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Psittacosaurs. Some dinosaurs may have had navels. Research by an international team on the fossil SMF R 4970

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Scientists have discovered what species may have been the first to possess the “navel”. Analyzes of a perfectly preserved horned dinosaur fossil found in China showed this. The researchers explained that the mark on the remains of the animal’s skin seems to bring to mind the so-called umbilical scars in the known crocodiles and alligators. Research on this topic has been published in the journal “BMC Biology”.

The researchers explained that the scar found is not an umbilical cord, as is the case with mammals. It comes from the yolk sac of an egg from which psittacosaurs hatched 130 million years ago. Some modern reptile and bird species have similar structures, but lose them within days or weeks of hatching. Others, like adult alligators, retain so-called umbilical scars for life.

The navel of a psittacosaurusJagged Fang Designs.

Perfectly preserved

The umbilical scar found in a psittacosaurus is more similar to that of a crocodile. The researchers found that it could last at least until puberty.

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This is the first example of a “navel” in a dinosaur that is not the ancestor of the birds we know. This discovery does not prove that all terrestrial dinosaurs had the same permanent umbilical scar, but it does not exclude the possibility.

“The psittacosaurus specimen is probably the most important fossil we have for studying dinosaur skin,” said vertebrate palaeontologist Phil Bell from the University of New England in Australia. ‘It still brings surprises that we can’ bring to life ‘with new technologies such as laser scanning,’ he added.

The fossil, known as SMF R 4970, was found in China in 2002. It is perfectly preserved, showing individual scales, long plumes of caudal bristles, and the first cloaca ever seen in a dinosaur of this type.

Using detailed laser scans, researchers were able to identify a change in the pattern of skin and scales exactly where the dinosaur’s navel would have been. This means that the yolk sac has been absorbed by the young dinosaur.

The navel of a psittacosaurusJulius T. Csotonyi

It has been suspected for a long time

Like the umbilical cord, the yolk sac provides oxygen and nutrients when an embryo grows within an egg. It is connected with allantoic – one of the amniotic membranes in the egg. By the time the animal hatches, these connections close and leave a long scar.

Scientists have long hypothesized that oviparous dinosaurs could have such a scar. However, the latest observations are only the first evidence to support this thesis. Soft tissue fossils have rarely been preserved through the ages, but SMF R 4970 gives us an unprecedented glimpse into a thin column of joined scales on an ancient abdomen. Their regular size and smooth edges suggest that the scar was not caused by physical trauma or disease.

“We have identified the distinctive scales that surround a long umbilical scar in a psittacosaurus specimen, as is the case with some modern lizards and crocodiles,” said palaeontologist Michael Pittman of the Chinese University of Hong Kong. – This type of scar is called the navel, in humans it is smaller. This specimen is the first dinosaur fossil in which a navel has been preserved, ‘he added.

The navel of a psittacosaurusBell et al. 2022

Main photo source: Jagged Fang Designs

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