Tuesday, December 15, 2009

Phylogenetics: A Horse of a Different Color

New research on horse DNA suggests that the number of horse species in the fossil record has been overestimated. The report, in Science Daily has this to say:
Lead author of the paper, Dr Ludovic Orlando from the University of Lyon, says the group discovered a new species of the distinct, small hippidion horse in South America.

"Previous fossil records suggested this group was part of an ancient lineage from North America but the DNA showed these unusual forms were part of the modern radiation of equid species," Dr Orlando says.

A new species of ass was also detected on the Russian Plains and appears to be related to European fossils dating back more than 1.5 million years. Carbon dates on the bones reveal that this species was alive as recently as 50,000 years ago.

"Overall, the new genetic results suggest that we have under-estimated how much a single species can vary over time and space, and mistakenly assumed more diversity among extinct species of megafauna," Professor Cooper says.

"This has important implications for our understanding of human evolution, where a large number of species are currently recognised from a relatively fragmentary fossil record.
The thorns in the side of phylogenetic analysis have always been intraspecies variation and the overall incompleteness of the fossil record. How do you know that the fossil sample that you have of any given species is representative of the entire range of variation for that species?

This does not have implications for evolutionary trajectories as much as it does for evolutionary taxonomy. Maybe Tiktaalik roseae had considerably more variation in traits than we know based on the sample that we have. But we do know that some of the individuals of the species had traits that link them to later tetrapods as well as some traits that link them to late fish.

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