Australia: home of the (prehistoric) crocs

Opalised fossils help tell the story of a small crocodile that lived among the dinosaurs.

An extinct genus of crocodyliform, Isisfordia, lived during the middle of the Cretaceous period (about 100 million years ago). It was first identified from fossils found in outback Queensland, but since then, opalised bones from Lightning Ridge show it also lived in New South Wales.

In fact, the first fossils of Isisfordia from Lighting Ridge were found around 1917 but were misidentified as belonging to something more like the modern Saltwater Crocodile. It was only until the nearly complete skeleton of Isisfordia was found in Queensland that valuable comparisons could be made.

Although the fossils of Isisfordia from Queensland are more complete, the remains from Lightning Ridge are preserved in opal – and as such are arguably more beautiful. Some of the bones even show flashes of precious opal colour – hues of reds, greens and blues.

During the Cretaceous period, this part of Australia was lush with vegetation and estuaries, on the fringe of an inland sea, and not the dry, barren desert it is now. Lightning Ridge was also home to a wide variety of other animals, including dinosaurs, birds, turtles, plesiosaurs, pterosaurs, fish and sharks, and even some tiny mammals.

Isisfordia was also much smaller than its living relatives, at less than 2 metres long when fully grown. However, it is significant in the crocodilian family tree, as it has features which place it as the oldest known direct ancestor of living crocodiles.

Thanks to these opalised fossils, we now know that it was relatively widespread in eastern Australia during the Cretaceous period. Considering the ubiquitous nature of crocodiles in Australia today, it comes as no surprise that their ancient relative was also highly successful.

Lachlan Hart, PhD student, Palaeontology – University of New South Wales & The Australian Museum.