The EQ or Encephalization Quotient is a simple way of measuring an animal’s intelligence. EQ is the ratio of the brain weight of the animal to the brain weight of a “typical” animal of the same body weight.
Assuming that smarter animals have larger brains to body ratios than less intelligent ones, this helps determine the relative intelligence of extinct animals. In general, warm-blooded animals (like mammals and birds) have a higher EQ than cold-blooded ones (like amphibians, reptiles and bony fish). Birds and mammals have brains that are about 10 times bigger than those of bony fish, amphibians, and reptiles of the same body size.
The primitive dinosaurs belonging to the group sauropodomorpha (which included Massospondylus, Riojasaurus, and others) were among the least intelligent of the dinosaurs, with an EQ of about 0.05. The troodontids (including Troodon) and dromaeosaurid dinosaurs (the “raptors,” which included Dromeosaurus, Velociraptor, Deinonychus, and others) had the highest EQ among the dinosaurs, about 5.8.
The Encephalization Quotient (EQ) was developed by the psychologist Harry J. Jerison in the 1970’s. James A. Hopson (a paleontologist from the University of Chicago) did further development of the EQ concept using brain casts of many dinosaurs. Hopson found that theropods (especially Troodontids) had higher EQ’s than plant-eating dinosaurs. The lowest EQ’s belonged to sauropods, ankylosaurs, and stegosaurids.
Reference: Hopson, J. A. 1980, Relative brain size in dinosaurs - implications for dinosaurian endothermy, pp. 287-310 , American Association for the Advancement of Science Symposium no. 28.