A smear job on T. rex. –  Thoughts on the controversy around exceptionally intelligent dinosaurs

Last week saw the publication of our paper on how (not) to deal with neuron count estimates in vertebrate palaeontology and to which extent they might allow inferences on behavior and intelligence in dinosaurs. In its core, the article is a direct response to a paper by famous neurologist Suzana Herculano-Houzel, who claimed that especially large-bodied theropods such as Acrocanthosaurus and Tyrannosaurus would have had remarkably large brains and high neuron counts. Based on that, she hypothesized that they were long-lived, used tools, and passed on cultural knowledge down the generations. We show that most of these claims result from methodological errors and ignore a vast body of critical evidence. Instead, based on the size and morphology of the brain in T. rex and other basal theropods, the traditional assumption of reptilian-grade cognition in these animals still appears most plausible. I don’t want to reiterate our arguments and perspectives on dinosaur behavior here. Darren Naish, co-author on the article, has already published a very accessible and concise overview of the paper’s contents on his blog that I recommend to anyone who does not have the time to get to grips with our admittedly long text.

I learned a couple of things over the course of the promotion for this article. For once, some researchers are very invested in the idea of whole brain or forebrain neuron counts as predictors of cognitive complexity, something that they just don’t live up to when we consider the current evidence. Furthermore, the old cliché of inept cognition in ectothermic vertebrates such as fish and reptiles is still strong. The “smart mammal/bird vs. the dumb reptile” narrative clearly resonated in a number of reactions to our article (although in interviews, the team did its best to disenchant it). Yet, it was perhaps most clearly voiced by Herculano-Houzel herself who considered us comparing cognition in T. rex to that of living crocodilians as “a smear job” on the animal’s reputation.

To be awe-inspiring to us, T. rex had to have exceptional cognition, apparently. What makes the Herculano-Houzel paper special within the discourse surrounding this topic is that it certainly represents the first quantitative attempt to support the presence of such smarts in Mesozoic dinosaurs. However, she is by no means the first or only researcher to have voiced such an opinion in recent years. Most relevant are perhaps the comments by Steve Brusatte who doubtlessly is one of the most sought-after palaeontologists working today and pays special attention to palaeoneurology in his work. That made it especially surprising when he infamously claimed that T. rex was “as smart as chimp” in 2018. This was a misconception resulting from the misreading of encephalization quotients, as he himself made clear later on. Frustratingly, he continues to publically advocate for exceptional cognition in T. rex without providing evidence for it. Earlier this year, he was quoted stating “some of today’s birds are extraordinarily intelligent, such as crows and parakeets. We can compare the intelligence of these birds with that of the tyrannosaurs”. Others are striking a similar cord: Yale professor Bhart-Anjan Bhullar, who also is well-versed regarding dinosaurian brain evolution made remarkable statements when being interviewed for Palaeocast in 2023: „The world becomes simpler and simpler as you get bigger. (…) The really big dinosaurs had a huge amount of cortical neuron tissue, thinking tissue, that was just sitting there.  (…) When you have all this excess brain matter you sit around and think about stuff “. Again, this clearly implies so far unappreciated cognitive capacities in Mesozoic dinosaurs, but Bhullar openly admitted that him believing in such cognitive feats largely comes from intuition rather than actual data. A compatible view was provided by neurologist Thomas Finger who, in a commentary on Herculano-Houzel’s paper, stated that the notion of monkey-like behaviors in T. rex, including tool use, would be in line with the fossil evidence …

By reiterating these takes I simply want to stress that exceptional cognition in dinosaurs does not seem to be a fringe opinion. Instead, I got the impression at times that we are facing the emergence of a baseless trope. This was, by the way, one of the greatest personal drivers for me to contribute to a formal response to Herculano-Houzel. Since dinosaur research is so intensively followed by the public eye, I feel that researchers engaged in it have a special responsibility to keep speculation (which obviously will always be part of our vision of extinct life) within reasonable bounds.

When being interviewed by a reporter about our paper, I was asked: “Why do people want T. rex to be so intelligent?”. I still wonder about that. Perhaps to make it even more “awesome” than it actually was so one can more easily justify a professional and/or emotional attachment to it – or rather, an attachment to the cultural projections that surround it?

To be the “baddest” predator, T. rex would need to be as smart as a crow or a monkey, because reptiles are simply, as Herculano-Houzel put it, “dumb”. This statement utterly dismisses the actual data: Cognition and behavior in these animals is far more sophisticated than even many biologists give them credit. Two very helpful reviews are Wilkinson & Huber (2012) and Font et al. (2023) which emphasize numerous parallels between reptilian and avian/mammalian cognition (but certainly not congruence, though). As David Attenborough put it in the opening to his mind-blowing series “Life in Cold Blood” (2008): “Reptiles (…] are sometimes thought of as primitive, dull, and dimwitted. In fact, of course, they can be lethally fast, spectacularly beautiful, surprisingly affectionate and very sophisticated.” What more do you want for your T. rex?

While our article defends the traditional view of reptile-grade intelligence in most dinosaurs (Maniraptoriformes, for instance, are obviously a different story), I want to emphasize that this does not mean that we can simply translate reptilian behavioral repertoires to them. A striking difference in ethology, for instance, would result from the high activity levels of dinosaurs that we find in no living non-avian reptile. In general, the story is obviously complicated and it’s not helpful to argue with terms such as “clever” and “dumb” which are imprecise and culturally charged. Retrospectively, I tend to think that we should have added a short paragraph on the current state of reptile cognition to emphasize its sophistication in our article …

A couple of years ago, I listened to an online talk by Paige Madison on the history of Neanderthal research and how the scientific and public opinion on cultural complexity in these fossil humans has changed over time. After the presentation, the question was raised if some contemporary takes on Neanderthal behavior might try to compensate for the scornful image they had for so long by exaggerating similarities to Homo sapiens. I wonder if we’re experiencing a related phenomenon with Mesozoic dinosaurs and ideas about their cognition right now. The important difference to outdated depictions of Neanderthals is, however, that reptile-grade cognition simply is not derogatory and only perceived as insulting because of the poor cultural reception of reptiles. Mesozoic dinosaurs don’t need to be saved from a problematic stigma. Statements from both Brusatte and Herculano-Houzel clearly indicate that they consider themselves on a mission to correct the public perception of dinosaurs, which they feel does not do them justice. Salon.com quotes Herculano-Houzel: ”I want to do right by dinosaurs, they do not deserve to go back to being considered as dumb as crocodiles.”

Maybe it’s not a misunderstanding of Mesozoic dinosaurs but one of crocodilians, squamates and turtles that needs to be fixed first – an urgent matter given they are still around and suffer from anthropogenic impacts in numerous ways. I’m convinced that the debate on this subject will continue and I hope that as more people are weighing in, they take their time engaging with the arguments instead of holding on to projections they might have.