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A Large Neosuchian Crocodyliform from the Upper Cretaceous (Cenomanian) Woodbine

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A Large Neosuchian Crocodyliform from the Upper Cretaceous (Cenomanian) Woodbine A large neosuchian crocodyliform from the Upper Cretaceous (Cenomanian) Woodbine Formation of North Texas THOMAS L. ADAMS, *, 1 CHRISTOPHER R. NOTO, 2 and STEPHANIE DRUMHELLER 3 1Witte Museum, San Antonio, TX, 78209, U.S.A., [email protected]; 2Department of Biological Sciences, University of Wisconsin–Parkside, P.O. Box 2000, Kenosha, Wisconsin 53141, U.S.A., [email protected]; 3Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 37996, U.S.A., [email protected] RH: ADAMS ET AL.—NEW CROCODYLIFORM FROM WOODBINE FM. *Corresponding author 1 ABSTRACT—A new taxon of neosuchian crocodyliform, Deltasuchus motherali, gen. et. sp. nov., is described on the basis of a partial skull recovered from the Arlington Archosaur Site within the Upper Cretaceous (Cenomanian) Woodbine Formation of north central Texas. This productive locality represents a delta plain ecosystem preserving a diverse coastal fauna including lungfish, turtles, dinosaurs (ornithopods and theropods), and crocodyliforms. Prior to this discovery, the only identified crocodyliforms from the Woodbine Formation had been the longirostrine taxa Terminonaris and Woodbinesuchus. This new taxon is differentiated from other known crocodyliforms by the presence of dual pseudocanines on both the dentary and maxilla;; anterior and posterior rami of jugal comparable in depth; anterolaterally facing margin on the dorsal portion of the postorbital; contact between the descending process of the postorbital and the ectopterygoid; and a large, deep fossa on the ventral surface of the quadrate. Phylogenetic analysis recovers D. motherali as the sister taxon to Paluxysuchus newmani from the Lower Cretaceous Twin Mountains Formation of Texas. This clade lies within Neosuchia basal to Goniopholididae + Eusuchia. The associated cranial elements of this new crocodyliform represent a large, broad snouted individual, an ecomorphotype often associated with the semi- aquatic ambush predator niche in this clade, and one not previously reported from the formation. 2 INTRODUCTION The terrestrial fossil record of North America in the Cretaceous is characterized by major temporal and spatial biases. In the Lower Cretaceous, rich fossil deposits are concentrated in the Aptian and Albian, while the Upper Cretaceous fossil record is dominated by Campanian and Maastrichtian assemblages (Weishampel et al., 2004). The stretch of time in between, representing roughly 20 million years, is comparatively poorly sampled (Jacobs and Winkler, 1998; Zanno and Makovicky, 2013). Additionally, the majority of these fossils are known from the western continent of Laramidia. Relatively little is known about Appalachia to the east, separated from the better studied, Laramidian assemblages by the Western Interior Seaway (Ullmann et al., 2012; Krumenacker et al., 2016; Prieto-Márquez et al., 2016). Recent research at the Arlington Archosaur Site (AAS), a fossil-rich outcropping of the Woodbine Formation located in the suburban enclave of Arlington, Texas, is starting to fill in this gap (Fig. 1). The AAS preserves a coastal environment, with both marine and freshwater influences, that includes sharks, bony fishes, lungfish, turtles, lissamphibians, mammals, crocodyliforms, and ornithopod and theropod dinosaurs (Noto et al., 2012). The site has been dated to the Cenomanian, placing it within the sparsely sampled middle Cretaceous interval. Deposited within an extensive deltaic system on the southwestern margin of Appalachia, the site also provides a window into the diversity of this poorly understood landmass. Here we present a new species of crocodyliform from the AAS. While crocodyliform fossils are relatively common throughout the middle Cenomanian (96 Ma) Woodbine Formation of north-central Texas, their remains are typically fragmentary and represented by isolated teeth, vertebrae, and osteoderms (Lee, 1997a; Head, 1998; Jacobs and Winkler, 1998; Adams et al., 3 2011). Previously, the only two taxa recognized from the Woodbine Formation have been Terminonaris Osborn, 1904 and Woodbinesuchus Lee, 1997 (Adams et al., 2011). Both these taxa are longirostrine neosuchians, with Terminonaris having been interpreted to occupy marginal to fully marine paleoenvironments (Hua and Buffetaut, 1997; Wu et al., 2001). The AAS, with its unusually well-preserved fossils in comparison to other Woodbine localities, has yielded at least four crocodyliform taxa, based on numerous isolated cranial and postcranial remains (Adams et al., 2015; Noto, 2015). The dominant constituent of the assemblage is a new species represented herein by a partial skull from a single large individual. The aim of this