Читать книгу Dinosaurs - Douglas Palmer - Страница 11

Fossil eggs, now known to be those of dinosaurs, were first found in France and England in the mid-19th century. But it was not until the amazing discoveries of the Roy Chapman Andrews’ expedition to Mongolia in the 1920s that we really began to get an idea of how dinosaurs reproduced in bird-like ways and how some of them looked after their babies.

Chapman and his team from the American Museum of Natural History in New York found fossil eggs and hatchlings clustered together in and around mud mounds. They even thought that they had found the remains of a dinosaur egg thief called Oviraptor in the act of stealing from a Protoceratop’s nest. However, we now know that it is more likely that the Oviraptor died defending its own nest.

Caption: A nesting Psittacosaurus dinosaur with babies.

Dinosaur eggs ranged in size and shape from tiny round eggs to long oval-shaped ones more than 50cm (20in) long and around 4.0l (8.5pts) in volume. These were, however, small compared to the biggest bird egg, which was laid by the extinct Elephant Bird (Aepyornis) and measured more than 1m (3ft) in circumference and 7.3l (15.4pts) in volume. Large eggs need thick shells but these also have to be porous to allow the foetus to ‘breathe’. Consequently, dinosaur eggs could not be too large. Like modern- day turtles, many dinosaurs laid large numbers of eggs because relatively few of the babies would survive into adulthood.

In the 1970s, finds from the so-called Egg Mountain site in Montana, USA, revealed what may have been a shared nesting ground and hatchery for the duck-billed dinosaur Maiasaura. Several nests up to 2m (6.6ft) wide have been found, made of layers of plant material and mud topped by a hollow in which up to 12 eggs were laid. The 9m-long (30ft) mother was far too big to have sat on the eggs but probably would have fed her babies, which could not have looked after themselves to begin with.

In contrast, hatchlings of the small theropod Troodon, which also nested around Egg Mountain, were much more precocious and probably began to feed themselves very early on. Surprisingly, there is evidence that even some of the biggest plant-eating sauropods stayed around their nests for some time, presumably to try to protect the eggs and babies from predators.

Caption: A Mussaurus hatchling. Some of the skeletons of this species could fit into the palm of a hand.