Biologists Reveal Two New Crocodile Species: ‘Totally Unexpected’

The “totally unexpected” discovery of two new crocodile species off Mexico’s Yucatán Peninsula is forcing scientists to reconsider long-held assumptions about the American crocodile—and raising alarms about the fragility of these newly identified populations.

“Most species of crocodiles are already endangered, and rapid shoreline development threatens nearly every population,” paper author and biologist Hans Larsson of McGill University said in a statement. “Our research aimed to uncover the true diversity of crocodiles on these isolated islands.”

Working in collaboration with Mexican researchers, Larsson and his team at McGill, identified the new species on the island of Cozumel and the Banco Chinchorro atoll.

These isolated groups were long believed to be local populations of the widespread American crocodile, which ranges from Baja California to Venezuela and throughout the Caribbean.

After sequencing their DNA and comparing their physical features, the researchers concluded that the Cozumel and Banco Chinchorro crocodiles were not simply geographic variants, but genetically distinct species.

“These results were totally unexpected,” said José Avila-Cervantes, the study’s lead author and a former graduate student in Larsson’s lab, in a statement.

“We assumed [the American crocodile] was a single species ranging from Baja California to Venezuela and across the Caribbean. Our study is the first to extensively explore genomic and anatomical variation in these animals.”

The findings, based on DNA sequencing and anatomical analysis, challenge previous taxonomies and highlight how little is still known about the biodiversity of remote tropical ecosystems.

The study was made possible by a field effort involving the capture and safe release of crocodiles, during which blood and scale samples were collected for genetic analysis.

At McGill, Avila-Cervantes performed the genomic sequencing that ultimately revealed big differences between the island populations and mainland counterparts. Additional research on skull morphology was conducted by fellow graduate student Hoai-Nam Bui, further cementing the conclusion that the reptiles represent distinct evolutionary lineages.

Although both newly discovered species appear to be stable, their populations are small, with each consisting of fewer than 1,000 breeding individuals.

Their restricted habitats and low numbers make them especially vulnerable to environmental disturbances, habitat loss, and the effects of climate change.

The discovery underscores the importance of localized conservation efforts, especially in areas that are often overlooked. The scientists are now calling for the crocodiles to be formally recognized as distinct species—a move that could unlock targeted protection in Mexico and internationally.

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about crocodiles? Let us know via science@newsweek.com.

Reference

Avila-Cervantes, J., Charruau, P., Cedeño-Vázquez, J. R., Bui, H.-N., Venegas-Anaya, M., Vargas, M., López-Luna, M. A., González-Cortés, H., Macías-Díaz, D. A., Pérez-Flores, J. S., Barrios-Quiroz, G., Salazar, J. M., McMillan, W. O., & Larsson, H. C. E. (2025). Novel island species elucidate a species complex of Neotropical crocodiles. Molecular Phylogenetics and Evolution, 207. https://doi.org/10.1016/j.ympev.2025.108341