The fossil remains of small dinosaurs which
burrowed into the ground were unearthed by scientists in Montana,
USA, in 2007.
The 95 million year-old bones were from an adult
and two juveniles and were discovered in a chamber at the end of
a 2.1m-long sediment-filled tunnel. The researchers said the
discovery was the first definitive evidence that some dinosaurs
dug dens and cared for their young in such structures. Details were
reported in the journal, Proceedings of the Royal Society B.
Burrowing also represented a mechanism by which
small dinosaurs may have exploited the extreme environments of
polar latitudes, deserts and high mountain areas, according to
Dr David Varricchio and colleagues.
The Montana dinosaurs had not previously been
seen by palaeontologists. They were given the scientific name
Oryctodromeus cubicularis, meaning 'digging runner of the
lair'. The team said the species' snout, shoulder girdle, and pelvis
had features one would expect to see in an animal that dug into the
Judging from the preserved vertebrae, the adult
would have been about 2.1m long (6.8 feet) from nose to tail, with
the major part of that (about 1.2m; 3.9 feet) being the tail itself.
The estimated width of the animal fitted neatly with the size of the
tube it was digging (about 30cm or one foot in diameter).
What was left of the tunnel structure was sloping
and had two sharp turns before ending in a chamber. The team stated
that its architecture was similar to the dens of modern burrowers,
such as the striped hyena, puffin, and some rodents.