First known dinosaur navel found in fossil

Representation of a recumbent Psittacosaurus, with insert showing the umbilical scar.

Representation of a recumbent Psittacosaurus, with insert showing the umbilical scar.
Drawing: Jagged fang designs

Forget the dinosaurs engaged in vicious fights. Put aside the terrifying fangs and claws. Scientists have discovered a softer side of dinosaurs: the reptilian equivalent of a navel.

For the first time, scientists have identified an umbilical scar on a non-avian dinosaur. The paper the announcement of this discovery is published in BMC Biology, and it is yet another exciting discovery of a particularly rare and well-preserved Psittacosaurus China fossil. (Other delicacies from this same specimen include a cesspool and backlight camouflage.)

For mammals, navels are the result of an umbilical cord detached at birth. But reptiles and birds, whose mode of reproduction is by laying eggs, do not have such a cord. Inside an egg, the abdomen of the embryo is connected to a yolk sac and other membranes. The scar occurs when the embryo detaches from these membranes directly before or at the time of hatching from the egg. Known as an umbilical scar, it is the non-mammalian form of a navel. And that’s exactly what the international team of scientists claim to have found on this fossil.

Psittacosaurusa bipedal dinosaur that lived in the early Cretaceous, is an early form of ceratopsian, a type of beaked herbivore that later in this same geological period would include Triceratops. Perhaps the most dazzling fossil of the species ever found remains frozen in time, lying on its back, complete with skin and tail hair. Its preservation, at around 130 million years, is breathtaking. And although released in 2002, it continues to be innovative and unique.

Michael Pittman has studied this particular fossil in detail. He is a paleobiologist, assistant professor at the Chinese University of Hong Kong and co-author of the new paper. He and co-author Thomas G. Kaye of the Foundation for Scientific Advancement were able to visit the fossil in Germany in 2016 at the Senckenberg Research Institute and the Natural History Museum in Frankfurt. The two scientists invented Laser stimulated fluorescence (LSF), a relatively new imaging technique. Thanks to this non-destructive method, they were able to reveal details in fossils that might otherwise remain invisible.

This “subtle scar,” as Pittman described it in an email, was found using LSF. And it was thanks to LSF that the team was able to study skin scales – their patterns, wrinkles and any scarring – with exquisite relief. To help work on the skin, the team turned to Phil Bell, a dinosaur paleontologist at the University of New England Paleoscience Research Center in Australia, who has considerable expertise on the subject. Bell is the lead author of the new document.

“LSF brings out the detail dramatically,” Bell said in a video interview. “It really looks like the animal can stand up and walk away. You can see every little wrinkle and bump in the skin. It looks so fresh. Imagining these animals as living, breathing entities, rather than as simple dead skeletons, is what fascinates me. Bringing them to life is one of the major objectives of my work.

Laser stimulated fluorescence (LSF) image of Psittacosaurus specimen showing umbilical scar and scales.

Laser stimulated fluorescence (LSF) image of Psittacosaurus specimen showing umbilical scar and scales.
Image: Bell et al. 2022

The team found evidence of wrinkled skin, but not in the abdomen where the umbilical scar is. Healed wounds would display regenerative tissue; there would be a distinct break in the scale patterns, with smooth granulation tissue over the injured area.

Instead, Pittman explained, “

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