Presentation on theme: "Introduction Amniotes appear in Paleozoic era (Pennsylvanian of Carboniferous) Sauropsida—gave rise to turtles, lizards, snakes, dinosaurs, and birds Synapsida—gave."— Presentation transcript:
1IntroductionAmniotes appear in Paleozoic era (Pennsylvanian of Carboniferous) Sauropsida—gave rise to turtles, lizards, snakes, dinosaurs, and birds Synapsida—gave rise to mammals
2FIGURE 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
6SynapsidaDominated terrestrial faunas during Permian and early TriassicMany synapsid groups went extinct during Permian extinction eventTherapsida survivedGave rise to cynodontsLater, other therapsids dwindleMammals arose from cynodont ancestor in late Triassic
7Synapsid Characters Single temporal fenestra on skull Jaw muscles move to outer braincaseFIGURE 02: Diagrammatic views of skulls of amniotes showing some of the arrangements of temporal openings
9FIGURE 03: Phylogeny and representative skulls of synapsids Synapsid phylogenyFIGURE 03: Phylogeny and representative skulls of synapsidsPhylogeny 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
10Synapsid Characters Maxilla contacts quadratojugal bone Caniniform maxillary teethNarrow neural arches on trunk vertebrae
11SynapsidsPermian synapsids include a paraphyletic group called PelycosaursFIGURE 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.
12Adapted 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.
13Therapsids Appear in middle Permian Diverse assembalage Include early cynodonts
17Therapsid Characters Feet shortened External auditory meatus within squamosalJaw joint in line with occiputAnterior coronoid bone absent
18Cynodont therapsids Masseteric fossa on dentary bone Two occipital condylesZygomatic arches flare laterallyAngular bone reducedTeeth absent from pterygoid bone
19Cynodont therapsids Incisors spatulate Accessory cusps on postcanine teethPartial secondary palateRibs reduced on lumbar vertebraeCalcaneal heel present on foot
20Early MammalsFIGURE 10: Reconstruction of Eozostrodon, a Triassic mammal of the family MorganucodontidaeAdapted from Crompton, A.W. & F.A. Jenkins, Jr., Biological Reviews 43 (1968): 427.
21Stem Mammals Dentary-squamosal jaw articulation Tabular bone absent in skullMedial wall of orbit enclosedDouble-rooted cheek teethCheek teeth include premolars and molars
22FIGURE 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.
23FIGURE 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.
24Stem Mammals Precise occlusion of cheek teeth Diphyodont dentition Mandibular symphysis reducedDerived features of soft tissuesMammary glands with teatsViviparitySeparate anal and urogenetal openingsDigastricus muscle lowers jaw
26Theria Tribosphenic molars Supraspinous fossa on scapula Cochlea spiraled
27Important Transformations Evolution of a new squamosal-dentary jaw jointArticular, quadrate, and angular bones of lower jaw detach and become part of ear apparatus (malleus, incus, and tympanic ring, respectively)
28Other Transformations Evolution of:More complex cusps on molarsSecondary palateFacilitated sucklingParasagittal movement of limbs (more mammalian limb posture)Endothermy
29Early Mammals Small bodied (e.g. 20–30 grams) Premolars and molars in cheek teethLarge brain sizeProbably insectivorous dietProbably nocturnal and arborealLactation and suckling likely
31Mesozoic Multituberculates Herbivorous or omnivorousAppear in late JurassicFossil record spans 100 million yearsSimilar in appearance to rodents2 or 3 incisors above and 2 on bottomDiastemaMassive, blade-like lower premolars
32FIGURE 16: Ptilodus (order Multituberculata) skull MultituberculatesFIGURE 16: Ptilodus (order Multituberculata) skullModified from Romer, A.S. Vertebrate Paleontology. University of Chicago Press, 1966.
34Multituberculates Some retained cervical ribs Unusual chewing mechanicsMultituberculates began to decline in late Paleocene—probably due to competition with condylarths, early primates, and rodents
35Cretaceous MammalsMetatherians and eutherians evolved from a clade of Mesozoic mammalsAngular process on dentaryTribosphenic molarsLower molars have talonid in some forms
36Cretaceous MammalsFIGURE 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.
38Cretaceous MammalsMuch biotic interchange between continents in Jurassic—sets the stageFlowering plants become dominant floraInsects radiate with flowering plants in CretaceousDinosaur fauna begins to declineMammal faunas begin to radiate