Oldest spinosaur brains revealed

Researchers from the University of Southampton and Ohio University have reconstructed the brains and inner ears of two British spinosaurs, helping uncover how these large predatory dinosaurs interacted with their environment.

Spinosaurs are an unusual group of theropod dinosaurs, equipped with long, crocodile-like jaws and conical teeth. These adaptations helped them live a somewhat-aquatic lifestyle that involved stalking riverbanks in quest of prey, among which were large fish. This way of life was very different from that of more familiar theropods, like Allosaurus and Tyran-nosaurus.

To better understand the evolution of spinosaur brains and senses, the team scanned fossils of Baryonyx from Surrey and Ceratosuchops from the Isle of Wight. These two are the oldest spinosaurs for which braincase material is known. The huge creatures would have been roaming the planet about 125 million years ago years ago. The braincases of both spec-imens are well preserved, and the team digitally reconstructed the internal soft tissues that had long rotted away.

The researchers found the olfactory bulbs, which process smells, weren’t particularly developed, and the ear was proba-bly attuned to low frequency sounds. Those parts of the brain involved in keeping the head stable and the gaze fixed on prey were possibly less developed than they were in later, more specialised spinosaurs.

“Despite their unusual ecology, it seems the brains and senses of these early spinosaurs retained many aspects in com-mon with other large-bodied theropods -- there is no evidence that their semi-aquatic lifestyles are reflected in the way their brains are organised,” said University of Southampton PhD student Chris Barker, who led the study.

One interpretation of this evidence is that the theropod ancestors of spinosaurs already possessed brains and sensory adaptations suited for part-time fish catching, and that ‘all’ spinosaurs needed to do to become specialised for a semi-aquatic existence was evolve an unusual snout and teeth.

“Because the skulls of all spinosaurs are so specialised for fish-catching, it’s surprising to see such ‘non-specialised’ brains,” said contributing author Dr Darren Naish. “But the results are still significant. It’s exciting to get so much infor-mation on sensory abilities -- on hearing, sense of smell, balance and so on -- from British dinosaurs. Using cutting-edged technology, we basically obtained all the brain-related information we possibly could from these fossils,” Dr Naish said.

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