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| Dr Alistair Evans (monash.edu.au) |
How fast a fauna evolved into a certain size, adaptability to radiation, the recovery from extinction becomes very important. From the research results are known, it takes 1.6, 5.1, and 10 million generations for terrestrial mammals to increase its mass to 100, 1000, 5000 fold. However, Values for whales were down to half the length (i.e., 1.1, 3, and 5 million generations), perhaps due to the reduced mechanical constraints of living in an aquatic environment.
This reasearch was led by Dr Alistair Evans of Monash University's School of Biological Sciences a team of 20 biologists and palaeontologists.
Dr Evans, an evolutionary biologist and Australian Research Fellow, said the study was unique because most previous work had focused on microevolution, the small changes that occur within a species.
“Instead we concentrated on large-scale changes in body size. We can now show that it took at least 24 million generations to make the proverbial mouse-to-elephant size change – a massive change, but also a very long time,” Dr Evans said.
"A less dramatic change, such as rabbit-sized to elephant-sized, takes 10 million generations."
Research led by Dr. Evan has taken samples of 28 different groups of mammals. Among others, elephants, whales, primates, from various continents and ocean basins over the last 70 years. Changes in the size of these mammals are tracked based on the generation, rather than by year. Thus expected to be generated comparisons more meaningful between species that live in different times.
Dr Erich Fitzgerald, Senior Curator of Vertebrate Palaeontology at Museum Victoria and a co-author, said changes in whale size occurred at twice the rate of land mammals.
“This is probably because it’s easier to be big in the water – it helps support your weight,” Dr Fitzgerald said.
Dr Evans said he was surprised to find that decreases in body size occurred more than ten times faster than the increases.
“The huge difference in rates for getting smaller and getting bigger is really astounding – we certainly never expected it could happen so fast!” Dr Evans said.
Many miniature animals, such as the pygmy mammoth, dwarf hippo and ‘hobbit’ hominids lived on islands, helping to explain the size reduction.
“When you do get smaller, you need less food and can reproduce faster, which are real advantages on small islands,” Dr Evans said.
The research furthers understanding of conditions that allow certain mammals to thrive and grow bigger and circumstances that slow the pace of increase and potentially contribute to extinction.
This article has edited by authors
Source: http://www.monash.edu.au/news/show/mouse-to-elephant-just-wait-24-million-generations
Publication: http://www.pnas.org/content/early/2012/01/26/1120774109.abstract
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