The crocodiles that swam the Atlantic

This weekend over a glass of beer I was discussing with my friend Ramesh, the incredible journey of the crocs that swam the Atlantic. The paper “A phylogenetic hypothesis for Crocodylus (Crocodylia) based on mitochondrial DNA: Evidence for a trans-Atlantic voyage from Africa to the New World” by Robert W. Meredith, Evon R. Hekkala, George Amato and John Gatesy provided fodder for the discussion.

The crux of the research emphasizes that crocodiles swam across the Atlantic Ocean from Africa in order to establish the species in the Americas. The researchers used nearly complete mitochondrial (mt) genomes (16,200 base pairs) for all described Crocodylus species, eight of which are new to their study, to derive a generally well-supported phylogenetic hypothesis for the genus.

The research clearly revealed that all four American species are most closely related to the Nile crocodiles of east Africa. It is assumed that they must have split away roughly 7 million years ago, quite a bit after Africa and South America began drifting apart 130 million years ago. By 7 million years ago, over 2800 kilometres of ocean lay between the two continents.

Palaeontologists have long speculated that crocodiles swam the Atlantic. Hekkala's finding provide concrete evidence in support of that hypothesis

Crocodiles are salt-tolerant and can go up to six months without eating and are able to process salt water through special glands. Females can carry sperm for couple of years after mating. This means that a single female could have crossed the Atlantic and produced a litter on the other side. Hekkala says out of the crocs that got lost at sea off the coast of Africa some may have been carried across on the westward-flowing equatorial currents. The sea journey could have taken some months.

Journal reference

A phylogenetic hypothesis for Crocodylus (Crocodylia) based on mitochondrial DNA: Evidence for a trans-Atlantic voyage from Africa to the New World

Robert W. Meredith, Evon R. Hekkala, George Amato and John Gatesy

Molecular Phylogenetics and Evolution
Volume 60, Issue 1, July 2011, Pages 183-191