Scientists' new discovery: The bigger the dinosaurs, the lower their intelligence?

Recently, the research team led by Han Fenglu, associate professor of the School of Earth Sciences at China University of Geosciences (Wuhan), in collaboration with researchers from the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Yunnan University, Nanjing Museum of Paleontology, and George Washington University in the United States, conducted an in-depth study of the cranial morphology of early ceratopsian dinosaurs and found that as their body size increased, ceratopsian dinosaurs experienced degeneration in hearing, smell, and intelligence . The relevant paper has been published in the internationally renowned journal Paleontology.

Although scientists have a deep understanding of the external form of dinosaurs, their understanding of their internal structure, especially the brain and sensory organs, is relatively limited. Although there are fossils of dinosaur brain soft tissues, they are very rare. The traditional method is to fill the inside of the dinosaur skull with resin and other materials to cast a physical model of the cranial cavity to study the dinosaur brain. Modern researchers mostly use computer tomography technology (micro CT scanning) to scan the dinosaur skull, reconstruct the dinosaur cranial cavity model, and use it as a substitute for its brain.

Ceratopsians are a type of herbivorous dinosaurs that lived in the Jurassic and Cretaceous periods. Early ceratopsians walked on two legs and were small, only 1 to 2 meters long, without horns, such as the Hidden Dragon and the Psittacosaurus. But by the late Cretaceous period, after nearly 100 million years of evolution, ceratopsians had become quadrupedal, huge (up to 9 meters long), and horned dinosaurs that could compete with Tyrannosaurus Rex, such as the famous Triceratops.

The changes in physical characteristics that accompany huge body sizes have always been a mystery that paleontologists hope to solve.

As early as 1996, one of the collaborators of this study, Kathryn Foster, conducted research on the brain cavity of Triceratops. In recent years, researchers have reconstructed a three-dimensional model of the cranial cavity of Triceratops (Figure 1). These studies have found that the brain of Triceratops is relatively small relative to the skull, the head moves slowly, and the head is used to tilting downward, which helps them show the horns and neck shields on their heads and is more adapted to listening to some low-frequency sounds. Therefore, the researchers inferred that Triceratops was not very smart.

Figure 1: Comparison of body size and brain cavity between early ceratopsians (Hyperostoma, left) and late ceratopsians (Triceratops, right)

So what did early ceratopsians look like? The research team used micro-computed tomography (CT) technology and three-dimensional model reconstruction methods to analyze in detail the cranial structures of three early ceratopsian dinosaurs found in China, including the Late Jurassic Cryptosaurus dangshi, the Early Cretaceous Liaoceratops and Psittacosaurus. They were found to have developed olfactory bulbs, obvious optic lobes, slightly protruding cerebellar flocculi, relatively long cochlear ducts and long and high anterior semicircular canals. Based on this, it is inferred that early ceratopsian dinosaurs had relatively developed sense of smell and hearing, which is in contrast to the lower sense of smell and hearing of late ceratopsian dinosaurs (such as Triceratops).

In addition, the brain volume of early ceratopsian dinosaurs was relatively large relative to their skulls, and their intelligence (brain quotient index) was significantly higher than that of Triceratops, and even higher than that of most existing reptiles . The researchers conducted a statistical analysis of the evolution of the brain cavity and inner ear of all known ceratopsian and ornithopod dinosaurs, and believed that the intelligence, hearing and smell of ceratopsians all degenerated during the evolution process (Figure 2).

Figure 2: Evolution of the brain and inner ear of ceratopsian dinosaurs

The researchers also explored the changes in head posture during the evolution of ceratopsians and found that the heads of early ceratopsians were more flexible, while the heads of later ceratopsians such as Triceratops were mainly tilted downward. This change in posture is likely related to their feeding methods (Figure 3).

Figure 3: Evolution of head posture in ceratopsians

"These findings are very interesting. Why did some organ functions degenerate during the evolution of ceratopsian dinosaurs? This is most likely related to their increased size. Early ceratopsians were small in size and needed to be vigilant against attacks from predators, so they performed well in hearing and smell. Later ceratopsians evolved into huge bodies and sharp bone horns, which were a strong deterrent to predators, so their functions in other aspects may have been weakened." Han Fenglu said: " This research is also very inspiring for our understanding of biological evolution, including human evolution. "

Source: Guangming Daily