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Dinosaurs burrowed to keep warm

Burowing dinosaur

Remains of this burrowing dinosaur, Oryctodromeus cubicularis, were found at the end of a long tunnel. Palaeontologists say its snout and other features suggest it could gouge out and shift soil (Image: Lee Hall)

Palaeontologists have found the remains of small dinosaurs that made their home in a burrow, a finding that suggests dinosaurs could exploit a much wider habitat than thought.

Fossilised bones and the dinosaurs' underground den were found in the US state of Montana.

Researchers have named the dinosaurs Oryctodromeus cubicularis, a mix of Greek and Latin that means "digging runner of the lair".

The burrow's soil has been dated to the mid-Cretaceous, a hothouse period that ran from about 135-115 million years ago.

"[It is] the first trace and body fossil evidence of burrowing behaviour in a dinosaur," the trio of US and Japanese researchers say.

Their paper appears in the Proceedings of the Royal Society B, a journal of the UK's Royal Society.

The burrow, long filled with sediment, comprises a sloping, sinuous tunnel more than 2 metres long and about 70 centimetres wide, and is somewhat similar to holes made today by striped hyenas and puffins.

It ends in a chamber, where the skeletal remains of an adult and two juveniles were found.

Their snout, shoulder girdle and pelvis have the telltale shape of bones found in animals capable of gouging out and shifting soil.

Based on the preserved vertebrae, the adult would measure around 2.1 metres long, with a weight of 22-32 kilograms, which made it small on the dinosaur scale.

The authors, led by Assistant Professor David Varricchio of Montana State University, say burrowing would help small dinosaurs survive in extreme climates.

Unlike mammals, reptiles cannot regulate their own body temperature. Thus, in deserts, a burrow would provide shelter from extreme heat, while in polar regions and chilly mountains, it would preserve warmth.

The burrowers may have survived, at least for a while, the twilight of the dinosaurs, the authors say.

The prevailing theory is that this happened around 65 million years ago, when a massive asteroid struck the Earth. That kicked up a thick veil of dust and ash that cooled the planet, killing off the kinds of vegetation on which the dinosaurs depended.

The end of the Cretaceous bequeathed the planet to avian, or bird-like, dinosaurs and other species that either thrived without the old predators around or found a niche in a suddenly-changed climate.

Tags: science-and-technology, dinosaurs, palaeontology