Three methods dating fossils

I apologize in advance for the length; I didn't want to cut it down any more than this, because horse evolution has been oversimplified too many times already.

I wanted people to see some of the detail and complexity of the fossil record of a fairly well known vertebrate group.

(See the horse tree for a lovely ASCII depiction.) Small preface: All equids (members of the family Equidae) are perissodactyls -- members of the order of hoofed animals that bear their weight on the central 3rd toe.

(Other perissodactyls are tapirs and rhinos, and possibly hyraxes.) The most modern equids (descendents of Parahippus) are called "equines".

Strictly speaking, only the very modern genus Equus contains "horses", but I will call all equids "horses" rather indiscriminately.

Most horse species, including all the ancestors of Equus, arose in North America.

Hyracotherium is shown giving rise to three lineages. The tree itself is unreadable to those who are visually impaired so skip the tree graphic.

2My Old & New World Equus \ | / \ | / 4My Hippidion Equus Stylohipparion | | Neohipparion Hipparion Cormohipparion | | Astrohippus | | | | | Pliohippus --------------------------- 12My Dinohippus Calippus \ | / | | Pseudhipparion \ | / | | | | ------------------------------------------- Sinohippus 15My \ | / | \ | / Megahippus | 17My Merychippus | | | Anchitherium Hypohippus | | | 23My Parahippus Anchitherium Archeohippus | | | (Kalobatippus?

Here, one could see the fossil species "Eohippus" transformed into an almost totally different-looking (and very familiar) descendent, Equus, through a series of clear intermediates.

his is a companion file for the Transitional Fossils FAQ and is part of the Fossil Horses FAQs.

In this post I will try to describe the modern view of evolution within the horse family.

As new fossils were discovered, though, it became clear that the old model of horse evolution was a serious oversimplification.

The ancestors of the modern horse Overall, the horse family demonstrates the diversity of evolutionary mechanisms, and it would be misleading -- and would be a real pity -- to reduce it to an oversimplified straight-line diagram.

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