Netherlands Journal of Geosciences — Geologie en Mijnbouw | 90 – 1 | 15 - 21 | 2011 New Nothosaurus skulls from the Lower Muschelkalk of the western Lower Saxony Basin (Winterswijk, the Netherlands) shed new light on the status of Nothosaurus winterswijkensis P.C.H. Albers Netherlands Centre for Biodiversity Naturalis, P.O. Box 9517, 2300 RA Leiden, the Netherlands. Email: [email protected]. Manuscript received: January 2011, accepted: March 2011 Abstract Three nothosaur skulls from the Lower Muschelkalk (Lower Anisian) locality of Winterswijk, the Netherlands, were recently acquired by museum Twentse Welle (Enschede) and have thereby become available for scientific description. Thus, these skulls had been identified as Nothosaurus winterswijkensis, but upon examination these skulls challenge the status of this Nothosaurus species. All diagnostic characters are somehow discredited, but the material can also not be unequivocably be considered as Nothosaurus marchicus, which is the only other obvious candidate. As these fossils originate from the same strata as the type of Nothosaurus winterswijkensis and there is no reason to assume that the animals occupied different ecological niches they are more plausibly considered one species, and Nothosaurus winterswijkensis therefore becomes a junior synonym of Nothosaurus marchicus. The diagnosis of Nothosaurus marchicus is enlarged to include all finds. Keywords: Nothosaurus winterswijkensis, Nothosaurus marchicus, revision. Introduction Up to now three species of nothosaur have been described from the Lower Muschelkalk locality of Winterswijk: the very The Winterswijk locality has become an increasingly more similar Nothosaurus winterswijkensis (Albers & Rieppel, 2003) important site where good quality fossils of Triassic reptiles and Nothosaurus marchicus (Albers, 2005a) and the distinctively and their fauna are being unearthened (e.g. Albers & Rieppel, smaller Nothosaurus winkelhorsti (Klein & Albers, 2010). The 2003; Albers, 2005a, b, Bickelmann & Sander, 2008, Klein & skull assigned to Nothosaurus marchicus could be disregarded Albers, 2009, Sander et al., submitted). Finds of Nothosaurus date considering Nothosaurus winterswijkensis as it was found back to the description in 1959 of Nothosaurus raabi (Hooijer, in an older layer of the quarry, but as its morphology hinted 1959) which since has been synoymised with Nothosaurus to a somewhat intermediate position between Nothosaurus marchicus (Rieppel & Wild, 1996). winterswijkensis and Nothosaurus marchicus, it thus already Recently the large and important private collection of questioned, to some extent, the status of Nothosaurus Gerben Diepenbroek, a true treasure trove of fossils from the winterswijkensis (Albers, 2005a). Winterswijk quarries, has been acquired by the museum Twentse The three skulls described in this study are a welcome Welle, Enschede, and has thus become available for scientific addition to our knowledge of variation of nothosaur skulls as research. This collection contains four nothosaur skulls of the intraspecific variation, size range and ontogenetic which three are sufficiently complete to allow a scientific diversity remain not well known (Rieppel 1994a; Rieppel & description. Two of these skulls have already been depicted in Wild 1996; Rieppel & Werneburg 1998). Oosterink & Diepenbroek (1990) and again in Oosterink et al. (2003) but were not critically examined and summarily depicted and also they were not prepared (eg the right temporal arch of one of the skulls was left completely covered with matrix). This warrants a new description of these skulls. Netherlands Journal of Geosciences — Geologie en Mijnbouw | 90 – 1 | 2011 15 Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.139, on 28 Sep 2021 at 13:09:49, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600000639 Description Premaxilla Institutional abbreviations The paired premaxillas have long and slender tapering posterior processes, which reach far back along the skull TW = Museum Twentse Welle, Enschede midline, extending beyond the external naris. In dorsal view the anterior medial margin of the external naris is bordered by Described material the premaxilla. Their posterior medial margin, however, is separated from the premaxilla by an anterior lateral tapering Four nothosaur skulls from the Diepenbroek collection in the process of the nasal. The suture between premaxilla and maxilla museum ‘Twentse Welle’, Enschede, with collection numbers: is located slightly posterior to the anteroventral corner of the TW480000375, TW480000376, TW480000377, and TW480000378. external naris, from where it extends in anterolateral (Photographs