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The nasal cavity of living mammals is a unique structural complex among tetrapods, acquired along a series of major morphological transformations that occurred mainly during the Mesozoic Era, within the Synapsida clade. Particularly, non-mammaliaform cynodonts document several morphological changes in the skull, during the Triassic Period, that represent the first steps of the mammalian bauplan. We here explore the nasal cavity of five cynodont taxa, namely Thrinaxodon, Chiniquodon, Prozostrodon, Riograndia, and Brasilodon, in order to discuss the main changes within this skull region. We did not identify ossified turbinals in the nasal cavity of these taxa and if present, as non-ossified structures, they would not necessarily be associated with temperature control or the development of endothermy. We do, however, notice a complexification of the cartilage anchoring structures that divide the nasal cavity and separate it from the brain region in these forerunners of mammals. [ABSTRACT FROM AUTHOR]

The colonization of deserts by tetrapods occurred for the first time in the late Paleozoic. In spite of amniotes being the most abundant and diverse taxon in such environments, fossil tracks indicate that anamniotes also inhabited late Paleozoic deserts. In this paper, the presence of the tetrapod-footprint ichnotaxa Ichniotherium sphaerodactylum and cf. Ichniotherium is documented in the eolian Coconino Sandstone (early Permian), based on 16 trackways found at several localities in Arizona, USA. Because there is a strong association between Ichniotherium and different species of diadectomorphs, we also discuss some aspects of the ichnotaxonomy of this ichnogenus. Diadectomorpha is considered the sister taxon of Amniota and, as a consequence, the tracks described in this paper represent the oldest evidence of occupation of deserts by non-amniote tetrapods. The presence of Ichniotherium in this environmental context also sheds light on the paleobiology of Diadectomorpha and, as a result, the emergence of features typically related to Amniota. The ichnofauna of the Coconino Sandstone has been used as a model for the Chelichnus ichnofacies, which supposedly indicates a low-diversity desert fauna. On the other hand, the tracks described here demonstrate that diadectomorphs were also important faunal components of such deserts and suggests that the significance of this ichnofacies should be reconsidered. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

The early evolution of lepidosaurs is marked by an extremely scarce fossil record during the Triassic. Importantly, most Triassic lepidosaur specimens are represented by disarticulated individuals from high energy accretion deposits in Laurasia, thus greatly hampering our understanding of the initial stages of lepidosaur evolution. Here, we describe the fragmentary remains of an associated skull and mandible of Clevosaurus hadroprodon sp. nov., a new taxon of sphenodontian lepidosaur from the Late Triassic (Carnian; 237–228 Mya) of Brazil. Referral to Sphenodontia is supported by the combined presence of a marginal dentition ankylosed to the apex of the dentary, maxilla, and premaxilla; the presence of 'secondary bone' at the bases of the marginal dentition; and a ventrally directed mental process at the symphysis of the dentary. Our phylogenetic analyses recover Clevosaurus hadroprodon as a clevosaurid, either in a polytomy with the Late Triassic to Early Jurassic Clevosaurus and Brachyrhinodon (under Bayesian inference), or nested among different species of Clevosaurus (under maximum parsimony). Clevosaurus hadroprodon represents the oldest known sphenodontian from Gondwana, and its clevosaurid relationships indicates that these sphenodontians achieved a widespread biogeographic distribution much earlier than previously thought. [ABSTRACT FROM AUTHOR]