Archive for October, 2010

The Paisley Cave Pre-Clovis Site

October 29, 2010

For this week’s blog entry I’m going to step away from southeastern North America and discuss a fascinating site in south central Oregon.  The Paisley Cave site collectively includes 8 different caves and rock shelters created when waves from an ancient Pleistocene Lake (Lake Chewaucan) eroded hollows into the upland bedrock about 17,000 years ago.  By 14,500 years ago weather patterns changed, becoming drier, and the lake receded away from the caves for a distance of about a mile.  But the climate here was still wetter than that of today, and the environment consisted of conifer woodland, meadow, and lakeside marsh; unlike the sagebrush desert which is now the primary type of ecotone at this location.  The caves were ideal shelters for Paleo-Indians, and the surrounding area provided abundant rock (obsidian) for tool-making, and a plentiful supply of big game, small game, waterfowl, fish, and edible wild plant foods.

Most of the caves contain evidence of early Holocene (~9,000o BP)occupation–charcoal from human-lit fires, basketry, and interesting tools such as wooden pegs and sagebrush rope.  But a cave known as Cave number 5 yielded evidence of pre-Clovis material including obsidian projectile points, debitage (the leftover flakes from stone tool processing), and scrapers, all associated with bones of megafauna–a camel ankle bone, the jaw bone of an extinct goat (Harrington’s Mountain goat? Oreamnos harringtoni), bison bones, and two long bones that looked like they were broken for the marrow.  There is one spot in this cave that’s been interpeted as a possible hearth, a  “a bowl-shaped depression with a rock lined base,” where a burned horse bone was discovered.  Moreover, very old processed grass fiber and muscle sinew were found in the cave.  Most importantly, however, was the fossilized human feces carbon dated to 14,290 calender years BP which predates the Clovis era (13,200-12,500 BP).

DNA testing of the feces indicates these people descended from Siberians, meaning they were Asiatic, like native Americans.  An analysis of their fecal content showed they ate bison, dog, squirrel, bird, fish, wild sunflower seeds, and grass.

The Topper site near Allendale, South Carolina (which I visited a couple of years ago) yields tools in soils dating to before Clovis also.

Archaeologists and crew excavating the pre-Clovis trench at the Topper Site in Allendale, South Carolina.  The people there were very nice to me when I visited two years ago.

Tools found in the Aucilla River in Florida also date to slightly before the Clovis era.  I theorize small bands of humans began crossing Beringia and migrating across North America before the LGM (28,000-15,000 BP) when glaciers would’ve blocked their passage.  The reason evidence is lacking is because they were so few in number and so scattered they left little proof.

References:

Pinson, Ariane

“Paisley Caves: What’s the scoop on the poop?”

Mammoth Trumpet 23 (4)  October 2010

www.uoregon.edu/-ftrock/paisley_caves_description.php

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Did the Rocky Mountain Locust Infest Southeastern North America During the Pleistocene?

October 22, 2010

The first frosts of fall are about to end the lives of most adult insects here in Georgia.  Before we say goodbye (and in some cases good riddance) to the denizens of the insect world, let’s consider a couple of interesting species.

We’ve all heard of comically cheap horror movies such as “The Monster that ate Toledo,” but the Rocky Mountain locust literally did eat great swaths of the midwest during several 19th century invasions when they consumed farmer’s crops, every blade of grass, all the leaves of trees and shrubs, fence posts, carrion, hanging laundry, sheep’s fleeces, leather shoes, and each other.  The natural world humbled our pioneer ancestors. However, no specimen of this species (Melanoplus spretus),  the swarming phase of the short-horned grasshopper, has been collected since at least 1899–an astonishing extinction because an 1875 swarm estimated to be in the trillions and covering a territory the combined size of New England and the mid-Atlantic states descended upon the midwest and devastated farmer’s crops.

Top: Illustration of the short-horned grasshopper.  Bottom:  Illustration depicting farmers’ futile attempts to stop these locusts from destroying their wheat fields.

Laura Ingalls Wilder, author of the Little House series, gives an account of this disaster in her book, On the Banks of Plum Creek.  Her father had bought a nice frame house and planted a field of wheat–both on credit.  He did this as a gift for his wife so she wouldn’t have to continue living in a sod house with a dirt floor.  Laura reported that one day a cloud of locusts appeared in such large numbers they blocked out the sun.  They settled on her father’s wheat field and destroyed his crop, forcing him to leave home for six months in order to earn money as a laborer and pay back his loan–a sad situation, especially in the days before the telephone when the only communication was the snail-like mail.

