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new sauropods: Amargatitanis and Nopcsaspondylus

Sebastián Apesteguía. in press. The sauropod diversity of the La Amarga Formation (Barremian), Neuquén (Argentina). Gondwana Research

Abstract: A study of the abundant and undescribed isolated and associated bones and teeth from the La Amarga Formation (Barremian of Neuquén, Argentina) permitted the recognition of additional clades of sauropod dinosaurs: basal titanosauriforms, both basal and derived titanosaurs, and rebbachisauroid diplodocoids, which are now added to the already known dicraeosaurids and a recently published basal diplodocoid. These forms substantially increase the knowledge on the Early Cretaceous sauropod diversity in Gondwana.


Titanosauria Bonaparte and Coria, 1993


Type species: Amargatitanis macni sp. nov.

Diagnosis: A. macni is diagnosed by the following associated characters. Robust, wide and flat scapula developed in a single plane, with straight, parallel anterior and posterior borders of the diaphysis. Acromion developed in straight line with respect to the diaphysis. Very short glenoid region, straight articulation for the coracoid, obtuse angle of coracoid articular surface with respect to the glenoid?scapular line, absence of scapular ventromedial process. Femoral fourth trochanter located at mid femur. Femur with a prominent head with respect to a moderately developed distal region. High astragalus with a deep crescentshaped fossa that bears two pairs of foramina on the upper part of the tibial side of the posterior astragalar fossa. On the fibular side, two foramina are visible also in a deep concavity.

Etymology: Amarga, referring the fossil locality; titanis (Greek), titan, giant, because of the affinities of the specimen with the titanosaurs.

A. macni nov. sp.

Diagnosis: same as for genus.

Etymology: In honor of the Museo Argentino de Ciencias Naturales (MACN) for the sustained contribution and human resources formed in Vertebrate Paleontology during the 19th and 20th centuries.

Holotype: MACN PV N51, 53, 34, represented by the following associated material collected in 1983: six caudal vertebrae, a scapula, a femur and one astragalus.

Horizont and locality: the fossil locality, as shown by the geologist Luis Cazau to Bonaparte, is located at the foot of the hill that rises over the left bank of the La Amarga stream, 2.5 km east from the 40th National Road. As described by Cazau and written by Bonaparte in his notebook, the levels correspond to the Kimmeridgian Pichi Picún Leufú Formation (Fossa Mancini et al., 1938), the basal unit of the Fortín Nogueira Group. If true, these fossils are much older than expected and very important because of their good preservation. However, the preservation is identical to that of bones coming form the La Amarga Formation and is here considered in that context.
Nopcsaspondylus gen. nov.

Type species: Nopcsaspondylus alarconensis sp. nov.

Diagnosis: diplodocoid sauropod characterized by mid to posterior dorsal vertebrae with very reduced centra, forked medial centropostzygapophyseal lamina, lateral lamina of the neural spine formed by the spinodiapophyseal lamina plus a lateral spinopostzygapophyseal (different from that forming the postspinal lamina).

Etymology: Nopcsa, referring the researcher that first studied this material; spondylus, Gr. vertebra.

Nopcsaspondylus alarconensis nov. sp.

Diagnosis: same as for genus.

Etymology: referring to Barda Alarcón, the original locality where from it was collected by the end of 19th century.

Holotype (lost), represented by a complete mid to posterior dorsal vertebra,with centrumand neural arch separated. The small centrum and large pleurocoel suggest that they derive from the same vertebra, as this is a common feature in rebbachisauroids.

Horizon and locality: coarse sandy levels of the lower section of the Candeleros Formation (presumably), Coniacian (Leanza and Hugo, 1997); Barda Alarcón, NE from Picún Leufú town, Neuquén Province, Argentina.
Description: see Nopcsa, 1902.

Comments: the small centrum and large pleurocoel present in Nopcsaspondylus are common features in rebbachisauroid sauropods that, combined with several other allometries, depict its highly heterochronic characteristics.

Nopcsa, F., 1902. Notizen uber Cretacischen Dinosaurier. Pt. 3. Wirbel eines sudamerikanischen Sauropoden. Sitz. Berlin Akademie der Wesenschaften, vol. 3, pp. 108?114.

Jose Ignacio Ruiz-Omeñaca
Museo del Jurásico de Asturias (MUJA)
E-33328 Colunga, Spain