How Big was a T. rex Brain?

Everything Dinosaur team members were sent a question by a young dinosaur fan who wanted to know how big was the brain of T. rex? We put our own brains trust to work on this intriguing question.

Having a large brain does not necessarily indicate intelligence, how that organ is configured, and its complexity can provide neuroscientists with an insight into the intelligence of organisms.

Ironically, a controversial study published earlier this year, postulated that Tyrannosaurus rex might have been as smart as a primate, it may have possessed a comparable number of brain cells to that of a monkey.

Picture credit: Everything Dinosaur

How Big was the Brain of T. rex?

CAT scans of theropod skulls have enabled palaeontologists to trace nerve pathways and to build up a picture of what some brains of dinosaurs might have looked like. The Tyrannosaurus rex fossil material known as Stan (BHI3033), has provided researchers with a detailed understanding of T. rex brain function. For example, fifty percent of the brain volume was dedicated to analysing smells. Hence the assertion that the sense of smell was extremely important to this carnivore.

As for brain size, estimates vary, but a recent paper published in the Journal of Comparative Neurology estimated the T. rex brain to have weighed around 350 grammes, and endowed this predator with considerable intelligence, putting the “King of the Tyrant Lizards” on a par with extant monkeys.

To read an article from 2013 that looks at research that indicated that dinosaurs had complex brains and postulated that they were capable of sophisticated behaviours similar to modern birds and mammals: Scientists Create a Detailed Map of a Dinosaur’s Brain.

Capable of Tool Use?

Author of the recently published paper, Dr Suzana Herculano-Houzel from the Department of Psychology at Vanderbilt University (Tennessee), postulates that Tyrannosaurus rex had approximately 3 billion cerebral neurons, a greater number than found in baboons.

The picture (above) shows an image of an articulated Tyrannosaurus rex from the Beasts of the Mesozoic range. To view this range of prehistoric animal figures: Beasts of the Mesozoic Models and Figures.

Using data on living birds and reptiles, Dr Herculano-Houzel inferred the number of neurons extinct creatures had based on calculations of brain mass, including many theropods such as Allosaurus, Archaeopteryx and T. rex.

Writing in the “Journal of Comparative Neurology”, a publication edited by Dr Herculano-Houzel, the doctor extrapolated how many brain cells T. rex possessed in its cerebrum (telencephalon), the most highly advanced part of the brain associated with higher cognitive functions.

Dr Herculano-Houzel postulates that Tyrannosaurus rex would have matured rapidly, lived to about forty years of age and was smart enough to use tools and to pass on acquired knowledge to offspring.

Controversial Ideas

Summarising her research, the doctor concludes:

“That theropods such as Tyrannosaurus and Allosaurus were endotherms with baboon and monkey-like numbers of telencephalic neurons, respectively, 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.”

As Clever as a Primate!

The paper has attracted scepticism from palaeontologists and other researchers. Gaining an understanding of the neuronal composition of the brains of dinosaurs would provide fundamental insights into their behavioural and cognitive capabilities.

However, brain tissue is rarely fossilised and to achieve her calculations Dr Herculano-Houzel assumed that the entire volume of the braincase was filled by brain tissue. This may not have been so. Perhaps, less than fifty percent of the braincase of T. rex was filled with brain tissue. Dinosaur brains could have been considerably smaller than the size postulated in the scientific paper.

In addition, how the brain is configured, its composition, if you like how it is “wired”, will have a significant impact on an organism’s intelligence.

Claiming that theropods such as Tyrannosaurus and Allosaurus were “the primates of their times”, is exceptionally difficult to substantiate in the absence of a living animal to study.

To read an article from October 2016 about the remarkable discovery of a preserved partial iguanodontid brain: Dinosaur Brain from Southern England.

Bird Brains

Assessing intelligence is challenging, even in living creatures. Pigeons for example, would perhaps not be regarded by many people as being particularly smart, but these avian dinosaurs are capable of remarkable feats of navigation. Many birds demonstrate advanced cognitive abilities such as corvids (crows and their relatives) using tools. Crows have much smaller brains than most monkeys, they have far fewer cerebral neurons but they can outperform some primates when it comes to cognitive assessment tasks.

Dr Herculano-Houzel argues that estimating neuron counts from brain mass is a method that has been applied to hundreds of mammal, bird, and non-avian dinosaur species, the methodology is robust.

However, claiming that T. rex was a smart as a monkey is quite a leap.

The Dinosaur Renaissance

A spokesperson from Everything Dinosaur commented:

“The research paper is free to access, so readers can make up their own minds. Whilst it is extremely challenging to try to work out how intelligent an extinct animal was, the days of regarding dinosaurs as creatures so stupid that they were an evolutionary dead end are long gone.”

The spokesperson added:

“Since the 1960s and the work of palaeontologist John Ostrom, the view of the Dinosauria has fundamentally changed. These animals were perfectly adapted to their environments and they were capable of complex behaviours just like mammals and their close relatives the birds. Just how smart T. rex was is difficult to quantify and validate with scientific evidence. Along with other theropods such as the dromaeosaurids and the oviraptorids these predators might have demonstrated very complex behaviours derived from their cognitive abilities.”

Unfortunately, as we are unlikely to ever observe a living non-avian dinosaur, assessments regarding dinosaur intelligence remain speculative.

How Big was the Brain of T. rex? Something to Ponder

However, the idea of a smart, 7 tonne carnivore measuring in excess of 12 metres long, it makes you think…

The scientific paper: “Theropod dinosaurs had primate-like numbers of telencephalic neurons” by Suzana Herculano-Houzel published in the Journal of Comparative Neurology.