1. Mammalian trends Endothermy Sensory specializations
Heterodont dentition
Skeletal simplification
Dentary/squamosal jaw joint
Lactation and increased parental care
See Table 2.2 for a longer list of diagnostic characteristics.

2. Mammalian Skin
Adapted from Romer, A. S., and Parsons, S. T. The Vertebrate Body. Saunders, 1977.

3. Skin Glands
Sweat glands
Sebaceous glands
Scent and musk glands

4. Mammary Glands
Adapted from Hildebrand, M. Analysis of Vertebrate Structure. John Wiley & Sons, 1974.

5. Mammary Glands Glandular ducts Teat, nipple, or hair tufts
Under endocrine control
Lactation and suckling promote social bonds
Milk composition varies
Seal milk has 12 times the fat and 5 times the protein of cow milk

6. Hair Dead epidermal cells with keratin Outer layer of cuticular scales
Deeper cortex and medulla layers
Color determined by pigments (melanin)
Pelage—coat of hair
Provides insulation
May undergo seasonal molting

7. FIGURE 03: Structure of a guard hair and cuticular scale patterns of the guard hairs of some mammals
Adapted from Teerink, B. J. Hair of West-European Mammals: Atlas and Identification Key. Cambridge University Press, 1991.

9. Pelage coloration Countershading Camouflage Disruptive coloration
Zebra stripes
Warning coloration
Skunks
Intraspecific communication
FIGURE 04: The pattern of postjuvenile molt in the golden mouse (Ochrotomys nuttalli)
Adapted from Linzey, D. W. and Linzey, A. V., J., Mammalogy. 48 (1967):

14. Fat and Energy Adipose tissue Desert or temperate zone mammals
Energy storage
Source of heat and water
Thermal insulation
Desert or temperate zone mammals
Store fat in tail or abdomen
Boreal or arctic mammals
Subcutaneous layer of blubber

15. Circulatory System Endothermy requires highly efficient circulation
Systemic and pulmonary circuits
4-chambered heart
Biconcave red blood cells
Heart rate varies with:
body size
activity state (e.g. hibernation)

16. FIGURE T03: Heart Rates of Selected Mammals
Circulatory System
FIGURE T03: Heart Rates of Selected Mammals
Data are from Altman and Dittmer (1964: 235); names updated.

17. Respiratory System Trachea—bronchi—bronchioles—aveolar ducts—alveoli
Human lungs contain ~300 million alveoli or 70 m2 of respiratory surface area
Muscular diaphragm aids ventilation
Limb and body movements also assist

18. Reproductive System Females Both ovaries functional
Ova fertilized in uterine tubes
Adapted from Smith, H. M. Evolution of Chordate Structure. Holt, Rinehart, and Winston, 1960.

19. FIGURE 08: Ventral view of penises of New Guinean murid rodents
Males
Erectile copulatory organ—penis
Os penis or baculum variable
Testes usually held in scrotum
FIGURE 08: Ventral view of penises of New Guinean murid rodents
Adapted from Lidicker, W. Z., Jr., J. Mammalogy 49 (1968):

21. FIGURE 09: Left sides of the brains of a hedgehog and a dolphin
Neopallium highly developed
Corpus callosum present
Brain
FIGURE 09: Left sides of the brains of a hedgehog and a dolphin
(Hedgehog) Adapted from Romer, A. S., and Parsons, S. T. The Vertebrate Body. Saunders, 1977; (dolphin) adapted by Norris, K. S. Whales, Dolphins and Porpoises. University of California Press, 1966.

22. FIGURE 10: Cutaway view of the nasal chamber of an Abert’s squirrel
Sense Organs
Olfaction
Olfactory receptors distributed across the mucosal surfaces of the mesethmoid and vomeronasal organ areas
FIGURE 10: Cutaway view of the nasal chamber of an Abert’s squirrel

23. Hearing High acuity (especially in nocturnal mammals) Sound use in:
Communication
Orientation to environment
Locating food
Avoiding enemies
Infrasound to ultrasound
External pinna leads to external auditory meatus
Middle ear has three ossicles encased in bony bulla

24. Middle ear
FIGURE 11: Lateral view of the right middle ear chamber (anterior is to the right) of Abert’s squirrel, with the auditory bulla largely removed

25. Other Senses Vision Tactile Similar to other amniotes
Tapetum lucidum in nocturnal mammals
Retina with photoreceptors (rods and cones)
Rods enable vision in low light (grayscale)
Cones enable color vision in brighter light
Eyes reduced in some fossorial mammals
Tactile
Vibrissae on muzzle (mystacial pad)

26. Digestive System Salivary glands Simple esophagus
Stomach simple or complex
Multi-chambered in many herbivores
Site of microbial fermentation in ruminants
Caecum
May be site of microbial digestion

27. FIGURE 13: The four-chambered “stomach” of a ruminant artiodactyl
Digestive System
FIGURE 13: The four-chambered “stomach” of a ruminant artiodactyl
Adapted from Storer, T. L., and Usinger, R. L. General Zoology. McGraw-Hill, 1965.

