Crocodiles and alligators are the largest living reptiles and form the last surviving direct link with the Age of Dinosaurs. Although greatly feared, crocodilians are shy creatures and good parents.

KEY FACTS

ORIGINS OF THE CROCODILIAN S

The first true crocodilians, which

have been found in South Amer­

ican and European fossil beds,

date from just over 200 million

years ago. But crocodilelike rep­

tiles occurred 230 million years

ago. The earliest ancestors of

crocodilians are the thecodonts,

primitive reptiles from over 245

million years ago that were also

the ancestors of dinosaurs and

modern birds.

Some thecodonts had ankle

joints that allowed two different

gaits. The animal could waddle

with its belly on the ground and

its legs splayed to its sides like a

lizard, or it could adopt a "high

walk" like a mammal's, with its

belly off the ground and its legs

striding almost under its body.

Modern crocodilians have a sim­

ilar ankle structure. They waddle

short distances but use a "high

walk" for long distances.

Early crocodilians were about

three feet long, with fairly long

legs. They may have lived exclu-

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Above: Morelet's crocodile of Cen­tral America live$ in freshwater la­goons and swamps.

sively on land. But by 190 mil­

lion years ago many were living

in the sea. Some possessed long,

narrow jaws with sharp teeth for

catching fish. Their limbs began

to develop paddlelike feet, and

some had dorsal fins. About 130

million years ago these sea croc­

odiles became extinct.

When the dinosaurs died out

65 million years ago, the croco­

dilians survived. This may have

been because they lived mainly

in fresh water. Other freshwater

animals also fared better than

sea or land creatures.

Modern crocodilians are di­

vided into two main subfamilies:

crocodiles and alligators, which

together contain 21 species. A

third subfamily, the gavialines,

consists of one species, the ga­

vial. This large, slender-snouted

crocodilian lives in northern In­

dia's deep, fast-flowing rivers.

left: The Indian gavial has weak legs since it spends most of its time in the water.

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The crocodilians include 22 species of crocodile, alligator,

and gavial. The smallest are the dwarf caimans of South

America, which reach five feet in length. The largest of all

reptiles is the great estuarine crocodile, which grows to a

length of over 23 feet and a weight of more than a ton.

~ CROCODILES The 14 true crocodile species

are found mostly in tropical re­

gions. The most fearsome is the

estuarine crocodile, which lives

in brackish estuaries and coastal

regions from the Indian Ocean

to the Pacific. The only crocodil­

ian that can survive in the open

ocean, it has reached small is­

lands up to 620 miles from the

mainland. It attacks and eats hu­

mans and may kill about 1,000

people every year.

Another true crocodile is the

American crocodile, an endan­

gered species in Florida. The Cu­

ban crocodile lives exclusively in

Cuban swamps. Morelet's croc-

Front cover: The young of anAmerican alligator rest on top of their mother's head, where they are protected from danger.

Front inset left: The gavi­al catches fish by sweeping its jaws sideways. Its sharp teeth help it grasp fish.

Front inset right: The rare Cuban crocodile is found only in two swamps in Cuba.

odile, which is similar in size to

the Cuban at under 12 feet, in­

habits parts of Mexico and Cen­

tral America. Some other species

include the Philippines' Siamese

crocodile, the New Guinea croc­

odile, and the Indian subconti­

nent's mugger, which may prey

on deer and small buffalo.

Some crocodiles have narrow

snouts, feeding on fish and oth­

er small prey such as frogs and

birds. These include the African

slender-snouted crocodile from

the Congo Basin, the Australian

crocodile in northern Australia,

and the false gavial of the Malay

Peninsula and Indonesia.

Crocodilians mate in the water.

Both sexes are polygamous, tak­

ing several partners each breed­

ing season. The female builds

her nest in the two months or

so before she lays her eggs. It is

usually a mound of earth and

vegetation or a hole dug in the

ground. Warmth is vital to the

embryos' survival in the eggs, so

all crocodilians create nest con­

ditions that generate a tempera­

ture close to 86° F. They may do

this by splashing water onto rot­

ting vegetable matter to boost

the heat generation. Schneider's

Left: After about two months of incubation, the young crocodile is ready to hatch from the egg.

Left: Crocodiles and alligators differ mainly in the structure of their heads and jawbones and the position of their teeth.

dwarf caiman lays its eggs in the

base of a termite mound.

