Romano et al.—Early Triassic Fishes of Elko County (Nevada)


Piveteau, 1944–1945; Lehman, 1952; Mutter et al., 2008; Kogan and Romano, 2016a). In PIMUZ A/I 4397, S. cf. elongatus, S. ornatus, and


S. toxolepis the lachrymal reaches anteriorly beyond the level of the posterior external naris, whereas in S. cf. ornatus and S. madagascariensis the lachrymal extends less far rostrally (e.g., Stensiö, 1925; Mutter et al., 2008; Romano et al., 2012; Kogan and Romano, 2016a). The significance of this character requires further study. The rostrum is often incompletely preserved in Saurichthys.


In addition to PIMUZ A/I 4397, largely complete, elongate rostra are preserved, for instance, in specimens ascribed to S. toxolepis, S. elongatus,and S. curionii (Stensiö, 1925;Rieppel, 1985;Mutter et al., 2008), as well as in an undescribed specimen from Idaho (PIMUZ A/I 4621).


Early Triassic vertebrate occurrences in the western USA


Localities yielding Early Triassic fishes are known from Greenland, Canada, and the USA (Schaeffer and Mangus, 1976; Wilson and Bruner, 2004; Brinkmann et al., 2010). Early Triassic paleoichthyological sites are absent in South America (López-Arbarello, 2004; Brinkmann et al., 2010) and, to our knowledge, there are no such localities in Central America and the Caribbean Islands. Consequently, our knowledge of Early Triassic fishes from the former western Pangean margin relies mainly on sites that were then located at mid or high latitudes in the northern hemisphere (i.e., localities in present-day northern North America and Arctic Eurasia). Marine Early Triassic fishes from Greenland are derived


from several horizons, all of earliest Triassic age (Griesbachian– ?early Dienerian; Perch-Nielsen et al., 1974). They have been extensively researched especially during the twentieth century (e.g., Stensiö, 1932; Nielsen, 1949; Mutter et al., 2008; Kogan, 2011). From Canada, Early Triassic fishes have been reported from sites in western Alberta (Neuman, 2015 and references therein), Ellesmere Island (Nunavut; Schaeffer and Mangus, 1976), and Wapiti Lake area, British Columbia. Fishes from the latter locality in particular have been the focus of several recent studies (e.g., Mutter and Neuman, 2006; Mutter et al., 2008; Wendruff and Wilson, 2012, 2013). The western Canadian fish fossils come from various layers, but age constraints are limited (e.g., Mutter and Neuman, 2006; Neuman, 2015). In addition to the aforementioned Canadian sites, Wignall and Newton (2003) reported the occurrence of well-preserved remains of cf. Bobasatrania in the upper Grayling Formation (Dienerian?) of Ursula Creek, northwest ofWapiti Lake. In contrast to Canada and Greenland, only a few, short


papers were dedicated to the fishes from the Early Triassic of the United States. Exposures of Lower Triassic, marine rocks, which are found in Alaska, Montana, Wyoming, Idaho, Utah, Nevada, and California, have yielded a plethora of marine invertebrate fossils, including the earliest metazoan reefs of the Mesozoic (e.g., Silberling and Tozer, 1968; Nichols and Silberling, 1979; Brayard et al., 2011, 2013, 2017; Hofmann et al., 2013a, b). Several formations produce Early Triassic vertebrate remains, but these occurrences have often only been


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casually mentioned (e.g., Oversby, 1972; Silberling, 1973; Schaeffer and Mangus, 1976; Poole and Wardlaw, 1978). On the other hand, the marine and freshwater fishes from the Middle Triassic of the USA have received slightly more research interest (e.g., Wemple, 1906; Wells, 1947; Schaeffer and Gregory, 1961; Sander et al., 1994; Rieppel et al., 1996; Cuny et al., 2001). One of the longest known collecting areas for Early


Triassic marine vertebrate fossils is southeast Idaho, yielding ichthyoliths (Evans, 1904; Goddard, 1907; Mutter and Rieber, 2005; Romano et al., 2012; Brayard et al., 2017), but also articulated fishes (Tanner, 1936; Romano et al., 2012), and some ichthyopterygian reptile remains (Massare and Callaway, 1994; Scheyer et al., 2014). In addition to these published specimens, new vertebrate material (isolated bones or arti- culated partial/complete skeletons) was recently discovered at several sites in Idaho, for instance in the middle Smithian ‘Meekoceras beds’ (personal observation, CR, JJ, KGB, HB, 2013–2016), the late Smithian Anasibirites beds (Saurichthys: PIMUZ A/I 4621, NMMNH P-77359; several unlabelled specimens of Actinopterygii indet.), and the early Spathian Tirolites beds (personal communication, A. Brayard, 2016; personal observation, JJ, KGB, HB, 2013–2016). Very little is known about marine vertebrate occurrences in


Lower Triassic formations in the other western states. Aside from the Smithian and Spathian fish material from Nevada described herein, some ichthyopterygian remains from Spathian layers were documented by Mazin and Bucher (1987) and Kelley et al. (2016). Isolated vertebrate remains have also been found in the Smithian ‘Meekoceras beds’ at Crittenden Springs as well as in Spathian strata at several sites in Nevada (personal observation, JJ, RJ, TMS, KGB, HB, 2010–2016). Articulated osteichthyan fossils of Dienerian age have recently been discovered in the Candelaria Hills in southwest Nevada (e.g., Brinkmann et al., 2010; Romano et al., in preparation). FromWyoming,Case (1936) described a sauropterygian reptile of Spathian age (Lovelace and Doebbert, 2015; Kelley et al., 2016). Most vertebrates from the Early Triassic of the Western


United States are Smithian or Spathian in age, whereas Griesbachian and Dienerian fossils are less well known. The material from Nevada presented herein is derived from equatorial shelfal series deposited on the North American Craton. Material from sites located farther to the East (Utah, Idaho) was deposited in a low-latitude, epicontinental sea (western USA basin; Brayard et al., 2013). The depth and areal extent of this Early Triassic sea were controlled by both regional tectonics and eustatic sea level changes (e.g., Paull and Paull, 1993; Brayard et al., 2013). In conclusion, several localities in the western USA yield


Early Triassic vertebrate remains, but for the most part these fossils received little interest by researchers. The specimens described herein, in combination with other published and unpublished material from the Smithian of the western USA, contradict Sun et al.’s (2012) notion of a near absence of ver- tebrates within low latitudes due to ‘lethally hot’ temperatures during this interval. This alleged ‘equatorial vertebrate eclipse’ largely ignored the contradictory data available from China (e.g., Tong et al., 2006), and was also based on a wrong con- odont age (Goudemand et al., 2013). Sun et al. (2012)


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