Neotropical crocodiles inhabit a broad geographic range with populations spanning from coastal, inland, and insular locations. In new research, scientists discovered a remarkable genetic diversity for the group and identified two new insular species: one living on the island of Cozumel and the other on the atoll of Banco Chinchorro, both off the Yucatán Peninsula.
An adult American crocodile (Crocodylus acutus) at La Manzanilla, Jalisco, Mexico. Image credit: Tomás Castelazo.
Crocodiles immigrated to the Neotropics from Africa approximately 5 million years ago and diversified into the four living species recognized today.
The American crocodile (Crocodylus acutus) inhabits a wide variety of environments from hypersaline to freshwater localities on the mainland, islands, cays, and coral atolls along the Neotropical Pacific and Caribbean coasts and is sympatric with populations of the three other species.
Although the Morelet’s crocodile (Crocodylus moreletii) is considered a species of Least Concern, the American crocodile is listed as vulnerable and the remaining two species are Critically Endangered on the International Union for Conservation of Nature’s Red List.
“Biodiversity is disappearing faster than we can discover what we’re losing,” said Professor Hans Larsson, a researcher at McGill University.
“Most species of crocodiles are already endangered, and rapid shoreline development threatens nearly every population.”
“Our research aimed to uncover the true diversity of crocodiles on these isolated islands.”
Professor Larsson and his team analyzed the genetic sequences of crocodile populations from Cozumel and Banco Chinchorro.
Comparing these sequences to those of crocodiles across the Caribbean, Central America and Mexico’s Pacific coast, they found striking levels of genetic differentiation, leading the researchers to conclude that these populations were not simply variants of the American crocodile.
“These results were totally unexpected,” said Dr. José Avila-Cervantes, also of McGill University.
“We assumed Crocodylus acutus 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 two new species live in small, isolated populations, each numbering fewer than 1,000 breeding individuals.
While both populations appear stable, their limited numbers and habitat restrictions make them vulnerable.
“The rapid loss of biodiversity can only be slowed if we know what species are most at risk,” Professor Larsson said.
“Now that we recognize these crocodiles as distinct species, it’s crucial to protect their habitats.”
“Limiting land development and implementing careful conservation strategies on Cozumel and Banco Chinchorro will be key to ensuring their survival.”
The team’s paper was published in the journal Molecular Phylogenetics and Evolution.
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Jose Avila-Cervantes et al. 2025. Novel island species elucidate a species complex of Neotropical crocodiles. Molecular Phylogenetics and Evolution 207: 108341; doi: 10.1016/j.ympev.2025.108341
