Dinosaurs had a belly button: an umbilical scar detected for the first time in a fossil

Psittacosaurus (Reference Image, Pixabay)


Although dinosaurs hatched from eggs, the developing embryo is attached to various extra-embryonic membranes during its pre-hatching period, leaving an umbilical scar.

Thanks to high-resolution laser images extracted from a Psittacosaurus fossil, it was revealed that dinosaurs had navels. This fossilized specimen was found in China 20 years ago. But it’s only now that they’ve detected his umbilical scar.

For it, the technique of ‘laser stimulated fluorescence’ (LSF) was applied to the fossilized skin of Psittacosaurus. This technique had to be of high resolution because the fossil dates from 130 million years ago.

“Under laser-stimulated fluorescence (LSF), the umbilicus is revealed as an elongated midline structure bounded by a row of paired scales on the abdomen,” the study, published in BMC Biology, states.

This scar was defined as a navel, because according to the researchers, it has always been on the skin of Psittacosaurus. “The relatively late (close to sexual maturity) ontogenetic stage estimated for the individual indicates that the navel was likely maintained throughout life,” they note.

dinosaurs have belly buttons
Study image: Oldest preserved umbilical scar reveals dinosaurs had ‘navels’, published in BMC Biology.

Did all dinosaurs have a navel?

Currently, dinosaur-derived species, such as reptiles and birds, lose the umbilical scar a few days or weeks after hatching from the egg. However, for this Cretaceous dinosaur, it was different.

The navel of Psittacosaurus persisted at least until sexual maturity. Similar to certain lizards and crocodiles with which it shares the closest morphological resemblance,” the study states.

This is believed to be the oldest record to date of a navel in a non-avian dinosaur, as some scars had previously been found in flying or bird-like species.

For the moment, scientists point out that these results are variable given that: “a persistent umbilical scar may not have been present in all non-avian dinosaurs.” Although the reverse has not yet been ruled out.

Scientific studies

This article is based on a scientific study which can be subjected to new tests to be validated or rejected. Your results should NOT be considered conclusive.

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