L1- Intro to Vertebrates

  • Vertebrates make up 4% of animals:

The extant vertebrate groups:

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

    • usually aquatic

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

    • usually terrestrial

    • split into two groups:

      • Sauropsids→ reptiles and birds

      • Synapsids→ mammals

      • the groups split >300 million years ago

      • they share similarities that have evolved convergently

  • Tetrapods→ have 4 limbs

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

Classification:

  • Phylogenetic Classification→ based on evolutionary history

    • uses DNA sequences and molecular techniques

  • Traditional Phenetic Methods→ based on similarities

    • cannot distinguish between homology and analogy

  • e.g. reptiles are not monophletic

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

  • Homology→ shared ancestry

  • Analogy→ convergent evolution

Convergent Evolution:

  • same selection

  1. 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

  2. Cichlids 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

  3. 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:

  • 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(occupied modes→ measure of diversity of habitat)

      → as mode increases, number of family increases

  • Size

    • e.g. Male Angler Fish→ 6mm

    • e.g. Paedocypris fish→ 7.9mm

    • e.g. Blue Whale→ 33m

  • Habitat

    • deep sea

    • himalayas

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

  • 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

  • It is energetically expensive to be a vertebrate

    • 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

  • Many vertebrates are now extinct

    • 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

  • 20% of vertebrates are endangered

    • e.g. Cave Catfish

      • is only found in one cave in Nambia

      • is vulnerable to water extraction