Origin of vertebrates

Question 1

What are the features of the Chordates

Answer 1

→ will have at some point in their life
Notochord
Dorsal, hollow nerve cord
Pharyngeal (gill slits)
Post-anal tail
Endostyle (becomes thyroid gland)

Question 2

Descibe the neural crest and its development

Answer 2

• Migratory and multipotent
• Responsible for new structures especially in head
• Another germ layer → quadroblastic

Question 3

Compare hox genes in invertebrate chordates and ancestral jawless vertebrates

Answer 3

Hox gene complex has been duplicated:
Invert chordates have 1 hox gene cluster
Ancestral jawless verts have 2

Question 4

Compare the brain of vertebrate chordates to invertebrate chordates

Answer 4

Verts: larger and has 3 parts (forebrain, midbrain, hindbrain)
Inverts: Smaller and not divided but genes similar except front or forebrain

Question 5

Since vertebrates have increased body size and activity, what cannot they rely on?

Answer 5

= Can’t rely on ciliary action or diffusion

Higher metabolic rate than non-vert chordates
Can sustain periods of anaerobic respiration
→ transition from filter feeding to active, predaceous mode of life

Question 6

Describe mineralised tissues

Answer 6

collagen fibres, proteinaceous tissue matrix and hydroxyapatite
- Arose in vert evolution but absent at start
- Unique mineral hydroxyapatite (calcium & phosphorus)
= More resistant to lactic acid after anaerobic respiration

Question 7

What mineralised tissue do sharks/ cartilaginous fishes use?

Answer 7

70% mineralised cartilage

Question 8

What mineralised tissue makes up the skeleton of bony fish and tetrapods?

Answer 8

Bone
- Highly vascularised
- 70% mineralised

Question 9

Describe the 2 types of bone

Answer 9

Dermal (grows in skin, e.g skull)
Endochondral (forms in body, only found in bony fishes and tetrapods). Cartilage precursor which is replaced by bone

Question 10

What mineralised tissue is associated with the teeth and dermal scales of cartilaginous fishes?

Answer 10

Enamel, enameloid & dentine
- 90-96% mineralised

Question 11

What is Cementum

Answer 11

Fastens teeth in sockets of some verts e.g mammals. 45% mineralised

Question 12

Describe the origin of mineralised tissues in vertebrates

Answer 12

• No mineralised tissue at start of vert evo
• Basic units in early verts - odontodes (dermal)
  E.g dermal armour of ostracoderms

Question 13

Why did mineralised tissues evolve?

Answer 13

• Defensive structure
• Protected/insulated electroreceptors (used by some groups to detect prey)
• Storage/regulation of phosphorus & calcium

Question 14

Describe the Ostracoderms

Answer 14

→ Jawless with mineralised tissue as armour
- 500 MY old
- Thought to be the oldest vertebrate group
- However… new fossils found in China are thought to be the oldest verts (530 MYA)

Question 15

Why do we think early vertebrates evolved in a marine environment?

Answer 15

Evidence:
- Paleontological - earliest fossils in marine sediments
- Comparative physiology:
Invert chordates (& other deuterostomes) are all marine
One of the most ancient extant vertebrates (hagfish) is marine with body fluids isotonic to mw