Posts Tagged ‘Rancho La Brea’

The Reddick Fossil Site in Marion County, Florida

November 26, 2014

One could almost refer to the Reddick Fossil Site in Florida as Rancho La Brea east.  It’s one of the richest eastern sites in species diversity, but nevertheless falls far short of Rancho La Brea’s treasure chest of fossils.  At least 147 species of vertebrates were recovered from Reddick compared to 231 from Rancho La Brea and the latter also far surpasses the former in quantity. Moreover, Rancho La Brea is still being excavated.  The Reddick Fossil Site was an abandoned limerock quarry excavated during the early 1960’s.  The Pleistocene topography consisted of limesink lakes and caverns with a soil chemistry that helped preserve the bones of many animals.  Owls roosted in the caves during the Pleistocene, and bones from the small mammals and birds they ate were found in their fossil pellets.  The composition of species shows that a wide variety of habitats occurred locally, including woodland, grassland, and wetland.  The fossil remains are thought to date to between ~200,000 BP- ~114,000 BP.  The presence of glyptodont, vampire bat, ocelot, and giant tortoise is evidence of a climate at least as warm as today’s Florida, even though this period of time includes the Illinois Ice Age.  This is the only site in southeastern North America where ocelot fossil remains have been found.  Only 32 of the 147 species are extinct.  Many of the large mammals were probably overhunted by man into extinction, and we know for sure passenger pigeons were.  However, some of the bird extinctions were local species that became extinct during marine high stages of the Sangamonian Interglacial when much of their terrestrial habitat was lost to high sea levels.  The following is the Reddick Fossil Site faunal list from the below referenced work.  * denotes extinct species.  + indicates an extant species no longer native to Florida.  The remarkable thing about this list is how few reptiles have gone extinct.  This suggests little environmental change in this region over the past 200,000 years.  (I’m not including the scientific name for most of these entries.  I feel lazy today and it’s almost a holiday.  Happy Thanksgiving.)

Map of Florida highlighting Marion County

Marion County, location of 1 of the best Pleistocene fossil sites in southeastern North America.

Greater siren

Mud siren

Ambystoma sp. (a type of salamander)

eastern spadefooted toad

oak toad

common toad

narrow-mouthed toad

tree frog sp.

leopard frog

Pseudemys sp. (a type of slider/cooter turtle)

box turtle (Terrepene carolina putnami)–an extinct subspecies but extant species

gopher tortoise

*medium-sized land tortoise–Hesperotestudo incisa

*giant land tortoise–H. crassicutata

soft-shelled turtle

green anole lizard

eastern race runner

5-lined skink

common glass lizard

Florida worm lizard

eastern ring-necked snake

mud snake

yellow-lipped snake

eastern hog-nosed snake

southern hog-nosed snake

rough green snake

black racer

coachwhip snake

indigo snake

king snake

corn snake

rat snake

pine snake

crowned snake

brown snake

garter snake

coral snake

pygmy rattlesnake

Rattle.jpg (68536 bytes)

 

 

 

 

 

 

All of the species of snakes found at the Reddick fossil site were still relatively common when Columbus reached North America

eastern diamondback rattlesnake

alligator

pied-billed grebe

*extinct grebe, a diver in the podiceps genus

mottled duck

pintail duck

shoveler

blue-winged teal

green-winted teal

ring-necked duck

*extinct condor–Gymnogyps amplus

turkey vulture

*extinct vulture–Coragyps occidentalis

Cooper’s hawk

sharp-shinned hawk

red-tailed hawk

red-shouldered hawk

peregrine falcon

sparrow hawk

caracara

quail

*extinct quail–Neotyx pennisubali

turkey

Virginia rail

sora

*extinct rail–Porzana auffenbergi

yellow rail

*extinct rail–Laterallus guti

*extinct coot–Fuliza merm

common crow

fish crow

blue jay

*extinct jay–in protocitta genus

house wren

*extinct wren–Gasthothanus brevs

maryland yellowthroat

cowbird

red-winged blackbird

grackle

eastern meadowlark

rufous-sided towhee

Henslow’s sparrow

Henslow

Henslow’s sparrow.  This species prefers weedy grassland habitat.  Ducks and rails prefer wetlands.  Passenger pigeons and woodpeckers need woodlands.  The composition of birds reflects varied habitats near this locality during the Pleistocene.

killdeer

lesser yellowlegs

common snipe

*passenger pigeon

mourning dove

barn owl

screech owl

burrowing owl

barred owl

yellow-shafted flicker

red-headed woodpecker

eastern kingbird

purple martin

*extinct swallow–Tachycinctus spelodytes

oppossum

*vampire bat–Desmodus stockii

southeastern myotis

red bat

Florida yellow bat

Brazilian free-tailed bat

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

*Harlan’s ground sloth

*Beautiful armadillo

*pampathere–a giant armadillo

*glyptodont

marsh rabbit

cottontail rabbit

southern flying squirrel

undetermined squirrel in scurius genus–probably a gray squirrel

southeastern pocket gopher

rice rat

harvest mouse

old field mouse

cotton mouse

Florida mouse

golden mouse

cotton rat

wood rat

pine vole

round-tailed muskrat

*Florida bog lemming–Synaptomys australis

*dire wolf

+coyote

gray fox

*Florida spectacled bear–Tremarctos floridanus

black bear

raccoon

+hog-nosed skunk

spotted skunk

striped skunk

+jaguar

cougar

+ocelot

aka, the dwarf leopard,

Reddick is the only fossil site in southeastern North America where remains of an ocelot have been found

bobcat

saber-tooth–Smilodon fatalis

mastodon

mammoth

+horse

*tapir

*long-nosed peccary

*flat-headed peccary

*large-headed llama

*stout-legged llama

white-tailed deer

bison

Reference:

Gut, James H.; and Clayton Ray

“The Pleistocene Vertebrate Fauna of Reddick, Florida”

Quarterly Journal of the Florida Academy of Science 1964

 

Logical Flaws in Studies of Pleistocene Carnivore Tooth Wear

January 17, 2013

Van Valkenburgh co-authored a study comparing rates of broken teeth suffered by large modern carnivores with those experienced by fossil carnivores excavated from the Rancho La Brean tar pits.

http://www.cof.orst.edu/leopold/class-reading/Van%20Valkenburgh%20and%20Hertel%201993.pdf

She found that large carnivores from the La Brean tar pits suffered 3 times as many broken teeth as modern day carnivores.  The fossils she examined from the pits included saber-tooth (Smilodon fatalis), American lion (Panthera atrox), cougars (Puma concolor), bobcats (Lynx rufus), dire wolves (Canis dirus), and coyotes (Canis latrans).  The modern species that she compared them to were lions, jaguars, leopards, cheetahs, bobcats, timber wolves, hyenas, and African hunting dogs.  The specimens from the tar pits dated to between ~36,000 BP-~12,000 BP.  She concluded that competition for prey was more fierce then than it is among modern large carnivores.  She believed increased competition for food forced large carnivores to utilize more of the carcass, and this led to more broken teeth from gnawing on bone.  She dismissed the alternate explanation that the higher rates of broken teeth among large Pleistocene carnivores were the result of attempting to take down larger prey than modern carnivores usually attack.  Dr. Valkenburgh suggested the larger size of the Pleistocene carnivores compensated for the larger size of the prey.

I never paid much attention to this study because using rates of durophagy as a proxy for carnivore competition seemed like a dubious assumption.  (Durophagy is just a fancy word for bone-eating.)  I think different species either eat more bone than other species because they have different nutritional needs, or they eat more for some other unknown reason that has nothing to do with competition.

Last year, a new study was published that completely contradicts Dr. Valkenburgh’s study.

http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052453

Several scientists looked at teeth from Rancho La Brean predators and extant carnivores using Dental Microwear Textural Analysis (DMTA).  DMTA requires a lot of fancy equipment and procedures including a white light confocal profilometer, a scale sensitive fractal analysis, and a scanning electron microscope.  The scientists are able to see the teeth on a computer screen in 3D.  This eliminates observer measurement error.  Carnivores that avoid bone, such as cheetahs and lions, have different types of microwear on their teeth than those that eat a lot of bone, such as African hunting dogs and hyenas.

This is the equipment used to look at tooth wear in animals.

These scientists found little difference in rates of durophagy between the extinct and extant carnivores, meaning the competition between predators in the late Pleistocene in this region was no more or less fierce than that of today’s Africa.  Of course, I don’t buy the whole proxy assumption in the first place.  Most of the broken teeth were canines rather than molars.  Canines are more likely to break when taking down prey; molars are more likely to break when chewing bones, therefore they conclude the larger size of prey was the factor that explains the higher incidence of broken teeth among large Pleistocene carnivores.

One of the conclusions of this more recent study has a logical flaw.  The scientists authoring this 2nd study used DMTA to look at the teeth of Smilodon and Panthera atrox over time.  Different tar pits hold fossils of different spans of time ranging from ~36,000 BP-~12,000 BP, so they looked at 5 specimens of each species from pits of chronologically different ages.  They found no difference in tooth wear between the older specimens and the young specimens that dated closer to the time of extinction.  Many scientists think large Pleistocene carnivores became extinct because the animals they preyed upon became extinct.   They expected evidence of increased durophagy among the most recent saber-tooths and lions as they were forced to utilize more of the carcass.  But they found no evidence of this.  I think this doesn’t disprove the likelihood that carnivores did die out because their prey disappeared.  The final sentence in the abstract seems to imply that it does though.  It states : “The difference in DMTA attributes from older to younger deposits offers little evidence that declining prey resources were a primary cause of extinction for these large cats.”  Brian Switek, who writes an online blog for National Geographic, discussed this study and even goes so far as to ask what caused the extinctions of large Pleistocene carnivores, as if this study somehow disproves declining populations of suitable prey was the cause.  In my opinion this is flawed thinking.  Besides the dubious assumption that certain species of carnivores utilize more bone if prey is scarce, it seems unreasonable to expect to find the last nutritionally-stressed members of a population to be represented in the fossil record.  The odds of an animal becoming fossilized is so rare that it’s extremely unlikely that a member of the last remnant of a species headed for extinction would become fossilized.  The sample size–just 5–is also way too insignificant to detect whether or not this was occurring.  Moreover, big cats that eat mostly meat and organs and avoid bone are more likely to die of starvation before they chew on many bones.

I contacted the main author of this study, Dr. Larisa Desantis, and pointed out the logical flaws of this conclusion but she never responded.  I tried to comment on Brian Switek’s blog but he wouldn’t even allow my comment to be published.

I believe competition with humans drove saber-tooths and American lions to extinction.  Humans directly hunted them and overhunted their prey, and it was this combination that made it impossible for these species to survive.  To expect to find evidence of this by looking at a handful of fossil teeth under a microscope is ridiculous.