Locust swarms were common during draught years throughout the 19th century, but apparently this insect became extinct around 1900.  Why did it become extinct?  Grasshoppers lay their eggs in the ground.  Scientists think farmers first cultivating land near the Rocky Mountains plowed the insect’s communal nesting grounds, destroying the buried eggs, and thus accidentally managed to wipe this disastrous pest into oblivion.  At first its extinction wasn’t even noticed because other species of grasshoppers took their place and did considerable damage as well.

The swarming behavior of this grasshopper species occurred only during drought years, much like that of swarming species of locust still found in Africa today.  Drought increases the nutritional content of plants by concentrating sugar and nutrients, and it weakens plant defenses.  The surviving plants exist in shrinking numbers near moist sites such as river valleys.  When these grasshoppers congregate in large numbers to feed on the shrinking number of surviving but highly nutritious plants, they begin coming into contact with each other.  Touching each other causes their serotonin levels to rise which in turn causes physical changes–they change color (turning red), they eat more, breed more, and it signals their swarming migratory behavior.

During the last glacial maximum from 28,000 BP-15,000 BP (calender years) drought conditions were prevalent in southeastern North America, and many upland sites probably consisted of scrub oak, cedar, and grass due to a dearth of lightning induced fires.  It occurred to me that this was the type of environment Rocky Mountain locusts would’ve found suitable.  The spread of closed canopy forests following the end of this severe glacial stage eliminated much of this suitable habitat east of the Mississippi.  During the 19th century, this species no longer occurred east of western Arkansas and did not penetrate the southeast.

Evidence that Rocky Mountain locusts swarmed in large numbers during the Ice Age can be found in the ice of Grasshopper Glacier located in Custer National Forest (Montana) where millions of dead mummified locusts are embedded. See the following link for a photo of one of these fossils

http://fcmdsc.wordpress.com/2010/09/17/the-rocky-mountain-locust/

Parts of swarms flew over this glacier and they succombed to the cold, dropped from the sky, and froze.  Today, global warming is causing this glacier to retreat, exposing these mummified locusts to decomposition.

In the southeast climatic conditions during the last glacial maximum were so dry that many river beds dried up, creating large amounts of exposed sand and sand bars.  Frequent winds blew this sand into large eolian sand dunes that rolled across the landscape until wetter conditions returned and plants took root and held these sand dunes down.  There are many of these sand dunes in Georgia today, such as the Ohoopee Dunes, but they’re covered in vegetation and hidden.

Many western species of vertebrates colonized what’s now Georgia, especially during the dry climate phases.  Paleontological evidence from Georgia and neighboring states show that 13-lined ground squirrels, jack rabbits, hog-nosed skunks, badgers, coyotes, prairie chickens, upland sandpipers, magpies, ravens, sharp-tailed grouse, and burrowing owls lived in the southeast.  If western species of vertebrates lived in the region, than it’s logical to assume western species of invertebrates lived here as well.  It’s likely that congregations of megafauna and locusts around shrinking waterholes during severe droughts denuded vegetation, thus contributing to the formation of eolian sand dunes.

North America’s Little Known Army Ants

Of the 150 species of army ants in the genus Neivamyrmex, only 3 are able to inhabit the climate of temperate North America with its freezing temperatures during winter.  These species are likely relics from a time previous to when the Ice Ages began to occur.  Before the Pliocene many more species of army ants likely occurred in North America for they’re believed to have originally evolved during the Cretaceous.  All 3 of the temperate species of army ants have been recorded in Georgia including Neivamyrmex carolinensis, though there are more North American species found in Texas and southern California and the southwest.

http://www.cs.unc.edu/~hedlund/playpen/ants/GenusPages/Ecitoninae/Neivamyrmex.html

I’ve seen this medium-sized, muscular-looking red ant on at least one occasion when I witnessed a dozen tearing apart an earthworm.  (I’m not an entomologist so I can’t guarantee my identification.)  The reason these species are little known is because they’re mostly nocturnal and don’t form enormous colonies, like their South American cousins.

