Fossil Overturns Ideas of Jurassic Mammals
By RANDOLPH E. SCHMID, AP Science Writer
5:24 PM PST,February 23 2006
WASHINGTON -- The discovery of a furry, beaver-like animal that
lived at the time of dinosaurs has overturned more than a century
of scientific thinking about Jurassic mammals.
The find shows that the ecological role of mammals in the time of
dinosaurs was far greater than previously thought, said Zhe-Xi Luo,
curator of vertebrate paleontology at Carnegie Museum of Natural
History in Pittsburgh.
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The animal is the earliest swimming mammal to have been found and
was the most primitive mammal to be preserved with fur, which is
important to helping keep a constant body temperature, Luo said in
a telephone interview.
For over a century, the stereotype of mammals living in that era
has been of tiny, shrew-like creatures scurrying about in the
underbrush trying to avoid the giant creatures that dominated the
planet, Luo commented.
Now, a research team that included Luo has found that 164 million
years ago, the newly discovered mammal with a flat, scaly tail like
a beaver, vertebra like an otter and teeth like a seal was swimming
in lakes and eating fish.
The team, led by Qiang Ji of the Chinese Academy of Geological
Sciences in Beijing, discovered the remains in the Inner Mongolia
region of China. They report their findings in Friday's issue of
the journal Science.
Matthew Carrano, curator of dinosaurs at the Smithsonian's National
Museum of Natural History, called the find "a big deal."
An important factor is how specialized the creature was, said
Carrano, who was not part of the research group.
"It gives a hint that early mammals were not just these shadowy
creatures at the time of dinosaurs" but were having their own
evolution. There have been hints of such animals in the past but
nothing equal to the remains found by Luo and colleagues, he
said.
Thomas Martin of the Research Institute Senckenberg in Frankfurt,
Germany, said the discovery pushes back the mammal conquest of the
waters by more than 100 million years.
"This exciting fossil is a further jigsaw puzzle piece in a series
of recent discoveries," commented Martin, who was not part of Luo's
team.
It's the first evidence that some ancient mammals were
semi-aquatic, indicating a greater diversification than previously
thought, the researchers said.
Modern semi-aquatic mammals such as beavers and otters and aquatic
mammals like whales did not appear until between 55 million years
ago and 25 million years ago, according to the researchers.
The new animal is not related to modern beavers or otters but has
features similar to them. Thus the researchers named it
Castorocauda lutrasimilis. Castoro from the Latin for beaver, cauda
for tail, lutra for river otter and similis meaning similar.
The researchers found imprints of the fur, both guard hairs and
short, dense under fur that would have kept water from the
skin.
Weighing in at between 1.1 and 1.7 pounds, about the size of a
small female platypus, Castorocauda is also the largest known
Jurassic early mammal.
The research was funded by the U.S. National Science Foundation,
National Natural Science Foundation of China, Ministry of Science
and Technology of China, Chinese Ministry of Land Resources,
National Geographic Society and Carnegie Museum.