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发帖数: 38600 | 1 Newly discovered fossil could prove a problem for creationists
http://www.washingtonpost.com/news/speaking-of-science/wp/2014/
Researchers report that they've found the missing link between an ancient
aquatic predator and its ancestors on land. Ichthyosaurs, the dolphin-like
reptiles that lived in the sea during the time of the dinosaurs, evolved
from terrestrial creatures that made their way back into the water over time.
But the fossil record for the lineage has been spotty, without a clear link
between land-based reptiles and the aquatic ichthyosaurs scientists know
came after. Now, researchers report in Nature that they've found that link
— an amphibious ancestor of the swimming ichthyosaurs named Cartorhynchus
lenticarpus.
"Many creationists have tried to portray ichthyosaurs as being contrary to
evolution," said lead author Ryosuke Motani, a professor of earth and
planetary sciences at the University of California Davis. "We knew based on
their bone structure that they were reptiles, and that their ancestors lived
on land at some time, but they were fully adapted to life in the water. So
creationists would say, well, they couldn't have evolved from those reptiles
, because where's the link?"
Now the gap has been filled, he said.
Motani and his colleagues, who include researchers from Peking University,
Anhui Geological Museum, the Chinese Academy of Science, University of Milan
and the Field Museum in Chicago, found the fossil in China's Anhui Province
in 2011. The creature is about a foot and a half long and lived 248 million
years ago
"Initially I was really puzzled by this fossil," Motani said. "I could tell
it was related [to ichthyosaurs], but I didn't know how to place it. It took
me about a year before I was sure I had no doubts."
Intense analysis put it smack dab in the middle of the ichthyosaur family.
But unlike previously discovered fossils in the lineage, this one wasn't
perfectly suited to life in the ocean. The key differences between this
specimen and previously known ichthyosaurs set it up as the perfect
amphibious intermediary.
The oldest basal ichthyosauriform, Cartorhynchus lenticarpus. (Ryosuke
Motani)
Ocean-bound ichthyosaurs had very long snouts (leading to their frequent
comparison to modern dolphins) that were made for capturing fish and squid.
This new animal had a shorter snout — more like a land-based reptile. It
also had large flippers and flexible wrists, which would have allowed it to
flop around on land like a seal.
One of the most important differences between this new ichthyosaur and its
supposed descendants comes down to being big boned: When other vertebrates
have evolved from land to sea living, they've gone through stages where they
're amphibious and heavy. Their thick bones probably allowed them to fight
the power of strong coastal waves and stay grounded in shallow waters. Sure
enough, this new fossil has much thicker bones than previously examined
ichthyosaurs.
The animal lived about 4 million years after the worst mass extinction in
our planet's history — so Motani and his colleagues believe the creature
gives insight into how long it took the ecosystem to recover.
"This animal probably had a happy life. It was in the tropics, and it was
probably a bottom feeder that fed on soft-bodied things like squid and
animals like shrimp," Motani said. "And for a predator like that to exist,
there has to be plenty of prey. This was probably one of the first predators
to appear after that extinction."
This single fossil hasn't revealed all of the ichthyosaurs' secrets. Motani
hopes to find the preceding evolutionary ancestor next — one that was also
amphibious, but spent slightly more of its time on land. "We're looking for
that one now," Motani said. | P**C
发帖数: 4333 | | n***c
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