Species extinction is a fundamental part of evolution: the best adapted species survive, while others die out. A new study examines why certain species can suddenly disappear, despite hundreds of thousands of years of successful survival.
Ice Age expert Prof. Ralf-Dietrich Kahlke from the Senckenberg Research Institute, Research Station of Quaternary Palaeontology Weimar, and paleoecologist Dr. Thomas M. Kaiser from the University of Hamburg, Biocentre Grindel now present a study in the journal Quaternary Science Reviews that shows why, after 800,000 years of successful survival, a species of rhinoceros known as the Hundsheim rhino (Stephanorhinus hundsheimensis) suddenly disappeared.
Like roe deer and red deer, rhinos were amongst the characteristic animals to inhabit Eurasia during the Ice Age. They were found across wide areas. Over the past 2.6 million years Europe has been inhabited by no less than six different types of highly varied species of rhinos with vastly differing ecological requirements. There were animals that were at home on the cold steppes of the northern and mid latitudes, whilst there were also species that preferred moderate and even warm climatic conditions. Occasionally multiple species of rhinoceros appeared at the same time. Did this coexistence have consequences for any of the species?
The research was based on 740 fossilized dental and bone remains, which originate from roughly 700,000-year-old clay in Voigtstedt and gravel deposits from Süssenborn in Thuringia, which are a few millennia younger. Both dig sites reveal evidence of the Hundsheim rhinoceros, which takes its name from an Austrian fossil site. With around 4000 preparations of Ice Age rhino remains, the Senckenberg research station in Weimar possesses the most comprehensive inventory of the extinct pachyderms in Europe.
On the basis of detailed examinations of the dental wear by means of mesowear analysis, it was possible to reconstruct the diet of the two rhino groups. The favored foods left traces on the teeth: The tooth relief changes itself in a characteristic manner, thus enabling conclusions to be drawn on what the animal ate. Whilst the Voigtstedt rhinoceros predominantly fed on soft foliage from vast forests, the tooth reliefs from the animals from Süssenborn revealed evidence of a harsh steppes diet almost entirely comprising grasses. Such greatly differing diet demonstrates an extremely broad ecological tolerance on the part of the Hundsheim rhino. Indeed, to date it has not been possible to identify any other extinct or living animal species with a similarly broad ranging diet of vegetation. These Ice Age rhinos were in fact true survivors, who dominated the environs of the steppes as well as those of the forests for almost one million years.
Their end came as new species of rhino developed -- most likely in Asia -- with an entirely different survival strategy. Around 600,000 to 500,000 years ago -- during extended cold and hot periods, respectively -- two highly specialized types came into being that were far more capable of processing the steppe and forest food than the previously unrivalled Hundsheim rhino. Now competition had moved into all areas of its living space; the steppes and the forests. Stephanorhinus kirchbergensis, also known as the Merck's rhinoceros, began to displace the Hundsheim rhino in forest habitats. Its anatomical characteristics show that this species was better adapted to forest habitats than the established species. At the same time, another competitor threatened the realms of the Hundsheim rhino on the open plains: Stephanorhinus hemitoechus, the steppe rhino. Remains of this species show that the animal was well-adapted to surviving on the food found on the steppes.
The flexible lifestyle of the Hundsheim rhino allowed thousands of generations of this animal to survive. Within just a few thousand years -- a brief period in the world's history -- the species had become entirely extinct. Stephanorhinus hundsheimensis died out without any effective changes in the environment and entirely without the influence of early man. It was superseded by better evolved species of rhinoceros. This process can be verified by paleontological finds.
"The fact that species die out is something entirely natural," states Professor Kahlke, "although this does not give carte blanche with respect to the environmental sins of modern industry, which have caused and continue to cause the mass extinction of species such as we have never seen before."
The above story is based on materials provided by Senckenberg Research Institute and Natural History Museum. Note: Materials may be edited for content and length.
- Ralf-Dietrich Kahlke, Thomas M. Kaiser. Generalism as a subsistence strategy: advantages and limitations of the highly flexible feeding traits of Pleistocene Stephanorhinus hundsheimensis (Rhinocerotidae, Mammalia). Quaternary Science Reviews, 2010; DOI: 10.1016/j.quascirev.2009.12.012
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