The end-Devonian to mid-Mississippian time interval has long been known for its depauperate palaeontological record, especially for tetrapods. This interval encapsulates the time of increasing terrestriality among tetrapods, but only two Tournaisian localities previously produced tetrapod fossils. Here we describe five new Tournaisian tetrapods (Perittodus apsconditus, Koilops herma, Ossirarus kierani, Diploradus austiumensis and Aytonerpeton microps) from two localities in their environmental context. A phylogenetic analysis retrieved three taxa as stem tetrapods, interspersed among Devonian and Carboniferous forms, and two as stem amphibians, suggesting a deep split among crown tetrapods. We also illustrate new tetrapod specimens from these and additional localities in the Scottish Borders region. The new taxa and specimens suggest that tetrapod diversification was well established by the Tournaisian. Sedimentary evidence indicates that the tetrapod fossils are usually associated with sandy siltstones overlying wetland palaeosols. Tetrapods were probably living on vegetated surfaces that were subsequently flooded. We show that atmospheric oxygen levels were stable across the Devonian/Carboniferous boundary, and did not inhibit the evolution of terrestriality. This wealth of tetrapods from Tournaisian localities highlights the potential for discoveries elsewhere.

The Post Quarry, within the lower part of the type section of the Upper Triassic Cooper Canyon Formation in southern Garza County, western Texas, contains a remarkably diverse vertebrate assemblage. The Post Quarry has produced: the small temnospondylRileymillerus cosgriffi; the metoposauridApachesaurus gregorii; possible dicynodonts and eucynodonts; a clevosaurid sphenodontian; non-archosauriform archosauromorphs (Trilophosaurus dornorum, simiosaurians, and possiblyMalerisaurus); the phytosaurLeptosuchus; several aetosaurs (Calyptosuchus wellesi,Typothorax coccinarum,Paratypothorax, andDesmatosuchus smalli); the poposauroidShuvosaurus inexpectatus(“Chatterjeea elegans”); the rauisuchidPostosuchus kirkpatricki; an early crocodylomorph; several dinosauromorphs (the lagerpetidDromomeron gregorii, the silesauridTechnosaurus smalli, a herrerasaurid, and an early neotheropod); and several enigmatic small diapsids. Revised lithostratigraphic correlations of the lower Cooper Canyon Formation with the Tecovas Formation, the occurrence ofLeptosuchus, and the overall composition of the assemblage indicate that the Post Quarry falls within the Adamanian biozone, and not the Revueltian biozone. Stratigraphic subdivision of the Adamanian biozone may be possible, and the Post Quarry may be correlative with the upper part of the Adamanian biozone in Arizona. The age of the Post Quarry assemblage is possibly late Lacian or earliest Alaunian (late early Norian or earliest middle Norian), between 220 and 215 Ma.

The sphenodontid genus Clevosaurus from the late Triassic of south west Britain is represented by at least two different species. Exceptionally abundant remains of Clevosaurus occur as part of a diverse assemblage of microvertebrates lodged within fissure deposits at localities in Glamorgan and Avon. Although the majority of specimens occur as beautifully preserved disassociated elements, certain associated and articulated remains have been recovered. Contemporaneous vertebrates include other sphenodontians, archosaurs and procolophonids. C. hudsoni is fully restored as a lizard-like reptile approximately 25 cm long. It was essentially insectivorous, although it may have also been facultatively herbivorous, breaking down food with a well-developed precision shear bite. A smaller species, C. minor , is less widespread and its remains are generally not as well preserved. It seems probable that a third species might be distinguished on the basis of dental characteristics, and the occurrence of a fourth species cannot be discounted. A distinct suite of apomorphic characters separates the Sphenodontida from other lepidosauromorphs and these apomorphies are readily identifiable in Clevosaurus . In certain late Triassic sphenodontians the lower temporal arcade was apparently incomplete, but, contrary to Robinson’s ( J. geol. Soc. Lond . 129, 457 (1973)) description, the lower temporal arcade was unbroken in Clevosaurus . However, the articulation between the jugal, squamosal and quadratojugal does not conform to the configuration exhibited by all other sphenodontians in which both temporal arcades are complete. In addition, the possession of a supratemporal in Clevosaurus is unique among known sphenodontians. The parietal table in Clevosaurus is intermediate between the broad, flat plesiomorphic condition, seen in forms such as Polysphenodon and Homoeosaurus , and the derived narrow median ridge displayed by Kallimodon and Sphenodon . Consequently, within the Sphenodontida the position of Clevosaurus is unclear; however, on the basis of the prominently flanged additional teeth, some reduction in tooth numbers and at least some partial reduction in the width of the parietal table, it would appear to share certain characteristics with Sapheosaurus and Kallimodon. Palaeopleurosaurus , described by Carroll (1985) as a primitive pleurosaur, may also have affinities with this grouping. Some of the earliest sphenodontians, such as Planocephalosaurus and Diphydontosaurus , exhibit fusion of the median skull roofing elements, a short temporal region and retention of a variable degree of pleurodonty in the marginal dentition. Together with Gephyrosaurus these genera may constitute a monophyletic assemblage forming the sister group of all other sphenodontians.

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Two Triassic sphenodontid reptiles, Brachyrhinodon taylori and Polysphenodon mulleri, are redescribed. Both genera are blunt-snouted forms but, as a result of distortion in the original fossils, the degree to which the snouts are shortened has previously been over-elaborated. An elongate temporal region and an interorbital width exceeding that of the parietal table are both derived characters in sphenodontids. Po!vsphenodon is plesiomorphic for both conditions, whereas Brachyrhinodon displays the derived states. Therefore, it is assumed that the reduced snout has been independently derived in each genus. The limb elements of Polysphenodon are long relative to the size of the skull and are similar in proportions to some species of Homoeosaurus. This resemblance is considered to be indicative of similar locomotory requirements rather than close evolutionary relationships. Ciadograms showing possible interrelationships within the Sphenodontida are based on twenty-nine character states.

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Atoposaurids were a clade of semiaquatic crocodyliforms known from the Late Jurassic to the latest Cretaceous. Tentative remains from Europe, Morocco, and Madagascar may extend their range into the Middle Jurassic. Here we report the first unambiguous Middle Jurassic (late Bajocian-Bathonian) atoposaurid: an anterior dentary from the Isle of Skye, Scotland, UK. A comprehensive review of atoposaurid specimens demonstrates that this dentary can be referred to Theriosuchus based on several derived characters, and differs from the five previously recognized species within this genus. Despite several diagnostic features, we conservatively refer it to Theriosuchus sp., pending the discovery of more complete material. As the oldest known definitively diagnostic atoposaurid, this discovery indicates that the oldest members of this group were small-bodied, had heterodont dentition, and were most likely widespread components of European faunas. Our review of mandibular and dental features in atoposaurids not only allows us to present a revised diagnosis of Theriosuchus, but also reveals a great amount of variability within this genus, and indicates that there are currently five valid species that can be differentiated by unique combinations of dental characteristics. This variability can be included in future broad-scale cladistics analyses of atoposaurids and closely related crocodyliforms, which promise to help untangle the complicated taxonomy and evolutionary history of Atoposauridae.

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