Origin of the Vertebrates

Question 1

What sub-phylums are in the phylum Chordata?

Answer 1

Vertebrata

Urochordata

Cephalochordata

Question 2

What are the features of the chordates?

Answer 2

Notochord - bewteen the gut and the nerve cord and is used as support BUT has been lost in the vertebrates

Dorsal, hollow nerve cord - becomes the brain and spinal cord in the vertebrates

Pharyngeal (gill) slits - slits are for filter feeding in the invert chordates but fish use them as gill slits

Post-anal tail

Endostyle - produces mucus and helps with filter feeding and concentrating iodine in the inverts. It is homologous with the thyroid gland in the vertebrates

Question 3

How does the notochord change from invertebrates to vertebrates?

Answer 3

Vertebrae replace the notochord

Some notochord becomes disks

Neural canal protects the nerve cord as the spinal cord runs through it

Question 4

What vertebrae do not have full formed vertebrae?

Answer 4

Hagfish and lampreys - have kept the notochord for supoort

They have rudimentary vertebral precursors (known as arcualia) instead

In lampreys - found along the body and dorsally

In hagfish - found in the tail region and ventrally

In their ancestor - found dorsally AND ventrally

Question 5

What can the cranium be made from?

Answer 5

Bones

Cartilage

Fibrous

Question 6

What can be known as another germ layer?

Answer 6

The neural crest

It is responsible for new structures (especially in the head) as the cells are migratory and multipotent

There are precursors found in the invertebrate chordates

As it can be classed as another germ layer, vertebrates could be called quadroblastic

Question 7

What do placodes give rise to?

Answer 7

Complex sense organs - homilogous in invertebrate chordates

They can migrate to form other sense structures (not in the head) such as the lateral line in fish

Question 8

What are the three main parts of a vertebrate brain?

Answer 8

Forebrain

Midbrain

Hindbrain

Question 9

What are the pros and cons of having an increased body size and activity?

Answer 9

Can no longer rely on ciliary action or diffusion so need to develop actual organs to survive e.g. a heart

Have a higher metabolic rate than invertebrate chordates

Can sustain periods of anaerobic respiration as no longer use diffusion

This allowed vertebrates to transition from filter feeding to active predators

Question 10

What are gill slits supported by?

Answer 10

Gill bars

Question 11

What is mineralised tissue?

Answer 11

Minerals being added to tissue

Examples being:

-hydroxyapatite - such as calcium and phosphorus (causes more resistance)

- collagen fibres - which can prevent cracks forming in tissues

**- proteinaceous tissue matrix **

Mineralisation allows resistance to lactic acid after anaerobic respiration

Question 12

What tissues can be mineralised?

Answer 12

Mineralised cartilage - forms main mineralised internal skeletal tissue of sharks/cartilaginous fishes = 70% mineralised

Bone - internal skeleton of bony fish and tetrapods and highly vascularised (dermal bone is in the skin and endochondral bone found in the body) = 70% mineralised

Enamel, enameloid and dentine - associated with teeth, exoskeleton, dermal scales of cartilaginous fishes = 90-96% mineralised

Cementum - fastens teeth in sockets = 45% mineralised

Question 13

What is the orgin of bones and mineralised tissues?

Answer 13

Formed in basic units in the early vertebrates - evolved into odontodes

Originated in the dermis so were classed as dermal bones

An example is the ostracoderm which used it as dermal armour

Question 14

Give a brief overview of mineralised tissue

Answer 14

Started with unmineralised endoskeleton e.g. like in lampreys

Formed into exoskeleton which is the orgin of the mineralised skeleton e.g. in the ostracoderms

Then formed the mineralised endoskeleton e.g. in the bony fish

Then there was a reduction of exoskeleton in the trunk but some was still found in the head region e.g. in the tetrapods

Question 15

What are some hypothesised reasons for the evolution of mineralised tissues?

Answer 15

Defensive structures

Protected/insulated electroreceptors

Storage/regulation of phosphorus and calcium

Question 16

Are conodonts the earliest vertebrate?

Answer 16

Debateable

Some think they show mineralised tissue due to convergent evolution

Ostracoderms possibly the earliest vertebrate

Myllokunmingia is the oldest vertebrate fossil (around 530MYA) - found skull and skeletal elements made of cartilage but show no mineralisation