New findings from the most complete evolutionary tree of the genus Crocodylus, featuring all but one of the living crocodile species, has revealed that crocodiles swam thousands of kilometers from Africa to colonise the Americas.
Upon sequencing ther mitochondrial genomes of 11 species , eight of which had not been mitochondrial DNA sequenced before , Evon Hekkala of Forham University in New York and colleagues havd learned that all four American species are closely related to the Nile crocodiles of East Africa. It is suspected that these crocofiles must have split away roughly 7 million years ago after South America and Africa began drifting apart over 130million years ago. By 7 million years ago, over 2800 kilometres of ocean lay between the two continents.
For this study Hekkala and her team have been able to use genetic data from Egyptian crocodile mummies to try to identify the baseline distribution of unique evolutionary lineages in the Nile crocodile.
It has been long suspected by palaeontologists that crocodiles swam the Atlantic, but Hekkala”s finding is “strong evidence in support of that scenario”, said Christopher Brochu of the University of Iowa in Iowa City.
Crocodiles are salt-tolerant and can go up to six months without eating and females can carry viable sperm for several months after mating, which means a single female could have crossed the Atlantic and produced a litter on the other side. It”s unlikely that a single such event would have given rise to all American crocodiles.
But Hekkala pointed out that animals that got lost at sea off the coast of Africa may well have been carried across on the westward-flowing equatorial currents.