Exaeretodon

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Exaeretodon
Temporal range: Ladinian-Norian
~235–205.6  Ma
Cynodont.jpg
Exhibit at Mori Tower
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Therapsida
Clade: Cynodontia
Family: Traversodontidae
Subfamily: Gomphodontosuchinae
Genus: Exaeretodon
Cabrera 1943
Species
  • E. argentinus(Cabrera 1943) (type)
  • ?E. major(Huene 1935-42 (originally Traversodon ))
  • E. riograndensisAbdala et al. 2002
  • ?E. statisticaeChatterjee 1982
Synonyms
  • TheropsisCabrera 1943
  • Ischignathus Bonaparte 1963
  • ProexaeretodonBonaparte 1963

Exaeretodon is an extinct genus of fairly large, low-slung traversodontid cynodonts from the southern parts of Pangea. Four species are known, from various formations. E. argentinus is from the Carnian-age (Late Triassic) Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina. E. major and E. riograndensis are from the Carnian-age portion of the Santa Maria Formation of the Paraná Basin in southeastern Brazil. [1] E. statisticae is from the Carnian-age Lower Maleri Formation of India.

Contents

Description

Restoration Exaeretodon BW.jpg
Restoration
Skull of Exaeretodon at the Royal Ontario Museum August 1, 2012 - Skull of Exaeretodon on Display at the Royal Ontario Museum (MC2 4483).jpg
Skull of Exaeretodon at the Royal Ontario Museum

This genus was an herbivore up to 1.8 meters (5.9 feet) 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.[ citation needed ]

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 Ischignathus 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 or eye socket is longer than that of Exaeretodon, as are the palatine bones. [2]

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 variation. [2]

See also

Related Research Articles

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<i>Bonacynodon</i> Extinct genus of cynodonts

Bonacynodon is an extinct genus of cynodonts that lived in what is now southern Brazil during the Triassic period. The genus is monotypic, containing only the type species Bonacynodon schultzi. B. schultzi is known from two specimens, consisting of two partial skulls and some badly preserved parts of the postcranium. Both specimens were recovered from the Pinheiros-Chiniquá Sequence, part of the Santa Maria Supersequence of the Paraná Basin. This sequence preserves a faunal association known as the Dinodontosaurus Assemblage Zone, which contains numerous other species of cynodonts, dicynodonts and reptiles. Bonacynodon was a small, likely insectivorous cynodont, whose length has been estimated at around 30 centimetres (12 in). It can be distinguished from other cynodonts by its large, serrated (saw-like) canine teeth. Together with the genus Probainognathus of Argentina, it made up the family Probainognathidae, one of the earliest-diverging lineages of the clade Probainognathia. It was a fairly close relative of mammals, the only group of cynodonts alive today.

References

  1. Langer, Max C.; Ramezani, Jahandar; Da Rosa, Átila A.S. (May 2018). "U-Pb age constraints on dinosaur rise from south Brazil". Gondwana Research. 57: 133–140. doi:10.1016/j.gr.2018.01.005.
  2. 1 2 Liu, J. (2007). "The taxonomy of the traversodontid cynodonts Exaeretodon and Ischignathus" (PDF). Revista Brasileira de Paleontologia. 10 (2): 133–136. doi: 10.4072/rbp.2007.2.07 .