FOSSIL CRAYFISH SHOWS POLAR REGIONS WERE ONCE WARMER
COLUMBUS, Ohio -- Half of a fossilized claw from a prehistoric crayfish found this summer in a remote area of Antarctica is changing the ideas scientists have about the evolution of these arthropods.
It even suggests that the animals first appeared near where the South Pole is today -- not in temperate zones as scientists have long thought.
Researchers from three universities are involved in the study of the fossil found in a 285 million-year-old lake bed near the Shackleton Glacier in the Transantarctic Mountains.
Its discovery pushes back the oldest known existence of freshwater crayfish 65 million years to the Carboniferous-Permian boundary. Before this, the oldest-known crayfish fossils dated back only to the Mesozoic Era, some 220 million years ago.
John Isbell, a geologist at the University of Wisconsin-Milwaukee, found the fossil while he investigated the site of an ancient glacial lake on Mount Butters. The fossil is only 1.6 inches long and is a smooth, blackish remnant imbedded in gray, fine-grained sandstone.
Loren Babcock, an associate professor of geological sciences at Ohio State University, determined that the fossil was the end of a fixed finger, the stationary part of the animal's claw. Based on its size, he thinks it came from a crayfish that was six to 12 inches long.
"For the first time, we now have fossils of freshwater decapod (10-legged) crustaceans that date back to the Paleozoic Era," Babcock said. "The presence of crayfish in deposits this old tells us that there probably were very complex freshwater ecosystems thriving by the end of the Paleozoic."
Babcock said this is important since most of the fossils that offer evidence of these ancient ecosystems only date back to the Cenozoic, no more than 66.4 million years ago. The new find is four times older than that, Babcock said.
A second fossil find this summer provides even more evidence of the importance of crayfish in early ecosystems. Molly Miller, a geologist at Vanderbilt University, and Jim Collinson, professor emeritus of geological sciences at OhioState, found intricate networks of ancient crayfish burrows in deposits of rock along Kitching Ridge, some 23 miles away from Mount Butters. These deposits date back to the Early Triassic Period -- 240 million years ago.
Miller and other scientists think the whitish, snake-like burrows were dug by crayfish that lived in the banks of streams when the environment was much warmer than it is now. Some of the burrows are nearly 3.5 feet long and nearly six inches in diameter.
"These fossilized burrows are almost identical to modern burrows in structure and location," Babcock said. "This means that the burrowing behavior of crayfish probably developed very early in their evolution, which is a surprise."
Crayfish play important roles both as a vehicle for cycling nutrients through freshwater ecosystems and as a primary food source. The fossil claw was probably part of the remains left from a predator's meal.
Since the crayfish were apparently thriving in the region, Babcock says researchers can infer important things about the locale at the time.
"Crayfish have a very narrow temperature range within which they have to live," Babcock explained. "They usually must have free running water that is between 10 and 20 degrees C (50 and 68 degrees F) for at least three months out of the year in order to grow and develop normally.
"So if they were there, the climate had to be at least that warm. This is among our best evidence yet of paleotemperatures in that part of Antarctica," Babcock said.
Scientists have thought that the crayfish first appeared in the temperate, mid-latitude regions of the globe. But the new fossils suggest the animals evolved in high southerly latitudes.
"Instead of starting in the low- or mid-latitudes, they may have gotten their start much closer to the South Pole," Babcock said.
He thinks that the Mount Butters area 285 million years ago probably resembled some parts of present-day New Zealand. The crayfish inhabited streams that fed into glacial meltwater lakes. The Kitching Ridge area -- some 45 million years later -- probably had braided streams developed on a broad floodplain.
Modern crayfish now inhabit a region of the globe bordered by Scandinavia to the north and New Zealand to the south. But the crayfish fossil finds come from a region only 5 degrees north of the South Pole.
"This suggests that the world, including the area around the poles, may have been considerably warmer at that time," Babcock said.
"We're talking about temperatures of 10 degrees C for three months or more each year, essentially at the South Pole. I don't know what that means for total world temperature but my impression is that it would be pretty warm."
Contact: Loren Babcock, (614) 292-0358; Babcock.firstname.lastname@example.org
Written by Earle Holland, (614) 292-8384; Holland.email@example.com
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