ZOOLOGY STUDY GUIDE - Ye. O. Nevedomska - 2013

LECTURE 18. CLASS MAMMALIA, or MAMMALS (Mammalia)

2. Classification of the Class Mammalia

The Class Mammalia comprises two subclasses:

1) subclass Prototheria (Egg-laying mammals, or Prototherians) with a single order Monotremata;

2) Subclass Theria (Therians, or True beasts) includes the infraclasses Metatheria (Marsupials, or Lower beasts) and Eutheria or Placentalia (Placentals, or Higher beasts).

Subclass Prototheria (Egg-laying mammals, or Prototherians)

The modern fauna includes 5 species of these most primitive mammals (1 species is the platypus, whose jaws are covered with horny sheaths, making them resemble a duck's bill, and 4 species of echidna, whose bodies are covered with stiff spines, making these animals resemble a hedgehog). They are distributed in Australia, New Guinea, and Tasmania.

General characteristics of egg-laying mammals, or prototherians:

✵ Adults lack Teeth. They feed on animals. The Stomach lacks digestive glands.

✵ The intestine and urogenital Organs open into a cloaca.

✵ In females, only the left side of the Reproductive System is functional (similar to birds).

✵ They lay (1-2, rarely 3) relatively large, yolk-rich eggs, but unlike reptiles, the eggs remain in the female's reproductive tract (allowing the embryo to undergo a significant part of its development inside the mother's body). Instead of a calcareous shell, the egg has a soft, leathery shell.

✵ Mammary Glands are poorly developed and tubular. There are no nipples, and the glands open via separate ducts onto glandular fields (the young lick milk from the mother's fur).

✵ The average body Temperature ranges from 25 to 36°C.

✵ They resemble reptiles in the Structural Features of their shoulder girdle, Heart, and Brain.

✵ By lifestyle, they are semi-aquatic (platypus) or terrestrial (echidnas) animals.

Subclass Theria (Therians)

Infraclass Metatheria (Marsupials, or Lower beasts)

There are about 250 species of marsupials. Typical representatives include kangaroos, marsupial squirrels, koalas (marsupial bears), marsupial cats, marsupial jerboas, Water opossums, marsupial moles, and marsupial gliding possums. They are distributed in Australia and adjacent islands, the Americas, and naturalized in New Zealand. They live in forests, open areas, water, and soil.

General characteristics of marsupials:

✵ Viviparity.

✵ A true Placenta is absent.

✵ The embryo feeds and develops mainly at the expense of the egg yolk (for 12.5 to 42 days), but even this is insufficient for complete development, so the newborns are extremely small (0.5 to 3 cm), weak, and helpless.

✵ The newborn animals complete their development over up to 250 days in the mother's pouch (marsupium), which is formed by Skin folds on the ventral side of the body.

✵ The presence of tubular mammary glands in the marsupium, which open via ducts on the nipples located within the pouch; milk is pumped into the offspring's Mouth through the contraction of specialized gland Muscles.

✵ The coat is solid-colored (reddish or brown).

✵ Teeth are weakly differentiated, tooth replacement is incomplete (only one premolar is replaced), and there is an unequal number of incisors on the jaws (with more on the upper jaw).

✵ In terms of diet, modern marsupials include both herbivores and carnivores.

✵ The brain is primitive.

Infraclass Placentalia, or Higher Mammals (Eutheria, Placentalia)

This group includes the majority of modern mammals. They are distributed worldwide on land, in seas, and in oceans. They are distinguished by a highly developed Cerebral Cortex. They always possess a placenta; the Vagina is single; the young are born relatively well-developed and can suckle independently.

Placentals comprise 17 orders.

General Characteristics of Selected placental orders

Order Insectivora: 900 species, 12 species in Ukraine (two species of hedgehogs: the common hedgehog and the long-eared hedgehog; eight species of shrews; one species of moles: the European mole; and one species of desmans: the Russian desman). These are small to medium-sized animals. They have adapted to various habitats: terrestrial, fossorial (underground), and aquatic. They are distributed worldwide, except for Australia and South America.

General CHARACTERISTICS OF THE Order Insectivora:

1. The snout is elongated into a mobile proboscis.

2. The SENSE OF SMELL is well developed.

3. The cerebral hemispheres are small and smooth (without convolutions).

4. Teeth are weakly differentiated.

5. They feed primarily on insects; some also consume earthworms, Mollusks, small mouse-like rodents, fish, eggs, plants, and plant seeds.

