Small, terrestrial, and extinct: the mysterious crocodilians that once roamed Pacific islands.

Nature · Published 3 October 2026 Swipe more like this →

In short: For millions of years, a genus of small, land-dwelling crocodiles thrived across Australia and the Pacific. Known as Mekosuchus, these creatures featured blunt snouts and specialized teeth, living far from the water. Despite their success, they vanished only recently, leaving behind a puzzle about their extinction and island migration.

Mekosuchus was a widespread genus of small-bodied crocodilians, typically measuring less than 2 meters in length. Unlike their modern, semi-aquatic relatives, these animals were terrestrial, possessing altirostral skulls with forward-facing nares and laterally directed eyes. Their anatomy, including strong limbs and robust neck vertebrae, suggests they were well-adapted to life on land, potentially filling ecological niches similar to monitor lizards. While early theories proposed they might have been arboreal, recent analysis of their toe bones has largely dismissed this.

The genus originated in mainland Australia during the Oligocene and Miocene, with species like M. whitehunterensis and M. sanderi found in the Riversleigh World Heritage Area. Over time, these crocodilians dispersed into the South Pacific, reaching islands like New Caledonia and Vanuatu. The species M. inexpectatus and M. kalpokasi represent some of the youngest known mekosuchines, with fossil evidence suggesting they survived into the Holocene. M. inexpectatus, in particular, possessed bulbous, molar-like teeth, likely used for crushing the shells of crustaceans and molluscs, a distinct departure from the blade-like teeth found in their older, mainland ancestors.

The extinction of these island-dwelling crocodilians remains a subject of debate. While some researchers suspect human involvement, there is no direct evidence of interaction, and the overlap between the animals and human settlements is poorly understood. Radiocarbon dating of fossils from New Caledonia, such as those from the Pindai Caves, suggests some populations may have persisted until approximately 1,720 years BP, though some estimates place their disappearance around 3,000 years ago. Regardless of the exact timing, their presence on isolated islands remains a testament to the unexpected evolutionary paths taken by this diverse, yet now vanished, group of crocodilians.

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