Oldest Australian Crocodile Fossils Dated to 55 Million Years Ago in Queensland

An international research team has announced the discovery of the oldest known fossilized crocodile remains in Australia, with initial dating establishing their age at approximately 55 million years. The findings, published in the Journal of Vertebrate Paleontology, concern the extinct crocodilian lineage Mekosuchinae, which represented a distinct evolutionary branch on the continent millions of years before the modern saltwater and freshwater species arrived roughly five million years ago.

The research, involving paleontologists from the University of New South Wales and the Miquel Crusafont Catalan Institute of Paleontology, included the analysis of fossilized eggshell fragments to gain insight into the reproductive behavior of these ancient reptiles. The specimens represent the oldest known member of the Mekosuchinae clade, with one specific species formally designated *Wakkaoolithus godthelpi*, a name honoring the Waka Waka people of the discovery region. The largest known members of this extinct group reportedly attained lengths up to five meters, indicating a significant presence in the ancient ecosystem.

These fossils were recovered from a sandstone layer in Queensland, specifically within strata dating to the Early Eocene epoch, a period when the Australian continent remained connected to Antarctica and South America as part of the Gondwana landmass. Mekosuchines occupied ecological niches that contrast with modern crocodiles, suggesting a greater diversity in lifestyle. Professor Michael Archer of the University of New South Wales noted that some species appear to have been terrestrial hunters within forests, while others were semi-aquatic ambush predators. Some riverine species were even hypothesized to be partially semi-arboreal, informally termed 'drop crocs' for their potential hunting method.

Analysis of the *Wakkaoolithus godthelpi* eggshells provided crucial data on reproductive strategies, indicating deposition along riverbanks as an adaptation to fluctuating environmental conditions. However, this specialized existence proved unsustainable; the gradual drying of inland rivers and a corresponding reduction in large prey populations contributed to their eventual decline. The paleontological site, located near Murgon in southeast Queensland, is recognized as a globally significant fossil location. Alongside these ancient crocodilians, the 55-million-year-old clays have yielded the world's oldest known fossil songbirds, the earliest Australian frog and snake fossils, and the oldest fossil marsupial remains on the continent, many showing connections to South America.

Researchers plan to expand excavation efforts in this historically rich region to further reconstruct the complex ecosystem that existed when the continent was linked to the southern landmasses. Dr. Xavier Panadès i Blas emphasized that studying eggshells offers a unique window into the intimate life history of extinct species, allowing scientists to investigate reproduction and adaptation beyond skeletal evidence. The microstructural features observed in these 55-million-year-old shells differ from those of modern crocodilians, offering distinct geochemical signals about their nesting environment among ancient tropical forests.