Stephanorhinus

The first part of the name is derived from that of King Stephen I of Hungary,[2] and the second part from 'rhinos' (ρινος, meaning "nose"), as with Dicerorhinus.

The taxonomic history of Stephanorhinus is long and convoluted, as many species are known by numerous synonyms and different genera, typically Rhinoceros and Dicerorhinus for the 19th and most of the early 20th century. The genus was named by Miklós Kretzoi in 1942.[3] It is thought that Stephanorhinus is more closely related to the Sumatran rhinoceros and woolly rhinoceros than other rhino species. A complete mitochondrial genome of S. kirchbergensis obtained from a 70,000 - 48,000 year old skull preserved in permafrost in arctic Yakutia showed that it was more closely related to the woolly rhinoceros than the Sumatran rhinoceros.[4] In 2019 a study of dental proteomes showed that the genus was paraphyletic as currently defined, as the genus Coelodonta was found to be derived from an early diverging lineage within Stephanorhinus, with the proteome sequence obtained from the enamel of a 1.77 million year old Stephanorhinus sp. tooth from Dmanisi outside the clade containing the woolly rhinoceros and S. kirchbergensis.[5]

The oldest known species of the genus are from the Pliocene of Europe, the species S. pikermiensis and S. megarhinus that were formerly considered to belong to Stephanorhinus are currently considered to belong to Dihoplus,[6] while the positions of “Stephanorhinus” miguelcrusafonti from the Early Pliocene of Western Europe and Stephanorhinus? africanus from the Middle Pliocene of Tunisia and Chad are uncertain.[7]

Skull of Stephanorhinus jeanvireti

Stephanorhinus jeanvireti, also known as S. elatus[8] is known from the Late Pliocene and Early Pleistocene of Europe. Its remains are relatively rare in comparison to other Stephanorhinus species. Specimens are known from the Late Pliocene of Germany[9] France, Italy,[10] Slovakia[11] and Greece,[12] and the Early Pleistocene of Romania.[13]

Skull of Stephanorhinus etruscus

Stephanorhinus etruscus first appears in the latest Pliocene in the Iberian Peninsula, around 3.3 Ma at Las Higueruelas in Spain and before 3 Ma at Piedrabuena, and during the latest Pliocene at Villafranca d’Asti and Castelnuovo di Barardenga in Italy and is abundant during most of the Villafranchian period in Europe, and is the sole rhinoceros species in Europe between 2.5 and around 1.3 Ma. A specimen is known from the Early Pleistocene (1.6-1.2 Ma) Ubeidiya locality in Israel. During the late Early Pleistocene it is largely replaced by S. hundsheimensis. The last known records of the species are from the latest Early Pleistocene of the Iberian peninsula, around 0.9-0.8 Ma.[14]

Stephanorhinus yunchuchenensis is known from a single specimen in Early Pleistocene deposits in Yushe County, Shaanxi while Stephanorhinus lantianensis is also known from a single specimen from late Early Pleistocene (1.15 Ma) deposits in Lantian County, Shaanxi.[15] These are stated to be synonyms of Stephanorhinus kirchbergensis by some sources.[16]

The first record of Stephanorhinus kirchbergensis is in China at Choukoutien Locality 13, in Fangshan District near Beijing which is around the Early-Mid Pleistocene transition at 0.8 Ma.[15]

Skull of Stephanorhinus hundsheimensis

Stephanorhinus hundsheimensis first definitively appears in the fossil record in Europe and Anatolia at around 1.2 Ma, with possible records in Iberia around 1.6 Ma and 1.4-1.3 Ma. The earliest confirmed appearance in Italy around 1 Ma.[17] The diet of S. hundsheimensis was flexible and ungeneralised, with two different early Middle Pleistocene populations under different climactic regimes having tooth wear analyses suggesting contrasting browsing and grazing habits.[18] The more specialised S. kirchbergensis and S. hemiotoechus, appear in Europe between 0.7-6 Ma and 0.6-0.5 Ma respectively, and replace S. hundsheimensis. S. kirchbergensis and S. hemiotoechus are typically interpreted as a browsing form and grazing form, respectively. The evolution of more specialized diets is possibly due to the change to the 100 Kyr cycle after the Mid Pleistocene Transition, which resulted in environmental stability allowing the development of more specialized forms.[19]

Skulls from top to bottom. S. kirchbergensis, S. hemitoechus and the woolly rhinoceros, showing the difference in head angle

From the late Middle Pleistocene onwards, the large Merck's rhinoceros (Stephanorhinus kirchbergensis) and the narrow-nosed rhinoceros (Stephanorhinus hemitoechus) were the only species of Stephanorhinus. S. kirchbergensis was broadly distributed over northern Eurasia, while S. hemitoechus was generally confined to the western Palearctic.[20] S. kirchbergensis is relatively rare in fossil record and known from few Italian, French, German, British, and East-European localities, mostly of the middle Pleistocene. In Asia it is known from Siberia, Central Asia (e.g. southeastern Kazakhstan), Central Korea, and China. It may have also occurred in Israel and Lebanon, but here it is unclear if it was really S. kirchbergensis or a similar species.[21] In eastern China, S. kirchbergensis was present throughout the Pleistocene between 30°N and 40°N.[16] It is stated by some sources that S. hemitoechus occurs in North Africa.[7]

In eastern Europe S. kirchbergensis disappeared during the earliest Late Pleistocene, where it is recorded in the Eemian in Poland. In the forests of the Caucasus it may have survived even until the early Weichselian. Apart from Europe it is also known from Syria, Israel, the Caucasus and from one Late Pleistocene locality close to Lake Baikal. This is the easternmost point of the known range. The latest fossils of the narrow-nosed rhinoceros are known from the Balkans, where it survived until the early late Weichselian.[20] The last records of S. hemitoechus in Italy date to around 41 kya.[22] Remains of S. kirchbergensis in the Russian Far East and South China are suggested to date to MIS 3 and 2, respectively.[23][24]