Merck's rhinoceros

The first part of the genus name is derived from that of King Stephen I of Hungary, and the second part from 'rhinos' (ρινος, meaning "nose"), as with Dicerorhinus. The species name was given by Georg Friedrich von Jäger in 1839 for Kirchberg an der Jagst in Baden-Württemberg, where the type specimens had been found.[2] It is often known in English (and equivalents in other languages) as Merck's rhinoceros after Carl Heinrich Merck, who gave the initial name to the species in 1784 as Rhinoceros incisivus, that is now considered a nomen oblitum, and who after a widely used junior synonym of the species, Rhinoceros/Dicerorhinus mercki (historically several alternate spellings) was named by Johann Jakob Kaup in 1841.[3]

The origin of the species is obscure, with various authors suggesting either a European or Asian origin. The earliest definitive records are from Choukoutien Locality 13, in Fangshan District near Beijing at around the Early-Middle Pleistocene transition[4], though the older records of Stephanorhinus lantianensis and Stephanorhinus yunchuchenensis have been suggested to be synonyms of S. kirchbergensis by some sources.[5] It appears in Europe during the early Middle Pleistocene between 0.7-0.6 Ma, existing alongside the already present S. hundsheimensis.[6] A complete mitochondrial genome obtained from a permafrost specimen[7] and proteome studies[8] suggest that it is more closely related to the Woolly rhinoceros than the Sumatran rhinoceros, but its relationship to other Stephanorhinus species remains unclear.

Range of Merck's rhinoceros, excluding arctic localities

Its range spans from Europe to East Asia, but appears to be absent from the Iberian Peninsula.[9][10] Its range extended into the Arctic Circle, with a 70–48 thousand-year-old skull known from arctic Yakutia in the Chondon River valley[7] and a late Middle Pleistocene aged lower jaw from the Yana River valley.[11] Teeth are known from a cave in Primorsky Krai[12] It is fairly common throughout the Pleistocene in North China,[5] but is a rarer component of South Chinese assemblages,[13] being known from around 30 localities in the region.[4] Antoine (2012) states that D. choukoutienensis, D. lantianensis, and D. yunchuchenensis are local names for the taxon, without elaboration.[5] Its range was strongly controlled by glacial cycles, with the species experiencing repeated cycles of expansion and contraction as the ice sheets advanced, this accounts for its relative rarity of its remains in comparison to the woolly rhinoceros.[9] The species' range underwent significant reduction during the Last Glacial Period, with the youngest records from Italy being in MIS 4 and 3.[14] The youngest reliable records in China are from the Rhino Cave in Hubei, which is early Late Pleistocene in age.[13] Though less definitive remains are known from near Harbin in Heilongjiang, which are thought to be 20 kya in age.[4] It is presumed to have had a preference for closed forest and woodland habitats, as opposed the to open grassland habitats favoured by S. hemitoechus.[1]

Comparison of the head angle of Merck's rhinoceros (top) with that of that of S. hemitoechus and the Woolly rhinoceros (middle and bottom, respectively)

Merck's rhinoceros appears to have been a mixed feeder with a more specialised diet than S. hundsheimensis and the grazing diet hypothesised for S. hemitoechus. Despite their morphological differences, its preferences were not significantly different than S. hemitoechus, suggesting dietary convergence due to low habitat variability during the Pleistocene.[6] Analysis of plant material embedded within teeth from the Neumark-Nord locality in Germany found remains of Populus, Quercus, Crataegus, Pyracantha, Urtica and Nymphaea as well as indeterminate remains of Betulaceae, Rosaceae, and Poaceae.[15] Preserved plant remains found with the teeth on the arctic Chonon skull included twigs of willow, birch and abundant larch alongside fragments of heather; sedges were notably absent.[7]

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  Partial skull in Stuttgart
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  300,000 year old dentary fragment from the United Kingdom in the NHM, London
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  Remains of Merck's rhinoceros from Germany
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  View of the top of the snout of a S. kirchbergensis skull, showing the rugose texture of the horn attachment area