It's a simple skull but it says a lot: the fossil of a now extinct African crocodile species has revealed a disturbing similarity to its modern American cousins, whose ancestors would have crossed the Atlantic Ocean at least ago. five million years ago, according to a study in the journal Nature Scientific Reports.
American crocodiles could therefore all be the descendants of a single pregnant female of this ancient African species, which would have been transported by the ocean currents to land in the New World, believe the authors of the study.
The American crocodile is today one of the largest species in the world, measuring four meters in length on average, but reaching up to seven meters. While it typically weighs 500kg, larger specimens can weigh a ton. In comparison, the standard size of its cousin the Nile crocodile, found in Africa, is 5 meters long. The American crocodile lives mainly around rivers and freshwater rivers, but it can also be found near mangroves, estuaries and brackish waters of coastal lagoons where it can store the heat of the sun. Yet they probably have the same origin.
A 50 cm long skull
In fact, in 1939, a crocodile skull of the species "Crocodylus checchiai" was discovered in Libya, on the site of As Sahabi, with four other identical specimens but unfortunately destroyed during the war or lost. Only the fifth has been preserved and stored at the Earth Sciences Museum of the Sapienza University in Rome, in fairly good condition despite being seven million years old.
It is this skull that was recently reexamined with a CT scan. Nearly 50 cm long, it could be reconstituted in 3D images, and revealed the secrets of its anatomy: "Crocodylus checchiai" had a particularity in the muzzle, giving it a rounded profile. A form that cannot be found anywhere else in Africa, but which is strangely reminiscent of four cousin species now inhabiting America, as well as ancient species from Venezuela, explains the study.
This shared skeletal structure therefore suggests a close evolution between “Crocodylus checchiai” and American crocodiles. Complementary morphological and molecular analyzes supported this thesis, and concluded that this African ancestor could be found at the base of the crocodile family tree, and would be the missing link between the African and American lineages.
Newsletter My Earth
Every week, the environmental news seen by Le ParisienI'm registering
Your email address is collected by Le Parisien to enable you to receive our news and commercial offers. Learn more
But how did the branches get mixed up? The study suggests that the large reptiles would have migrated from Africa to America to disperse on the continent, in the Miocene era, between 11 and 5 million years ago.
500 km traveled in one month
Yet at that time, the Atlantic Ocean already represented "a gigantic paleobiogeographical barrier", explains to AFP Massimo Delfino, the main author of the study. In other words, each region of the world already had a geographical distribution of living things. The divide in the Atlantic Ocean was therefore not easily crossed at the time.
But the presence of several currents, in particular the north-equatorial current, probably facilitated the dispersal of the crocodiles, develops the researcher from the University of Turin.
The extinct species is close to a present-day Australasian species that is "capable of traveling nearly 500 km in a month simply by floating and being carried by the current, as satellite images have shown", adds- he, specifying that further studies will be necessary to better understand the modalities of this dispersion.