How Did Spinosaurs Hunt? Study Revealing Brains Of The Oldest Of These Predators Gives Clues

Spinosaurs, or spined reptiles were an unusual group of theropod dinosaurs known for their "sail back" feature. Researchers have reconstructed the brains and inner ears of two British Spinosaurs.

Researchers from Southampton University in England and Ohio University in the United States have revealed the brains of the oldest Spinosaurs, providing clues to how the large predators interacted with the environment, including how they hunted their prey. The researchers used computed tomography (CT) scanning to reconstruct the brains and inner ears of two British Spinosaurs. 

The study describing the findings was recently published in the Journal of Anatomy. 

What are Spinosaurs?

Spinosaurs, or spined reptiles were an unusual group of theropod dinosaurs known for their "sail back" feature, created by tall vertebral spines. They were equipped with adaptations such as long, crocodile-like jaws and conical teeth, which helped them live an aquatic lifestyle wherein they stalked riverbanks in search of prey. Spinosaurs' prey included large fish. 

The way Spinosaurs led their lives was very different from that of other theropods such as Allosaurus and Tyrannosaurus. 

What are Allosaurs?

Allosaurs were large carnivorous dinosaurs that lived from 150 million to 144 million years ago during the Late Jurassic Period, grew to lengths of 10.5 metres, and had strong hind limbs. Half the body length of Allosaurs consisted of a well-developed tail, and the dinosaurs' skull was distinguished by a large roughened ridge just in front of the eye, according to Britannica. 

What are Tyrannosaurs?

Tyrannosaurs were predatory dinosaurs that lived from the late Jurassic Period to the end of the Cretaceous Period, which means they roamed the surface of Earth about 150 million to 65 million years ago. Tyrannosaurs mostly had very large skulls that often exceeded a full metre in length. The usual posture of Tyrannosaurs was horizontal, with their bodies being parallel to the ground, and their tails held off the ground as a counterbalance. 

What were the two Spinosaurs studied?

In order to better understand the evolution of the brains and senses of Spinosaurs, the researchers scanned fossils of Baryonyx from Surrey and Ceratosuchops from the Isle of Wight, the two oldest Spinosaurs for which braincase material is known. These creatures roamed the surface of Earth about 125 million years ago. 

According to the study, the braincases of both Baryonyx and Ceratosuchops are well preserved, and the researchers digitally reconstructed the internal soft tissues that had long rotted away. 

What were the olfactory bulbs and ears of the Spinosaurs like?

The olfactory bulbs, which process smells, were not particularly developed, the study found. The ears were probably attuned to low frequency sounds, according to the researchers. The parts of the brain of the two oldest Spinosaurs involved in keeping the head stable and gaze fixed on prey were possibly less developed than they were in later, more specialised Spinosaurs. 

In a statement released by Southampton University, Chris Barker, who led the study, said despite their unusual ecology, it seems the brains and senses of these early Spinosaurs retained many aspects in common with other large-bodied theropods. He added that there is no evidence that the semi-aquatic lifestyles of Spinosaurs are reflected in the way their brains are organised. 

Spinosaurs’ theropod ancestors already had adaptations suited to catching fish

Theropod ancestors of Spinosaurs already possessed brains and sensory adaptations suited for part-time fish catching, the authors noted in the paper. Therefore, the only thing Spinosaurs needed to do to become specialised for a semi-aquatic existence was evolve an unusual snout and teeth. 

Dr Darren Naish, one of the co-authors on the paper, said because the skulls of all Spinosaurs are so specialised for fish-catching, it is surprising to see such 'non-specialised' brains. He said, however, the results are still significant, and it is exciting to get so much information on sensory abilities such as hearing, sense of smell, and balance, from British dinosaurs. 

The researchers used cutting-edge technology to obtain as much brain-related information as possible from the fossils.

Where was the research conducted?

The EvoPalaeo Lab at the University of Southampton has conducted substantial research over the last few years on new Spinosaurs from the Isle of Wight. In 2021, the team itself announced Ceratosuchops. In 2022, the team published a study on another new Spinosaur — the gigantic White Rock Spinosaur. 

The researchers scanned the braincase of Ceratosuchops at the μ-Vis X-ray Imaging Centre at the University of Southampton. This is home to some of the most powerful CT scanners in England. A model of the brain of Ceratosuchops, alongside its bones, will be on display at Dinosaur Isle Museum in Sandown, on the Isle of Wight. 

Significance of the study

Lawrence M Witmer, one of the co-authors on the paper, said the new research is just the latest in what amounts to a revolution in palaeontology due to advances in CT-based imaging of fossils. Witmer belongs to the team who scanned Baryonyx. 

Witmer added that the team is now in a position to be able to assess the cognitive and sensory capabilities of extinct animals and explore how the brain evolved in behaviourally extreme dinosaurs like Spinosaurs. 

Dr Neil Gostling, who leads the University of Southampton's EvoPalaeoLab, said the new study highlights the significant role British fossils have in researchers' constantly evolving, fast-moving understanding of dinosaurs, and shows how the United Kingdom, and the University of Southampton in particular, is at the forefront of Spinosaur research. 

Gostling added that Spinosaurs themselves are one of the most controversial of all dinosaur groups, and the study is a valuable addition to ongoing discussions of their biology and evolution.