Prior to this discovery it was unclear whether crocodiles reached the Americas from Africa, via a hypothesized transatlantic voyage, or vice-versa. Massimo Delfino and colleagues used CT imaging to re-examine a skull of C. checchiai that was discovered in 1939 in As Sahabi, Libya and is stored at the Earth Sciences museum of La  Sapienza University of Rome.

Original skull of C. cecchiai (Bruno Mercurio / La Sapienza Rome University)

The authors identified several new skull structures including a protrusion in the middle of the snout of C. checchiai that has not been identified on any other African crocodile species but that is present on the skulls of the four living American crocodile species Crocodylus intermedius, C. moreleti, C. acutus and C. rhombifer. This shared skeletal structure indicates a close evolutionary relationship between C. checchiai and American crocodiles.

3D model of the C. checchiai skull from CT scan images (Bruno Mercurio / La Sapienza University of Rome).

Further analyses of the evolutionary relationships between species suggest that C. checchiai may be part of the same lineage as the four crocodile species found in North and South America today. The remains of C. checchiai have been dated to around seven million years ago while the oldest remains of an American crocodile, the extinct C. falconensis, have been dated to around five million years ago. Based on these findings, the authors propose that crocodiles reached America by migrating westwards from Australasia via Africa.

Main image: Recreation of C. checchiai and its paleoenvironment (Dawid Iurino / Universitat de Roma La Sapienza)

Original article: Delfino, M., Iurino D., Mercurio B., Piras P., Rook L. & Sardella R. (2020). Old African fossils provide new evidence for the origin of the American crocodiles. Scientific Reports. http://nature.com/articles/s41598-020-68482-5.