''Rinconsaurus'' 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 ...

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

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 ...

from the Late

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

in what is now

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 ...

. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, ''Rinconsaurus caudamirus'', was described by Calvo and Riga in 2003, and is based on three partial skeletons.

Description

Like all sauropods, ''Rinconsaurus'' was a large long-necked

quadruped Quadrupedalism is a form of locomotion in which animals have four legs that are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four legs is said to be a quadruped (fr ...

al animal, with a long, whip-like tail and four pillar-like legs. ''Rinconsaurus'' was an unusually slender sauropod. Although fossil discoveries are incomplete, and no complete necks or heads have been found, fully grown ''Rinconsaurus'' are estimated to have been 11 meters (36 ft) long and approximately 2.5 meters (8 ft) high at the shoulder. The body mass of ''Rinconsaurus'' has been estimated to be between 3.21 and 5.39 tonnes.

Discovery and species

Fossils of ''Rinconsaurus'' were discovered in 1997 by Gabriel Benítezin strata belonging to the

Bajo de la Carpa Formation The Bajo de la Carpa Formation is a geologic formation of the Neuquén Basin that outcrop, crops out in northern Patagonia, in the provinces of Río Negro Province, Río Negro and Neuquén Province, Neuquén, Argentina. It is the oldest of two for ...

near Rincón de los Sauces, in the Neuquen province of Argentina. The fossils, which consisted of three individuals (two adults and one juvenile), were excavated by Jorge Calvo of the Paleontology Museum of the National University of Comahue. The

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

, and only known species, ''Rinconsaurus caudamirus'', was described by Calvo and Bernardo J. González Riga of the Paleovertebrate Laboratory in Mendoza, Argentina, in 2003. The authors noted derived traits unique to the genus, including distinctive tail vertebrae with bony processes. The fossil remains included

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, limb bones,

scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...

, hip bones ( pubis, ilium, and

ischium The ischium (; : is ...

) and several ribs. Two teeth are also known. These teeth resemble those of another titanosaurid, '' Malawisaurus dixeyi''. Calvo and González Riga initially interpreted two elements as belonging to the skull of ''Rinconsaurus'', a prefrontal and part of the mandible, but these were subsequently identified as the ilium of the

crocodyliform Crocodyliformes is a clade of Crurotarsi, crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the ...

Pehuenchesuchus ''Pehuenchesuchus'' (meaning "Pehuenche crocodile", after the Mapuche name for the region in which it was found) is an extinct genus of sebecosuchian mesoeucrocodylian. It was discovered in rocks of the late Turonian-Coniacian-age Upper Cretac ...

'' and part of a rib of ''Rinconsaurus'' respectively. The generic name refers to Rincón de los Sauces, where the fossils were discovered, while the specific name, ''caudamirus'', means "amazing in the tail" in

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

, in reference to the unusual shape of the tail vertebrae, especially a strange sequence of procoelous, amphicoelous, opisthocoelous, biconvex and ultimately again procoelous vertebrae shown by one individual.

Classification

''Rinconsaurus'' is a

. Within the titanosaurs, Calvo and Riga regard this dinosaur as closely related to ''

Aeolosaurus ''Aeolosaurus'' (; "Aeolus' lizard") is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period (geology), Period of what is now South America. Like most sauropods, it would have been a quadrupedal herbivore with a long neck an ...

'' based on several derived traits. In 2007, Casal ''et al.'' assigned ''Rinconsaurus'', '' Gondwanatitan'', and ''Aeolosaurus'' to the Aeolosauridae, a proposed stem-based

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 ...

of titanosaurs. ''Rinconsaurus'' would form a smaller clade Rinconsauria with '' Muyelensaurus''.Casal, G.; Martínez, R.D.; Luna, M.; Sciutto, J.C; and Lamanna, M.C. (2007). "''Aeolosaurus colhuehuapensis sp. nov.'' (Sauropoda, Titanosauria) de la Formación Bajo Barreal, Cretácico Superior de Argentina 'Aeolosaurus colhuehuapensis sp. nov''. (Sauropoda, Titanosauria) from the Bajo Barreal Formation, Upper Cretaceous of Argentina. ''Revista Brasileira de Paleontologia'' 10(1):53-62 It remains to be seen, however, if this classification will receive widespread acceptance.

Paleobiology

Diet

''Rinconsaurus'', like all sauropods, was an

herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

. Fossilized dung associated with late Cretaceous titanosaurids has revealed phytoliths, silicified plant fragments, that offer clues to a broad, unselective plant diet. Besides the plant remains that might have been expected, such as

cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...

s and

conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

s, discoveries published in 2005 revealed an unexpectedly wide range of

monocotyledon Monocotyledons (), commonly referred to as monocots, ( Lilianae '' sensu'' Chase & Reveal) are flowering plants whose seeds contain only one embryonic leaf, or cotyledon. A monocot taxon has been in use for several decades, but with various ranks ...

s, including

palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand * Palm plants, of family Arecaceae ** List of Arecaceae genera **Palm oil * Several other plants known as "palm" Palm or Palms may also refer to: Music ...

s and grasses (

Poaceae Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and species cultivate ...

), including ancestors of

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

and

bamboo Bamboos are a diverse group of mostly evergreen perennial plant, perennial flowering plants making up the subfamily (biology), subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family, in th ...

, which has given rise to speculation that herbivorous dinosaurs and grasses co-evolved. Titanosaurid teeth are usually spatulate (spoon-shaped) or shaped like pegs. Teeth found in association with ''Rinconsaurus'' have been described as "pencil-chisel-like teeth" and had sharply inclined wear facets. Without the ability to grind food, ''Rinconsaurus'', like other sauropods, would have stripped foliage.

References