Evolution What the Fossils Say and Why it Matters

Bossies and Blowholes 333

were widespread in North America and Eurasia through most of the past 50 million years,
although their teeth are adapted for chopping leaves, so they have always been restricted
to the more forested regions. Tapirs, too, have an impressive fossil record of their evolution
(fig. 14.8). The early more primitive forms like Homogalax mentioned earlier (fig. 14.5) can
barely be distinguished from the earliest horses and rhinos. The only clue is that the cross
crests on their molars are slightly more developed (foreshadowing the strong crests on later
tapir teeth), but otherwise their skulls and skeletons look almost identical to the earliest
rhinos and horses. However, through the rest of the Eocene they become more and more
specialized, and more and more like living tapirs. Even by the middle Eocene, their teeth

FIGURE 14.8. Evolution of the tapirs from primitive forms with skulls much like Eocene horses and rhinoceroses,
through progressively more specialized forms that have a deeper retraction of the nasal notch, indicating a
larger proboscis. (Modified from Prothero and Schoch 2002)

Tapirus terrestris Tapirus indicus

Tapirus (Megatapirus)

Miotapirus

“Protapirus”

Lophiodon

Homogalax

Colodon

Isectolophus Lophialetes

Heptodon

Helaletes

LO

HIO

DO

NT

IDA

E

ISECTO-LOPHIDAE

HELA-LETIDAE

LO

PH

IA-

LET

IDA

E D

EPE

RE

TE

L-

LID

AE

RHINOCERO

TOIDEA

EQUOIDEA

TAP

IRID

AE

?

Quaternary

Miocene-Pliocene

Oli

gocene

Eocene

Paleocene

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