Predator and Prey in the Early Pleistocene of Florida

Pleistocene ecosystems supported a great variety of large predators.  During the early Pleistocene the saber-toothed cat (Smilodon gracilis, ancestor of S. fatalis) and Edward’s wolf (Canis edwardii, possible ancestor of C. dirus) were 2 important carnivores that kept herbivore populations in check.  A study analyzed the chemistry of megafauna bones from 2 early Pleistocene-aged sites in Florida to determine what these 2 predators chose to prey upon.  The study included data from 110 specimens of 12 species excavated from Leisey Shell Pit, and 51 specimens of 9 species found at Inglis 1A.  Species used from Leisey Shell Pit in addition to the 2 carnivores mentioned above included mammoth, mastodon, gompothere, horse, 2 kinds of llama, 2 kinds of peccaries, white tail deer, and tapir.  Subfossil remains from this site date to between 1.5 million years BP-1.1 million years BP during an interglacial climate phase when the environment is thought to have been lowland forest and swamp, though there must have been some grassland.  Species used from Inglis 1A were mastodon, white-tail deer, peccary, tapir, horse, llama, and an extinct species of pronghorn along with Smilodon and Edward’s wolf.  Subfossil remains from Inglis 1A date to between 1.9 million years BP-1.6 million years BP during a glacial climate phase when the environment is thought to have been a mix of longleaf pine savannah, oak scrub, and forest.

Jaw bone of the extinct Edward’s wolf, 1 of the oldest wolf species known to have lived in North America.

Photoshopped Smilodon gracilis, the evolutionary ancestor of the late Pleistocene Smilodon fatalis.

The results of the study indicate Edward’s wolf ate a greater variety of prey than Smilodon, but both species were adaptable to changing environments.  During the interglacial period Smilodon ate herbivores that fed in forest environments (mastodon, deer, tapir, paleollama), while wolves mostly ate grassland herbivores (mammoth, horse).  However, during glacial periods when grasslands predominated Smilodon adapted by eating more grassland herbivores.  Choice of prey among individual saber-toothed cats varied.  Some individual cats ate nothing but forest herbivores, while others ate just grassland herbivores.  I think this shows saber-tooths were territorial animals that stayed in the same home range their entire life.  They ate whatever prey occurred within their established territory.  Herbivores that fed in both forest and grassland (large-headed llamas, gompotheres, peccaries) likely fell prey to both carnivores.

Reference:

Feranec, Robert; and L. Desantis

“Understanding Specifics in Generalist Diets of Carnivores by Analyzing Stable Carbon Isotope Values in Pleistocene Mammals of Florida”

Paleobiology 40 (3) 2014

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The Leisey Shell Pit

During the late 1970s, Frank Garcia and other amateur fossil collectors often searched the spoil piles of the Leisey Shell Pit located about a mile east of Tampa Bay, Florida.  The Leisey family owned the site and mined the sand and seashells which are used in construction to make concrete and other building materials.  One day, Mr. Garcia discovered a wall of fossils exposed when a bulldozer stripped away a large layer of sand.

Arrow points to a layer of fossils found in the Leisey Shell Pit.

I think this is a photo of Frank Garcia standing next to the wall of fossils found at this site.  The fossils probably accumulated here through a combination of river and tidal action.  A major river that no longer exists may have flowed into Tampa Bay then.

Typical density of the fossils found at the shell pit.  Note the saber-tooth tiger canine in the middle.  The fossiliferous layer of one section was 2000 square meters.  If my math is correct, that’s the equivalent of about a square mile.  The site is so rich, paleontologists could have named a land mammal age after it.  Too bad the Irvingtonian Land Mammal Age already had a name.

