Two new crocodile species have been identified on isolated islands in the Caribbean, and they both face the threat of extinction.
The reptiles were previously believed to be American crocodiles. They separately inhabit the island of Cozumel and the atoll reef Banco Chinchorro off the Yucatán Peninsula in Mexico.
The two island populations are part of the Mesoamerican Barrier System, where ocean currents kept genetic exchange with nearby coasts at a minimum, allowing isolated groups to go down new evolutionary roads.
Researchers identified the two species while studying the genetics of crocodiles across Mexico's Pacific coast, Central America, and the Caribbean. They do not have names yet.
They found major genetic differences between the populations on Cozumel and Banco Chinchorro and the rest of the American crocodile species. So, the research team concluded that the island crocodiles were separate species.
"These results were totally unexpected," said José Avila-Cervantes, the lead author of the study. "We assumed Crocodylus acutus was a single species ranging from Baja California to Venezuela and across the Caribbean."
American crocodiles (Crocodylus acutus) live across 18 countries in warm, tropical regions, ranging from the southern tip of Florida to the Caribbean and northern South America.
Some of their range overlaps with Cuban crocodiles (Crocodylus rhombifer) in Cuba and Morelet's crocodiles (Crocodylus moreletii) in Mexico, Belize, and Guatemala.
They evolved from ancestors that spread from Africa to the Americas around five million years ago. The researchers were looking into variations across the three species when they discovered the two new species on Cozumel and Banco Chinchorro. They captured and released crocodiles to collect blood and tissue samples for DNA analysis.
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In addition, the team used genetic data from previous studies and compared the physical characteristics of the crocodiles. The primary physical difference between the species was their skull shape and length. For instance, the crocodiles from Banco Chinchorro have a longer and broader snout than those on the island of Cozumel.
The discovery of the two new species could help with conservation efforts. The rapid loss of biodiversity could be slowed if scientists know which species are most at risk. Crocodiles in the region are under threat from human activities like pollution, urbanization, and tourism.
According to the researchers, the populations on Cozumel and Banco Chinchorro seem to be relatively stable, but they are still vulnerable due to their small size and limited habitat range. There may only be about 1,000 crocodiles left, an estimated 500 individuals in each population.
"Now that we recognize these crocodiles as distinct species, it's crucial to protect their habitats," said Hans Larsson, the principal investigator of the study and a biology professor at McGill University. "Limiting land development and implementing careful conservation strategies on Cozumel and Banco Chinchorro will be key to ensuring their survival."