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Did Dinosaurs Have Two Brains? The Smartest Dinosaurs Listed!

Dinosaurs have long become extinct, and fossils were the only remains that link us to their existence. These fossils sparked human curiosity, which later led to paleontological works, with a few probing this human predecessor’s intelligence. Dinos were popular to have brains like walnuts, but scientists had discovered far more than that. One of the early mysteries considered was, if their brains were so small, did they have two? I remember this was one angle of thinking when I was younger (in the 1970s) and first learning about dinosaurs. When I learned about Stegosaurus, it was mentioned that perhaps they had a brain for the tail.


So, did dinosaurs have two brains? No, completely false. The two-brain theory was a mere myth. The existence of an enlarged neural canal near the hip region of huge dinosaurs like Stegosaurus was initially thought of as the second brain’s location, to control the motions of the tail. Paleontologists have found no proof for this claim.

The Stegosaurus, a notable member of the large dinosaurs, exhibits a unique anatomy. This distinctive physical structure has spurred fascinating debates in neurology, primarily concerning its brain structure. Within the span of the Cretaceous Period, scientists have tried to decipher this prehistoric creature’s brain size and functions.

The mystery of the dinosaur’s brain started unfolding with the discovery of a large cavity in its hip region. This led researchers down a path of intriguing hypotheses, surmising that this dinosaur, during the infamous Dinosaur era, might have a ‘second brain’. This unique neurology proposition significantly influenced the entire scientific discourse surrounding the biology and evolution of such gigantic creatures.

The contributions of Paleontologists in deciphering this mystery have been instrumental. Guided by fossils, the traces of prehistoric life, they have driven scientific investigations into the dinosaur’s neurology. These paleontological findings have thrown light on the likely functions of the supposed second brain, shifting the focus from cognitive functions to metabolic roles.

Through evolutionary biology studies, it’s now understood that this ‘second brain’ might not be a center of cognition. Instead, it could have served as a location for storing glycogen, aiding the functioning of the dinosaur’s nervous system.

Even though the two-brain theory has been largely debunked, the exploration process has enriched our understanding of complex creatures from the prehistoric era. It has blended elements of anatomy, biology, evolutionary study, and paleontology, and remains a significant part of our ongoing quest to unravel the mysteries of life’s past epochs.

The two-brain issue will be discussed in detail to prove otherwise. The brain sizes of dinosaurs and their correlation to intelligence will also be examined as dinosaur traits and movements can be inferred from this relationship.

Dinosaurs Had Only One Brain – Why This Is So And Some Interesting Facts

Paleontologists now know for certain that dinosaurs had only one brain. It is interesting, though, how this fact evolved from a double brain tale, citing a relevant work that suggested a butt brain’s existence. Here are the details of this fascinating two brain myth.

Origin Of The Butt Brain Myth

The double brain issue originated from the work of the 19th-century Yale paleontologist Othniel Charles Marsh. In Marsh’s assessment of the sauropod Camarasaurus, the canal located in the vertebrae just above the dinosaur’s hips enlarged and expanded as it went down the bottom rear section. 

It was the most suggestive fact of a butt brain with a 20 times larger space than that of the brain cavity.

In 1881, a similar expansion in the neural canal or that bony tube housing the spinal cord of the Stegosaurus was called by Marsh as a posterior braincase. Despite the 5 to 10 ton size of the Stegosaurus, its brain was said to be a little bigger than a walnut. 

This conclusion further theorized that the large, hollow space near the spine’s hip region must have contained the second brain. (Source)

This theory was later on adopted and subjected to further investigation by other scientists. For one, dinosaur brain expert Emily Buchholtz outlined this theory in her book “The Complete Dinosaur.”

What The Second Brain Was Believed To Do

Sauropods and Stegosaurus were the perfect candidates for the butt brain theory due to their stature. Being huge, these species accordingly had second brains, which were believed to have helped coordinate their back legs and tails. Their butt brains might have sped up signals from the back half of their bodies and aided in reflex control.

The hindbrain could have also protected a Stegosaurus from predator threats by giving it a temporary boost. The sacral brain space was discovered to be similar to a hollow feature in birds. 

This so-called glycogen body in a bird was likewise found in the hip and was without any brain-like function. Its use or purpose remains unclear up to this day.

By this evidence found in birds, it was concluded that dinosaurs did not have butt brains. The supposed braincase space wasn’t functional in any way. The large cavity in the hips of species like Stegosaurus and Sauropods, however, remains puzzling as to its purpose. 

Which Dinosaur Had The Largest Brain? About Dinosaur Brain Sizes

Once regarded as idiotic creatures, dinosaurs had been said to possess very small brains. Brain size, however, differs among dinosaur species according to studies. A comparison of estimated brain sizes among a few species will clarify this better.

Brain Size Estimation and Use Of Encephalization Quotient (EQ)

Brain size is said to be positively correlated to the body size of animals as brain size usually increases with body size. For instance, smaller animals do have smaller brains compared to large ones. 

In dinosaurs, EQ is applied by estimating the brain size as a certain volume of the endocast. An endocast is an internal cast of the cranial vault made for brain study.

Hans Larsson noted that no valid approach in this estimation technique could be derived from a set ratio because of the transition history from reptiles to birds. Birds were said to have descended from theropod dinosaurs, a theory championed by John Ostrom in the 1960s. 

EQ is also the ratio of the animal’s brain weight to a “typical” animal given the same body weight. The spinal cord of theropods also typically ran from the brain along the spine of the dinosaur. (Source

Estimated Brain Sizes Of Some Species

Tyrannosaurus Rex

Called the tyrant lizard king, T. Rex was a meat-eating dinosaur measured up to 40 feet long, about 15 to 20 feet tall, and around 5 to 7 tons in weight. T. Rex is considered the biggest brained dinosaur of all species. 

