Oceanic dispersal of dinosaurs between Europe and Africa shows how low-probability, high-impact events drive evolution.
Dinosaurs couldn’t just walk there. Sixty-six million years ago, when duckbills suddenly appear in Africa’s fossil record, the world’s land masses formed a series of islands. A seaway divided eastern and western North America; Europe was an archipelago. South America, India, Australia and Madagascar were all island continents, surrounded by ocean.
The first duckbill dinosaurs evolved in North America around 90 million years ago – after all the land connections were broken, when Africa was isolated by hundreds of kilometres of open sea. North American and Asian duckbills were giants: they grew up to 15 metres long and could weigh 10 to 20 tonnes. Minqaria was just a few metres long and weighed maybe 250kg; Ajnabia was similar in size. Two bones found a few kilometres away – a humerus and a femur – come from bigger duckbills, 5-6 metres long, hinting at a third, larger species.
Hundreds of kilometres of ocean separated Africa and Europe in the Cretaceous. Emergent islands may have helped to bridge the gap, but there’s little evidence for a land bridge. Duckbills couldn’t walk to Africa. That leaves us with an ocean crossing. when you have eliminated the impossible, then whatever remains, no matter how improbable, must be the truth.
Sometimes animals hitch a ride on floating vegetation. In 1995, after a hurricane hit the Caribbean, a group of iguanas washed up on Anguilla, clinging to debris. They probably came from Guadeloupe, 300km away.