Eurhinosaurus Abel 1909

Eurhinosaurus Abel, 1909 Type species and holotype. Eurhinosaurus longirostris (Mantell, 1851), NHMUK PV OR 14566. Revised diagnosis of the genus. Mandible considerably shorter than skull, <60 percent of skull length; snout, premaxillary, and prenarial ratios each> 1.0; orbital ratio ≥ 0.20. Unpaired carotid foramen in the parabasisphenoid *. Pelvic girdle is tripartite, without fusion of pubis and ischium. Long-bodied, preflexural vertebrae> 85, but probably not> 95; presacral vertebrae probably> 44. Fore- and hindfins both long and slender; number of elements in longest digit of forefin> 17; forefin at least half as long as skull; hindfin well developed, approaching length of forefin. Forefin with 4 or 5 digits (5 th digit might be an additional postaxial digit). Presence of sheathed-bicapitate dorsal ribs *. Presence of ossified haemal arches in the anterior caudal vertebrae *. Large adult body size (up to 7 meters in the largest individuals). Remarks. Characters marked with an asterisk (*) indicate newly added diagnostic features. Maisch (2022), in his description of Eurhinosaurus quenstedti and validation of Eurhinosaurus huenei, did not provide a diagnosis for the genus Eurhinosaurus. Hence, the most recent diagnosis for this genus is that from McGowan and Motani (2003), who indicated that the diagnosis for Eurhinosaurus longirostris (monospecific at the time of publication) is the same as for the genus. Accordingly, this diagnosis remains the most recent diagnosis for the species Eurhinosaurus longirostris. This revised diagnosis for the genus is largely based on the diagnosis provided by McGowan and Motani (2003, pages 81–83). However, Maisch and Matzke (2000) originally described the unpaired carotid foramen in the parabasisphenoid and the dorsal ribs that are not clearly double-headed as diagnostic traits of Eurhinosaurus longirostris (considered monotypic at the time of publication). We here add these features considered characteristic of Eurhinosaurus (highlighted by an *) to the most recent diagnosis established by McGowan and Motani (2003). Note that the not clearly double-headed condition of the dorsal ribs mentioned by Maisch (2022) is recognized in this study to be highly similar to the condition described in Argovisaurus (Miedema et al. 2024) (see description). Miedema et al. (2024) described this specific condition as “ sheathed-bicapitate ” and we therefore apply this same terminology to Eurhinosaurus. Although notching in fin elements of the leading digit is part of the diagnosis for the genus Eurhinosaurus provided by McGowan and Motani (2003) and also frequently described in other ichthyosaurs (e. g., Maxwell et al. 2014; Lomax et al. 2017; Anderson 2019) and notched elements are present in the specimens of this study (Figs 3, 13) the presence or absence of notching as well as the number of notched elements (when present) is highly variable in Eurhinosaurus and this variability has already been reported in previous studies (von Huene 1951; McGowan 1994; McGowan and Motani 2003; Maisch 2022). Furthermore, von Huene (1951) hypothesized that the variation in number of notched elements in the limbs of Eurhinosaurus could possibly be explained by sexual dimorphism. Therefore, due to the highly variable nature of this character and the uncertainty regarding its significance, we do not consider the characters that regard the notching of fin elements to be truly informative for diagnosing Eurhinosaurus and they are here excluded from the revised diagnosis. It should be noted that the basioccipital morphological traits identified by McGowan and Motani (2003) have been excluded from the revised generic diagnosis, as our study indicates that basioccipital morphology holds specific significance rather than generic. As originally reported by von Huene (1926), Eurhinosaurus shows the characteristic presence of ossified haemal arches in the anterior caudal vertebrae. This observation is confirmed by the specimens from Mistelgau and we therefore added this characteristic condition to the generic diagnosis. Type locality and horizon. Lower Jurassic (Lower Toarcian), Whitby, Yorkshire, England (Mantell 1851; McGowan 1994). Distribution. Holzmaden, Ohmden, Bad Boll, Aalen, Dotternhausen, Schömberg, in Baden-Wuerttemberg (von Jaeger 1856; von Huene 1922, 1926, 1928, 1931 a, 1951; Maisch 2022), Banz (von Theodori 1854; von Huene 1922), Mistelgau (this study), in Bavaria, Schandelah and Hondelage, in Lower Saxony (Hauff et al. 2017; Kosma 2018), Germany; Whitby (Mantell 1851; McGowan 1994), Yorkshire, in the United Kingdom; Dudelange, in Esch-sur-Alzette (Godefroit 1994), Luxembourg; Pic-Saint-Loup, in Hérault (Lamaud 1979), Noirefontaine, in Franche-Comté (Pharisat et al. 1993), Marcoux, in Alpes-de-Haute-Provence (Fischer et al. 2011), France; Staffelegg, in Aargau, Switzerland (Reisdorf et al. 2011; Klug et al. 2024). Stratigraphic distribution. Toarcian (Lower Jurassic).