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

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of basal

titanosauria Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of Sauropoda, sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with tax ...

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 b ...

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

which existed during the middle of the

Cretaceous Period The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 77.1 million years, it is the ninth and longest geologi ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. Like most sauropods, 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 as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Jorge Orlando Calvo Jorge Orlando Calvo (27 April 1961 – 10 January 2023)José Fernando Bonaparte named ''Andesaurus'', which refers to the

Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

and also includes the

Greek Greek may refer to: 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 of all kno ...

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 preserve ...

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

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

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 Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the individual shops are all owned by individual franchisees. The chain has three ...

. Elements of the

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

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 the city of Naples. It is the largest of the Phlegrean Islands. Although inhabited since the Bronze Age, as a Ancient G ...

and a pubis bone, along with

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

fragments and an incomplete

humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

and

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

Description

''Andesaurus'' was a medium-sized sauropod. Total length estimates place the known remains at Paul, G.S., 2010, ''The Princeton Field Guide to Dinosaurs'', Princeton University Press p. 205 to long,Holtz, Thomas R. Jr. (2012) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2011 Appendix.
/ref> and around in body mass. The

dorsal vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...

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 ''Argentinosaurus'' (meaning "lizard from Argentina") is a genus of giant sauropod dinosaur that lived during the Late Cretaceous Period (geology), period in what is now Argentina. Although it is only known from fragmentary remains, ''Argentinos ...

'' or ''

Epachthosaurus ''Epachthosaurus'' (meaning "heavy lizard") was a genus of titanosaurian sauropod dinosaur from the Late Cretaceous. It was a basal Lithostrotia, lithostrotian titanosaur. Its fossils have been found in Central and Northern Patagonia in South Ame ...

'', 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 ''Malawisaurus'' (meaning "Malawi lizard") is an extinct genus of titanosaurian sauropod dinosaur. It is known from the Dinosaur Beds of northern Malawi, which probably date to the Aptian stage of the Early Cretaceous. The type species is ''M. di ...

''.

Classification

Several plesiomorphic (primitive) features characterize ''Andesaurus'' as the most basal known member of Titanosauria. In fact, this

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

has been defined to contain ''Andesaurus'', ''

Saltasaurus ''Saltasaurus'' (which means "lizard from Salta") is a genus of saltasaurid dinosaur of the Late Cretaceous Period (geology), period of Argentina. Small among sauropods, though still heavy by the standards of modern creatures, ''Saltasaurus'' was ...

'', 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 ''

'' and '' Puertasaurus'', were also sauropods of enormous size. The most derived group of titanosaurs, the

Saltasauridae Saltasauridae (named after the Salta region of Argentina where they were first found) is a family of armored herbivorous sauropods from the Upper Cretaceous. They are known from fossils found in South America, Africa, Asia, North America, and Eur ...

, 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 Candeleros Formation is a geologic formation that outcrop, crops out in the Rio Negro Province, Río Negro, Neuquen Province, Neuquén, and Mendoza Province, Mendoza provinces of northern Patagonia, Argentina. It is the oldest formation in the ...

, the oldest formation within the

Neuquén Group The Neuquén Group is a geologic unit, group of geologic formations found in Argentina. Rocks in the Neuquén Group fall within the Cenomanian to early Campanian stages of the Late Cretaceous Period. It overlies the older Lohan Cura Formation and ...

Neuquén Province Neuquén () is a Provinces of Argentina, province of Argentina, located in the west of the country, at the northern end of Patagonia. It borders Mendoza Province to the north, Rio Negro Province to the southeast, and Chile to the west. It also me ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. This formation dates to the

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

stage of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

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

braided river A braided river (also called braided channel or braided stream) consists of a network of river channel (geography), channels separated by small, often temporary, islands called ''braid bars'' or, in British English usage, ''aits'' or ''eyots''. ...

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

Buitreraptor ''Buitreraptor'' (meaning "La Buitrera seizer") is a genus of dromaeosaurid dinosaurs that lived during the Late Cretaceous of Argentina at the Candeleros Formation. ''Buitreraptor'' was described in 2005 and the type species is ''Buitreraptor g ...

'' and ''

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

'', as well as other sauropods including the

rebbachisaurid Rebbachisauridae is a Family (biology), 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 M ...

Limaysaurus ''Limaysaurus'' ("Limay lizard") is a genus represented by a single species of rebbachisaurid sauropod dinosaurs, which lived during the mid-Cretaceous period, about 99.6 to 94 million years ago, in the Cenomanian, in what is now South America (n ...

''.

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 ''Ameghiniana'' is a peer-reviewed scientific journal covering palaeontology published by the Asociación Paleontológica Argentina. It is named after the 19th century Italian Argentine palaeontologist Florentino Ameghino. The discovery of many d ...

''. 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.