Dinosaur Intelligence
Dinosaur intelligence refers to the cognitive abilities and behaviors of dinosaurs, a topic that has evolved significantly over time. Early assumptions pegged dinosaurs as unintelligent due to their relatively small brain sizes compared to their bodies, aligning them with reptiles. However, advancements in paleontology, particularly the development of the encephalization quotient (EQ) in the 1970s, have shifted these views. The EQ measures brain size relative to body mass, suggesting that some dinosaurs, particularly theropods, might have had intelligence levels comparable to modern birds.
Recent research utilizing computed tomography (CT) has enabled scientists to create accurate models of dinosaur brains, allowing for more comprehensive analyses of their cognitive capacities. Notably, studies indicate that theropod dinosaurs may have had higher neuron densities similar to those found in modern primates, hinting at sophisticated intelligence. While debates continue regarding the best methods to assess intelligence—whether through absolute or relative brain size—the consensus is that dinosaurs exhibited a range of cognitive abilities, making them some of the most complex animals of their time. Future research may further clarify their intelligence and its implications for understanding the evolution of cognition in both dinosaurs and their avian descendants.
Dinosaur Intelligence
Introduction
Early paleontologists assumed that dinosaurs were unintelligent, based on both the size of their brains in relation to their bodies and because they were considered closely related to reptiles. Paleontologists made little progress in understanding dinosaur cognition until the 1970s, when scientists developed a new system for estimating intelligence based on relative brain size, called the encephalization quotient (EQ).
Paleontologists are currently debating whether absolute brain size or relative brain size is the best way to estimate intelligence. In addition, the realization that birds evolved from theropod dinosaurs led some paleontologists to theorize that dinosaur intelligence might be more appropriately based on studies of avian intelligence and the structure of birds’ brains.
Modern medical imaging techniques, including computed tomography (CT), allow paleontologists to create accurate three-dimensional representations of dinosaur cranial anatomy, thus enabling better evaluations of brain size, shape, and function. Virtual models are gradually replacing endocasts (internals casts of the skull) as the preferred method for studying the cranial anatomy of extinct animals.
Key Terms
Computed Tomography (CT): CT is a diagnostic imaging method that uses multiple x-ray scans rotated around a central axis that creates a three-dimensional representation of a structure.
Encephalization Quotient (EQ): EQ is the ratio of actual brain mass to expected brain mass relative to the animal's body weight. Paleontologists believe that higher EQ values are positively correlated with greater intelligence.
Endocast: An endocast is a mold of the internal structure of a hollow object, often used to study internal structure of crania and other hollow anatomical structures.
Intelligence: Intelligence is a living creature's capacity for learning, reasoning, and problem solving, as well as the ability to understand information obtained from the environment.
Theropod: Theropods are a large group of saurischian dinosaurs that lived from the Triassic to the end of the Cretaceous, most of which were bipedal, predatory animals.
Key Players
Harry Jerison: Psychologist Harry Jerison created the encephalization quotient (EQ) system for measuring intelligence from molds of animal brains, largely replacing the standard method of measuring intelligence as a function of brain size relative to body mass. In Evolution of the Brain and Intelligence (1973), Jerison claimed that brain size has increased throughout evolutionary time, in concert with increasingly complex predator-prey interactions. Jerison's EQ system was a major development in animal intelligence research.
James Hopson: University of Chicago paleontologist J. A. Hopson was the first to measure EQ values for dinosaurs, as presented in his 1977 article “Relative Brain Size in Dinosaurs: Implications for Dinosaurian Endothermy.” Hopson's EQ values have become the standard measurement tool used to estimate dinosaur intelligence and have been cited in dozens of research studies since the publication of his early research.
Dale Russell: In a 1982 publication, “Reconstructions of the Small Cretaceous Theropod Stenonychosaurus inequalis and a Hypothetical Dinosauroid,” paleontologist Dale Russell proposed that certain species of dinosaurs, if they had survived the mass extinction at the end of the Cretaceous, might have given rise to human-like dinosaur ancestors. While Russell's theories have been controversial, his research has been instrumental in advancing the study of dinosaur intelligence.
Hans Larsson: Paleontologist Hans Larsson conducted detailed measurements of theropod brain structure, published in his 2001 article “Endocranial Anatomy of Carcharodontosaurus saharicus (Theropoda: Allosauroidea) and its Implications for Theropod Brain Evolution,” indicating that theropod brains were intermediate in size (relative to body mass) between those of reptiles and birds. Larsson's research indicates that estimates of brain size on certain dinosaurs may need to be modeled on avian brain structure, rather than reptilian brains.
