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