A Triassic crown squamate

Mammals, birds, and squamates (lizards, snakes, and relatives) are key living vertebrates, and thus understanding their evolution underpins important questions in biodiversity science. Whereas the origins of mammals and birds are relatively well understood, the roots of squamates have been obscure. Here, we report a modern-type lizard from the Late Triassic of England [202 million years (Ma)], comprising a partial skeleton, skull, and mandibles. It displays at least 15 unique squamate traits and further shares unidentatan and anguimorph apomorphies. The new discovery fixes the origin of crown Squamata as much older than had been thought, and the revised dating shows substantial diversification of modern-type squamates following the Carnian Pluvial Episode, 232 Ma ago., The specimen is NHMUK PV R36822. We performed two scans, using the X-Tek XT H 225 ST micro-focus CT scanner (Nikon Metrology), with a micro-focus 225 kV source, which is fitted with a tungsten reflection target, and Perkin Elmer detector (XRD 1620 detector), belonging to the Palaeobiology Research Group, and located in the Life Science Building, University of Bristol. The scan settings for the left mandible and associated anterior portion of the articulated skeleton of NHMUK PV R36822 used 222 kVp, 153 μA, 500 ms exposure, and 3141 projections which were acquired by a full rotation of 360o using 4 frames per projection. A 17.5-μm reconstructed voxel resolution resulted from a source-to-object distance of 103 mm and source to detector distance of 1176 mm. There was no filtration of these scans other than the beryllium window. The scan settings for the associated skull of NHMUK PV R36822 used 200 kVp, 200 μA, 708 ms exposure, and 6,284 projections which were acquired by a full rotation of..., All 3D files are saved in .stl format, which can be viewed through many standard graphics programs, including Preview on Mac computers.