Researchers unveil two new crocodile species Yucatán islands, highlighting urgent conservation needs for isolated Cozumel and Banco Chinchorro populations.
In an interesting discovery for conservation biology, a joint research team from McGill University and Mexican institutions has identified two previously unknown crocodile species living in isolation off the coast of the Yucatán Peninsula. These unexpected discoveries overturn decades of assumptions about the American crocodile’s distribution and underline how incomplete our understanding of island biodiversity can be.
For years, scientists treated the American crocodile (Crocodylus acutus) as a single, widely distributed species ranging from Baja California to Venezuela, including Caribbean coastlines. By systematically sampling crocodile populations on the islands of Cozumel and Banco Chinchorro, researchers demonstrated that these populations are genetically and anatomically distinct enough to warrant classification as two separate species. Recognizing them as unique species raises immediate conservation flags because neither population exceeds 1,000 breeding individuals.
Background and Rationale
The research team embarked on this study after noting signs of genetic variation among island populations that did not align with known mainland groups. Professor Hans Larsson of McGill University emphasized, “Biodiversity is disappearing faster than we can discover what we’re losing. Most species of crocodiles are already endangered, and rapid shoreline development threatens nearly every population.” This sense of urgency drove the investigators to collect blood and scale samples directly from wild crocodiles on Cozumel and Banco Chinchorro, then compare their DNA and skull morphology with individuals from the broader Caribbean, Central America, and Mexico’s Pacific coast.
Field Methods and Genetic Analysis
During carefully planned field expeditions, researchers captured crocodiles on both islands, obtaining small blood draws and scale fragments before releasing the animals back into their habitats. In the lab, geneticists sequenced mitochondrial and nuclear DNA markers to assess genetic divergence. In parallel, the team measured skull characteristics to look for morphological traits that would support the genetic findings. Comparing these island samples against over two dozen mainland populations revealed pronounced genetic differentiation—far beyond what one would expect for mere population subspecies.
Lead author José Avila-Cervantes, formerly a graduate student under Larsson, remarked, “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.” This discovery underscores how genomic tools can uncover hidden diversity, even among well-studied large predators.
Identification of Two New Species
Genetic comparisons showed that the Cozumel and Banco Chinchorro populations each form distinct evolutionary lineages with no recent gene flow to mainland or other island populations. Consequently, the team concluded that these lineages represent two separate species—neither yet formally named—isolated on their respective islands. Each population likely consists of fewer than 1,000 breeding adults, making their total global population extremely limited.
Cozumel’s crocodiles inhabit freshwater lagoons and wetlands that have experienced increasing human development. Banco Chinchorro’s atoll hosts its own small crocodile assemblage, similarly facing habitat pressure from tourism and coastal infrastructure. Despite apparent population stability, the restricted island ranges and low numbers place both new species in a precarious conservation position.
Conservation Implications
Discovering two new crocodile species on islands already recognized for high endemism amplifies concerns about the rapid loss of biodiversity in the Mesoamerican Barrier Reef System. This reef, the largest in the Western Hemisphere, borders both Cozumel and Banco Chinchorro, making it a hotspot for unique marine and terrestrial species. While both new crocodile species appear stable now, their small population sizes and reliance on limited habitat sets make them vulnerable to environmental change, pollution, and human encroachment.
Larsson stressed that “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.” These recommendations align with wider calls to bolster conservation measures for other threatened New World crocodile populations.
Broader Biodiversity Context
Prior to this study, scientists recognized four New World crocodile species: the American crocodile (C. acutus), Morelet’s crocodile (C. moreletii), the Cuban crocodile (C. rhombifer), and Orinoco crocodile (C. intermedius). With these two newly identified island populations, the count rises to six. Each crocodile species plays a critical ecological role as apex predators, helping regulate fish and other aquatic populations. Their decline can ripple through ecosystems, reducing overall biodiversity and resilience.
These findings echo past cases where island populations once thought to belong to widespread species were later elevated to full-species status—cases like the Komodo dragon (Varanus komodoensis) on Komodo Island or the Alameda whipsnake (Masticophis lateralis euryxanthus) in California. Recognizing island endemics has been essential for directing targeted conservation action, from habitat protection to captive breeding when necessary.
Next Steps and Recommendations
Given the new classification, researchers recommend immediate conservation assessments under IUCN Red List criteria. Cozumel and Banco Chinchorro authorities should consider restricting further development near key wetland habitats, enforcing stricter pollution controls, and launching public education campaigns about these crocodile species’ importance. Collaborative efforts between Mexican government agencies, non-profit organizations, and local communities can establish protected zones to ensure minimal human disturbance.
Scientists also urge ongoing monitoring of population trends via annual field surveys and continued genetic sampling. Establishing a long-term research presence would allow rapid detection of declining population sizes or habitat degradation. Any observed declines could trigger more aggressive conservation interventions, such as limited translocations or ex-situ breeding programs.
The discovery of two new crocodile species hiding in plain sight on Cozumel and Banco Chinchorro serves as a powerful reminder that even well-studied regions can harbor undocumented biodiversity. By pairing modern genomics with careful fieldwork, researchers have reshaped our understanding of crocodile diversity in the New World. Now, with conservation planning on a tight timeline, stakeholders must act swiftly to protect these island populations from habitat loss and other anthropogenic threats. Failure to do so could cost two unique crocodile species their chance at survival.
