A latest genetic study confirms that the crocodiles that historically lived on the Seychelles Islands in the Indian Ocean belong to the westernmost population of saltwater crocodiles (scientific name: Crocodylus porosus). This result provides a clear answer to a natural mystery that has been unresolved for 250 years. Research shows that this population can not only drift long distances in the ocean, but its historical distribution range once exceeded 12,000 kilometers, extending from Vanuatu in the Pacific to the Seychelles.
According to expedition records in the mid-18th century, there were once "herds of crocodiles" on the coast of the Seychelles Islands. However, after people began to settle permanently in the area in 1770, the number of crocodiles dropped rapidly and was completely wiped out within about 50 years, becoming one of the early cases of island species extinction caused by human activities.
The scientific community has long debated which species the Seychelles crocodile belongs to. Previous speculations mainly relied on physical features such as skulls and comparisons with saltwater crocodiles that are widely distributed along the coasts of the Indian Ocean and the Western Pacific, but direct molecular evidence has always been lacking. The latest research provides the first clear conclusion through genome analysis: the Seychelles crocodile is an isolated island population of saltwater crocodiles, and its extinction means that the westernmost boundary of the natural distribution of this species has been artificially "truncated."
This research was completed by scientific research teams from Germany and Seychelles. The scientists sampled the DNA sequences of living saltwater crocodile individuals, and also extracted and analyzed mitochondrial genome information from multiple museum specimens of the genus Crocodylus, including the remains of the Seychelles crocodile that disappeared about 200 years ago. These rare specimens come from the few remaining incomplete skulls in the Seychelles National Museum and represent one of the few physical evidences of this extinct population.
The results showed a clear genetic link between individual Seychelles crocodiles and modern saltwater crocodiles, suggesting they were once a fringe population within the same widespread species rather than an independent species. Through a comprehensive analysis of genetic pedigrees and geographical distribution, the research team believes that saltwater crocodile populations have maintained a certain degree of genetic exchange over a long period of time, which reflects the species' excellent long-distance migration ability.
Saltwater crocodiles are one of the largest reptiles in existence. They can be more than 6 meters long and weigh more than a ton. They often live in estuaries, mangroves and shallow coastal waters. Unlike other crocodiles, saltwater crocodiles have a physiological structure that is highly adapted to marine life, especially special salt glands that can excrete excess salt from the body, allowing them to survive in seawater environments for long periods of time. It is this ability to tolerate salt and marine environments that gives them the ability to spread and establish new populations across oceans separated by thousands of kilometers.
The research team pointed out that the "ancestors" of the Seychelles crocodiles had to cross at least 3,000 kilometers of the Indian Ocean to reach this remote archipelago, and the actual drift distance was likely to be longer. This means that a single or a few saltwater crocodiles are very likely to complete an extremely rare but not impossible "oceanic landing" under the combined action of ocean currents, wind direction and their own swimming, thereby opening up new genetic branches on isolated islands.
On a global scale, saltwater crocodiles are still one of the most widely distributed reptiles, inhabiting the coastal waters of Southeast Asia, northern Australia, and many Pacific and Indian Ocean islands. Before the Seychelles population was wiped out by humans, the species' natural distribution range stretched from Vanuatu in the central Pacific to the Seychelles off the east coast of Africa, spanning multiple ocean basins and showing transoceanic continuity.
Stéphanie Agnet, first author of the paper and from the University of Potsdam, said that geographical patterns in the genetic structure of saltwater crocodiles show that although the population is dispersed across vast oceans, there has always been cross-regional gene flow for a long time. This connectivity is based on its high ocean mobility. The research not only clarified the true identity of the Seychelles crocodile, but also provided new key clues for understanding how saltwater crocodiles and even other coastal reptiles use ocean currents to spread and reshape their distribution patterns.
The relevant research paper is titled "The Mitochondrial Genome Phylogeny of Crocodyliformes and the Population Structure of Saltwater Crocodiles (Including the Extinct Seychelles Population)" and was published in the journal "Royal Society Open Science" on January 28, 2026.