6. The eyes are small, and in some species, reduced.

7. The coat is short and soft, bristly, or spiny, and dark in color.

8. The limbs are five-toed (pentadactyl) and plantigrade.

9. Scent glands are typically present (e.g., in shrews).

10. They are active at night, and some are active around the clock.

11. Gestation lasts 11-43 days.

12. There are 1-2 litters per year (with 2-21 young per litter).

Significance of members of the Order Insectivora:

✵ they control insect pests;

✵ important furbearing species (desman, mole);

✵ some destroy birds' eggs (hedgehogs).

Order Chiroptera: comprises about 1000 species, with 25 found in Ukraine (horseshoe bats, noctules, the common bent-wing bat, mouse-eared bats, pipistrelles). They are distributed worldwide, except for polar regions and certain oceanic islands, and are most abundant in the tropics. The smallest bat in Ukraine is the common pipistrelle (weight does not exceed 5 grams; wingspan is 18 cm).

Early naturalists named them 'Chiroptera' (hand-winged) because a bat's wing is formed primarily by a leathery membrane 'stretched' over the forelimb (hand). Only the slightly modified thumb of the forelimb remains free, helping the bat to cling while crawling. Neither the teeth nor the limbs of bats are adapted for building shelters, so they roost in natural cavities or man-made and animal-made structures.

General characteristics of the order Chiroptera:

1. The appearance of a bat is characterized by soft fur, moderately large ears, and leathery wings.

2. The only group of mammals adapted for true flight:

* a fold of skin forms between the second digit of the forelimbs and the body, extending to the tip of the tail and functioning as a wing;

* the digits of the forelimb (except the first) are significantly elongated;

* similar to birds, the Sternum has a well-developed keel;

* the chest musculature is well-developed, powering wing movement;

* the bones are strong, thin, and light.

3. The hind limbs are rotated outward at the knee joints.

4. The number of teeth ranges from 20 to 38, and the central pair of incisors is absent. The intestine is relatively short. They feed on animal (mostly insects) and plant food (fruits, pollen, or flower nectar). On average, a bat requires a daily amount of food equal to half of its own body weight. For example, 4000 mosquitoes make up the required 9 grams of food for Daubenton's bat, a medium-sized species.

5. The fur is predominantly dark, soft, and short, covering only the body and HEAD.

6. The presence of scent glands is characteristic.

7. Their Vision is poorly developed. The ears are their most important sensory organ. Bats use THE PRINCIPLE OF echo-orientation, or echolocation: during flight, they constantly emit ultrasonic signals and, receiving them back as waves reflected from surrounding objects, are able to 'hear an image' of the surrounding space, forming an accurate picture of their environment (this allows them to navigate during flight and capture prey in the air).

8. They are nocturnal and crepuscular animals, hiding during the day in attics, tree hollows, and caves. They live in colonies. Females form shared maternity colonies in tree hollows or attics, where they raise their young together. During this time, males live separately from females, either solitarily or in small groups.

9. Some species undergo seasonal Migrations, while others hibernate. To sustain themselves through the winter, they accumulate fat reserves in late summer. To conserve energy during winter, bats possess an extraordinary ability: they can lower their body temperature to 10 or even 0 degrees (depending on the temperature of their winter roost). In this cooled state, all vital bodily Functions are reduced to a minimum. While an active bat's heart beats over 400 times per minute, during hibernation The Heart rate barely exceeds 10 beats over the same period. Furthermore, the bat's body consumes so little oxygen that its breathing rate drops to 5-6 breaths per minute.

11. They do not form permanent pairs. Females give birth once a year (usually in June) to a single pup, rarely two. During birth, females hang head-up and use their wing and interfemoral membranes to form a pouch into which the newborn pup slides. As soon as it is born, the pup finds a teat and firmly attaches itself to its mother's abdomen. From birth, the young hang head-down in the typical bat fashion.

12. Parental care is provided solely by females; males play no part in raising the offspring. Females carry their young with them constantly, even during evening hunting flights. Later, they leave the pups in the roost, where they huddle together waiting for their mothers. A young bat's body requires constant grooming. First and foremost, their growing wings are repeatedly coated with an oily secretion to prevent drying and maintain elasticity. For 3-5 weeks, the pups feed exclusively on mother's milk. The nursing period lasts until they grow large enough to attempt their first flight.

