326 Evolution? The Fossils Say YES!
Protorohippus, while others are assigned to a variety of genera, including previously pro-
posed names such as Xenicohippus, Systemodon, and Pliolophus, as well as new genera such as
Sifrhippus, Minippus, and Arenahippus. The old days when all early Eocene horses could be
lumped into one genus (whether Eohippus or Hyracotherium) are long gone!
From these early Eocene horses, there is a general size increase through Eocene forms
like Orohippus and Epihippus, culminating in the German shepherd–sized horse Mesohippus
and Miohippus from the late Eocene and Oligocene (Prothero and Shubin 1989). These horses
had three robust toes on their hands and feet, slightly higher-crowned teeth, and many other
more horselike features of the snout and skull. By the early Miocene, horses began an explo-
sive radiation (fig. 14.3) into multiple lineages. Some of these Miocene horses retained low-
crowned teeth for leaf eating (the anchitherines), but most evolved higher-crowned teeth for
eating gritty grasses and also developed longer legs and toes (with reduced side toes) to run
fast across the grasslands. Finally, most of these diverse horse lineages went extinct in the
late Miocene, leaving only the lineage leading to the modern genus Equus to flourish in the
Pliocene and Pleistocene.
The biggest difference between the old pattern of horse evolution (fig. 14.2) and our
modern one (fig. 14.3) is its bushiness. Back in the late 1800s and early 1900s, there were
only a few horse fossils known at each level, and it was easy to imagine one continuous
lineage evolving through time in a “ladder-like” fashion. But tens of thousands of addi-
tional horse fossils have been collected since the 1920s. Just as we have seen in every other
instance, horse evolution is a bushy, branching pattern, with multiple lineages coexisting
at the same time (fig. 14.3). Gingerich (1980, 1989) and Froehlich (2002) document multiple
species of horses coexisting in the early Eocene. Prothero and Shubin (1989) found that
three different species of Mesohippus and two of Miohippus coexisted in some upper Eocene
beds in Wyoming. Some Miocene quarries in Nebraska, such as Railroad Quarry A in the
Valentine Formation of north-central Nebraska, yield as many as 12 different contemporary
species of horses. Even today, the genus Equus is very speciose, with not only domesticated
horses and their ancestral stock, Przewalski’s horse, but three species of zebras, and several
more species of wild asses and onagers. Thus the general trend of the classic diagram shown
in figure 14.2 is factually correct, but a gross oversimplification that does not capture the
bushy pattern that we now recognize.
Naturally, this example has been presented so often that creationists feel obligated to
attack and distort it and defuse its powerful impact. Their lies about the horse evolution
story never actually involve looking at real specimens or doing their own research. They are
just quotations out of context that distort what the author is really saying or quotations from
really old sources that are no longer describing the current state of our knowledge. For exam-
ple, Gish (1995:189–197) devoted nine pages to the topic, all of which are highly misleading
and dishonest. His most common tactic is quotes out of context that have authors pointing
out that the old simplistic linear horse evolution story (fig. 14.2) is no longer valid—without
giving the rest of the quote in which the author points out that the fossil record is now much
better, and the horse phylogeny is very bushy! In other cases, he quotes authors as saying that
we have few gradual transitions between species—but as we showed in chapter 4, under the
model of punctuated equilibrium, we don’t expect gradualism in horses. Nevertheless, by
looking at the features of each successive species, we can see the evolutionary trends in the
group just fine. Remember, just because they don’t show gradual continuous change doesn’t
mean that they show no evolution! In fact, some paleontologists argue that they can show