Urtinotherium
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''Urtinotherium'' (meaning "Urtyn beast" in
Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
) 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 paracerathere mammals. It was a large animal that was closely related to ''
Paraceratherium ''Paraceratherium'' is an extinct genus of hornless rhinocerotoids belonging to the family Paraceratheriidae. It is one of the largest terrestrial mammals that has ever existed and lived from the early to late Oligocene epoch (34–23  ...
'', and found in rocks dating from the
Late Eocene The Priabonian is, in the International Commission on Stratigraphy, ICS's geologic timescale, the latest age (geology), age or the upper stage (stratigraphy), stage of the Eocene epoch (geology), Epoch or series (stratigraphy), Series. It spans ...
to
Early Oligocene The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ...
period. The remains were first discovered in the Urtyn Obo region (now Dorbod Banner,
Ulanqab Ulanqab or Ulan Chab ( zh, s=乌兰察布, p=Wūlánchábù; ''Ulaɣančab qota-means in Mongolian Ulaan-red, Tsab/tsav is-hills''; Mongolian Cyrillic: Улаанцав хот) is a region administered as a prefecture-level city in south-centr ...
) in
Inner Mongolia Inner Mongolia, officially the Inner Mongolia Autonomous Region, is an Autonomous regions of China, autonomous region of China. Its border includes two-thirds of the length of China's China–Mongolia border, border with the country of Mongolia. ...
, which the name ''Urtinotherium'' is based upon. Other referred specimens are from northern
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
.


Description

''Urtinotherium'' was a representative of the large family
Paraceratheriidae Paraceratheriidae is an extinct family of long-limbed, hornless rhinocerotoids, native to Asia and Eastern Europe that originated in the Eocene epoch and lived until the end of the Oligocene. They represent some of the largest terrestrial mammals ...
, and almost reached the proportions of ''
Paraceratherium ''Paraceratherium'' is an extinct genus of hornless rhinocerotoids belonging to the family Paraceratheriidae. It is one of the largest terrestrial mammals that has ever existed and lived from the early to late Oligocene epoch (34–23  ...
''. ''Urtinotherium'' evolved from Juxia and represents the beginning of paracerathere gigantism. It could reach a weight of about 5 tonnes, and was among the largest animals living in its environment, alongside the brontothere ''Embolotherium''. It is known from several findings in central and eastern
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
, though no complete skeletons are known. The holotype fossil (catalog number IVPP V.2769) includes a complete lower jaw in length, comparable to the smallest known of ''Paraceratherium''. The jaw is wedge shaped, very low in height, and with elongated branches. The symphysis was solid and extended to the beginning of the second premolars. The jaw's dentition is complete, having three front
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, wher ...
s and
canine Canine may refer to: Zoology and anatomy * Animals of the family Canidae, more specifically the subfamily Caninae, which includes dogs, wolves, foxes, jackals and coyotes ** ''Canis'', a genus that includes dogs, wolves, coyotes, and jackals ** Do ...
. The first two incisors protrude forward with a crown length of , with forms similar to daggers. The other incisors and canines had much smaller crowns. Between each tooth is a small space, similar to its phylogenetically primitive relatives such as ''
Juxia ''Juxia'', ‘joo-she-a’, (from ) is an extinct genus of Paraceratheriidae, paraceratheriid, a group of herbivorous mammals that are related to the modern rhinoceros. The type species is ''Juxia sharamurenensis'', named by Zhou Mingzhen and in ...
''. Its back teeth, which are separated from the front teeth by a small
diastema A diastema (: diastemata, from Greek , 'space') is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition may be referred to ...
, consist of four
premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...
s and three
molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...
. These are similar in structure to those of ''Paraceratherium'', with small premolars and larger molars. The latter have low crowns (are
brachyodont The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone tooth ...
) and had few enamel folds.


Distribution

The remains of ''Urtinotherium'' are found mainly in the eastern and central Asia, consisting mostly of jaw fragments and isolated teeth. The holotype jaw was found in the early 1960s in the Urtyn-Obo Formation of
Inner Mongolia Inner Mongolia, officially the Inner Mongolia Autonomous Region, is an Autonomous regions of China, autonomous region of China. Its border includes two-thirds of the length of China's China–Mongolia border, border with the country of Mongolia. ...
, which dates from the
Late Eocene The Priabonian is, in the International Commission on Stratigraphy, ICS's geologic timescale, the latest age (geology), age or the upper stage (stratigraphy), stage of the Eocene epoch (geology), Epoch or series (stratigraphy), Series. It spans ...
. Additional findings came from
Yunnan province Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...
in China and Late Eocene deposits of Khoer-Dzam in
Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...
. Further findings have been made in Saissansee Aksyir Svita basin in eastern
Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a landlocked country primarily in Central Asia, with a European Kazakhstan, small portion in Eastern Europe. It borders Russia to the Kazakhstan–Russia border, north and west, China to th ...
, also of the same age. ''Urtinotherium'' likely survived into the
Early Oligocene The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ...
, as fossils probably from it have been found in the Mera Formation of
Transylvania Transylvania ( or ; ; or ; Transylvanian Saxon dialect, Transylvanian Saxon: ''Siweberjen'') is a List of historical regions of Central Europe, historical and cultural region in Central Europe, encompassing central Romania. To the east and ...
,
Romania Romania is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern and Southeast Europe. It borders Ukraine to the north and east, Hungary to the west, Serbia to the southwest, Bulgaria to the south, Moldova to ...
.


Classification

''Urtinotherium'' pertains to the
Paraceratheriidae Paraceratheriidae is an extinct family of long-limbed, hornless rhinocerotoids, native to Asia and Eastern Europe that originated in the Eocene epoch and lived until the end of the Oligocene. They represent some of the largest terrestrial mammals ...
subfamily Paraceratheriinae. These in turn are part of the superfamily
Rhinocerotoidea Rhinocerotoidea is a superfamily (taxonomy), superfamily of Perissodactyla, perissodactyls that appeared 56 million years ago in the Paleocene. They included four extinct families, the Amynodontidae, the Hyracodontidae, the Paraceratheriidae, an ...
and therefore represent close relatives of 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 ...
es. The paraceratheres are distinguished by the formation of large sharp incisors in their upper and lower jaws, while rhinoceroses only have a two on the lower jaw. ''Urtinotherium'' was thought of by Leonard Radinsky to be a transitional form between earlier paraceratheres, like ''Juxia'', and later forms, such as ''Paraceratherium'' and '' Indricotherium'' (now ''Paraceratherium transouralicum''). This genus represents a primitive form of paracerathere that developed in the late Eocene. It is possibly descended from ''Juxia'', which lived during the
Middle Eocene The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', ' Dawn') a ...
in northern China, and which shares with it having a full set of teeth in its jaws. However, ''Urtinotherium'' differs by its larger body size and greater specialization in the incisors. ''Urtinotherium'' and later ''Paraceratherium'' form the most derived section of the largest known rhinocerotoid lineage. In their specialization emphasizes that compared to ''Urtinotherium'', they possessed significantly reduced dentition with only a couple of incisors in the lower jaw. The first description of ''Urtinotherium'' was published in 1963 by Zhou Ming-Zhen and Chiu Chan-Siang, based on the lower jaw. The type species is recognized as ''Urtinotherium incisivum''. The genus name comes from the location, and from the
Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
word () meaning "beast". The species name refers to its elongated incisivos.


References

{{Taxonbar, from=Q1699664 Paraceratheriidae Eocene rhinoceroses Inner Mongolia Oligocene rhinoceroses Hyracodonts Fossil taxa described in 1963