and hyperdisease as the ultimate causes of megafauna extinction, though they do concede that anyone of these factors could’ve caused an initial population collapse.  Curiously, they made no mention of a protracted overkill model of extinction, which in my opinion this study strongly supports.

It occurs to me that previously disregarded recent dates of megafauna fossils my not be in error.  For example the Devil’s Den fossil site in Levy County, Florida yields remains of Jefferson’s ground sloth, dire wolf, Florida spectacled bear, southeastern lemming, saber-tooth cat, mastodon, horse, and flat headed peccary.  The fossils from this site were radiocarbon dated to be 7,000-8,000 years old–several thousand years later than when scientists believe these species became extinct.  Therefore, scientists disregard these dates as inaccurate due to some kind of contamination or obsolete carbon dating techniques.  I suggest scientists redate these fossils, as well as those from other sites with unusually young dates, using the more updated and improved methods of carbon dating.  It seems likely the Pleistocene megafauna may have survived in southeastern North America for several thousand years longer than previously thought.

References

Halle, James et. al.

“Ancient DNA reveals late survival of mammoth and horse in interior Alaska”

http://www.pnas.org/content/early/2009/12/16/0912510106.full.pdf

www.devilsden.com/

Rabbits will Inherit the Earth

February 16, 2011

Matthew 5:5 (“Blessed are the meek for they shall inherit the earth”) always reminds me of rabbits for these meek creatures surely could outlast man.  Imagine if humans destroyed each other with nuclear, chemical, or biological weapons.  With a penchant for rapid breeding, rabbits could rapidly recolonize the world after the warlike species, Homo sapiens, annihilated itself.

Georgia is home to 4 species of rabbits, and during the Pleistocene the southeast also harbored at least 2 kinds of hares.  At various times the lagomorphs (hares and rabbits) may have been more abundant (as a biological mass) than any single species of megafauna.  Scientists interpeted a fossil site near Gainesville, Florida to have been a dire wolf den because they found a skull belonging to Canis dirus in association with hundreds of rabbit bones.  Rabbits must have been an easy and abundant food source, more reliable than any single species of megafauna.  Rabbits easily survived the Pleistocene extinction event that wiped out many of the larger, fiercer animals.  The meek really did inherit the earth.

Here’s a review of rabbit and hare species found or formerly found in Georgia.

Rabbits

Eastern Cottontail–Sylvilagus floridanus

Photo of an eastern cottontail from google images.

While this species is by no means endangered, there are likely far fewer than there were as recently as 50 years ago.  Suburbs and shopping centers are replacing the early successional forests they prefer.  And the natural areas we let remain are maturing into older stands of timberland which is not as favorable a habitat for rabbits.  Rabbits like young forests with saplings, shrubs, and grassy open areas.  This type of habitat was abundant during the Pleistocene, thanks to rapid climate fluctuations, unchecked fires, and megafauna foraging.

New England Cottontail–Sylvilagus transitionalis

In a blog entry from a few weeks ago I listed the species found at the Ladds fossil site and mistakenly noted, about the New England cottontail, that I thought it was doubtful a subspecies could be determined based on a bone.  I didn’t realize the New England cottontail was a distinct species, not just a subspecies.  Today, the New England cottontail is being considered a candidate for the endangered species list.  Hunters introduced the eastern cottontail to New England, and it is doing well, but the New England cottontail is not adapting to suburbanization and is restricted to a small number of locations.  It looks much like an eastern cottontail.  They can hybridize with eastern cottontails in captivity but won’t do so in the wild.  Before advances in DNA research, scientists had to compare skulls to determine whether a cottontail was an eastern or a New England.  But now scientists can analyze the DNA of rabbit scat to identify species.  However, the fossil specimen from Ladds that Clayton Ray identified as a New England cottontail was probably an Appalachian cottontail.

Appalachian cottontail–Sylvilagus obscura

Photo of an Appalachian cottontail.  They look exactly like New England cottontails.  Only DNA analysis can determine the difference.  For that matter, visual inspection can’t differentiate between this and the eastern cottontail.  A skull comparison or a DNA anlysis is necessary for species determination between those species as well.

This species wasn’t identified or recognized until 1992.  Before then, it was considered the same species as the New England cottontail.  Scientists noted enough genetic differences to mark it as a distinct species, though there is academic debate about this.  Again, visual determination of live speciments can’t distinguish the difference between this and the eastern cottontail.  Instead, DNA tests or skull measurements are necessary.  The Appalachian cottontail inhabits heath balds in the north Georgia mountains.