After burying her clutch of up

to 100 hard-shelled eggs, the fe­

male guards the nest from pred­

ators. After two or three months,

the baby crocodiles in the eggs

utter squeaks, telling the moth­

er that they are ready to hatch.

She digs them up, picks up the

hatchlings in her jaws, and car­

ries them to a quiet pool, where

she releases them. She also care­

fully opens any unhatched eggs.

The young may stay close to her

for several weeks.

Right: After tossing her young in the air, the female Nile crocodile carries them safely in her mouth.

~ ALLIGATORS When Spanish explorers discov-

ered crocodilians in the south­

eastern United States, they gave

the animal the name ellagarto, meaning "the lizard." This even­

tually evolved into alligator. The seven alligator species are

the Chinese alligator, American

alligator, common caiman, black

caiman, broad-snouted caiman,

Schneider's dwarf caiman, and

Cuvier's dwarf caiman . All live in

the Americas-€xcept the Chi­

nese alligator. This small species,

under six and a half feet long,

inhabits lakes and marshes near

China's lower Yangtze River.

The American alligator is the

only North American species. It

inhabits a broad, coastal plain

from the southern part of Virgin­

ia to the Rio Grande, which di­

vides Texas from Mexico. This

alligator is widespread in the

Left: Dwarf caimans are among the large numbers of caimans that are illegally caught for their skins.

Mississippi River's drainage ba­

sin. Although humans have de­

stroyed much of its habitat, its

population has grown in some

areas with the construction of

canal systems as well as water­

ing holes for cattle.

The five caiman species live in

South America's Amazon basin.

The common caiman favors riv­

ers and is often seen along their

banks. The black caiman prefers

flooded forests around lakes and

slow-moving rivers . The broad­

snouted caiman inhabits shal­

low swamplands along South

America's eastern coast, but it

is also found in the river basins

of Brazil and Argentina. Cuvier's

dwarf caiman spends most of its

time on land, favoring flooded

forests and trees flanking small

savanna streams. Schneider's

dwarf caiman prefers relatively

small streams in the rainforest,

where adults find shelter in nat­

ural dens such as hollow logs.

Insectivores are found in a variety of habitats from deserts to cold mountain streams. Most of these small mammals have mobile,

pointed snouts and small, sharp teeth for catching insects.

KEY FACTS

c: SPECIAL FEATURES OF INSECTIVORES

Fossils show that the earliest pla­

cental mammals were similar to

today's insectivores. They were

shrewlike creatures with teeth

that could crunch hard-cased

I insects. They probably foraged

at night on the forest floor or in

bushes and trees.

Most modern insectivores re­

tain primitive features. The ani­

mal usually has a flat brain case

and a long, often mobile snout.

The brain itself is fairly smooth

compared with the ridged brain

of a more advanced mammal.

I All insectivores walk on the

flats of their feet so their heels

touch the ground. Many lack

separate external openings for

the anus and genitals. Instead,

a passage called a cloaca serves

the genital and urinary systems.

To find food, insectivores use

Below: There are at least 27 species of tenrec, some of which look very much like hedgehogs.

DID YOU KNOW? • The Hottentot golden mole

excavates tunnel systems up

to 800 feet long.

• A newborn hedgehog has

skin over its spines to ease its

smell and their sensitive whis­

kers. Their ears and eyes are of­

ten less developed than in most

mammals. External earflaps are

usually small and are missing in

some burrowers. A mole or a

golden mole has a fur covering

over its eyes and can draw this

back to see. It may just distin­

guish bright and dim light.

Many insectivores' teeth are

specialized, particularly the in­

cisors. They have small canines

and primitive molars. The cusps

are arranged in a triangular pat­

tern for slicing and crushing.

birth. After fluid in the skin is ab­

sorbed into the body, the skin

contracts and the spines appear.

• The African forest shrew is 17

times heavier than the pygmy

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Left: A golden mole possesses a blunt, stream­lined body and burrows pow­erfully with its forelimbs . Inver­tebrates are its main prey.

Above: The star·nosed mole has sensitive protrusions on its nose to help it locate its prey.

Below: Young hedgehogs live to­gethe" but they become very terri­torial after their first year.

white-toothed shrew, which

weighs only one-tenth ounce.

• Hedgehogs are immune to

natural toxins like arsenic and

cantharidin in their prey.

