''Rinconsaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

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 th ...

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 bo ...

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 ...

from the Late

Cretaceous 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 th ...

in what is now

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, th ...

. The

type species In 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 species that contains the biological type specimen ...

, ''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 where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor' ...

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 crops out in northern Patagonia, in the provinces of Río Negro and Neuquén, Argentina. It is the oldest of two formations belonging to the Río Colorado Subgroup ...

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, 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 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 characteristic ...

e, limb bones,

scapula The scapula (plural 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 eithe ...

, hip bones ( pubis, ilium, and

ischium The ischium () form ...

) 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 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 only pseudo ...

'' Pehuenchesuchus'' 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 branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

, 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 of what is now South America. Like most sauropods, it would have been a quadrupedal herbivore with a long neck and tail. ''Aeolos ...

'' based on several derived traits. In 2007, Casal ''et al.'' assigned ''Rinconsaurus'', ''

Gondwanatitan ''Gondwanatitan'' (meaning "giant from Gondwana") was a titanosaurian sauropod dinosaur. ''Gondwanatitan'' was found in Brazil, at the time part of the southern supercontinent Gondwana, in the late Cretaceous Period (70 mya). Like some other ...

'', and ''Aeolosaurus'' to the Aeolosauridae, a proposed stem-based

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

of titanosaurs. ''Rinconsaurus'' would form a smaller clade

Rinconsauria Rinconsauria is an extinct clade of giant titanosaurian sauropods known from the late Cretaceous period of Argentina. Systematics Rinconsauria was coined by Calvo et al. (2007) to include their new titanosaur ''Muyelensaurus'' and the previously ...

with ''

Muyelensaurus ''Muyelensaurus'' (meaning "Muyelen lizard", after an indigenous name for the Colorado River in Argentina) is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous of Argentina. It was more slender than other titanosaurs. Fossils h ...

''.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 adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

. 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 single ...

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

monocotyledon Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of ...

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 * Several other plants known as "palm" Palm or Palms may also refer to: Music * Palm (ba ...

s and grasses (

Poaceae Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...

), including ancestors of

rice Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima ''Oryza glaberrima'', commonly known as African rice, is one of the two domesticated rice species. It was first domesticated and grown i ...

and

bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, bu ...

, 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