Seventy-seven million years ago, did a dinosaur mother sat on a nest of a dozen eggs on a sandy river bank, brooding whether to abandon the unhatched offspring to vagaries of nature and scramble to safety?
Today, scientific detective work conducted by University of Calgary and Royal Tyrrell Museum researchers have used this unique fossil nest and eggs to learn more about how nest building, brooding and eggs evolved.
"Working out who the culprit was in this egg abandonment tragedy is a difficult problem to crack," says Darla Zelenitsky, University of Calgary paleontologist and co-author of a paper, according to a Calgary release.
"After further investigation, we discovered that this find is rarer than we first thought. It is a one of a kind fossil. In fact, it is the first nest of its kind in the world."
Zelenitsky informed she first saw the nest in a private collection which had been collected in Montana in the 1990s. The nest was labelled as belonging to a hadrosaur (duck-billed) dinosaur, but she soon discovered it was mistakenly identified.
In putting all the data together, she realised they had a small theropod (meat-eating) dinosaur nest. "Nests of small theropods are rare in North America and only those of the dinosaur Troodon have been identified previously," said Zelenitsky.
"Based on characteristics of the eggs and nest, we know that the nest belonged to either a caenagnathid or a small raptor, both small meat-eating dinosaurs closely related to birds. Either way, it is the first nest known for these small dinosaurs."
"Our research tells us a lot about the dinosaur that laid the eggs and how it built its nest," said Francois Therrien, a co-investigator in the study and curator of dinosaur palaeoecology at the Royal Tyrrell Museum in Drumheller, Alta.
The fossil nest is a mound of sand about half a metre across and weighing as much as a small person. The eggs were laid two at a time, on the sloping sides of the mound, and form a ring around its flat top, where the nesting dinosaur would have sat and brooded its clutch.
"Based on features of the nest, we know that the mother dug in freshly deposited sand, possibly the shore of a river, to build a mound against which she laid her eggs and on which she sat to brood the eggs," said Therrien.
These findings were published Friday in Palaeontology.