Trait Pelycosaurs Therapsids CynodontsPosture: sprawling intermediateupright

Teeth: weakly heterodont increasingly heterodontstrongly hetero

Palate: no secondary palate partialcomplete

“-apsidy” small temporal fenestra enlarged fenestravastly expanded

Postdentary bones: present, large present, reducedabsent

greatly reduced

Mammaliaformes (formation of dentary-squamosal“single jaw hinge” complete)

Mammalia: All descendants fromthe MRCA of living mammals.

cynodonts

Mammaliamorpha (transition todentary-squamosal joint begins)

MammaliamorphaMammaliaformes

Mammalia

Morganucodon

•Completion of dentary-squamosal jaw joint•Cheekteeth divided into premolars and molars•Diphyodonty

•BUT TINY! For 170 million years!

Pal

eozo

icM

esoz

oic

Mammalia (and some mammaliaforms)

Mammaliamorpha

Mammaliaformes

Mammalia: All descendants fromthe MRCA of living mammals.

cynodonts

Multituberculates (extinct prototherians)

Late Jurassic-Mid. Miocene (ca. 150 m.y.)

Diverse, found on all continents

Ever-growing lower incisors,plagialacoid (blade-like)molariform teeth

Outcompeted to extinction? (rodents, early primates...)

MammaliamorphaMammaliaformes

Mammalia (CLASS)

Met

athe

riaM

etat

heria

Euth

eria

Euth

eria

Theria(SUBCLASS)

ProtoPrototheria (SUBCLASS)theria (SUBCLASS)

(INFRACLASSES)(INFRACLASSES)

Extant mammalian diversity

1 Order (Monotremata)2 Families3 5 species

Infraclass Metatheria

Infraclass Eutheria

7 Orders19 21 Families272 331 species

18 21 Orders114 130 Families4354 5078 species

Subclass Prototheria Subclass Theria

Class MAMMALIA

x xxxxx

xxxxx

xxxx

The radiation of placental mammals

Since end of Mesozoic, placental (eutherian) mammals dominant terrestrial vertebrates on all continents except Australia and Antarctica.

When and why did this diversification occur?

“Age of Mammals”

“Age of Dinosaurs”

K/T boundaryK/T boundary

K/TK/Tboundaryboundary

Most/all eutherian orders originated & diversifyAFTER K/T

(traditionally, fossils supported this)

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

Subclass Prototheria