''Mussaurus'' (meaning " mouse 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 nom ...

herbivorous 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 mouthpar ...

sauropodomorph Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...

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 ...

that lived in southern

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 ...

during the Early Jurassic, with a maximum age of 192.78 ± 0.14 Ma. It receives its name from the small size of the skeletons of juvenile and infant individuals, which were once the only known specimens of the genus. However, since ''Mussaurus'' is now known from adult specimens, the name is something of a misnomer; adults possibly reached in length and weighed more than . ''Mussaurus'' possesses anatomical features suggesting a close, possibly transitional evolutionary relationship with true sauropods.

Discovery

Infant and juvenile fossils of ''Mussaurus'' were first discovered by an expedition led by

Jose Bonaparte Jose is the English transliteration of the Hebrew and Aramaic name ''Yose'', which is etymologically linked to ''Yosef'' or Joseph. The name was popular during the Mishnaic and Talmudic periods. * Jose ben Abin * Jose ben Akabya *Jose the Galile ...

during the 1970s to the Laguna Colorada Formation."Mussaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. ''The Age of Dinosaurs''. Publications International, LTD. p. 40. . There the team found fossilized eggs and hatchlings, which added insight into the reproductive strategies of ''Mussaurus'' and other sauropodomorph dinosaurs. The first adult specimens of ''Mussaurus'' were described in 2013. Some of these specimens had first been described in 1980 and were originally attributed to the genus ''

Plateosaurus ''Plateosaurus'' (probably meaning "broad lizard", often mistranslated as "flat lizard") is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 214 to 204 million years ago, in what is now Central and Northern Eur ...

''.

Phylogeny

Previous to the discovery of adult specimens of ''Mussaurus'', the

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

position of this taxon was difficult to establish. Infant and juvenile fossils are known to show more basal traits than adult specimens of the same taxon. Furthermore, the recently discovered of one subadult and three adult specimens assigned to ''Mussaurus'' are more complete than other material assigned to it. Therefore, a cladistic analysis of basal sauropodomorphs performed by Otero and Pol (2013) to test the phylogenetic relationships of ''Mussaurus'', included information only from adult specimens. The following

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

is simplified after their analysis (relationships outside

Plateosauria Plateosauria is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to the Late Cretaceous. The name Plateosauria was first coined by Gustav Tornier in 1913. The name afterwards fell out of use until the 1980s. Classificat ...

are not shown).

Palaeobiology

Reproduction

''Mussaurus'' specimens have been found in association with nests that are believed to contain multiple eggs apiece. The skeletons of ''Mussaurus'' infants were small, only six inches long excluding the tail, but a total of long. This is about the size of a small lizard. Juveniles differed from adults in proportion in addition to size and mass. As is common for dinosaurs, juvenile ''Mussaurus'' had tall skulls with short snouts and large eyes. These proportions are common in many infant vertebrates and are often associated with species that provide parental care during the vulnerable early stages of life. Adults are expected to have longer snouts and necks, as typical in early

Locomotion

A study published in May 2019 shows that while ''M. patagonicus'' probably walked on all four limbs (was

quadrupedal 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 ...

) during the first year of its life, changes in the relative proportions of its body during growth (

ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the s ...

) caused its

centre of mass In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...

to move backwards towards its pelvis, resulting in the animal adopting a two-legged (

bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

) stance later in life.

References

External links

{{Taxonbar, from=Q132857 Sauropodomorphs Dinosaur genera Norian life Late Triassic dinosaurs of South America Fossils of Argentina Triassic Argentina Fossil taxa described in 1979 Taxa named by José Bonaparte