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Journal of Paleontology 91(5):1025–1046
posteriorly to the frontals, but the boundaries between these elements are mostly unclear. Rostrum.—The margins between the bones composing the
rostrum are only partly visible. The tip of the rostrum is formed by the large, unpaired rostropremaxilla (Fig. 6). Posterolaterally, the rostropremaxillary bone tapers on both sides. Caudal to the rostropremaxilla lies the small lachrymal, which is possibly preserved on the left side. The nasaloantorbital forms the anterior border of the orbit. This bone is wedged between the lachrymal and the posterolateral part of the rostropremaxilla ventrally, and the frontal dorsally. Its anterior end is elongate and probably acute. The nasaloantorbital contains both external narial openings, which are well visible on the right side of the skull (Fig. 6). The anterior naris is deeper than the posterior one. The nasaloantorbital also includes the junction of three sensory canals, which is situated ventral to the nares. The supraorbital canal enters the nasaloantorbital dorsally and runs between the narial openings. The ethmoidal canal passes laterally through the rostropremaxilla and pierces the nasaloantorbital through its anteroventral margin. The infraorbital canal enters the nasaloantorbital coming from the lachrymal.
Remarks.—PIMUZ A/I 4397 is a saurichthyid but, identification to the species level is complicated due to its incomplete preservation. The majority of diagnostic traits differentiating species of Saurichthys pertain to the postcranium, which is not preserved in the specimen from Palomino Ridge (see Discussion). The skull has a preserved length of ~132mm, suggesting
that it belonged to a medium-sized saurichthyid (sensu Tintori, 2013). The rostrum is subcomplete and long (~100mmfrom the tip of the snout until the anterolateral margin of the orbit).
Actinopterygii indet. Figure 7
Occurrence.—Early late Spathian Fengshanites/Prohungarites beds (Thaynes Group), Crittenden Springs, northeast Elko County, Nevada, USA (Fig. 1).
Description.—NMMNH P-77357 (Fig. 7) is a posterior body portion of a medium-sized actinopterygian (estimated total
length: ~25–30 cm). Preserved are the scales, most of the caudal fin, and the basal portions of some lepidotrichia of the dorsal and anal fins. The skeletal elements are largely in situ and mostly preserved as imprints, which have been affected weakly to strongly by surface erosion. Squamation.—The squamation consists of rhombic scales
arranged in oblique vertical rows (Fig. 7). Scales are also developed on the proximal part of the dorsal caudal lobe. About 31 scale rows are counted along the lateral midline of the trunk, from the anterior end of the fossil to the caudal inversion. Dorsally, some of the vertical scale rows seem to split into two rows. The scales along the flank are about as long as they are deep, whereas those in the dorsal and ventral areas are less deep. The scale ornamentation and the lateral line sensory canal are not preserved, and a peg-and-socket articulation is not visible. Fins.—The proximal parts of at least six lepidotrichia of the dorsal fin are preserved in situ near the rostral end of P-77357
rows posterior to the dorsal fin. At least seven anal fin rays are discernible. Each fin ray is segmented into several short, close-set units, and some of the lepidotrichia bifurcate at least once. The caudal fin is abreviated-heterocercal, exhibiting a reduced, scaled body lobe (Fig. 7). The distal ends of the dorsal
and ventral caudal lobes are not preserved. Most of the caudal fin web is not well visible, but the lepidotrichia are clearly segmented into short elements and at least the central fin rays are distally branched. The leading margin of the dorsal caudal fin ramus is preceded by one lanceolate scute, followed posteriorly by three unpaired basal fulcra and ~12 paired basal fulcra (Pattern II of Arratia, 2009). The first (anterior) unpaired basal fulcrum has a weakly concave anterior margin, whereas the two caudally following ones have distinctly concave anterior borders. Small fringing fulcra are observed along the leading margin of the ventral caudal lobe.
Remarks.—Preservation of NMMNH P-77357 is not sufficient for an attribution at low taxonomic rank, and it is thus left in open nomenclature.
Taxonomy and comparative anatomy
Birgeria Stensiö, 1919.—Birgeria is known from most marine Triassic fish localities, with up to 11 nominal species (Stensiö, 1919, 1921, 1932; Boni, 1937; Lehman, 1948, 1952; Nielsen, 1949; Savage and Large, 1966; Schwarz, 1970; Beltan, 1980; Bürgin and Furrer, 1992, 1993; Jin, 2001; Liu et al., 2006; Romano and Brinkmann, 2009; this study). Its occurrence in the Permian of Bolivia is questionable (Beltan et al., 1987; Cione et al., 2010). Contrary to Saurichthys (Romano et al., 2012), species richness of Birgeria remained relatively low and steady during the Triassic. Fossils of Birgeria are often (but not always) relatively rare within fish assemblages (e.g., Lombardo and Tintori, 2005; Scheyer et al., 2014), a fact that has been ascribed to the anatomically inferred offshore habitat of this taxon (e.g., Schwarz, 1970). From the eastern Panthalassan rim, Birgeria has thus far
been described from the Early Triassic of western Canada (Schaeffer and Mangus, 1976; Neuman, 2015), Greenland (Stensiö, 1932; Nielsen, 1949; Jessen, 1972; Ørvig, 1978; Bartsch, 1988), Spitsbergen (Stensiö, 1921, 1932; Scheyer et al., 2014), and Arctic Russia (Berg et al., 1964). The Canadian and Russian birgeriids are poorly known. Birgeria was also reported from Lower Triassic exposures near Bear Lake, Idaho, USA (Dunkle cited in Schaeffer and Mangus, 1976, p. 552), but this material has not been described in the literature and the repositories are unknown. Lastly, cranial remains from the Late Triassic of California described as Xenestes velox Jordan, 1907 have been reassigned to Birgeria by Stensiö (1932); however, this poorly known species needs revision. The specimens described herein represent the first fossil evidence for the occurrence of Birgeria in the Early Triassic of the western USA. Birgeria encompasses species of large size that, together
with some species of Saurichthys Agassiz, 1834, pertained to the actinopterygian apex predators of the Triassic (Lombardo and Tintori, 2005). One of the largest individuals of Early
(Fig. 7). The fin rays are subdivided into short segments. The anal fin, although incomplete as well, seemingly inserts a few scale
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