Scientists have identified what are believed to be the oldest crocodilian eggshells ever found in Australia, unearthed in a grazier’s back yard in regional Queensland.
The 55m-year-old eggshells – found at a fossil deposit in Murgon, approximately 270km north-west of Brisbane – likely belong to a group of extinct crocodiles known as mekosuchines, new research suggests.
Modern saltwater and freshwater crocodiles only arrived in Australia about 3.8m years ago. “Before they got here, these weird mekosuchine crocs were all over the place,” said study co-author Prof Michael Archer, a palaeontologist at the University of New South Wales.
Some mekosuchines were partial tree dwellers, such as the ridge-headed crocodile, which has been nicknamed the “drop croc” because it may have climbed trees and dropped on to animals passing below.
“The idea of ‘drop crocs’ isn’t as crazy as it sounds. We probably did have crocodiles that were spending time in the trees and jumping out on prey,” Archer said.
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The fossil eggshells found at Murgon likely belonged to an earlier genus of mekosuchines known as Kambara.
“We know we’re looking at the oldest crocodile eggshells certainly in Australia … the Kambara mekosuchines are the first ones we know of this whole group,” Archer said.
The research focused on 12 fossil eggshells that were incidentally collected over several years in the 1990s, but which were only recently analysed by study lead author, Dr Xavier Panadès i Blas of the Miquel Crusafont Catalan Institute of Palaeontology in Barcelona.
He said eggshells “preserve microstructural and geochemical signals that tell us not only what kinds of animals laid them, but also where they nested and how they bred”.
“Eggshells should be a routine, standard component of palaeontological research – collected, curated and analysed alongside bones and teeth,” he said in a statement.
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The structure of the mekosuchine eggshells “do not resemble any other crocodilian eggshells”, Archer said, pointing to their association with a crocodile group unique to Australia.
“We still do not know what the relationships of this group of crocodiles is to all the other crocodiles of the world. All we do know is that when the salt and freshwater crocodiles did get into Australia … that was the beginning of the end for this particular group.”
Dr Matthew McCurry, a vertebrate palaeontologist at the Australian Museum who was not involved in the research, said mekosuchines were “representative of the fact that crocodiles in the past did a lot more than they do in modern ecosystems”.
“If we go right back to the Cretaceous [period, 66m to 143m years ago], crocodiles did a huge range of different things: some were fully marine and had paddle-like limbs, some fed on plants exclusively,” he said.
“When most people think palaeontology, they think of the bones and the teeth of the organisms – they’re often the parts that fossilise the most easily. Trackways are probably the second most common thing … footprints left behind.
“We occasionally do find the bones of these animals, but eggs are comparatively more rare.”
The study was published in the Journal of Vertebrate Paleontology.
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