After Mr. Garcia’s discovery, professional paleontologists descended on the site and excavated over 50,000 fossils in a decade of work, gaining valuable information about the early Pleistocene.  The majority of the fossils were found in 2 sections, labled IA and 3A, though fossils were also found in 2 smaller sections, on the surface, and in spoil piles.  In 1992 the Leisey family stopped mining sand here.  There was no need to keep operating the pumps, so because the location is slightly below sea level this site became flooded.  Fossil hunting here now requires scuba gear.

Scientists had difficulty dating the age of the fossils found in the Pleistocene strata at this site.  They are too 0ld for radio-carbon dating and nearly too old for uranium series dating.  Scientists can’t use pottassium-argon dating because there is no volcanic ash in Florida.  Instead, scientists had to use inexact indirect methods to estimate the age of the fossils here.  A study of strontium isotope ratios found in mollusc fossils narrowed the time range to between 1 million-2million years BP.  A geomagnetic chronology study determined the fossils were at least 780,000 years old. (See http://www.geo.arizona.edu/palynology/geos462/12paleomag.html for an explanation of geomagnetic chronology).  Using index fossils, scientists narrowed the time frame further to between 1.5 million-1.1 million years BP.  There are no fossils known exclusively from the Blancan Land Mammal Age in the fossil rich strata.  This age ended approximately 1.5 million years ago.  But there are some fossils of species not thought to have survived past 1.1 million years ago, thus explaining why scientists narrowed it down to this time range.

The site is named for the abundant sea shells found all through the sand.  Scientists catalogued 98 species of bivalves, 113 of snails, 16 of bryozoans, 1 worm, 9 arthropods, and 1 starfish.  3% of the species of sea shells found here are extinct.  I looked in vain on google images for a photo of one to put on this blog.  But there are pictures of these obscure extinct species in the publication linked below.  The vast majority of mollusc fossils here are of marine species, but a few are freshwater.  Two of the freshwater species no longer occur in peninsular Florida, becoming extirpated during a sea level rise that inundated much of the state.  Morphology studies show that predatory snails and whelks bored holes in 33% of the bivalves.  I remember showing my ex-brother-in-law a whelk in the process of feeding upon a mussel, and he didn’t believe me–he thought it was part of the whelk shell.

Section IA of the Leisey Shell Pit is thought to represent a paleo-brackish environment.  The most common fossil species of fish found in that section are in order: 1. alligator gar 2. snook 3. mullet 4. bull shark 5. eagle ray 6. porcupine fish.  As I discussed last week, alligator gar no longer occur in peninsular Florida due to a later marine transgression.  Great white sharks are an open ocean species, but fossils of this shark are found here in surprising numbers.  They likely hunted close to shore for monk seals and manatees.  Three extinct species of sharks and 1 extinct species of ray that were common during the Pliocene still swam near the Florida coast 1.1 million years ago, perhaps making their last stand.  They were an extinct species of mako shark (Isuris hestalis), an extinct nurse shark (Ginglymosoma serus), an extinct snaggletooth shark (Hemipristis sp.) and an extinct guitar fish (Rhynochobatus sp.).

Guitar fish still live in the Indo-Pacific Oceans. They are shaped like a guitar, hence the name.  An extinct species used to live in the Atlantic as recently as the early Pleistocene.

Fossil hunters love snaggletooth shark teeth.  Snaggletooth sharks also still live in the Indo-Pacific Oceans but have been extinct in the Atlantic for about 1 million years.

Section 3A of the Leisey Shell Pit is thought to represent a more freshwater environment.  The most common fossil species of fish found in this section are in order: 1. redear sunfish 2. mullet 3. bowfin 4. lake chubsucker 5. brown bullhead 6. Seminole killifish.  Redbreast sunfish and largemouth bass were also common here.  In all, scientists identified 73 species of bony fish and 23 species of sharks and rays at the shell pit.

Scientists catalogued 29 species of reptiles and amphibians among the fossils of the Leisey Shell Pit.  All of them still live in peninsular Florida with the exception of 2 species of giant land tortoises that became extinct and 2 species of freshwater turles that no longer occur in this region–pond sliders and alligator snapping turtles.  Again, rising sea levels eliminated habitat for those 2 species, and they have failed to recolonize the region.