In some cases, the T. Rex brain is 2-3 times larger than other comparable dinosaurs. It lived during the Cretaceous period and was a fierce predator.

T.rex’s brain is much bigger than the human brain, but the cerebrum, or that part used for thinking, was amazingly tiny. Cerebrum volume is more of avian proportion. Its brain is long and shaped like a cylinder. (Source


Human-sized and having the largest brain in proportion to body weight, Troodon is a theropod. It was believed to have measured up to 11.5 feet long and might have weighed about 110 pounds or 50 kilograms. 

The cerebrum-to-brain-volume ratio was estimated at 31.5% of a nonavian reptile and 63% of the avian segment. This nonavian reptile comparison was due to the common ancestor of dinosaurs and crocodiles. 

On the other hand, modern birds evolved from the feathered dinosaur group, the lone survivor during the massive dinosaur extinction 65 million years ago. Hence, the cerebrum does the thinking function, directly affecting a dinosaur’s intelligence and measured.

Allosaurus fragilis

This Allosaurus species is a large meat-eating dinosaur and the biggest in North America during the late Jurassic period. Its name means “different lizard.” It lived as a powerful predator and was up to 38 feet long, 16.5 feet tall, and about 1,400 kilograms. 

The brain volume was said to resemble that of Carcharondontosaurus saharicus, and its brain shape is similar to the modern-day crocodile.

Carcharondontosaurus saharicus

A description of its endocranium was published in 2001 by Hans Larsson. Known as the shark-tooth lizard, it measured the utmost 44 feet long and weighed up to 8 tons, much larger than the Tyrannosaurus Rex. Its skull was as big as a human’s, but the brain is smaller than that of the T. Rex.

The size ratio between the brain and the cerebrum was more like a traditional reptile than that of a bird.


Dinosaur – Brain Size – Comparable To

What Is The Most Intelligent Dinosaur? How Smart Was a Velociraptor Or a T. Rex?

Brain size is undoubtedly a factor in the intelligence of dinosaur species. Intelligence is measured by the Encephalization Quotient ratios but is prevalent in these creatures’ behavior and locomotion.

Related Dinosaur Articles You Might Also Be Interested In:
Would A T-Rex Really Shake The Ground?
The 13 Best-Known, Most-Loved Dinosaurs and Why
What Are Long Neck Dinosaurs (Types, Size, List)?

EQ As An Intelligence Measure

EQ results from J.A Hobson’s work in 1980 showed how intelligence varied among reptiles and dinosaurs. The least intelligent were the Sauropodomorphas, Sauropods like the Brontosaurus or Apatosaurus, and Ankylosaurs. 

Mid-range were the Stegosaurus, Ceratopsians, Ornithopods, Crocodiles, and Carnosaurs. Based on the figures, Dromaeosaurids and Troodontids were the smartest. 

Most Intelligent Dinosaurs


As smart as modern birds, Troodon was the smartest dinosaur in history. Its intelligence sets it apart in terms of traits and movements. Dubbed as the wounding tooth, Troodon’s tooth had serrated edges that helped its activities as a carnivore. 

Troodon was a lightweight dinosaur, with two bird-like legs that made it a fast runner. It had large eyes and may have had a good sense of hearing. It also possessed three long-clawed fingers that were ideal for grasping its prey. It also lived during the Cretaceous period.


A kind of Dromaeosaurid, the Deinonychus, was among the smartest dinosaurs based on the EQ ratio and were very deadly predators. They might have hunted in packs and attacked even larger animals. 

The Deinonychus are also known for their terrible claws and sharp, serrated teeth. With a relatively large brain and large, keen eyes, the Deinonychus are indeed built to kill. 


The name Compsognathus means pretty jaw, and this dinosaur looks like a bird. Its long tail acted as a counterbalance and was used for stability during fast turns. It walked on two long, slender legs and was a fast, agile dinosaur.

Tyrannosaurus Rex

T. Rex was a fierce predator that walked on two powerful legs. The large visual lobes in its brain gave it the ability to process visual cues. Its brain also had a uniquely large area for processing odors, which helped seek its prey.

With eyes facing forward and fronting its skull, the T. Rex as a predator had depth perception that helped hunt prey. 

Dinosaurs that were hunted (like the plant-eating herbivores) normally had eyes placed on the sides of their heads, the exact opposite of the T. Rex. Its tail also served as a counterbalance for its enormous head.


Dubbed as the egg robber, the Oviraptor was a small, bird-like dinosaur. It had a short, toothless beak with a very powerful jaw for crushing. It was a relatively large-brained dino that knew how to care for its eggs. The Oviraptor was a fast runner given its long legs, was lightweight, and more similar to an ostrich.


Velociraptor’s name means “speedy thief” as it was a fast-running two-legged dinosaur that reached roughly 40 mph or 60 km/hr for short bursts. It was among the fastest in the dinosaur world and could probably jump. 

As it was a Dromaeosaurid, the Velociraptor’s stiff tail worked as a counterbalance and enabled quick turns. Velociraptors were deadly predators and might have hunted in packs, perhaps attacking very large animals. (Source)


Despite their disappearance centuries ago, dinosaurs and their way of life had always been interesting. Ironic as it may seem, their enormous stature depended on fragile, little brains for survival. 

It is so intriguing that the double brain tale became a popular story. While a dinosaur’s intelligence could not be compared to modern-day contemporaries, it holds the missing link to the ancient Mesozoic era. It’s significant in the continuing quest for truth and knowledge. After all, this world couldn’t be much better without them.