L2 Mills - Mammal characteristics and Evolution

Question 1

How many Aortic arches did each have?

a) ancestral vertebrates
b) elasmobranchs

Answer 1

a) 6

b) 5

Question 2

Why might coexistence of early mammals with ‘ruling reptiles’ in Triassic and Jurassic periods favoured naturalism?

Answer 2

Predators are not at large at night

Question 3

How did nocturnalism lead to endothermy, insulation and hair?

Answer 3

Insulation is provided by hair due to cooler temperatures at night

Question 4

Why might nocturnalism increased brain size?

Answer 4

High activity rate at night requires sophisticated senses - leading to a large brain size

Question 5

What gland by the eye produces waterproofing oil?

Answer 5

Harderian gland

Question 6

Explain the evidence for lactation having preceded and predisposed the evolution of precise occlusion and diphyodonty

Answer 6

If the need for teeth in early life is reduced (due to lactation) then the number of complete sets of teeth can be reduced

Question 7

What gland could have preceded the mammary gland?

Answer 7

Sebaceous glands may have secreted chemical signals for mother-young recognition and or immune protection - this then ingested by young

Sebaceous glands are associated with hair follicles, and mammary hair is retained in lower mammals

Question 8

What are the 2 types of Monotreme?

Answer 8

Platypus

Echnida

Question 9

Briefly describe the Platypus

Answer 9

• egg laying with extended maternal care; incubation followed by lactation via hair
• nest in burrows
• 2 eggs from a single functional left ovary
• 16 weeks maternal care
• temporary molars

Question 10

Briefly describe the Echnida

Answer 10

• 2 species in Australia and New Guinea

- lays single eggs and incubates the in a pouch (homoplastic/convergent evolution with marsupial condition)

Question 11

How many species of Marsupial are there and where are they found?

Answer 11

around 334 extant species

70% live in Australia, and the rest live in S.America and a few in North and Central America

Question 12

Marsupials have convergent evolution with Placental mammals on a large scale.

Give 3 examples of marsupials and their placental mammal equivalent

Answer 12

1. Thylacine - wolf
2. Wombat - groundhog
   - very low metabolic rate therefore a slow gut movement (cubic poo) don’t share food
3. Sugar glider - flying squirrel

Question 13

What does Monotreme mean?

Answer 13

Monotreme means ‘single hole’ – all urogenital and sexual activity though this

Testes are outside of the body wall

Question 14

What is the gestation period of marsupials like?

Answer 14

It is very short compared to monotremes (10-20 days) for example kangaroos do the majority of their growth in the pouch - different milk types

Paired vagina and bifid penis

Question 15

What are the mammary glands of monotremes and marsupials like?

Answer 15

monotremes = skin releases milk that collects via hairs

Question 16

What happens after the birth of marsupials

Answer 16

Birth through medial canal - young finds their own way into the pouch

Attach to a teat, secondary palate allowing simultaneous breathing and swallowing

Joeys have high protein low fat milk
Young kangaroos have low protein high fat milk

Question 17

What is Autopomorphy?

Answer 17

an autopomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon.

That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to the focal taxon