Journal of Paleontology, 91(5), 2017, p. 1025–1046 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2017.36
Marine Early Triassic Actinopterygii from Elko County (Nevada, USA): implications for the Smithian equatorial vertebrate eclipse
Carlo Romano,1 James F. Jenks,2 Romain Jattiot,1,3 Torsten M. Scheyer,1 Kevin G. Bylund,4 and Hugo Bucher1
1Paleontological Institute and Museum, University of Zurich, Karl Schmid-Strasse 4, 8006 Zurich, Switzerland ⟨
carlo.romano@
pim.uzh.ch⟩;
⟨
romain.jattiot@pim.uzh.ch⟩; ⟨
tscheyer@pim.uzh.ch⟩; ⟨
hugo.fr.bucher@
pim.uzh.ch⟩ 21134 Johnson Ridge Lane, West Jordan, Utah 84084, USA ⟨
jenksjimruby@gmail.com⟩ 3UMR CNRS 6282 Biogéosciences, Université de Bourgogne, 6 Boulevard Gabriel, 21000, Dijon, France ⟨
romain.jattiot@pim.uzh.ch⟩ 4140 South 700 East, Spanish Fork, Utah 84660, USA ⟨
kevin@ammonoid.com⟩
Abstract.—The Early Triassic vertebrate record from low paleolatitudes is spotty, which led to the notion of an ‘equatorial vertebrate eclipse’ during the Smithian. Here we present articulated ray-finned fishes (Actinopterygii), collected from the marine Lower Triassic Thaynes Group at three new localities in Elko County (Nevada, USA), which were deposited within the equatorial zone. From the Smithian of the Winecup Ranch, we describe two partial skulls of the predatory actinopterygian Birgeria (Birgeriidae), attributed to B. americana new species and Birgeria sp. Birgeria americana n. sp. is distinguished from other species by a less reduced operculogular series. With an estimated total length of 1.72–1.85 m, it is among the largest birgeriids. We confirm that Birgeria encompasses species with either two or three rows of teeth on the maxilla and dentary, and suggest that species with three well-developed rows are restricted to the Early Triassic. From the latest Smithian of Palomino Ridge, we present a three-dimensional, partial skull of the longirostrine predator Saurichthys (Saurichthyidae). This and other occurrences indicate that saurichthyids were common in the western USA basin. From the early late Spathian of Crittenden Springs, we describe a posterior body portion (Actinopterygii indet.). This find is important given the paucity of Spathian osteichthyan sites. We provide a summary of Early Triassic vertebrate occurrences in the United States, concluding that vertebrate fossils remain largely unstudied. The presence of predatory vertebrates in subequatorial latitudes during the Smithian confirms that Early Triassic trophic chains were not shortened and contradicts the ‘equatorial vertebrate eclipse’.
Introduction
The end-Permian mass extinction event (~251.9 Ma; Burgess et al., 2014) was the most severe biotic crisis of the Phanerozoic, marking a significant change within marine and continental biocoenoses (e.g., Raup, 1979; Sepkoski, 1984). In the aftermath of this catastrophic event, the surviving and newly evolved clades went through a series of subsequent crises during the Early Triassic, which selectively affected their recovery (e.g., Galfetti et al., 2007b; Orchard, 2007; Brayard et al., 2009, 2011, 2017; Song et al., 2011;Hofmann et al., 2013a, b; Hochuli et al., 2016). Bony fishes (Osteichthyes) displayed relatively lower
diversity during the Paleozoic, but radiated extensively after the end-Permian mass extinction event (e.g., Tintori et al., 2014a; Friedman, 2015; Romano et al., 2016a). The Triassic fossil record bears testimony to the first diversification event of the Neopterygii, the group to which over half of all living vertebrate species belongs.Whereas most neopterygians were small during the Triassic, the ‘Palaeopterygii’ (non-neopterygian actino- pterygians) were predominantly represented by large species, suggesting that this group was important at higher trophic levels (Romano et al., 2016a).
recovery of the various clades of fishes remain unsettled because Early Triassic taxa are not as well studied as Middle Triassic ones (Scheyer et al., 2014; Tintori et al., 2014a; Romano et al., 2016a, b). Although Early Triassic fish assemblages have been described from numerous localities around the world (Brinkmann et al., 2010), some large paleogeographical domains and time intervals still suffer from a scanty record (e.g., López-Arbarello, 2004; Romano et al., 2016a, b). For example, little is known about low-latitude Early Triassic vertebrate faunas (e.g., Scheyer et al., 2014; Romano et al., 2016a)—a circumstance that led Sun et al. (2012) to speculate about an ‘equatorial vertebrate eclipse’, which they linked to extreme temperatures during the Smithian. Furthermore, the fossil record of Osteichthyes is marked by an extended interval with only a few, scattered occurrences during the Spathian (late Early Triassic). This Spathian gap in the osteichthyan fossil record potentially overlaps with the onset of the first neopterygian radiation (Romano et al., 2016a). Here we describe for the first time articulated fish remains
Despite recent advances, the detailed pattern and tempo of
from the Early Triassic of Nevada (USA)—a paleogeographic domain situated near the paleoequator. The presented material
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