Romano et al.—Early Triassic Fishes of Elko County (Nevada)
of vertical and overturned beds in isolated outcrops, is highly faulted, with outcrops abutting against other outcrops with differing attitudes, making detailed logging impossible. Contact with Permian rocks is not visible and alluvial material covers much of the upper beds (Clark, 1957). Approximately 460m of probable Spathian sediments, consisting of massive gray limestone and gray shaly limestone yielding bivalves, brachio- pods, and ammonoids crop out in the higher hills ~6km south of the ranch (Clark, 1957). A succession of Smithian, dark-brown limestone overlain
by 60–90m of black shaly limestone is repeated several times on the east side of an unimproved road ~3km south of the ranch (Clark, 1957). These rocks are relatively incompetent and, consequently, the topography in this particular area consists of sagebrush flats and a few, very low rolling hills. Outcrops are few—weathered shale covers most of the area and small pieces of dark-brown limestone occasionally found lying on the surface usually indicate the position of subsurface beds. A few well-preserved middle Smithian ammonoids (e.g., Inyoites oweni) belonging to the ‘Meekoceras zone’ of Clark (1957) have been found by JJ andHB in these limestone beds of the ThaynesGroup at two sites located 340m apart. Oversby (1972) mentioned the occurrence of bones (large vertebrae and fish remains) in the study area, but neither described nor depicted them. The discovery sites of NMMNH P-66225 (N41°22'58.2'',
W114°40'11.9'') and NMMNH P-77117 (N41°22'49.5'', W114°40'24.8'') are located ~2.75km south-southeast of the Winecup Ranch. P-77117 was found at the most prolific ammonoid locality together with Pseudaspidites, Procurvoceratites, pro- ptychitid indet., and prionitid indet., which, combined with I. oweni, indicate a late early Smithian to early late Smithian age (Brayard and Bucher 2008; Brühwiler et al., 2010; Brayard et al., 2013). P-66225 was found more or less on strike ~300m northeast of the P-77117 locality. Conodonts or ammonoids have not been detected in the matrix surrounding P-66225, but a similar age as P-77117 is likely. Fish remains and ammonoids sampled in this area all occur in organic-rich, unbioturbated, alternating thin-bedded limestone and shale, indicative of anoxic bottom waters.
Palomino Ridge.—Specimen PIMUZ A/I 4397 was found on the eastern slopes of Palomino Ridge (Elko County, northeast Nevada; Fig. 1.2). Palomino Ridge, a ~5 km long and ~2.5km wide, north-northwest to south-southeast trending structure, is located ~15km northwest of Currie (southern Elko County) and ~2.5km west of US Route 93, in T29N, R63E. The backbone of Palomino Ridge is formed by steeply
dipping, highly competent, medium- to thick-bedded limestone of the Permian Gerster Formation, which strikes more or less parallel to the ridge. The base of the Lower Triassic Thaynes Group crops out intermittently on the lower eastern slopes of Palomino Ridge. The Thaynes Group is also exposed in other, nearby localities north of Currie (Lucas and Orchard, 2007). At Palomino Ridge, Smithian strata directly overly a 4m thick chert conglomerate in sharp unconformable contact with the underlying Gerster Formation. The Smithian succession consists of a thick series of shale, interbedded shale and thin- bedded limestone, and thicker limestone beds. Most of these beds are fossiliferous and, consequently, the section represents a
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much-expanded Smithian ammonoid succession (Jattiot et al., in press), similar in scope but slightly less complete than the successions described by Brayard et al. (2013) from the Confusion and Pahvant ranges of western Utah. Referring to Jattiot et al. (in press), the oldest ammonoid-
bearing beds at Palomino Ridge are of late early Smithian age. The next overlying strata contain middle Smithian ammonoids, including the Inyoites oweni fauna of late middle Smithian age. Above the Inyoites beds are several, 5–10cm thick limestone beds, which yield an early late Smithian cosmopolitan ammonoid assemblage characterized by Anasibirites (Jattiot et al., 2015). Ammonoids are less abundant in the next overlying beds that yield Xenoceltites subevolutus and Pseudosageceras augustum. PIMUZ A/I 4397 was found in situ in these latest Smithian P. augustum beds (layer PLR 35, Unitary Association Zone 6 of Jattiot et al., in press) in Section 2 (N40°23'00.0'', W114°50'09.9''; Fig. 2) of Jattiot et al. (in press). The P. augustum beds are typically represented by black shales with minor, very thin-bedded (cm), dark limestone. Here again,
local anoxic bottom waters favored a good preservation of the fish fossil.
Crittenden Springs.—Specimen NMMNH P-77357 was found at Crittenden Springs (northeast Elko County, Nevada). The classical ammonoid collecting site referred to as Crittenden Springs (e.g., Kummel and Steele, 1962; Jenks, 2007; Jenks et al., 2010) is located on the north side of Long Canyon (township/range coordinates: W½SW¼ Sec 3, T42N, R69E) ~29km north of Montello, Elko County (Fig. 1.2). Thousands of exceptionally well-preserved Smithian ammonoids, many of which retain relict color bands, and other fossils have been collected from the site since it was discovered in the early 1950s (Mullen, 1985; Jenks et al., 2010). Disarticulated vertebrate bones are occasionally found in association with the ammonoids of the ‘Meekoceras beds’ (personal observation, JJ,KGB, TMS, HB, 2010–2016). Lower Triassic marine sediments, consisting of the
Dinwoody Formation and units belonging to the overlying Thaynes Group, crop out in the hills immediately north of the Long Canyon road and extend to the northeast for ~8 km, covering an area of ~33km2 (Clark, 1957; Mullen, 1985). Good exposures of Spathian shales are limited to a few seasonal storm drainage channels. One such channel cuts numerous, gently northward dipping layers with early diagenetic limestone nodules, most of which are barren, but a few yield ammonoids (e.g., Stacheites) typical of the early late Spathian Fengshanites/ Prohungarites fauna (Bucher, 1989; Guex et al., 2010). A float concretion found in the same channel contains a partial skeleton of an actinopterygian (NMMNH P-77357), which is described herein. Additional, articulated cranial material (PIMUZ A/I 4641; Birgeria?) has recently been recovered from the Spathian of Crittenden Springs and is currently undergoing preparation for eventual study.
Materials and methods
The described material is curated in part by theNMMNH,and in part by the PIMUZ. PIMUZ A/I 4397 from Palomino Ridge and one specimen from the Winecup Ranch (NMMNH P-66225)
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