That Tyrannosaurus rex might have been as intelligent as a baboon was posited by a 2023 study that used bony braincases to infer dinosaur smarts. It was an incredible and intimidating concept for a predator, but one that’s now been rebutted by a paper that claims in truth, T. rex was more comparable to a “smart giant crocodile”.
A new study authored by an international team of 11 scientists took a magnifying glass to the methods used to predict the size and neuron count in dinosaur brains in the 2023 study from Herculano-Houzel. It found the methodology was unreliable, resulting in an incorrect estimation of neuron count and brain size, and shining a light on the complexity of endocast translation.
“An endocast is simply a cast of the inner cavity of the braincase,” explained study author Dr Kai Caspar to IFLScience. “It is therefore not equivalent to the brain itself. “
“The information provided by an endocast differs between groups of animals and depends on how faithfully it captures the shape of the brain. In birds and mammals, the fit is typically very good. In living reptiles and most extinct dinosaurs, the brain only fills a fraction of the skull cavity, so that the shape and size of the endocast differs substantially from that of the actual brain.”
A cast of a Tyrannosaurus rex braincase at the Australian Museum, Sydney.
Furthermore, it’s the authors’ view that neuron count alone isn’t enough data to work from when trying to infer the intelligence of an extinct animal. What evidence do you need to evaluate intelligence? We asked Caspar just that.
“Ideally, the extinct animal in question would have close living relatives to compare it, too – something that is unfortunately missing for dinosaurs such as T. rex. Furthermore, anatomical data on the size but especially the proportions of the brain and its components, which can be derived from endocasts would be desirable.”
I think it’s absolutely reasonable to imagine a dinosaur like T. rex as social with long-term bonds (as in, with family members and with reproductive partners).
Dr Darren Naish
“Then, evidence from fossil trackways or feeding traces might shed further light on specific behaviors and social habits. Frustratingly, however, we simply need to admit that a lot of information about how exactly extinct animals behaved is lost to us.”
The study presents revised estimates of encephalization (the development of large brain size relative to body size) and neuron counts in dinosaurs, using modeling informed by extant related species and an amended set of brain cavity measurements. These new estimates didn’t paint a picture of intelligence to match macaques and baboons as proposed in Herculano-Houzel’s work, instead being closer to a crocodile or lizard, which is still pretty incredible.
“One of the things we really tried to make clear in our results is that being ‘only’ as smart as a lizard or crocodile is no bad thing in view of what we currently understand about the intelligence and behaviour of those animals,” Dr Darren Naish told IFLScience.
“By combining what we know of modern reptile behaviour with inferences from the fossil record, I think it’s absolutely reasonable to imagine a dinosaur like T. rex as social with long-term bonds (as in, with family members and with reproductive partners), as a co-operative animal that would have worked with other individuals of its species when it was advantageous, as an explorative, sometimes inquisitive animal, as capable of play and counting, and as a creature with complex body language and vocalisation that it used in sending signals.”
T. rex lived at the end of the Late Cretaceous between 69 and 66 million years ago, and – regretfully – science hasn’t given us a real-life Jurassic Park just yet. Without it, we’re left with an incomplete fossil record to work from when trying to establish how extinct animals lived and behaved, so there’s bound to be some back and forth in our conclusions (just ask Spinosaurus). It’s all par for the course in palaeontology, and part of the joy of science, but as time goes by – and with close consideration of our methodology – there are plenty of new and remarkable discoveries on the horizon.
“Our knowledge of the geological past is woefully incomplete, but things are improving all the time as new information is gleaned and new analyses are run: even at this point in history there is, frankly, still so much work to do and so much that remains poorly known or under-studied,” added Naish.
“Our vision of the past is constantly becoming more complex, more vibrant. But it’s also important to remember that our view of the past is often biased, partly because we’re still relying on stereotypes about the past, or because we often can’t help but think that living things in the past were ‘less good’ than those of today.”
“We now have a reason to challenge that view, and, in fact, there’s quite a bit of data showing that extinct animals were often at least as capable of those of today, if not more so.”
So, chin up, T. rex. Who needs to be a brainy baboon when you can be a terrible lizard?
The study is published in The Anatomical Record.