The crocodile’s brain has remained virtually unchanged for 100 million years

Scientists used computed tomography to look inside the skulls of modern crocodiles, alligators, caimans and gavials, as well as their extinct relatives.

The study has been published in the Journal of Anatomy.

The main conclusion is not that crocodiles ‘have not evolved’. They have evolved — and in a great variety of ways. But the internal anatomy of the skull, relating to the brain, the inner ear and sensory structures, turned out to be much more stable than might have been expected.

What exactly did the scientists study?

The brains of ancient crocodiles are almost never preserved on their own. Therefore, rather than studying soft tissue, the researchers examined the endocranial anatomy — the internal shape of the skull where the brain, nerves, blood vessels and balance organs were located.

To do this, they use CT scanning. This allows them to visualise hidden cavities and channels inside the skull without damaging the rare fossils. The study’s abstract emphasises that the application of computed tomography to vertebrate skulls has revealed a wealth of previously hidden information about their endocranial anatomy.

Put simply, the scientists have created digital ‘casts’ of the inside of the skulls. This makes it possible to understand the shape of the cranial cavity, the positioning of the inner ear and other structures, and to compare modern crocodiles with their ancient counterparts.

Why crocodiles are not as ‘simple’ as they seem

Today, crocodiles, alligators, caimans and gavials are mainly associated with the tropics, rivers, swamps and ambush hunting near water. But their evolutionary history was far richer.

Crocodilians — a group comprising modern crocodiles and their extinct relatives — have a fossil record stretching back more than 200 million years. The extinct forms were not merely semi-aquatic predators: they included marine, terrestrial and other ecologically diverse species. Their skulls and lifestyles differed far more significantly than those of modern crocodiles.

This is precisely why the findings of this new study are so interesting: whilst crocodiles and their relatives may have differed greatly in appearance, many features within the skull remained conservative.

The brain remained almost unchanged, whilst the skulls evolved

One of the main mysteries of crocodilian evolution is their long, narrow snouts. This shape emerged independently several times throughout the group’s history. This is known as convergent evolution: different lineages arrive at a similar external solution because they face similar challenges.

Because of this, it can be difficult for palaeontologists to determine which ancient long-snouted crocodiles are actually close relatives, and which are simply similar in appearance. The abstract of the new study explicitly notes that in some cases it is difficult to determine which long-snouted lineage an extinct species belongs to, particularly in relation to the gavialoids.

CT scans help to resolve this problem. The internal anatomy of the skull may retain signs of kinship where external form is misleading. If two ancient crocodiles have similar snouts but differ in the internal structure of their skulls, this may mean that they evolved similar forms independently.

Why is this called ‘evolutionary stability’?

Scientists have discovered that many features of the brain and inner ear in crocodiles have not changed radically. This is not a sign of ‘backwardness’. Rather, it is an example of a successful evolutionary design.

If an organism is well adapted to its niche, evolution does not need to rebuild everything from scratch every time. Crocodiles may have changed in size, snout shape, habitat and hunting methods, but the basic internal architecture of their heads remained effective.

This is precisely why crocodiles are often regarded as ‘living fossils’, although this expression dangerously oversimplifies the picture. It would be more accurate to say that whilst their external and ecological history has been diverse, certain internal structures of the skull have proved remarkably stable.

What this means for science

This research is important not only because it sheds light on the crocodilian brain. It also helps to refine the evolutionary tree of extinct species.

If a palaeontologist has a fragmented skull of an ancient crocodile, external features may not be sufficient. But a CT scan allows us to see the cranial cavity, the inner ear, nerve canals and sinuses. These features can be used as additional ‘clues’ to understand which group the animal belonged to.

Similar methods are already being applied to other ancient crocodilians. For example, a study of the Early Cretaceous Pholidosaurus purbeckensis also utilised CT data and showed that the shape of the olfactory tract and brain may reflect not only ecology but also phylogenetic relationships.

Why this is important for understanding the survival of crocodiles

Crocodiles survived catastrophes that wiped out many other groups of animals. But their success is not necessarily down to the fact that they ‘did not change’. On the contrary, fossil crocodilians were highly diverse.

Studies of macroevolution show that ancient crocodilians rapidly colonised different ecological niches, and the diversity of their skull and jaw shapes was particularly great during the Mesozoic. These included the marine talattozuchii and the terrestrial notozuchii, which developed specialised skull and jaw structures.

Against this backdrop, the stability of the brain appears even more intriguing. Evolution may have experimented with the body, snout and lifestyle, but it did not significantly alter the underlying neuroanatomical framework.

In simple terms

Crocodiles did not ‘freeze’ in their evolution. They changed, spread, went extinct, and new forms emerged.

But if we look not at the teeth and snout, but deep inside the skull, the picture is different: the cranial cavity and its associated structures have remained similar in many crocodiles over an immense period of time.

It’s like an old but reliable engineering design: the outer shell can be adapted for different tasks, but the internal system remains almost the same because it works well.

Background

Modern crocodiles are just a small part of a vast ancient group. Their relatives appeared long before the end of the age of the dinosaurs, survived mass extinctions and occupied various ecological niches.

This is why the new CT scans are particularly important: they reveal not only the external shape of the skull, but also hidden structures that help us understand the relationships, lifestyle and evolutionary resilience of these animals.

Source

Study: Paul M. J. Burke, Philip Mannion — “Computed tomography reveals the endocranial anatomy of Crocodylia: Implications for phylogenetic relationships and ecomorphological convergence across Crocodylomorpha”, Journal of Anatomy, 2026.