amniote early evolution and ancestors

Question 1

• Structure of the amniotic egg

Answer 1

• Shell - leathery or hard calcified 
		○ Protection and gas exchange (pores)
	• Albumen - fluid layer
		○ Water (hydration), protein reservoir, cushioning/shock absorber 
	• Yolk
		○ Nutrient supply

Question 2

extra embryonic membranes (describe)

Answer 2

• Chorion 
		○ Ectoderm and mesoderm 
		○ Enclosing other membranes
		○ Maintains integrity of the egg 
	• Amnion - unique!!! 
		○ Ectoderm and mesoderm 
		○ Enclosing embryo in fluid filled space 
		○ Cushioning 
		○ Protecting from desiccation 
	• Allantois 
		○ Endoderm and mesoderm 
		○ Grows out of hindgut - connects embryo to food source
		○ O2 and CO2 gas exchange 
		○ Waste storage - uric acid

Question 3

morula?

Answer 3

• Morula - solid mass that divides after egg and sperm fertilize - blastocoel - blastula - forms blastopore and archenteron - gastrula

Question 4

arose from? features?

Answer 4

• Arose from anthracosaurian “amphibians”
• Extinct “stem amniote” reptilomorph
• Diadectomorphs from carboniferous and Permian
• Amniote sister group
• Loss of lateral line system
• More “modern” atlas-axis complex - skull can turn at the neck
• Most were carnivores - canine teeth
• Diadectes
○ Specialized dentition with grinding surface - can tear flesh or have plants (bc grinding teeth)
○ First terrestrial herbivore????

Question 5

sauropside amniote ancestors?

Answer 5

Question 6

Review paleozoic to mesozoic

Answer 6

• Review of geological, climatic and biological conditions
• Paleozoic (542 mya) to end of Mesozoic (66 mya)
○ Small land blocks and large epicontinental seas
○ Radiation of jawless and jawed fishes
○ Formation of Pangaea (end of Paleozoic)
○ Pangaea breaks up (jurassic-cretaceous)
○ Devonian - age of fishes (and tetrapodomorphs)
○ Carboniferous to permian - age of “amphibians”
○ Mesozoic - age of reptiles (or sauropsids)

Question 7

general amniote features?

Answer 7

1. One occipital condyle
   
   2. Body covered with dry scales of two types:
      • Epidermal scales
      ○ Ecdysis: periodic shedding of scales
      § Outer epidermis loses blood supply
      § Becomes keratinized and dies
      § Lymph loosens outer epidermis
      § Shed altogether or in pieces
      • Dermal plating (scutes, internal)

Question 8

how are amniotes classified?

Answer 8

• Classification based largely on skull features
• Skull more ossified than in lissamphibians
• Classification based on the number and position of temporal fenestration (openings):
○ “anapsid”: none
○ Synapsid: 1 opening
○ Diapsid: 2 openings

Question 9

Answer 9

Fenestrae allowed expansion of jaw muscles -temporal opening keeps jaw bones together so that the organism can expand its jaws open to ingest prey bigger than itself

Question 10

lineages of aminotes? (important)

Answer 10

1. Anapsid condition 
	• Extinct parareptiles and eureptiles 
	2. Synapsid: 1 opening
	• Mammal like reptiles 
	• Lineages that gave rise to mammals 
	3. Diapsid: two openings 
	• Euryapsids (closure of lower fenestra) 
	• Extinct marine reptiles 
Classified as lepidosauromorpha

Question 11

• Euryapsids

Answer 11

• Icthyosaurs 
		○ "dolphin like" 
Live birth
	• Plesiosaurs 
		○ Long necked 
Large paddle-like flippers
	• Plesiosaurs and pliosaurs 
		○ Long and short necked pelagic predators

Question 12

jurassic and triassic

Answer 12

• Extinctions of dinosaurs, marine reptiles, some terrestrial mammals, temperate zone plants, cephalopods
  
  • Not appearing to be as affected were tropical plants, small animals, and freshwater organisms