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      Anatomical notes and discussion of the first described aetosaur Stagonolepis robertsoni (Archosauria: Suchia) from the Upper Triassic of Europe, and the use of plesiomorphies in aetosaur biochronology

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      PeerJ
      PeerJ Inc.
      Triassic, Aetosauria, Biostratigraphy, Apomorphy, Osteoderms, Pseudosuchia

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          Abstract

          Stagonolepis robertsoni, from the Late Triassic of Scotland, was the first named aetosaurian. Known mostly from a series of natural molds from two localities, the osteology of this taxon has been difficult to interpret. Detailed work on this material in the late 1950s resulted in a monograph that set the standard for the understanding of aetosaurians, making Stagonolepis robertsoni the best known aetosaurian; however, little has been done with this material since. Reanalysis of this material shows that despite its limitations the early 1960s reconstruction work depicts the preserved characteristics faithfully, especially in the skull. The first cervical rib is extremely anteroposteriorly elongate as in Alligator, a character not previously recognized in aetosaurians. Diapophyseal and zygapophyseal vertebral laminae are present in the cervical and trunk vertebrae. The ilium is autapomorphic with distinct pre- and post-processes of the iliac blade. The osteoderms differ from North and South American material that has been ascribed to the genus. Those assignments are based on plesiomorphies within Aetosauria, such as a radial ornamentation and a posteriorly located and medially offset dorsal eminence. Biostratigraphic correlations using taxonomic conclusions based on plesiomorphic characters should not be used. The holotype specimen of S. robertsoni is currently diagnostic, in part because ventral osteoderms are not known for many aetosaurian taxa and the surface ornamentation of randomly distributed, closely packed oblong pits found in S. robertsoni is unique within Aetosauria.

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          A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs

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            Basal Archosaurs: Phylogenetic Relationships and Functional Implications

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              Triassic Reptiles from the Elgin Area: Stagonolepis, Dasygnathus and Their Allies

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                Author and article information

                Contributors
                Journal
                PeerJ
                PeerJ
                peerj
                peerj
                PeerJ
                PeerJ Inc. (San Francisco, USA )
                2167-8359
                28 August 2018
                2018
                : 6
                : e5455
                Affiliations
                [-1] Division of Science and Resource Management, Petrified Forest National Park , Petrified Forest, AZ, United States of America
                Article
                5455
                10.7717/peerj.5455
                6118205
                89843bed-ddbc-4826-aa42-93a5da133f03
                ©2018 Parker

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ) and either DOI or URL of the article must be cited.

                History
                : 12 March 2018
                : 26 July 2018
                Funding
                Funded by: Jackson School of Geosciences at the University of Texas at Austin
                Funded by: Lundelius Fund
                Funded by: Francis L. Whitney Endowed Presidential Scholarship
                Funded by: Ronald K. DeFord Scholarship Fund
                Funded by: Systematics Association
                Financial assistance for this project was provided by the Jackson School of Geosciences at the University of Texas at Austin, the Lundelius Fund, the Francis L. Whitney Endowed Presidential Scholarship, the Ronald K. DeFord Scholarship Fund, and the Systematics Association. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Paleontology
                Taxonomy

                triassic,aetosauria,biostratigraphy,apomorphy,osteoderms,pseudosuchia

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