First known dinosaur navel found in fossil

Reproduction of a reclining Psittacosaurus, with insert showing the umbilical cord.

Reproduction of a reclining Psittacosaurus, with insert showing the umbilical cord.
Illustration: Jagged Fang design

Forget dinosaurs that are engaged in evil battle. Put scary fangs and claws aside. Scientists have discovered a softer side of dinosaurs: the reptile equivalent of a navel.

For the first time ever, scientists have identified a umbilical cord on a non-bird dinosaur. The paper announcement of this finding is published in BMC Biology, and it is another exciting discovery from a particularly rare and well-preserved Psittacosaurus fossil from China. (Other pleasures from this same copy include one cloaca and counter-shadow camouflage.)

For mammals, the umbilicus is the result of a loose umbilical cord at birth. But reptiles and birds, whose method of reproduction is to lay eggs, have no such leash, and inside an egg the embryo’s stomach is connected to a yolk sac and other membranes. The scar occurs when the embryo detaches from these membranes just before or when it hatches from the egg. Known as a umbilical scar, it is the non-mammalian shape of a navel. And that is exactly what the international team of scientists claims to have discovered on this fossil.

Psittacosaurusa bipedal dinosaur that lived in the early Cretaceous is an early form of ceratopsian, a type of platypus that will later in the same geological period include Triceratops. Perhaps the most dazzling fossil of the species found remains frozen in time, lying on its back, complete with skin and tail bristles. Its conservation, about 130 million years old, is amazing. And even though it was made known to the public in 2002, it continues to break new and unique ground.

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 article. He and co-author Thomas G. Kaye, from 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 Frankfurt. The two researchers invented Laser stimulated fluorescence (LSF), a relatively new imaging technique. With this non-destructive method, they have been able to reveal details in fossils that may otherwise remain unseen.

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

“LSF brings out the details in a spectacular way,” Bell said in a video interview. “It really looks like the animal can get up and walk. You can see every little wrinkle and bump in the skin. It looks so fresh. To imagine these animals as living, breathing units, rather than just dead skeletons, is what fascinates me. Bringing them to life is one of the main goals of my work. “

Laser-stimulated fluorescence (LSF) image of the Psittacosaurus sample showing the umbilical cord and the shells.

Laser-stimulated fluorescence (LSF) image of the Psittacosaurus sample showing the umbilical cord and the shells.
Picture: Bell et al. 2022

The team found evidence of wrinkled skin, but not in the abdomen where the umbilical cord is located. Healed injuries will show regenerative tissue; there would be a clear break in scale patterns, with smooth granulation tissue over the damaged area.

Instead, Pittman explained, “