Csiki, Z. & Vremir, M. (2011) A large-sized (?)Late Maastrichtian titanosaur from Râpa Roşie, Sebeş The 8th Romanian Symposium on Paleontology, Bucharest, September 29-30 pp. 28-29 [Abstract]

The red-coloured detritic continental deposits cropping out at Râpa Roşie, near Sebeş, were historically interpreted as representing the Upper Oligocene-Lower Miocene (e.g., Grigorescu, 1987, Codrea & Vremir, 1997). Nevertheless, the presence in these deposits, of dinosaur and other vertebrate remains, reminiscent of those commonly found in the Maastrichtian beds of the Haţeg Basin, represented a problematic issue. Consequently, the vertebrate fossils were interpreted as being reworked from underlying Upper Cretaceous continental deposits (see also Codrea et al., 2008), an idea also supported by their fragmentary nature. Nevertheless, more recently caution was expressed as to their purely allochthonous origin (e.g., Codrea et al., 2010), or this was rejected entirely, favouring an autochthonous setting of most vertebrate remains from the outcrop (e.g., Vremir et al., 2009).

Recent fieldwork in the Râpa Roşie outcrop led to the discovery of new vertebrate remains in the upper part of the local section, some of these of rather large dimensions and showing a remarkably good degree of preservation, including a partial cervical vertebra of a gigantic azhdarchid (Vremir et al., 2009). Accordingly, these occurrences suggested reassessment of the age of the Râpa Roşie redbeds, and their referral to the Maastrichtian (probably the upper Maastrichtian).

The fossiliferous bed, represented by light grey, red-spotted coarse and poorly sorted sandstones with rip-up clasts and exotic peebles, is interpreted as a channel deposit laid down by shallow and wide meandering rivers. Besides azhdarchids, other vertebrates from the same bed include turtles (Kallokibotion), crocodilians (possibly Doratodon), and dinosaurs (Telmatosaurus, titanosaurs; Vremir, 2010).

One of the most complete remains from this taphocoenosis is represented by a well-preserved midposterior dorsal vertebra of a titanosaur, preliminarily described by Vremir (2010). This specimen is remarkable due to its relatively large size (centrum length over 148 mm), and moderately dorsoventrally compressed centrum (width to height ratio - 1.21), both features uncommon in other titanosaur dorsals known from the nearby Hațeg Basin. Moreover, despite its occurrence within a coarse channel sandstone, the dorsal vertebra is well preserved (although incomplete), showing several features poorly preserved or obscured in other titanosaur dorsals from Romania.

The centrum is markedly opisthocoelous, as common in titanosaurs, laterally excavated by deep, large and acuminate pleurocoels; it is rather short and moderately dorso-ventrally depressed. Both the centrum and the neural arch (including the prezygapophyses) show a somphospondylous internal texture. The prezygapophyses are short and robust, the parapophyses are dorsally displaced to lie slightly anterior and ventral to the (broken) diapophyses. The neural arch lamination (including the prsl, sprl, cprl, acpl, pcpl, pcdl, cpol, ppdl, spdl and spol; see Wilson, 1999) are relatively well developed, separating a series of fossae whose pneumatic nature is suggested by their smooth, crenulated, and shiny bone surface (Wilson et al., 2011).

The vertebra shows a moderate amount of left-right assymmetry in the development of the postzygo-diapophyseal lamina (present on the left side, but apparently absent, or dorsally displaced, on the right side), and that of the prezygapophyseal parapodiapophyseal fossa (Wilson et al., 2011), antero-posteriorly narrower, slit-like, on the left side. Additionally, three titanosaur caudal vertebral fragments were recovered from the same level and from within 1.5 to 5 m distance of the mid-posterior dorsal; only one, a middle-distal caudal, is complete enough to allow description. Its most prominent features are the weakly opisthocoelous centrum, with a small anterior condyle, as well as the dorso-ventrally compressed morphology, visible especially at the more completely preserved distal articular surface (compression ratio - 1.35). The second, smaller, more distal caudal is reminiscent of the former in the dorso-ventrally depressed centrum mid-section. The third specimen is a well-preserved, but fragmentary neural arch, bearing one almost complete prezygapophysis. They are commensurate in size with, and might belong to the same individual as the dorsal, although this appears contradicted by their different preservational features.

These titanosaur vertebrae are remarkable especially for their relatively large size, the dorsal being significantly larger (almost twice as long) than most dorsals from the Haţeg Basin, suggesting an individual about 11-12 m in legth; moreover, they are also different in being moderately dorso-ventrally compressed. The dorsal, especially, differs from those of the recently described Paludititan (Csiki et al., 2010), as well as those of the Spanish genus Liranosaurus (Sanz et al., 1999), and the French taxa Ampelosaurus (Le Loeuff, 2005) and Atsinganosaurus (Garcia et al., 2010), respectively, in combination of its characters.

A sauropod left femoral midshaft (256 mm preserved length, from the distal part of the fourth trochanter to the base of the supracondylar ridges) was also recovered from a slightly lower, conglomeratic bed. It shows several of the characteristics present in some titanosaur femora from the Haţeg Basin, such as the presence of an angular, longitudinal midline ridge dissecting the anterior face, the presence of a deep, double depression on the posterior face, just lateral to the distal part of the fourth trochanter, a wide, rounded parasagittal ridge bordering this double depression laterally, and the presence of a weaker, but still well-marked ridge extending disto-laterally on the posterior face of the shaft, from the base of the parasagittal ridge towards the lateral edge of the posterior face.

The shaft cross-section is largely tranversely oval, with a definitively angular anterior face. Although it was discovered close to the vertebrae, the femur appears to be too slim and small as to belong to the same individual( s) as the vertebrae; this is also suggested by the slightly different levels at which the remains were encountered. Accordingly, remains of at least two different-sized titanosaur individuals are present in the upper levels of Râpa Roşie; whether these imply ontogenetic or taxonomic distinction is as yet unclear, pending on further, more complete discoveries.

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