Morganucodon

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Early Mammals Morganucodontids
Morganucodon
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Early Mammals Triconodonts

• Till recently, known only from teeth and a few
  other skeletal fragments.
• Similar to Morganucodontids, except the cusps are
  linear.

Jeholodens
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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.

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Triconodonts cont.,
Repenomamus giganticus
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Early Mammals Multituberculates
Kryptobataar.
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Multituberculates cont.
Ptilodus
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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)

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Early Mammals Recent finds
Bishops, Ausktribosphenos
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Prototheria
Eutherians
Metatherians
Pantotheres
Trichodonts
Multituberculates
Monotremes
Morganucodontids
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Monotremes
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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

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Monotremes Fossil Record cont.

• Tertiary Fossils
• Obdurodon insignis (1970), O. dicksoni (Archer
  1992)
• Miocene
• Kept teeth at maturity
• May have been terrestrial

• Megalibgwilia ramsayi (Griffiths 1991),
  Zaglossus hacketti
• Giant echidnas
• Z. hacketti largest monotreme ever

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Monotreme origins and distribution Paleocene
platypus tooth discovered in Argentina (Pascual,
1992)
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Monotremes

• Often called primitive a misnomer
• Mosaics of primitive and derived traits

Tachyglossus - short-beaked echidna
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Monotremes Primitive characters
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Monotremes Primitive characters
Reproductive characters
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Monotremes Derived characters
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Tachyglossidae - Echidnas (2 G, 2 s)
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Tachyglossidae - continued
Tachyglossus aculeatus
Atelerix frontalis
Zaglossus bruijni
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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
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Ornithorhynchidae (Platypus) Ornithorhynchus
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Grant et al 1998
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Grant et al 1998
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Grant et al 1998