BIOL 329 Lecture Notes - Lecture 28: Cynodont, Mammary Gland, Prototheria
6 May 2018
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Lect 28
2) theriodonts – dominant predators (late Permian – early Triassic). Coronoid process on dentary =
increased jaw strength.
Therapsids displaced by reptiles in the Triassic – largely extinct by end of the Triassic. Cynodonts showed
progressive reduction in body size throughout the Triassic – small groups persisted throughout the
Cretaceous. Jaws sculptured, heavily vascularized – face highly innovated with nerves, whiskers,
turbinate bones (in most endotherms). Possibly heterothermic or fully endothermic. 7 cervical vertebra.
First true mammals (late Triassic) evolved from small bodied cynodonts.
Cynodont-mammal transition
1) locomotion – lizards cannot run and breathe simultaneously (lateral undulations vs bounding
locomotion).
2) almost complete separation of nasal passages from the mouth
3) turbinate bones in all living endotherms
Evolution of mammalian endothermy:
Nasal turbinates reduce desiccation associated with high pulmonary ventilation rates. Respiratory
turbinals first appear in two groups of advanced therapsids = evolution of mammalian oxygen
consumption rates may
Nocturnality in synapsids predates the origin of mammals:
Early groups were nocturnal (in warm and cool areas of the globe). Nocturnality thought to be more
recently developed but in fact dates back to the origin of mammals (early-mid Paleozoic).
4) hair – suspected (whiskers)
5) lactation – probably not in cynodonts but occurred in first mammals. Requires major facial muscles
for generating a suction seal
6) dentary-squamosal jaw hinge: ability to hear is tied to the use of these bones present in early diapsids
and synapsids
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Document Summary
Lect 28: theriodonts dominant predators (late permian early triassic). Coronoid process on dentary = increased jaw strength. Therapsids displaced by reptiles in the triassic largely extinct by end of the triassic. Cynodonts showed progressive reduction in body size throughout the triassic small groups persisted throughout the. Jaws sculptured, heavily vascularized face highly innovated with nerves, whiskers, turbinate bones (in most endotherms). First true mammals (late triassic) evolved from small bodied cynodonts. Cynodont-mammal transition: locomotion lizards cannot run and breathe simultaneously (lateral undulations vs bounding locomotion), almost complete separation of nasal passages from the mouth, turbinate bones in all living endotherms. Nasal turbinates reduce desiccation associated with high pulmonary ventilation rates. Respiratory turbinals first appear in two groups of advanced therapsids = evolution of mammalian oxygen consumption rates may. Nocturnality in synapsids predates the origin of mammals: Early groups were nocturnal (in warm and cool areas of the globe).
