SCIENTISTS have unveiled the first evidence of burrowing dinosaurs.
A set of fossils 95 million years old, described for the first time in a report in the journal Proceedings of The Royal Society, reveals the existence of a previously unknown type of dinosaur that made a snug home in the ground.
They comprise the preserved remains of a dinosaur family, found in an underground den in Montana in the US.
They are the first burrowing dinosaurs ever discovered. Scientists say the 2.1 metre-long lizard would have raised its young in burrows and used them to shelter from extreme weather, so they could live in harsh environments such as the Arctic regions and deserts.
The find also casts doubt on the theory that a giant asteroid from space that crashed into the earth wiped out the dinosaurs.
It is thought that dinosaurs died out because they did not have shelter, unlike burrowing creatures that survived past the Cretaceous age, but according to this assumption, the burrowing dinosaur should also have survived - yet it has not been found after the period the asteroid is thought to have hit Earth.
Named Oryctodromeus cubicularis, which translates as "digging runner of the den", the dinosaur, a herbivore, was ideally adapted to its life in the Cretaceous period.
Its snout was shovel-shaped to help it shift earth, while large bony shoulders provided attachments for powerful muscles used to burrow, and a strengthened hip helped to brace the creature during digging.
The fossils of an adult and two juvenile dinosaurs were found in a two-metre-long burrow with a large chamber..
The bones are from an adult, 2.1 metres long, and two 1.3-metre-long youngsters, which suggests a strong family bond, say scientists.
Dr David Varricchio, of Montana State University, who led the research, said: "The discovery uniquely preserves both an adult-young association and direct evidence of denning in the form of a dwelling trace.
"Although growth rates were probably fast, the large size of the juveniles suggests that the parent-young bond persisted for a minimum of several months."
However, the discovery may lead to confusion among scientists, as Dr Varricchio claims it raises questions about the theory of dinosaur extinction.
He continued: "By denning, small dinosaurs could have potentially withstood severe conditions, such as aridity, drought and daily or seasonal temperature extremes.
"Such behaviour would have allowed dinosaurs to occupy high mountains, desert environments and polar regions.
"Survivability of terrestrial vertebrates at the end- Cretaceous event has been attributed to sheltering behaviour, with the extinction of non-avian dinosaurs resulting from their inability to find an appropriate cover.
"Burrowing dinosaurs would challenge this argument, but these are yet to be found in the latest Cretaceous formations," Dr Varricchio said.