Lab 5: Mammal Info

Question 1

Mammals

Answer 1

have a favorable combination of primitive reptilian characteristics and unique features such as mammary glands and hair.

The presence of endothermy (a feature which evolved independently in birds) is associated with high metabolic and growth rates and has allowed some mammals to become the largest animals on earth.

Mammals have been most successful in terrestrial habitats, although some groups have become highly specialized for aquatic living or flight.

Question 2

Evolution of Mammals

Answer 2

Mammals arose from the reptilian synapsids (amniotic vertebrates with a single temporal opening in the skull) that had radiated widely in the terrestrial habitat in the Paleozoic Era, long before the radiation of the diapsids (Archosauria). The radiation of the mammals began some 210 million years ago, during the late Triassic Period, and peaked during the Cenozoic Era.

Mammalian characteristics began to appear in the therapsids, a varied group of synapsids that flourished during the late Triassic. Only one of these lineages, the cynodonts, actually gave rise to the extant mammalian groups.

Question 3

Fossil evidence shows

Answer 3

that one cynodont, Cynognathus, had many advanced mammallike characteristics including a secondary palate, which shunts air from the external nares (nostrils) at the front of the mouth.

This feature is important for endotherms in allowing the animal to continue breathing (and thereby support a high metabolic rate) while chewing food.

Thrinaxodon had, in addition to a secondary palate, thin scrolled-shaped bones in the nasal cavity (nasal turbinates) that had membranes to warm incoming air.

Cynognathus also shows indications of possessing a muscular diaphragm and a mammalian stance, while at the same time retaining a reptilian jaw articulation.

Although Cynognathus is not a direct ancestor to mammals, it does seem close to the main line of mammalian evolution.

Other, more advanced cynodonts (such as Diarthrognathus and Probaruognathus) developed both reptilian and mammalian jaw articulations functioning at the same time.

Question 4

Characteristics of Mammals

1. Jaw articulation

Answer 4

changed from quadrate-articular joint to a dentary-squamosal joint. This led to the following adaptations:
- dentary bone increased in size and articulates with the cranium.
- quadrate and articular bones become the incus and malleus bones of the
middle ear.

ransition of the jaw and history of the ear ossicles. (A) Simplified transition of the jaw structure from reptiles through mammal-like reptiles to mammals, showing the increase in size of the dentary bone and decrease in postdentary bones. The quadrate and articular bones of mammal-like reptiles eventually changed from a dual role of jaw joint and sound transmission to solely sound transmission in mammals. (B) Outer ear (OE), middle ear (ME), and inner ear
(IE) of modern mammals

Question 5

Characteristics of Mammals

Answer 5

2. Retention of two occipital condyles, allowing for greater range of head movement while supporting a large, heavy skull.
3. Development of secondary palate.
4. Tendency toward heterodont dentition (having a variety of tooth types), including the development of double-rooted cheek teeth (molars).
5. Ribs reduced or lost on cervical and lumbar vertebrae.
6. Limb posture more upright.
7. Endothermy (also found in birds due to convergent evolution).
8. Presence of hair.
9. Presence of a muscular diaphragm
10. Presence of a four-chambered heart, allowing complete separation of oxygenated and deoxygenated blood flow.
11. Development of the neopallium, a centre for coordination, memory and intelligence in the upper cerebrum of the brain.
12. Mammary glands, coupled with the presence of diphyodont dentition (“milk or baby teeth”), in development.
13. External pinna allowing for a 3-D perception of sound reception.

Question 6

Integumentary adaptations

Answer 6

Mammals show a great diversity of integumentary modifications. All are derived from the epidermis, although some may also be supported by or associated with the dermis

Question 7

Integumentary adaptations

Integumentary glands.

Answer 7

The three major types of glands are sebaceous glands, apocrine glands and eccrine glands.

Sebaceous glands open into a hair follicle and produce sebum that lubricates and waterproofs the hair and skin.

Apocrine glands have a limited distribution on the body and their secretions are used in chemical communication, although some scent glands are sebaceous glands.

Eccrine gland secretions are mainly watery and function to improve adhesion and tactile perception in some mammals and as sweat glands in others.

Other integumentary glands, such as mammary glands, are specializations of the other types.

Question 8

Integumentary adaptations

Epidermal scales

Answer 8

are modifications of hardened epithelium and are never bony.

Several species of mammals have epidermal scales on their tails and/or feet.

Only the armadillos and pangolins have a major portion of their body covered with scales of epidermal derivation.

