![]() ![]() Sauropterygians first appeared in the fossil record of the Germanic Basin within the Upper Buntsandstein (late Olenekian, Early Triassic). Pachypleurosaur taxa are underlined in this figure. The interrelationships of the Lower Muschelkalk pachypleurosaurs Dactylosaurus and Anarosaurus are also unclear (own data). suggested that the pachypleurosaur Keichousaurus is possibly a basal nothosaurid, questioning the monophyly of Pachypleurosauria. 1B) Sauropterygian relationships modified after Holmes et al. Plesiosauria are known from the Rhaetian (Late Triassic) until the end of the Cretaceous. Among the Pistosauroidea Cymatosaurus is restricted to the Anisian, pistosaurs disappear in the Carnian (early Late Triassic). Placodonts are known until the Rhaetian (Late Triassic). Nothosaurs and pachypleurosaurs vanish in the Ladinian (late Middle Triassic). All these groups appear nearly simultaneously in the early Anisian (early Middle Triassic). Placodonts are regarded as a plesiomorphic sister group to all other Sauropterygia. Cymatosaurus) form the Eusauropterygia, which are combined with the Pachypleurosauroidea in the Eosauropterygia. Hereafter the Nothosauroidea and Pistosauroidea (incl. Phylogenetic hypothesis of early Sauropterygia summarized after Rieppel. Phylogenetic relationships of Sauropterygia.ġA) Current phylogenetic relationships of Sauropterygia. Contrary to these new finds, the stratigraphically younger pachypleurosaur Neusticosaurus shows the plesiomorphic lamellar-zonal bone type and an incomplete endochondral ossification, like Nothosaurus.įigure 1. Histotype B is related to the pachypleurosaur Anarosaurus. ![]() Histotype A is assigned to Cymatosaurus, a basal member of the Pistosauroidea, which includes the plesiosaurs as derived members. ![]() This pushes the origin of fibrolamellar bone in Sauropterygia back from the Cretaceous to the early Middle Triassic (early Anisian). Unexpectedly, both of these histotypes reveal abundant fibrolamellar bone throughout the cortex. In contrast to the enormous morphological variability of eosauropterygian humeri not assigned to Nothosaurus, their long bone histology is relatively uniform and can be divided into two histotypes. Nothosaurus shows a typical plesiomorphic lamellar-zonal bone type, but varying growth patterns and the occurrence of a new humerus morphotype point to a higher taxonomic diversity than was known. ![]()
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