Scientists found the remains of 45 species of birds at the Leisey Shell Pit of which 15 are now extinct.  A new species of extinct condor, Gymnogyps kofordia, was discovered here.  Two species of teratorns scavenged alongside G. kofordia, including Teratornis incredibilis, a spectacular bird with an 18 foot wingspan.  Woodward’s eagle (Amplibuteo woodwardii) was another impressive species.  Possible ancestors of today’s roseate spoonbill and avocet flew here, but extinct species of a stork (Ciconia), a loon, geese, and flamingos left no ancestors.  The oldest known fossil of a trumpetor swan was found in the pit.  Trumpetor swans no longer occur in Florida.

Here’s the list of fossil mammal species found at the site.  Scientists estimated the approximate abundance of each large land species based on their abundance in the fossil composition.  I added that information too.  The authors of the study caution that mastodons, mammoths, and ground sloths may be underrepresented because their bones were too heavy to be transported by water which is how most of these animals ended up deposited in the shell pit.

beautiful armadillo

Pachyarmatherium leiseyi–a large species of extinct armadillo

pampathere–also a large species of extinct armadillo

glyptodont

Wheatley’s ground sloth–the evolutionary ancestor of Jefferson’s ground sloth

Harlan’s ground sloth

Eremotherium sp.–a 4-clawed giant ground sloth as big as an elephant

Nothrotheriops texanus–a ground sloth related to the Shasta ground sloth found in the La Brea tar pits.  All ground sloths together equaled 6% of the total fossil composition of large land mammals.

Armbruster’s wolf

Edward’s wolf

monk seal

raccoon

Arctodus pristinus–the lesser short-faced bear, probable ancestor to Arctodus simus

river otter–earliest record

spotted skunk

scimitar-toothed cat

Smilodon gracilis–saber-tooth cat ancestor to Smilodon fatalis.  All large carnivores equaled 6% of the population of large land mammals with this species the most common carnivore.

bobcat

cheetah

giant beaver

gopher

porcupine

capybara

cotton rat

bog lemming

Townshend’s hare

cottontail

tapir–<1%

horse–14%

donkey–8%

flat-headed peccary–9%

long-nosed peccary–1%

large-headed llama–7%

stout-legged llama–38%

white tailed deer–2.5%

bottlenose dolphin

spinner dolphin

pilot whale

manatee

mastodon–1%

gompothere–a species of proboscidean related to mastodons

Hay’s mammoth–2.5%. ancestor to the Columbian mammoth

Stout legged llamas were the most common large mammal living in Florida then, totaling 38% of the total.  Both species of llamas made up 45% of the total, while both horses and donkeys totaled 22%, making them the next most common.  Note that white-tailed deer only comprised 2.5% of the population.  65% of the herbivores were mixed browsers and grazers, while 35% were strictly grazers. Cottontails and gophers were the most common small mammals.  Smilodon gracilis was by far the most common large carnivore.

Gnaw marks on the bones of llamas and horses match those of wolves.  Gnaw marks on the proboscideans and ground sloths match those of Arctodus pristinus, a short faced bear.  Wolves hunted and scavenged llamas and horses, but bears probably just scavenged sloths and proboscideans which would have been too large or tough for the bears to subdue.  Perhaps the bear took control of the larger carcasses when the beasts died naturally and were able to keep wolves away.  Armbruster’s wolf and Edward’s wolf overlapped in time at this site, but the former eventually replaced the latter and may be ancestral to the late Pleistocene dire wolves.

Illustration of paleolama and Eremotherium.  Paleolama myrifica was the most common large mammal living in Florida then.