Question 9

Integumentary adaptations

Hair

Answer 9

is a unique mammalian adaptation that has no direct homologue in other vertebrates.

The pelage of a mammal refers to the combination of hair types and colors it exhibits.

Question 10

Integumentary adaptations

Hair

Classifications of hair:

Answer 10

a. Vibrissae – long stiff hairs with well innervated bases. They serve primarily as tactile receptors. They may be found on legs, nose, and around the mouth and eyes.

b. Guard hairs – the most conspicuous hair on most mammals. Serves insulation (may be hollow) and protective functions. May be modified as seen in porcupine quills.

c. Underhair – functions primarily for insulation.

Question 11

Integumentary adaptations

Hair

Hair replacement – molting

Answer 11

a. Many mammals have seasonal molts. This is the most conspicuous in species that change from brown summer pelage to white winter pelage. Hormones, photoperiod, and temperature influence these changes.

b. Pelage, the name used to describe the hair coat, usually differs in juvenile and adult mammals.

Question 12

Integumentary adaptations

Hair

Hair coloration

Answer 12

a. The color of an individual hair is affected by numerous factors. The kind, amount, and distribution of pigment granules in a hair can vary to produce different effects. In addition, hair texture, thickness, and the amount of air space in the hair core can alter the way in which light is reflected.

b. Mammalian hair has two types of pigments, which combine in various concentrations to produce shades of black and brown (eumelanin), and red and yellow (pheomelanin). White is the complete lack of pigment. Greens and blues are rare in mammals.

c. Uses of color: color plays many important roles in the life of mammals. Appendix B, Adaptive Coloration, defines the major types of coloration and their functions. The examples on display illustrate some of these.

Question 13

Integumentary adaptations

Claws, Nails, and Hooves

Answer 13

The extremities of all mammalian digits, except whales and sirenians, are protected by plates or sheaths formed of keratinized epidermal cells.

1. Claws – composed of a dorsal sac-like plate (unguis) and a ventral plate (subunguis). The unguis, the better developed and harder of the two, is curved, and encloses the subunguis between its lower edges. Usually fixed in position except in cats where they are retractable. Claws function in increasing traction and stability in running mammals, protection, aid in excavating in digging mammals, aid in climbing in arboreal mammals, and aid in holding or killing prey in many carnivorous mammals.
2. Hooves – found in ungulate mammals (Artiodactyla and Perissodactyla). The unguis curves almost completely around the end of the digit and encloses the subunguis with it. Ungulate hooves come into direct contact with the ground, providing good traction and preventing wear.
3. Nails – modified claws that cover the dorsal surface of the end of the digit. In nails the unguis is broad and flattened and the subunguis is reduced to a small remnant that lies under the tip of the nail. Nails provide less protection for the ends of the digits than claws but they also allow for greater precision in manipulation of objects and for increased tactile perception.
4. Spurs – found in male monotremes on the back of the hind leg. This is not a digital keratinization since it projects from the ankle. The spur in the platypus is grooved for the passage of poisonous glandular secretions.

Question 14

Integumentary adaptations

Horns and Antlers

Answer 14

In modern mammals, head ornamentation in the form of horns and antlers is confined to the hoofed orders, Artiodactyla and Perissodactyla. These structures are variously used for sexual display, competition, and defense. Head ornamentation of living mammals may be divided into five major groups based on structure and the method of embryonic formation:

Question 15

Integumentary adaptations

Horns and Antlers

True Horns

Answer 15

True horns – (family Bovidae – buffalo, sheep, goats, cattle, antelopes, etc.). Unbranched and permanent. They are composed of an inner bony core formed from the frontal bone, and an outer layer of true horn formed from keratinized epidermis. Horns may be present on both sexes or only on males. Usually, each season’s growth produces a ring at the base of the horn sheath.

Question 16

Integumentary adaptations

Horns and Antlers

Pronghorns

Answer 16

(found in North American pronghorn, Antilocapra americana, only) Basic structure is similar to that of a true horn except that keratinized sheath is branched. This keratinized sheath is shed annually. Female pronghorns are almost hornless and frequently lack prongs (branches).

Question 17

Integumentary adaptations

Horns and Antlers

Antlers

Answer 17

(occur on males of most deer species, and in both sexes of caribou or reindeer).

Full-grown structures are entirely bony structures that are branched and shed annually.

While the antler is growing, the bone is covered with a layer of skin, the “velvet”, which carries blood vessels and nerves supplying bone growth.