Swamp rabbit–Sylvilagus aquatica

As this photo from google images shows, swamp rabbits readily take to water.  This is the rabbit that attacked President Carter.

Many readers of this blog may be too young to know about an event that occurred involving this species during the presidency of Jimmy Carter.  On vacation from the presidency Jimmy Carter sat in a canoe and fished a  Georgia swamp.  A swamp rabbit attacked his boat–probably the only instance when a sitting president was attacked by an animal.  I guess the rabbit was swimming in the swamp and felt threatened by the canoe.

Swamp rabbits occur alongside rivers and streams in the Georgia piedmont.  They’re known as canecutters because they eat bamboo cane which used to grow in thick stands many miles long in low areas of central Georgia.  Though canebrakes are rare today, swamp rabbits still can reside near the existing and numerous beaver ponds, another favored habitat.

Marsh rabbit–Sylvilagus palustris

Photo of a marsh rabbit from google images.

The range of this species takes up where the swamp rabbit’s leaves.  Whereas swamp rabbits occur in low areas of the piedmont, marsh rabbits inhabit coastal plain wetlands.

Hares

Antelope Jackrabbit–Lepus alleni

 

 

Photo of an antelope jackrabbit from google images.

Fossil hunters occasionally find jackrabbit bones in florida.  Antelope jackrabbits inhabited the southeast until, at least, the middle Pleistocene (~300,000 BP).  Dry climate phases created large scale grassland and even desert-like chapparel habitats where antelope jackrabbits shared the range with pronghorns, cheetahs, and camels.  As I speculated in my blog entry “The disjunct range of the burrowing owl,” a corridor between western grasslands and eastern grasslands must have existed until the Stagell Interglacial.  Forested habitats increased during this lengthy interglacial, and this probably ended the occurrence of many western species (though not all) in the east.  The skeleton of a large unnamed extinct species of jackrabbit, estimated to be about 2 million years old, has also been discovered in Florda.  Both species undoubtedly occurred in what’s now Georgia.  Today, antelope jackrabbits must be considered a relic species, restricted to southwestern deserts.

Snowshoe hare–Lepus americanus

 

 

Lynx attacking a snowshoe hare.  Photo from google images.

Fossil evidence proves Arkansas was home to snowshoe hares during the last Ice Age.  It’s quite possible snowshoe hares occured in north Georgia during the Pleistocene, and they probably lived in what’s now Tennessee.  Arkansas is well south of the present day range of this species.

Red Stewed Rabbit

In my irregular series on this blog, “If I could live in the Pleistocene,” I imagine living 41,000 years ago in what’s now east central Georgia but with modern conveniences such as a nice adobe brick home with solar-powered electricity, woodstoves,  running water from a well, and fresh produce grown in a well protected garden. (See my September and December archives) Though I raise poultry and milk cows in this imaginary utopia, I try to utilize as much game and fish as I can.  Rabbit would likely have to be an item in my diet, though I’m not too keen on killing them–their alarm call sounds like a human baby crying.  In real life I’ve experimented with rabbit and have learned that it is a good stewing meat.  Rabbit is all white meat with a flavor slightly superior to chicken.  If you’ve never had it, and someone served it to you, and you didn’t notice the different bone structure, you would think you were eating chicken. There’s not much fat on a rabbit but that’s the only part that might taste a little unusual in my opinion.

Many people fry rabbit like chicken.  It’s ok this way but I think a little dry.  Other cooking methods are apt to make the rabbit have a rubbery texture.  That’s why I recommend stewing rabbit in a crockpot.  Here’s the best recipe for rabbit I know.

Marinate a disjointed rabbit in 1 cup of soy sauce, 2 tbls of vegetable oil, 2 tbls of honey, 1 bunch of chopped green onions, and 5 spice powder and ginger powder to taste.  Place the rabbit pieces and the marinade in the crockpot and cook for 6 hours.  The meat falls of the bone.  A little bit of the sauce goes a long way–it’s a marinade, not a gravy, but a couple of sp0onfuls will season a side of egg noodles well.

Rabbit meat stewed in a crockpot with just onions, water, and salt also makes a good base for a Brunswick stew.  Just shred the meat, remove the bones, and add crushed tomatoes, cooked potatoes, canned limas, canned corn, and red and black pepper.

