Earth Sciences 2266F/G Lecture Notes - Lecture 24: Incus, Zygomatic Arch, Occipital Condyle
3 Apr 2020
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Early Mammals
• surviving cynodont lead to the development of true mammals
Mammal: warm-blood vertebrate that possess hair/fur and female secrete milk, live young
- useful for modern day mammals not for fossil study
Transition from Therapsida to Mammals
• cynodontia were advance therapsids and acquired characteristics that are considered
mammal like
• flaring of zygomatic arch to accommodate large coronoid process
• double occipital condyle
• secondary palate to separate breathing (eat/breath at the same time)
Modification of Jaw
Pelycosaur: multiple bones in lower jaw
Early Therapsid: back bones are reduced
Cynodont: expansion of corticoid process
Early Mammals: continue expansion for better bite, jaw modification (earbone)
Jaw to Ear
• going from basal synapids to therapsid to mammals
• start with attachment at articulate and quadrate bone which migrate into 2 joints and
finally have joint b/w dentary and squamosal
→migrate hinge area from lower skull to higher up
-angular becomes ectotympanic to hold eardrum
-articular becomes malleus (hammer)
-quadrate becomes incus (anvil)
-stapes remains the same
*develop of stronger bite and middle ear became stimulatously
Basal Mammals
1. Small bodies danger of heat loss →development of fur
2. Insect diet would favour complex teeth for crushing exoskeleton
3. Nocturnal lifestyle led to heightened olfactory
4. Nocturnal favour ability to see in dim light
Mammal Teeth
• double-rooted, molar like cheek teeth
• milestone with development of tribosphenic molar (cutting & crushing)
• triangulation of cusp:
-distinct chew/grind (foreward/backward & up/down)
Document Summary
Early mammals: surviving cynodont lead to the development of true mammals. Mammal: warm-blood vertebrate that possess hair/fur and female secrete milk, live young. Useful for modern day mammals not for fossil study. Early mammals: continue expansion for better bite, jaw modification (earbone) Jaw to ear: going from basal synapids to therapsid to mammals, start with attachment at articulate and quadrate bone which migrate into 2 joints and finally have joint b/w dentary and squamosal. Migrate hinge area from lower skull to higher up. *develop of stronger bite and middle ear became stimulatously. Basal mammals: small bodies danger of heat loss development of fur, insect diet would favour complex teeth for crushing exoskeleton, nocturnal lifestyle led to heightened olfactory, nocturnal favour ability to see in dim light. Mammal teeth: double-rooted, molar like cheek teeth, milestone with development of tribosphenic molar (cutting & crushing) triangulation of cusp:
