Exam 5

Question 1

Explain the origin of mammals:

Answer 1

• evolved from Synapsids, a group of amniotes, during the Late Paleozoic Period.

Synapsids = a group of amniotes w/ 1 temporal fenestra.

Question 2

What events opened the door for the radiation of mammals?

Answer 2

• climate drying, loss of O2 in the atmosphere leads to non-mammalian synapsids to take over.
• Cretaceous-Paleogene Extenction (66mya) wipes out 75% of species, opening the door for mammals as they could adapt easier to the global changes.

Question 3

Mammal

Answer 3

milk-producing endotherms.

Question 4

What are the unique characteristics of mammals?

Answer 4

• nourish young w/ milk.
• viviparous (exception w/ monotremes).
• hair.

monotremes =mammals that lay eggs.
NOT ALL MAMMALS HAVE THESE TRAITS

Question 5

What are the defining features of mammals?

Answer 5

• mammary glands.
• endothermy.

Question 6

How did mammalian characteristics evolve from Synapsids?

Answer 6

a single temporal fenestrae.

Question 7

How did mammalian characteristics evolve from Therapsids?

Answer 7

• upright limb posture due to wrist/ankle joints.
• differentiated teeth (homodont to heterodont)
• loss of some trunk ribs.

Question 8

How did mammalian characteristics evolve from Cycodonts?

current understanding to be all modern mammalian ancestor

Answer 8

• secondary palate to allow breathing while CHEWING.
• loss of lumbar ribs, gain diaphragm for respiration.
• calcaneum becomes heel for flexion.
• pelvis/pectoral girdle brings the limbs under the body.
• flexible wrist joint for grasping.
• JAW CHANGES

Question 9

What were the changes to the jaw structure in mammalians?

Answer 9

• lower jaw is now a single bone, DENTARY.
• jaw attaches between the dentary and squamosal bones (previously quadrate and articular).
• quadrate and articular become moddle ear bones (stapes, incus, malleus).
• increase in jaw muscles (move on multiple planes).