Mammalian characteristics:
Cranial (skull) features
Anapsida Diapsida
SynapsidaSaurapsida
Turtles
Lizards & snakesCrocodilesDinosaurs & birds
Mammals &reptile-like mammals
Amniota -evolution of cleidoic (shelled) egg; ca. 350 mya (late Paleozoic)
Amphibians
-ca. 320 mya
-apsid conditions
Anapsid Synapsid Diapsid
PelycosaurModern mammal
Double occipitalcondyle:
greater range of motion
Pelycosaur
Therapsid
s
Single bone in mandible: dentary
post-dentary bones
Dentary-squamosal articulation
Reptile:
Mammal:
stapes
stapes
stapes
(incus)
incusmalleus
(malleus)
(stapes)(incus)
(malleus)
3 inner ear ossicles
Tympanic bone (="annulus" or "tympanic ring")
tenrec skull; no auditory bulla
Mammalian characteristics:Dental features
Heterodont dentition
Diphyodonty (vs. polyphyodonty)
Matched shear surface on upper & lower teeth
Complex occlusal surface on cheeckteeth
Secondary palate
Mammalian characteristics:Postcranial (skeletal) features
Modified limbs and pelvic girdle
Reptile-like Mammal-like
Sprawling posture Upright postureLateral gait Fore-aft gaitPoorly developed calcaneus Well-developed calcaneus
calcaneus
fibula
femur
tibia
pelvicgirdle
calcaneus
fibulatibia
femur
astragalusastragalus
Indeterminite growth vs. Determinite growth
Long-bone epiphyses
Stabilized and regionally specialized vertebral column
AtlasAtlas Axis
Dorsal-ventralflexion Rotation
Simplified skeleton
Mammalian characteristics:Soft anatomy, sensory,
and physiological features
Hair (=fur or pelage)
Mammal hair:invagination Bird feather: evagination
cuticle
cortex: pigment
medulla: dead cells containing air; variably present.
Hair structure
New PNAS article on originof hair: PNAS November 25, 2008 vol. 105 no. 47 18419-18423
Hair function: tactile perception (vibrissae)
Hair function: locomotory specializations
Hair function: defense
Hair function: aggression and display
Hair function: communication
Mammary glands (=mammae), structural variation
Monotreme Nipples(most mammals)
Teat(e.g., cows)
Skin glands
4-chambered heart
Mammal
Crocodyle
Enucleated blood cells
Muscular diaphragm
Improved olfaction
Endothermy---Body temperature regulated internally.
Homeothermy---Body temperature maintained within a narrow range.
An integrated package?
•Natural selection favored increasingly efficient use of energy
•Endothermy facilitated nocturnal activity
•Endothermy is especially difficult for young
•Diphyodonty, lactation, social behavior
Did these all appear simultaneously????
How do we know???
Occipital condylesDentary, ear ossiclesDentitionUpright postureDeterminite growth/ephiphysesSimplification of skeletonVertebral columnMammary glands4-chambered heartEnucleated red blood cellsDiaphragmEndothermy/homeothermyOlfactionHair
Fossil evidence?
Occipital condylesDentary, ear ossiclesDentitionUpright postureDeterminite growth/ephiphysesSimplification of skeletonVertebral columnMammary glands4-chambered heartEnucleated red blood cellsDiaphragmEndothermy/homeothermy(??)Olfaction (??)Hair
Fossil evidence?