''Gyrinodon'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of toxodontid notoungulate that lived from the Late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

and Early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

and

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

Description

This animal was approximately the size of a modern

rhinoceros A rhinoceros ( ; ; ; : rhinoceros or rhinoceroses), commonly abbreviated to rhino, is a member of any of the five extant taxon, extant species (or numerous extinct species) of odd-toed ungulates (perissodactyls) in the family (biology), famil ...

, and they were similar in build as in appearance. Like most of its close relatives, ''Gyrinodons size was substantially larger than any other mammal in its habitat. The frontal region of the skull passed softly into the anterior portion of the temporal fossa. The postorbital processes were reduced. Unlike some of its relatives, neither the upper edge of the orbit nor the roof of the nasal cavity were swollen. The lateral upper incisors were curved, and formed an arch of 180° or more. The first two upper molars had a small metaloph, while the third molar had a long and concave ectoloph, but was devoid of metaloph. The symphysis of the mandible did not exceed the second lower molar. The third lower molar lacked a second posterior crease in the enamel of the lingual surface.

Classification

''Gyrinodon quassus'' was first described by Hopwood in 1928, based on fossils found in Early Pliocene terrains of

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

. Other fossils attributed to the species were later found in

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

in terrains dated from the Late Miocene, and remains attributed to ''Gyrinodon'' were also discovered in the Urumaco Formation of

. ''Gyrinodon'' was a member of the Toxodontidae, a family of well-known notoungulates with heavy and large shapes. ''Gyrinodon'' may have been a rather derived form, forming a clade with its relatives '' Falcontoxodon'', '' Mixotoxodon'', and '' Piauhytherium''.

Bibliography

*A. T. Hopwood. 1928. Gyrinodon quassus, a new genus and species of toxodont from Western Buchivacoa (Venezuela). Quarterly Journal of the Geological Society 84:573-583 *O. J. Linares. 2004. Bioestratigrafia de la fauna de mamíferos de las Formaciones Socorro, Urumaco y Codore (Mioceno medio - Plioceno temprno)de la región de Urumaco, Falcon, Venezuela. Paleobiologia Neotropical 1:1-26 *M. A. Cozzuol. 2006. The Acre vertebrate fauna: Age, diversity, and geography. Journal of South American Earth Sciences 21:185-203 Toxodonts Prehistoric placental genera Pliocene mammals of South America Miocene mammals of South America Neogene Brazil Fossils of Colombia Neogene Colombia Fossils of Brazil Fossil taxa described in 1928 {{notoungulate-stub