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Trait Pelycosaurs Therapsids Cynodonts Posture: sprawling intermediate upright Teeth: weakly heterodont increasingly heterodont strongly hetero Palate: no secondary palate partial complete “-apsidy” small temporal fenestra enlarged fenestra vastly expanded

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TraitPelycosaursTherapsidsCynodonts

Posture: sprawling intermediate upright

Teeth: weakly heterodont increasingly heterodont strongly hetero

Palate: no secondary palate partial complete

“-apsidy” small temporal fenestra enlarged fenestra vastly expanded

Postdentary bones: present, large present, reduced absent

greatly reduced


cynodonts

Mammaliamorpha (transition to

dentary-squamosal joint begins)

Mammaliaformes

(formation of dentary-squamosal

“single jaw hinge” complete)

Mammalia: All descendants from

the MRCA of living mammals.


Mammalia

Mammaliaformes

Mammaliamorpha


Mesozoic

Morganucodon

Paleozoic

Mammalia (and some mammaliaforms)

  • Completion of dentary-squamosal jaw joint

  • Cheekteeth divided into premolars and molars

  • Diphyodonty

  • BUT TINY! For 170 million years!


cynodonts

Mammaliamorpha

Mammaliaformes

Mammalia: All descendants from

the MRCA of living mammals.


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...)


(INFRACLASSES)

Prototheria (SUBCLASS)

Metatheria

Eutheria

Theria

(SUBCLASS)

Mammalia (CLASS)

Mammaliaformes

Mammaliamorpha


Extant mammalian diversity
Extant mammalian diversity

Class MAMMALIA

Subclass Prototheria

Subclass Theria

Infraclass Metatheria

1 Order (Monotremata)

2 Families

3 5 species

7 Orders

19 21 Families

272 331 species

xx

x

xxx

Infraclass Eutheria

xx

18 21 Orders

114 130 Families

4354 5078 species

xxx

xxxx


The radiation of placental mammals
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”

K/T boundary

“Age of Dinosaurs”


K/T

boundary


Most/all eutherian orders originated & diversify

AFTER K/T

(traditionally, fossils supported this)

Orders originate BEFORE K/T but don’t diversify until

AFTER K/T

(more recently discovered fossils support)

Most orders originate & diversify BEFORE K/T

(older molecular studies support)


Subclass Prototheria

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

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


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