Trait
Pelycosaurs
Therapsids
Cynodonts
Teeth:
weakly heterodont
increasingly heterodont
strongly hetero
Palate:
no secondary palate
partial
complete
“-apsidy”
small temporal fenestra
enlarged fenestra
vastly expanded
present, reduced
absent
greatly reduced
Posture:
sprawling
Postdentary bones: present, large
intermediate
upright
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
Mammalia (and some mammaliaforms)
•Completion of dentary-squamosal jaw joint
•Cheekteeth divided into premolars and molars
•Diphyodonty
Mesozoic
•BUT TINY! For 170 million years!
Paleozoic
Morganucodon
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...)
Eutheria
Prototheria (SUBCLASS)
Metatheria
(INFRACLASSES)
Theria
(SUBCLASS)
Mammalia (CLASS)
Mammaliaformes
Mammaliamorpha
Extant mammalian diversity
Class MAMMALIA
Subclass Prototheria
1 Order (Monotremata)
2 Families
x3 5 species
Subclass Theria
Infraclass Metatheria
7 Orders
19 21 Families
xx
272 331 species
xxx
Infraclass Eutheria
18 21 Orders
xx
xxx
114 130 Families
xxxx
4354 5078 species
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.
Warren et al. (2008). Nature 453, 175-183.
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