Sunday, November 4, 2018

[Paleontology • 2018] Lavocatisaurus agrioensis • A New Rebbachisaurid Sauropod from the Aptian–Albian, Lower Cretaceous Rayoso Formation, Neuquén, Argentina

Lavocatisaurus agrioensis 
Canudo, Carballido, Garrido & Salgado, 2018

Illustration: Gabriel Lio. 

Rebbachisaurids are a group of basal diplodocimorph sauropods that diversified in Gondwana at the end of the Early Cretaceous and the beginning of the Late Cretaceous. It is a group of great palaeobiogeographical interest, for it  clearly illustrates various processes of dispersal throughout Gondwana and to Laurasia prior to the breakup of Africa and South America. However, the relationships within the group are still under discussion owing to the scarcity of cranial material that would help clarify them. In the present paper we describe the new rebbachisaurid Lavocatisaurus agrioensis gen. et  sp. nov. from the Aptian–Albian (Lower Cretaceous) of Neuquén (Argentina). Remains have been recovered belonging to an adult specimen (holotype) and two immature specimens (paratypes). Taken together, almost all the bones of the taxon are represented, including most of the cranium. Lavocatisaurus agrioensis gen. et sp. nov. is the first rebbachisaurid from Argentina with an almost complete cranium, making it possible to recognize differences with respect to other rebbachisaurids, such as the highly derived Nigersaurus. Among its most notable characters are the presences of a large preantorbital fenestra and maxillary teeth that are significantly larger than those of the dentary. Our phylogenetic study places Lavocatisaurus amongst basal rebbachisaurids, as the sister lineage to Khebbashia (the clade formed by Limaysaurinae + Rebbachisaurinae). This position, which is somewhat more derived than that previously suggested for Comahuesaurus and Zapalasaurus (the Argentinean rebbachisaurids closest in geographical and geological terms), reaffirms the presence of different basal rebbachisaurid lineages in the Early Cretaceous of Patagonia.

Key words: Dinosauria, Rebbachisauridae, phylogeny, Cretaceous, Rayoso Formation, Argentina.

Fig. 2. Rebbachisaurid sauropod Lavocatisaurus agrioensis gen. et sp. nov. from Agrio del Medio (Argentina), Aptian–lower Albian. A. MOZ-Pv1232, axis in lateral view (A1, photograph; A2, drawing); eight cervical vertebrae in lateral view view (A3, photograph; A4, drawing, ); anterior caudal vertebra in lateral view (A5); middle caudal vertebra in lateral view (A6); posterior caudal vertebra in lateral view (A7); posteriormost caudal vertebra in lateral view (A8); left tibia in lateral view (A9). B. MOZ-Pv 1255, left scapula from a juvenile specimen, in lateral view. C. Skeletal reconstruction based on the holotype and paratype specimens. Scale bars 10 cm. 

Saurischia Seeley, 1887
Sauropoda Marsh, 1878
Diplodocoidea Marsh, 1878 sensu Upchurch, 1995
Diplodocimorpha Calvo and Salgado, 1995
Rebbachisauridae Bonaparte, 1997

Genus Lavocatisaurus nov.

Etymology: In honour of the French researcher René Lavocat (1909–2007), who described Rebbachisaurus, the first known representative of Rebbachisauridae.

Lavocatisaurus agrioensis sp. nov.

Etymology: In reference to the locality of Agrio del Medio, from which the new species was found

Illustration: Gabriel Lio.  

Lavocatisaurus agrioensis is the first of the South American rebbachisaurids that preserves the rostral region of the cranium, which has allowed us to undertake a reliable enough reconstruction of the skull. The skull has a combination of morphological characters that justifies its definition as a new taxon within Rebbachisauridae along with the less derived rebbachisaurids from the Early Cretaceous of Argentina such as Zapalasaurus and Comahuesaurus. Our phylogenetic study situates Lavocatisaurus as the sister lineage of Khebbashia (Fig. 5). Lavocatisaurus is the most derived basal rebbachisaurid known to date, providing reliable information on the evolutionary steps that occurred just prior to the diversification of Rebbachisaurinae.

José I. Canudo, José L. Carballido, Alberto Garrido and Leonardo Salgado. 2018. A New Rebbachisaurid Sauropod from the Aptian–Albian, Lower Cretaceous Rayoso Formation, Neuquén, Argentina. Acta Palaeontologica Polonica. in press. DOI: 10.4202/app.00524.2018 

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