1. Mammalian Characteristics
Chapter 20

2. Lactation Presence of Mammary Glands for which the class is named.
This is a unique feature of the class,
Function is lactation – provide milk to the developing young,
All mammalian females lactate
Mammary glands absent from males of marsupials but present in male monotremes and eutherians
Only Eutherians have nipples, others have mammary hairs, so young ones suckle from the mother’s fur

3. Determinate growth Epiphyses feature of determinate growth in mammals
Growth zones of cartilage between diaphysis and epiphysis until cartilage is used up (limited growth span)
At maturity ossify with diaphysis (shaft)

4. Skeletal System: Cranial Features
Heterodentition
Incisors, canines, premolars & molars
2 sets of dentition
1st set = milk teeth: incisors, canines and premolars
2nd set = second set of original teeth + later-erupting teeth the molars
Mammals are the only animals that masticate food and swallow it as a bolus of food
Therians have special molars called tribosphenic molars

5. Cranial & Postcranial features
Dermal bones completely enclose the brain
Zygomatic arch : bowed out bones of that formed the lower boarder of temporal opening
3-boned middle ear
Dentary; single bone that forms the mammary lower jaw
Upright posture with limbs underneath the body –now : dogs, cats, horses
In opossums, semi-sprawling stance –primitive condition

6. Postcranial features (fig 20.4)
Unique ankle joint called crurotarsal joint
Between tibia and ankle bone called astragalus
Proximal ankle bone the calceneum projects to form the calcaneal heel
The heel is the point of insertion of calf muscles : Gastrocnemius

7. Postcranial features Ilium is rod shaped, & directed forward
Pubis and ischium are short
Contrast with plate-like pubis of & ischium of reptiles
Femur has a trocanter for the attachment of gluteal muscles which are the major retractors of the hind limbs

8. Postcranial features All have 7 cervical vertebrae
exceptions giraffe (8); matees (7)
Unique atlas-axis complex
Formed by the 1st two cervical vertebrae
Joint between head & atlas allows up & down head movement
Joint between atlas & axis allow the side to side movement

9. Postcranial features Ribs restricted to the thoracic vertebrae
Jaw adductor muscles
Temporalis:
from head to dentary’s coronoid process
Masseter
Extend from the zygomatic arch to outside of the lower jaw
Unique in mammals
Enables sideways movement of jaws

10. Postcranial features Diagastric muscles
Jaw opening muscles in Therian mammals
Innervated by Cranial Nerves 7 (back ½) and 5 (front ½)
Facial expression muscles-unique
Innervated by cranial nerve 7.

11. Integument
Skin has epidermal, dermal and hypodermal (with fat cells) layers
Epidermis varies in thickness
Humans thickest in palms and soles
Rodents – very delicate epidermis
Elephants, rhinoceroses, hippopotamuses once classified as pachyderms because, epidermis is several hundred cells thick

12. Integument: Hair Camouflage Communication
Sensation via (vibrissae or whiskers)
Grow on muzzle, eyes, lower legs, & have touch receptors
Insulation
Composed of keratin
Grows from hair follicles

13. Integument: Glands Secretory glands that develop from the epidermis
3 major types of skin glands
Eccrine gland:
produce a watery secretion with little organic content
Function as sweat glands in humans
In most animals, restricted to soles of the feet, tail and areas that contact surfaces to improve adhesion

14. Integument: Glands Sebaceous glands Apocrine Over entire body
Produce oily lubricant sebum that lubricates and waterproofs the hair
Apocrine
Type of gland in which the apical part of the secretory cell breaks down in the process
Secretions used in chemical communication
In humans found in armpits and pubic region

15. Integument: Claws, Nails, Hooves, Horns
Part of the integument
Claws, nails and hooves are accumulation of keratin that protect the terminal phalanx of the digits
Horns can be keratin (e.g. rhino) or bone covered by keratin as in cows

16. Cardiovascular system
Heart is four chambered
Complete ventricular septum
Single systemic arch (aorta)
Birds retained right systemic arch
Mammals retained the left systemic arch as aorta
Do not have the double systemic arch seen in reptiles
Mature Red blood cells lack a nucleus

17. Respiratory system Large lobed lungs
Finely branching bronchioles that terminate as alveoli
Diaphragm that aids in breathing
Divides the pleurocavity into the
Peritoneal cavity: surround viscera
Pleural cavity surround the lungs

18. Urogenital system Retain bladder, secretes dilute urine
Cloaca replaced by separate openings for urogenital and alimentary canal systems
Testes placed in a scrotum outside of the body
Urethra common passage for urine and sperms, hence is the penis
Glans= tip of penis; single in eutherians and forked in monotremes and marsupials
os penis (baccalum) contain bone

19. Urogenital system Renal portal system does not appear in mammals
Have the loop of Henle which is ideal for salt secretion
Marine reptiles and birds have salt glands in their heads that secrete excess salt

20. Sex determination Genetic X & Y chromosomes
Gene on Y chromosome initiates male gonadal development and female gonadal development occurs in its absence

21. The brain
Highly developed neopallium (roof of the forebrain): extended portion of the forebrain
tectum (visual center in lower vertebrates) reduced to corpora quadrigemina: functions mainly as a relay center for auditory information and to control visual reflexes
corpus callosum in eutherians provides additional communication

22. Major Lineages of Mammals
Allotheria (Multituberculates)
Extinct
Prototheria
Monotremes
Theria
Metatheria or Marsupials or
Eutheria: Placentals

