Evolution What the Fossils Say and Why it Matters

Bossies and Blowholes 325

the creationists. Shortly after Darwin’s book was published, fossil horses in Europe were
connected into an apparent evolutionary series by Thomas Henry Huxley, French paleon-
tologist Albert Gaudry, and Russian paleontologist Vladimir Kowalewsky. Then, in 1876,
Huxley made a trip to North America, where he visited the amazing collections of fossil
horses at Yale University amassed by crews working for the pioneering paleontologist
Othniel C. Marsh. Huxley soon realized that the few European fossil horses were occasional
immigrants to the Old World, not a continuous lineage that evolved in Europe, and that most
of horse evolution had taken place in North America. Marsh pulled out drawer after drawer
of specimens for Huxley, completely documenting the stages in the transition from tiny four-
and three-toed early Eocene horses up to the modern Equus. Huxley was so amazed that he
threw out his planned lecture notes and used Marsh’s specimens for his featured lecture
instead. This early research on horses continued until it culminated in the famous book on
horse evolution published by Matthew (1926), quoted in the epigraph above (fig. 14.2).
In general terms, these century-old diagrams are still valid. Horses did start as tiny
beagle-sized animals with four toes on their front feet and three on their hind feet, low-
crowned teeth for eating soft leaves, and relatively small brains and short snouts. These
early Eocene horses have long been known as Eohippus (but that name is invalid for most
of them) and Hyracotherium (but Hooker [1989] showed that Hyracotherium is a member of a
native European group known as palaeotheres, not a true horse). Froehlich (2002) analyzed
the North American fossils in detail and found that the old name Eohippus is only applicable
to one of the species, E. angustidens. Instead, many of these early Eocene horses belong to

FIGURE 14.2. The evolution of horses as it was portrayed a century ago when there were relatively few fossils.
The overall trend through time is clear: larger size, longer limbs, reduction of side toes, development of a
longer snout and larger brain, and especially the development of higher-crowned cheek teeth for eating gritty
grasses. However, a century of further collecting has shown that horse evolution is a more complicated bushy
branching tree, rather than this oversimplified linear sequence. (After Matthew 1926)

Quaternary or

Age of Man

Tertiary or

MammalsAge of

Recent

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

ReptilesAge of CretaceousJurassic

Triassic

Equus

Protohippus

Mesohippus

Protorohippus

Hyracotherium(Eohippus)

One Toe

2nd and 4th Splints of

digits

Three Toes

not touchingSide toes

the ground

Three Toes

not touchingSide toes

the ground

One Toe

2nd and 4th Splints of

digits

Three Toes

Side toestouching

the ground

Four Toes

Four Toes

Splint of1st digit Splint of5th digit

Three Toes

Three Toes

touching the Side toes

ground; splintof 5th digit

Formations in Western United States and Characteristic Types of Horse in Each Fore Foot Hind Foot Teeth

crowned,Long-

cement-covered

crowned,Short-

withoutcement

Hypothetical Ancestors with and Teeth like those of Monkeys, etc.Five Toes on Each Foot

SHERIDAN

BLANCO

LOUP FORK

JOHN DAY

WHITE RIVER

UINTA

BRIDGER

WIND RIVER

WASATCH

PUERCO AND TORREJON

http://www.ebook3000.com