Mammal characteristics

Soft anatomy

Skin glands(sweat, scent, sebaceous)

Lactation

Hair

Diaphragm

4-chambered heart

High metabolic rate

Hard anatomy (i.e., in fossil record)

Three ear ossicles

Single bone in mandible

Complex teeth (heterodont & diphyodont)

Trirachodon Cynognathus

Therapsida – advanced cynodonts

Probainognathus

Jaw evolution – pelycosaur to mammal

Secondary Palate

Secondary Palate

Procynosuchus Probainognathus CanisPrimitive cynodont advanced cynodont modern mammal

premaxilla

maxilla

palatine

PELVIS & HIND LIMB

Posterior Lateral

Pelycosaur

Dimetrodon

Therapsid Thrinaxodon

HEAD ARTICULATION occipital atlas - axix condyle

Pelycosaur

Dimetrodon

Therapsid Thrinaxodon

Mammal

Felis

Feeding1) expansion of temporal opening, elaboration of

jaw muscles2) reduction in post-dentary jaw bones, “second”

jaw articulation3) tooth specialization (heterodonty)

Breathing1) secondary palate2) reduction in lumbar ribs, formation of ribcage (& diaphragm?)3) nasal turbinals (temp. & water conservation)

Posture & locomotion1) double occipital condyle, atlas & axis2) enlargement of limb girdles3) specialization of lumbar & sacral regions4) vertical orientation of limbs5) formation of a heel bone

Hearing 1) reduced size & flexible attachment of post-

dentary 2) reduction in size of stapes

MAMMALIAN “GRADE” TRENDS IN CYNODONTS

LOBE-FIN AMPHIBIAN PELYCOSAURFISH

MAMMAL

AMPHIBIAN

CYNODONT

Evolution of the ear

Synapsids -- size and position of stapes

Sphenacodont pelycosaurs

Advanced cynodonts

Synapsids – reduction of post-dentary jaw elements (lateral views)

Dimetrodon primitive theriodont

primitive advanced cynodont cynodont

Morganucodon primitive therian

Therapsid – mammal ear transition

Sorex (Recent shrew) – ear region

TYMPANIC(angular)

MALLEUS (articular)

Synapsids -- jaw machanics

Trithelodont (Ictidosaur)

Jaw mechanics - development of double articulation

Early mammal (or proto-mammal?) Morganucodon (late Triassic)

MORGANUCODONTS vs ADVANCED CYNODONTS

CONTRASTS BETWEEN LATE TRIASSICVERTEBRATES

EARLY DINOSAURS medium-large sizedherbivores & carnivoresprobably diurnal, some endothermic

CROCODILESsmall-medium sized, carnivores

LATE THERAPSIDSSmall-medium sized, probably nocturnalherbivores (tritylodonts) insectivores (ictidosaurs)carnivores (cynodonts)

EARLY MAMMALSVery smallInsectivoresprobably nocturnal, endothermic

Coelophysis (carnivorous dinosaur)

Tritylodon (herbivorous therapsid)

Morganucodon(insectivorous “mammaliaform”)

3 meters

1 meter

10 cm

Plateosaurus(herbivorous dinosaur)

10 meters

LATE TRIASSIC VERTEBRATES

Late Permian (250 mya)

Late Triassic (210 mya)

Pelycosaurs& early therapsids

(worldwide)

Cynodonts(worldwide)

Earliest mammals(Laurasia)

Late Jurassic (150 mybp)

Late Cretaceous (70 mybp)

Diversification ofearly mammals

(Eurasia & N. Amer.)

Origin & diversification of

therians(worldwide)

Isolation of southerngroups