Andesaurus is a genus of basal titanosaurian sauropod dinosaur which existed during the
middle of the Cretaceous Period in South America. Like most sauropods, it would have had a small
head on the end of a long neck and an equally long tail. Andesaurus was a very large sauropod,
as were many others of its relatives, which included the largest animals ever to walk
the Earth. In 1991, paleontologists Jorge Calvo and Jose
Bonaparte named Andesaurus, which refers to the Andes Mountains and also includes the
Greek word sauros, because of the proximity of this animal's remains to the Andes. Andesaurus
fossils were found by Alejandro Delgado, after whom the single known species is named.
The only known material of Andesaurus is a partial skeleton consisting of a series of
four vertebrae from the lower back, as well as 27 tail vertebrae, divided up into two
series from separate parts of the tail. The vertebrae from the middle part of its tail
had elongated centra. Elements of the pelvis were also discovered, including two ischia
and a pubis bone, along with rib fragments and an incomplete humerus and femur. Size
estimates place Andesaurus at roughly 15 metres in length, and 7 metric tons in weight.
These fossils were discovered in the Candeleros Formation, the oldest formation within the
Neuquén Group of Neuquén Province, Argentina. This formation dates to the early Cenomanian
stage of the Early Cretaceous Period, or about 100 to 97 million years ago. For the most
part, the Candeleros represents an ancient braided river system, and besides Andesaurus,
also contains fossils of theropods like Buitreraptor and the enormous Giganotosaurus, as well as
other non-related sauropods such as Limaysaurus. Several plesiomorphic features characterize
Andesaurus as the most basal known member of Titanosauria. In fact, this clade has been
defined to contain Andesaurus, Saltasaurus, their most recent common ancestor, and all
of its descendants. The most prominent plesiomorphy is the articulations between its tail vertebrae.
In most derived titanosaurs, the tail vertebrae articulate with ball-and-socket joints, with
the hollowed-out socket end on the front, while in Andesaurus, both ends of the vertebrae
are flat, as seen in many non-titanosaurian sauropods. Andesaurus itself is only characterized
by a single feature, the tall neural spines on top of its back vertebrae, and needs further
study. Some other basal titanosaurs from Argentina,
including Argentinosaurus and Puertasaurus, were also sauropods of enormous size. The
most derived group of titanosaurs, the Saltasauridae, included some of the smallest known sauropods,
including Saltasaurus itself. Thus it is possible that the largest sizes were attained among
the more basal members of the clade Footnotes
References
Calvo, J.O. & Bonaparte, J.F. 1991. [Andesaurus delgadoi n. g. n. sp. a titanosaurid dinosaur
from the Río Limay Formation, Neuquén, Argentina.] Ameghiniana. 28: 303-310. [In Spanish]
Mannion, P. D. and Calvo, J. O., Anatomy of the basal titanosaur Andesaurus delgadoi from
the mid-Cretaceous Río Limay Formation, Neuquén Province, Argentina: implications for titanosaur
systematics. Zoological Journal of the Linnean Society, no. doi:10.1111/j.1096-3642.2011.00699.x
Novas, F.E., Salgado, L., Calvo, J.O., & Agnolin, F. 2005. Giant titanosaur from the Late Cretaceous
of Patagonia. Revista del Museum Argentino de Ciencias Naturales 7(1): 37-41.
Salgado, L., Coria, R.A., & Calvo, J.O. 1997. Evolution of titanosaurid Sauropods. I: Phylogenetic
analysis based on the postcranial evidence. Ameghiniana. 34: 3-32.
Tidwell, V., Carpenter, K. & Meyer, S. 2001. New Titanosauriform from the Poison Strip
Member of the Cedar Mountain Formation, Utah. In: Mesozoic Vertebrate Life. D. H. Tanke
& K. Carpenter. Indiana University Press, Eds. D.H. Tanke & K. Carpenter. Indiana University
Press. 139-165. Upchurch, P., Barrett, P.M, & Dodson, P. 2004.
Sauropoda. In: Weishampel, D.B., Dodson, P., & Osmolska, H.. The Dinosauria. Berkeley:
University of California Press. Pp. 259–322. Wilson, J.A. & Upchurch, P. 2003. A
revision of Titanosaurus Lydekker, the first dinosaur genus with a ‘Gondwanan’ distribution.
Journal of Systematic Palaeontology 1(3): 125–160.