Scientists believe that numerous species of mammoth roamed across the North American continent many years ago. Now, a new study sheds even more light on these unique creatures, providing DNA evidence that they liked participated in interbreeding.
A species is a group of similar animals that has the ability to breed with each other and create healthy, fertile offspring. Although numerous North American mammoth species - who should only mate within their species boundaries - have been identified through fossilized teeth, researchers believe that there might be another story behind these fossils.
"Species boundaries can be very blurry," said Hendrik Poinar, a professor at McMaster University and co-lead author of the study. "We might find differences in features of the teeth or skeleton that closely correspond to what we think are real species boundaries. But other features may not correspond to those boundaries, suggesting that what we formerly regarded as separate species are in fact not at all."
Poinar and his team examined tiny fossils of mammoth bone, teeth and feces and extracted DNA from the samples to create a family tree of their evolution.
The results showed that although some North American mammoths, such as the Columbian and Woolly Mammoths, are believed to originate from two separate species, they might have actually originated from the same species - the Steppe Mammoth.
"Individuals of the Woolly and Columbian mammoths look like they represent different species in terms of their molar teeth, but their genetics say that they were not completely separate in the evolutionary sense and could successfully interbreed," said Ross MacPhee, a professor at the American Museum of Natural History and co-lead author of the study along with Poinar.
"Mammoths were much better at adapting to new habitats than we first thought - we suspect that subgroups of mammoths evolved to deal with local conditions, but maintained genetic continuity by encountering and potentially interbreeding with each other where their two different habitats met, such as at the edge of glaciers and ice sheets," Poinar added.
The DNA results suggest that although mammoths evolved differences in their phenotype in order to adapt to various environments, they still participated in cross-breeding that produced healthy offspring. Despite this adaptability, it could not prevent their extinction from the Earth 10,000 years ago.
"Humans are suspected to be the cause, but this is not by any means proven," MacPhee said. "Explaining the loss of mammoths and a host of other Ice Age creatures continues to be a fascinating conundrum in paleobiology,"
The findings were published in the April 21 issue of the open-access journal Frontiers in Ecology and Evolution.
