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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
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
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
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
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