The first discovery of a small hadrosaurid in Morocco from the very end of the Cretaceous has forced a rethink of how dinosaurs dispersed between continents.
Hadrosaurids, known for the duck-like bills, were plant-eating dinosaurs that dominated the Cretaceous ecology of North America and spread to Europe and Asia, back then joined together as Laurasia. Africa, on the other hand, was isolated from the other continents. So it was quite a surprise to the University of Bath's Dr Nicholas Longrich to find a hadrosaurid in 66 million-year-old rocks not far from Casablanca, on the Atlantic coast of Morocco.
"It was completely out of place, like finding a kangaroo in Scotland. Africa was completely isolated by water – so how did they get there?” Longrich said (presumably not counting wallaby escapees).
The team, led by Longrich, has described the new dinosaur in Cretaceous Research, naming it Ajnabia odysseus to reflect its long journey (Ajnabi is Arabic for foreigner, while Odysseus was famous for his convoluted journey home from Troy). Ajnabia was small by hadrosaurid standards, just 3 meters (10 feet) long when its counterparts on other continents reached 15 meters (50 feet). However, its teeth and jawbones mark it clearly as a member of the Lambeosaurinae subfamily of hadrosaurids, and not a different dinosaur line that evolved a bill through convergent evolution.
Lambeosaurs, distinguished by their hollow crests, spread widely across Laurasia. Judging by some of the rocks in which they were found it seems likely they could take to the water when necessary, crossing rivers powered by their large tails and strong legs. That's altogether different from a land-based creature swimming across an entire ocean, but somehow Ajnabia, or an ancestor, made the crossing.
“Sherlock Holmes said, once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth," Longrich said. "It was impossible to walk to Africa. These dinosaurs evolved long after continental drift split the continents, and we have no evidence of land bridges. The geology tells us Africa was isolated by oceans. If so, the only way to get there is by water."
Living creatures, such as monkeys and spiders are thought to have crossed oceans on "rafts", perhaps when a tree they were living in fell into a river and was washed into the open ocean. However, even at 3 meters long, Ajnabi seems large for such a precarious mode of transport, and its ancestors were probably bigger still. Perhaps a flood washed some offshore and they just kept swimming?
"Over millions of years, once-in-a-century events are likely to happen many times," Longrich said. "Ocean crossings are needed to explain how lemurs and hippos got to Madagascar, or how monkeys and rodents crossed from Africa to South America."
Longrich and co-authors think Ajnabi belonged to the Arenysaurini clade, suggesting the ancestor reached Africa from Europe rather than North America.
With no other specimens, we don't know how long hadrosaurs had been in Africa. It seems a bit of a waste to have made such a difficult journey less than a million years before being taken out by the asteroid.