Andesaurus

Taxobox
name = "Andesaurus"
fossil_range = Late Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Sauropodomorpha
infraordo = Sauropoda
unranked_familia = Titanosauria
familia = Andesauridae
familia_authority = Calvo & Bonaparte, 1991
genus = "Andesaurus"
binomial = "Andesaurus delgadoi"
binomial_authority = Calvo & Bonaparte, 1991

"Andesaurus" (pronEng|ˌændɨˈsɔrəs AN-de-SAWR-us; "Andes lizard") 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" ("lizard"), 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 ("A. delgadoi") 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. Elements of the pelvis were also discovered, including two ischia and a pubis bone, along with rib fragments and an incomplete humerus and femur.

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 (primitive) 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 (Salgado "et al.", 1997; Wilson & Upchurch, 2003). 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 ("procoelous" caudal vertebrae), while in "Andesaurus", both ends of the vertebrae are flat ("amphiplatyan" caudals), 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 (Upchurch "et al.", 2004).

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 (Novas "et al.", 2005).

References

*Calvo, J.O. & Bonaparte, J.F. 1991. ["Andesaurus delgadoi" n. g. n. sp. (Saurischia, Sauropoda) a titanosaurid dinosaur from the Río Limay Formation (Albian-Cenomanian), Neuquén, Argentina.] "Ameghiniana". 28: 303-310. [In Spanish]
*Novas, F.E., Salgado, L., Calvo, J.O., & Agnolin, F. 2005. Giant titanosaur (Dinosauria, Sauropoda) 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.
*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.
*Wilson, J.A. & Upchurch, P. 2003. A revision of "Titanosaurus" Lydekker (Dinosauria – Sauropoda), the first dinosaur genus with a ‘Gondwanan’ distribution. "Journal of Systematic Palaeontology" 1(3): 125–160.