Exaeretodon

Exaeretodon Temporal range: Middle Triassic–Late Triassic PreЄ Є O S D C P T J K Pg N
Exhibit at Mori Tower
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Order:	Therapsida
Clade:	Cynodontia
Family:	†Traversodontidae
Subfamily:	†Gomphodontosuchinae
Genus:	†Exaeretodon Cabrera, 1943
Species
†E. frenguelli (type species) †?E. argentinus Bonaparte, 1962 †?E. major (Huene, 1935-42 (originally Traversodon)) †E. riograndensis Abdala, Barbarena, and Dornelles, 2002 †?E. statisticae Chatterjee, 1982 †?E. vincei (Bonaparte, 1963 (originally Proexaeretodon))
Synonyms
Theropsis Cabrera, 1943 Ischignathus Bonaparte, 1967

Exaeretodon is a genus of traversodontid cynodont; several species are known, from various formations. E. argentinus, E. frenguelli, and E. vincei are from the Carnian-age (Upper Triassic) Ischigualasto Formation of Argentina. E. major and E. riograndensis are from the Ladinian-age (Middle Triassic) portion of the Santa Maria Formation of Brazil. E. statisticae is from the Carnian-age Lower Maleri Formation of India.

Description

Restoration

Skull of Exaeretodon at the Royal Ontario Museum

This genus was an herbivore up to 1.8 meters long (5.9 ft), with a specialized grinding action when feeding.^[1]

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. Another point of interest is that these cynodonts had deciduous teeth, which is a characteristic of mammals and means that babies could not chew, and required specialized parental care. Only older juveniles had permanent teeth.^{[citation needed]}

Taxonomy

Exaeretodon is one of the largest traversodontids, but the traversodontid species Ischignathus sudamericanus was reported in 1967 to be even larger. I. sudamericanus was based on a single skull from the Ischigualasto Formation in the same deposit as Exaeretodon argentinus.^[2]

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 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

• Paleorrota

References

External links

• Exaeretodon at Palaeos.com.
• Dinosaurs of Rio grande do Sul.

v t e Fauna and Flora of Paleorrota Geopark Rio Grande do Sul Fauna Aetosaurs Stagonolepis Archosaurs Barberenachampsa nodosa Barberenasuchus brasiliensis Cerritosaurus Chanaresuchus Decuriasuchus Fitossauros Karamuru vorax Prestosuchus chiniquensis Procerosuchus Proterochampsa nodosa Protorosaurus Rauisuchus tiradentes Rhadinosuchus gracilis Spondylosoma Teyumbaita sulcognathus Teyuwasu Cynodonts Belesodon magnificus Brasilitherium Brasilodon Candelariodon Chiniquodon Charruodon Tetracuspidatus Exaeretodon riograndensis Gomphodontosuchus Brasiliensis Irajatherium hernadezi Luangwa Massetognathus Menadon Minicynodon Protheriodon estudianti Protuberum cabralensis Prozostrodon brasiliensis Riograndia Santacruzodon hopsoni Therioherpeton cargnini Traversodon Stahleckeri Dicynodonts Dinodontosaurus pedroanum Dinodontosaurus turpior Jachaleria candelariensis Stahleckeria Trucidocynodon Dinosaurs Staurikosaurus Guaibasaurus Pampadromaeus Sacisaurus Saturnalia tupiniquim Unaysaurus Mesosaurus Mesosaurus Pareiasaurus Provelosaurus brasiliensis Procolophons Candelaria barbouri Procolophon brasiliensis Procolophon pricei Procolophon trigoniceps Rhynchosaurs Hyperodapedon huenei Hyperodapedon mariensis Hyperodapedon sanjuanensis Temnospondylis Bageherpeton longignathus Sangaia lavinai Stereospondyli Insects Sanctipaulus mendesi Others Clevosaurus brasiliensis Dinocephalians Pampaphoneus biccai Soturnia caliodon Tiarajudens eccentricus Paleorrota's Flag. Dinotchê: The mascot Paleorrota. Flora Lycophytas Brasilodendron pedroanum Cyclodendron sp. Pteridospermatophytas Dicroidium odontopteroides Dicroidium zuberi Pteridophytas Asterotheca sp. Botrychiopsis plantianum Botrychiopsis valida Neomariopteris sp. Osmundites brasiliensis Pecopteris sp. Stephanophyllites sp. Sphenophytas Phyllotheca brevifolia Phyllotheca longifolia Sphenopteris sp. Neocalamites sp. Glossopteris Gangamopteris obovata Gangamopteris sulriograndensis Glossopteris angustifolia Glossopteris. brasiliensis Glossopteris browniana Glossopteris communisi Glossopteris indica Glossopteris occidentalis Cordaites Cordaites hislopii Kawizophyllum sp. Ginkgophytas Baieroxylon cicatricum Cheirophyllum speculare Chiropteris sp. Ginkgoites antarctica Sphenobaiera sp. Conifers Brachyphyllum sp. Buriadia sp. Cordaicarpus brasilianus Cordaicarpus cerronegrensisi Cordaicarpus fanatinensis Cordaicarpus truncata Coricladus quiteriensis Kaokoxylon zalesskyi Pagiophyllum sp. Samaropsis gigas Samaropsis kurtzii Samaropsis millaniana Samaropsis rigbyi Samaropsis seixasi Sommerxylon spiralosus Bennettitales Nilssonia sp. Williamsonia sp.