The laterosphenoid bone of early archosauriforms

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Abstract
The laterosphenoid is an ossification of the pila antotica neurocranial cartilage in the anterior sidewall of the braincase of crocodylians and birds. Contrary to published reports, the bone is present in the basal archosauriforms Proterosuchus fergusi, Euparkeria capensis, and Erythrosuchidae, taxa that diverged prior to the origin of the archosaurian crown group. Its presence is thus a synapomorphy of Archosauriformes rather than of Archosauria. The bone appears to have been induced by shifting jaw muscle origins from the skull roof to the anterolateral wall of the braincase. Additional innovations in the archosauriform feeding apparatus, such as a mandibular fenestra, appear to reflect changes in jaw muscles that may, in turn, facilitate predaceous habits. We review the historical development of the names of bones in the anterior sidewall of the amniote braincase and argue for the use of the term laterosphenoid, rather than either pleurosphenoid or orbitosphenoid, for this bone in all Archosauriformes.

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