BIOL 2003 Lecture Notes - Lecture 24: Arrector Pili Muscle, Sebaceous Gland, Synapsid
Synapsids
December 2-4, 2015
Synapsids – the fabulous furballs
• Include extinct lineages related to mammals
• Goes back to ancient split that occurred at same time of amniote split
• Outgroup: birds, turtles, crocodiles, lizards, snakes diapsid
Synapsids are distinguished by skull openings
• Anapsid – ancestral amniote (no holes behind dermal bones)
o Only contains orbit opening for the eye
• Synapsids – first seen 312 mya (end of Carboniferous) *same time as first known amniote (split
quickly)
o Lateral temporal opening
• Diapsid
o Dorsal and lateral temporal openings
Changes to Mammalian body plan:
• Changes associated with a more active lifestyle (locomotion, feeding, chewing)
• Movement:
o Strengthened ankle joint
o Elbows rotated back, knees forward
o Legs are brought underneath the body
o Abdominal ribs lost
• Feeding
o New jaw joint
o Enlarged temporal hold
o Complex cheek teeth (form a mating pair; are only replaced once)
▪ Associated with complex structure of teeth used for processing and breaking up
food efficiently
▪ Defined with basis of teeth (replacements)
o New ear
Mesozoic mammals (same time of dinosaurs): small, nocturnal, shrew/rodent like
• More mammal like specialized teeth, smaller body size, more active
• Mammals profited from dinosaur extinction
• May not be sensitive to colour – nocturnal lineages
• High metabolism – keep inside warmer than environment (hair)
Mammalian Marker
• Hair – may have originated before mammals *is NOT derived from scales
o Associated with dermal glands (sebaceous glands)
o Functions:
▪ Insulation (undercoat)
▪ Waterproofing (guard hairs)
▪ Camouflage
▪ Sensory bristles
o Membrane of cells are part of the mechanism regarding the movement of water
o Oil in skin waterproofing
o Goosebumps: hair follicle stands up via arrector pili muscle contractions (thermal regulatory
boundary) *uses = in cold, to make animals look bigger
o Sebaceous gland may be basis of mammary glands (secrete oil)
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Document Summary
Include extinct lineages related to mammals: goes back to ancient split that occurred at same time of amniote split, outgroup: birds, turtles, crocodiles, lizards, snakes diapsid. Synapsids the (cid:498)fabulous furballs(cid:499: anapsid ancestral amniote (no holes behind dermal bones) Synapsids first seen 312 mya (end of carboniferous) *same time as first known amniote (split. Synapsids are distinguished by skull openings: only contains orbit opening for the eye, lateral temporal opening, diapsid, dorsal and lateral temporal openings. Not in dogs panting (flow of air over tongue: ex. Rodents cover themselves in their own saliva to cool off. *birds don"t have sweat glands: evolved more than one in separate lineages, overheating: heat exhaustion or heat stroke. Changes to synapsid head: teeth at front of jaw. *ancestor to all mammals laid eggs: marsupials (metatheria, specialized for swimming, usually marine animals, sprawling in secondary, 3 species!
