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Orders originate BEFORE K/T but don’t diversify untilAFTER K/T
(more recently discovered fossils support)
Most orders originate & diversify BEFORE K/T(older molecular studies support)
1 Order (Monotremata) 2 Families
Tachyglossidae (echidnas or “spiny anteaters”)4 species.
Ornithorhynchidae (platypus)1 species
Subclass Prototheria
Few fossils, never very diverse. BUT PERSISTED.
Echidnas: fossils from 55-60 Mya, oldest in S. AMERICA
Platypus: fossils from 120 Mya, oldest in AUSTRALIA(Paleocene fossils in S. AMERICA).
Many plesiomorphic features, but some apomorphies.
Subclass Prototheria
SKULL FEATURES:
•No teeth in living adults BUT fossil platys & living neonates have, then lose. LOSS=apomorphy•No lacrimals (APOMORPHY)•Cranial sutures fused, indistinct (APOMORPHY)•Jugal reduced or absent (APOMORPHY)
Subclass Prototheria
SKELETAL FEATURES:•Epipubic bones present, large (PLESIOMORPHY)•Cervical ribs (PLESIOMORPHY)•Horny, hollow spur on inside of ankle (APOMORPHY)•Pectoral girdle with large precoracoids, coracoids, interclavicle (PLESIOMORPHY)•Skeleton sprawling, “reptilian” (PLESIOMORPHY) BUT, good for swimming, digging.
Subclass Prototheria
Warren et al. (2008). Nature 453, 175-183.
OTHER FEATURES:•Pouch (echidnas only)•Testes permanently abdominal (no scrotum)•Uteri fused•Leathery egg with nutrient-rich yolk•Rostrum lacks vibrissae, elongate•cloaca (but...)•Endothermic, but low Tb and metabolic rates•Electroreception (snout), including echidnas