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.
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, “[t]The umbilical scales have regular sizes, smooth margins and are arranged along the midline of Psittacosaurus. This suggests that the scar was not the result of an injury.
In order to determine the age of the dinosaur, most cut the bone. The extreme rarity of this fossil means researchers want to avoid such destructive analysis. The team therefore compared the length of his femur to that of other Psittacosaurus specimens and estimated that this particular animal was about 6 or 7 years old. In other words, this dinosaur was approaching sexual maturity.
Not all reptiles or birds living today retain an umbilical scar into adulthood. The authors note that a particular exception is the American alligator (alligator mississipiensis). Additionally, some scars are the result of yolk sac infections in birds or crocodiles reared under poor conditions. With all these variables, it is not certain that all dinosaurs, or even all Psittacosaurus— would have an umbilical scar.
Pittman described how he and Kaye “collected a huge library of LSF data from the Psittacosaurus specimen in 2016″, which they are still going through and studying. “It led to a paper that year on an observed backlit camouflage pattern, the first identified in a dinosaur. We planned to further analyze the LSF data because our images provided so much additional information about the skin.
“We are currently finalizing a detailed description of the skin of Psittacosaurus,” he added. “That forced us to examine every square inch of the fossil.” And that’s how this umbilical scar discovery happened.
Looking at preserved skin in such detail is Bell’s area of expertise. He explained that few scientists focus on fossil skin, thus making any research subject to exciting discoveries. Plus, he says, when talking with the general public, he finds they’re often surprised to hear that fossil skin exists, let alone what it reveals. Even within paleontology, he says, the focus remains on bones.
“I think the takeaway is that scaly reptiles are interesting,” Bell said. He hopes the public and the wider scientific community realize how much we still have to learn about dinosaur skin and its biological function. Noting that “the skin is the largest organ in the body,” he referred to how, for example, scales protect modern reptiles from dehydration and UV rays. Bell wants to change the perception that scales are less exciting than feathers.
“It’s an absolutely magnificent specimen,” Bell remarked of the Psittacosaurus fossil. “And the fact that he still gives surprises 20 years [from the time] it was first announced to the public is extraordinary, and it is because of the development of these new imaging techniques.
These surprises – the knowledge we have gained so far – would not have been possible had the fossil remained in private hands. This magnificent Psittacosaurus specimen has a controversial story. Its exact provenance is unknown, as it passed from one private collector to another prior to its purchase by the Senckenbergs. Then, as now, there are those who hope the fossil will be repatriated to China. At the end of their article, the authors write: “There is an ongoing debate regarding the legal ownership of this specimen and efforts to repatriate it to China have been unsuccessful. Our international team of Australian, Belgian, British, Chinese and American members all hope and support an amicable solution to this ongoing debate. We believe it is important to note that the specimen was acquired by the Senckenberg Museum to prevent its sale to private individuals and to ensure its availability for scientific study.
Jeanne Timmons (@most mammoths) is a New Hampshire-based freelance writer who blogs about paleontology and archeology at most mammoths.wordpress.com.