''Gyrinodon'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

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 ...

toxodontid Toxodontidae is an extinct family of notoungulate mammals, known from the Oligocene to the Holocene (11,000 BP) of South America, with one genus, ''Mixotoxodon'', also known from the Pleistocene of Central America and southwestern North Americ ...

notoungulate that lived from the Late

Miocene The Miocene ( ) is the first 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 means "less recen ...

and Early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Brazil 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 ...

and

Colombia Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...

Description

This animal was approximately the size of a modern

rhinoceros A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species o ...

, 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

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whe ...

s 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 ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...

. Other fossils attributed to the species were later found in

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 ...

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

Urumaco Formation The Urumaco Formation is a formation in Venezuela that includes deposits from the Late Miocene. It is the site of several "giant forms": the turtles, crocodiles, sloths and rodents of Urumaco are among the largest of their groups. Location Th ...

. ''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 ''Falcontoxodon'' is an extinct genus of toxodontid notoungulate that lived from the late Pliocene to the Pleistocene in what is now Venezuela. Fossils of this genus have been found in the Chapadmalalan-Uquian Codore Formation, as well as in th ...

'', ''

Mixotoxodon ''Mixotoxodon'' ("mixture ''Toxodon''") is an extinct genus of notoungulate of the family Toxodontidae inhabiting South America, Central America and parts of southern North America during the Pleistocene epoch, from 1,800,000—12,000 years ago. ...

'', and ''

Piauhytherium ''Piauhytherium'' is an extinct genus of herbivorous notoungulate mammal of the family Toxodontidae. It lived during the Late Pleistocene, about 10,000 years ago; fossils have been found in Brazil. The only known species is ''Piauhytherium capi ...

''.

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 {{paleo-mammal-stub