A layer of strata at the base of the Leisey Shell Pit did contain fossils of Miocene-age species of 3-toed horses.  Bison fossils found at the shell pit likely date to the late Pleistocene rather than the early Pleistocene.  Bison didn’t colonize North America until about 300,000 BP (probably).

The paleobotanists who examined the fossil pollen and plant macrofossils found here remarked that if they hadn’t known the age of the site, they would have assumed they were studying data from a modern day site.  The plant composition of the early Pleistocene is no different from that of the present day in central Florida.  Pine, oak, hickory, sweetgum, herbs, grass, and composites dominated the pollen assemblage.  Identified plant macrofossils found included loblolly or slash pine cones, live oak, sabal palm, saw palmetto, cypress, wax myrtle, hazel nut, and grape.  The region was interpeted as being an open oak and pine woodland with some wetlands, but little cypress swamp.

Reference:

Hulbert, Richard; Gary Morgan, and David Webb

“Paleontology and Geology of the Leisey Shell Pit, Early Pleistocene of Florida”

Bulletin of the Florida Museum of Natural History 37 (1) 1995

http://ufdc.ufl.edu/UF00095791/00001/1j

The Ancient Armored Gar

Fish from the gar family (Lepisosteidae) swam in fresh and brackish waters when dinosaurs roamed the earth.  During the Cretaceous Era gar had a worldwide distribution, but today they’re restricted to the Americas.  They are a top predator among fish–their armor makes them invulnerable to attack from other bony fish, though alligators, bull sharks, and man can overcome this defense.  They have long sharp teeth that helps them subdue minnows, bream, crustaceans, baby alligators, and even birds.  Their eggs are highly toxic, so do not eat them, thinking they’re an alternative to caviar.  These tough fish can breathe through their air bladder as well as their gills, allowing them to survive droughts when oxygen in water  falls to low levels that kill other fish.  Gar are commonly found in brackish water as well and can tolerate higher levels of salinity than other freshwater fish.

On the North American continent, there are 4 species of gar.  All but the alligator gar live in Georgia.

Long-nosed gar (Lepisosteus osseus)

Spotted gar (Lepisosteus oculatus)

Florida gar (Lepisosteus platyrhincus)  According to the guide, this was the species I was seeing in Wakulla Springs, Florida.  The word gar is archaic for spear.  The fish is shaped like a spear, hence the name.

Alligator gar (Atractosteus spatula) They formerly reached lengths of up to 10 feet long and weights of 350 pounds.  Note the skull.  It’s really shaped like an alligator’s head.

Gar have more robust scales and bones than most other species of fish and are therefore recognized more easily in fossil deposits.  Today, alligator gar distribution is limited to the Mississippi River drainage.  They occur just west of Georgia in Alabama Rivers that eventually flow into the mighty Mississippi, and they are completely absent from the peninsula of Florida.  But alligator gar fossils have been found in several peninsular Florida fossils sites, indicating the species inhabited that region until at least the late Pleistocene.  At the Leisey Shellpit fossil site (the subject of next week’s blog entry) they are the most abundant species in a section labeled IA which is thought to represent a paleo-brackish habitat.  Pond sliders (Chrysemys scripta) and alligator snapping turtles (Macroclemys temmincki) are also absent from peninsular Florida today but did inhabit the region during the Pleistocene.  Rising sea levels during the Sangamonian Interglacial (~132,000 BP-~118,000 BP) eliminated freshwater habitat in peninsular Florida where alligator gars, pond sliders, and alligator snapping turtles lived, and all 3 species have failed to recolonize habitat that seems suitable for them today.

