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Morganucodon
Early Mammals: Morganucodontids
Jeholodens
Early Mammals: Triconodonts
•Till recently, known only from teeth and a few other skeletal fragments.
•Similar to Morganucodontids, except the cusps are linear.
• 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.
Triconodonts cont., Jeholodens
Repenomamus giganticus
Triconodonts cont.,
Kryptobataar.
Early Mammals: Multituberculates
Ptilodus
Multituberculates cont.
Paraphyletic- used informally
•Mid Jurassic
•Earliest bifunctional teeth - single cheek tooth with grinding and shearing function.
•Tribosphenic molars, ( primitive tooth type for living mammals)
Early Mammals: Pantotheres
Bishops, Ausktribosphenos
Early Mammals: Recent finds
Morganucodontids
Monotrem
es
Trichodonts
Multituberculates
Pantotheres
Metatherians
EutheriansPrototheria
Monotremes
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
Archer et al 1985
Monotremes: Fossil Record
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
Monotreme origins and distribution: Paleocene platypus tooth discovered in Argentina (Pascual, 1992)
Monotremes
Often called ‘primitive’… a misnomer
•Mosaics of primitive and derived traits
Tachyglossus - short-beaked
echidna
Monotremes: Primitive characters
Monotremes: Primitive characters
Reproductive characters
Monotremes: Derived characters
Tachyglossidae - Echidnas (2 G, 2 s)
Tachyglossidae - continued
Atelerix frontalis
Zaglossus bruijni
Tachyglossus aculeatus
Ornithorhynchidae (Platypus) Ornithorhynchus
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
Grant et al 1998
Grant et al 1998
Grant et al 1998