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6244Euparkeria - A Reptile of the Triassic

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  • Neal Robbins
    Nov 13, 2013
          An illustration of Euparkeria is on this link.
          Euparkeria capensis was a reptile of the Triassic. The systematic paleontology of it is:
      Reptilia Laurenti 1768
      Diapsida Osborn 1903
      Archosauromorpha Huene 1946
      Archosauriformes Gauthier 1986
      Euparkeriidae Huene 1920
      Euparkeria Broom 1913
      Euparkeria capensis Broom 1913
          Euparkeria capensis had a length of about 55 cm. (1.8 ft.). The holotype (SAM 5867) is a skeleton. It was found in the Burgersdorp Formation (Beaufort Group) at the Aliwal North American site in South Africa (Eastern Cape). This fossil specimen dates to the Anisian age (247.2 - 242.0 million years ago) of the Triassic. [Note - The source of this information is The Paleobiology Database.]
          Lucas J. Legendre, Loic Segalen, and Jorge Cubo wrote an article titled Evidence for high bone growth rate in Euparkeria obtained using a new paleohistological inference model for the humerus. It was published in 2013 in the Journal of Vertebrate Paleontology 33(6): 1343-1350. This quote from the abstract says:
      The study of bone growth rate and metabolic rate evolution in archosaurs (crocodiles, dinosaurs including birds, and pterosaurs) and close outgroups has become a subject of major interest among paleontologists in recent years. In this paper, we estimate the bone growth rate of Euparkeria using a new statistical inference model for the humerus. We modified the taxonomic range of extant species used in previous studies, on which we performed quantitative measurements of histological features and bone growth rates. Bone growth rate values estimated for Euparkeria are crucial in understanding the ancestral condition for archosaurs because this taxon is considered the closest relative to the archosaur crown group. We obtained an instantaneous growth rate of 6.12 μm/day, suggesting that Euparkeria shared with other non-archosaurian archosauromorphs (Prolacerta, Proterosuchus, and Erythrosuchus) a condition of high growth rate compatible with endothermy. This derived state may have been inherited by some Triassic crurotarsans, as suggested by the high instantaneous bone growth rate (14.52 μm/day) estimated in this study for Postosuchus. Jurassic crurotarsans may have lost endothermy during the transition from terrestrial habitats and active predation to aquatic habitats and sit-and-wait predation behaviors, so that Cretaceous crocodiles may be secondarily ectothermic, as suggested by δ18O values. In conclusion, we provide new evidence for the hypothesis of an ancestral endothermic state for the last common ancestor of archosaurs, and show that non-archosaurian archosauromorphs and Triassic crurotarsans may have been characterized by a thermometabolism more similar to that of dinosaurs than to that of lepidosaurs and turtles.
          Neal Robbins