Abstract
This paper discusses that, for many years, paleontologists held that the evolution of horses, as evident in the fossil record, was anagenetic, or progressing in a virtually straight, single line of evolution; but more recently paleontologists have found evidence supporting a cladogenetic evolutionary pattern in the Miocene, which created a multiplicity of horse species or "branches" on the evolutionary trunk. The author points out that, as the fossil record yields more and more of its "secrets" to paleontologists through new investigative technologies, the established theories require revision.

Table of Contents
Abstract
Introduction
Discussion
Anagenesis and Cladogenesis
The Emergence of Speciated Branching
Summary and Conclusions

From the Paper
"The fossil record of horses (family Equidae) over the past 55 million years is a classic example of macroevolution. North America is the ancestral home of horses and many fossil sites across the continent have been identified as containing abundant remains of ancient members of the family. ... states that any given fossil locality in North America from about 50-55 to 20-25 million years ago, it is usually possible to find 2-4 species of horses that seem to have lived side-by-side. However, from about 20-10 million years ago, the fossil record suggests that horses evolved rapidly, adapting to various environments and ways of life."

Tags:fossil, branch, species, anagenetic, theories

Abstract
Describes the evolutionary development of horses. Evidence obtained from fossil records that supports the anagenetic view of horse phylogeny as well as cladogenetic pattern. Fossil record as a clasic example of macroevolution. Branching speciation. Support of the view that a gradual microevolutionary process occurred within the species. Focuses on the North American Eocene and Oligocene fossil records.

From the Paper
"A Cladogenetic View of the Early Evolutionary History of Horses

Abstract
Drawing upon the theoretical and empirical literature, this report describes the evidence obtained from the fossil record that supports the anagenetic view of the horse phylogeny and its early evolutionary development. The anagenetic perspective advances the notion that a gradual microevolutionary process has occurred within a species. It is also associated with phyletic transformation from ancestral to descendant species. The fossil record for horses presents, in general, a progressive replacement of one genus with another without a strong indication of temporary overlapping. However, the literature also suggests that anagenetic development was dominant within the Eocene and Oligocene, while genetic diversity (branching) suggesting a ..."