The velvet is rubbed off leaving a bony structure.

The antler is shed generally after the mating season and a new one begins to grow in the spring.

Question 18

Integumentary adaptations

Horns and Antlers

Giraffe “horns”

Answer 18

(giraffes and okapi). Consist of a pair of short, unbranched, permanent bony processes arising from the anterior region of the cranium, covered with skin and hair.

These occur in both sexes.

Question 19

Integumentary adaptations

Horns and Antlers

Rhinoceros horn

Answer 19

the only living non-artiodactyl to possess keratinized head ornamentation.

The “horn” is composed of a sold mass of epidermal cells that are formed from a cluster of long dermal papillae (protrusions of the dermis into the epidermis).

Question 20

Teeth

Answer 20

A. Mammalian teeth are composed of two layers of extremely hard material (dentine on the inner and enamel on the outer surface) surrounding a central core of nerves and blood vessels. In mammals, teeth are important for chewing food as well as procuring it.

B. Teeth of most mammals are heterodont, consisting of several functional types:
1. Incisors – chisel – shaped, for nipping/slicing.
2. Canines – sharp and pointed, for cutting, stabbing, and gripping.
3. Premolars - flat and ridged, for chewing and grinding.
4. Molars – same as premolars, more posterior.

C. The diet of mammals determines the level of specialization of the different teeth types. For example, carnivores (meat-eaters) may have enlarged canines, while herbivores (planteaters) typically have highly adapted chewing teeth.

Question 21

Sensory Systems and Communication

Answer 21

Most mammal species communicate using chemical or auditory cues rather than visual cues. Refer to Appendices B (Adaptive coloration) and C (Communication) for terms and definitions.

Question 22

Sensory Systems and Communication

Chemical communication

Answer 22

1. Although it has not been well studied, chemical communication in mammals is thought to be very important, since most species have highly refined chemosensory systems for detecting food and predators.
2. Pheromones have many functions, including marking territory boundaries, signaling alarm to group member, and recognizing individuals, to name a few. Rodents such as ground squirrels have complex communication systems using scents released from various glands on their body and can distinguish kin based on their smell.
3. Chemical communication is particularly important for sexual behavior, such as sexual advertisement, courtship, and copulation. Male deer use smell to judge the relative dominance of other males in the herd during the rutting season, and they can smell the urine of females to determine their level of sexual receptivity. In some primate species, primer pheromones may coordinate estrus (the period of sexual receptivity) within a social group, since the scent of one receptive female initiates estrus in the other female members of the group.

Question 23

Sensory Systems and Communication

Visual system

Answer 23

1. Vertebrate eyes contain light-sensing cells called cones (responsible for high visual acuity and color vision; mammalian cones are not homologous with the cones of other vertebrates) and rods (responsible for vision at low light levels) in the retina.

With the exception of the primates, most mammals have few or no cones, so color vision and visual acuity is typically poor compared to other vertebrates such as lizards and birds.
Many nocturnal mammals, however, have large concentrations of rods for excellent night vision. Mammalian “cones” are anatomically and physiologically modified rod cells.

2. Mammalian coloration is not typically as vivid as that of birds and fishes, but still may play a key role in communication.

a. Many mammals are cryptically colored, whether prey or predator. Disruptive colouration is particularly common, with spots or stripes on the back to break up the body shape.

b. Mammals such as skunks show distinct aposematic coloration

c. Coordinated group movements may be facilitated by color patterns, such as the white rump patches of deer or the lateral stripes and swirls of dolphins.

d. Individual recognition is usually by smell, but color and facial features can also be important.

3. Postures and displays are important in mammalian communication, particularly between members of a group. In wolves, subordinates typically try to appear smaller than they are, by lowering their tail and flattening their ears. When alarmed, mammals such as cats erect their fur.

