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Evolution and Diversity of Early Mammals: A Comprehensive Overview

Explore the fascinating world of early mammals, from Morganucodontids to Monotremes. Learn about their unique characteristics, evolutionary paths, and significant fossil records. Uncover the diverse lineages and key traits that define these primitive and derived species.

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Evolution and Diversity of Early Mammals: A Comprehensive Overview

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  1. Early Mammals: Morganucodontids Morganucodon

  2. Early Mammals: Triconodonts • Till recently, known only from teeth and a few other skeletal fragments. • Similar to Morganucodontids, except the cusps are linear. Jeholodens

  3. Triconodonts cont., Jeholodens • Discovered in China a few years ago • Mammalian pectoral girdle • (scapula and clavicle only– loss of coracoids and interclavicle) • Pelvic girdle is still ancestral • ilium, ischium and pubis are separate, epipubic bones are present. • Sprawling posture – limbs not rotated under body. • Demonstration of mosaic evolution. • pectoral girdle is derived, but the pelvic girdle is primitive.

  4. Triconodonts cont., Repenomamus giganticus

  5. Early Mammals: Multituberculates Kryptobataar.

  6. Multituberculates cont. Ptilodus

  7. Early Mammals: Pantotheres • Paraphyletic- used informally • Mid Jurassic • Earliest bifunctional teeth - single cheek tooth with grinding and shearing function. • Tribosphenic molars, ( primitive tooth type for living mammals)

  8. Early Mammals: Recent finds Bishops, Ausktribosphenos

  9. Prototheria Eutherians Metatherians Pantotheres Trichodonts Multituberculates Monotremes Morganucodontids

  10. Monotremes

  11. Monotremes: Fossil Record Archer et al 1985 • Steropodon galmanii • 125 MYA (Lightning Ridge sandstone deposits, New South Wales) • Teeth resemble those of a juvenile platypus • Second find- Kollikodon ritchiei, 1995, suggests diversification by early Cretaceous

  12. Monotremes: Fossil Record cont. • Tertiary Fossils • Obdurodon insignis (1970), O. dicksoni (Archer 1992) • Miocene • Kept teeth at maturity • May have been terrestrial • Megalibgwiliaramsayi (Griffiths 1991), Zaglossus hacketti • Giant echidnas • Z. hacketti = largest monotreme ever

  13. Monotreme origins and distribution: Paleocene platypus tooth discovered in Argentina (Pascual, 1992)

  14. Monotremes • Often called ‘primitive’… a misnomer • Mosaics of primitive and derived traits Tachyglossus - short-beaked echidna

  15. Monotremes: Primitive characters

  16. Monotremes: Primitive characters Reproductive characters

  17. Monotremes: Derived characters

  18. Tachyglossidae- Echidnas (2 G, 2 s)

  19. Tachyglossidae- continued Tachyglossus aculeatus Atelerix frontalis Zaglossus bruijni

  20. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences No. 1372, Platypus Biology: Recent Advances and Reviews, Jul. 29, 1998, pp. 1057-1238 Ornithorhynchidae (Platypus) Ornithorhynchus

  21. Ornithorhynchidae (Platypus) Ornithorhynchus

  22. Grant et al 1998

  23. Grant et al 1998

  24. Grant et al 1998

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