23. Multituberculates Rodent or squirrel- like semi-arboreal omnivores
Could rotate foot backward to descend trees headfirst.
Prehensile tail (figure 20.20
Narrow pelvis: maybe gave birth to poorly developed young
Broad molars that are multicusped and specialized for grinding rather than shearing

24. Monotremes vs Therians
Toothless bird-like beak which contains receptors for sensing prey
Reptile-like cervical ribs
Reptile like pectoral girdle with clavicle, interclavicle, precoracoid, coracoid, scapula
Large epipubic bone on pelvic girdle
Lay 1 or 2 eggs, incubate 7-10 days
No nipples

25. Monotremes vs Therians
Lay eggs
No teeth in adults
No nipples
No cochlea
No external ear( pina)
Retain sclerotic ring around eyes
Septomaxilla bone
Retain ribs on cervical vertebrae
Therians
Give birth to young
Tribosphenic molars
Nipples
Cochlea in inner ear
External ear (pina)
No sclerotic rings around the eyes
No septomaxilla bone
No cervical ribs

26. Monotremes vs Therians
No crurotarsal joint
Reptile like pectoral girdle with clavicle, interclavicle, coracoid, scapula (not as big)
Large epipubic bone on pelvic girdle
Crurotarsal ankle joint with complete superposition of astragalus on the calceneum (fig 20.12)
Lost interclavicle & coracoid, expanded the scapula. Clavicle lost in dogs and horses
Small epipubic bones

27. Eutherian vs Marsupials
Non inflected angle to the dentary bone
Rectangular shape of nasal bones
Auditory bulla (bone elaboration around the ear to increase hearing
Post-orbital bar bone (bar of bone behind orbit in herbivores
Marsupials
Inflected angle (distinct)
Flared or diamond shaped nasal bones
Lack an auditory bulla or a very small one from a different bone
No postorbital bar

28. Eutherians vs Marsupials
Replaces all teeth except molars
Dental formula
I3/3; C1/1; P4/4; M3/3 ( 44 teeth, e.g whales)
Many have fewer teeth; primitive
Humans have
I2/2; C1/1; P2/2; M3/3
Lack epipubic bone
Replace only last molars
Dental formula
I3/4 C1/1 P3/3 M4/4
55 teeth
More incisors and molars
Epipubic bone that project forward from the pubis

29. Monotremes Toothless as adults, but teeth in juveniles
Egg laying mammals
Have primitive anatomical features
Reptile-like pectoral girdle with clavicle, coracoid and scapula
Large epipubic bone on pelvic girdle
Lay 1 or 2 eggs, incubate 7-10 days
Platypus : Australia
Echidna: Australia ( short nosed) Guinea (long nosed)

30. Therians: Marsupials Diverse (275 spp): See Table 20.1
See also figure 20.16
Smaller brain than eutherians
Short gestation length
New borne crawl into pouch & attach to the nipple
Separated from Eutherian since late mesozoic
Central and South America, Australia and New Guinea

31. Therians: Eutherians Placental mammals 93% of all mammals
Approximately 4100 spp
Chorio-allantoic placenta
Longer gestation period
Young are more developed
Relatively short lactation length
Rapid growth & development- facilitated by high energy milk

32. Major orders of placental mammals
Insectivora
Shrews, moles, hedgehogs, Madagascan tenrecs
Chiroptera (bats)
Carnivora (bears, canids, felids, cats, seals, sea lions, walruses
Rodentia: mice & squirrels
Lagomorpha: pikas, rabbits, hares
Perissodactyla:odd toed ungulates)
Artiodactyla:even toed ungulates)
Cetacea:whales, dolphins
Primates: monkeys, apes, gorillas, humans

33. Anatomical differences between Eutherians and Marsupials
Non-inflected angle to the dentary bone
Rectangular shape of the nasal bones
Auditory bulla- bone elaboration around the ear region
Post-orbital bar- bar of bone behind the orbit
Replace all teeth except molars
Marsupial
Inflected angle to the dentary bone
Flare or diamond shaped nasal bones
Lack a bulla or it is a very small formed from a different bone
Lacks post-orbital bar
Replaces only the last premolar

34. Anatomical differences between Eutherians and Marsupials
Dental formula
I3/3 C1/1 P4/4 M 3/3
Many have fewer teeth than this e,g humans have 32, dolphins ~ 44
Lack epipubic bones
Marsupial
Dental formula
I3/4 C1/1 P3/3 M4/4
Have epipubic bones that project forward from the pubis

35. Anatomical differences between Therians and Monotremes
Give birth to young
Have nipples
No sclerotic rings around the eyes
Lack septomaxilla bone in skull
No ribs on cervical vertebrae
Lay eggs
No nipples
Sclerotic cartilage rings. Do not ossify to form bone
Have septomaxilla bone in skull
Ribs retained in monotremes

36. Anatomical differences between Therians and Monotremes
More derived hinge joint between tibia and the astralagus in the ankle
There is complete superposition of astragalus on the calceneum
Shoulder girdle more derived
Coracoid & interclavicle bones do not appear in the shoulder girdle
Clavicle lost in running eutherians (dogs & horses)
Scapula expanded by appearance of scapula spine
Monotremes
Not seen in monotremes
Reptile-like shoulder girdle
Coracoid & interclavicle present
Clavicle present