0160200951 PACKET 95

Insectivores form a primitive mammalian order., retaining

several features of the first placental mammals. This order

includes a variety of moles, shrews, and hedgehogs. The

world's smallest mamma" the pygmy white-toothed shrew,

is an insectivore. There are also aquatic insectivores, such

as the aquatic tenrec and the giant otter shrew, which is

described in African folktales as half-fish and half-mammal.

~ HEDGEHOGS & MOONRATS Hedgehogs are found in Africa and across Europe and Asia to the northern tree line. Their fam­ily also includes Southeast Asia's and China's moonrats, which some zoologists believe to be spineless hedgehogs.

A hedgehog's spines evolved from hairs, and each is erected by its own muscles. Because of its loose skin, the animal can roll into a tight ball if threatened.

Hedgehogs have a varied diet. Their teeth can scoop up small invertebrates, impale larger prey, and slice and crush tough mate-

rial. Desert hedgehogs eat small rodents in the absence of other prey. They, as well as long-eared hedgehogs, dig short burrows.

Hedgehogs hibernate when the climate is cold and food is scarce. They can live on little or no food when dormant.

The five moonrat species in­clude the shrew hedgehog . All moonrat species have long, mo­bile snouts. The greater moon­rat and shrew hedgehog have long, thin, ratlike tails. The great­er moonrat forages in watery areas for shellfish and small fish.

European hedgehog: Prefers worms but

also eats beetles, caterpi llars, slugs,

birds' eggs, and car­rion . When food is plentiful in winter, it does not hiber­

nate , despite the cold.

Giant otter shrew: Swims underwater with a side-to­side motion, using its muscular tail as a rudde r. It search es fo r insects and cru staceans wi th its long , sensitive whiskers and keen nose.

.. GOLDEN MOLES, TENRECS, OTTER SHREWS "'IIIIIIII & SOLENODONS

Among the golden moles of sub- largest insectivores, weighing up Saharan Africa are Stuhlmann's to three pounds. The closely re-golden mole, which burrows in- lated hedgehog tenrecs have a to swamp moss in mountainous much spinier appearance. They habitats, and the giant golden resemble true hedgehogs and mole, which may be nearly nine can curl into a ball when threat-inches long. A golden mole has a ened. The rice tenrec resembles sleek, rounded body with gleam- a mole, with similar velvety fur ing fur lying toward the rump, and small eyes and ears. The unlike a true mole's velvety fur. long-tailed tenrec and the otter

Golden moles dig with their shrews of Central and West Af-shoulders, forefeet, claws, and padded noses. Desert species burrow just below the sand and may drag lizards down from the surface to eat. Golden moles eat mostly earthworms, snails, crick­ets, and other invertebrates.

Tenrecs are native to Madagas­car, although a few have been introduced onto other Indian Ocean islands. They all have fair­ly small brains and low, variable body temperatures but vary in form . The common tenrec has short, sturdy legs and a tailless body that is covered in coarse hair and spines. It is one of the

Front cover: The pygmy shrew is found in all of Europe except the Mediterranean region.

Front inset left: A solenodon sniffs out invertebrates in the humid soil of tropical forests.

Front inset right: Although a mole has poor eyesight, it has an excel­lent sense of smell.

rica have the strong tails and short muzzles of true otters.

The two solenodon species of Cuba and Hispaniola are rare, due to competition with rodents and plundering by flesh eaters introduced onto these islands. A solenodon looks a bit like the common tenrec, but its long, mobile snout overshoots its low­er jaw. In the Hispaniola species, a socket joint attaches the snout to the skull, increasing its flexi­bility. A solenodon uses its long, sharp foreclaws to dig up prey such as insect larvae. It can para­lyze a victim with its toxic saliva.

European mole: Has an especially sensitive snout and sensory whis­kers to detect prey that falls into its tunn els. Its short tai l also has sen ­sory hairs.

~ MOLES & DES MANS Burrowing moles have dense, short, velvety fur that offers no resistance to the soil and stays fairly clean. They have tiny eyes, and those of the Mediterranean mole are covered by skin . Moles are built for digging, with strong claws, paddlelike forelimbs, and powerful shoulder muscles.

The largest mole family mem-

~ SHREWS The 246 shrew species comprise the largest family of insectivores. They live everywhere except the poles, most of southern South America, Australasia, and the major African deserts.

A typical shrew is small and shy, with a pointed snout and sensory whiskers. It resembles a mouse but lacks constantly growing incisor teeth .

Because a shrew is so tiny, it loses heat rapidly and must eat several times its body weight every day. The American south-

ber is the Russian desman. The Pyrenean desman is found in mountain streams. A desman has waterproof underfur with shiny guard hairs, a long, pad­dlelike tail, and webbed hind feet. It uses its tubular snout as a snorkel. It eats insect larvae, shrimps, and snails. The Russian desman also eats fish and frogs .

west's desert shrew can release energy slowly if food is scarce.

The various American, Euro­pean, and Asian water shrews are aquatic. The Tibetan species has webbed feet, but the others have fringes of stiff hairs on their feet and tails to help them swim or rush across the water surface.

Some shrews have poisonous bites. The American short-tailed shrew kills frogs with its venom. Many shrews exude bad-tasting substances from skin glands to dL . ~r predators.

Common European shrew: Digs tun ­nels but ranges far beyond these fo r

food . This solitary, aggressive animal fiercely defends its chosen territory.

WATERFOWL .'-:=======================- GROUP 8: ANIMAL BEHAVIOR

Waterfowl include swans, geese, and ducks. Since most species spend much of their life on water, they have webbed feet and dense, waterproof plumage with thiele, insulating down underneath.

KEY FACTS ~------~--~---- --~~----------------------------~~----------------~

DIFFERENT GROUPS OF WATERFOWL

I The waterfowl family, Anatidae, contains 152 swan, goose, and duck species. Most of the seven swan species are very large, pri­marily white birds. The largest is the trumpeter swan, which weighs up to 35 pounds and has a wingspan of over six feet. The 15 true goose species are I found only within the Northern Hemisphere. Unlike swans, they have long legs set near the mid­dle of their bodies and can walk and run well.

The perching geese and ducks occur mainly in the tropics and subtropics, as do the eight spe­cies of whistling-duck. The 17 species of shelduck and sheld­goose, especially the Cape Bar­ren goose of Australia, may form a link between geese and ducks.

The six species of merganser have long, slender, hooked bills, which they use to seize fish un­derwater. The bills' toothlike ser­rations point backward to hold slippery prey.

The pochards occur mainly on fresh water worldwide. Most ob­tain food by diving and spend little time on land.

DID YOU KNOW? • The fastest-flying bird in lev­el flight is the eider duck. It has been timed by radar fly­ing at 47 miles per hour. • Some of the highest-flying birds are waterfowl. The bar­headed goose migrates across the Himalayas at altitudes of almost 30,000 feet. In 1967 a flock of about 30 whooper

The largest waterfowl group is the dabbling ducks, with 40 species. Found worldwide, they include mallards, pintails, teals, wigeons, and northern shovel­ers. A dabbling duck usually has an iridescent patch of feathers, called the speculum, on each of its wings. In the Northern Hemi­sphere, most males have bright breeding plumage, which is re­placed by a dull "eclipse" plum­age, like that of females, during

swans was spotted from an air­plane at an altitude of just over 27,000 feet. The birds used the winds of the jet stream to travel at a ground speed of about 85 miles per hour. • A few duck species are special­ly adapted for life in fast-flowing waters. The torrent duck, for example, lives in the turbulent

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Left: The mag­pie goose is in a subfamily of its own because it differs so much from other wa­terfowl. This ungainly look­ing bird has long legs with only slightly webbed, long­toed feet. The magpie goose does not molt all of its flight feathers at the same time, so it does not un­dergo a flight­less period.

the birds' flightless period after the breeding season. In contrast, Southern Hemisphere males are relatively dull all year.

Using its bill, a dabbling duck reaches into the water for plant matter and invertebrates. It does this from the surface or by up­ending its body underwater, so its tail sticks up in the air. A dab­bling duck is an impressive flier and can take off almost vertical­ly from the water or land.

streams of the Andes in South America. It has a streamlined body, sharp claws for gripping slippery rocks, and a long, stiff tail, which it uses to steer in the fast-moving water. • A swan's neck has 25 verte­brae-more than any other bird's neck and 18 more than a giraffe's neck.

0160200941 PACKET 94

Many people have seen mallards dabbling industriously

for food in a pond in the suburbs or even a city park.

