Wednesday, October 8, 2008

The Mystery of Hyracotherium

Perhaps I reminisce too much, but when I was a child, dinosaurs and prehistoric mammals were much simpler. Take, for example, the evolution of the horse: what once seemed a straightforward line from hyracotherium to Equuus caballus has now become a complex cluster of related species from a number of eras, more resembling a jumbled cloud of LiveJournal interests than a simple family tree. While scientists have accepted the many-armed tree of equine evolution for quite a long time, it has taken time to trickle down into the popular consciousness. More recent discoveries have shifted some relatives further from the central trunk of this complex family tree, and revealed others as the ancestors of non-equine species as well as of modern horses.

We can thank computers for that. The science of paleontology has evolved in leaps and bounds over the past twenty-odd years thanks to improvements in computer technology. Paleozoologists can now access medical advancements to closely scrutinize the cellular structure of fossilized bones and take ultrasounds of skulls, which gives them a clearer picture of how prehistoric animals are related and how they might have evolved into their modern counterparts.

We know now that while hyracotherium (or Eohippus, meaning 'dawn horse') is the forerunner of modern horses, its place in the family tree is not so straightforward. This nine-inch-high herbivorous mammal also spawned the species that would eventually evolve into rhinoceroses and tapirs, which makes it a valuable link among Perissodactyla, or odd-toed hoofed mammals. Its classification has changed, as well, and it is now a member of the Paleotheriidae family rather than the horse family. Paleotheriidae includes a number of species, many of which took a divergent path from hyracotherium: the genus paleotherium, for example, is more closely related to tapirs than horses.

This demonstrates paleozoologists' expanding knowledge on prehistoric evolution and the many divergent paths that led to our modern biodiversity. The hyracotherium is most certainly the ancestor of our modern horse, but it also plays an important part in the development of a number of diverse species.