''Andesaurus'' ( ; "Andes lizard") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

titanosaurian

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

which existed during the middle of the

Cretaceous Period The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

. Like most sauropods, belonging to one of the largest animals ever to walk the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

, it would have had a small head on the end of a long neck and an equally long tail.

History of discovery

Andesaurus-Scale-Diagram-SVG-Steveoc86-001

In 1991,

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

s Jorge Orlando Calvo and

José Fernando Bonaparte José is a predominantly Spanish and Portuguese form of the given name Joseph. While spelled alike, this name is pronounced differently in each language: Spanish ; Portuguese (or ). In French, the name ''José'', pronounced , is an old vernacul ...

named ''Andesaurus'', which refers to the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

and also includes the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

word ''sauros'' ("lizard"), because of the proximity of this animal's remains to the Andes. ''Andesaurus''

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s were found by Alejandro Delgado, after whom the single known

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

(''A. delgadoi'') is named. The only known material of ''Andesaurus'' is a partial skeleton consisting of a series of four

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characterist ...

e 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 Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures approximately east to wes ...

and a pubis bone, along with rib fragments and an incomplete

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

and

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

Description

''Andesaurus'' was a medium sized sauropod, reaching in length and in body mass.Paul, G.S., 2010, ''The Princeton Field Guide to Dinosaurs'', Princeton University Press p. 205Holtz, Thomas R. Jr. (2012) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2011 Appendix.
/ref> The dorsal vertebrae of ''Andesaurus'' bear the typical features of an centrum and large lateral (pneumatic depression). Unlike related '' Phuwiangosaurus'', there is no ventral keel under any of the vertebrae, and there is a pneumatic feature on the front of the , the latter being found in most neosauropods. Potentially diagnostic for ''Andesaurus'', there is an additional ridge supporting the lower articulation for the ribs (), although poor preservation in other vertebrae means it can only be identified on one bone. The of ''Andesaurus'' are smaller than more basal sauropods, but less reduced than in '' Argentinosaurus'' or '' Epachthosaurus'', where the surface is only articular ridges, and also less reduced than more derived titanosaurs where the articulation is entirely absent. Pre- and post-spinal are present in the vertebrae of ''Andesaurus'', like in other somphospondylans. Tail vertebrae (caudals) of ''Andesaurus'' are slightly , where the anterior face is concave and the posterior face of convex. This convexity is less prominent than more derived titanosaurs, but is still diagnostic of the clade as a whole. The first caudal has a flat anterior and slightly convex posterior face, different from the subsequent vertebrae similar to in ''Epachthosaurus''. A prominent depression is present on the bottom surface of some anterior caudals, a feature present in diplodocids and multiple titanosaurs. Anterior caudals are shorter proportionally, the bones becoming almost double the proportional length towards the end of the tail. Lateral pleurocoels are present on some vertebrae, as well as small lateral foramina. These foramina are known in some titanosaurs and non-titanosaurs, but their phylogenetic distribution is poorly understood. Like in all titanosauriformes, the neural arch is on the anterior portion of the centrum, and the neural spines are elongate and rectangular. The variation along the caudal series is similar to ''Epachthosaurus'' and '' Malawisaurus''.

Classification

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. 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. Some other basal titanosaurs from Argentina, including '' Argentinosaurus'' and ''

Puertasaurus ''Puertasaurus'' is a genus of sauropod dinosaur that lived in South America during the Late Cretaceous Period. It is known from a single specimen recovered from sedimentary rocks of the Cerro Fortaleza Formation in southwestern Patagonia, Arge ...

'', 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.

Palaeoecology

These fossils were discovered in the Candeleros Formation, the oldest

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

within the Neuquén Group of Neuquén Province,

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

. This formation dates to the Cenomanian stage of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

period, about 99.6 to 97 million years ago. For the most part, the Candeleros represents an ancient

braided river A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, '' aits'' or ''eyots''. Braided streams tend to occur in rivers with high sedime ...

system. Besides ''Andesaurus'', the formation also contains fossils of the theropods '' Buitreraptor'' and ''

Giganotosaurus ''Giganotosaurus'' ( ) is a genus of theropod dinosaur that lived in what is now Argentina, during the early Cenomanian age of the Late Cretaceous period, approximately 99.6 to 95 million years ago. The holotype specimen was discovered in the ...

'', as well as other sauropods including the

rebbachisaurid Rebbachisauridae is a family of sauropod dinosaurs known from fragmentary fossil remains from the Cretaceous of South America, Africa, North America, Europe and possibly Central Asia. Taxonomy In 1990 sauropod specialist Jack McIntosh included t ...

'' Limaysaurus''.

References

Bibliography

* Novas, F.E., Salgado, L., Calvo, J.O., & Agnolin, F. 2005. Giant titanosaur (Dinosauria, Sauropoda) from the Late Cretaceous of Patagonia. '' Revista del Museo 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 (Sauropoda) from the Poison Strip Member of the Cedar Mountain Formation (Lower Cretaceous), Utah. In: Mesozoic Vertebrate Life. D. H. Tanke & K. Carpenter (eds.). 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. (Eds.). ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. Pp. 259–322.