Agustinia

''Agustinia'' is a genus of sauropod dinosaur from the Early Cretaceous Period of South America. It contains the single species ''Agustinia ligabuei'', a single specimen which was recovered from the Lohan Cura Formation of Neuquen Province in Argentina. It lived about 116–108 million years ago, in the Aptian-Albian stage of the Early Cretaceous Period.

The name ''Agustinia'' honors the discoverer of the specimen, Agustin Martinelli. This dinosaur was originally named in a 1998 abstract written by famous Argentine paleontologist Jose Bonaparte.Bonaparte, J.F. 1998. An armoured sauropod from the Aptian of northern Patagonia, Argentina. In: Tomida, Y., Rich, T. H. & Vickers-Rich, P. (Eds.). ''Second Symposium Gondwana Dinosaurs, 12–13 July 1998, Abstracts with Program''. Tokyo: National Science Museum. Pg. 10. The original generic name was "Augustia", which, as it turned out, was already preoccupied by a beetle (see also: ''Megapnosaurus'', ''Protognathosaurus''). Bonaparte changed the name to ''Agustinia'' in a full paper published in 1999.Bonaparte, J.F. 1999
An armoured sauropod from the Aptian of northern Patagonia, Argentina
In: Tomida, Y., Rich, T. H. & Vickers-Rich, P. (Eds.). ''Proceedings of the Second Gondwanan Dinosaur Symposium'' Tokyo: National Science Museum Monographs #15. Pp. 1–12. There is one named species (''A. ligabuei''), which is named in honor of Dr. Giancarlo Ligabue, a philanthropist who provided financial support to the expedition which recovered the remains.

Description

Only fragmentary remains are known. These include fragments of vertebrae from the back, hips, and tail regions of the spinal column. Parts of the lower hind limb were also recovered: a fibula, tibia, and five metatarsals. A femur (thigh bone) was found at the site, but was too fragmented to collect.Upchurch, P., Barrett, P.M., & Dodson, P. 2004. Sauropoda. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.) ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. Pp. 259–322.

''Agustinia ligabuei'' was well known for its distinctive supposed armor plates (osteoderms), initially interpreted as a series of wide, vertical spikes and plates down the center of its back, somewhat like the unrelated ''Stegosaurus''. However, subsequent research has challenged the interpretation of these elements as osteoderms. Further study of the poorly preserved fossil material showed that these "plates" were in fact more likely to be fragments of ribs and hip bones. This reassessment was reaffirmed subsequently by histology of the purported osteoderms, which do not match the internal structure of other titanosaurian osteoderms. The fragmentary hip bone was tentatively identified as part of the ilium.

Aside from the supposed armor, very little has been described of the anatomy of ''Agustinia''. A fibula (lower leg bone) has been recovered that is about long. When compared to the same bone in related dinosaurs, this indicates that ''Agustinia'' may have been about long. However, the remains are incomplete and do not appear to have many distinctive characteristics which can be used to separate it from other sauropods. With the supposedly distinctive armor discredited, some authors have considered ''Agustinia'' a ''nomen dubium'', for being based on remains not adequate to compare with related dinosaurs. The lower half of the tibia was thin when viewed from the front (anteroposterior), indicating that the tibia was thinner than that of titanosaurs such as ''Antarctosaurus'' or ''Saltasaurus''. The pedal elements correspond to those of the titanosaurs.

Discovery

The only specimen of ''Agustinia'' so far was discovered in 1997 by an expedition from the Museo Argentino de Ciencias Naturales in Buenos Aires, a few kilometers west of the city of Picún Leufú in the south of the Neuquén province. The rocks of the site belong stratigraphically to the upper section of the Lohan-Cura Formation . This excursion was part of a program run by the museum in 1996 and 1997 to discover new vertebrate fossils in the Lohan-Cura Formation. A year earlier (1996) a new sauropod was discovered 50 kilometers west of Picún Leufú.

The name ''Agustinia'' honors then-student Agustin Martinelli, who discovered the skeleton and was part of the excavation team of the Museo Argentino de Ciencias Naturales. The specific epiteth ''ligabuei'' honors Giancarlo Ligabue, an Italian supporter of the 1997 expedition into the Lohan-Cura Formation.

Classification

Because of its supposedly unusual armor, ''Agustinia'' was originally assigned to its own family, Agustiniidae. This family name has not come into wide acceptance. ''Agustinia'' is difficult to classify because of its fragmentary nature, and because it exhibits features of both diplodocoid and titanosaurian sauropods. What few distinctive features do exist in the only known specimen suggests it is a member of the clade Somphospondyli, but it is not possible to determine its relationships with any more accuracy beyond that. Kristina Curry Rogers classifies ''Agustinia'' within the Titanosauria in the clade Lithostrotia.

A 2022 paper by Flavio Bellardini ''et al.'' found ''Agustinia'' to be a rebbachisaurid, more derived than ''Amazonsaurus''. The cladogram below displays the results of their phylogenetic analyses:

References

{{Taxonbar, from=Q131756

Sauropods
Early Cretaceous dinosaurs of South America
Cretaceous Argentina
Fossils of Argentina
Fossil taxa described in 1999
Taxa named by José Bonaparte