[Michael_Michaelangelo]

Howdy! I was wondering if you could comment as to what came before Hyracotherium? I have been doing some reading and have yet to find anything that fills the 'gap'. Also, how was the connection between Hyracotherium and Mesohippus derived? The fact that one was found in earlier strata and they looked similar?

[VadeRetro]

Howdy! I was wondering if you could comment as to what came before Hyracotherium? I have been doing some reading and have yet to find anything that fills the 'gap'.

Hyracotherium is barely more specialized than a small, late condylarth. Condylarths are the likely ancestors of the even-and-odd toed ungulates and perhaps a few other groups, I forget.

[VadeRetro]

Also, how was the connection between Hyracotherium and Mesohippus derived? The fact that one was found in earlier strata and they looked similar?

Modernman's 101 gives a nice summary of the overall history with this site. From the fossil you get a picture of a tree of a tree structure with extinctions and new branchings. Again, the earliest horses aren't very horselike and are very little specialized or "derived" from the ancestral condylarth line. Later species are increasingly specialized and on some branches are more like modern horses. Common descent is not a great leap of inference, here.