 

Cretaceous Non-Dinosaur Fossils Found in Georgia and Alabama

February 11, 2011

This week’s blog entry is a continuation of last week’s, but I’m going to highlight the non-dinosaur species of the Cretaceous that left fossils in the two state region.  Remember, half of this region was under ocean water, so most Cretaceous fossils found here are marine.

Mosasaurs–various species

I took this photo of a  tylosaurus skeleton at the Georgia Southern Museum in Statesboro.  Tylosaurus was a large species of mosasaur.  Disarticulated specimens are occasionally found in Georgia and Alabama, but nearly complete skeletons are rare.  Therefore, this specimen was imported from North Dakota where more complete specimens are more commonly found.

Scientists debate whether mosasaurs were more closely related to snakes or to monitor lizards.  They were much like giant replicas of the latter but with flippers instead of legs.  At least 4 species swam the shallow seas that inundated what’s now Georgia’s and Alabama’s coastal plain.  Tylosaurus, a 40 foot long monster, was the largest and king of the seas, preying on fish, octopus, sharks, plesiosaurs, and other mosasaurs.  Plenty of mosasaur fossils bear evidence of interspecific battles.  Platecarpus and Clidastes were two other common mosasaurs.  Globidens, named for its globe-shaped teeth, fed upon shellfish which it crushed with its specialized dentition.

Plesiosaurs–various species

Illustration of plesiosaur from google images.

The many species of plesiosaurs can be split into two general types: the long-necked and the thick-necked.  The long-necked types had ponderous, probably camouflaged, bodies.  They quietly swam into schools of fish before their head went into action, snapping left and right to destroy and consume schools of fish.  The thick-necked kinds were more active predators resembling mosasaurs in habit.

The Robust Crocodylian–Deinosuchus rugosus

Wow!  Look at the size of the skull on this monster.  This is a famous photograph of  a Deinosuchus skull mounted for many years at the Natural History Museum in New York.  David Schwimmer, the leading authority on this species, now writes that this skull was mistakenly reconstructed and the species was not quite this big, but still was almost as large…big enough to kill and eat tyrannosaurs.

I discuss this species more thoroughly in my blog entry, “Shit-eating sharks and fish of the Cretaceous,” from my October archives.  The largest crocodylian of all time likely fed upon tyrannosaurs and hadrosaurs, but turtles made up most of its diet.  It crushed the chelonians with blunt teeth powered by the the strongest jaw crushing strength in the history of the natural world.

Cretaceous turtles

I took this photo of Protostega gigas at the McWane Science Center in Birmingham.  It was the largest sea turtle of all time.

Cretaceous turtles are split into two genus: Toxochelyds and Protochelyds.

Ginsu Shark–Cretoxyrhina mantelli

All these shark teeth come from one species.  This photo is from the oceans of kansas website.

Scientists named 7 different species based on all the teeth from this single species.  Then in 1891, someone discovered a skeleton and found all these different teeth on one animal.  The fish is named after the famous knives advertised on late night television.

Armoured fish–Xiphactinus audax

I took these photos of a Xiphactinus audax replica skelton mounted at the McWane Science Center in Birmingham, Alabama.

Coelacanth

Photo of a coelacanth from google images.

This ancient species, a real living fossil, predates the age of the dinosaurs.  It’s closely related to the ancestor of the evolutionary link between fish and amphibians.  Coelacanths originally evolved 400 million years ago–long before dinosaurs evolved.  They survived the extinction of the dinosaurs 65.5 million years ago, and still survive today because they’re not good eating for humans who have only been around in our present form for .2-.3 million years.

No Cretaceous age  mammal fossils have been discovered in the two state region, but they may have been more common than dinosaurs in the upland areas.  They were probably small insectivorous animals, nocturnal in habit.  They didn’t live in a situation that would be prone to preserving them as fossils.   Dr. Schwimmer has found one leg bone of a Cretaceous bird from the Hesperornidae family.  Species from this family grew to 7 feet tall and were wingless, armless oddities that ate fish.  Primitive birds may have also been common in the upland areas but perchance didn’t live in a place that would make them likely candidates for fossilization.

References:

www.oceansofkansas.com

Be sure to check the above website out.  It’s a fantastic site.

