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Mammal characteristics Soft anatomy Skin glands (sweat, scent, sebaceous) Lactation Hair

Mammal characteristics Soft anatomy Skin glands (sweat, scent, sebaceous) Lactation Hair Diaphragm 4-chambered heart High metabolic rate Hard anatomy (i.e., in fossil record) Three ear ossicles Single bone in mandible Complex teeth (heterodont & diphyodont).

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Mammal characteristics Soft anatomy Skin glands (sweat, scent, sebaceous) Lactation Hair

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  1. Mammal characteristics • Soft anatomy • Skin glands • (sweat, scent, sebaceous) • Lactation • Hair • Diaphragm • 4-chambered heart • High metabolic rate • Hard anatomy (i.e., in fossil record) • Three ear ossicles • Single bone in mandible • Complex teeth (heterodont & diphyodont)

  2. Therapsida – advanced cynodonts Trirachodon Cynognathus Probainognathus

  3. Jaw evolution – pelycosaurto mammal

  4. Secondary Palate

  5. Secondary Palate premaxilla maxilla palatine Procynosuchus Probainognathus Canis Primitive cynodont advanced cynodont modern mammal

  6. PELVIS & HIND LIMB Posterior Lateral Pelycosaur Dimetrodon Therapsid Thrinaxodon

  7. HEAD ARTICULATION occipital atlas - axix condyle Pelycosaur Dimetrodon Therapsid Thrinaxodon Mammal Felis

  8. MAMMALIAN “GRADE” TRENDS IN CYNODONTS • Feeding • 1) expansion of temporal opening, elaboration of • jaw muscles • 2) reduction in post-dentary jaw bones, “second” • jaw articulation • 3) tooth specialization (heterodonty) • Breathing • 1) secondary palate • 2) reduction in lumbar ribs, formation of ribcage • (& diaphragm?) • 3) nasal turbinals (temp. & water conservation) • Posture & locomotion • 1) double occipital condyle, atlas & axis • 2) enlargement of limb girdles • 3) specialization of lumbar & sacral regions • 4) vertical orientation of limbs • 5) formation of a heel bone • Hearing • 1) reduced size & flexible attachment of post-dentary • 2) reduction in size of stapes

  9. Evolution of the ear LOBE-FIN AMPHIBIAN PELYCOSAUR FISH AMPHIBIAN CYNODONT MAMMAL

  10. Synapsids -- size and position of stapes Sphenacodont pelycosaurs Advanced cynodonts

  11. Synapsids – reduction of post-dentary jaw elements (lateral views) Dimetrodon primitive theriodont primitive advanced cynodont cynodont Morganucodon primitive therian

  12. Therapsid – mammal ear transition

  13. Sorex (Recent shrew) – ear region TYMPANIC (angular) MALLEUS (articular)

  14. Synapsids -- jaw machanics

  15. Trithelodont (Ictidosaur) Jaw mechanics - development of double articulation

  16. Early mammal (or proto-mammal?) Morganucodon (late Triassic)

  17. MORGANUCODONTS vs ADVANCED CYNODONTS

  18. CONTRASTS BETWEEN LATE TRIASSIC VERTEBRATES EARLY DINOSAURS medium-large sized herbivores & carnivores probably diurnal, some endothermic CROCODILES small-medium sized, carnivores LATE THERAPSIDS Small-medium sized, probably nocturnal herbivores (tritylodonts) insectivores (ictidosaurs) carnivores (cynodonts) EARLY MAMMALS Very small Insectivores probably nocturnal, endothermic

  19. LATE TRIASSIC VERTEBRATES Plateosaurus (herbivorous dinosaur) 10 meters Coelophysis (carnivorous dinosaur) 3 meters Tritylodon (herbivorous therapsid) 1 meter Morganucodon (insectivorous “mammaliaform”) 10 cm

  20. Pelycosaurs & early therapsids (worldwide) Late Permian (250 mya) Late Triassic (210 mya) Cynodonts (worldwide) Earliest mammals (Laurasia)

  21. Diversification of early mammals (Eurasia & N. Amer.) Late Jurassic (150 mybp) Late Cretaceous (70 mybp) Origin & diversification of therians (worldwide) Isolation of southern groups

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