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Dinosaurs brain

Brain and sensory systems

Recent studies have contributed to the fall of the accepted ideas on the intelligence of dinosaurs and on the way they perceived their universe. Like most soft tissues, the brain, nerves and sensory system of a dinosaur do not fossilize. But we can learn many things about them by observing the bones in which the brain, eyes and ears were lodged, and the various places where the nerves passed. The brain is inside a bone box that has approximately the size and shape of it. The cavity left by the latter can then be used to make a molding. But this technique is delicate and can damage the skull. CT scanning, on the other hand, makes it possible to explore the skull in three dimensions using X-rays and to analyze the brain configuration on a computer screen.

Erroneous ideas

Stegosaurus brain
Stegosaurus brain - Wikimedia commons

Since the description of the first casts in 1896 by the American paleontologist Othniel Charles Marsh, it was believed that dinosaurs had a relatively small brain for their size which in reality is false. In living animals today, the size of the brain actually increases with weight, but to a lesser extent. The difference in volume between the brain of a large animal and that of a smaller animal is small compared to their size difference. However, although small, the brain of dinosaurs was proportionally the same size as that of reptiles or amphibians today. In some small theropods, this size was comparable to that of the current ratites such as the ostrich and the emu. Of all terrestrial vertebrates, Stegosaurus was the one with the smallest brain in relation to its size. According to another old popular belief from Marsh's Stegosaurus study, some dinosaurs had a "rescue" brain at the pelvis level. Marsh had noticed in the basin a space where a bulge of the spinal cord could have been lodged. This ganglion could have been used to transmit the messages to the posterior part of the animal or even to control it, releasing the tiny brain located in the head to fulfill other cognitive functions. This rather whimsical idea is out of date today.

Senses

The eyes, ears and nasal cavities of the dinosaurs were also inside bony boxes, the observation of which helps us understand the nature of these organs. In theropods, the eyes were generally well developed, with a ring of bones inside the globe: the sclera ring. Similarly, the part of the brain that commanded the view was hypertrophied, so we think they relied primarily on sight to locate a prey. For their part, some herbivores such as ornithopods and pachycephalosaurs seemed to rely on their sense of smell to spot distant predators. In the small ornithopod Leaellynasaura, the immense eyes and optic lobes in the brain probably helped it to see in the middle of the long Antarctic night. The little theropods probably had a sharp sense of balance because that part of their brain was hypertrophied.

Fossil interpretation

Parasaurolophus skull
Parasaurolophus skull

Interpreting bone fossils without a single piece of flesh requires good deductive reasoning. This is especially true for structures such as the nasal cavities of ankylosaurs and hadrosaurs. In some, as in others, the skull had convolutions that allowed the passage of air. The most striking example is that of Parasaurolophus, which had ducts passing the air over the entire length of the ridge that it carried on its head, more than 1 m long. These tubular structures, which produced resounding sounds, may have been an instruments of communication. There are other theories according to which these tubes were lined with olfactory cells which gave the animal a very fine sense of smell or which brought warm air to the lungs or captured the moisture of the exhaled air or even kept the brain cool. It is likely that they performed several functions at the same time.