History
Early Concepts of Dinosaur Intelligence: In the mid-1800s, several paleontologists noted in publications that many dinosaurs had surprisingly small brains compared to their body size. Stegosaurusarmatus, for instance, had a brain that weighed around 75 grams (2.65 oz), compared to the animal's adult weight of up to 6,500 kilograms (14,300 lb). Early paleontologists believed that dinosaur behavior was similar to the behavior of existing reptiles, such as crocodiles and monitor lizards. Most scientists believed that dinosaurs, like reptiles, were generally less intelligent than both birds and mammals.
Early animal behaviorists recognized that absolute brain size provides a poor measure of intelligence, because some animals with smaller brains appear more intelligent than animals with larger brains. Although larger animals tend to have larger brains, brain size and intelligence do not increase at the same rate. Therefore, the ratio of brain size to intelligence is difficult to calculate.
Encephalization Quotient: In the 1970s, psychologist Harry Jerison developed the encephalization quotient to measure relative brain size within a group of related animals. To determine an EQ value, scientists measure the size of an animal's brain, from a cranial endocast or a CT scan, and then compare the actual size to the “expected” brain size for an animal of the same mass. Each EQ value is therefore placed on a curve containing relative brain sizes for similar animals.
The EQ scale stretches from 0.0 to 8.0, the value generally given for the human brain. Therefore, animals with higher EQ values are assumed to be more intelligent. The value of 7.0 for Homo sapiens (humans) means that the human brain is roughly seven times larger than expected for a mammal of similar mass.
In the late 1970s, paleontologist James Hopson measured EQ values for a variety of dinosaurs, creating the scale of dinosaur intelligence that is still used by most paleontologists. Hopson obtained his EQ values by creating a scale based on a 1.0 value for the crocodile brain. Hopson found that most large dinosaurs had EQ values below 1.0.
The large sauropods and thyreophorans (armored dinosaurs), such as Stegosaurus, had EQ values around 0.2, making them among the least intelligent dinosaurs. By contrast, theropod (bipedal saurischian) dinosaurs had substantially higher EQ values, reaching as high as 6.0 in a few species. Theropods, at the upper end of the curve, may have been similar in intelligence to some modern birds.
Current Research and Implications
Dinosaur and Bird Brains: The realization that dinosaurs were closely related to birds came about in the late 1970s, urging many paleontologists to reexamine their concepts of dinosaur behavior. Estimates of dinosaur brain size have traditionally been based on reptile brains, in which the brain is surrounded by a significant amount of tissue separating it from the skull. In birds, the brain takes up a larger portion of the cranium.
Some paleontologists, including researcher Hans Larrson, have theorized that measurements of dinosaur EQ values should be compared to birds rather than reptiles. In 2001, Larrson conducted a series of measurements indicating that some theropods had intermediate EQ values somewhere between birds and reptiles. Larrson's findings may indicate that EQ values for other dinosaur species must be reexamined.
Virtual Dinosaur Brains: The application of CT scanning to dinosaur fossils in the 1990s was a major advancement in the study of dinosaur intelligence. CT scans of dinosaur skulls provided more accurate models of dinosaur brains than those developed using cranial endocasts. In 2007, researcher Ke-Qin Gao and colleagues used CT scans to estimate the brain size of Psittacosaurus, a small ceratopsian (beaked herbivores) that lived in the Early Cretaceous. With the increased accuracy of the CT measurements, Gao found that Psittacosaurus had a larger brain than expected, calling into question the EQ values estimated for some dinosaur species. (See Zhou et al. 2007.)
Relative Brain Size and Evolution: In 1982, paleontologist Dale Russell published results of his study of the small theropod Troodon formosus, the species with the highest EQ value so far calculated for a dinosaur. According to Russell, Troodon had an EQ similar to ratites (large, flightless birds) and may have been similar in intelligence.
Most paleontologists believe that even intelligent dinosaurs such as Troodon were not as intelligent as modern mammals. However, Russell and other paleontologists have noted that at the time Troodon lived, its brain was more advanced than the brains of birds and mammals living in the same period. In terms of relative intelligence then, Troodon may have been among the most intelligent animals living on Earth in the Cretaceous.
Continuing Questions: Paleontologists and behaviorists agree that estimates of dinosaur intelligence are highly problematic and may be far from accurate. In some cases, researchers have found that overall brain size is a more reliable indicator of intelligence than relative brain size, as was discussed in a 2007 study of primates. It may be true that the intelligence curve for dinosaurs, like primates, could depend more on absolute brain size.
In 2010, researcher Jan Gläscher and colleagues published the results of a study indicating that general intelligence in humans depends on several areas of the brain across both hemispheres and that the greatest determinant of intelligence appears to be the connections between these areas of brain activity. Findings like these make it clear that intelligence depends on many factors that cannot be well estimated from fossilized specimens.
