Pinacosaurus

About Pinacosaurus

Features of Pinacosaurus and Its Complex Nasal Structure

Pinacosaurus was a medium-sized armored dinosaur (ankylosaur) that lived widely across the Asian continent (modern-day Mongolia and northern China) during the Late Cretaceous period. It was relatively lightweight among the Ankylosauridae and had a flat body shape.

Its most prominent feature is the presence of two to five multiple egg-shaped holes (accessory nares) opening near the nostrils (external nares).

These winding nasal passages functioned as an "air conditioner (heat exchanger)" that humidified and warmed inhaled air, and recovered moisture and heat from exhaled air. This prevented their huge bodies, covered in heavy armor, from overheating and suffering from heatstroke.

It is also known that Pinacosaurus retained five digits on its forelimbs, but the digits on its hindlimbs had degenerated to three.

Group Life of Juveniles

In the past, it was thought that armored dinosaurs acted alone because they possessed heavy armor. However, Pinacosaurus overturned this idea.

In places like the Gobi Desert, bone beds have been discovered where dozens of juvenile Pinacosaurus died piled on top of each other. Since no adult individuals are mixed in, it is thought that they lived apart from their parents, forming groups consisting only of juveniles.
In their youth, the armor on their backs was undeveloped, and they did not have the weapon (tail club) at the tip of their tails. Therefore, they developed sociality to form herds in order to protect themselves from carnivorous dinosaurs.

From the condition of the fossils, it is speculated that they were caught in the collapse of a sand dune, or their feet got stuck in the mud of a dried-up pond and they were buried alive.

Communication with Bird-like Calls

In 2023, the world's first fossilized "larynx" for a non-avian dinosaur was discovered in a Pinacosaurus fossil. Since the larynx of reptiles and birds is made of cartilage, it is extremely rare for it to be preserved as a fossil.

This suggests that Pinacosaurus did not just emit simple groans like crocodiles, but used complex sounds selectively like birds. They likely engaged in advanced communication to call herd members or signal danger.

Secrets of the Tail Club

The huge lump of bone at the tip of the tail (tail club) that symbolizes the ankylosaur family was already complete in the time of Pinacosaurus.

It is known that this tail club was not always this shape, but evolved over tens of millions of years. First, the tail bones fused firmly to create a "stiff handle," and tens of millions of years later, the "knob" at the tip evolved. This is because if only the tip became heavy while the tail remained flexible, the centrifugal force of swinging it would dislocate their own tail.

Swinging a hard, giant tail club had enough power to crush the bones of large dinosaurs. On the other hand, the inside of the knob at the tip was made of spongy bone, making it light, and devised to be swung quickly. In addition, since a small, insufficiently developed tail club did not have the power to break bones, it is thought that it was used not only to repel carnivorous dinosaurs, but also for territorial disputes and displaying among peers.

Discovery and Paper Description

In the 1920s, the American Museum of Natural History conducted an excavation survey in the Gobi Desert in Mongolia. In 1923, paleontologist Walter W. Granger discovered fossils including a skull from the strata of Shabarakh Usu (Flaming Cliffs).

In 1933, American paleontologist Charles W. Gilmore named these fossils a new genus, Pinacosaurus (Pinacosaurus grangeri), in the paper "Two new dinosaurian reptiles from Mongolia with notes on some fragmentary specimens."

Since then, many well-preserved skeletal fossils have been discovered from all over Asia, and Pinacosaurus has become an important entity for unraveling the growth process and ecology of armored dinosaurs.