28. Muscular System Limb muscles highly adapted to style of locomotion
Trunk muscles aid postural control and breathing
Superficial muscles allow skin to move
Assist in suckling
Facial expression
Ear movements

29. The Skeleton Simplification of skeletal elements Metabolic savings
Lighter skeleton for quicker movements
Greater ossification
Well-braced muscle attachments
Determinate growth
Epiphysis fuses to diaphysis

30. Adapted Stock, C. Rancho. La Brea: A record of Pleistocene life in California, Science Series, no. 13. Los Angeles County Museum, 1949.

34. The Skull Akinetic skulls Single craniomandibular jaw joint
Braincase large
Sagittal and lambdoidal crest may be present
Zygomatic arch usually present
Secondary palate present
Turbinal bones within nasal cavities
Foramina pass cranial nerves and vessels
Three middle ear bones transmit sound to cochlea
Tympanic bulla
Hyoid bones support tongue

35. FIGURE 17A: Side view of the skull of the African wild dog (Lycaon pictus), showing the bones, foramina, and teeth

41. Teeth Heterodont dentition Deciduous dentition
Incisors, canines, premolars, molars
Deciduous dentition
Incisors, canines, and premolar “milk teeth” replaced by permanent dentition

42. Dental formula OR (3/3, 1/1, 4/4, 2/3) × 2 = 42
Specifies number and position of teeth on one side
Incisors 3/3, Canines 1/1, Premolars 4/4, Molars 2/3 OR
(3/3, 1/1, 4/4, 2/3) × 2 = 42
Individual teeth designated with upper case letters for upper teeth and lower case letters for lower teeth
P3 is upper premolar 3
M2 is lower molar 2

45. Evolution of teeth
Adapted from Spencer, R. S. Major Features in Vertebrate Evolution: Short Courses in Paleontology. No. 7. Paleontological Society, University of Tennessee, 1994.

46. Tribubercular pattern 3 cusps in triangle in upper molars
Talonid added to lower molars (triboshenic)
Adapted from Crompton, A. W., and Hiiemae, K., Discovery 5 (1969): 23.

55. FIGURE 21: Molars of the Virginia opossum
Mastication
Complex chewing movements
Initially crush and puncture food
Later sliced by shearing surfaces of molars
FIGURE 21: Molars of the Virginia opossum
(B) Adapted from Crompton, A. W., and Hiiemae, K., Discovery 5 (1969): 23.

56. Carnivory vs. Herbivory
Carnivores
Cheek teeth become blade-like (carnassials)
Adapted for slicing flesh
Jaw action is scissor-like
Herbivores
Cheek teeth become quadrate with hypocone
Jaw action is horizontal and transverse

57. FIGURE 22: Comparisons of the occlusal surfaces of the right upper cheek teeth of a carnivore
Adapted from Crompton, A. W., and Hiiemae, K., Discovery 5 (1969): 23.

68. Tooth structure Cementum binds tooth to jaw Inner dentine Outer enamel
FIGURE 23: Generalized sections of mammalian teeth, showing the internal structure

69. Terminology Brachydont—short-crowned teeth
Hypsodont—high-crowned teeth
Ever-growing—grow continuously
Diastema—space between incisors/canines and cheek teeth
Bunodont—rounded cusps on molars
Lophodont—cusps form ridges
Selenodont—cusps form crescents

70. FIGURE 25: Basic cusp pattern of mammalian molars
Cusp terminology
FIGURE 25: Basic cusp pattern of mammalian molars
Modified from Romer, A.S. Vertebrate Paleontology. University of Chicago Press, 1966.

72. FIGURE 26: Vertebrae of the gray fox
Axial Skeleton
Rib cage and sternum
Vertebral column
Greater head movement
Dorsoventral flexion of spine
Five vertebrae types
Cervical, Thoracic, Lumbar, Sacral, Caudal
FIGURE 26: Vertebrae of the gray fox

73. Limbs and Girdles Main form of propulsion in most mammals
Fore and aft movement of limbs
Pelvis
Ilium, ischium, and pubis
Shoulder girdle
Scapula and clavicle (clavicle may be reduced or absent)

74. Manus and Pes Manus (hand or forefoot) Pes (foot or hindfoot)
Five digits is ancestral—highly modified in several lingeages
Pollex (thumb) and Hallux (big toe) have two phalanges—remaining digits have three phalanges

76. Wrist and Ankle