Final Assessment Zoology (Mammals)

• This note will cover the Class Mammals, or Mammalia

Endothermy

• Mammals are endothermic
• This means they can regulate their body temperature and maintain its relative constancy regardless of the surrounding temperature

The Skin

• Mammalian skin has two layers:
  • A superficial nonvascular epidermis
  • An inner dermis (corium)

Sensory Skin

• The skin has sensory functions enabled by:
  • Meissner's corpuscles for light touch
  • Free neuronal endings for pain, itch, hot, and cold sensations
  • Ruffini corpuscles for deep pressure and skin distortion,
  • Hair follicle endings for light touch and vibration
  • Pacinian corpuscles for deep pressure or vibration

Hair

• Hair is a unique characteristic of mammals
• Most mammals have hair covering at least part of their body at some time during their lives, unlike other animals
• An individual hair is a rod of cells reinforced by keratin
• Hair grows from skin cells called follicles
• Hair can take on several different forms, including:
  • Thick fur
  • Long whiskers
  • Defensive quills
• Hair serves several functions:
  • Provides insulation
  • Protects the skin
  • Serves as camouflage
  • Provides sensory feedback

Blubber

• Blubber is a specialized subcutaneous fat layer only in marine mammals
• It differs from other adipose tissue types in that it's anatomically and biochemically adapted
• It serves as an efficient, adjustable thermal insulator

Horns vs Antlers

• Horns and antlers are unique integumentary structures found in some mammals.
• Horns are keratinized structures with a bony core and are not typically shed
• Antlers are bony outgrowths that are shed and regrown annually.
• Keratin Fiber Horns:
  • A hard, conical structure present on the nasal region of the skull in Rhinoceroses
  • It consists of fused bony fibers and keratinized cells from the epidermis projecting from a dermal papilla
  • These fibers are not true hair, and their bases lack follicles.
• Hollow Horns:
  • A pair is present on the frontal bone in artiodactyls.
  • The horn consists of a bony projection from the frontal bone covered by a cornified layer of epidermis, with a cavity entering the bony projection
  • The horny layer is never shed.
• Prong Horns:
  • A conical projection on the frontal bone covered by a horny epidermal sheath that usually has prongs.
  • Unique to antelope, Antelocopra americana of Western America

Antlers

• Mesodermal derivatives made of hard bony structures developing on the frontal bone beneath the integument.
• Antlers are referred to as "velvet" due to the integument covering them.
• The velvet dries and falls away
• Antlers are restricted to members of the deer family
• They are only present in males, except for caribou (reindeer)
• Antlers are shed and replaced annually
• Mature antlers have many branches.
• Giraffe is unique in that the skin covering of the antlers never sheds and remains throughout life.

True Horns

• True horns are in ungulate mammals
• They have an inner core of bone outgrowing the frontal bone.
• Encased in a keratinized, epidermal covering
• True horns grow continuously and are not shed

Hooves, Claws and Nails

• In ungulate mammals, thick unguis, remains the end of the digits, called a hoof, sub-unguis is also present on the hoof
• In claws and nails, a rudimentary sub-unguis plate is attached with the pad of the digit
• The unguis is sharp and needle-like.
• Felines can withdraw their claws within the paws
• Unguis is broad and flat in nails; sub-unguis is rudimentary and remains at the nail's base

Skin Functions and Glands

• The primary function of skin is defense, and it is modified in mammals to serve diverse roles
• It manages thermoregulation and provides the nourishment of young
• Secretions of sweat glands promote cooling by evaporation
• Mammary glands are a type of apocrine gland

Glands in Mammals

• Sebaceous glands produce a lipid mixture known as sebum that is secreted onto the hair and skin for lubrication
• The Sebaceous glands are located over most of the body
• Eccrine glands produce sweat, which is mainly composed of water
• Eccrine glands found in limited areas of the body in most mammals.
• Primates have these glands prominently figured in thermoregulation
• Apocrine glands, or scent glands, secrete substances enabling chemical communication, such as in skunks
• Mammary glands produce milk used to feed newborns
• Male monotremes and eutherians possess mammary glands, male marsupials do not

Digestive System

• Processing food involves:
  • Ingestion (eating)
  • Digestion (mechanical and enzymatic breakdown)
  • Absorption (cellular uptake of nutrients)
  • Elimination (waste removal)

Oral Cavities and Teeth

• Most mammals are diphyodonts
• This means that they have two sets of teeth in their lifetime: deciduous ("baby") teeth and permanent teeth
• Some mammals lack teeth

