Saltwater crocodiles crossed the Indian Ocean to reach the Seychelles — before humans arrived and wiped them out

Photo looking head-on at a saltwater crocodile underwater.

New study finds saltwater crocodiles used to be in a lot more places than they are today. (Image credit: Getty Images)

Saltwater crocodiles used to occupy a massive range that stretched across the Indian Ocean to the Seychelles, new DNA research confirms.

The now-extinct population of crocodiles in the Seychelles, an archipelago in the western Indian Ocean, was not a group of Nile crocodiles (Crocodylus niloticus), nor was it a separate species. Instead, it was likely the westernmost population of saltwater crocodiles (Crocodylus porosus), which today live in India, Southeast Asia, Australia and islands across the Western Pacific, researchers reported Jan. 28 in the journal Royal Society Open Science.

The Seychelles used to be home to a large population of crocodiles, according to expedition notes from more than 250 years ago. But when human settlers arrived in the late 18th century, they wiped out all of the crocodiles on the islands. The remains of a few specimens were kept in museums in the Seychelles, London and Paris.

Initially, Western scientists thought the Seychelles crocodiles were part of a population of Nile crocodiles that had migrated from Africa. But in 1994, researchers reclassified the preserved remains as saltwater crocodiles based on their physical traits.

In the new study, a different team of scientists confirmed that conclusion using genetic material. They collected mitochondrial DNA from the skulls and teeth of several older museum specimens of various crocodile species and then compared that DNA with tissue samples from modern museum specimens and living crocodiles.

Photo of a person examining the top half of a crocodile skull. The person is wearing gloves, a hair net, a mask and glasses and is holding the skull on a table so that the nose is pointed up and the viewer sees the inside of the top of the mouth. — Sampling the Seychelles crocodiles. Three incomplete skulls from the Seychelles National Museum are among the few preserved remains of the Seychelles crocodiles. (Image credit: Kathrin Glaw)

The genetic markers of the Seychelles crocodiles matched closely with those of the saltwater crocodiles, the team found. That suggests that saltwater crocodiles' range stretched over 7,500 miles (12,000 km) from east to west before the Seychelles population was exterminated.

"The genetic patterns suggest that saltwater crocodile populations remained connected over long periods and across great distances, pointing to the high mobility of this species," study co-author Stefanie Agne, an evolutionary biologist at the University of Potsdam in Germany, said in the statement.