http://www.nature.com/news/2007/070319/full/070319-5.html Published online: 21 March 2007; | doi:10.1038/news070319-5
Burrowing dinosaur unearthed
Fossilized family broadens picture of extinct reptiles.John Whitfield
| An artist's impression shows the "digging runner of the lair" had a broad snout for burrowing. Lee Hall |
|
The
discovery of a dinosaur family fossilized in its burrow could make us
rethink where the animals lived, how they behaved, and even what wiped
them out, say researchers.
David
Varricchio of Montana State University in Bozeman and his colleagues
found the jumbled remains of two juveniles and an adult together in
what looks to be the remains of a custom-built hole in southern
Montana.
The
discovery provides the first evidence that dinosaurs could burrow, and
the best evidence yet for long-term parental care in dinosaurs, says
team member Anthony Martin, an expert in animal traces at Emory
University in Atlanta, Georgia. "I imagine that two juveniles curled up
in a small space with an adult," he says.
The team has named the beast
Oryctodromeus cubicularis,
meaning 'digging runner of the lair'. It belongs to a group of small
herbivorous dinosaurs, and lived 95 million years ago during the
mid-Cretaceous period.
The
skeletons are incomplete, but they show that when fully grown, the
animal was about 2.1 metres long, of which more than half was tail. The
dinosaur had a broad snout and powerful shoulders well adapted for
digging, and sturdy hips that would help it to brace itself as it dug.
It could also run on its back legs.
Secret entranceThe
burrow's presence was betrayed by a patch of rock that differed from
its surroundings, in an area known to contain dinosaur fossils. The
burrow seems to have been dug on the edge of a river flood plain and
filled with mud during a flood, burying its occupants, the researchers
report in
Proceedings of the Royal Society1.
| Dig this: an adult Oryctodromeus cubicularis (far left) was probably 2.1 metres long. Lee Hall |
|
The
den was just over two metres long, with a pronounced s-bend - making it
harder for predators to enter - opening out into a terminal chamber.
The close fit between the sizes of burrow and beast convinced the team
that
Oryctodromeus had dug its own den, rather than simply
displacing a previous occupant. "It's not just a random attempt," says
Martin. "It's very well constructed."
"It
was generally assumed that dinosaurs wouldn't dig - they tend to be
either runners or very large," says palaeontologist Paul Barrett of the
Natural History Museum, London. "This is quite a departure."
Varricchio
and his colleagues had previously found what seemed to be a family of
dinosaurs in what could have been a collapsed burrow in China, but no one had seen an actual tunnel space until now.
Safe undergroundBurrowing
may have helped dinosaurs to survive in harsh climates, increasing the
range of habitats available to them. No one knows exactly what the
environment of this part of the world was like when these dinosaurs
lived there, although it was probably semi-arid.
Related
dinosaurs are known to have lived in southern Australia, which was
close to the South Pole at the time, and South Africa, which was hot
and dry. These species and locations would be good places to look for
further evidence of burrowing, says Barrett.
The lack of an ability to burrow has also been suggested
as a factor in the demise of dinosaurs 65 million years ago, at the end
of the Cretaceous. Many of the mammals, reptiles and amphibians that
survived a mass extinction at this time could burrow, perhaps
sheltering them from whatever catastrophe caused the massive cull.
"The
absence of burrowing has been proposed as one reason why dinosaurs
didn't make it," says Martin. "You can't use that as a reason now."
Using
one specimen to speculate about the dinosaurs' extinction is "quite a
big inference", says Barrett. "It might be taking the data too far," he
cautions.
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