Dinosaurios del yacimiento de Gnatalie (Utah) en el 11th North Paleontological Conference (California, USA)

Recientemente se ha presentado en el 11th North Paleontological Conference, NAPC 2019, en Riverside (California, USA) una comunicación oral sobre el trabajo paleontológico desarrollado en colaboración con el Dinosaur Institute do Natural History Museum of Los Angeles County y el Instituto Dom Luiz, en el yacimiento de Gnatalie del Jurásico Superior de la Formación Morrison (EE.UU.). 

Aquí va el pequeño resumen titulado “Gnatalie Quarry, a window to understand the dinosaurian paleodiversity of the Late Jurassic of Southeastern Utah (Morrison Fm., USA)”: 

A new Morrison Fm. bone-bed (Brushy Basin Member) from San Juan County (Utah) has been reported. The 'Gnatalie quarry' (locality LACM 7683; all specimens are housed at the Dinosaur Institute of the Natural History Museum of Los Angeles County) is one of the most important bone accumulations from the Upper Jurassic of Utah yielding multiple partial skeletons in anatomical connection or with a low dispersion of their skeletal elements in a moderate to low degree of articulation. More than 400 bones were found belonging to crocodylomorphs and dinosaurs including theropods (Allosaurus sp.), sauropods, ornithopods and thyreophorans (Ankylosauria indet. and Stegosauria indet.). Sauropods are represented by two taxa, one diplodocine and one camarasaurid. This fossil-site has produced several partially complete diplodocine individuals (at least five individuals), and the performed phylogenetic analyses place all these sets within the clade Barosaurus+Diplodocus, sharing the presence of a double posterior centroparapophyseal lamina on posterior dorsal vertebrae, straight ventral surface with projected chevrons facets in midcaudal vertebrae, or high twisted humeral shaft (>40º). The presence of pneumatic foramina until the 16th caudal vertebra (and perhaps beyond), deep ventral hollow in anterior- and middle-caudal vertebrae, or hook-like ambiens process, all support the inclusion of these specimens within Diplodocus. The recovered phylogenetic hypothesis and the detailed comparative analyses support a close relationship of the Gnatalie diplodocines with Diplodocus hallorum. In addition, the camarasaurid specimen found in Gnatalie comprises skull remains, dorsal, sacral and caudal vertebrae, dorsal ribs, chevrons and some partial appendicular elements. The detailed study of several specimens attributed to Camarasaurus reveals a possibly closer  relationship with the type specimen of Camarasaurus lewisi. Both specimens share the presence of (i) posterior centroparapophyseal lamina (that can be double in some vertebrae) in the middle-posterior dorsal vertebrae; (ii) sacral neural spines with transversely concave anterior and posterior face; (iii) bridged chevrons; (iv) dorsoventrally short neural canal; and (v) and anterior tuberosities on the ventral face of the middle caudal vertebrae. However, the Gnatalie camarasaurid is also characterized by an exclusive set of features, which might justify the establishment of a new taxon, and includes the presence of a dorsoventrally short quadrate fossa; markedly robust anterior chevrons with an anteroposteriorly compressed distal end and a very short haemal canal; and a robust fourth trochanter displaced to the midline of the femoral posterior face. For the moment, the Gnatalie assemblage appears to comprise only one diplodocine and one camarasaurid form, corresponding to the most  southwestern occurrence of Diplodocus hallorum and Camarasauridae in the Morrison Formation, west to the paleo-lake T'oo'dichi'.

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