And so it is justified to describe the latest fossil discovery from China as a Triassic reptilian platypus.
The long body of Eretmorhipis is superficially almost crocodilian, bestowed with oversized paddle-limbs that would make it at home in any Aardman animation. Running down the spine from shoulder to hip are a series of bony nodules arranged like speedbumps. At one end of the body, the heavy tail tapers to a dagger-tip, while at the other sits a preposterously tiny head.
Eretmorhipis’ noggin is not only surprising for its small size, but also for the equally miniscule eyes that peeped out of it. When the international team of researchers from China and the US who studied the fossil plotted its eye size against body length, they found their new specimen fell well below other reptiles. In fact the proportions of the eyes were more similar to the mammalian platypus.
“There are some four-legged vertebrate animals today with unusually small eyes,” Ryosuke Motani, Professor of Palaeontology at University of California, Davis, and co-author of the study, “relying on another sense to forage in the dusk or darkness - including duck-billed platypus. We now have the oldest record of such small eyes, in Eretmorphipis.”
But the similarities don't end there.
The platypus is often wrongly referred to as ‘duck-billed’, but its snout is quite unlike a bird’s. Rather than a hard structure, the platypus snout is soft and bendy. It is also packed with over 40,000 mechano- and electroreceptors, making it exquisitely sensitive to touch. As they swim through the freshwater rivers and lakes of mainland Australia and Tasmania, these singular mammals close their little eyes and lobeless ears, and their snout feels for food along the river bottom - like a hand reaching out in the dark. It is an incredible adaptation, proving that although the platypus may retain features from their ancient ancestors like laying eggs, other aspects of their anatomy are far from ‘primitive’.
The landscape this ancient reptile swam through was unlike anything on earth today. Hubei Province, where its bones were discovered, was a tropical sea in the early Triassic, extending for hundreds of kilometres. It was so shallow you could have walked across most of it - albeit bumping into the occasional duck-billed reptile undulating across the sea-floor in search of shrimps and worms.
Eretmorhipis provides yet another example of the crazy experimentation taking place among vertebrate animals in the Triassic. From giant-headed carnivores to hump-backed Indian rhino-dragons, after the biggest mass extinction of all time at the end of the Permian, the Triassic was a time when surviving lineages explored new ecologies and body plans. Dinosaurs, pterosaurs, marine reptiles and mammals all have their origins in the Triassic. It was an era of evolutionary exploration.
“Eretmorhipis lived at time when there were a lot of open opportunities,” explains Motani. “The end-Permian mass extinction destroyed the ecosystem about five million years before, and the ecosystem was finally recovering, providing many open niches. So Eretmorhipis could live just fine despite its strange body design.”
This new fossil belongs to a group that remains poorly understood. You are probably familiar with ichthyosaurs, the fish-like marine reptiles that populated the oceans of the Triassic, Jurassic and Cretaceous. These reptiles provide a fascinating example of a terrestrial lineage of animals returning to the sea, a trick that the ancestors of cetaceans (dolphin and whales) would repeat to equal effect around 200 million years later, in yet another example of convergent evolution. But tucked in at the base of the ichthyosaur family tree lie their less-well known relatives, the Hupehsuchia. It is to them that Eretmorhipis belongs.
|An artist's reconstruction of the closely related hupehsuchian, Hupesuchus. (Image: Wikipedia)|
There remain many unanswered questions about these ancient Chinese reptiles,
Such puzzling creatures are part of what makes palaeontology such a fascinating discipline. The Early Triassic remains, without doubt, one of the most intriguing time-periods of them all.
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Find the paper here:
Cheng L Motani R, Jiang D-Y, Yan C-B, Tintori A, and Rieppel O. 2019. Early Triassic marine reptile representing the oldest record of unusually small eyes in reptiles indicating non-visual prey detection. Scientific Reports.