Wednesday, April 12, 2006
Instead of Everglades sawgrass, scorching heat and a sky full of herons, imagine towering oaks, a chilly breeze and sloths bigger than elephants.
About 20 miles south of Lake Okeechobee, paleontologists scoured a clay pit Tuesday for the hefty remains of a giant sloth that trudged the broad Florida peninsula more than 10,000 years ago.
Scientists unearthed half the skeleton of one gigantic sloth and discovered a tooth and a few bones of a smaller version of the same animal. The second sloth was a close relative, probably the size of a big bull, but no less ancient.
Lee County paleontologists Mark Renz and Steve Bufter spent most of Tuesday sloshing through blue-gray water, sifting out bones from clay in the middle of an Everglades restoration project.
By the end of the day they recovered an impressive amount of bones.
“Half is excellent,” Renz said. “That was a significant amount found for that animal.”
Part of the find included half the creature’s jaw, which Renz said will help scientists piece together the story of the animal’s life.
The bones were shipped to the University of Florida’s Museum of Natural History in Gainesville, where they will be analyzed along with sediments and fossilized bones of other creatures found on the same dig.
The bones could be anywhere from 10,000 to 1.5 million years old, said archeologist John Whitaker of Janus Research.
The South Florida Water Management District hired Janus Research to monitor Everglades restoration projects to make sure rare artifacts unearthed during construction would be salvaged or preserved. Whitaker said he never expected workers to encounter prehistoric bones.
About 2 million years ago the Florida peninsula spread out like a fat notch jutting from the North American continent. While most of the Earth and its oceans sat under glaciers, giant sloths roamed Florida’s woodlands and plains with woolly mammoths and mastodons.
Giant sloths grew as big as 20 feet tall from tail to nose and weighed in at about 5 tons — bigger than similar sloth specimens found in the Midwest. The claw bones alone grew to a length of about 1.5 feet. The actual claw would have been much longer.
“You could probably sit in the hands of the animal,” Renz said.
A vegetarian with a penchant for trees, the mammal chomped down an estimated 300 to 500 pounds of food a day, Bufter and Renz said.
Pointing to the porous-looking ends of the sloth’s leg bones, Bufter said it was probably a young adult. Bone ends become smooth in fully grown mammals, he said.
Russell McCarty, senior biologist with the paleo-preparation lab at the Florida Museum of Natural History, said sloths originated in South America more than 3.5 million years ago, before volcanoes formed the Panamanian land bridge and connected North America to South America. The giant sloths made their way up the southern continent into Florida, possibly by swimming, he said.
Finding the bones of creatures embedded in the earth helps scientists like McCarty recreate the past. Other animals found within the same dig indicate what the environment was like at the time.
“You don’t look at just one fossil. You look at all the fossils around it,” McCarty said.
Mixed among the find Tuesday were the bones or teeth of prehistoric armadillos called glyptodont, deer, horses, camel-llamas, turtles and manatee-like dugong.
The sloth might have washed to the site sometime after it died.
“Obviously you have a saltwater layer and you have a land animal in it,” Renz said.
The animal could have died in a river that emptied into a saltwater bay. Another possibility is that the animal died in fresh water that disappeared without a trace, leaving a layer of saltwater shells on top of the marine layer of clay from a different period.
But Renz said he’s speculating and has learned from past paleontological digs that nothing turns out to be what it seems.
Whitaker said the museum will test the shell layers above and below the clay layer to narrow down the sloth’s age.
Even without knowing all the specifics, McCarty said the find already has meaning.
“This is important, because it certainly establishes the presence of this (sloth) in other places,” McCarty said. In researching the past, he said, it is important to know the where animals ranged.
Until recent weeks, giant sloths had not been found in the Everglades, but they had been discovered in a quarry near Gainesville, in the Osceola River and in LaBelle.
The find is also important because the animal’s bones were well preserved and not scattered about too far.
“Any time you find a complete or nearly complete animal it’s significant to science,” Renz said.
But the test of how significant depends on the animal’s age, and older isn’t necessarily better.
Fossils records go back millions of years, but Renz said there is a gap between 120,000 and 1 million years ago.
Florida’s a good place to try to fill in that gap, however.
In terms of finding the fossilized bones of mammals that lived within the last 25 million years, Florida is second only to Nebraska, Renz said.
“Very few places in the whole of planet Earth is the past so easily accessible,” he said.
Knowing that, it’s not so surprising that Everglades restoration workers, who were digging a borrow pit just west of the Rotenberger Tract, found the sloth bones on April 1 and reported the find to Janus Research. The district decided to stop using the area for digging up fill to plug up unnecessary canals.
“Kudos to the people who stopped work and notified the proper authorities,” Renz said. “Usually when people see something like that they start seeing dollar signs.”