Spinosauridae is an anomalous clade of long-snouted, large theropod dinosaurs with representative taxa and important specimens from the fossil records of Europe, Asia, Africa, and South America. They had long, crocodile-like jaws and cone-shaped teeth.

These adaptations helped them lead a somewhat aquatic lifestyle, stalking riverbanks in search of prey, including large fish. This way of life was very different from that of more well-known theropods, such as Allosaurus and Tyrannosaurus.

To better understand the evolution of spinosaur brains and senses, scientists from the University of Southampton and Ohio University have reconstructed the brains and inner ears of two British spinosaurs. To do this, they scanned fossils of Baryonyx from Surrey and Ceratosuchops from the Isle of Wight.

These two are the earliest spinosaurs for which brain material is known. 125 million years ago, the huge beasts would have strolled around the Earth. The brain shells of both specimens are in good condition, and the scientists used digital reconstruction to recreate the inner soft tissues that had long since decayed.

The olfactory bulbs, which process odors, were not well developed and the ear was probably tuned to low-frequency sounds, the experts said. The brain regions responsible for maintaining balance and a fixed gaze on prey may have been less developed than in later, more specialized Spinosaurus.

Baryonyx endocast and braincase
Three-dimensional reconstruction of the brain cavity and associated nerves and blood vessels in the braincase of the iconic British spinosaurid Baryonyx walkeri. Credits: WitmerLab/Chris_Barker

The University of Southampton Ph.D. student Chris Barker, who led the study, said: “Despite their unusual ecology, it appears that the brains and senses of these early spinosaurs share many aspects in common with other large-bodied theropods — there is no evidence that their semi-aquatic lifestyle is reflected in the way their brains are organized. .”

“One interpretation of this evidence is that the theropod ancestors of spinosaurs already possessed brains and sensory adaptations suitable for part-time fishing and that ‘all’ spinosaurs had to do to specialize for a semi-aquatic existence was to develop a unusual muzzle and teeth.”

Contributing author Dr. Darren Naish said: “Because the skulls of all spinosaurs are so specialized for catching fish, it is surprising to see such ‘non-specialised’ brains. But the results are still significant. It’s exciting to get so much information about sensory abilities – hearing, smell, balance, and so on – from British dinosaurs. Using advanced technology, we extracted all possible brain-related information from these fossils.”

Co-author Lawrence M. Witmer, professor of anatomy at Ohio University Heritage College of Osteopathic Medicine, said: “This new research is just the latest in what amounts to a revolution in paleontology due to advances in CT-based imaging of fossils. We are now able to assess the cognitive and sensory abilities of extinct animals and investigate how the brain evolved into behaviorally extreme dinosaurs like spinosaurs.”

Ceratosuchops endocast
Three-dimensional reconstruction of the brain cavity (purple), cranial nerves (yellow), inner ear (pink) and blood vessels (red and blue) of the British spinosaurid Ceratosuchops inferodios. This predator likely had an unusual sense of smell and could hear low-frequency sounds. Credit: Chris Barker

Dr. Neil Gostling, who leads the University of Southampton’s EvoPalaeoLab, said: “This new study highlights the important role British fossils play in our constantly evolving, rapidly changing understanding of dinosaurs, and shows how the UK – and the University of Southampton in particular – is at the forefront of spinosaur research. Spinosaurs are themselves a of the most controversial dinosaur groups and this study is a valuable addition to ongoing discussions about their biology and evolution.”

Magazine reference:

  1. Chris Tijani Barker et al. Modified skulls but conservative brains? The paleoneurology and endocranial anatomy of baryonychin dinosaurs (Theropoda: Spinosauridae). Diary of Anatomy. DOI: 10.1111/joa.13837