A total of 144 species of ants have been recorded from Georgia; 218 from Florida.  There are probably many more that scientists haven’t surveyed.  Here’s a good source for indentifying ants– www.antweb.org

References:

Ipser, Reid; et.al.

“A survey of ground dwelling ants (Hymenoptera: Formicidae) in Georgia”

Florida Entomologist 87 (3) September 2004

Lockwood

Locust: The Devastating Rise and Mysterious Disappearance of an Insect

2004

Shit-eating Sharks and Fish of the Cretaceous

October 15, 2010

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.

Why did Fanged Cats have Long Forelimbs and Sloping Backs?

October 8, 2010

Until about 13,000 calender years ago, two species of large, powerful, fanged cats stalked the beautiful forests and plains of southeastern North America.

Smilodon depicted in top illustration; Dinobastis on the bottom.

The more famous saber-tooth (Smilodon fatalis) is well known from the thousands of specimens found in the La brae tar pits in California, but many have also been discovered in Florida, and some fossils of them have turned up in Alabama, Tennessee, and South Carolina.  Fossils of the scimitar-tooth (Dinobastis serus) are less common–nearly complete skeletons in North America only being discovered in Friesenhahn Cave, Bexar County, Texas, though individual specimens have been found in Oklahoma, Tennessee, Florida, and some western states, such as Alaska.  This latter species had a worldwide distribution, leaving fossils in what today is England as well as Africa.

Sketch of skull found in Friesenhahn Cave from The Bulletin of the Texas Memorial Museum number 2 September 1961.

The skulls of both species of fanged cats are similar, but the two differ greatly in dentition.  The scimitar-tooth had larger incisors, but its fangs or canines were shorter and smaller.  Smilodon’s fangs were serrated in front; Dinobastis’s were serrated on both sides. When Smilodon closed its mouth, the fangs extended lower than the jaw, while Dinobastis’s fangs only reached the bottom of the jaw.

Both species had longer forelimbs than hindlimbs.  The scimitar-tooths had even longer forelimbs than the saber-tooth’s, but they weren’t quite as heavily built.

Based on anatomical characteristics, scientists believed saber-tooths and scimitar-tooths were closely related, and a recent study of DNA supports this hypothesis.  They are considered a sub-family within the Felidae.  The fanged cats are in the Machairodontinae, while all other cats, including every extant species, are considered to be in the Felinae.  See: http://www.adelaide.edu.au/acad/publications/papers/SmilodonFinal.pdf

The fanged cats had a sloping back, much like modern day hyenas (Crocuta crocuta), and likely ran about in a gait that would have resembled that of a hyena.  I’ve often wondered why they were built like this.  Some scientists speculate the longer forelimbs gave them an advantage when hunting juvenile proboscideans.  But it occurred to me after watching videos of a hyena fighting off a pack of wild African hunting dogs, that perhaps this build made it easier for them to do battle with packs of wild canids, such as their most important ecological competitor, the dire wolf, though dholes or red Indian dogs also occurred in the central part of North America during the Pleistocene, and were probably an important competitor there as well.

http://www.youtube.com/watch?v=YiqAxa1tJ5g

Perhaps with a sloping back, it was easier for the fanged cats to sit on their haunches and use their paws and fangs to defend themselves against packs of wolves that would’ve tried to nip them from behind and even bite their hamstrings.

Cats are distantly related to hyenas.  The cat branch on the evolutionary tree is placed next to the hyena branch, and the machairodontinae sub-family is the closest cat related to the hyenas.  The trait of a sloping back and longer forelimbs evolved millions of years before the Pleistocene, perhaps originating with some common ancestor of hyenas and cats.

Friesenhahn Cave in Bexar County, Texas

This is a really nice sketch of Friesenhahn Cave from the previously mentioned periodical.  The artist’s name isn’t given.

A sinkhole on a cattle ranch in south central Texas opens to an ancient cave where thousands of Pleistocene age fossils have been preserved.  Two nearly complete skeletons of the scimitar cat were discovered here about fifty years ago, along with the skeletons of two scimitar cat kittens.  This species periodically must have used the cave as a den for millennia.  The Pleistocene-age fossils are dated from between 19,000-17,000 years BP.  Some other fossils in the cave date to 9,000 BP, and some are even more recent, dating to less than 300 years BP.   Scientists believe the surrounding environment was mostly arid grassland, but occasional heavy rains (due to the drastically fluctuating Ice Age climate) caused flash floods that washed sediment into the cave, burying the bones of dead animals.  Later, the cave entrance collapsed, sealing the bones from the atmosphere.  Moreover, the limestone in the soil contributed to the preservation of the fossil material.  The sinkhole formed recently, providing the opportunity for people to discover the cave.

