This may be the oldest ‘asshole’ print on Earth
The fossils show exceptionally rare evidence of a cloacal vent – the slit that most vertebrates use to excrete, have sex and lay eggs – which could shed light on the evolution of the vent.
By Taylor Mitchell Brown edited by Andrea Thompson
Fossil impression of the hind limb, tail, and cloacal vent of Cabarzichnus pulchrus, a small lizard-like reptile.
Lorenzo Marchetti
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About 299 million years ago, volcanic eruptions buried an area of mud in what is now central Germany. Amidst the impressions of scales, tails and legs fossilized in the stain, there was something else: The oldest known “asshole” footprint on Earth.
“Rediscover a feeling of [an] “The animal squatting in the mud and being preserved with such fidelity is quite a scoop,” says Jakob Vinther, a paleontologist at the University of Bristol in England, who was not involved in a new study describing the discovery in Current Biology. “The animal has literally cemented itself – and its nether regions – in eternal history like movie stars on the Hollywood Walk of Fame.”
The structure imprinted in the fossilized mud is a slit technically called a cloaca. Unlike marsupials and placental mammals that divide their “business units” into separate openings, “most other animals have the Swiss Army knife equivalent of a rear opening,” says Vinther. This gives them “one opening for everything: poop, pee, have sex and lay eggs.”
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Lead author Lorenzo Marchetti, a paleontologist at the Berlin Natural History Museum, discovered the vent by examining rare diagonal and hexagonal indentations in the fossil. “I noticed something unusual and after a comparison with modern animals it became clear what it was,” he says.
Let’s take a closer look at the fossilized impression of the cloacal vent.
Lorenzo Marchetti
Cloacal vents vary in size and shape across the reptile world, but lack of fossil preservation has kept their evolution mysterious.
“Only two examples of this structure are currently known in fossil reptiles,” says Marchetti. They are this one and that of a 130 million year old ceratopsian called Psittacosaurus, which Vinther and colleagues reported in 2021. Radioisotopes of ash present in the new fossil suggest its cheeky footprints were planted about 170 million years before the fossil’s advent. Psittacosaurus fossil.
Scale and footprint prints in the ancient mud helped Marchetti and his colleagues determine that the butt belonged to a previously unnamed species. The animal, which the researchers named Cabarzichnus Fair, was a small lizard-like reptile that probably basked in the mud to cool off, Marchetti says.
“It’s quite remarkable to see the smallest details preserved from such a small animal,” says Phil Bell, a paleontologist at the University of New England in Australia, who was not involved in the research. “The consistency of the mud must be absolutely perfect for such an imprint to occur.”
Fossil cloacas “are as rare as hen’s teeth,” Vinther says, “and discovering another one is exciting to say the least.” »
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