| Sinotherium | |
|---|---|
 | |
| Skull ofSinotherium | |
 | |
| Life restoration ofS. lagrelii | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Perissodactyla |
| Family: | Rhinocerotidae |
| Subfamily: | †Elasmotheriinae |
| Genus: | †Sinotherium Ringstrom, 1923 |
| Type species | |
| †Sinotherium lagrelii Ringstrom, 1923 | |
| Other species | |
| |
Sinotherium ("Chinese Beast") is an extinctgenus of single-hornedelasmotheriine rhinocerotids that lived from thelate Miocene (Tortonian -Messinian) toEarly Pliocene. It was ancestral toElasmotherium, demonstrating a very important evolutionary transition from nasal-hornedelasmotheriines tofrontal-hornedelasmotheriines. Its fossils have been found in theKarabulak Formation ofKazakhstan, lower jaw and teeth have been found inMongolia, and a partialskull is known from the upper part of theLiushu Formation of westernChina.Sinotherium diverged from the ancestralgenus,Iranotherium, first found inIran, during theearly Pliocene. Some experts prefer to lumpSinotherium, andIranotherium intoElasmotherium.
The type species ofSinotherium isS. lagrelii. It is also known to have an additional species from the Zaisan depression of Kazakhstan calledS. zaisanensis, however, doubt has been raised on its validity.[1]
Finds ofSinotherium are rather rare and often only fragmentary. The first fossils, which also led to the description of therhinoceros genus, came to light at the beginning of the 20th century and were discovered by JG Andersson in theBaode district in the Chinese province ofShanxi in deposits from the Upper Miocene. These mainly consisted of isolated teeth, an upper jaw fragment with the preserved row of teeth from the second premolar to the penultimate molar, and a lower jaw fragment.[2][3] From north-westernMongolia near Chono-Khariakha, a 72 cm long, well-preserved lower jaw was discovered which dates to the Lower Pliocene.[4] Other individual finds are known fromKazakhstan, including a rear part of the skull with part of the teeth and several skeletal elements of the body.[1] The most complete skull to date was found in the upper area of theLiushu Formation near Houaigou in the Guanghe District of Gansu Province. The Liushu Formation is about 100 m thick and over wide ranges of Linxia basin digested. This section is dated to about 7 to 6.4 million years and thus belongs to the end of theMiocene. The geological deposits of the Linxia Basin have already produced numerous well-preserved fossil rhinoceros remains, including numerous representatives of the Elasmotheriinae. Only the part of the snout is missing from the skull and it provided evidence of the location of the horns inSinotherium.[5]
The horns of olderelasmotheriines are present on theirnasals (nose), whereas the horn ofSinotherium's descendantElasmotherium is present on itsfrontals (forehead),Sinotherium shows a unique condition in which its horn is present in an intermediate "naso-frontal" position.[5] This represents the horn shifting from its ancestral nasal position to the derived frontal position, eventually resulting in the completely frontal restricted position ofElasmotherium.[5]
In addition to the nasofrontal horn,Sinotherium also preserves a rugosity on its forehead, just behind the nasofrontal horn, which implies that the animal had two horns.
Earlyelasmotheriinegenera of the line leading toElasmotherium, have adolichocephalicskull supporting a horn growing on theirnose, just like any otherRhinocerotid, however,Elasmotherium was the sole member ofElasmotheriinae that had abrachycephalicskull and supported a horn on itsforehead instead.[5] Atransition between this state ofnose-horned toforehead-hornedelasmotheriines remained missing until 2012, when the first cranial remains ofSinotherium lagrelii, (specimenIVPP V 18539, a partialskull housed at theInstitute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences inBeijing) was described, demonstrating a very important transition from nose-hornedelasmotheriines likeNingxiatherium to forehead-hornedelasmotheriines likeElasmotherium.[5]
While the horns ofNingxiatherium-likeelasmotheriines are present on theirnasals, and the horn ofElasmotherium on itsfrontals,Sinotherium shows its horn to be present in a "nasofrontal" position, (present on both the nose and the forehead).[5] This shows the horn shifting from its ancestral nasal position to a more derived frontal position, eventually resulting in the completely frontal restricted position ofElasmotherium.[5]
Sinotherium first appeared during theLate Miocene, occupyingeast Asian and Mid-Asian regions, but remains dating to theEarly Pliocene can be found fromeastern Asia to as far as theKumo-Manych depression of South-WesternRussia.[6] This showed that at the beginning of thePliocene (5.3–4.8 Mya),Sinotherium had significantly expanded its range westward.[6]Sinotherium is known fromPliocene toLate Miocene deposits ofKazakhstan,Mongolia, andChina.
In China, the speciesS. lagrelii is known from an age of 7Ma from the Late MioceneLiushu Formation in theLinxia Basin,Gansu Province.[5][7]Pollen analysis from the red beds of the Liushu Formation suggests that the unit was once a subarid to arid steppe, as evidenced by a high frequency ofxerophilous and sub-xerophilous grasses and lower frequency of warmtemperatebroadleaf trees.[5][8] Other fauna present in the Liushi Formation include bears (Ursavus sp.),mustelids (Parataxidea sinensis), hyenas (Hyaenictitherium wongii,H. hyaenoides,Ictitherium sp.),felids (Amphimachairodus giganteus,Metailurus major,Felis sp.),chalicotheres (Ancylotherium sp.), horses (Hipparion coelophyes), deer (Dicrocerus sp.), giraffids (Palaeotragus microdon), andbovids (Sinotragus wimani,Tsaidamotherium hedini andProtoryx sp.).[5][9]
InKazakhstan,Sinotherium zaisanensis is known from theKarabulak formation which dates to 6.3–6.5Ma (Late Miocene). It coexisted with fourcaniforms (Martes sp.,Promeles sp.,Plesiogulo crassa Teilhard,Indarctos punjabiensis), threefeliforms (Adcrocuta eximia,Hyaenictitherium hyaenoides orlovi,Amphimachairodus kurteni), threeperissodactyls (Hipparion hippidiodus,H. elegans,Chilotherium sp.), and sixartiodactyls (Cervavitus novorossiae,Procapreolus latifrons,Samotherium cf. irtyshense,Paleotragus (Yuorlovia) asiaticus,Tragoportax sp.,Gazella dorcadoides). The climate thatSinotherium zaisanensis lived in was mild and arid. It was a habitat of wide, open steppes.[10]
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