![]() 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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