Lecture Eighteen - Animal diversity IV

Question 1

Explain the evolution of tetrapods.

Answer 1

Gnathostomes (jawed vertebrates) with limbs. 
Around 365 mya. 
Developed a neck. 
Stronger vertebral column. 
Ribs. 
Supporting girdles.

Question 2

Describe the class of Amphibia.

Answer 2

External fertilisation (female lays egg and male then inserts sperm).
- Lay eggs in water. 
Larvae are aquatic. 
- Gills. 
- Finned tail. 
Adults: 
- Legs. 
- Lungs. 
- Often terrestrial. 
- Carnivorous. 
- Gas exchange through skin. 
- Moist habitats.

Question 3

What orders are in the Amphibia class?

Answer 3

Urodela (tailed ones):

• Salamanders and newts.
• Mostly aquatic.
• Paedomorphosis.

Anura (tail-less ones):

• Frongs and toads.
• More terrestrial.
• Legs for jumping.

Apoda (leggless):

• Caecilians.
• Tropical.
• Burrowing.
• Look like snakes.

This order is under threat.

Question 4

What terrestrial adaptations have the Amniotes undergone?

Answer 4

Amniotic egg:

• Amnion (the innermost membrane that encloses the embryo of a mammal, bird, or reptile and acts as cushioning).
• Allantois (the fetal membrane lying below the chorion used for gas exchange, waste storage and becomes the bladder).
• Chorion (the outermost membrane surrounding an embryo of a reptile, bird, or mammal and used for gas exchange - is the egg shell).
• Enlarged yolk sac (storage of nutrients).

Thicker skin:

• Reduced water loss.
• Keratin (scales, hair, feathers, claws and hoofs.)
• No gas exchange though skin.

Question 5

How are birds dependants of dinosaurs?

Answer 5

Highly modified reptiles. 
Survived K-T extinction 65.5 mya. 
Adaptations include: 
- Toothless beak. 
- Wings. 
- Feathers. 
- Modified breastbone (sternum). 
- Reduced weight (hollow-ish bones). 
Most species of tetrapods.

Question 6

Describe the class of Mammalia.

Answer 6

Produce milk (mammary glads). 
Hair (thermal, sensory and protection) and subcutaneous fat (thermal isolation). 
Differentiating teeth. 
Endothermic - can be active at night. 
Larger brains relative to body size. 
Originate 200 mya, originally quite small. 
Three groups: 
- Monotremes (egg-laying mammals). 
- Marsupials (pouched mammals). 
- Eutheria (placental mammals).

Question 7

Describe reproduction in mammals.

Answer 7

Monotremes (egg-laying mammals):

• Lay eggs.
• Milk through skin (no nipples).
• Only in Australia (and PNG).

Marsupials (pouched mammals):

• In Australia and America.
• Simple (yolk sac) placenta.
• Short gestation (process or period of developing inside the womb between conception and birth) and feeding (lactation) in pouch.

Eutheria (placental mammals):

• Worldwide.
• Complex (yolk sac + allantois) placenta.
• Long gestation period.

Question 8

Describe the characteristics of Primates.

Answer 8

Combination fo characteristics:

• Hands and feet for grasping.
• Flat nails (not claws).
• Short jaws (face).
• Relatively large brains.
• Forward looking eyes.
• Opposable thumbs.
• Parental care and social behaviours.

Question 9

Describe the characteristics of Hominins.

Answer 9

Specific characteristics did not evolve in unison:

• Reduced canine teeth and flat face.
• Upright position and bipedal gate.
• Dextrous hand and tool use.
• Less hair.
• Large brain.