In drawings or renderings of dinosaurs, we generally don't see the beasts sporting human-like belly buttons. The reptiles did have an equivalent to a navel, however, and scientists have recently discovered the first known fossilized example of one.
In people and other mammals, the belly button is a scar that remains at the point where the umbilical cord was connected to the fetus' body.
Even though dinosaur embryos weren't attached to an umbilical cord per se, they were directly attached to their egg's yolk sac via a slit-like abdominal opening. That slit produced a long thin umbilical scar, which remained on their belly region throughout their lives.
Utilizing a relatively new technique known as laser-stimulated fluorescence (LSF) imaging, an international team of paleontologists has now discovered such a scar on the 130-million-year-old fossilized skin of a dinosaur known as Psittacosaurus. The 2-meter (6.6-ft)-long herbivorous creature lived in what is now China, during the Cretaceous period.
This particular specimen was unearthed back in 2002, and has since been on display in Germany's Senckenberg Museum. Until now, however, its navel-equivalent had gone unnoticed.
"Using LSF imaging, we identified distinctive scales that surrounded a long umbilical scar in the Psittacosaurus specimen, similar to certain living lizards and crocodiles," said The Chinese University of Hong Kong's Dr. Michael Pittman, joint-corresponding author of the study. "We call this kind of scar a belly button, and it is smaller in humans. This specimen is the first dinosaur fossil to preserve a belly button, which is due to its exceptional state of preservation."
A paper on the research – which also involved scientists from Australia's University of New England, Argentina's Unidad Ejecutora Lillo in San Miguel de Tucumán, and the Arizona-based Foundation for Scientific Advancement – was recently published in the journal BMC Biology.