Stephanorhinus

Stephanorhinus is an extinct genus of two-horned rhinoceros native to Eurasia and North Africa that lived during the Late Pliocene to Late Pleistocene. Species of Stephanorhinus were the predominant and often only species of rhinoceros in much of temperate Eurasia, especially Europe, for most of the Pleistocene. The last two species of Stephanorhinus – Merck's rhinoceros (S. kirchbergensis) and the narrow-nosed rhinoceros (S. hemitoechus) – went extinct during the last glacial period.

Etymology
The first part of the name, Stephano-, honours Stephen I, the first king of Hungary. (The genus name was coined by Kretzoi, a Hungarian.) The second part is from  (Greek for "nose"), a typical suffix of rhinoceros genus names.

Taxonomy
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. Genomes obtained from Stephanorhinus kirchbergensis suggests that Stephanorhinus is more closely related to Dicerorhinus (which contains the living Sumatran rhinoceros) and Coelodonta (which contains the woolly rhinoceros), than it is to other living rhinoceroses, and is more closely related to Coelodonta than to Dicerorhinus, with the date of divergence between Coelodonta and Stephanorhinus estimated at around 5.5 million years ago, with the estimated split between their last common ancestor and Dicerorhinus estimated at around 9.4 million years ago. The genus is also closely related to the fossil rhinoceros genera Dihoplus and Pliorhinus, known from the Late Miocene and Pliocene of Eurasia, which may be ancestral to Stephanorhinus. Although a study based on dental proteomes suggested that the genus was paraphyletic with respect to Coelodonta, a 2023 morphological study recovered Stephanorhinus as monophyletic.

Placement of Stephanorhinus kirchbergensis among recent and subfossil rhinoceros species based on nuclear genomes (Liu, 2021):

Bayesian morphological phylogeny (Pandolfi, 2023) Note: This excludes living African rhinoceros species.

Description
Species of Stephanorhinus were large-sized rhinoceroses, with body masses estimated between 1500-3000 kg. Stephanorhinus species have proportionally long (dolichocephalic) skulls. They had two horns, a frontal and a nasal horn. The nasal septum was partially ossified (turned to bone), which connected the nasal bones with the premaxillary bones. The incisors were either lost completely or very heavily reduced in size.

Species and evolution
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 and Pliorhinus'', respectively. “Stephanorhinus” miguelcrusafonti from the Early Pliocene of Western Europe has also been assigned to Pliorhinus in recent studies.

The position of Stephanorhinus? africanus from the Middle Pliocene of Tunisia and Chad is uncertain. Some authors have suggested that Stephanorhinus likely originated from members of the genus Pliorhinus.

Stephanorhinus jeanvireti, also known as S. elatus 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, France, Italy, Slovakia and Greece, and the Early Pleistocene of Romania, with its temporal span being around 3.4 to 2 million years ago.

Stephanorhinus etruscus first appears in the latest Pliocene in the Iberian Peninsula, around 3.3 million years ago (Ma) at Las Higueruelas in Spain and before 3 Ma at Piedrabuena, and during the latest Pliocene at Villafranca d’Asti and Castelnuovo di Berardenga 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. Stephanorhinus etruscus is thought to have had a browsing based diet.

Stephanorhinus migrated from its origin in western Eurasia into eastern Eurasia during the Early Pleistocene. Stephanorhinus yunchuchenensis is known from a single specimen in probably late Early Pleistocene aged deposits in Yushe, Shaanxi, China, while Stephanorhinus lantianensis is also known from a single specimen from late Early Pleistocene (1.15 Ma) deposits in Lantian, also in Shaanxi. These may be synonymous with other named Stephanorhinus species, with a 2022 study suggesting that they were likely synonyms of S. kirchbergensis and S. etruscus respectively.

The first definitive record of Stephanorhinus kirchbergensis (Merck's rhinoceros) is in China at Zhoukoudian (Choukoutien; near Beijing), around the Early–Mid-Pleistocene transition at 0.8 Ma. 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. The diet of S. hundsheimensis was flexible and ungeneralised, with two different early Middle Pleistocene populations under different climatic regimes having tooth wear analyses suggesting contrasting browsing and grazing habits. The more specialised S. kirchbergensis and S. hemitoechus, appear in Europe between 0.7-6 Ma and 0.6-0.5 Ma respectively. S. kirchbergensis and S. hemitoechus are typically interpreted mixed feeders tending towards browsing and grazing, 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.

Stephanorhinus hundsheimensis is typically suggested to have gone extinct at around 0.5 Ma, though a 2023 study suggested that the species may have persisted as recently as the latest Middle Pleistocene-earliest Late Pleistocene around 130,000 years ago, based on fossils found in Spain.

S. kirchbergensis was broadly distributed over northern Eurasia from Western Europe to East Asia, while S. hemitoechus was generally confined to the western Palearctic, including Europe, West Asia, and North Africa.

In Europe, the timing of the extinction of S. kirchbergensis is uncertain, though it is sometime after 115,000 years ago. The latest records of S. hemitoechus in Europe are known from the Iberian Peninsula, where they survived until at least 34,000 years ago, and possibly at late as 15,500 years ago in the Levant. In the Altai region, S. kirchbergensis survived until at least 40,000 years ago. In South China, the species may have survived into Marine Isotope Stage 2 (~29-14,000 years ago).

Relationship with humans
Remains of Stephanorhinus species have been found in sites across Europe with break or cut marks indicating that they were butchered by archaic humans. The earliest such site is Vallonnet Cave in France dating to around 1.2 to 1.1 million years ago, where remains of S. hundsheimensis have been reported with cut marks. Another early site is Boxgrove in England, dating to around 500,000 years ago, where an indeterminate species of Stephanorhinus was found with cut marks thought to have been created by Homo heidelbergensis. The youngest sites are known from the late Middle Paleolithic (around 100-50,000 years ago), which were created by Neanderthals. At some sites hunting is suggested to be the more likely than scavenging based on mortality profiles.