13. They live up to 20 years.

Importance of the order Chiroptera:

✵ they destroy harmful nocturnal insects (inaccessible to birds);

✵ they cause damage to fruit farming (fruit bats, as they feed on fruit) and livestock farming (vampire bats, as they feed on animal Blood);

✵ some carry pathogens of infectious diseases, particularly rabies.

Order Rodentia: the most numerous group of mammals (about 2000 species, with 40 species in Ukraine). They are distributed worldwide. Representatives include: capybara, Eurasian red squirrel, porcupine, beaver, dormouse, blind mole-rat, mice (house mouse, wood mouse), rats (brown rat, black rat), hamster, vole, lemming, muskrat, and coypu. Most lead a semi-fossorial lifestyle, feeding On the surface; There are also arboreal and semi-aquatic forms.

General characteristics of the Order Rodentia:

1. The coat ranges from thick and soft to sparse, bristly, or needle-like (porcupine); coloration is diverse.

2. Teeth are adapted for cutting and chewing plant food:

* canines are absent, replaced by a gap called a diastema;

* four incisors (two in each jaw); the incisors are chisel-shaped and well-developed; they are rootless and grow continuously throughout life; the front surface is covered with enamel, while the back consists of dentin (which wears away faster, making the incisors self-sharpening);

* molars with a flat chewing surface.

3. Well-developed cecum (acting as a "Fermentation vat").

4. Predominantly herbivorous, some are omnivorous, insectivorous, or piscivorous.

5. Cerebral hemispheres are smooth, without convolutions.

6. Imperfect thermoregulation.

7. Active year-round, though some hibernate.

8. Lifespan of small species is 1.5–2 years, while large ones (bobak marmots, beavers) live for 4–7 years.

Sexual maturity is reached at 2–3 months in small species, and In the second year of life in large ones.

High fecundity of small rodents: 6–8 litters per year with 8–15 young in each.

Significance of the Order Rodentia:

✵ burrowing activity affects the physical state of the soil, which increases vegetation productivity;

✵ subjects of commercial hunting and captive breeding for fur (coypu, muskrat, squirrel, beaver);

✵ pests of agricultural plants (voles, mice, rats, hamsters);

✵ vectors of pathogens of dangerous diseases (plague, tularemia, encephalitis) — mice, rats, hamsters, marmots, voles.

Order Lagomorpha: a small group of mammals in terms of species diversity (65 species, with 2 species in Ukraine). Representatives include hares and domestic rabbits. In Ukraine, the European hare and the mountain hare are found.

In terms of Anatomical Features, lagomorphs are close to rodents. Lagomorphs differ from rodents in the following ways:

✵ the presence of two pairs of incisors in the upper jaw (instead of one pair in rodents);

✵ a more complex stomach Structure consisting of two functional compartments (bacterial fermentation of food occurs in the first, while gastric juice Enzymes act in the second).

The Significance of Representatives of the order Lagomorpha:

✵ they are of great importance as game animals for their fur and meat;

✵ during years of population outbreaks, herbivorous lagomorphs can cause damage to forestry and horticulture.

The Order Carnivora: includes about 240 species. Distributed on all continents except Antarctica (carnivorans were introduced to Australia during its colonization). The 7 main families are:

1. Felidae (cats) — tiger, lion, panther, leopard; in Ukraine — wildcat, domestic cat, lynx;

2. Canidae (canids) — wolf, dog, Arctic fox, jackal, fox, raccoon dog; in Ukraine — 4 species;

3. Ursidae (bears) — polar, brown, black (Asian black) bears; in Ukraine — 1 species (brown bear);

4. Mustelidae (mustelids) — pine marten, sable, polecat, mink, ermine, weasel, otter; in Ukraine — 12 species, most of which are listed in the Red Data Book of Ukraine;

5. Hyaenidae (hyenas) — spotted hyena, brown hyena, aardwolf;

6. Procyonidae (procyonids) — raccoon, panda, coati;

7. Viverridae (viverrids) — mongooses, genets.

General characteristics of the order Carnivora:

1. The coat is dense and soft in most species.

2. Teeth are well-differentiated (Fig. 82):

* incisors are small;

* canines are the most highly developed;

* molars are tuberculate, with sharp cusps;

* one molar on each side of the jaw is modified into a so-called carnassial tooth (large in size, with a sharp cutting edge).

Fig. 82. Teeth of a dog (top) and a cat (bottom) (after Naumov, Kartashev, 1979):

1 — incisors; 2 — canines; 3 — premolars; 4 — molars; 5 — carnassial teeth.

