The origin of pareiasaurs (and turtles).

Revised July 13, 2014 with a new image of Sclerosaurus.

Pareiasaur (Anthodon) and its phylogenetic predecessor, Stephanospondylus, a robust millerettid.

Figure1. Pareiasaur (Anthodon) and its phylogenetic predecessor, Stephanospondylus, a robust millerettid and an ancestor to turtles. Note the close correspondence of dorsal skull elements.

Earlier we looked at the ancestry of hard shell turtles (starting with Proganochelys) and soft shell turtles (starting with Odontochelys). According to the large reptile tree, the closest sister taxon to turtles is the clade Pareiasauria, represented above by Anthodon (Fig. 1). Stephanospondylus is basal to pareiasaurs followed more distantly diadectids, bolosaurids and ultimately Milleretta. So pareiasaurs AND turtles are sisters to diadectids and millerettids,

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx.

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx.

Sues and Reisz (2008) considered Sclerosaurus a procolophonid, but their concept of a procolophonid was much greater (includes more taxa) than is appropriate, according to the results of the large reptile tree.

References
Broom R 1938 On the Structure of the Reptilian Tarsus: Proceedings of the Zoological Society of London, v. 133, 108, p. 535-542.
Broom R 1948. A contribution to our knowledge of the vertebrates of the Karroo beds of South Africa: Transactions of the Royal Society of Edinburgh, Endinburgh 61: 577-629.
Gow CE 1972. The osteology and relationships of the Millerettidae (Reptilia: Cotylosauria). Journal of Zoology, London 167:219-264.
Hartmann-Weinberg AP 1933. Evolution der Pareiasauriden: Trudy Palaeontological institute Academe Nauk, SSSR, 1933, n. 3, p. 1-66.
Lee MSY 1997. Pareiasaur phylogeny and the origin of turtles. Zoological Journal of the Linnean Society 120: 197-280.
Owen R 1876. Descriptive and Illustrated Catalogue of the Fossil Reptilia of South Africa in the Collection of the British Museum. London, British Museum (Natural History).
Sues H-D and Reisz RR 2008. Anatomy and Phylogenetic Relationships of Sclerosaurus armatus (Amniota: Parareptilia) from the Buntsandstein (Triassic) of Europe. Journal of Vertebrate Paleontology 28(4):1031-1042. doi: 10.1671/0272-4634-28.4.1031 online

wiki/Anthodon
wiki/Deltavjatia
Deltavjatia paleocritti
wiki/Pareiasaur
Sclerosaurus paleocritti
wiki/Milleretta

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