Teeth & Dental Formula

• The mammalian class is identified through its teeth and dental formula
• Dental formula: written for 1/2 of the upper and lower jaw
• Example: 3 - 1 - 4 -3 x 2 = 44 (dental formula of horse and pig)

Saliva

• Three major glands secrete saliva:
  • The parotid
  • The submandibular
  • The sublingual
• Saliva contains:
  • Mucus
  • Immunoglobulins and lysozymes
  • Salivary amylase, lipase

Pharynx and Passage Ways

• The pharynx opens to two passage ways:
  • The trachea, which leads to the lungs
  • The esophagus, which leads to the stomach

Esophagus

• A tubular organ that connects the mouth to the stomach
• It transfers food from the mouth to the stomach by peristaltic movements

Stomach

• A large part of digestion happens here

Small Intestine

• Villi are folds on the small intestine lining
• These folds increase the surface area and facilitate nutrient absorption

Large Intestine

• The large intestine is an organ in vertebrates that absorbs water from the remaining indigestible food matter and transmit the useless waste material from the body

Accessory Organs

• The liver is the largest internal organ in humans
• Plays important roles of digesting fats and detoxifying blood
• The pancreas is an important gland that secretes digestive juices
• Gastric juices from the stomach have a high acidity.
• The gallbladder is a small organ aiding the liver in storing bile
• The gallbladder concentrates bile salts

Circulatory System

• Divided into 4 chambers consisting of two atria and two ventricles

• The heart is divided into four chambers including 2 atria & 2 ventricles

• The atria receive blood, the ventricles pump blood

• The right atrium receives blood from the superior and inferior vena cavas and coronary sinus

• The lungs re-oxygenate the blood and send it to the left atrium

• The heart consists of three layers:

  • Epicardium (outer layer)
  • Myocardium (middle layer),
  • Endocardium (inner layer)

Respiratory System

• The air passes through the nasal cavity, warming and humidifying it

Nervous System

• Compared to other vertebrates, mammals have very large brains for their body size.

Vision

• Binocular vision (stereoscopic) is useful for estimating distance
• Side vision (peripheral) allows each eye to send separate signals to the brain
• Animals that have side vision are generally herbivores that need to detect predators

Excretory System

• The urinary system contains of the kidneys
• This is where the urine is produced
• Ureters
• Urinary bladder
• Urethra

Reproductive Systems

• Double = (rodents and lagomorphs) 2 uterine cervices and two separate uterine horns
• Bicornuate = (ruminants, swine, equidae, carnivores, cetaceans) 1 cervix, 1 uterine body and 2 uterine horns
• Simplex = (primates, bats) 1 cervix and 1 uterine body

Marsupial Reproductive Traits

• Urogenital Tracts have 2 uteri with separate cervix
• The two lateral vaginas pass around the ureters
• Semen travels through two canals

Subclasses of Mammals

• There are three groups/subclasses of mammals
  • Eutherians (Placental mammals)
  • Marsupials
  • Monotremes (metatherians)

Monotremes

• 3 are living species of monotremes
  • The platypus
  • 4 species of echidnas(spiny anteaters)
• Monotremes lay eggs

Marsupials

• Marsupials can be found in the Americas/Australia
• The young continue to develop in a pouch
• Marsupials lack a complex placental connection

Eutherians(Placental)

• Eutherians are the most widespread of the mammals
• Species possess a complex placenta that connects a fetus to the mother for gas, fluids, and nutrient exchange

Review of Even-toed and Odd-toed Ungulates

• Examples of Eutherians:
  • Order. Even-toed ungulates (Artiodactyla)
  • Order. Odd-toed ungulates (Perissodactyla)
  • Order. Carnivores (Carnivora)
  • Order. Insectivores (Insectivora)
  • Order. Lagomorphes (Lagomorpha)
  • Order. Rodents (Rodentia)
  • Order. Bats (Chiroptera)
  • Order. Primates (Primates)
  • Order. Xenarthrans (Xenarthra)
  • Order. Proboscideans (Proboscidea)

Classes and Subclasses of Vertebrae

• Amniotes are tetrapod vertebrates comprising reptiles, birds, and mammals
• Characterized by having an egg adapted to lay eggs on land
• Anamniotes are an informal group comprising fishes and birds who lay their eggs in the water

Summary of Mammalian Characteristics

• Mammals share at least three characteristics not found in other animals:
  • Three middle ear bones
  • Hair
  • Mammary glands

Body Covering

• Amphibians = moist skin
• Birds = Feathers
• Fish = scales made out of bony plates
• Mammal = hair
• Reptiles = scales made out of keratin