October 25, 2012
100-Million-Year-Old Fossil From Texas Is New Fish Species
April Flowers for redOrbit.com - Your Universe Online
100-million year old pieces of tiny fossil skull found in Fort Worth, Texas, have been identified as a new species of coelacanth fish, according to paleontologist John F. Graf of Southern Methodist University (SMU) in Dallas.
At 400 million years, the coelacanth has one of the longest lineages of any animal. The coelacanth is the most closely related fish to vertebrates, including humans. The findings of this discovery were published in Historical Biology: An International Journal of Paleobiology.
This specimen is the first coelacanth from the Cretaceous geologic period, which extended from 146 million years ago to 66 million years ago, found in Texas.
Graf, who identified the fossil, named the new species Reidus hilli. R. hilli is the first coelacanth identified from the Dallas area and the youngest coelacanth found in the Lone Star State. Before this discovery, the youngest coelacanth discovery was that of a 200-million-year-old coelacanth from the Triassic period.
Few coelacanths have been found in Texas, according to Graf, although coelacanth fossils have been found on every continent except Antarctica. Scientists estimate that the coelacanth reached its maximum diversity during the Triassic, and were assumed to have gone extinct about 70 million years ago. That assumption was proven false when live specimens were found off the coast of Africa in 1938.
“These animals have one of the longest lineages of any vertebrates that we know,” Graf said in a press release.
There was a greater diversity among coelacanths during the Cretaceous period than scientists previously thought, as the SMU specimen revealed.
“What makes the coelacanth interesting is that they are literally the closest living fish to all the vertebrates that are living on land,” he said. “They share the most recent common ancestor with all of terrestrial vertebrates.”
Coelacanths have boney support in their fins. Boney supports are the predecessors to true limbs.
“Boney support in the fins allows a marine vertebrate to lift itself upright off the sea floor,” Graf said, “which would eventually lead to animals being able to come up on land.”
R. hilli was identified from a partial skull. The skull included gular plates, which are the bones that line the underside of the jaw.
“Coelacanths are not the only fish that have gular plates, but they are one of the few that do,” Graf explained. “In fact, the lenticular shape of these gular plates is unique to coelacanths. That was the first indicator that we had a fossil coelacanth.”
Graf said that R. hilli was of an average size for the time in which it lived. R. hilli was probably no larger than 15.75 inches, though modern coelacanths can grow as large as 10 feet. The skull of the ancient fish is 1.75 inches long by 1 inch wide. This is a typical body size for the new family of coelacanths, Dipluridae (not to be confused with the tarantula family of the same name). Graf named and described the new species, choosing the name for the least primitive coelacanth in the family, Diplurus, which lived in the Triassic.
“Reidus hilli helped me tie a group of coelacanths together into what I identify as a new family of coelacanths,” he said. “This family represents a transition between the two large groups of youngest living coelacanths from the fossil record, Mawsoniidae and Latimeriidae.”
The Mawsoniidae and Latimeriidae are the most closely associated with the Diplurid coelacanths, which are the smallest of the three. Graf said that Mawsoniidae and Latimeriidae both have late Cretaceous members with large body sizes, ranging from 3 to 10 feet in total body length.
Graf partially named the new species after Robert R. Reid, an amateur collector who discovered the fossil.
Reid is a Fort Worth resident who has collected fossils for decades. He found the Reidus hilli specimen while exploring land that is being prepared for new home construction, noticing the fossil lying loose on the ground in a washed out gully.
Reid was surprised to learn he had collected a new species of coelacanth.
“When I found it, I could tell it was a bone but I didn´t think it was anything special,” said Reid, recalling the discovery. “I certainly didn´t think it was a coelacanth.”
Reid donated the specimen to SMU's Shuler Museum of Palentology to have it scientifically identified. R. hilli is the latest fossil Reid has discovered, and others have been named for him as well.
“It is astounding what can be learned from the discoveries that people like Rob Reid make in their own backyards,” said Louis L. Jacobs, an SMU professor of earth sciences. “The discovery of living coelacanths in the Indian Ocean after being presumed extinct for 70 million years highlights one of the great mysteries of ocean life. Where were they all that time? The new fossil from Texas is a step toward understanding this fascinating history.”
Reid found the fossil in the Duck Creek Formation, which is a layer-cake band of limestone and shale about 40 feet thick that is rich in fossils. Graf said that Reid found the fossil in marine sediments. The Western Interior Seaway covered North Texas about 100 million years ago. The Seaway divided North America from the Gulf of Mexico to the Arctic Ocean.
“That is unique to younger coelacanths,” Graf said. “The oldest coelacanths were usually found in freshwater deposits and it wasn´t until the Cretaceous that we start seeing this transition into a more marine environment.”
The "hilli" portion of Reidus hilli's name is to honor Robert T. Hill, a geologist with the U.S. Geological Survey who led surveys of Texas during the 1800s. Hill is known as the "Father of Texas Geology," for his description of much of the geology of Texas, including the Duck Creek Formation.
Counting the R. hilli specimen, there are 81 species known worldwide, including the two that are living currently. 229 living coelacanths have been caught since 1938.