New rebbachisaurid (Sauropoda, Diplodocoidea) materials from El Chocón come with a hypothesis of the homology of the spinodiapophyseal laminae in Diplodocoidea.

HALUZA, ALEJANDRO; CANALE, JUAN IGNACIO

Neuquén

Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

New Rebbachisaurid materials from Las Campanas locality, Huincul Formation (Upper Cenomanian-Turonian), 20 km southwest of Villa El Chocón, Neuquén Province, Argentina are presented. They are represented by a partially articulated skeleton (MMCH-Pv-49) including seven articulated cervical vertebrae, four articulated anterior dorsal vertebrae, six disarticulated mid-posterior dorsal vertebrae, right scapula and humerus and disarticulated ribs. Rebbachisaurid synapomorphies observable in this materials, includes: “petal-shaped” dorsal neural spines; absence of hyposphene-hypantrum; racquet-shaped scapular blade; presence of accessory laminae (AL1) connecting postzygodiapophyseal (podl) and spinoprezygapophyseal (sprl) laminae (Apesteguía and Gallina, 2005). The vertebral series, from the cervical to the dorsal vertebrae is preserved, providing a possible explanation of the anatomical changes in the lamination of the “pectoral series” (Wilson, 1998) at least within the Rebbachisaurids. Changes in the vertebral series begin with a ventral flexion of the sprl in the posterior cervicals, leaving two segments: the dorsal part of the sprl herein called “Spinal segment” and the ventral part of the sprl or “Prezygapophyseal segment”.  Posteriorlly, the anteriormost dorsals show a shortening of the accessory lamina (AL1) that reaches the podl. Finally, it can be observed a lateral migration of the spinal segment constituting the spdl and mergence of the prezygapophyseal segment of the (now non existent) sprl to the prezygodiapofiseal lamina. Several authors have remarked the presence of the spinodiapophyseal lamina (spdl) as an important synapomorphy of an inclusive clade of derived sauropods (Wilson, 2002; Salgado et al., 2006). Some interpretations of the changes that occur in the “pectoral series” of sauropods (Salgado et al., 2006) suggest that, generally, the spdl arise as a posterior longitudinal division at the base of the sprl. The new evidences show that the “spinal segment” of the spinoprezygapophyseal lamina in posterior cervical vertebrae should be a homologue of the spinodiapophyseal lamina of the dorsal vertebrae, at least within Rebbachisauridae.