Question 24

Sensory Systems and Communication

Auditory system

Answer 24

1. The mammalian ear is unique among vertebrates, consisting of an external, often movable pinna which concentrates the sound, and a tympanic membrane (eardrum) and three bones (malleus, incus, and stapes) which transmit the sound vibration to the inner ear (cochlea).
2. Mammals produce sounds in the larynx, a region of the trachea reinforced with cartilage, by vibration of the vocal cords when air is exhaled. Some species such as howler monkeys and orangutans also have additional resonating chambers to modify the sound. Sound can also be produced by beating the substrate with a limb or other object, as is done by beavers and rabbits.
3. Sounds are frequently used for alarm signals, since the receiver does not need to be paying attention to the sender. Alarm calls are typically high-pitched and loud. Vervet monkeys have distinctive alarm calls for different predators, such as snakes, eagles, or leopards.
4. Many vocalizations are used in social interactions. In chimpanzees, threats may include growls, grunts, roars, and shrieks. Wolves howl to maintain contact with pack members. Infant mammals usually make high-pitched sounds when distressed. Elephants use infrasonic (below the hearing range of humans) sound to communicate within a dispersed group.
5. Whales and dolphins have a derived auditory system; sound (such as whistles, clicks, and squeaks) is produced in the passages leading to the blowhole and directed out of the body through an oil-filled chamber in the cranium. Sound vibrations are channeled through the mandible to the inner ear. The elaborate songs of humpback whales are used primarily by competing males during the breeding season. Migrating sperm whales use very low-frequency pulses to contact group members hundreds of miles away.
6. Echolocation is NOT a form of communication, but it is produced by the auditory system of mammals such as bats, toothed whales, many insectivores and some rodents and pinnipeds. Echolocation makes use of rapid, ultrasonic pulses that bounce off object such as prey items of geographical features. By analyzing the echo, the animal can detect its distance from the object. Thus, echolocation is an adaptation for foraging and navigating.

Question 25

Reproduction and Development

Modes of reproduction.

Monotremes

Answer 25

All mammals reproduce sexually by way of internal fertilization. Mammals show a graduation of adaptations from oviparity to matrotrophy. Mammals display a specialization of matrotrophy, associated with the evolution of the placenta.

a. Monotremes retain their basic reptilian heritage as oviparous (“egg layers”) and have a cloaca. As with birds, only the left ovary is functional in monotremes. The eggs contain a large amount of yolk (making monotremes lecithotrophic) and are fertilized prior to the entrance to the uterus. The eggs are then coated with a leathery shell and laid. The embryos of monotremes possess an egg tooth to break out of the shell.

i. The platypus lays two eggs and incubates them in a nest.

ii. The echidna lays a single egg and then carries it in a pouch analogous to a marsupium of metatherians.

Question 26

Reproduction and Development

Modes of reproduction.

Marsupials

Answer 26

Marsupials are matrotrophic. Fertilization occurs in the fallopian tubes and the embryo’s intrauterine life is very short. At birth the embryos are small and very immature (altricial state), with well-developed forelimbs that enable them to crawl from the vagina into the marsupium. In the marsupium the embryos attach to a teat that swells after grasping so that the young will not drop off.

Question 27

Reproduction and Development

Modes of reproduction.

placental

Answer 27

In placental mammals the oviduct often fuses to form a uterus. The small egg(s), with relatively little yolk, is fertilized in the fallopian tubes. The fertilized egg(s) implants within the uterus and form a placenta. The placenta is a highly vascularized extraembryonic structure that forms from the material uterus and the extraembryonic membranes.

Question 28

Reproduction and Development

ReproductiveCycle.

Answer 28

The reproductive cycle of the female mammal is termed estrus. Estrus is divided into four phases. The final phase, metestrus, occurs if no conception takes place. In primates metestrus is terminated by a menses, whereby the uterine lining is discharged (menstruation).

1. Female mammals exhibit many modifications of the ovarian cycles including variations in timing of estrus (one or multiple estrus cycles in a year), initiation of ovulation (ovulation is triggered by signals from the female’s own system or ovulation is triggered by external signals), and timing of fertilization/implantation (in most mammals, fertilization and implantation are immediate, but some allow delays).
2. The major differences in the reproductive systems of males mammals are in the structure and location of the penis and scrotum, as well as whether the testes are scrotal (external) or abdominal (retained inside the body wall).
3. All carnivores and pinnipeds, most rodents, bats, and some insectivores have a bone, the baculum or os penis, within the penis. The shape of this bone can be systematically important.
4. Many species of mammals exhibit secondary sex characteristics which are frequently related to sexual recognition, courtship, or both:

a. The presence of antlers in males only – e.g., cervids.

b. Enlarged canines in males but absent in females – e.g., some horses and deer.

c. Variation in pelage coloration.

d. Variation in the degree of development of certain areas of hair – e.g., lion’s mane and male human facial hair.

e. Differences in body size – usually the male is larger than the female.

Question 29

Reproduction and Development

Mammary Glands (modified sweat glands)

Answer 29

1. Monotreme mammary glands lack nipples and resemble modified sweat glands.
2. Marsupial and eutherian mammary glands with nipples.