Two Pleistocene Carnivore Dens Near Miami, Florida (Part 2)

Scientists unearthed thousands of bones from the Cutler Hammock site during the mid-1980’s.  The fossils were identified, catalogued, and sent to the University of Florida Museum.  Many of the specimens remain unstudied in detail, and this rich assortment offers an opportunity for paleontologists looking for research material.  The site itself was not completely excavated and is potentially available for future study.  Originally, it was a cone-shaped sinkhole cave filled with sediment, rocks, and fossils. The lower half was below the water table.  The suface was 5 meters by 6 meters wide and from 3 meters to 5 meters deep in various places.  Workers bulldozed sand over the unexcavated section, making it easy for future scientists to re-dig but protecting it from unauthorized fossil hunters.    It’s located on land that is part of Deering Estate Park–a protected environmental, historical, and archaeological preserve of 444 acres in extent.  The preserve is a rare natural area within the suburban sprawl of Miami, Florida and includes endangered pine rocklands, tropical hardwood hammock, mangrove woods, and salt marsh.

The Deering Estate.  Deering was an industrialist who decided to protect his estate from development in perpetuity.  The Cutler Hammock fossil site is located on this property.

Gary Morgan and Steve Emslie studied many of the large vertebrate bones found at Cutler Hammock, and they wrote the paper from which I mined most of the information I used for this blog entry.  They noticed a high number of bones here had gnaw marks on them and concluded this former cave served as a carnivore den during the Pleistocene.  The most common large carnivore fossils found at this site were from dire wolves (Canis dirus), totaling 42 individuals.  This is the third largest dire wolf assemblage in the world behind the La Brea Tar Pits and San Josecito Cave in Mexico.  They also found bones from 9 spectacled bears (the extinct Tremarctos floridanus), 5 coyotes (Canis latrans), 4 jaguars (Panthera onca), 3 bobcats (Lynx rufus), 1 sabertooth (Smilodon fatalis), 1 American lion (Panthera atrox), 1 cougar (Puma concolor), and 1 black bear (Ursus americanus).   The authors of the study suggest the cave was a rendezvous site for packs of dire wolves and not a place where pups were birthed.  They speculate the cave was near a source of water that attracted various prey species.  In another paper Gary Morgan mentioned that the coyote fossils found at Cutler Hammock were unusually small.  Some think they may actually belong to dogs (Canis familiaris) brought by man.  If so, it’s possible the bones may be from yellow dogs, the American dingos, which readily revert to the wild state and are capable of surviving without humans.

Photos of deer and peccary bones gnawed by dire wolves at the Cutler Hammock site.  Click to enlarge. From the below referenced paper.

Photo of dire wolf lower jaw and dire wolf teeth found at the Cutler Hammock site.  Click to enlarge.  Also from the below referenced paper.

Most of the bones from prey species have puncture marks–a telltale characteristic of canid gnawing.  The extinct long-nosed peccary (Mylohyus nasatus) was the most common victim of dire wolves, numbering 75 individuals of which one-third were juveniles.  Horses were the next most common dire wolf victim, though 17 of the 19 individuals were juveniles.  Next in descending order of abundance were white-tailed deer, bison, llamas, and 1 mammoth that was probably scavenged.

Tremarctos floridanus was a close relative of the extant spectacled bear (Tremarctos ornatus) of South America.  Spectacled bears are primarily vegetarian but occasionally eat meat.  Bones scavenged by bears show recognizable differences from bones scavenged by canids.  None of the Cutler Hammock bones show evidence of bear gnawing.  (Hint to professional paleontologists: the authors of this study didn’t examine the bones for evidence of big cat gnawing.  It’s a potential topic for future research.)  Scientists also found bones from mastodon, Harlan’s ground sloth, and the pampathere (a 300 pound grass-eating armadillo) at Cutler Hammock but these showed no evidence of being gnawed upon.

A hearth and bones from 3 adult and 2 juvenile humans (Homo sapiens) were found just above the level where Pleistocene fossils were found.  This material dates to ~11,100 calender years BP.  A human bone found associated with dire wolf bones (in situ) was found as well.  The radiocarbon dating on this bone is considered unreliable.  It’s possible this human bone is as old as the dire wolf bones.  However, there has been much bioturbation at this site.  Land crabs dig holes in this locality, and their actions can mix bones of different ages together.  Or humans may have buried the corpse into the fossil deposit.  Nevertheless, this human bone has dire wolf gnawmarks on it–evidence this person was scavenged (or even killed) by dire wolves.

The below referenced article lists all the vertebrate species identified from Cutler Hammock, and as I read through the list, I noticed a few interesting bird species I neglected to mention in my discussion from part 1 of this blog entry.  The extinct hawk-eagle (Spizaetus grinnelli) flew the skies of Pleistocene south Florida.  It was larger than its closest living relative, Spizaetus ornata.

South American hawk-eagle.  It some times takes prey 5 times its size.  A bird like this lived in Ice Age Florida.

An extinct species of caracara (Milvago reidei), closely related to the living yellow crested caracara, also of South America, lived on the open plains of Florida then.  Passenger pigeons (Ectopistes migratorius) must have occasionally darkened the skies.

The Monkey Jungle Hammock site is thought to have been a carnivore den site as well but as far as I know no study has been conducted on the morphology of bones found there (Another hint to paleontologists.)

