Description
This genus was smaller than Thomashuxleya and Periphragnis , and did not exceed 50 kilograms in weight. Its build was comparable to a modern peccary, with a body relatively massive and strong and sturdy legs. Compared to other Eocene notoungulates, like basal Notohippidae and Notostylopidae, Isotemnus had an humerus whose distal part had a high medial trochlear crest, while the bicipital radial tuberosity was almost unexistant. The astragalus had a broad and low trochlea with a short neck. The calcaneus had rectangular fibular facets, and an unusually thick sustentaculum. Several of the distinctive anatomical leg characteristics of Isotemnus could be due to its smaller size ; Periphragnis and Thomashuxleya, while very similar, had different characteristics.
Classification
Isotemnus is the eponymous genus of the family Isotemnidae, a possibly paraphyletic group of notoungulates including the most basal forms of toxodonts. Isotemnus was one of the most archaic and basal of the isotemnids. The type species is Isotemnus primitivus, first described in 1897 by Florentino Ameghino, based on fossil remains found in terrains dating back from the Early Eocene of Argentine Patagonia. Other species were later attributed to the genus, such as I. ctalego (Early Eocene), I. haugi (Early Eocene, initially described as Leifunia haugi), I. latidens (Middle Eocene). Fragmentary remains attributed to Isotemnus were discovered in Late Paleocene formations in Argentina.
Henricosborniidae is a family of extinct notoungulate mammals known from the Late Paleocene to Middle Eocene of Argentina, Bolivia and Brazil. The name honors U.S. paleontologist Henry Fairfield Osborn.
Prosotherium is an extinct genus of hegetotheriid notoungulate. It lived during the Late Oligocene, and its fossilized remains were found in South America.
Ernestokokenia is an extinct genus of mammal, belonging to the Didolodontidae. It lived during the Early Eocene and the Middle Eocene, and its fossils were discovered in South America.
Proadiantus(Ameghino, 1897) is an extinct genus of adianthid litoptern. It lived during the Late Oligocene, in what is today South America. It consists of only 1 species, Proadiantus excavatus.
Henricosbornia is an extinct genus of henricosborniid notoungulate that lived from the Late Paleocene to the Middle Eocene of what is now Argentina and Brazil.
Eohyrax is an extinct genus of Notoungulate, belonging to the suborder Typotheria. It lived during the Middle Eocene, and its remains were discovered in South America.
Transpithecus is an extinct genus of Notoungulates, belonging to the suborder Typotheria. It lived during the Middle Eocene in what is today South America.
Propachyrucos is an extinct genus of hegetotheriid notoungulate. It lived from the Late Oligocene to the Early Miocene, in what is today South America.
Periphragnis is an extinct genus of isotemnid notoungulates that lived from the Middle Eocene to the Early Oligocene in what is now Argentina and Chile.
Pleurostylodon is an extinct genus of notoungulate belonging to the family Isotemnidae. It lived during the Middle Eocene, in what is now Argentina.
Eomorphippus is an extinct genus of notohippid notoungulate that lived from the Late Eocene to the Early Oligocene in what is today South America.
Morphippus is an extinct genus of notohippid notoungulate that lived during the Middle to Late Oligocene in what is now South America.
Ancylocoelus is an extinct genus of mammal, belonging to the order Notoungulata. It lived during the Late Oligocene, in what is today Argentina, in South America.
Archaeopithecus is an extinct genus of Notoungulate, belonging to the suborder Typotheria. It lived during the Middle Eocene, in what is today Argentina.
Oldfieldthomasia is an extinct genus of Notoungulate, probably related to the suborder Typotheria. It lived during the Middle Eocene, in what is today South America.
Ultrapithecus is an extinct genus of oldfieldthomasiid notoungulate that lived during the Middle Eocene of what is now Argentina.
Argyrohyrax is an extinct genus of interatheriid notoungulate that lived during the Late Oligocene, of what is now Argentina and Bolivia.
Notopithecus is an extinct genus of Notoungulate, belonging to the suborder Typotheria. It lived from the Middle to the Late Eocene and its fossilized remains were discovered in South America.
Machlydotherium is an extinct genus of cingulate of uncertain systematic affinities, perhaps belonging to the Pampatheriidae. It lived from the Middle Eocene to the Early Oligocene, and its fossilized remains were found in South America.
Glyptatelus is an extinct genus of glyptodont. It lived from the Late Eocene to the Middle Oligocene in what is now Argentina and Bolivia.
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