Early Amniotes and Move onto Land

Question 1

What are some defining characteristics of the early amniotes?

Answer 1

• small, ~20cm long
• ossified, lizard-like skeleton
• modified jaws, neck, teeth for predation
• evolved early-mid carboniferous

Question 2

What are the two major groups within the amniotes?

Answer 2

• synapsids (mammals)

- sauropsids (reptiles and birds)

Question 3

What two groups are within the sauropsids (reptiles and birds)?

Answer 3

• anapsids

- diapsids (lepidosaurs: lizards and snakes, archosaurs: dinosaurs, birds, crocs)

Question 4

Which group do turtles fit into?

Answer 4

• still debated

- could be anapsid or diapsid within the sauropsids

Question 5

What are features of the amniote/cleidoic egg?

Answer 5

• semi permeable shell, allows gas exchange but keeps fluids inside
• extra embryonic membranes, protects and allows gas transfer
• won’t dry out if laid on land/in dry environment

Question 6

Briefly describe the extra embryonic membranes

Answer 6

• amnion surrounds embryo with water
• chorion surrounds embryo and yolk sac
• allantois fills with waste as yolk proteins are used

Question 7

What’s the significance of the cleidoic egg?

Answer 7

• removes larval stage, organism develops on land
• being on land=more efficient respiration
• embryo can become larger before hatching, more energy invested per egg

Question 8

How is dessication prevented in amniotes?

Answer 8

• low skin permeability
• greater variation in skin
• lipids and keratin

Question 9

Briefly describe the derived characteristic of ventilation in amniotes

Answer 9

• aided by ribs
• allows for long neck, able to draw air through long tube
• space for elaboration of nerves supplying forelimb

Question 10

T or F: increased weight (gravity) on land requires light skeletons that aren’t very strong/stiff

Answer 10

False, increased weight required stronger and stiffer skeletons to support the body

Question 11

Briefly describe features of the amniote axial skeleton

Answer 11

• lumbar ribs lost in some
• no ribs in the way of hindlimb fwd movement
• allows vertical plane flexion; easier limb oscillation, faster
• reduced centra and processes

Question 12

What are two joints that are important for head movement in the amniotes?

Answer 12

• skull&atlas joint: for vertical nodding and horizontal tilting
• atlanto-axial joint: for twisting movement

Question 13

What are some features of the vertebral column that aid in body support?

Answer 13

-body suspended between legs
-vertebral column=bridge, arch for support
-trunk vertebrae held in arch by abdominal muscles and sternum
cervical vertebrae held in arch by neck ligaments
-hip acts as fulcrum, balances heavy parts against each other
-vertebrae tied together by ligaments

Question 14

List and briefly explain the different categories of temporal fenestrae

Answer 14

Anapsid: no temporal fenestrae (in earliest amniotes, turtles)
Synapsid: one lower temporal fenestrae (in extincy synapsids and mammals)
Diapsid: two temporal fenestrae (in reptiles, birds, dionsaurs)