Most fishermen consider gar a trash fish, but along with eels they were a favorite among Native Americans who roasted them whole in fire.  The fire burned the tough scales off the succulent white meat.  It is difficult to cut through the armor of a gar.  Cajuns still eat gar and do wonderful things with it.  They make a spicy smoked tasso ham from gar.  More commonly, they make fish meatballs called boulettes that they smother in gravy and serve with rice.  The following 2 videos show how they butcher, clean, and cook gar.  Those gar fish boulettes look delicious.

http://www.youtube.com/watch?v=Hcp8nxBIiVg

http://www.youtube.com/watch?feature=player_detailpage&v=nFz_odxvq6o

Pleistocene Bears of Southeastern North America

Nothing demonstrates wilderness more than a robust population of free roaming bears.  During the Pleistocene before people were around to kill them and destroy their habitat, there must have been tens of thousands of bears living within the boundaries of what today is Georgia.  It’s possible that 5 different species could have been found here in the same time span, though we can be more sure there were at least 3 sharing the same range.  Today, only 1 species of bear resides in Georgia–an estimated 5100 black bears still roam the mountains, the Okefenokee Swamp, the Altamaha and Ocmulgee river bottoms, and Houston County.  Occasional stragglers leave these last strongholds and raid urban dumpsters and suburban bird feeders, but these occurrences are rare.  One study of Georgia bears determined that suitable habitat can support 1 bear for every 3 square kilometers.  That means ideally, Pleistocene Georgia hosted a population of 30,000-40,000 bears.  (*Georgia is about 60,000 square miles. 1.86 square miles =3 square kilimeters.  Moreover, during stadials Georgia’s land mass increased by about 10,000 square miles due to the fall in sea level.)

Here’s a review of every known bear species that lived during the Pleistocene in southeastern North America.

Black bear–Ursus americanus

Photo from google images of a black bear in the Okefenokee Swamp.

Ursus abstruscus is the probable evolutionary ancestor of American and Asian black bears which once consisted of a geographically continuous population.  Glacial ice separated the two populations at the beginning of the Pleistocene, resulting in two different species.  Bjorn Kurten notes that Pleistocene black bears grew as large as modern day grizzlies.  I believe Pleistocene black bears were larger and fiercer than their modern day descendents because they had to survive confrontations with saber-tooths, giant panthers, jaguars, and packs of dire wolves.  Cavers and scientists discovered black bear fossils at Ladds and Kingston Saltpeter Cave in Bartow County, and the Isle of Hope Site in Chatham County.  They’re also commonly found in Florida fossil sites but only a few have been recorded from South Carolina.

Florida spectacled bear–Tremarctos floridanus

Photo of a spectacled bear, Tremarctos ornatus,  from google images.  This is the only living species from the once widespread short-faced bear family.  It is a close relative of the extinct Tremarctos floridanus.  Of course, scientists have no way of knowing whether Tremarctos floridanus was also spectacled, but they call it that anyway.

Now extinct, this was likely the second most common species of bear in southeastern North America during the Pleistocene.  Only 1 specimen has ever been recovered in Georgia (at Ladds), but its fossils have commonly been found in Florida and South Carolina.  It’s thought of as primarily a vegetarian, but a recent study of Pleistocene bears concluded that all were opportunistic omnivores that would eat anything they could obtain.  Tremarctos’s range in the late Wisconsinian Ice Age seems to have been restricted to the southeast.  During warm interglacials it expanded as far north as Kentucky.  It probably just lived in the coastal plain of Georgia and South Carolina as well as Florida during colder climatic stages.

Lesser short-faced bear–Arctodus pristinus

Photo of a fossil jaw bone of Arctodus pristinus from Additions to the Pleistocene Mammal Fossils of South Carolina, North Carolina, and Georgia by Albert Sanders.

Photo of fossil bear teeth from the above mentioned publication.

