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See geology/time.htm

See http://geology.com/time.htm. Monotremes. Metatherians. Eutherians. Node - Divergence Event Branch - Common Ancestor. Captorhinomorphs- 350 MYBP (Carboniferous). Synapsids- 320 MYBP. Synapsida: ‘Together Arch’. anapsid. synapsid.

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See geology/time.htm

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  1. See http://geology.com/time.htm

  2. Monotremes Metatherians Eutherians

  3. Node - Divergence Event Branch - Common Ancestor

  4. Captorhinomorphs- 350 MYBP (Carboniferous) Synapsids- 320 MYBP

  5. Synapsida: ‘Together Arch’ anapsid synapsid j: jugalp : parietalpo : postorbitalsq : squamosal

  6. Pelycosaurs Dimetrodon

  7. Early Therapsids Lycaenops

  8. Cynodonts*: Advanced Theraspids (*’dog teeth’) Cyognathus

  9. ~250 MYA

  10. Mammalian classification (especially fossil-based): The ‘key character’ approach Ovis aries Dixeya (a late therapsid) Q-A vs. D-S jaw joint- the defining ‘key character’ for 80 years

  11. Using a ‘Key Character approach’…Morganucodontids as first mammals? Q-A D-S ~250 MYA

  12. Probainognathus Diarthrognathus

  13. Shift to a ‘Suite of Characters’ approach… (Feldhammer et al.) 1) D-S jaw joint 2) Strongly heterodont dentition

  14. Shift to a ‘Suite of Characters’ approach… (Feldhammer et al.) 3) Molars with occlusion, complex surface, wear facets 4) Alternate side chewing

  15. Shift to a ‘Suite of Characters’ approach… (Feldhammer et al.) 5) Well developed inner ear (Petrosal)

  16. Shift to a ‘Suite of Characters’ approach… (Feldhammer et al.) 6) Small 7) Axial skeleton (dorso-ventral flexion, thoracic rib placement)

  17. And… based on a ‘suite of characters’ approach, where does the mammal/non-mammal division lie? ~250 MYA

  18. Both approaches (‘Key character’, ‘Suite of Characters’) are referred to as ‘Grade-based’ definitions Problems? • Evolution is a continuum (many transitional fossils) • Traits evolve at multiple locations on phylogeny

  19. Reptilia Archosauria • Reptiles- a grade based definition • Scales • Lack of feathers • Lack of hair Possible common traits of members of Archosauria?

  20. Our definition… clade-based to the Morganucodontid node • ***Mammal-like fossils (e.g. Sinocondon) can be referred to as Mammaliaformes ~250 MYA

  21. Reasons behind evolution of Mammalian characters? • Unknowable- can only be inferred, hypothesized • Many hypotheses exist… we’ll look at one • The Size-Refugium hypothesis

  22. Size-Refugium hypothesis, cont. Size: an animals squared dimension Volume: an animal’s cubed dimension • Radius = 5 • Surface area = 314 • Volume = 355 • Size/volume = 0.88 • Radius = 10 • Surface area = 1256 • Volume = 2842 • Size/volume = 0.44 • S/V ratio decreases as organisms gain body size • Lower S/V ratio equates to lower thermal inertia

  23. Size-Refugium hypothesis, cont. Early therapsids were large, and therefore were ectothermic homeotherms (gigantothermy) The Size-Refugium hypothesis posits a physiological adaptation over ~ 100 million years of large size

  24. *** Size-Refugium hypothesis, cont.

  25. Evolutionary consequences of endothermy

  26. Evolutionary consequences of endothermy Behavioral Implications Loris tardigradus Exploitation of marginal environments

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