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Mammalian characteristics:

Mammalian characteristics:. Cranial (skull) features. Lizards & snakes Crocodiles Dinosaurs & birds. Mammals & reptile-like mammals. Turtles. Anapsida. Diapsida. Amphibians. Saurapsida. Synapsida. -ca. 320 mya. Amniota. -evolution of cleidoic (shelled) egg;

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Mammalian characteristics:

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  1. Mammalian characteristics: Cranial (skull) features

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

  3. -apsid conditions Anapsid Synapsid Diapsid Pelycosaur Modern mammal

  4. Double occipital condyle: greater range of motion

  5. Single bone in mandible: dentary Therapsids Pelycosaur

  6. Dentary-squamosal articulation post-dentary bones

  7. 3 inner ear ossicles stapes Reptile: stapes (incus) (malleus) (incus) (stapes) Mammal: stapes incus malleus (malleus)

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

  9. Mammalian characteristics: Dental features

  10. Heterodont dentition

  11. Diphyodonty (vs. polyphyodonty)

  12. Matched shear surface on upper & lower teeth

  13. Complex occlusal surface on cheeckteeth

  14. Secondary palate

  15. Mammalian characteristics: Postcranial (skeletal) features

  16. Modified limbs and pelvic girdle Reptile-like Mammal-like femur pelvic girdle femur fibula calcaneus tibia tibia fibula astragalus astragalus calcaneus Sprawling posture Upright posture Lateral gait Fore-aft gait Poorly developed calcaneus Well-developed calcaneus

  17. Indeterminite growth vs. Determinite growth Long-bone epiphyses

  18. Stabilized and regionally specialized vertebral column

  19. Dorsal-ventral flexion Rotation Atlas Atlas Axis

  20. Simplified skeleton

  21. Mammalian characteristics: Soft anatomy, sensory, and physiological features

  22. Hair (=fur or pelage)

  23. Mammal hair: invagination Bird feather: evagination

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

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

  26. Hair function: tactile perception (vibrissae)

  27. Hair function: locomotory specializations

  28. Hair function: defense

  29. Hair function: aggression and display

  30. Hair function: communication

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

  32. 4-chambered heart Mammal Crocodyle

  33. Enucleated blood cells Muscular diaphragm

  34. Improved olfaction

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

  36. 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

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

  38. Fossil evidence? 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

  39. Fossil evidence? 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

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