new sauropods: Amargatitanis and Nopcsaspondylus

[jigruiz@unizar.es]

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.

Includes:

Titanosauria Bonaparte and Coria, 1993

AMARGATITANIS gen. nov.

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.
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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.

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

www.museojurasicoasturias.com
www.aragosaurus.com