Designated as Wakkaoolithus godthelpi, this distinct eggshell classification has been attributed to mekosuchine crocodiles, marking the earliest crocodilian eggshells ever unearthed in Australia.
Mekosuchine crocodiles. Image credit: Armin Reindl / CC BY-SA 4.0.
The now-extinct mekosuchines (Mekosuchinae) constituted a unique, indigenous lineage of Australia’s crocodilian fauna.
These ancient reptiles were the dominant inhabitants of the continent’s inland waterways during the Early Eocene epoch, approximately 55 million years ago.
They belonged to the broader group encompassing extant species such as alligators, true crocodiles, gharials, and caimans.
However, mekosuchines represent a considerably more ancient evolutionary branch compared to the saltwater and freshwater crocodiles currently found in Australia.
The contemporary species of crocodiles journeyed to the continent at a much later juncture, following its eventual collision with Southeast Asia, a process that commenced roughly 5 million years ago.
Diverging from their modern counterparts, mekosuchines occupied unusual ecological niches.
“It is a peculiar notion. Nevertheless, some of them seemingly functioned as terrestrial predators within forest environments,” posited Professor Michael Archer from the University of New South Wales.
“Indications of this behavior have been observed across a diverse array of younger mekosuchine fossil discoveries, previously unearthed from 25-million-year-old strata in a different locale: the Riversleigh World Heritage Area, situated within Boodjamulla National Park on Waanyi country in northwestern Queensland.”
“Certain riverine species in that region attained lengths of at least 5 meters. Some also exhibited evidence of being at least partially semi-arboreal, functioning as ‘drop crocs’.”
“Their hunting strategy might have resembled that of leopards – ambushing unsuspecting prey from arboreal positions for their sustenance.”
The Wakkaoolithus godthelpi eggshells are associated with the most ancient known representative of the Mekosuchinae clade.
“These eggshells have provided us with invaluable insights into the life cycles of mekosuchines,” stated Dr. Xavier Panadès i Blas, a paleontologist affiliated with El Museu de la Conca Dellà, the Institut Català de Paleontologia Miquel Crusafont, and the Universitat Autònoma de Barcelona.
“We are now equipped to explore not only the unusual anatomical features of these crocodiles but also their reproductive methodologies and their adaptive strategies in response to environmental shifts.”
The research team meticulously analyzed the Wakkaoolithus godthelpi shell fragments employing both optical and electron microscopy.
Their microstructural examination suggests that these crocodiles deposited their eggs along the edges of a lake, with their reproductive tactics evolving in tandem with fluctuating environmental conditions.
“Mekosuchine crocodiles may have relinquished a substantial portion of their inland territory due to the expansion of arid terrains, ultimately compelling them to contend for resources in diminishing water bodies, facing competition not only from newly arrived fauna to Australia but also from a dwindling population of their megafaunal-sized prey,” commented Dr. Michael Stein, a paleontologist at the University of New South Wales.
“The Murgon lake was enveloped by a verdant forest, which also served as the habitat for the world’s earliest known songbirds, Australia’s inaugural frog and snake species, a diverse assemblage of small mammals with South American affiliations, as well as one of the planet’s most ancient bat species.”
The research consortium asserts that fossil eggshells represent an underutilized resource within the field of vertebrate paleontology.
“They preserve microstructural and geochemical signatures that elucidate not only the identity of the animals that laid them but also their nesting sites and reproductive behaviors,” Dr. Panadès i Blas elaborated.
“Our investigation unequivocally demonstrates the profound significance of these fragmented remains.”
“Eggshells ought to be considered a standard, integral component of paleontological research endeavors – systematically collected, preserved, and subjected to analysis alongside skeletal elements and dental structures.”
The discoveries were formally presented this week in the Journal of Vertebrate Paleontology.
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Xavier Panadès I Blas et al. Australia’s oldest crocodylian eggshell: insights into the reproductive paleoecology of mekosuchines. Journal of Vertebrate Paleontology, published online November 11, 2025; doi: 10.1080/02724634.2025.2560010
