The earliest proboscideans, the elephants and their relatives, first
appeared in the late Eocene of Africa and were about the size of a small
modern elephant but had larger heads and shorter trunks. Proboscidean
development is marked by an increase in size, change in skull and tooth
structure, and elongation of the trunk. Two well-known fossil
proboscideans are the _mammoth_ and the _mastodon_, both of which
inhabited Texas during Pleistocene time. The mastodons resembled the
elephants, but the structure of their teeth was quite different (fig.
25). Moreover, the mastodon skull was lower than that of the elephant
and the tusks were exceptionally large—some reaching a length of 9 feet.
[Illustration: Plate 47
CENOZOIC MAMMALS]
DINOBASTIS × ¹/₂₀
CANIS DIRUS × ¹/₁₅
HYRACOTHERIUM × ¹/₁₀
PLIOHIPPUS × ¹/₂₀
There were several types of mammoths, and the _woolly mammoth_ is
probably the best known. This animal lived until the end of the
Pleistocene and, like the woolly rhinoceros discussed below, is known
from ancient cave paintings and frozen remains. Information gathered
from these sources indicates that this great beast had a long coat of
black hair with a woolly undercoat (Pl. 49).
[Illustration: Fig. 25. Sketches of Pleistocene (a) mastodon tooth (×⅙)
and (b) mammoth tooth (×⅙).]
During the Pleistocene, mammoths were widespread over the United States,
and their remains are abundant in many stream deposits of this age.
Proboscidean bones have been reported from Pleistocene rocks in many
parts of Texas, where they are commonly found in sand and gravel pits.