A new postcranial skeleton of an elasmosaurid

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Otero, R., Soto, S., Vargas, A., Rubilar-Rogers, D. 2014. A new postcranial skeleton of an elasmosaurid plesiosaur from the Upper Cretaceous of central Chile and reassessment of the historic species Cimoliasaurus andium Deecke. Cretaceous Research 50: 318-331.

Transcript of A new postcranial skeleton of an elasmosaurid

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    Article history:Received 19 July 2013Accepted in revised form 12 May 2014Available online

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    twenty-nine vertebrae, 25 fragments of neural spines (regarded asspinal apophyses), 25 rib fragments, eight fragmentary teeth(comprising plesiosaur and sclerorhynchid teeth), one phalanx, twoadditional ilia (making three total for this specimen association),and ten indeterminate bone fragments. These authors recoveredadditional remains in the following years, including elements that

    mprised a secondcentimetres belowle the trunk regionments oriented tointo a display that,postcranial skel-

    te Museum on thewere returned toional Museum ofspection revealed

    the parts of at least two individuals. Unfortunately, much of therelevant information about the original discovery was lost. There-fore, the specimens had to be separated using criteria that includedpreservation, morphology, relative size, and vertebral measure-ments (including graphic bivariate analysis of cervical proportions).One of the two specimens (SGO.PV.6507) is preliminary identiedas an indeterminate aristonectine (subfamily AristonectinaeO'Keefe and Street, 2009, sensu Otero et al., 2012). This skeletonincludes the atlas-axis and anterior cervicals rstly described by* Corresponding author.

    Contents lists availab

    Cretaceous

    els

    Cretaceous Research 50 (2014) 318e331E-mail address: paracrioceras@gmail.com (R.A. Otero).1. Introduction

    During the early 1990s, marine reptile remains were discoveredin the town of Pelluhue, central Chile (Fig. 1). The rst fossils weredescribed by Castillo et al. (1992), who identied them as Plesio-sauria indet. and assigned a Late Cretaceous age without additionalchronostratigraphic resolution. The gured material includes 6most anterior cervical vertebrae (including the atlas-axis), a midposterior cervical vertebra, one tooth, and one ilium (misidentiedas a fragment of humerus). Among non-gured elements are

    were found by locals. These new elements coskeleton (reported here), and were found a fewthe rst. The neck was oriented to the north whiwas twisted and crushed, leaving the caudal elethe west. Later, both specimens were combinedtogether, included the parts of a near completeeton. This display was kept on exhibit in a privacity of Santiago until 2010. When the skeletonsthe Museo Nacional de Historia Natural (NatNatural History, Santiago, Chile), a preliminary inElasmosauridUppermost CretaceousQuiriquina FormationSoutheastern Pacichttp://dx.doi.org/10.1016/j.cretres.2014.05.0080195-6671/ 2014 Elsevier Ltd. All rights reserved.a b s t r a c t

    We describe a new specimen of an elasmosaurid plesiosaur from the upper Maastrichtian of centralChile. The specimen includes a relatively complete dorso-caudal series, a few cervical vertebrae, and afragmentary pelvic girdle. The specimen is identied as a sub-adult non-artistonectine elasmosaurid(Sauropterygia, Plesiosauria) based on graphic bivariate analysis of the cervical vertebral proportions. Thecaudal vertebrae have distinctive features such as neural arches that are recurved cranially, with pedicelsoverlapping the dorso-posterior surface of the immediately anterior centrum, and terminal centra withtwo pairs of deep dorsal articulations for the neural arches. These unusual features are present in severallate Maastrichtian adult specimens from the Quiriquina Formation of central Chile, and have beenincluded within the hypodigm of the historic taxon Cimoliasaurus andium Deecke (nomen dubium). Thespecimen studied here likely represents the same taxon or a closely related form, showing slightdifferences in both size and ontogenetic stage. The preserved elements of this new skeleton affordcomparison with several other late Maastrichtian specimens from Chile that were previously, albeittentatively, referred to C. andium. The similarity of these specimens suggests that the late Maastrichtianelasmosaurid diversity of central Chile (excluding aristonectines) may be represented by taxa with lowmorphological disparity, or by a single taxon.

    2014 Elsevier Ltd. All rights reserved.Area de Paleontologa, Museo Nacional de Historia Natural, Casilla 787, Santiago, ChileA new postcranial skeleton of an elasmUpper Cretaceous of central Chile and randium Deecke

    Rodrigo A. Otero a, *, Sergio Soto-Acu~na a, b, Alexanda Red Paleontologica U-Chile, Laboratorio de Ontogenia y Filogenia, Departamento de B3425, Santiago, Chileb

    journal homepage: www.aurid plesiosaur from thessessment of Cimoliasaurus

    O. Vargas a, David Rubilar-Rogers b

    ga, Facultad de Ciencias, Universidad de Chile, Las Palmeras

    le at ScienceDirect

    Research

    evier .com/locate/CretRes

  • s ReCastillo et al. (1992). The second postcranial specimen studied here(SGO.PV.6506) preserves a good part of its axial skeleton andfragments of the pelvic girdle, which show that it is not an arti-stonectine, but rather closely related to the long-necked plesiosaursmore common to the Cretaceous of the Northern Hemisphere.