study is to describe this new crocodyliform taxon from the AAS and to assess its evolutionary relationships and ecological role in a middle Cretaceous coastal community. Anatomical Abbreviations—bo, basioccipital; bos, basioccipital suture; cqc, cranio- quadrate canal; ect, ectopterygoid; ects, ectopterygoid sutural surface; exos, exoccipital sutural surface; fae, foramen aëreum; gf, glenoid fossa; ics, intercondylar sulcus; itb, intertemporal bar; j, jugal; js, jugal sutural surface; leu, lateral Eustachian foramen; lhc, lateral hemicondyle; meu, median Eustachian foramen; mg, maxillary groove; mhc, medial hemicondyle; mx, maxilla; na, nasal; nar, naris; nvf, neurovascular foramina; oto, otoccipital (opisthotic-exoccipital); parop, paroccipital process; pcf, posterior carotid foramen; pmx, premaxilla; po, postorbital; pob, postorbital bar; polp, postorbital lateral process; pop, postorbital process; pts, pterygoid sutural surface; q, quadrate; qad, quadrate anterodorsal process; qat, adductor tubercle of the quadrate; qd, quadrate dorsal process; qjs, quadratojugal suture; qpt, quadrate pterygoid process; qfv, ventral fossa of the quadrate; qs, quadrate suture; roe, external otic recess; sps, splenial suture; sq, squamosal; sqs, squamosal sutural surface; sus, surangular sutural surface; sym, mandibular 4 symphysis; IX–XI, foramen for glossopharyngeal, vagus, and accessory nerves; XII, foramen for hypoglossal nerve. Institutional Abbreviation—DMNH, Perot Museum of Nature and Science, Dallas, Texas, U.S.A.; SMU, Southern Methodist University Shuler Museum of Paleontology, Dallas, Texas, U.S.A. ; TMM, Texas Memorial Museum, University of Texas, Austin, Texas, U.S.A. AGE AND GEOLOGIC SETTING The Upper Cretaceous Woodbine Formation of North Texas unconformably overlies the Grayson Marl, the uppermost formation of the Washita Group, and is overlain by the Eagle Ford Group (Fig. 2A; Dodge, 1969; Lee, 1997a, 1997b; Jacobs and Winkler, 1998). In outcrop, it extends from the Red River and thins to the south (Dodge, 1969; Jacobs and Winkler, 1998). Dodge (1969) designated four lithologic units within the formation near Dallas and Fort Worth, in ascending order: the Rush Creek, Dexter, Lewisville, and Arlington members. The lower Woodbine sediments (Rush Creek and Dexter members) represent marginal marine to fully marine deposits (Bergquist, 1949; Dodge, 1969; Oliver, 1971). The uppermost Lewisville and Arlington members represent a terrigenous coastal depositional system with fluvio-deltaic influences (Powell, 1968; Dodge, 1969; Lee, 1997a, 1997b; Jacobs and Winkler, 1998). The Arlington Archosaur Site is located within the Lewisville Member of the upper strata of the Woodbine Formation (Fig. 2A). The ammonite Conlinoceras tarrantense, a zonal marker for the base of the middle Cenomanian, was found within the Lewisville Member and in the Tarrant Formation (lowermost Eagle Ford Group), indicating an age no younger than early middle 5 Cenomanian (approximately 96 Ma; Kennedy and Cobban, 1990; Emerson et al., 1994; Lee, 1997a; Jacobs and Winkler, 1998; Gradstein et al., 2004). PALEOECOLOGY AND TAPHONOMY The Arlington Archosaur Site preserves a diverse community of vertebrates, invertebrates, and plants deposited in a lower delta plain system created during a regressive phase along the southeastern margin of the Western Interior Seaway (Oliver, 1971; Main, 2005; Adams and Carr, 2010; Noto et al., 2012). Exposures consist of a hillside 200 m in length, with approximately 50 m representing the main fossil quarry (Fig. 2B). South of the hillside patches of sandstone containing shark teeth, trace fossils representing a Skolithos ichnofacies, and ripple marks are exposed (Seilacher, 2007; Main, 2013). While their precise relation to hillside exposures is uncertain, the sandstone likely sits lower in section. The following description includes the most common and laterally extensive facies of the hillside exposure. Facies A forms the primary fossil quarry from which the majority of specimens have been recovered. It consists of a dark brown sandy siltstone at least 50 cm deep overlain by a 30– 40 cm thick dark gray layer of carbonaceous sandy siltstone, the upper portion of which contains slickensides. Sulfur bands, gypsum, and pyrite are prevalent throughout this layer. Abundant plant material is preserved in the form of broad, lenticular mats of featureless carbonized remains as much as 4 cm thick, compressed but well-preserved carbonized tree sections 15–20 cm wide, and smaller fragments of permineralized wood (Main, 2013). A high abundance of terrestrial palynomorphs (primarily ferns), well-preserved microscopic organic matter, rare dinoflagellates, 6 absence of foraminifera, lungfish toothplates, non-marine turtles, and lissamphibians, indicates fluvial deposition with minor marine input (Main, 2013). Fragmentary
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