Hundsheim Rhinoceros-Stephanorhinus hundsheimensis

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Hundsheim Rhinoceros-Stephanorhinus hundsheimensis


Oil painting of S. hundsheimensis; C. C. Flerov, Sammlungen Senckenberg Weimar

Temporal range: Early to middle Pleistocene (Calabrian to Ionian; 1.4-0.6Ma[1])

Scientific classification:

Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Superphylum: Deuterostomia
Phylum: Chordata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Suborder: Cynodontia
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Subcohort: Exafroplacentalia
Magnorder: Boreoeutheria
Superorder: Laurasiatheria
Clade: Ungulata
Order: Perissodactyla
Suborder: Ceratomorpha
Superfamily: Rhinocerotoidea
Family: Rhinocerotidae
Genus: †Stephanorhinus
Species: †S. hundsheimensis

The Hundsheim rhinoceros is an species of extinct rhinoceros within the genus Stephanorhinus. It lived in the western Palaearctic from ~1.4-0.6 million years ago.[1]

Description:
All members of the genus Stephanorhinus were dolicocephalic, two horned animals with molariform premolars and absent incisors. A relatively large sized male specimen of S. hundsheimensis appears to have been about 130 centimeters tall at the shoulder.[1]

Diet:
Analysis of the dentition shows that the Hundsheim rhinoceros' diet varied between predominant grazing and browsing among different regions. This suggests that it was an ecologically tolerant mixed feeder. The dietary flexibility of S. hundsheimensis may be why it was such a common faunal element of the Pleistocene Palaearctic.[1]

Extinction:
The same dietary flexibility that made this rhinoceros species so successful is (ironically) thought to have caused its extinction. Around 600,000 years ago, two other species of Stephanorhinus, S. kirchbergensis (forest rhinoceros) and S. hemitoechus (steppe rhinoceros), arrived in the habitat of the Hundsheim rhinoceros. When the elephantid Palaeoloxodon antiquus appeared in Europe and occupied a specialized browsing niche in the same habitat as S. kirchbergensis, it migrated into the western Palaearctic. This is because the forest rhino, with its moderately hypsodont teeth, long legs, and high head posture, was also a specialized browser. While it browsed on a different height than the straight-tusked elephant, it browsed on the same level as the Hundsheim rhino, making it a formidable, and more specialized (read: more effective) competitor of the browsing niche in forested areas. This may not have been such a big problem had it not been for the fact that S. hemitoechus also arrived in the western Palaearctic. The steppe rhino, with its low-slung cranium, relatively short limbs, and hypsodont dentition, was a specialized grazer, more specialized for grazing than the generalist Hundsheim rhino. It would thus have been a formidable and more effective competitor for graze. The presence of two competitors better adapted for either grazing or browsing left the Hundsheim rhino nowhere else to "fall back on" in terms of ecological niches. As a result, Stephanorhinus hundsheimensis went extinct.[1]

References:

[1] Kahlke, R-D.; Kaiser, T.M. Generalism as a subsistence strategy: advantages and limitations of the highly flexible feeding traits of Pleistocene Stephanorhinus hundsheimensis (Rhinocerotidae, Mammalia). Quaternary Science Reviews. doi: 10.1016/j.quascirev.2009.12.012

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Some notes on this animal's morphology and inferred ethology.

S. etruscus and S. hundsheimensis were brachyodont species, with typically low crowned teeth. S. etruscus was smaller than S. hundsheimensis; both were cursorially built.

The subvertically arranged occiput and the supraoccipital crests more extended laterally than in other rhinoceroses, suggests that S. etruscus and S. hundsheimensis bore their heads and their necks quite high above the ground and that the lateral and rotational movements of the head were favoured against the vertical ones. Asian rhinoceroses, even grazers as R. unicornis, bear their heads high above the ground, but this is due to the fact that they live in environments with dense and tall vegetation. The environments which S. etruscus and S. hundsheimensis are supposed to have inhabited seem to have been more open, judging by their skeletal characteristics and by the faunal contexts in which their remains are commonly found. The structure of the occipital regions of S. etruscus and S. hundsheimensis suggests that they were poorly aggressive rhinoceroses, or that they developed a high ritualisation of their contentions, maybe with extensive horn-wiping, since fights impose ample vertical movements of the head.

Whatever the case, the widening and elongation of the narial notch extends the areas for the insertion of the upper lip muscles. When this is accompained [sic] by well developed preorbital pits and by nasals with sharp, rough edges, there is a sound possibility that the animal had a strong, prehensile upper lip. This is exactly the condition shown by S. etruscus and S. hundsheimensis. Elasmotherium was apparently equipped with a even more developed, strong and prehensile upper lip. On the other hand, S. hemitoechus and C. antiquitatis may have had a relatively weak, semi-prehensile upper tip, like those of the Indian rhinoceroses, while S. kirchbergensis may have been a <<square-lipped>> rhinoceros as Ceratotherium.

In a previous paper (1988), the writer observed that, judging by its limb bones, S. etruscus probably was a relatively swift moving animal, and that its slender, delicate nasal bones probably would have not supported a full-speed impact, although rhinoceros horns are rather elastically implanted on the skull and in these forms the nasals were strengthened by the ossification of the septum. The writer also excluded that horns could be used for sexual display, but rather for feeding. It is likely that these Pleistocene species used their horns to perform more than a single function. The black rhinoceros uses its horns for fights, either ritualised or effective, but also for breaking the branches or twigs on which it feeds. The high position of the orbits in S. etruscus and S. hundsheimensis suggests that among these species male confrontations may have been more ritualised than in present day black rhinoceroses. During ritualised fights, contenders evaluate each other's body mass, strength and horn development; white rhinoceroses sweep the ground with their front horn to display their weapons and to simulate an attack. Hornwiping was probably adopted also by S. etruscus and S. hundsheimensis, as part of fight ritualisation and/or as a habit connected with feeding.

We can gather a few things from all of this.

1.) S. hundsheimensis was relatively cursorial (or rather, subcursorial) species, given its slender legs. This is in contrast with S. kirchbirgensis, S. hemitoechus, Coelodonta antiquitatis, and Ceratotherium simum, which are characterized as graviportal (rhinocerotids in general may be characterized as mediportal animals overall, given that their limbs are built primarily for weight bearing with some adaptations for relatively fast locomotion).

2.) The morphology of this rhino's occipital region suggests that it held its head and neck high up above the ground. Even the orbits were relatively high up on the skull, which would allow it to watch over fairly wide and open territories.

3.) The occipital region shape also suggests that this rhino emphasized lateral and rotational movements of the head over vertical ones. Since using the horn for actual combat would necessitate strong vertical movements of the head to push, shove, and gore opponents, we can expect this rhino to have been either less aggressive than modern African rhinos or having a highly ritualistic behavior involving horn wiping on the ground. In short, fights and use of the horn were less violent and more ritualistic (compare this with S. hemitoechus, which has a skull sharing many similarities with those of white rhinos and a morphology suggesting effective fights).

4.) The skull anatomy suggests a strong, prehensile upper lip.

Reference: Mazza, P., & Azzaroli, A. (1993). Ethological inferences on Pleistocene rhinoceroses of Europe->