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.

Distribution of Mormoops megalophylla

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

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2 Responses to “Two Pleistocene Carnivore Den Sites near Miami, Florida (Part 1)”

  1. James Robert Smith Says:

    This is one place in Florida I’ve never seen. When we’re not paddling to see the first magnitude springs, we’re always on the lookout for locations like this. When most people think of Florida they center their attention on the amusement parks and the beaches. So many people miss this kind of place. Geologically, and biologically, Florida is one of my favorite places.

  2. markgelbart Says:

    It’s a long drive to south Florida. There’s enough interesting stuff in north and central Florida to make the drive farther south unnecessary.

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