A New Polycotylid Plesiosaur with Extensive Soft
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Boletín de la Sociedad Geológica Mexicana / 2017 / 87 A new polycotylid plesiosaur with extensive soft tissue preservation from the early Late Cretaceous of northeast Mexico Eberhard Frey, Eric W. A. Mulder, Wolfgang Stinnesbeck, Héctor E. Rivera-Sylva, José Manuel Padilla-Gutiérrez, Arturo Homero González-González ABSTRACT Eberhard Frey ABSTRACT RESUMEN [email protected] Staatliches Museum für Naturkunde Karl- sruhe, Geowissenschaftliche Abteilung, Erb- A nearly complete skeleton of a poly- Se describe el esqueleto casi completo de un prinzenstraße 13, 76133 Karlsruhe, Germany. cotylid plesiosaur is described from nuevo plesiosaurio polycotílido. El ejemplar the early Late Cretaceous laminat- procede de las calizas laminares de Valle- Eric W. A. Mulder Museum Natura Docet Wonderryck Twente, ed limestones at Vallecillo, northeast cillo del noreste de México y fue asignada Oldenzaalsestraat 39, 7591 GL Denekamp, Mexico. It shows extensive soft tissue estratigráficamente a la parte temprana del the Netherlands. preservation. In some exceedingly Cretácico Tardío. En las porciones mejor well preserved areas there are trans- preservadas de las partes blandas se iden- Wolfgang Stinnesbeck Universität Heidelberg, Institut für Geowis- versely elongate rectangular to trap- tificaron estructuras milimétricas, alarga- senschaften, Im Neuenheimer Feld 234-236, ezoid millimetric scale-like structures das transversalmente de forma rectangular 69120 Heidelberg, Germany. arranged in longitudinal rows. The a trapezoidal, y con orden longitudinal. En trailing edge skin flap preserves fibers la solapa, el borde posterior de la piel pre- Héctor E. Rivera-Sylva José Manuel Padilla-Gutiérrez and scale rows perpendicular to the serva fibra y escamas, ordenadas en filas y Arturo Homero González-González trailing edge. A thick layer of subder- perpendiculares al borde de salida. Se iden- Museo del Desierto, Carlos Abedrop Dávila mal tissue is present, especially along tificó una capa de tejido subdermal, la que 3745, Centro Metropolitano, Parque Las the tail base. It was responsible for es particularmente gruesa en la base de la Maravillas, 25022 Saltillo, Mexico. the hydrodynamic drop-shaped body cola y debe haber contribuido al contorno hi- contour, with the body and tail form- drodinámico en forma de gota del animal, ing a single unit. The body shape formándose una entidad entre el cuerpo y la determined from the preserved soft cola. De acuerdo con el contorno y los teji- tissues suggests a swimming speed dos blandos, se presume que la velocidad del similar to extant leatherback turtles. animal debe de haberse aproximada a la de Based on the unique osteology of the una tortuga laúd. La enigmática osteología palate, which is intermediate between del paladar, intermedio entre Dolichorhyn- Dolichorhynchops and Trinacromerum, chops y Trinacromerum, la morfología única and according to the unique mor- de los cinturones y propodiales, igual que las phology of the girdles and propodi- vértebras gastrales medialmente convergentes, als as well as the medially converging permiten asignar el nuevo espécimen a un gastralia, the new specimen is placed nuevo género y especie de los Polycotilidae, in a new genus and species of Poly- Mauriciosaurus fernandezi gen. et sp. nov. cotylidae, Mauriciosaurus fernandezi gen. et sp. nov. Palabras clave: Paleontología de vertebrados, Plesiosauria, Poly- Keywords: Vertebrate palaeon- cotylidae, Cretácico Tardío, nor- tology, Plesiosauria, Polycotyli- este de México, preservación de BOL. SOC. GEOL. MEX. 2017 dae, Late Cretaceous, northeast partes blandas, paleoecología. VOL. 69 NO. 1 P. 87 ‒ 134 Mexico, soft tissue preserva- tion, palaeoecology. Manuscript received: December 4, 2016 Corrected manuscript received: December 29, 2016 Manuscript accepted: December 31, 2016 A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico 88 / Boletín de la Sociedad Geológica Mexicana / 2017 1. Introduction been fabricated. There is discussion on whether plesiosaurs could crawl on land, as do sea turtles Plesiosauria are one of the dominant groups of and pinnipeds, and on how fast they could swim INTRODUCTION Mesozoic marine reptiles. Besides the enigmatic (Taylor, 1986). The discovery of a pregnant fe- Pistosaurus and its allies of Middle to late Triassic male of a polycotylid plesiosauroid, a longirostrine age, two ‘suborders’ are distinguished in tradition- group of Late Cretaceous plesiosaurs, provides ev- al systematics, the either long- or short-necked idence that Plesiosauria were viviparous and did Plesiosauroidea and the exclusively short-necked not need to emerge on land for the purpose of egg Pliosauroidea (Carpenter, 1997; Druckenmiller laying (O’Keefe and Chiappe, 2011). and Russell, 2008; Ketchum and Benson, 2010; Despite numerous complete and fully articulated O’Keefe, 2001). A body with a rounded triangu- skeletons being available, there is a lack of soft lar or oval cross-section and a tail, whose length is tissues in the fossil record of Plesiosauria. Even shorter than the body, are the main features that in localities where soft tissue preservation is well characterize all Plesiosauria. Plesiosaurs swam known from other vertebrates in the assemblage with four hydrofoil-shaped flippers of almost equal there is no unequivocal record of soft tissue for size with dorsoventrally flattened limb bones, a plesiosaurs. In one single Holzmaden specimen of unique pattern of aquatic locomotion. Among Hydrorion brachypterygius in the collection of the Ge- Plesiosauria, flipper size varies with respect to ologisch-Paläontologisches Institut at Tübingen, body size (Ellis, 2003; Hampe, 1992). The skele- Germany (GPIT/RE/3185), a black substance tal anatomy of these predatory marine reptiles is trailing the proximal half of the posterior margin known from numerous excellently preserved spec- of the front fins is preserved suggesting a skinny imens, and much is known about their life style, flexible trailing edge (Großmann, 2006; Robinson, but little about their reproduction and ontogeny 1975). Besides the tail fin (Dames, 1895) this rep- (Noé, 1999; O’Keefe and Carrano, 2005; O’Keefe resents the only record of soft tissue preservation and Chiappe, 2011; Taylor, 1986). The diet of in plesiosaurs. Information on the body shape of elasmosauroids and pliosauroids is evidenced by plesiosaurs and the surface structure of their skin rare fossil stomach contents and the body cavity of remains a mystery. some specimens also contains gastroliths, the role Polycotylid plesiosaurs are a cosmopolitan taxon of which is still debated (Brown, 1904; Cicimurri with a temporal range extending from the Early and Everhart, 2001; Cope, 1872; Martill, 1992; Aptian to the Late Maastrichtian (Druckenmiller McHenry et al., 2005; Taylor, 1993). While sub- and Russell, 2009). One of the currently oldest aqueous flight is generally accepted as the main representatives, the Australian Umoonasaurus dem- mode of locomotion, the mode of flipper opera- oscyllus (Kear et al., 2006), is no longer referred tion remains debated as the role of the tail (Frey to Polycotylidae by most authors (Druckenmiller and Riess, 1982; Godfrey, 1984; Halstead, 1989; and Russell, 2009). The same is true for Edgaro- Lingham-Soliar, 2000; Robinson, 1975; Sanders et saurus muddi from the Late Albian Thermopolis al., 2004; Taylor, 1981). Reconstructions of plesio- Shale of the United States which, according to saurs with a tail fin are based on a single specimen many authors, lies outside Polycotylidae (Albright of Seeleyosaurus guilelmiimperatoris (Dames, 1895) III et al., 2007a; Benson et al., 2013; Schumacher, from the Early Jurassic of Holzmaden (South 2007; Schumacher et al., 2016) Two specimens, Germany). This specimen shows a black expand- AM 6206-6298 and SAM P36356, both from ed substance dorsal to the posterior quarter of the the Aptian or Albian Bulldog shale of Australia posterior vertebral column. However, Großmann (Kear, 2006), have not been formally named. The (Großmann, 2006) states that after a detailed study earliest polycotylid from North America, TMP of the specimen that this tail fin is likely to have 95.87.01, comes from the Albian Clearwater For- A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico Boletín de la Sociedad Geológica Mexicana / 2017 / 89 mation of Alberta, Canada, and is also unnamed. This report describes a new genus and species of Thus, the earliest named polycotylids are those polycotylid plesiosaur (collection number INAH reported from the Cenomanian of North Amer- CPC RFG 2544 P.F.1) from the Late Cretaceous ica [Eopolycotylus rankini, (Albright III et al., 2007a), of northeast Mexico. The specimen comes from Palmulasaurus quadratus, (Albright III et al., 2007a, laminated limestones cropping out around the INTRODUCTION b), Pahasapasaurus haasi, (Schumacher, 2007)] and town of Vallecillo (26°39’N 99°59’W), about 100 Morocco [Thililua longicollis, (Bardet et al., 2003)]. km north of the City of Monterrey, Nuevo León The geologically youngest polycotylid has no for- (Figure 1). The skeleton is complete, fully articu- mal name or collection number and comes from lated and represents the first plesiosaur preserving New Zealand (Kear, 2006: p. 847, Figure 2E). The dermal surface structures in fine detail. The spec- geologically youngest named species, Sulcusuchus imen was discovered in summer 2011 by a group erraini comes from near the Campanian/Maas- of workmen in an active limestone quarry in the trichtian