Others may have caught sight of a mute swan beating its

wings slowly and majestically as it flies overhead. In the

fall and spring the honks of flocks of Canada geese are

a common sound. The familiarity of these and other

water birds reflects their mastery of both air and water.

~ORIGINS The first duck fossil is from the Oligocene period, 30 million years ago. Waterfowl may have a common ancestry with game birds, such as pheasants. But in 1979 a fossil bird called Presby­ornis was discovered with fea­tures in between those of ducks and waders. Dating back over 50 million years to the Eocene period, this fossil suggests that waterfowl may be more closely related to waders, with which they are often grouped.

Front cover: The black swan occa­sionally forms huge flocks.

Front insets: The Baikal teal (left) and Egyptian goose (right) both feed on plant matter.

~ BREEDING Many waterfowl species have dramatic courtship displays. A male duck, in particular, often shows his bright or elongated feathers to attract a mate.

Swans, geese, and most ducks nest on the ground. Some build loose platforms from vegetation, while others make scrapes.

The female usually builds the nest and incubates the eggs. She often lines the nest with warm, soft down that she plucks from her breast. If she leaves the eggs

Red-breasted merganser: Often swims with its head submerged

when searching for food . It has a saw-toothed bill for gripping fish .

The drake (male) has a long, spiky crest during the bre ~di~g season .

~ WATERFOWL &: MAN Drainage of wetlands, pollution, lead poisoning, and overhunt­ing take their toll on waterfowl.

For thousands of years, people have used waterfowl as a source of meat, eggs, or feathers. Many species are still hunted for food and sport. People still harvest eider ducks' warm, soft down feathers to stuff comforters.

to feed, she covers them with the down to keep them warm and hide them from predators. Her camouflaged plumage and habit of staying mostly on the nest help reduce the number of eggs taken by predators.

Many birds live in captivity in parks, zoos, and private collec­tions. Their wings are clipped to stop them from flying away.

Some species have long been domesticated-including the greylag goose, the ancestor of most domestic geese, and the mallard, the ancestor of most domestic ducks.

Some species lay only two or three eggs. But many, such as the mallard and shovelers, may lay more than 10 eggs, which take about four weeks to hatch.

Many waterfowl species in­crease their chances of raising young by nesting on small is­lands or other sites out of reach

~ FOOD &: FEEDING A waterfowl species' diet can of­ten be inferred from the shape of its bill. The most common bill is broad and vertically flattened, ending in a horny "nail" that is used to hook or dislodge food . Since the bird often strains food particles from water, it has lamel­lae, or toothlike ridges, along the sides of its bill's mandibles.

Waterfowl eggs are generally white or a pastel color, without the elaborate markings of many ground-nesting birds' eggs. Be­cause waterfowl eggs are usual­ly large and numerous, patterns are of little value as camouflage.

of most mammalian predatc'rs~~~tAlI!tlt~@J •• The downy young can run or

swim as soon as they dry off af­ter hatching. Their parents usu­ally lead them to the water.

~ AQUATIC ADAPTATIONS Waterfowl live on lakes, rivers, marshes, and other inland wet­lands, as well as in estuaries and coastal waters. Almost all have strongly webbed feet for swim­ming and diving. The big webs completely join the front three toes, while the hind toe is small and at a higher level.

Another aquatic adaptation is a broad, boat-shaped body with a flattened underside. The bird also possesses dense, waterproof plumage, with an underlayer of thick, warm down.

Many species have long necks to reach underwater for food. They frequently have short legs that are set back on their bodies, making them good swimmers

but giving them a slow, ungainly walk on land. In contrast, geese, shelducks, and sheldgeese have legs nearer the middle of their bodies, so they are able to stand upright and walk more easily.

Northern shov­eler: Draws water through the front of its bill. As it pumps water out of the side, it sifts out food.

Mergansers have narrow bills with sharp, toothlike serrations for seizing fish underwater. Oth­er diving ducks possess strong, broad bills for prying mollusks from rocks and crushing their shells. Geese have short, blunt bills for grazing plants. Their thick tongues have spiny teeth along the edges to seize food.

Black-necked swan: Found in southern South

America. Prefers lakes and marshes,

feeding mainly on aquatic plants as

well as fish spawn and insects. The grayish juvenile

does not gain its adult plumage un­til its second year.