Posted on 02/24/2006 4:50:26 AM PST by S0122017
'Jurassic beaver' find stuns experts 19:00 23 February 2006 NewScientist.com news service Jeff Hecht
Enlarge image The discovery of a Jurassic beaver-like creature suggests early mammals were more diverse than thought (Image: Mark A. Klinger/CMNH)Related Articles
Nanjing University (in Chinese) Dinosaur special report, New Scientist Science
The discovery of a new, remarkably preserved fossil of a beaver-like mammal that lived 164 million years ago is shaking palaeontologists’ understanding of early mammals.
Looking as if it was put together from pieces of platypus, river otter, and beaver, the creature was nearly half a metre long and weighed about half a kilogram. This makes it the largest mammal ever found in the Jurassic Period, from 200 million to 145 million years ago.
The fossil of the semi-aquatic mammal Castorocauda lutrasimilis was discovered in the middle Jurassic Jiulongshan formation in Inner Mongolia, China, by Qiang Ji at Nanjing University, and colleagues. It boasts the oldest fossil fur ever found.
Palaeontologists had long thought the mammals living under the feet of the dinosaurs were tiny shrew-like animals. But recent discoveries have challenged this notion.
Full pelt In 2005, Repenomamus giganticus from China showed that land mammals had reached a metre in length about 130 million years ago, during the Cretaceous Period.
But the newly found fossil reveals that early mammals were also far more diverse than thought. The discoveries "are completely reconfiguring our understanding of Mesozoic mammals," says Hans-Dieter Sues of the Smithsonian Institution's National Museum of Natural History.
Castorocauda was preserved in exquisite detail, flattened in sediments at the bottom of an ancient lake. Hair impressions surround the body, which includes a 20-centimetre-long flat, beaver-like tail. Two slabs of sedimentary rock include most of the body and part of the skull.
The animal had "a full mammalian pelt, with guard hairs and under fur, and scales on the tail" like a modern beaver, says Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh, US, and one of the team.
Warm-blooded metabolism Castorocauda’s webbed feet, limbs and broad flat tail are adapted for swimming, and its teeth specialised for catching fish, making it the earliest mammal known to live partly in the water. Another 100 million years would pass before ancestral whales and manatees turned to the water.
The creature probably lived like a modern platypus, says Luo, "digging a tunnel to nest and lay eggs, and going from the tunnel into the water to feed".
The discovery shows that fur and modern skin structures and warm-blooded metabolism originated very early in mammals. "Hair keeps us warm, and sweat glands help us to dissipate heat, so skin is part of the adaptation to constant body temperature," Luo told New Scientist.
"This is a pretty amazing find," Sues told New Scientist. What excites palaeontologists is the new-found diversity and complex evolutionary history of early mammals – a group previously known mostly from scattered teeth. More complete fossils have been very rare.
"Traditionally, Mesozoic mammals were not the path to glory," says Sues.
Journal reference: Science (vol 311, p 1123)
My immediate thought too!
See, I knew it.
I see a lack of "transitional" creatures which led up to the Jurassic Beaver.
Seems like you've got the Theory well in hand and are now awaiting the evidence to support it. And this is science?
Seems like you've got the Theory well in hand and are now awaiting the evidence to support it. And this is science?
ELSIE!!!!!
I'm... Shocked! Shocked I tell you!
(Nice pun!)
Cheers!
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