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prasejarah Terminonaris adalah asli Texas , fosil menunjukkan
Prehistoric crocodile Terminonaris was Texas native, fossil suggests
Date:
July 21,
2011
Source:
Southern Methodist University
Summary:
A prehistoric crocodile thought to have originated in
Europe now appears to have been a Texas native, new research shows. The switch
for the genus Terminonaris is based on the identification of a well-preserved
fossil snout that was discovered near the waters edge of a Dallas-area lake.
The 96-million-year-old fossil is the oldest of its kind worldwide, indicating
Terminonaris likely originated in Texas and dispersed northward.
............................
Making its first appearance in Texas, a prehistoric
crocodile thought to have originated in Europe now appears to have been a
native of the Lone Star State.
The switch
in origins for the genus known as Terminonaris is based on the
identification of a well-preserved, narrow fossil snout that was discovered
along the shoreline of a lake near Dallas.
The
96-million-year-old fossil from Texas is the oldest prehistoric crocodile of
its kind in the world, according to paleontologist Thomas L. Adams at Southern
Methodist University, Dallas, who identified the reptile.
A distant
cousin of modern crocodiles and alligators, Terminonaris was similar to
the modern-day Indian gharial, only much larger.
"With
the recognition of Terminonaris here in Texas, this actually changes a
lot about what we thought we knew about this group," Adams said.
"Now we
know the group had a wider distribution range, and that it's much older. It represents
a unique find for Texas. This is the first occurrence of Terminonaris in
Texas. It's also the oldest occurrence of Terminonaris in the world, and
it's also the southernmost occurrence of Terminonaris anywhere."
There are
six other known Terminonaris fossil specimens: five from North America
and one from Europe. The European specimen, from Germany, previously was
thought to be the oldest. Scientists had concluded that Terminonaris
originated in Europe and then traversed the Atlantic and dispersed throughout
North America.
"Now we
know Terminonaris most likely originated here in Texas and dispersed
northward," said Adams, a doctoral candidate in SMU's Roy M. Huffington
Department of Earth Sciences at SMU.
Big Texas
crocodile swam the shores of North America's prehistoric seaway
Adams
identified the reptile primarily from its long snout, which measures more than
2 feet long and 7 inches wide, or 62 centimeters. With a snout that long, Adams
estimates the head would have been about one meter long.
"Based
on Nile crocodiles and the Indian gharial, which are both large crocodiles, a
regression analysis indicates this Terminonaris probably would have been
23 to 25 feet long," said Adams. "The largest living crocodile today
is the saltwater crocodile, which can reach up to 20 feet in length."
The Texas Terminonaris
was an adult and most likely weighed more than a ton, he said.
Adams
identified the fossils in "First Occurrence of the Long-Snouted
Crocodyliform Terminonaris (Pholidosauridae) from the Woodbine Formation
(Cenomanian) of Texas" in the Journal of Vertebrate Paleontology.
Prehistoric
crocodiles such as Terminonaris together with living crocodiles make up
a large group called crocodyliformes. While technically there are differences
between living crocodiles and each of the different types of fossil crocodile
forms, all of them are often commonly referred to as crocodiles.
Today there
are only 23 species of living crocodiles, a small number compared to the many
species of mammals, birds, lizards, snakes and fish alive today, Adams said.
That's in stark contrast to prehistoric times.
"In the
past, the crocodilian forms were very diverse and they were very successful.
There were hundreds of species. Even at the time of the Texas Terminonaris,
they were found everywhere," Adams said.
Texas
specimen fills gap, expands age and range of group
Texas Terminonaris
was discovered by Dallas-area amateur fossil enthusiast Brian Condon, a rural
mail carrier. Condon discovered the heavy pieces of the snout and a vertebrate
in 2005 while fossil hunting near his home on Lake Lewisville, a 26,000-acre
recreational and fishing lake managed by the U.S. Army Corps of Engineers. He
spotted the first of the pieces along the shoreline. Condon donated the fossils
to SMU's Shuler Museum of Paleontology.
In
prehistoric times, Texas Terminonaris would have made its home in a
marine setting, along the eastern shore of North America's vast prehistoric
Western Interior Seaway. One hundred million years ago the seaway was a wide,
shallow sea that split the North American continent in half from the Arctic to
the Gulf of Mexico, said Adams, lead author on the scientific article. The
seaway would have covered Lake Lewisville's location.
In its
day-to-day life on the seaway, Terminonaris would have kept close to
shore, perhaps in a shallow lagoon or estuary, also venturing into the seaway's
warm salty water to hunt for fish. Like modern crocodiles and alligators, Terminonaris
would have eaten whatever it could catch, Adams said. Its long, slender snout
was well-suited for devouring fish, small mammals and even small dinosaurs.
North
America's other Terminonaris fossil specimens also were found along the
seaway. A Kansas specimen is the youngest, about 91 million years, while those
from Saskatchewan, Canada, and Montana are 93 million years old. The German specimen
is 94 million years old.
"Terminonaris
now here in Texas fills in a gap that we didn't have information for,"
Adams said. "It tells us that as a group, as a genus, they were around
much longer, because we extend the age back to 96 million years. The range for
them is now expanded, because this is the most southern occurrence of
them."
Well-preserved
fossil offers no clues to adult reptile's cause of death
While the
Texas fossil is well-preserved, how the reptile died remains a mystery since
only the snout was found.
It probably
died in the water or washed out into the open sea, where it floated to the
bottom and was buried very quickly, said Adams. The discovery of seven Terminonaris
fossil specimens worldwide is significant, he said.
"To be
fossilized, it requires they die at the right time in the right place, be
buried very quickly, then eventually be exposed and uncovered," he said.
"So the odds of being fossilized and being found as a fossil are very
slim."
Condon found
one piece at the water's edge of Lake Lewisville. The other pieces were further
up a bank that sloped toward the shore, Condon said. The pieces had been
deposited on the ground by receding water, pulled from the Woodbine Formation
by constant waves that had washed away a soil bank and uncovered the heavy
fossils. The outcrop of the Woodbine Formation visible at Lake Lewisville
starts at the Red River in North Texas and thins as it nears Dallas.
Condon, who
had previously found other fossils in the area, initially thought the pieces were
petrified wood.
"This
piece looked like a loaf of bread from Subway. It was all wrinkled,"
Condon said. "Then I picked it up and turned it over and saw it had teeth
-- big, round conical teeth -- and I thought, 'This is amazing. It's a
jaw.'"
Co-authors
on the article were SMU paleontologists Michael J. Polcyn, Dale A. Winkler and
Louis L. Jacobs, and also paleontologist Octavio Mateus, Universidade Nova de
Lisboa, Portugal.
The research
was funded by Southern Methodist University's Institute for the Study of Earth
& Man.
Story
Source:
