Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
The phylogeny of the horse family is perhaps the most complete record of organic evolution that modern science has discovered. This article is an attempt to show briefly the outstanding steps in the development of the modern horse.
Benson, M. R.
"Evolution of the Horse,"
Iowa State University Veterinarian: Vol. 2
, Article 10.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol2/iss2/10