    The remains of the SGO.PV.6506 include a nearly completecaudal series with interesting features. The neural arches beardistinctive morphologies such as an anterior displacement of theneural pedicels, causing the posterior vertebrae to have an overlapof the neural arch into the immediately anterior centrum. The

    Fig. 1. Map indicating the locality of Pelluhue in central Chile (35480200S, 72340500W)and its relative distance to the main outcrops of the Quiriquina Formation in the areaof the homonymous island.

    R.A. Otero et al. / Cretaceouextreme representation of this condition is observed in the caudal-most centrawhere an additional pair of facets appears on the dorsalsurface of these centra. Displaced neural arches overlapping theiranterior centra have been observed among other Late Cretaceousfossils from Chile, particularly, in the specimens regarded as cer-vical vertebrae of the taxon Cimoliasaurus andium Deecke (inSteinmann et al., 1895) (nomen dubium) from upper Maastrichtianbeds of Quiriquina Island, central Chile. The cervical vertebrae ofC. andium are actually caudal vertebraewith neural arches similarto those present in the specimen SGO.PV.6506. In addition, thecombination of characters form the caudals, cervical vertebrae, andpelvic girdle of SGO.PV.6506 were compared with other LateCretaceous specimens from theWeddellian Biogeographic Province(Zinsmeister, 1979, WBP hereafter) where similar anatomical ele-ments are preserved and/or described. Based on these compari-sons, we group these Chilean specimens within a singlemorphotype, which appears to be different from other non-aristonectine elasmosaurids from the WBP (at least based on thedistinctive ilium and the caudal features). However, because of thelack of the skull material and the incompleteness of each specimen,we conservatively refrain any attempt of generic or specicdetermination.

    2. Locality and geologic setting

    Pelluhue (35480200S, 72340500W) is in central Chile, about320 km southwest of Santiago (Fig. 1). The southern part of thetown, Mariscadero, has basement rocks conformed by massivesandstones with intercalated levels of concretionary nodules andcross-bedding, including a rich fossil diversity of both invertebratesand vertebrates. Thiele and Tavera (1967) analyzed fossil verte-brates and invertebrates collected from Loanco (25 km N from thestudied locality), assigning for rst time a Senonian age to thefossil-bearing levels. Later, Biro-Bagoczky (1982) formalized thename of Quiriquina Formation for those Upper Cretaceous bedsexposed 100 km southwest from the locality studied here, con-straining the age of the formation to the CampanianeMaastrichtianbased on biostratigraphic correlations. In addition, offshore wellsstudied by Mordojovich (1976) and taken 100 km in front of FaroCarranza (35 km north from Pelluhue) showed 1000 m of UpperCretaceous marine sediments, a basin large enough to include thedeposits from type locality of the Quiriquina Formation and thosefrom Pelluhue, located 100 km N from the rst. Cecioni (1983)attempted to formalize the status of the sandstones of FaroCarranza-Pelluhue, by erecting the Chanco Formation. Cecioni(1983) indicated that the Chanco Formation was correlated to thebase of the Quiriquina Formation, and assigned it a late Campanianage based on fossil invertebrates. Mordojovich (1976) and Cecioni(1980, 1983) recognized the existence of Eocene beds in the area,based on drillings performed offshore. These studies indicate thatthe Quiriquina Formation and the sandstones of Faro Carranza-Pelluhue belong to the same basin that existed at least since theUpper Cretaceous, and was deposited until the Eocene. Stinnesbeck(1986) considered the beds of the Chanco Formation as equivalentto the Quiriquina Formation based on the fossil invertebrates,rening its age to the Maastrichtian. Later, Tavera (1988) correlatedthe levels of Pelluhue with the lower levels of the QuiriquinaFormation.

    Based on eld data collected during this current research, thesection exposed at Pelluhue (Fig. 2) comprises a basal conglomer-atic, yellowish, sandstone with ne conglomerate lenses includingvariable clasts under 10 cm. The base of this level is not visible andthe exposed thickness is estimated close to 2 m. Conglomeratesandstones are overlaid by near 1 m of very bioturbated sandstoneswith abundant traces of Thalassinoides isp. The bioturbated layer isconformably overlain by approximately 2 m of massive mediumgrain, yellow to grey, sandstones. The plesiosaur specimensSGO.PV.6507 and 6506 were found in this sandstone layer.SGO.PV.6507, tentatively identied as aristonectine elasmosaurid,was found a few centimetres above SGO.PV.6506. Fossiliferousconcretions are present near the roof of the bioturbated sandstoneand include remains of vertebrates r