In the 2020s, numerous scientific studies were published further analyzing the potential for dinosaur intelligence, brain size in relation to function, and comparative capabilities among modern primates, birds, and other animals. Biologist and neuroscientist Suzana Herculano-Houzel of the Vanderbilt Brain Institute at Vanderbilt University published a study that suggested theropods had telencephalic neurons similar to modern-day primates, suggesting a higher level of intelligence than previously thought, perhaps even as advanced as humans. However, Anton Reiner, Professor of Anatomy and Neurobiology at The University of Tennessee Health Science Center, in a study published just months after Herculano-Houzel's in 2023, suggested that the architectural design complicates matters and that the development of the neocortex in mammal brains makes coginitive capabilites more feasible. While Reiner did not completely reject the idea that dinosaurs could have a level of intelligence beyond what has been perceived for decades, he believed it to be unlikely that they could have evolved cognitive abilities comparable to humans.
Ultimately, estimating intelligence is problematic even in living species, but is far more difficult in extinct animals. Without the ability to conduct behavioral studies, theories on dinosaur intelligence can never be well corroborated. What is clear from research is that dinosaurs were among the most complex and intelligent animals in the Mesozoic and their ancestors, the birds, have evolved into some of the most intelligent animals in the modern world.
Bibliography
Currie, Phillip J., et al. Feathered Dragons: Studies on the Transition from Dinosaurs to Birds. Bloomington: Indiana University Press, 2004.
Deaner, Robert O., et al. “Overall Brain Size and Not Encephalization Quotient, Best Predicts Cognitive Ability across Non-Human Primates.” Brain, Behavior and Evolution, vol. 70, 2007, pp. 115–24.
Emery, Nathan J. “Cognitive Ornithology: The Evolution of Avian Intelligence.” Philosophical Transactions of the Royal Society of Biology, vol. 361, 2006, pp. 527–43.
Fastovsky, David E., and David B. Weishampel. Dinosaurs: A Concise Natural History. New York: Cambridge University Press, 2009.
—. Evolution and Extinction of the Dinosaurs. New York: Cambridge University Press, 2005.
Feduccia, Alan. Origin and Evolution of Birds. New Haven, CT: Yale University Press, 1999.
Isler, Karin, and Carel P Van Schaik. “Why Are There So Few Smart Mammals (But So Many Smart Birds)?” Biology Letters, 5, 2009, pp. 125–29.
Herculano-Houzel, Suzana. "Could a Theropod like T. Rex Have Had Human-like Numbers of Neurons?" Journal of Comparative Neurology, vol. 531, no. 9, 2023, pp. 959-961. Wiley Online Library, doi.org/10.1002/cne.25472. Accessed 27 Sept. 2024.
Herculano-Houzel, Suzana. "Theropod Dinosaurs Had Primate-like Numbers of Telencephalic Neurons." Journal of Comparative Neurology, vol. 531, no. 9, 2023, pp. 962-974. Wiley Online Library, doi.org/10.1002/cne.25453. Accessed 27 Sept. 2024.
Martin, Anthony J. Introduction to the Study of Dinosaurs. New York: Wiley Blackwell, 2006.
Marino, Lori. “Absolute Brain Size: Did We Throw the Baby Out with the Bathwater?” Proceedings of the National Academy of Sciences in the United States of America 103 (2006): 13563–64.
Norell, Mark, Eugene S. Gaffney, and Lowell Dingus. Discovering Dinosaurs: Evolution, Extinction and the Lessons of Prehistory. Berkeley: University of California, 2000.
Reiner, Anton. "Could Theropod Dinosaurs Have Evolved to a Human Level of Intelligence?" Journal of Comparative Neurology, vol. 531, no. 9, 2023, pp. 975-1006. Wiley Online Library, doi.org/10.1002/cne.25458. Accessed 27 Sept. 2024.
Reiner, Anton. "How Smart Dinosaurs?" Journal of Comparative Neurology, vol. 531, no. 9, 2023, pp. 956-958. Wiley Online Library, doi.org/10.1002/cne.25471. Accessed 27 Sept. 2024.
Van Valkenburgh, Blaire, and Ralph E. Molnar. “Dinosaurian and Mammalian Predators Compared.” Paleobiology 28 (2002): 527–43.
Weishampel, David B., et al. Dinosauria. Berkeley: University of California Press, 2004.
Zhou, Chang-Fu, et al. “Endocranial Morphology of Psittacosaurus.” Paleoworld, vol. 16, no. 4, 2007, pp. 285–93.