 

 

 

Cretaceous Dinosaur Fossils Discovered in Georgia and Alabama

February 4, 2011

A fiery extraterrestrial object cooked the atmosphere and caused the extinction of all vertebrates not in the safety of water or in underground burrows 65.5 million years ago.  This event ended the reign of the dinosaurs which had been the dominant large animals for 140 million years and probably would still be today, if not for the evolutionary altering armageddon.  During this 140 million year period, thousands of species of dinosaurs evolved, became extinct, and were replaced with other dinosaur species.  Most of the evidence has vanished, destroyed by earth’s tectonic forces.  Evidence of Jurassic and Triassic age dinosaurs is absent in southeastern North America.  Though there are Jurassic outcroppings in the piedmont region of Georgia, none are fossiliferous.  However, a small piece of the state does yield Cretaceous age dinosaur fossils.  Dr. David Schwimmer, a geologist teaching at Columbus State, combed Hannahatchee Creek, a tributary of the Chattahoochee River, and in 1979 discovered a number of dinosaur fossils–a first for Georgia.  He’s returned to this site numerous times, and he frequently discovers disarticulated dinosaur remains though fossil shark teeth, fish bones, and turtle shells are far more common.  Hannahatchee Creek cuts through a Cretaceous lag deposit.  A lag deposit forms when an impediment on the ocean bottom collects bones drifting with the tides and currents.  Fossils accumulate in this same place and are cemented together.  The creek has since eroded through the deposit. Cretaceous Georgia was much different than modern Georgia.  Half of what’s now the state was under a shallow sea, south along a line from Augusta to Macon to Columbus.  A vast saltmarsh existed adjacent to the coast.  Inland habitats consisted of deep swamp with a few high and dry pine forests.  Grass had not evolved yet.  The climate was like a muggy July heat wave…year round.  There was no change of seasons. The following is a list of species that have left fossil evidence in Georgia and Alabama. Appalachiosaurus montgomeriensis

Fossil replica of the Appalachian tyrannosaur, one of at least two species of tyrannosaur that lived on the Appalachian side of North America. I photographed this replica at the McWane Science Center in Birmingham, Alabama.

It’s likely there was at least one other tyrannosaur on the Appalachian side of North America which was then split into three continents separated by a vast inland sea.  Neither grew as big as Tyrannosaurus Rex which lived on the western part of North America.  Along the coast of Appalachia, tyrannosaurs were not top predators–the giant crocodylian, Deinosuchus was.

This and the next two images are from  “A New Genus of Tyrannosauroid from the late Cretaceous (Middle Campanian) Demopolis Formations of Alabama” by Thomas Carr, Thomas Williamson, and David Schwimmer, JVP 25 (1) pp. 119-143 March 2005.  This illustration show which parts of the specimen were recovered.

Photos of actual Appalachiosaurus skull bones found in Alabama.

Illustrations comparing different species of tyrannosaur.  One of the ways to determine the anatomical difference between species of tyrannosaur is to compare the maxillary finestra.  This is a hole in the skull of tyrannosaurs found below the eye socket.  This hole is of a different size and shape in different species of tyrannosaurs.

Velociraptor sp.

Most velociraptors probably had feathers or protofeathers.  Most scientists believe they’re ancestral to birds. Illustration from google images.

Only one tooth of a velociraptor has ever been discovered on the Appalachian side of North America.  Nevertheless, they probably were common.  They’re almost invisible in the fossil record of eastern North America because they lived in upland habitats where the processes of fossilization were rare. Hadrosauridae

Parasaurolophus, 'beside Saurolophus,' a late Cretaceous herbivore with a hollow crest extending from the back of its skull.

Illustration from google images. Large herds of this communally nesting dinosaurs roamed Georgia.  These herbivorous giants ecologically replaced the famous sauropods.  They were able to chew their food–a big evolutionary advance.

Ornithomimids

Though they were birdlike, this is not the line considered ancestral to birds.

Nodosaurs

These vegetarians must have been tough nuts for predators to crack.

Pterosaurs

Most pterosaurs probably had feathers or protofeathers.  A recent study suggests they took a couple hops and used all 4 limbs to leap into the air commencing flight, a method unlike any flying animal existing today.  Pterosaurs weren’t dinosaurs but rather flying reptiles.  Most probably ate fish.

References Carr, Thomas; Thomas Williamson, and David Schwimmer “A New Genus of Tyrannosauroid from the Late Cretaceous (Middle Campanian) Demopolis Formation of Alabama” Journal of Vertebrate Paleontology 25 (1) 118-143 March 2005

www.auburn.edu/~kingdat/dinosaur_webpage.htm www.palaeos.com/vertebrates/Lists/Glossary/