Endocranial anatomy of therizinosaurs and its implications for sensory and cognitive function
Therizinosaurs are an unusual group of theropod dinosaurs from the Cretaceous Period. Members of this group had evolved into up to 7 m large animals, equipped with more than 50 cm long, razor-sharp claws on the forelimbs, elongate necks and covered by a coat of primitive, down-like feathers along their bodies. Although closely related to notorious meat-eating dinosaurs such as Tyrannosaurus rex and Velociraptor, and in spite of their bizarre appearance, therizinosaurs were probably more peaceful plant-eaters.
Life and skeletal reconstruction of Erlikosaurus andrewsi, with magnified virtual models of the brain and inner ear
Inspired by this paradox, our team, consisting of Stephan Lautenschlager and Emily Rayfield from the University of Bristol, Perle Altangerel of the National University of Ulaanbaatar, Lindsay Zanno of the North Carolina Museum of Natural Sciences and North Carolina State University and Larry Witmer of Ohio University, took a first close look inside the heads of these enigmatic dinosaurs. By studying the brain and inner ear anatomy of three different therizinosaur taxa (Erlikosaurus andrewsi, Falcarius utahensis, Nothronychus mckinleyi), it was our aim to find out more about their sensory and cognitive capabilities and how these had evolved with the transition from carnivory to herbivory.
Fossil skull of the Cretaceous therizinosaur Erlikosaurus andrewsi
In the focus of the study was the skull of Erlikosaurus andrewsi – a 3-4 m large therizinosaur, which lived more than 90 million years ago during the Cretaceous Period in what is now Mongolia. As the actual brain tissue is no longer preserved in fossil skulls, we applied high-resolution CT-scanning and 3D rendering techniques to visualise the cavities in the skull, which were once occupied by the brain and the inner ear.
The endocranial anatomy of the three studied taxa reveals that the senses of smell, hearing and balance were well developed in therizinosaurs and might have affected or benefited from an enlarged forebrain. This is a bit of a surprise, as exceptional sensory abilities would be expected from predatory and not necessarily from plant-eating animals, but our results suggest that therizinosaurs would have used their well-developed sensory repertoire to their advantage. For herbivorous animals this means, their keen senses must have played an important role in foraging or, the evasion of predators or social complexity.
Link to the article (including supplementary information with 3D PDFs) published in PLoS ONE