''Exaeretodon'' is an extinct

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 ...

of fairly large, low-slung traversodontid

cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...

s from the southern parts of Pangea. Four species are known, from various formations. ''E. argentinus'' is from the Carnian-age (

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

) Cancha de Bochas Member of the

Ischigualasto Formation The Ischigualasto Formation is a Late Triassic fossiliferous formation and Lagerstätte in the Ischigualasto-Villa Unión Basin of the southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation da ...

in the

Ischigualasto-Villa Unión Basin The Ischigualasto-Villa Unión Basin ( es, Cuenca de Ischigualasto-Villa Unión) is a small sedimentary basin located in the Argentine Northwest, Argentina. It is located in the southwestern part of La Rioja Province and the northeastern part of ...

in northwestern

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 ...

. ''E. major'' and ''E. riograndensis'' are from the Carnian-age portion of the Santa Maria Formation of the Paraná Basin in southeastern

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. ''E. statisticae'' is from the Carnian-age

Lower Maleri Formation The Lower Maleri Formation is a sedimentary geological formation, rock formation found in Andhra Pradesh and Telangana, India. It is the lowermost member of the Pranhita–Godavari Basin. It is of late Carnian to early Norian age (Upper Triassi ...

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

Description

This genus 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 ...

up to long, with a specialized grinding action when feeding. An analysis of the size of the bones of calves collected in Paleorrota concluded that the mother ''Exaeretodon'' had one or two calves, for one

pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...

Taxonomy

When he first named the species, Argentine paleontologist José Bonaparte mentioned several features that distinguish it from all other traversodontids. The tooth rows of the upper jaw are more parallel to each other in ''I. sudamericanus'' than they are in ''Exaeretodon'', and they are also inset closer to the inside of the mouth. There are also more postcanine teeth oriented toward middle of the subtemporal fenestrae (two holes in the bottom of the skull) and ascending rama of the dentary (projections of the lower jaw that extend up to the skull). The ascending rama are also wider and taller in the ''I. sudamericanus'' specimen. The

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

or eye socket is longer than that of ''Exaeretodon'', as are the

palatine bone In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxillae, they comprise the hard palate. (''Palate'' is derived from the Latin ''pa ...

s. Despite the differences, a 2007 study concluded that the ''I. sudamericanus'' skull represents the same species as ''E. argentinus''. Using allometry, paleontologist Jun Liu found ''I. sudamericanus'' to be the largest known example of a growth series in ''E. argentinus''. Thus, ''Ischignathus'' is now regarded as a junior synonym of ''Exaeretodon''. As the animal grew, the proportions of bones changed. These differing proportions were initially seen as species-distinguishing characters, but are now regarded as natural

ontogenic 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 stu ...

variation.

References

{{Portal bar, Paleontology Traversodontids Prehistoric cynodont genera Ladinian first appearances Carnian extinctions Triassic synapsids of Asia Fossils of India Late Triassic synapsids of South America Triassic Argentina Fossils of Argentina Ischigualasto Formation Triassic Brazil Fossils of Brazil Santa Maria Formation Fossil taxa described in 1943 Taxa named by Ángel Cabrera

Description

Taxonomy

See also

References