[Paleopsych] NYT: When Dinosaurs Ruled, a Mammal Ate (a Little) One

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When Dinosaurs Ruled, a Mammal Ate (a Little) One
NYT January 13, 2005
By JOHN NOBLE WILFORD

[You may already have heard about this.]

In the time of dinosaurs, mammals were the meek that had
yet to inherit the earth. They were small creatures, many
no bigger than mice, and essentially nocturnal, feeding
mainly on insects and cowering in holes and underbrush from
the terrible tread of the reptilian lords of the land.

Two newly discovered fossils show that this lowly image of
early mammals, long the reigning view of science, did not
do them justice. A few of these animals were as large as a
dog and spunky enough to devour dinosaurs, at least
juvenile dinosaurs.

The 130-million-year-old fossils, announced yesterday by
Chinese paleontologists, challenge conventional thinking
and lead to a new and more diverse perception of mammal
life in the Mesozoic era, 280 million to 65 million years
ago.

In interviews and a report being published today in the
journal Nature, the researchers described finding the skull
and most of the bones of what they say is the largest
mammal known to live in the age of dinosaurs. The animal's
skull was half again the length of the next largest mammal
of the period. The entire body probably weighed 30 pounds
and stretched more than three feet, longer than a good-size
basset hound's.

>From the same fossil beds in northern China, the
paleontologists also uncovered the remains of a related
species about 15 inches long, the size of an opossum, and
made a striking observation. The mammal's last meal had
been a juvenile dinosaur. Its limbs, fingers and teeth were
lodged within the mammal's rib cage where its stomach had
been.

The dog-size animal has been named Repenomamus giganticus.
The smaller one is a specimen of Repenomamus robustus.

"Our discoveries," the scientists wrote in the journal
report, "constitute the first direct evidence that some of
these mammals were carnivorous and fed on small
vertebrates, including young dinosaurs, and also show that
Mesozoic mammals had a much greater range of body sizes
than previously known."

The scientists further concluded that "Mesozoic mammals
occupied diverse niches and that some large mammals
probably competed with dinosaurs for food and territory."

Dr. Anne Weil, a paleontologist at Duke University who was
not involved in the research, agreed that the fossils were
a fascinating discovery and certain to shake up the field
of early mammal studies.

In an accompanying article in Nature, Dr. Weil said, "These
latest finds should trigger another avalanche of questions
and speculation."

She and other paleontologists said several recent
discoveries had yielded clues suggesting that some species
were at least as large as robustus and might have been as
large as giganticus. But the new fossil skeletons are more
complete and definitive, they said.

Dr. Jin Meng, a paleontologist at the American Museum of
Natural History in Manhattan and a member of the discovery
team, said that any Mesozoic mammal remains were rare and
that these were "giving us a drastically new picture" of
many of the animals of the age of dinosaurs.

Standing in the museum laboratory with the carefully
cleaned bones of the mammal that ate the little dinosaur,
Dr. Meng said, "Now we have to see how common was the
phenomenon of these larger, carnivorous species."

But in one respect, he added, the general pattern of
Mesozoic life remained unchanged: although other large
early specimens may be found, most of the mammals were
still small and no match for the dominant reptiles.
Primitive mammals presumably had little chance to evolve in
stature because the dinosaurs and other reptiles were
stronger, lived longer and moved faster than the mammals in
the competition for food and favorable habitats.

Only with the extinction of dinosaurs 65 million years ago
could the mammals begin to assert themselves and flourish
in size and diversity, evolving into lions and tigers and
bears and, in time, humans who are curious about life when
the world was younger.

The two skeletons were collected in 2003 by farmers at the
abundant fossil deposits in Liaoning Province in China,
where many dinosaurs and a sprinkling of their mammalian
contemporaries have been uncovered in recent years. The
fossils caught the eye of visiting scientists, who bought
them and took them to the Institute of Vertebrate
Paleontology and Paleoanthropology in Beijing for detailed
examination.

Yaoming Hu, a researcher at the institute and a graduate
student the City University of New York, is the lead author
of the journal report of the discovery. The co-authors are
Dr. Meng, Mr. Hu's dissertation adviser; and Dr. Yuanqing
Wang and Chuankui Li, both of the Beijing institute.

An artist's rendering of the two species, giganticus and
robustus, showed animals with low-slung bodies with short
legs and long tails, as suggested by the fossils. They are
covered in dark, short-haired fur, for which there is no
direct evidence; if the animals were primarily nocturnal,
it is assumed that evolution would have favored those with
dark fur for concealment.

The researchers said giganticus, though it resembled no
animal living today and has no living descendants, was
somewhat comparable to a Tasmanian devil, a squat,
carnivorous marsupial living on the Australian island of
Tasmania. Analysis of the giganticus teeth indicated that
the specimen was an adult. Its combined head and body was
60 percent longer than that of its robustus cousin.

The well-preserved remains of giganticus are at the
paleontology institute in Beijing. A full-scale replica is
being prepared for a new dinosaur exhibition at the
American museum, opening in May.

Geological dating of sediments in the fossil beds showed
that both species lived at approximately the same time,
about 130 million years ago. The animals that were
fossilized in the region probably died in volcanic
eruptions.

The first fossils of robustus were excavated in 2000, when
it was recognized as the largest known Mesozoic mammal
represented by substantially complete remains. Dr. Wang was
one of the discoverers. The specimen was assigned the genus
Repenomamus, combining words for reptiles and mammals to
reflect the animal's reptile-mammal attributes.

The big surprise about the new robustus fossils being
reported now was not revealed until researchers had a close
look in the Beijing laboratory. Mr. Hu pointed to the
skeleton, in the American museum lab, and showed the patch
of small bones in the rib cage. They were the tiny limbs,
fingers and teeth of a juvenile psittacosaur, a two-legged
herbivorous dinosaur common in the Chinese fossil beds.

The baby dinosaur, Mr. Hu said, was only five inches long,
a third the size of the animal that ate it. An adult
psittacosaur was often six feet tall. Judging by the
mammal's teeth and jaws, it did not chew its food, but
swallowed the dinosaur in chunks.

http://www.nytimes.com/2005/01/13/science/13mammal.html