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)
Secondary Palate
Procynosuchus Probainognathus CanisPrimitive cynodont advanced cynodont modern mammal
premaxilla
maxilla
palatine
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
Synapsids – reduction of post-dentary jaw elements (lateral views)
Dimetrodon primitive theriodont
primitive advanced cynodont cynodont
Morganucodon primitive therian
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)