Endocranial anatomy of Allosaurus supports neural trends among non-avian theropod dinosaurs

Abstract

ABSTRACT Endocranial cavities preserve a record of neural anatomy often used for hypotheses of behavior in extinct organisms. Two reconstructions of cranial endocasts of Allosaurus fragilis and A. jimmadseni from computed tomography data expand understanding of theropod endocranial anatomy including endocranial volume, inner ear shape, and trigeminal ganglion size. Endocranial and trigeminal ganglion volumes are compared with a sample of birds, crocodylians, and non-avian theropod dinosaurs. Allosaurus is found to have a relatively small trigeminal foramen for its body size when compared with foramina of birds and crocodylians. The inner ear is fragmentary but similar in shape to semicircular canals of other large-bodied theropod dinosaurs. These findings suggest Allosaurus had generalist neural structures relative to other non-avian theropod dinosaurs. Like other large-bodied theropod dinosaurs, Allosaurus likely had a large dural venous sinus, potentially important for brain cooling. Allosaurus did not have a derived sense of facial somatosensation akin to that found in crocodylians or some birds. Additional data like these, collected from other tetanuran dinosaurs, will help clarify the evolution of neurosensory systems in the lineage.