Could theropod dinosaurs have evolved to a human level of intelligence?

Abstract

Noting that some theropod dinosaurs had large brains, large grasping hands, and likely binocular vision, paleontologist Dale Russell suggested that a branch of these dinosaurs might have evolved to a human intelligence level, had dinosaurs not become extinct. I offer reasons why the likely pallial organization in dinosaurs would have made this improbable, based on four assumptions. First, it is assumed that achieving human intelligence requires evolving an equivalent of the about 200 functionally specialized cortical areas characteristic of humans. Second, it is assumed that dinosaurs had an avian nuclear type of pallial organization, in contrast to the mammalian cortical organization. Third, it is assumed that the interactions between the different neuron types making up an information processing unit within pallium are critical to its role in analyzing information. Finally, it is assumed that increasing axonal length between the neuron sets carrying out this operation impairs its efficacy. Based on these assumptions, I present two main reasons why dinosaur pallium might have been unable to add the equivalent of 200 efficiently functioning cortical areas. First, a nuclear pattern of pallial organization would require increasing distances between the neuron groups corresponding to the separate layers of any given mammalian cortical area, as more sets of nuclei equivalent to a cortical area are interposed between the existing sets, increasing axon length and thereby impairing processing efficiency. Second, because of its nuclear organization, dinosaur pallium could not reduce axon length by folding to bring adjacent areas closer together, as occurs in cerebral cortex.

Dinosaurs: Clever creatures or bird brains?

“…A complementary contribution by Reiner (2023) asks whether dinosaurs could ever have gained the capability of being even smarter, approaching human levels of intelligence. This study approaches the question of dinosaur intelligence from another perspective, that of potential limitations on information flow and scalability of dinosaur brains, again basing the argument on the presumed similarity between dinosaurs and birds.…”

How smart dinosaurs?

“…What would have happened, however, without the meteor strike? In my own article (Reiner, 2023), I imply there was nothing inevitable about the decline of dinosaurs and the concomitant rise of mammals from the viewpoint of brain capacity. Although their pallial regions were extremely likely to have different designs-nuclear in dinosaurs like in extant birds versus cortical in mammals-the nuclear design in and of itself works as well as the cortical.…”

“…Second, dinosaurs were not doomed by brain power that was too insufficient (compared to mammals) to be able to continue their reign. Rather, as emphasized in my own article (Reiner, 2023), numerous published studies have presented various lines of evidence that many dinosaur species functioned at least at an avian level of behavioral and cognitive complexity. In her own article, Dr. Herculano-Houzel takes this a step further, and from what we know about the relationship between brain size and neuron numbers suggests that larger theropod dinosaurs had an abundance of pallial ("cortical") neurons comparable to that in some non-ape primates such as baboons (Herculano-Houzel, 2023a).…”

“…In my article, I lay out lines of thought that lead me to conclude that this would have been unlikely (Reiner, 2023). The reasons deal with a potential wiring inefficiency inherent to the nuclear pallial plan that would have been exacerbated with the expansion needed to reach a pallial complexity and neuron number equivalent to that in humans.…”

Could a theropod like T. rex have had human‐like numbers of neurons?

“…The next question is, of course, the one that Reiner (2023) addresses in his study: did baboon-like numbers of neurons in T. rex mean baboon-like cognitive capacities, too? And, more critically: if a theropod could have reached human-like numbers of neurons, would that have endowed said theropod with human-like cognitive capacities?…”