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17 September 2014
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The Ballad of Big Al

Big Al

'Big Al' is the name given to a real Allosaurus fragilis skeleton. But Big Al wasn't big at all - he wasn't even fully grown. Dr Alexandra Freeman worked on this Walking with Dinosaurs special and tells the story of the real Big Al.

Where did it all start?

The Ballad of Big Al is the story of an Allosaurus, a large carnivorous dinosaur, which lived in the Late Jurassic around 145 million years ago. Big Al was found near Howe Quarry in the Morrison Formation of North America. The skeleton was unusually well preserved - over 95% of his bones were found - and they were all in the same positions as when he died. Big Al took his name from the completeness of his skeleton.

The bones told a story. Big Al had many injuries which were picked up in the last few years of his life. Piecing together the evidence from his bones and those of other animals found in the Morrison Formation, we could reconstruct how Al may have lived and died.

It started with an egg

The story opens as Big Al hatches from an egg buried in a nest chamber underground. The nest of a dinosaur very like Allosaurus has been found near Lourinha, Portugal. There were about 100 eggs in the nest and there may have been many more. Inside some of the eggs were tiny fossilised embryos that revealed the type of dinosaur that laid them. Eggshells have tiny pores to let the embryos inside breathe. Eggs which are buried underground have bigger pores than those incubated above ground. By examining the pores on the eggs in Portugal, we could tell that the nest had originally been underground.

Allosaurus and nest

Allosaurus mothers probably dug the new hatchlings out of an underground nest.

Hatching out

Allosaurus eggs have been found which would have contained tiny embryos. In the programme, Al's mother is nearby and helps dig out the youngsters as they hatch. This is speculation based on the behaviour of other animals which bury their eggs. For these animals, good nesting sites tend to be rather rare. The fact that many fossil dinosaur nests have been found in the same areas suggests that there was stiff competition to find a good nest site among dinosaurs too. This means that a mother who has laid all her eggs in one nest has a risk of her eggs being dug up by another nesting female. The large numbers of eggs found in the nest in Portugal indicates that they probably did this. Both crocodiles and Komodo dragons (a large lizard which also buries its eggs) guard their nests to prevent this happening.

Next - mother's help

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