The small, two-legged theropod dinosaur known for decades as Troodon has long been cited as the smartest non-avian dinosaur. This slender predator lived roughly 76 million years ago in what is now North America. Scientists quantify the intelligence of this extinct animal by examining its preserved anatomy to estimate its cognitive capacity.
Measuring Extinct Intelligence
Paleontologists rely on two primary methods to estimate the intelligence of extinct species, both requiring analysis of the cranial cavity. The first is creating an endocast, a mold of the braincase interior that approximates the brain’s size and shape. Since the brain of many dinosaurs fit snugly within the skull cavity, the endocast provides a reliable estimate of volume and general structure, allowing for the examination of specific brain regions.
The second, more quantitative method is the Encephalization Quotient (EQ), which compares the actual brain size to the size expected for an animal of its body mass. EQ is calculated by dividing the measured brain mass by the predicted brain mass based on the animal’s overall size. A higher EQ suggests the animal possessed a larger brain than necessary for basic survival, with the excess mass dedicated to higher-order perception and cognition. However, this approach does not account for the density or internal organization of the neural tissue itself.
Anatomical Evidence for Advanced Cognition
Applying these methods to the dinosaur formerly grouped under Troodon reveals its reputation for intelligence. Analysis of the cranial cavity, particularly in specimens now referred to as Stenonychosaurus, shows a brain volume unusually large relative to its estimated body mass compared to most other dinosaurs. Its Encephalization Quotient was placed at the lower end of the range seen in modern birds and mammals, significantly higher than the values calculated for the majority of other non-avian dinosaurs, many of which charted well below an EQ of 1.
The endocast shape is also revealing, showing a brain structure that resembles modern birds, with a characteristic triangular form when viewed from above. This shape suggests a notable expansion of the forebrain, or cerebrum, the area responsible for complex functions like memory and problem-solving. The enlarged cerebrum relative to the rest of the brain structure is interpreted as an anatomical marker for elevated cognitive capabilities. The well-defined bony capsule surrounding the middle ear cavity also suggests advanced hearing capabilities, a trait associated with complex sensory processing.
Inferred Behavior and Ecological Strategy
The inferred cognitive abilities of this dinosaur are thought to have translated into a sophisticated ecological strategy. The large size of the eye sockets suggests a high visual acuity and possibly a nocturnal or crepuscular lifestyle, requiring advanced brainpower to process visual information in low-light conditions. Furthermore, the forward-facing position of the eyes provided stereoscopic vision, which is a significant advantage for accurately judging distance while hunting.
The structure of the forelimbs suggests a degree of manual dexterity not common in other large theropods. The hands were equipped with opposable or semi-opposable fingers, which could have been used for grasping and manipulating objects with precision. The combination of high visual processing, a large brain, and grasping hands has led to speculation about complex hunting behaviors, such as coordinated group hunting. Although the teeth were unusual for a meat-eater, resembling those of some plant-eaters, analysis suggests its diet was omnivorous, requiring a flexible foraging strategy that supports the idea of an intelligent animal.
The Taxonomy Controversy and Modern Understanding
The dinosaur central to this discussion was known as Troodon for much of the 20th century, but this name is now considered questionable by many paleontologists. The original Troodon name was based solely on a single, isolated tooth found in 1856, an insufficient specimen to definitively characterize an entire species. Because the teeth of many troodontids are similar, this original classification has been deemed a nomen dubium, or a doubtful name.
The vast majority of the skeletal material and anatomical data that established the reputation for intelligence actually belong to the species Stenonychosaurus inequalis. Stenonychosaurus was originally named in 1932, but was grouped under Troodon in a controversial 1987 reclassification that has since been reversed. Today, the scientific consensus is that the dinosaur with the high cognitive rank is Stenonychosaurus or a closely related species, such as Latenivenatrix. This reclassification does not diminish the dinosaur’s standing as one of the most cognitively advanced non-avian species known, but it provides a more accurate name for the subject of the intelligence debate.