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An “exquisitely” preserved fossil that lived 125 million years ago shows evidence of the navel in at least some dinosaurs
Laser image of the bipedal Psittacosaurus showing the scar and umbilical scales. Photo of Bell et al., BMC Biology, 2022
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An “exquisitely preserved” dinosaur fossil has revealed the soft belly of a horned dinosaur from China.
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Specifically, paleontologists using high-tech laser imaging technology found evidence of a dinosaur that lived 125 million years ago and had a navel.
The long umbilical scar of the Psittacosaurus specimen is similar to that found in some lizards and crocodiles. Unlike mammals, this reptile shape of the navel is a cleft-like opening that connects the embryo to the yolk sac of the egg and other membranes. The yolk sac is absorbed by the dinosaur immediately before or shortly after hatching, leaving behind an opening in the sealing abdominal wall and appearing as a long scar.
Although scientists have hypothesized that egg-laying dinosaurs would develop these scars, this is the first time it has been observed in a non-avian dinosaur.
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“We call this type of scar a navel and it is smaller in humans. This specimen is the first dinosaur fossil to have a navel, which is due to its exceptional state of preservation,” said Michael Pittman, one of the authors of the study and paleontologist at the Chinese University of Hong Kong.
The size, softness, and location of the umbilical scar rule out a trauma or infection as the cause, the study says. The pattern of the abdominal scale was not disrupted, while a healed injury would have a “smooth, flaky connective tissue over the open wound,” the authors note.
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Psittacosaurus (name meaning ‘parrot lizard’) was a two-meter-long herbivore that lived in the early Cretaceous. The fossil used in this study was made public in 2002 and has led to major discoveries due to its exceptionally well-preserved state, with scales, horn and “long tail bristle feathers,” the researchers write.
“This specimen of Psittacosaurus is probably the most important fossil we have for studying dinosaur skin. But it continues to give surprises that we can bring to life with new technologies such as laser imaging,” the lead author told Phys.org. study, Phil R. Bell, of the University of New England at Armidale in Australia.
Paleontologists compared the length of the specimen’s femur to that of other Psittacosaurus to estimate its age as slightly shy of sexual maturity, about 6 or 7 years. It is unclear whether the umbilical cord of dinosaurs lasts into adulthood.
The precious specimen can be seen at the Senckenberg Museum in Frankfurt, Germany.