Journal of Paleontology, 90(1), 2016, p. 92–101 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2016.26


Owenettids and procolophonids from the lower Keuper shed new light on the diversity of parareptiles in the German Middle Triassic


Agustín G. Martinelli,1 Marina Bento Soares,1 and Rainer R. Schoch2


1Laboratório de Paleontologia de Vertebrados, Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS). Av. Bento Gonçalves 9500, Agronomia, 91540-000 Porto Alegre, RS, Brazil. ⟨agustin_martinelli@yahoo.com.ar⟩,


⟨marina.soares@ufrgs.br⟩ 2Staatliches Museum für Naturkunde, Rosenstein 1, D-70191 Stuttgart, Germany. ⟨rainer.schoch@smns–bw.de⟩


Abstract.—We report three isolated humeri of small-sized parareptiles, which represent two different taxa, from the lower Keuper (Erfurt Formation) of Germany. They constitute the first definitive evidence of parareptiles in the lower Keuper. The specimens represent the first records of an owenettid procolophonian (aff. Barasaurus) from Europe and of a putative gracile-built procolophonid. This indicates the coexistence in the Middle Triassic of Germany of two procolophonian lineages that first appeared in the fossil record in the late Permian and survived the Permian–Triassic extinction. Although based on isolated limb bones, they highlight the taxonomic diversity of the still poorly known tetrapod assemblage of the lower Keuper in southwestern Germany.


Introduction


The Middle Triassic forms an especially interesting time for terrestrial vertebrates as it is wedged between the still poorly understood extinction recovery phase in the Early Triassic and the dinosaur-dominated Late Triassic (Fraser and Henderson, 2006; Sues and Fraser, 2010). Nonmarine faunal assemblages from the Middle Triassic are particularly well known from Argentina and Brazil (e.g., Langer et al., 2007; Abdala et al., 2009), with Tanzania, Russia, and North America having pro- duced promising but less diverse faunas. The lower Keuper (now formally named Erfurt Formation; Deutsche Stratigraphische Kommission, 2005), amixed terrestrial–shallowmarine deposit in Germany and adjacent regions in France and Poland, is late Middle Triassic (Ladinian: Longobardian) in age and falls within this time interval (Schoch, 1999, 2002; Sues and Fraser, 2010). It has been known since the early nineteenth century and has pro- duced temnospondyl amphibians and pseudosuchian archosaurs (Schoch, 2002, 2011). In recent times, excavations in the lower Keuper strata have yielded large quantities of terrestrial reptile material, ranging from small diapsids (rhynchocephalians, lepidosauromorphs, choristoderes, and a tiny stem turtle) to archosauriforms and paracrocodylomorphs (e.g., Schoch and Sues, 2014, 2015; Schoch, 2015). In addition to these diverse diapsids, further amniote material was collected, albeit so far of indeterminate status. The most distinctive of these remains are partial mandibular rami referred to the genus Colognathus,adis- tinctive amniote with superficial resemblance to procolophonians but whose affinities remain uncertain (Sues and Schoch, 2013). We report three isolated humeri of small-sized parareptiles


(Figs. 1–3) that represent two distinct taxa. They form the first definitive evidence of parareptiles in the lower Keuper. The material was found in the same horizon (Untere Graue


92


Mergel, Anoplophoraschichten) of the lower Keuper (Ladinian) at two different localities, Vellberg and Kupferzell. These localities are located some 25 km apart in southwestern Germany and were situated in two separate lake basins at the time of deposition. Although based on isolated postcranial elements, the specimens represent the first records of an owenettid procolophonian (aff. Barasaurus) in Europe and a putative procolophonid. The discovery of these parareptiles increases the taxonomic diversity of the poorly known tetrapod assemblage of the lower Keuper in southwestern Germany.


Material and methods


Repository and institutional abbreviation.—The three speci- mens here described (Figs. 1–3) are housed in the collection of the Staatliches Museum für Naturkunde Stuttgart (SMNS), Stuttgart, Germany. For descriptive purposes, we assume that the humeri belong


to strictly sprawling animals. Therefore, the laterally expanded distal end is positioned horizontally (i.e., the entepicondyle and ectepicondyle are in the same plane) to establish the dorsal and ventral surfaces of the humerus. The dorsal surface is character- ized by the main exposure of the humeral head at the proximal end and the ventral surface by the main exposure of the capitellum (radial condyle) at the distal end. When positioning the humerus perpendicular to the sagittal plane of the body, ‘anterior’ refers to the side of the ectepicondyle, and ‘posterior’ refers to the side of the entepicondyle. Muscle placements and most humeral processes follow


Romer (1922, 1956), Holmes (1977), and Angielczyk et al. (2009; see Fig. 4). For the well-developed posteroventral process of the proximal half of the humerus, set off from the proximal articular surface, we use the term ‘lesser tuberosity.’


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