Frederickson and Davis—First actinopterygian from Lower Jurassic Navajo Sandstone
549
Salt Lake City UTAH COLORADO 89
Inset Area
OMNH V1700
ARIZONA 100 km Flagstaff Figure 1. Map showing extent of Navajo Sandstone exposures in southwestern USA; inset shows location of OMNH V1700. Modified fromWinkler et al. (1991). Study of the vertebrate paleobiota of the Navajo Sandstone
has understandably been focused on its ichnofauna. Vertebrate trackways are diverse and locally abundant (see summary in Irmis, 2005; Milàn et al., 2008), and complex burrows poten- tially made by small mammaliaforms have also been found (Riese et al., 2011). However, some body fossils are known from the Navajo; while incomplete,most are articulated and very well preserved. Though most specimens are indeterminate below family or order, the assemblage is clearly taxonomically diverse (Irmis, 2005). Some specimens (at least two sauropodomorphs) were discovered in eolian sandstones: a partial skeleton first reported by Brady (1935, 1936) and described later by Galton (1971); and the sauropodomorph Seitaad (Sertich and Loewen, 2010), which was preserved in a dune-collapse deposit. The majority of body fossils, however, have been recovered from interdune deposits. These represent paleoenvironmentswith better preservational potential than the surrounding dunes, and likely served as beacons to concentrate animals (Winkler et al., 1991; Irmis, 2005). Despite the inferred persistence and scale of some Navajo interdunes (from plant and invertebrate remains, e.g., Eisenberg, 2003; Parrish and Falcon-Lang, 2007), aquatic taxa such as fish have not been described, and the known record of vertebrates is limited to tetrapods (crocodylomorphs, dinosaurs, and tritylodontids, though turtles are also yet unknown). It is unclear if this reflects a lack of suitable distribution routes between Navajo interdunes and larger surrounding bodies ofwater or,more likely, poor sampling. In 2013, an OMNH field party discovered small patches of articulated fish scales in an interdune deposit within the Navajo
Sandstone along the Paria River in Grand Staircase-Escalante National Monument, southern Utah (OMNH locality V1700, Fig. 1). These exposures are within the Cockscomb, a portion of the East Kaibab monocline (see Doelling et al., 2010). The entire section is heavily tilted and folded such that the Navajo partly overlies the stratigraphically higher Carmel Formation at their contact. The interdune deposit is positioned towards the top of the Navajo, but the contact with the Carmel has been deformed so its precise position in the section is difficult to determine. The deposit is ~5–8m thick, and begins with a lower, structureless, dark-reddish sandstone that weathers into large, angular boulders. This is followed by a thinly laminated (5mm beds), well-cemented purple siltstone that transitions upwards to a pale yellow, indurated but still laminated siltstone. A blocky, yellow, tabular sandstone with ~ 30 cm beds caps the sequence. Typical eolian sandstone beds are present above and below the interdune deposit, with fairly sharp contacts. The specimens described in this paper were recovered from the purple siltstone beds. Precise locality information is on file at the OMNH, and is available to qualified investigators upon request.
Systematic paleontology Class Actinopterygii Klein, 1885
Subclass Neopterygii Regan, 1923
Order Semionotiformes Arambourg and Bertin, 1958 sensu Olsen and McCune, 1991 Family indeterminate
NEW MEXICO 5 km
COCKSCOMB
COCKSCOMB
COCKSCOMB
Cottonwood Canyon Rd.
Paria R.
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