Parareptilia (Olson 1947) • An extinct group among basal amniotes • Upper Pennsylvanian to Upper Triassic • Do not have a temporal fenestra and have been called Anapsida (Williston 1917) when the taxon included the turtles.
Parareptilia (Olson 1947) These varied from small aquatic to large terrestrial forms Procolophon, broad and flattened burrowing animals from the upper Permian to the Triassic. Image by Arthur Weasley, Wikipedia Mesosaurus, a small aquatic animal. Scutosaurus, a pareisaur, once thought to be the group from which the turtles emerged. Image by Nobu Tamura Image by Arthur Weasley, Wikipedia
Class Eodiapsida • These are the basal diapsids and include 2 very different groups: • Younginomorpha (Pennsylvanian to Lower Triassic) • Ichthyosauromorpha (Mid Triassic to Mid Cretaceous) ? The relationship between the two groups that are merged here to create the Eodiapsida, a sister group to the Lepidosauromorpha and Archosauromorpha. In general, this figure is based on Benton (2005) and shows the relationship between this group and the other higher taxa of gnathostomes.
Rhynchosaurs, beaked archosaurs Protorosaurus, a long-necked rhynchosaur from the upper Permian. Hyperodapedon, a strange basal Archosauromorph that was a herbivore. Notable adaptations included a distinctive narrow beak, specialized cheek teeth, and hind claws adapted to digging.
The Dinosaurian Clade • longer hind legs than front legs • the skeleton and musculature of the hind legs that causes them to be underneath the body rather than splayed, including the distinct offset head an ball of the femur • a reduction of the digits in the manus and pes (usually to 3 or 4) • an acetabulum, hip joint, that has a hole in the center • a sacrum of at least 3 fused vertebrae • a reduced fibula • a crest that runs much of the way down the humerus for the attachment of the deltoid and pectoral muscles Weishampel et al. (1990), Soreno (1999), and Benton (2005)
Brusatte, S.L., S.J. Nesbitt, R.B. Irmis, R.J.Butler, M.J. Benton, and M.A. Norell. 2010. The origin and early radiation of dinosaurs. Earth-Science Reviews 101(1-2): 68-100. Fig. 2. A cladogram of the major groups of archosaurs. Archosauria is divided into two major groups, the crocodile line (Crurotarsi) and the bird line (Avemetatarsalia). The crocodile line is further subdivided into several subgroups (the longsnouted and semi-aquatic phytosaurs, the heavily armored aetosaurs, the mostly predatory rauisuchians, and true crocodylomorphs), whereas the bird line includes dinosaurs, birds, and a handful of close “dinosauromorph” cousins. Silhouettes not to scale. Cladogram delineated by Simon Powell, University of Bristol.
Brusatte et al. (2010) Fig. 3. Skeletal reconstructions of four Late Triassic–Early Jurassic dinosaurs, representing the major subgroups of early dinosaurs. These reconstructions are designed to provide a general guide to early dinosaur skeletal anatomy, and should not be used for fine-scale anatomical comparison or character state scoring in phylogenetic analysis. A, Herrerasaurus ischigualastensis (Dinosauria incertae sedis, possibly a theropod or stem saurischian outside the theropod + sauropodomorph clade); B, Dilophosaurus wetherilli (Theropoda); C, Saturnalia tupiniquim (Sauropodomorpha); D, Heterodontosaurus tucki (Ornithischia).
Benton, M.J., J. Forth, and M. Langer. 2014. Models for the rise of dinosaurs. Current Biology 24(2): R87-R95. Figure 3. Time-calibrated phylogeny of the first dinosaurs and their closest relatives. The figure also shows some key evolutionary acquisitions. Orange depicts known range of fossil records for each clade; ghost lineages (missing fossil record implied by sister group) in blue. (A) Phylogeny of basal dinosaurs and their nearest relatives, plotted against geological time. (B–E) ‘Typical’ dinosaur or dinosauromorph traits: (B) filamentous integumentary cover in the tail of the ornithischian Psittacosaurus; (C) fibrolamellar cortical bone (arrow) in the femur of Saturnalia, indicative of rapid growth; (D) pneumatic foramen for air sac diverticuli (arrow) in a vertebra of the theropod Majungasaurus; (E) Silesaurus reconstructed in bipedal stance , although this posture is debated. Positions in the cladogram where those features first appear are tentatively indicated, but the conditions in surrounding taxa are mostly ambiguous. Based on phylogenies of basal dinosaurs , where herrerasaurids are placed as basal saurischians rather than basal theropods, as sometimes suggested .
Ornithischian Clade Painting of an ornithopod hadrosaur, a member of the ornithischian dinosaurs. The animal has a bipedal stance, but it can also move about as a quadruped. An image of Triceratops, which was an obligate quadruped.
Saurischian Clade Tyranosaurus, one of the last theropod non-avian dinosaurs Diplodocus, one of the giant sauropods had pillar-like legs, an enormous body, and long neck and tail. As illustrated here, the animals likely walked with their tails elevated, which served as a counterbalance.
Busatte, S.L., J.K. O’Connor, and E.D. Jarvis. 2015. The origin and diversification of birds. Current Biology 25: R888-R898. Figure 1. Summary phylogeny (genealogical tree) of birds. The phylogeny shows where birds fit into the larger vertebrate family tree and the relationships of the earliest birds and their closest dinosaurian relatives (based on  and other studies cited therein). Timescale values are in millions of years; thick red line denotes the mass extinction at the Cretaceous–Paleogene boundary caused by asteroid impact (denoted by fireball on the right); arrows denote lineages that survived the extinction; circles represent species known from a particular point in time; thick line sections of branches indicate direct fossil evidence and thin lines are temporal distributions implied by phylogenetic ghost lineages; Cz, Cenozoic interval after the end-Cretaceous extinction. Silhouette anatomical features in the lower part of the figure are plotted approximately where they evolve on the phylogeny. Species silhouettes at the top of the image are from phylopic.org and designed by (from left to right): Nobu Tamura, Anne Claire Fabre, T. Michael Keesey, Steven Traver, Andrew A. Farke, Mathew Wedel, Stephen O’Connor/T. Michael Keesey, Brad McFeeters/T. Michael Keesey, Scott Hartman, T. Michael Keesey, Scott Hartman, Scott Hartman, Matt Martyniuk, Matt Martyniuk, Matt Martyniuk, Matt Martyniuk, Nobu Tamura/T. Michael Keesey, Matt Martyniuk, J.J. Harrison/T. Michael Keesey. ‘Bipedal posture’ silhouette by Scott Hartman.
Views of Turtle Evolution Three different cladograms regarding the relationships of the living amniotes. Cladogram A assumes that the turtles are sisters to the diapsids. Cladogram B assumes that the turtles arose from within the diapsids. Cladogram C assumes that the turtles arose from a basal line of amniotes. A=Anapsid; AM=Amniote; D=Diapsid; S=Synapsid.
Early Turtles Restoration of Odontochelys, one of the oldest turtles. Developmental and molecular evidence suggests that they evolved from within the diapsids. Are they Lepidosaurs or Archosaurs? Adapted from Lee (2013) Adapted from Schoch and Sues (2015)