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Mammalian characteristics: Cranial (skull) features

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AnapsidaDiapsida SynapsidaSaurapsida Turtles Lizards & snakes Crocodiles Dinosaurs & birds Mammals & reptile-like mammals Amniota -evolution of cleidoic (shelled) egg; ca. 350 mya (late Paleozoic) Amphibians -ca. 320 mya

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-apsid conditions AnapsidSynapsidDiapsid Pelycosaur Modern mammal

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Double occipital condyle: greater range of motion

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Pelycosaur Therapsids Single bone in mandible: dentary

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post-dentary bones Dentary-squamosal articulation

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Reptile: Mammal: stapes (incus) incus malleus (malleus) (stapes) (incus) (malleus) 3 inner ear ossicles

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Tympanic bone (="annulus" or "tympanic ring") tenrec skull; no auditory bulla

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Mammalian characteristics: Dental features

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Heterodont dentition

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Diphyodonty (vs. polyphyodonty)

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Matched shear surface on upper & lower teeth

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Complex occlusal surface on cheeckteeth

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Secondary palate

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Mammalian characteristics: Postcranial (skeletal) features

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Modified limbs and pelvic girdle Reptile-likeMammal-like Sprawling postureUpright posture Lateral gaitFore-aft gait Poorly developed calcaneusWell-developed calcaneus calcaneus fibula femur tibia pelvic girdle calcaneus fibula tibia femur astragalus

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Indeterminite growth vs. Determinite growth Long-bone epiphyses

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Stabilized and regionally specialized vertebral column

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Atlas Axis Dorsal-ventral flexion Rotation

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Simplified skeleton

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Mammalian characteristics: Soft anatomy, sensory, and physiological features

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Hair (=fur or pelage)

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Mammal hair: invagination Bird feather: evagination

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cuticle cortex: pigment medulla: dead cells containing air; variably present. Hair structure

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New PNAS article on origin of hair: PNAS November 25, 2008 vol. 105 no. 47 18419-18423

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Hair function: tactile perception (vibrissae)

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Hair function: locomotory specializations

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Hair function: defense

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Hair function: aggression and display

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Hair function: communication

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Mammary glands (=mammae), structural variation Monotreme Nipples (most mammals) Teat (e.g., cows) Skin glands

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4-chambered heart Mammal Crocodyle

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Enucleated blood cells Muscular diaphragm

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Improved olfaction

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Endothermy---Body temperature regulated internally. Homeothermy---Body temperature maintained within a narrow range.

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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

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Did these all appear simultaneously???? How do we know???

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Occipital condyles Dentary, ear ossicles Dentition Upright posture Determinite growth/ephiphyses Simplification of skeleton Vertebral column Mammary glands 4-chambered heart Enucleated red blood cells Diaphragm Endothermy/homeothermy Olfaction Hair Fossil evidence?

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Occipital condyles Dentary, ear ossicles Dentition Upright posture Determinite growth/ephiphyses Simplification of skeleton Vertebral column Mammary glands 4-chambered heart Enucleated red blood cells Diaphragm Endothermy/homeothermy(??) Olfaction (??) Hair Fossil evidence?