Mammalia

Question 1

Summary

Mammals evolved from

Answer 1

1. synapsids

dentary-squamosal jaw articulation

three bones in inner ear

teeth with prismatic enamel which are shed a maximum of once

fur

milk production

Question 2

Summary

Three modern groups

Answer 2

Monotremes
Marsupials
Placentals

Question 3

What is a mammal?

Answer 3

1. A synapsid amniote

2. Class Mammalia contains all living descendants of the Synapsida

Question 4

Synapsida: “Pelycosauria”

4 points

Answer 4

1. Mostly Permian
2. 308 to 260 Mya
3. Paraphyletic taxon of basal synapsids
4. Lack epidermal scales; have osteoderms and scutes instead

Question 5

Synapsida: Therapsida

7 points

Answer 5

1. Late Permian to Triassic
   275 Mya to present (or 100 Mya for non-mammalian therapsids)
2. Taxon of advanced synapsids
3. (Mostly) erect gait
4. Large temporal fenestra
   increases bite force
5. Differentiated teeth
   incisors, canines, molars [needed for different purposes]
6. Endotherms (probably) [warm blooded]
7. Cynodonts gave rise to the mammals

Question 6

Mammalia: Definition

8 points

Answer 6

Synapsids with:
1. A dentary-squamosal jaw articulation

2. Middle ear with a chain of three bones
3. Tooth replacement occurs once (or not at all) [unlike diapsid which has constant replacement]
4. Prismatic enamel on teeth
5. Occlusion between upper/lower molars [Teeth fit together. Tight articulation]
6. Two occipital condyles at the base of the skull
7. Sweat glands, including those specialised to produce milk [characteristic of modern mammals]
8. Hair or fur (possibly older than mammals)
9. First mammal was Sinoconodon in early Jurassic (193 Mya)

Question 7

Body plan

Answer 7

1. Seven cervical vertebrae [vertebrae in the kneck. Not universal but vast majority of mammals]
2. Three skin layers (epidermis, dermis, hypodermis)
3. Vocal folds in larynx
   allow sounds other than hissing
4. Fur
   Insulation [key reason], protection, sensory [whiskers], waterproofing, camouflage [sexual markings and identification, recognising opposite sex]
5. Milk

Question 8

Respiration

2 points

Answer 8

1. Lungs are spongy

2. diaphragm divides thorax from abdomen [can just use ribs to breath]

Question 9

Circulation

2 points

Answer 9

1. Four-chambered heart

2. Complete separation between oxygenated and deoxygenated blood

Question 10

Digestion

Answer 10

1. Adaptations to herbivorous diet

fermenting stomach (artiodactyls) [segmented stomach, getting as much nutrients out of something that they can (chewing the cud)]

Coprophagy (rodents, lagomorphs)

Question 11

Excretion

3 points

Answer 11

1. Bilirubin (waste from blood cells)
   brown faeces [iron oxide inside bilirubin]
2. Excrete urea
3. Kidneys have clearly distinguishable cortex [outer area, high filtration] and medulla [urine gathered]

Question 12

Nervous system

Answer 12

1. Neocortex
   unique to mammals

“grey matter”

cognition, spatial reasoning, communication

Question 13

Senses

3 points

Answer 13

1. Ear made of three bones
2. Well-developed eye with colour vision
3. Sense of smell
   primary sense in most mammals
   drove the evolution of a large brain

Question 14

Reproduction

3 points

Answer 14

1. Ancestral condition: undeveloped young

soft-shelled eggs (monotremes)

direct vivipary (marsupials [still in embryonic form and cared for in pouch until developed enough]) [birth to live young]

2. Placental mammals: prolonged inter-uterine development

Placenta connects foetus to uterine wall for nutrient uptake [rather than relying on yolk]

3. Mammary glands producing milk

prolacteal fluid may have evolved to keep eggs moist and free from infection

monotremes have a mammary patch [young hatch from egg. No teats. Area licked on bellies. Homologous structure to teats]

marsupials and placentals have teats

Question 15

modern groups
Monotremata
5 points

Answer 15

1. Single duct for urinary, digestive, and reproductive systems
2. Eggs hatch within 10 days
   Modern species lack teeth as adults
3. Electroreception [sensitive to electric pulses. Use to find prey]
4. Venom

male monotremes have spur on leg

powerful venom in platypuses

5. Australosphenid monotreme mammals

Question 16

modern groups
Marsupialia
6 points

Answer 16

1. Metatherian marsupial mammals
2. Genitalia
   male: no baculum, forked penis, scrotum often anterior to penis

female: two lateral vaginas each leading to a [separate] uterus, a third median vagina for giving birth
3. Epipubic bones [pic]

4. Marsupium
   external development of infant

Question 17

modern groups

Placentalia

Answer 17

1. Eutherian placental mammals
2. A placenta
   specifically a chorioallantoic placenta (chorion + allantois)
   Marsupials also have a choriovitelline placenta (chorion + yolk sac)
   relatively long gestation
3. Loss of epipubic bones [prevent having a large fetus. ]
   these bones prevented expansion of torso needed for prolonged pregnancy

became baculum

Question 18

3 main groups of Placentalia

Answer 18

Afrotheria

Boreoeutheria

Xenarthra

Question 19

Afroinsectiphilia (Afrotheria)

2 points

Answer 19

1. “African insect-lovers”

2. Clade identified using molecular phylogenetic studies, no morphological evidence.

Question 20

Euarchontoglires (Boreoeutheria)

2 points

Answer 20

1. “true rulers and dormice”

2. Clade identified using molecular phylogenetic studies, no morphological evidence.

Question 21

Paenungulata (Afrotheria)

Answer 21

1. “almost ungulates”
2. Males lack a scrotum
3. Females have teats near axillae (armpits) [high up]
4. Nails rather than claws

Question 22

Laurasiatheria (Boreoeutheria)

Answer 22

1. “Laurasian beasts”

2. All evolved on the northern supercontinent

Question 23

Xenarthra

4 points

Answer 23

1. “strange jointed ones”
2. Extra articulations in vertebrae
3. Low metabolic rates
4. lack pineal body