“Theropod Dinosaurs Had Primate-Like Numbers of Telencephalic Neurons”, 2022-06-21 ():
Understanding the neuronal composition of the brains of dinosaurs and other fossil amniotes would offer fundamental insight into their behavioral and cognitive capabilities, but brain tissue is not fossilized. However, when the bony brain case is preserved, the volume and therefore mass of the brain can be estimated with computer tomography; and if the scaling relationship between brain mass and numbers of neurons for the clade is known, that relationship can be applied to estimate the neuronal composition of the brain.
Using a recently published database of numbers of neurons in the telencephalon of extant bird and non-avian reptiles, here I show that the neuronal scaling rules that apply to these animals can be used to infer the numbers of neurons that composed the telencephalon of dinosaur, pterosaur and other fossil reptile species, after using the relationship between brain and body mass to determine whether bird-like (endothermic) or non-avian reptile-like (ectothermic) rules apply to each fossil species.
This procedure indicates that theropods such as Tyrannosaurus rex and Allosaurus had monkey-like numbers of telencephalic neurons, which would make these animals not only giant but also long-lived and endowed with flexible cognition, and thus even more magnificent predators than previously thought.
…Importantly, the use of endotherm (avian) scaling rules to estimate numbers of telencephalic neurons in theropods versus ectotherm (non-avian reptile) scaling rules in ornithischians is supported by recent metabolite findings in these species. The distinction is highly consequential: if the Tyrannosaurus brain scaled like a non-avian reptilian ectotherm brain, it would have an estimated 0.455b telencephalic neurons—still as many as in a large dog, but less than 15% of the baboon-like 3.4 billion telencephalic neurons estimated if basal bird-like scaling rules applied (Table S1).