in addendum online: www.njgonline.nl). direction. In ventral view it curves around the alveolus of the anteriormost maxillary tooth until about the height of the Referred material anterior margin of the internal naris, but remains excluded therefrom by a contact of the maxilla with the vomer at the Two additional skulls described as Nothosaurus winterswijkensis anterior margin of the latter. The premaxilla carry five tooth (Albers & Rieppel, 2003), one skull attributed to Nothosaurus positions, comprising four premaxillary fangs followed by a marchicus (Albers, 2005a) and one skull described as Nothosaurus distinctly smaller premaxillairy tooth. Several teeth remain in winkelhorsti (Klein & Albers, 2009). situ (see figure) as well as one replacement visible in the alveolus of the fourth position on the left side of Stratum typicum TW480000376. The skulls were found in the Lower Wellenkalk layer 9 (Oosterink, Maxilla 1986), Vossenveld Formation (lower Anisian, lowermost Middle Triassic) in the ‘Winterswijkse Steen- en Kalkgroeve, Winterswijk, From posterior to the anteroventral corner of the external naris Netherlands’, a quarry of the Ankerpoort consortium; see also the maxilla reaches backwards carrying the tooth row until the tectonic map and geological profiles of Harsveldt (1973). about 10-15% of the length of the longitudinal diameter of the Gauss-Krüger coordinates: R 2252,6/H 5758,6. upper temporal fenestra. The maxilla has a foramen at the anterior part along the lateral margin of the external naris, General remarks and measurements serving the exit of a lateral branch of the superior alveolar nerve, as is common in most species of Nothosaurus (Rieppel & All four skulls are relatively small seized. Two skulls, are Wild, 1996). Laterally the maxilla shows a slight bulge just complete, one prepared in dorsal view (TW480000375) and one behind the level of the posterior margin of the external naris, prepared in ventral view (TW480000376). The third skull is accommodating the roots of the maxillary fangs. Behind the very incomplete and not diagnostic, its right temporal fenestra external naris, the maxilla meets the lateral margin of the nasal is intact and the corresponding frontal and parietal skull table in a posteromedially trending suture, until it meets the frontal, and the medial outline of the orbits with the front broken off as is common for Nothosaurus marchicus (Rieppel & Wild, 1996), just posterior to the external naris. A small part of the left side except for the left maxilla of TW480000375 were the maxilla is of the skull is present but below elements belonging to the excluded from the frontal by a small anteromedial process of palate eg the pterygoid and the basisoccipital are or appear to the prefrontal, as typical of Nothosaurus winterswijkensis (Albers be completely missing. (see photograph in addendum online: & Rieppel, 2003). www.njgonline.nl). The fourth skull (TW480000378) is complete In ventral view the maxilla forms the lateral margin of the except for most of the premaxilla. For estimation of sizes the internal naris and extends posteriorly lateral to the palatine missing premaxilla was considered to be of about equal size as and the ectopterygoid. The suture between the premaxilla and that of TW480000375. See Table 1 for general measurements and the maxilla is clearly identifiable on both sides of the skull of Table 2 for derived measures and dentition. Unless specifically TW480000376 and indicates four tooth positions (2 teeth in mentioned otherwise the descriptions below refer to skulls situ) before the maxillary fangs on the left side of the skull and TW480000375 and TW480000378 when features in dorsal view five tooth positions (3 teeth in situ) before the maxillary fangs are described and refer to TW480000376 when features in on the right side of the skull. Five tooth positions before the ventral view are described (see Fig. 1) . maxillary fangs are diagnostic for Nothosaurus marchicus (Rieppel & Wild, 1996). Lateral views of both other skulls (TW480000375 and TW480000378) do not seem to accommodate more room than three tooth positions (with either 1 or 2 teeth 16 Netherlands Journal of Geosciences — Geologie en Mijnbouw | 90 – 1 | 2011 Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.139, on 28 Sep 2021 at 13:09:49, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600000639 Table 1. General measurements of nothosaur skulls from Winterswijk. Nothosaur skulls from the Winterswijk locality winterswijkensis1 marchicus2 TW480000375 TW480000376 TW480000378 winkelhorsti3 Tip of the snout to occipital condyle 126.7 130* 101.4 107 94* 46 Tip of the snout to posterior margin 122.8 - 98.3 -