It’s unclear from the fossil record whether this species co-existed with its larger cousin, the giant short-faced bear, or was simply ancestral to it.  Its fossils have only been recovered from a few eastern sites in Florida, South Carolina, Maryland, and West Virginia.  Teeth attributed to this species overlap in size with those of Arctodus simus.  Florida fossils of this species, including those from Leisey Shell Pit, indicate this animal lived from the early to mid-Pleistocene (~1.8 million-300,000 BP), whereas giant short-faced bear fossils in Florida date to the late Pleistocene (~300,000-~11,000 BP).  However, fossils of the lesser short-faced bear were found in South Carolina sediments thought to date from the Sangamonian Interglacial (~132,000-~118,000 BP) which is also considered late Pleistocene.  These South Carolina specimens haven’t been radiometrically dated, so no one knows exactly how old they are.  Perhaps this species did survive as a relic species in some geographical locations until the megafauna extinction.  Arctodus pristinus is considered more of a general feeder; Tremarctos floridanus a more herbivorous species; Arctodus simus a more carnivorous bear.

Giant short-faced bear–Arctodus simus

Dan Reed’s photo-shopped reconstruction of a giant short-faced bear.   

The giant short-faced bear ranks up there with mammoths, mastodons, ground sloths, and saber-tooths as among one of the most spectacular creatures of this era.  Studies suggest it lived by aggressive scavenging.  It’s extremely acute sense of smell detected blood from a great distance.  Then, the beast would relentlessly trot toward the source of the appetizing odor, and its sheer size would intimidate the partially satiated carnivore that actually made the kill into surrendering the carcass.  Arctodus simus fossils are more common in western fossil sites, but a few have been discovered in the southeast, proving it did occur here, at least sporadically.  An Arctodus simus skeleton rested in the Fern Cave system in Jackson County, Alabama which borders northwestern Georgia, until it was discovered by cavers in 1970.  In addition a number of teeth from this species have recently been discovered in north Florida fossil sites, and some Arctodus simus material was also discovered in Virginia.

Grizzly bear–Ursus arctos

Photo of a grizzly bear and cub from google images.

Welsh cave in Kentucky yields grizzly bear fossils dating to about 12,000 BP.  This is the easternmost known occurrence of this species.  Grizzly bears roam hundreds of miles, so it’s likely if they lived in Kentucky then that they must have entered Tennessee.  But the lack of grizzly bear fossils in other southeastern states suggests they never penentrated the region in significant numbers.  Still, I believe a few irregular stragglers may have wandered into what’s now north Georgia.  It may be that the existence of 3 or 4 other species of bears prevented grizzly bears from colonizing much of the southeast during the Pleistocene, and then man arrived, creating another obstacle blocking their migration into the region.  Grizzly bears are a relatively recent addition to North America’s mammalian fauna, but they did live on the continent prior to the LGM, 30,000 years BP.  They’re the same species as the Eurasian and Alaskan brown bears.

If I could live in the Pleistocene (part 4).

For those unfamiliar with this blog, I occasionally fantasize living during the Pleistocene but with modern conveniences, such as an adobe house with woodstoves, solar heating, electricity, and a time tunnel that connects me to the modern world.

I’ve thought of a simple way to observe bears from my abode.  Connected to my Pleistocene house is a 5 story watchtower designed in the shape of a lighthouse in which I can view the surrounding landscape.  I would take a barbecue grill to the fifth story which has a canopy but an open window stretching for 360 degrees around.  There, I would grill meats.  The aroma should attract bears and other carnivores from miles around.  A bear could potentially climb up the side of a light-housed shaped building, so I would have to have some kind of designed guards that would prevent this. 

I would avoid hunting bears, if possible.  I think modern hunters who kill bears are jerks.  I can understand why the pioneers did it.  They didn’t have grocery stores and had to eat and make use of what they could obtain.  But there is no reason to hunt bears today, unless they prove a danger to tourists.  They don’t reproduce as rapidly as deer, and it’s just not ecologically necessary to hunt them.

Bears were a valuable source of meat and fat for early settlers.  Early accounts reveal an important dish of the Indians.  The Indians frequently diced up venison (which is very lean) and fried it in bear fat.  Bear fat was also the number one source of cooking fat in New Orleans in 1800.  It was gradually replaced by lard as the settlers brought in hogs.