Reference:

Emslie, Steve; and Gary Morgan

“Taphonomy of a Late Pleistocene Carnivore Den in Dade County, Florida”

Late Quaternary Environments and Deep History: Tributes to the Career of Paul Martin

Edited by David Steadman and Jim Mead

Hot Springs South Dakota Inc. Reasearch Papers Volume 3 1995

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Two Pleistocene Carnivore Den Sites near Miami, Florida (Part 1)

Many tropical hardwood hammocks dot the low lying Everglades, southwest of Miami, Florida.  Two of them have sinkholes where scientists unearthed Pleistocene-aged fossils. Monkey Jungle Hammock and Cutler Hammock along with a West Palm Beach site are the southeasternmost Pleistocene fossil localities in North America.

The Monkey Jungle fossil site is named after an adjacent tourist attraction which is kind of a monkey zoo.

The bedrock in south Florida is known as Miami limestone, built from eons of buried sea shells and coral that transformed into rock.  Rain water dissolved caverns within the limestone, and these caves attracted bats, owls, and large carnivores, and they also contain everything the meat-eaters dragged inside.  Scientists can’t use radiocarbon dating on the fossils found at these localities because the conditions have leached too much organic material from the bones.  Nevertheless, they can safely assume the fossils accumulated during the Last Glacial Maximum between ~28,000 BP- ~15,000 BP. These caves are flooded today due to the rise in sea level following the end of the last Ice Age, but they were well above the water table then.

The sinkhole in Monkey Jungle Hammock was discovered in 1969; the one in Cutler Hammock was found in 1985.  The West Palm Beach site, also discovered in 1969, is probably not a sinkhole.  Cutler Hammock is the richest of the 3 sites, yielding the abundant remains of 47 species of mammals, 51 of birds, 9 of reptiles, 7 of amphibians, and 5 of fish.  Remains of dire wolves, spectacled bears, and jaguars were the most common large carnivore bones found here.   Horses, upland bison (Bison antiquus), and long nosed peccary (Mylohyus nasatus) were apparently the most common prey animals dragged into the cave, and most of the bones were from juveniles.  Many of the bones have been gnawed upon–evidence the cave served as a carnivore den site.  Cottontail rabbits, cotton rats, and wood rats, were the most common small mammals.  Monkey Jungle Hammock is also thought to have been a carnivore den site as well as an owl and bat roost.  41 species of mammals were found here.  Only 17 species of mammals were found at the West Palm Beach site, and most of the fossils–capybaras, tapirs, alligators, turtles, and fish–indicate it was an aquatic environment rather than a cave.

The abundance of several species at these fossil sites suggests Ice Age south Florida consisted of dry longleaf pine savannah instead of the sawgrass wetlands of today.  Fossils of indigo snakes and gopher tortoises, denizens of pine savannah, are especially common.  Fossils of Hesperotestudo incisa, a dwarf version of the extinct giant tortoise (Hesperotestudo crassicutata) have been found as well.  It likely was a dry upland dweller.  Pine voles and pocket gophers inhabited south Florida then but are absent today due to the expansion of wetland environments.  Pine savannahs were maintained by occasional hurricanes and lightning-induced wildfires that kept the environment open and grassy, but the climate was more arid than it is today, and there were far fewer wetlands.

There are no above ground caves in south Florida and the West Indies today, but during the Ice Age, all of the caverns presently inundated with fresh and saltwater served as roosts for enormous bat colonies.  The extinct mustached bat (Pteronotus pristinus), the ghost-faced bat (Mormoops megalphylla), the big brown bat (Eptesicus fuscus), and the southeastern myotis (Myotis austrarpririus) all formerly hunted flying insects in the skies of Ice Age south Florida and the Caribbean Islands.  Sea level rise caused the extinction of the mustached bat, and the extirpation of the other 3 species because the cave roosts became flooded. 

An upside down flying Ghost-faced Bat (Mormoops megalphylla).  The feed on large nocturnal moths.

Present day range of the ghost-faced bat.  During the Ice Age they also lived in south Florida and the West Indies and nested in caves.  Following the end of the Ice Age and the corresponding rise in sea level, those caves were flooded, thus eliminating their roosting sites.

Mexican free-tailed bats (Tadarida brasiliensis), evening bats (Nycticius humeralis), Seminole bats, (Lasiurius sp.?) and Wagner’s mastiff bats (Eumops glaucinus) still live in south Florida.  The former is the most abundant in the region today.  They survived sea level rise because they roosted in trees, but today they almost exclusively make use of man-made structures.

Barn owl.  What a ghostly colored creature.  Here’s a link to an excellent documentary about them. http://www.youtube.com/watch?v=5NLFLO8LN78

Barn owls (Tyto alba) were common in south Florida and the West Indies during the Ice Age, thanks to the caves that provided them with roosing sites.  Other notable birds that lived in south Florida then include the terratorn, California condors, an extinct stork (Ciconia malthus), the extinct hawk-eagle (Spizatus sp.), and the whooping crane (now absent from the region.)

The reason I’m splitting this essay into 2 parts is because I’m waiting for the mailman to deliver an obscure scientific article about these 2 sites that is not available on the internet.  That article should have more information on the morphology of the gnawed and broken bones found at these sites.  4 of the 5 species of big Pleistocene cats as well as dire wolves, bears, and a small canid utilized these caves as den sites over the millenia.  I should get the article anyday now.

See also: https://markgelbart.wordpress.com/2011/11/11/banana-hole-fossil-sites/

Reference:

Morgan, Gary

“Late Rancholabrean Mammals from Southeastern Florida and the Neotropical influence in Florida’s Pleistocene Fauna”

Cenozoic Mammals of Land and Sea: Tributes to the Career of Clayton Ray

Smithsonian Press 2002