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Trait Pelycosaurs Therapsids Cynodonts Posture: sprawling intermediate upright

Trait Pelycosaurs Therapsids Cynodonts Posture: sprawling intermediate upright Teeth: weakly heterodont increasingly heterodont strongly hetero Palate: no secondary palate partial complete “-apsidy” small temporal fenestra enlarged fenestra vastly expanded

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Trait Pelycosaurs Therapsids Cynodonts Posture: sprawling intermediate upright

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  1. TraitPelycosaursTherapsidsCynodonts Posture: sprawling intermediate upright Teeth: weakly heterodont increasingly heterodont strongly hetero Palate: no secondary palate partial complete “-apsidy” small temporal fenestra enlarged fenestra vastly expanded Postdentary bones: present, large present, reduced absent greatly reduced

  2. cynodonts Mammaliamorpha (transition to dentary-squamosal joint begins) Mammaliaformes (formation of dentary-squamosal “single jaw hinge” complete) Mammalia: All descendants from the MRCA of living mammals.

  3. Mammalia Mammaliaformes Mammaliamorpha

  4. Mesozoic Morganucodon Paleozoic Mammalia (and some mammaliaforms) • Completion of dentary-squamosal jaw joint • Cheekteeth divided into premolars and molars • Diphyodonty • BUT TINY! For 170 million years!

  5. cynodonts Mammaliamorpha Mammaliaformes Mammalia: All descendants from the MRCA of living mammals.

  6. Multituberculates (extinct prototherians) Late Jurassic-Mid. Miocene (ca. 150 m.y.) Diverse, found on all continents Ever-growing lower incisors, plagialacoid (blade-like) molariform teeth Outcompeted to extinction? (rodents, early primates...)

  7. (INFRACLASSES) Prototheria (SUBCLASS) Metatheria Eutheria Theria (SUBCLASS) Mammalia (CLASS) Mammaliaformes Mammaliamorpha

  8. Extant mammalian diversity Class MAMMALIA Subclass Prototheria Subclass Theria Infraclass Metatheria 1 Order (Monotremata) 2 Families 3 5 species 7 Orders 19 21 Families 272 331 species xx x xxx Infraclass Eutheria xx 18 21 Orders 114 130 Families 4354 5078 species xxx xxxx

  9. The radiation of placental mammals Since end of Mesozoic, placental (eutherian) mammals dominant terrestrial vertebrates on all continents except Australia and Antarctica. When and why did this diversification occur?

  10. “Age of Mammals” K/T boundary “Age of Dinosaurs”

  11. K/T boundary

  12. Most/all eutherian orders originated & diversify AFTER K/T (traditionally, fossils supported this) Orders originate BEFORE K/T but don’t diversify until AFTER K/T (more recently discovered fossils support) Most orders originate & diversify BEFORE K/T (older molecular studies support)

  13. Subclass Prototheria 1 Order (Monotremata) 2 Families Tachyglossidae (echidnas or “spiny anteaters”) 4 species. Ornithorhynchidae (platypus) 1 species

  14. Subclass Prototheria Few fossils, never very diverse. BUT PERSISTED. Echidnas: fossils from 55-60 Mya, oldest in S. AMERICA Platypus: fossils from 120 Mya, oldest in AUSTRALIA (Paleocene fossils in S. AMERICA). Many plesiomorphic features, but some apomorphies.

  15. Subclass Prototheria SKULL FEATURES: •No teeth in living adults BUT fossil platys & living neonates have, then lose. LOSS=apomorphy •No lacrimals (APOMORPHY) •Cranial sutures fused, indistinct (APOMORPHY) •Jugal reduced or absent (APOMORPHY)

  16. Subclass Prototheria SKELETAL FEATURES: •Epipubic bones present, large (PLESIOMORPHY) •Cervical ribs (PLESIOMORPHY) •Horny, hollow spur on inside of ankle (APOMORPHY) •Pectoral girdle with large precoracoids, coracoids, interclavicle (PLESIOMORPHY) •Skeleton sprawling, “reptilian” (PLESIOMORPHY) BUT, good for swimming, digging.

  17. Warren et al. (2008). Nature 453, 175-183.

  18. Subclass Prototheria OTHER FEATURES: •Pouch (echidnas only) •Testes permanently abdominal (no scrotum) •Uteri fused •Leathery egg with nutrient-rich yolk •Rostrum lacks vibrissae, elongate •cloaca (but...) •Endothermic, but low Tb and metabolic rates •Electroreception (snout), including echidnas

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