Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.

<h4>Background</h4>Sauropterygia is an abundant and successful group of Triassic marine reptiles. Phylogenetic relationships of Triassic Sauropterygia have always been unstable and recently questioned. Although specimens occur in high numbers, the main problems are rareness of diagnostic...

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Autor principal:	Nicole Klein
Formato:	article
Lenguaje:	EN
Publicado:	Public Library of Science (PLoS) 2010
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/f3351f94311344489f06d3dff8889035
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spelling	oai:doaj.org-article:f3351f94311344489f06d3dff88890352021-12-02T20:19:55ZLong bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.1932-620310.1371/journal.pone.0011613https://doaj.org/article/f3351f94311344489f06d3dff88890352010-07-01T00:00:00Zhttps://www.ncbi.nlm.nih.gov/pmc/articles/pmid/20657768/?tool=EBIhttps://doaj.org/toc/1932-6203<h4>Background</h4>Sauropterygia is an abundant and successful group of Triassic marine reptiles. Phylogenetic relationships of Triassic Sauropterygia have always been unstable and recently questioned. Although specimens occur in high numbers, the main problems are rareness of diagnostic material from the Germanic Basin and uniformity of postcranial morphology of eosauropterygians. In the current paper, morphotypes of humeri along with their corresponding bone histologies for Lower to Middle Muschelkalk sauropterygians are described and interpreted for the first time in a phylogenetic context.<h4>Methodology/principal findings</h4>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. 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. Unexpectedly, both of these histotypes reveal abundant fibrolamellar bone throughout the cortex. This pushes the origin of fibrolamellar bone in Sauropterygia back from the Cretaceous to the early Middle Triassic (early Anisian). Histotype A is assigned to Cymatosaurus, a basal member of the Pistosauroidea, which includes the plesiosaurs as derived members. Histotype B is related to the pachypleurosaur Anarosaurus. Contrary to these new finds, the stratigraphically younger pachypleurosaur Neusticosaurus shows the plesiomorphic lamellar-zonal bone type and an incomplete endochondral ossification, like Nothosaurus.<h4>Conclusions/significance</h4>Histological results hypothetically discussed in a phylogenetical context have a large impact on the current phylogenetic hypothesis of Sauropterygia, leaving the pachypleurosaurs polyphyletic. On the basis of histological data, Neusticosaurus would be related to Nothosaurus, whereas Anarosaurus would follow the pistosaur clade. Furthermore, the presence of fibrolamellar bone, which is accompanied with increased growth rates and presumably even with increased metabolic rates, already in Anarosaurus and Cymatosaurus can explain the success of the Pistosauroidea, the only sauropterygian group to survive into the Jurassic and give rise to the pelagic plesiosaur radiation.Nicole KleinPublic Library of Science (PLoS)articleMedicineRScienceQENPLoS ONE, Vol 5, Iss 7, p e11613 (2010)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q Nicole Klein Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.
description	<h4>Background</h4>Sauropterygia is an abundant and successful group of Triassic marine reptiles. Phylogenetic relationships of Triassic Sauropterygia have always been unstable and recently questioned. Although specimens occur in high numbers, the main problems are rareness of diagnostic material from the Germanic Basin and uniformity of postcranial morphology of eosauropterygians. In the current paper, morphotypes of humeri along with their corresponding bone histologies for Lower to Middle Muschelkalk sauropterygians are described and interpreted for the first time in a phylogenetic context.<h4>Methodology/principal findings</h4>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. 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. Unexpectedly, both of these histotypes reveal abundant fibrolamellar bone throughout the cortex. This pushes the origin of fibrolamellar bone in Sauropterygia back from the Cretaceous to the early Middle Triassic (early Anisian). Histotype A is assigned to Cymatosaurus, a basal member of the Pistosauroidea, which includes the plesiosaurs as derived members. Histotype B is related to the pachypleurosaur Anarosaurus. Contrary to these new finds, the stratigraphically younger pachypleurosaur Neusticosaurus shows the plesiomorphic lamellar-zonal bone type and an incomplete endochondral ossification, like Nothosaurus.<h4>Conclusions/significance</h4>Histological results hypothetically discussed in a phylogenetical context have a large impact on the current phylogenetic hypothesis of Sauropterygia, leaving the pachypleurosaurs polyphyletic. On the basis of histological data, Neusticosaurus would be related to Nothosaurus, whereas Anarosaurus would follow the pistosaur clade. Furthermore, the presence of fibrolamellar bone, which is accompanied with increased growth rates and presumably even with increased metabolic rates, already in Anarosaurus and Cymatosaurus can explain the success of the Pistosauroidea, the only sauropterygian group to survive into the Jurassic and give rise to the pelagic plesiosaur radiation.
format	article
author	Nicole Klein
author_facet	Nicole Klein
author_sort	Nicole Klein
title	Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.
title_short	Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.
title_full	Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.
title_fullStr	Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.
title_full_unstemmed	Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.
title_sort	long bone histology of sauropterygia from the lower muschelkalk of the germanic basin provides unexpected implications for phylogeny.
publisher	Public Library of Science (PLoS)
publishDate	2010
url	https://doaj.org/article/f3351f94311344489f06d3dff8889035
work_keys_str_mv	AT nicoleklein longbonehistologyofsauropterygiafromthelowermuschelkalkofthegermanicbasinprovidesunexpectedimplicationsforphylogeny
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Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.

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