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.

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

Skin Glands Sweat glands Sebaceous glands Scent and musk glands

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

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

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

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.

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): 326-241.

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

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)

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.

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

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.

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): 609-643.

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.

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

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

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

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)

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

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.

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

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

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

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

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

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

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

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.

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.

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.

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

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.

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

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

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.

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

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)

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

Wrist and Ankle