Several new specimens of the Triassic therocephalian Tetracynodon darti have become available in recent years, allowing substantial corrections and expansions to previous descriptions. We here analyze T. darti in the context of therocephalian relationships and biology, using computed tomographic (CT) scanning to reveal details of the skull. Histological sections, as well as the degree of ossification of individual elements, both suggest that the available specimens are subadults (rather than rapidly growing neonates), and probably yearlings. A maxillary shelf bearing a long suture with the vomer similar to that of Lycideops is present, and T. darti also shares a nasal-lacrimal contact with that taxon. There is no evidence for the presence of maxilloturbinal bones. The postcranial skeleton is slender and similar to that of regisaurids and other small baurioids. The skull bones show clear indentations demarcating the major divisions of the brain, allowing one of the most detailed reconstructions of a non-mammalian therapsid brain published to date. The brain is strikingly plesiomorphic in many features, particularly in the retention of large dorsally positioned optic lobes of the tectum, but generally shows features that are intermediate between gorgonopsians and cynodonts, thus clarifying this stage of the evolution of the synapsid brain. A cladistic analysis of 33 therapsid taxa and 131 morphological characters supports the monophyly of Therocephalia, and there is evidence for a monophyletic Lycideopidae within Baurioidea. Lycideopidae contains species with long snouts, nasal-lacrimal contacts, and incipient secondary palates, including Lycideops, Choerosaurus, T. tenuis, and T. darti.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.