Mammoth evolution as a model for species origins
Museum researchers are using fossil mammoth molars to study how animals adapted to a tropical climate evolved into the woolly mammoth of the late ice age.
Fossils from the Quaternary ice ages provide excellent opportunities for tracing the origin of new species through time.
The fossil record of this period:
- covers a relatively short period of geological time (roughly the last two million years of Earth history)
- contains very well-preserved fossils that can be accurately dated
- allows us to trace changes in the form of particular lineages and species through time and in relation to changing environments
In other words, we can use it to observe evolution in action. The lineage leading to the woolly mammoth provides one of the best examples of this.
The woolly mammoth model
The mammoth's ancestors arose in Africa, and were tropically-adapted browsing animals closely related to the living elephants.
Around 3 million years ago, they spread into the northern hemisphere and began a process of transformation leading to the highly-specialised woolly mammoth of the late ice age, adapted to cold, treeless environments and a diet of grass.
We have traced this process of transformation in most detail using fossilised molar teeth.
By measuring samples of fossil mammoth molars from dozens of localities across Europe, northern Asia and North America, we have been able to chart an increasing adaptation to a tougher diet.
Molars showed an increase in:
- crown height
- number of enamel grinding ridges
By comparing fossils between different regions and time intervals, we have also shown that the process of change involved at least 2 transitions involving the origin of new species.
In particular, it appears that the first major step in the origin of the woolly mammoth occurred in China as much as 2 million years ago, while the final changes took place in north-east Siberia about a million years later.
In both cases it is plausible that the changes were driven by known changes in climate and vegetation.
It has become clear that the process by which species originate involves a complex pattern of individual populations evolving, migrating, interbreeding with each other, and in some cases dying out. The net process over time is one of changing morphology.
We are collaborating with colleagues in Germany, Sweden, the US and the UK to investigate the evolution of the woolly mammoth using ancient DNA. This technique is used extensively to study mammoths.
We have mapped the reduction in genetic diversity that led up to the mammoth's extinction, which may have contributed to its ultimate demise. We have also shown how one genetic group, originating in North America, spread over a period of 40,000 years of the last ice age to replace populations in Siberia and ultimately Europe.
With our collaborators we are currently investigating the possible role of hybridisation in the origin of Late Pleistocene mammoth populations, and the origin and spread of genes adaptive to the ice age environment.
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