1. Introduction
Amniotes appear in Paleozoic era (Pennsylvanian of Carboniferous) Sauropsida—gave rise to turtles, lizards, snakes, dinosaurs, and birds Synapsida—gave rise to mammals

2. FIGURE 01: Phylogeny of Tetrapods
Adapted from Gauthier, J, A.G. Kluge and T. Rowe., Cladistics, 4 (1988):105–209; adapted from Benton, M.J. Vertebrate Palaeontology, Second edition. Chapman and Hall, 1997; and adapted from Carroll, R.L. Vertebrate Palaeontology and Evolution. W. H. Freem

5. Figure 18-1

6. Synapsida
Dominated terrestrial faunas during Permian and early Triassic
Many synapsid groups went extinct during Permian extinction event
Therapsida survived
Gave rise to cynodonts
Later, other therapsids dwindle
Mammals arose from cynodont ancestor in late Triassic

7. Synapsid Characters Single temporal fenestra on skull
Jaw muscles move to outer braincase
FIGURE 02: Diagrammatic views of skulls of amniotes showing some of the arrangements of temporal openings

9. FIGURE 03: Phylogeny and representative skulls of synapsids
Synapsid phylogeny
FIGURE 03: Phylogeny and representative skulls of synapsids
Phylogeny adapted from Wible, J.R., et al., American Museum Novitates 3149 (1995) 1–19; adapted from Rowe, T., J. of Vertebrate Palaeontology, 8 (1998): 241–264; adapted from Rowe, T. Mammal Phylogeny: Mesozoic Differentiation, Multituberculates, Monotre

10. Synapsid Characters Maxilla contacts quadratojugal bone
Caniniform maxillary teeth
Narrow neural arches on trunk vertebrae

11. Synapsids
Permian synapsids include a paraphyletic group called Pelycosaurs
FIGURE 05: Reconstructed skeletons of primitive and derived synapsids, showing changes in the postcranial skeleton.
Modified from Romer, A.S. Vertebrate Paleontology. University of Chicago Press, 1966.

12. Adapted from Jenkins, FA Jr., Journal of Zoology 165 (1971): 303–315;
Adapted from Jenkins, F.A. Jr., Evolution 24 (1970):
Adapted from Jenkins, F.A. Jr. Primate Locomotion. Academic Press, 1974.

13. Therapsids Appear in middle Permian Diverse assembalage
Include early cynodonts

14. Figure 18-5

15. Therapsid Characters Enlarged temporal opening
Sagittal crest and zygomatic arches
Upper canines enlarged
More upright limb posture
Deep acetabulum

16. Figure 18-7

17. Therapsid Characters Feet shortened
External auditory meatus within squamosal
Jaw joint in line with occiput
Anterior coronoid bone absent

18. Cynodont therapsids Masseteric fossa on dentary bone
Two occipital condyles
Zygomatic arches flare laterally
Angular bone reduced
Teeth absent from pterygoid bone

19. Cynodont therapsids Incisors spatulate
Accessory cusps on postcanine teeth
Partial secondary palate
Ribs reduced on lumbar vertebrae
Calcaneal heel present on foot

20. Early Mammals
FIGURE 10: Reconstruction of Eozostrodon, a Triassic mammal of the family Morganucodontidae
Adapted from Crompton, A.W. & F.A. Jenkins, Jr., Biological Reviews 43 (1968): 427.

21. Stem Mammals Dentary-squamosal jaw articulation
Tabular bone absent in skull
Medial wall of orbit enclosed
Double-rooted cheek teeth
Cheek teeth include premolars and molars

22. FIGURE 09: Stages in the development of the lower jaw and ear region in a young opossum Monodelphis (Didelphidae)
Adapted from Ghiselin, M. T., and Pinna, G. New Perspectives on the History of Life. California Academy of Sciences, 1994.

23. FIGURE 08: Selected major stages in the evolution of the mammalian jaw joint and ear region
Adapted from Ghiselin, M. T., and Pinna, G. New Perspectives on the History of Life. California Academy of Sciences, 1994.

24. Stem Mammals Precise occlusion of cheek teeth Diphyodont dentition
Mandibular symphysis reduced
Derived features of soft tissues
Mammary glands with teats
Viviparity
Separate anal and urogenetal openings
Digastricus muscle lowers jaw

26. Theria Tribosphenic molars Supraspinous fossa on scapula
Cochlea spiraled

27. Important Transformations
Evolution of a new squamosal-dentary jaw joint
Articular, quadrate, and angular bones of lower jaw detach and become part of ear apparatus (malleus, incus, and tympanic ring, respectively)

28. Other Transformations
Evolution of:
More complex cusps on molars
Secondary palate
Facilitated suckling
Parasagittal movement of limbs (more mammalian limb posture)
Endothermy

29. Early Mammals Small bodied (e.g. 20–30 grams)
Premolars and molars in cheek teeth
Large brain size
Probably insectivorous diet
Probably nocturnal and arboreal
Lactation and suckling likely

30. Figure 15-1

31. Mesozoic Multituberculates
Herbivorous or omnivorous
Appear in late Jurassic
Fossil record spans 100 million years
Similar in appearance to rodents
2 or 3 incisors above and 2 on bottom
Diastema
Massive, blade-like lower premolars

32. FIGURE 16: Ptilodus (order Multituberculata) skull
Multituberculates
FIGURE 16: Ptilodus (order Multituberculata) skull
Modified from Romer, A.S. Vertebrate Paleontology. University of Chicago Press, 1966.

34. Multituberculates Some retained cervical ribs
Unusual chewing mechanics
Multituberculates began to decline in late Paleocene—probably due to competition with condylarths, early primates, and rodents

35. Cretaceous Mammals
Metatherians and eutherians evolved from a clade of Mesozoic mammals
Angular process on dentary
Tribosphenic molars
Lower molars have talonid in some forms

36. Cretaceous Mammals
FIGURE 17: Molar of Aegialodon, an early Cretaceous tribosphenidan (family Aegialodontidae)
Parts c and d modified from Romer, A.S. Vertebrate Paleontology. University of Chicago Press, 1966.

37. Figure 20-7

38. Cretaceous Mammals
Much biotic interchange between continents in Jurassic—sets the stage
Flowering plants become dominant flora
Insects radiate with flowering plants in Cretaceous
Dinosaur fauna begins to decline
Mammal faunas begin to radiate

41. Figure 20-2

43. Figure 19-1

47. Figure 19-3

49. Figure 20-17

50. Figure 20-18

51. Figure 20-19

52. Figure 19-4