L1- Intro to Vertebrates

what percentage of animals do vertebrates make up?

4%

the extant vertebrate groups:

Non-amniotes:

• embryo is surrounded by a membrane from the reproductive tract of the female

  • usually aquatic

Amniotes:

• embryo is surrounded by a membrane from the embryo itself (extraembryonic membrane)

  • usually terrestrial

  • split into two groups:

    • sauropsids

    • synapsids

Sauropsids vs Synapsids:

• Sauropsids→ reptiles and birds

• Synapsids→ mammals

• the groups split >300 million years ago

• they share similarities that have evolved convergently

Tetrapods

have 4 limbs

Vertebrates phylogeny:

→ cartilaginous fish and bony fish have evolved independently, not from one another

Types of classification:

1. phylogenetic classification

2. traditional phenetic methods

Phylogenetic Classification:

• based on evolutionary history

  • uses DNA sequences and molecular techniques

Traditional Phenetic Methods:

• based on similarities

  • cannot distinguish between homology and analogy

vertebrates classification e.g.:

• e.g. reptiles are not monophletic

• e.g. birds are seen as a group of dinosaurs

Homology:

shared ancestry

Analogy:

convergent evolution

Convergent Evolution + examples:

same selection

1. forelimbs

2. cichlid fish

3. body shape

CE→ forelimbs:

• early tetrapods had many digits (polydactyl)

• some have lost digits throughout evolution e.g. horses have 2 digits

• pentadactyl plan→ has 5 digits

• both bats and birds have wings but they are structured differently

CE→ cichlid fish in african great lakes:

• evolved independently in Lake Malawi and Lake Tanganyika

• look similar when pairing up

• fill the same niches in different lakes separately from each other

CE→ body shape in ichthyosaur, porpoise and shark:

• same shape to adapt to water movement

• all are fusiform→ move rapidly through water

• have different skeletons but similar shapes

Vertebrates differ in…

1. number of orders

2. size

3. habitat

4. reproductive behaviours

Differences→ number of orders:

could be due to earth’s fragmentation

→ during the second fragmentation, birds and mammals diversified, pangaea is the main birthplace of terrestrial vertebrates (300 million years ago)

• could be due to the extinction of dinosaurs

• could be due to birds and mammals both being endothermic

  → are not dependent on environmental temperatures

Differences→ size:

• e.g. Male Angler Fish→ 6mm

• e.g. Paedocypris fish→ 7.9mm

• e.g. Blue Whale→ 33m

Differences→ habitat:

• deep sea

• himalayas

• e.g. Snail fish→ found in the deep sea (8000m)

Differences→> reproductive behaviours:

• eggs

• live birth

• care for young

• no care

• e.g. Killifish→ have the fastest growth rate (reproduce at 17 days old)

Vertebrates are usually:

• large

• at the top of food chains

to be a vertebrate is energetically…

expensive

• most are jawed and have different feeding modes

• lamprey are jawless

new vertebrates are..

• being discovered all the time

  • could be species previously thought to be another species

  • there are hotspots

extinct vertebrates:

• reach maximum 12-14 million years ago

• e.g. Thylacine (Tasmanian Tiger)

• e.g. Golden Toad and Southern Gastric Brooding Frog

  • decline due to climate change or human-spread Chytrid fungus

endangered vertebrates:

• 20% of vertebrates are endangered

  • e.g. Cave Catfish

    • is only found in one cave in Nambia

    • is vulnerable to water extraction