Gto

Quick Lab

Comparing Gestation Periods

Materials paper, pencil Procedure

1. Make a table of gestation periods for different mammals. Make three columns labeled "Mammal," "Gestation period," and "Offspring per pregnancy."

2. Fill in your table with the following data:

Bat, 210 days, 1 offspring Gerbil, 19-21 days, 4-7 offspring Horse, 332-342 days, 1 offspring Monkey, 226-232 days, 1 offspring Rabbit, 31 days, 3-6 offspring Squirrel, 44 days, 3 offspring Whale, 420-430 days, 1 offspring Wolf, 63 days, 4-5 offspring Analysis Make a graph that relates gestation length and the number of offspring per pregnancy. Then, propose a hypothesis to explain this relationship.

TABLE 43-1 Minor Orders of Mammals

Order

Description

Examples

Macroscelidea

ground-dwelling insectivores with long, flexible snouts; 15 species found only in Africa

elephant shrews (not true shrews)

Pholidota

insectivores with protective scales composed of fused hair; resemble reptiles; found in Africa and southern Asia

pangolins or scaly anteaters (not true anteaters)

Tubulidentata

nearly hairless insectivores with piglike bodies and long snouts; found in southern Africa

aardvarks

Scandentia

squirrel-like omnivores that live on ground and in trees; feed on fruit and small animals; found in tropical Asia

tree shrews (not true shrews)

Dermoptera

only two species exist; glide in air using a thin membrane stretched between their limbs; found only in parts of Asia

colugos or flying lemurs (not true lemurs)

Hyracoidea

small rabbitlike herbivores; 7 species found mostly in Africa

hyrax

Order Proboscidea

Members of the order Proboscidea (PROH-buh-SID-ee-uh) have a nose that is modified into a long, boneless trunk, or proboscis. The only living species of this order are the Asian elephant and the African elephant, which is the largest living land mammal. Mammoths and mastodons are extinct members of this order. The African elephant can reach 6,000 kg (13,200 lb). To sustain such a large body, an elephant feeds on plants for up to 18 hours a day. The trunk allows an elephant to gather water or gather leaves from high branches. Modified incisors, called tusks, efficiently dig up roots and strip bark from branches. Large, jagged molars at the back of the jaw can grow up to 30 cm (1 ft) long and grind plant material.

Elephants have long gestation periods. A calf takes 20 to 22 months to develop. Female elephants can continue to give birth until the age of 70, and elephants can live to be 80 years old.

Other Orders of Placental Mammals

The 12 orders just described include most of the familiar placental mammals. The 6 remaining orders contain just 1 percent of the mammalian species and are summarized in Table 43-1.

Pregnancy And Childbirth

Pregnancy And Childbirth

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