Thousands of baby mammoth teeth were recovered here–evidence that scimitar cats ambushed them and dragged them in the cave.  Though a pond that existed in the cave may have attracted herbivores seeking drinking water, the sheer number of individual baby mammoth specimens that accumulated here must have been the result of scimitar-tooth cat predation.  Scimitar-tooth cats must have specialized in preying on juvenile proboscideans–baby mastodon teeth were found here too.  How they successfully hunted baby mammoths, guarded by adults, is a mystery.  I assume they ambushed ones that wondered too far from the herd.

In addition to the scimitar cat fossils, the cave was the final resting place for many other Pleistocene animals.  One tooth of the other fanged cat, Smilodon fatalis, was found here along with many coyote fossils, and some of black bear.  Other remains include mammoth, mastodon, ground sloth, deer, bison, horse, camel, tapir, long-nosed peccary (a nearly complete skeleton), flat-headed peccary, black-tailed jack rabbit, cottontail rabbit, eastern chipmunk, pocket gopher, bog lemming, pine vole, eastern mole, short-tailed shrew, desert shrew, giant tortoise, box turtle, aquatic turtles, toads, snakes, and lizards.  There may be some human artificats, but nothing definite because it’s sometimes difficult to distinguish natural artifacts from manmade ones.

Scientists think the Pleistocene environment that existed at the time the specimens were deposed is one that no longer occurs anywhere.  They believe that what was to become Bexar County was mostly an arid grassland interspersed with riparian woodlands consisting of deciduous trees.  It is strange that the desert shrew, a species of the southwest desert, lived near the eastern chipmunk which lives in moist woodlands.  And indeed grassland species (bison, horse, camel, mammoth) and woodland species (mastodon, deer, long-nosed peccary, tapir) both found suitable habitat near the cave.

 

The Paw Paw, a Favored Fruit of the Mastodon

October 1, 2010

A large exotic fruit used to be a common component of North America’s virgin bottomland forests.  The paw paw (Asimona triloba), also known as the prairie banana, the Hoosier banana, the Michigan banana, and the custard apple is the only temperate member of a tropical family of fruit trees.

Paw paw fruit cut in half.

It looks delicious and is related to the cherimoya which can occasionally be found in some supermarkets.  Reportedly, paw paws taste like banana custard, a rich flavor that some love but others find too cloying.  Unfortunately, when shipped, it turns to brown mush, so unless the curious epicure has a tree in their neighborhood, they’re out of luck.  I’ve wanted to try this fruit for decades but have been frustrated–none grow in the second growth woods around Augusta, Georgia.  I did come across some on a hike through the Congaree Swamp in South Carolina many years ago, but the fruit wasn’t ripe in July–it ripens in September and October.   I have tasted cherimoya which is flavored like a cross between a pear and a pineapple.

Paw paws are still found in the wild today but are rare because they require shade to grow.  98% of North American forests have been cleared at one time or another, and once the virgin forest canopy is eliminated, paw paws don’t return.   Horticulturalists are breeding the trees for home gardeners, however.

Paw paws have large seeds that can go right through an animal’s digestive tract without being destroyed.  A number of scientists believe this species was dependent on the alimentary tracts of mastodons and giant ground sloths for dispersal.  No herbivore living in North America today is able to swallow the seeds whole.  Paw paws are only found in the wild alongside rivers and streams, despite growing well on upland sites when transplanted by humans.  Following the extinction of the megafauna, flooding was the only way the seeds could spread, explaining why they’re only found in the wild near waterways.  But during the Pleistocene, when mastodons and sloths ate the fruit, they carried them to upland sites and defecated the viable seeds there, so it’s likely this fruit had a more continous range then than it does today. 

Fossils of paw paws are known from as early as 50 million years ago during the Eocene.  It’s possibly an older species than that, being a food of dinosaurs as well.  Most of the family is tropical, but at least this species was able to adapt to temperate climates that began with the coming of the Pleistocene.

(I’ll send a free copy of my book to anyone who will ship paw paw seeds and/or fruit to me.)