3. They feed predominantly or exclusively on animal food.

4. Clavicles are rudimentary or completely absent.

5. They are active mainly at twilight and at night.

6. Their lifestyle is solitary or family-based.

7. Offspring are born blind and develop slowly.

8. Sexual Dimorphism is barely pronounced; only in some species are males slightly larger than females.

Significance of representatives of the order Carnivora:

✵ Most species are valuable fur-bearing animals, subjects of the fur trade;

✵ they prey on mouse-like rodents;

✵ certain species (wolves, foxes) can sometimes cause damage to livestock and may carry the rabies virus.

The Order Artiodactyla comprises about 170 species: wild boar, European bison, moose, reindeer, hippopotamuses, giraffes, bison, antelope, roe deer, goats, cows, sheep.

Anatomical features: each limb has four toes, of which the second and third are well-developed. The toes are encased in horny hooves. Clavicles are absent. Most are ruminants with a complex stomach consisting of 4 compartments: rumen, reticulum, omasum, and abomasum.

The Order Perissodactyla comprises 16 species: horses, zebras, donkeys, rhinoceroses, tapirs

Anatomical features: most have one or (less commonly) three hoofed toes on each FOOT. In three-toed limbs, the third digit is the most developed. Clavicles are absent. The stomach is simple.

The Order Cetacea includes about 90 species: blue and gray whales, sperm whales, dolphins (bottlenose dolphin, common dolphin).

Anatomical features: the body shape is torpedo-like, subcutaneous fat is highly developed, and the Lungs have a large volume. The forelimbs are modified into flippers, while the hindlimbs are reduced. Hair and external ears are absent. Teeth in toothed whales are large and single-cusped, while baleen whales lack teeth. There is a filtering apparatus formed by baleen; a caudal (and in some species, dorsal) fin is present. They navigate using echolocation.

The Order Pinnipedia contains 30 species: walrus, seal, fur seal, ringed seal.

Anatomical features: both pairs of limbs are modified into flippers, with a thick web of skin between the digits. There is a thick layer of subcutaneous fat. The body is large and streamlined.

The Order Proboscidea: 2 species (Asian and African elephants).

Anatomical features: very large animals. The Nose and upper lip are modified into a trunk. There are tusks, which are modified upper incisors. Canines are absent. As the molars (two on the upper and lower jaws) wear down, new ones grow to replace them.

The Order Primates: over 200 diverse species. Distributed in subtropical and tropical regions of Asia, Africa, and the Americas. Representatives include lemurs, marmosets, howler monkeys, spider monkeys, guenons, macaques, baboons, gibbons, orangutans, chimpanzees, and gorillas.

General characteristics of the order Primates:

1. Limbs are five-digited and prehensile; the first digit on both pairs is opposable to the others, allowing for a wide range of hand movements. Highly mobile upper limbs are the result of the presence of clavicles in the shoulder girdle.

2. Almost all species have Nails instead of claws on their digits. There are papillary lines and ridges on the palms and soles.

3. The coat is well-developed, in shades of red, gray, or black; most have manes, whiskers, beards, or tufts on their ears and tails.

4. Teeth are differentiated into incisors, canines, premolars, and molars; deciduous (milk) teeth are replaced by permanent ones.

5. Shortened jaws and a reduced facial region of the Skull. The skull has a relatively large braincase.

6. The brain:

* is relatively large;

* highly developed cerebral hemispheres with numerous sulci and gyri;

* enlarged occipital lobe (visual area), frontal and temporal lobes (controlling Muscle activity and the vocal apparatus).

7. Particularly well-developed vision (stereoscopic, color), with eyes facing forward (rather than to the sides, as in other vertebrates; binocular vision), providing The ability to judge distances to objects.

8. Well-developed Hearing, poorer sense of smell.

9. Herbivorous, less commonly omnivorous, some insectivorous.

10. Arboreal, some species are terrestrial or semi-terrestrial.

11. Predominantly gregarious, diurnal, crepuscular, or nocturnal.

12. High level of communication—reacting to the movements, gestures, and vocalizations of conspecifics; complex social structure with a hierarchical system of dominance and submission.

13. Breeding occurs year-round; gestation lasts from 4 to 10 months (correlating with body size). A single offspring is born (more or less helpless), rarely 2–3. There is one pair of pectoral mammary glands.

Significance of representatives of the order Primates:

* Used as laboratory animals in biological and medical experiments;

* chimpanzees serve as a model for studying the cognitive Features of human anthropoid ancestors (sharing similarities with fossil Dryopithecus).