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)
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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”
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