Morocco dinosaur discovery gives clues on why they went extinct

By Nicholas R. Longrich, University of Bath

66 million years ago, the last dinosaurs vanished from Earth. We’re still trying to understand why. New fossils of abelisaurs – distant relatives of the tyrannosaurs – from north Africa suggest that African dinosaurs remained diverse up to the very end. And that suggests their demise came suddenly, with the impact of a giant asteroid.

The causes of the mass extinction have been debated for two centuries. Georges Cuvier, the father of palaeontology, thought extinction was driven by catastrophes. Charles Darwin  thought gradual changes in the environment and competition between species slowly drove lineages extinct.

As our understanding of the fossil record improved, it became clear that the Cretaceous period (145 million years to 66 million years ago) ended with an extraordinary wave of extinction. Huge numbers of species disappeared, worldwide, in a brief period. The discovery of the 180km-wide Chixculub asteroid impact crater in Mexico suggested a sudden extinction of dinosaurs and other species, driven by the impact. But others have argued that a long, slow decline in dinosaur diversity contributed to their extinction.

Piecing together the story is hard. It’s not just that dinosaur fossils are so rare; the fossil record is also patchy.

Most of what we know about the dinosaurs’ final days is the result of intensive study of a few places in the United States, Canada and Mongolia. Far less is known about dinosaurs of the southern landmasses – South America, India, Madagascar, Australia, Antarctica, New Zealand.

Partly that’s down to geography; it’s hard to find dinosaurs in rainforests. Partly there have, historically, just been more palaeontologists and museums in the northern hemisphere. The question is whether the picture is biased.

Because it’s such a huge landmass, Africa probably had far more dinosaur species than North America. Yet until recently we’ve known hardly anything about Africa’s end-Cretaceous dinosaurs. Africa has few terrestrial rocks from this period. That’s because high levels of volcanic activity pushed sea levels up, submerging much of Africa under shallow seas.

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