7 - vertebrate evolution

vertebral column

• Belong to humans, sharks, fish, frogs, hares, crocodiles, birds

  • All inherited from a common ancestor

• Primitive characteristic of all vertebrates

notochord

• found in Ancestors of vertebrates had another cord instead of a vertebral column

• Evolution of notochord is the first step towards the evolution of vertebrates

cephalochordata

• Notochord + head

• ex. Pikaia

  • Earliest ancestor of all vertebrates

  • Around 5 centimeters

  • Marine

  • Found in the burgess shale

  • 505,000,000 years ago

chordates

• No head, just a notochord

arculia

• instead of a bony vertebral column

• runs down the body

vertebra

• evolved jointed vertebral column

• Did not have jaws hence called jawless fish

  • causes them to die off cuz fish with jaw have better access to food

  • less likely to reach sexual reproductivity

• ex. Hagfish and lampreys

gnathostomes

• Evolved jaws From the pre-existing support structures found in the gills

• Skeleton is made of cartilage

  • fossil records only contain teeth mostly and some vertebral column

• Sharks

osteichthyes

• Evolved calcified/mineralized skeletons

• Fish

• Split into two groups

  • Ray finned fish

    • Typical fish

    • Vertebral column, jaws, mineralized skeleton

  • Lobe finned fish

    • aka sarcopterygii

    • Fins become fleshy and limb like

    • Vertebral column, jaws, mineralized skeleton, limb like fins

    • ex. Tiktaalik

• Until this point all vertebral life was restricted to the ocean

tiktaalik

• new anatomical adaptations

• Weight bearing elbows, simple wrist bones, simple fingers along with gills and lungs

• Lived in shallow waters

• Which is why AKA Fishapod

  • Fish with feet

tetrapods

• Vertebrates with four true limbs

  • Were able to move onto land as a result

• Most have lost gills but retained lungs

• Primitive tetrapods are amphibians

  • Still need water to reproduce

  • Eggs are laid in water and without it they dry out

• 1st to move to land = ichthyostega

  • Bound to the water for reproduction

amniota

• Membrane in eggs that allowed amny oats to be fully terrestrial

  • Egg is protected from being dried out

• Evolution of calcified or leathery shell, yolk for nutrition, waste management system all at the same time

• Some laid egg and others retain the fertilized egg internally like humans and other mammals

• Two groups characterized by temporal fenestra

  • Synapsids and Diapsids

  • Can also be accommodated by bulging jaw muscles

  • In both, braincase is visible through the lower temporal opening

synapsids

• One pair of openings behind the eyes

• Only Lower temporal opening

diapsids

• Two pairs of openings behind the eyes

• Upper temporal and lower temporal fenstra

• Includes dinosaurs so they're grouped with crocodiles and birds

• Can be further split into two clades

  • Lepidosauropmorphs

    • Short non-overlapping vertebrae in the neck

  • Archosauromorphs

    • Longer overlapping vertebrae in the neck

    • Provide support for longer necks

clades in vertebrate evolution

• Cephalochordata

• Vertebrata

• gnathostoma

• osteichtyes

• sarcoptergii

• Tetrapoda

• amniota

  • Synapsida

  • Diapsida

issue of reptilia (linnaean)

• intended to include all cold-blooded vertebrates

• but find out later that birds are dinosaurs which are warm-blooded

archosauria

• Subset of archosauromorphs

• Additional openings called antorbital fenestra

  • Between the eyes and snout

• Don't know the purpose

• Crocodiles, pterosaurs, birds, dinosaurs

• Two groups due to the structure of the ankle

  • Crurotarsi

    • Sprawling stance

    • Crocodiles

  • Ornithodira

    • Upright stance

    • Pterosaurs, birds, dinosaurs

ornithodira

• Hind limbs are positioned directly under the body

  • Can only move front to back

  • Simple hinge like ankles

• Includes two groups

  • pterosauria

    • Adaptations for flight

    • Elongation of a digit to support a wing

    • Avian Dinosaurs

  • Dinosauria

dinosauromorpha

• Before dinosauria

• Digitigrade posture

  • Standing on the balls of the feet

  • Allows for longer stride

  • Efficient and continuous

  • Short bursts of speed

• Most primitive were small

  • A meter or less

  • Light build

  • Insectivorous or carnivorous

  • Walked on all fours but ran bipedally

• Dinosauromorphs most closely related to dinosaurs were bipedal

  • So primitive characteristic was bipedal

  • Quadrupedal evolved secondarily

    • Dinosaurs reverted back to the quadrupedal stance

• Fossils found all over the world

  • Late triassic

    • Pangea still intact