Natural Science Forum / Biology / Paleontology / April 2005

Do fossilised eggs prove this dinosaur cared for its young?
By Steve Connor, Science Editor
15 April 2005

A fossilised dinosaur has been found in China with two pineapple-sized eggs,
their shells intact, in its pelvic cavity.

Scientists believe the discovery adds further weight to the theory that modern
birds evolved from a group of feathered dinosaurs.

The eggs are nearly 7ins in diameter and are of roughly equal size, suggesting
they would probably have been laid at the same time - unlike birds which lay
single eggs at intervals.

Finding a fossil with a pair of eggs ready for laying suggests that female
reproduction in dinosaurs was at a stage somewhere between that of reptiles,
such as crocodiles, which lay all their eggs at once, and birds.

Tamaki Sato of the Canadian Museum of Nature in Ottawa, Ontario, and her
colleagues describe the fossil in the journal Science. They say it sheds fresh
light on the mystery of how dinosaurs reared their young.

The pelvis belonged to a type of dinosaur called an oviraptor, which means "egg
stealer" because, when it was first discovered, it was found near to a nest of
eggs. Subsequent discoveries revealed that oviraptors were almost certainly
guarding their own nests rather than raiding those of other dinosaurs.

Oviraptors, which lived between 80 million and 120 million years ago, were
similar to birds in that they had a toothless beak and stood on two legs. But
they could grow to 13ft in length and had long, powerful legs with front limbs
that were armed with sharp, powerful claws.

The latest specimen of a fossilised pelvis, recovered from a site near to the
city of Ganzhou in the southern Chinese province of Jiangxi, shows the two eggs
side by side with their more pointed ends facing backwards ready for laying.

Dr Sato and her colleagues believe it was unlikely the dinosaur produced
multiple pairs of shelled eggs in its two oviducts, which is the case with
crocodiles and other reptiles.

"Unless sequential egg formation and shelling was very rapid and/or there was an
extremely prolonged period of egg-laying, the preservation of only two tightly
juxtaposed eggs in the specimen strongly indicates each of the paired oviducts
simultaneously produced a single egg," the researchers wrote.

"This supports the theory that [oviraptor-like] dinosaurs retained two
functional oviducts like crocodiles but had reduced the number of eggs ovulated
to one per oviduct, as in birds," they say.

Because the pointed end of the eggs were laid first, and fossilised dinosaur
nests have been found with the eggs pointing out from the nest, the scientists
suggest that females laid their eggs in pairs from the centre of the nest in
neat, multilayered, ring-shaped clusters.

Arguments over whether dinosaurs cared for their young after they had hatched
are still unresolved. Last year, however, an adult dinosaur was found that
appeared to have died while it was protecting a clutch of 34 offspring.

Scientists saidthe discovery was compelling evidence in support of the idea that
dinosaurs cared for their young for some time after they hatched - unlike many
modern reptiles.

The evolution of feathers also occurred in dinosaurs and probably came about
initially as a primitive form of heat insulation. Feathered dinosaurs are now
considered to be the direct ancestors of birds.

http://news.independent.co.uk/world/science_technology/story.jsp?story=629519