Homo sapiens Neanderthals and other younger human relatives may have begun to "scale down" large mammal species 90,000 years earlier than previously thought.
Elephant Dwarves Wooly Mammoths, Elephants Large sloths and various saber-toothed cats were some of the giant mammals that roamed Earth 2.6 million to 12,000 years ago. Previous research suggested that such large mammals in Australia began to disappear faster than their smaller counterparts about 35,000 years ago, a phenomenon known as size-related extinction.
Using new data from older fossil and geological records, it estimates that this extinction of size began in Africa at least 125,000 years ago. At this time, the average African mammal was already 50 percent smaller than that on other continents, the study reports, despite the fact that larger land masses can typically support larger mammals.
But as humans emigrated from Africa, other orders of magnitude extinction began in regions and on timelines consistent with known human migration patterns, the researchers found. Over time, the average size of mammals approached these other continents and then dropped far below those of Africa. Mammals that survived during the span were generally much smaller than those that died out.
The size and extent of the recent extinction of size has outperformed any other during the last 66 million years, according to the study led by the University of New Mexico's Felisa Smith.
"It was not until human influences became a factor that caused large body sizes to make mammals more susceptible to extinction," says Kate Lyons of the University of Nebraska-Lincoln
"The anthropological record indicates that Homo sapiens was identified as a species about 200,000 years ago, so that this did not happen very long after the birth of us as a species.
"From a life-philosophical point of view, it makes sense. If you kill a rabbit, you will feed your family for one night. If you can kill a large mammal, you will feed your village. "
In contrast, the research team found little support for the idea that climate change has led to widespread extinctions in the last 66 million years, with large and small mammals also vulnerable to temperature changes during this period, the authors report. [1
What would happen if the mammals now considered endangered or endangered die out within the next 200 years?
In this scenario, Lyons says, the largest remaining mammal would be the domestic cow, with an average body mass of less than six Pounds go down – about the size of a Yorkshire Terr
"If this trend continues and all currently threatened (mammals) are lost, the flow of energy and taxonomic composition will be completely restructured," says Smith, a professor of biology in New Mexico. "In fact, the size of mammals around the world will return to what the world looked like 40 million years ago."
Lyons says the restructuring could have "profound implications" on the world's ecosystems. Large mammals are usually herbivores that devour large amounts of vegetation and effectively transport the nutrients around an ecosystem. If they went further, the remaining mammals would play a bad role in important ecological roles.
"The types of ecosystem services provided by large mammals are very different from those obtained from small mammals." Lyon says. "Ecosystems will be very, very different in the future, the last time mammal communities looked and had a medium body size that was small after the extinction of the dinosaurs.
Has a limping mammoth mother left these tracks?"
"What we may be 40 to clear 45 million years of mammalian body size development in a very short span of time.
Coauthors of the study, which appears in Science come from Stanford University and UC San Diego. The team received support from the National Science Foundation.
Source: University of Nebraska-Lincoln