UNIT 4 DAY 1 - Your Inner Fish Flashcards
what kind of rocks are the fossils found in
sedimentary rock (formed as small rock particles settled out of water)
scientists who looked for a fossil intermediate between fishes and tetrapods found a fossil locality that…
had rocks right of the age, which are now located in the artic
serendipity is the last step in finding fossils because
once looking in rocks of the right age and time, you still have to be lucky to find the fossils
sonic hedgehog
gene that is turned on during development of limbs in vertebrae
tikaalik
transitional fossil between fish and amphibians with a wrist
ADD FIGURE
the vertebrate archeotype, which Charles Darwin viewed as the platonic form of all vertebrates
homologies
similar structure but adapted for different purposes
lines of evidence in reconstructing our history
- fossils
- genes
- embryos
- living adult bodies
maximising chances of fossil finding
- identify time period
- find the rocks
- look for areas where rocks are accessible
- bones are “weathering out”
- planning takes palaeontologist to promising sites but also must think on their feet
homologies
same organs in different animals under every variety of form and function
tetrapod (Ancestral Terrestrial Vertebrate) pattern
1,2, many, 5
sharing homologous organs
- group species within nested groups, but can have different lives
forearm
humerus, radius & ulna, carpals, metacarpals & phalanges
Grand Facts 2 and 3
- reflected aspects of gods mind in creation
archetype
model summarising the homologies characteristics a group of organisms
why do homologies exist
- homologies exist because species in evolving from one to another, pass on their descendant species, same structures they possessed
- structures modified as descendants of common ancestor evolve new ways of life, but still recognise similarity due to descent
Phylogeny
history of life –> evolutionary tree
How can we use the the features of living adult bodies to reconstruct evolutionary history of a group?
- Everything in the figure has a head, so heads must be homologous structure that evolved in the ancestor of all four species of the page. We’ll place heads at the base of the tree
- Humans, dogs, and salamanders also all have legs, so legs must have evolved in the ancestor of humans, dogs, and salamanders, after fish had branched off the tree
- Humans and dogs both have hair and mammary glands (breast), so hair and breasts must have evolved in the ancestor of humans and dogs after salamanders had branched off the tree
- Only humans walk on two legs, so that must have evolved in the ancestor of humans after dogs had branched off the tree
How can we use the the features of fishes to reconstruct evolutionary history of a group?
- the fossil amphibian Acanthostega (360 mya) had everything humans have, a humerus, radius, ulna, wrist, and digits
- Based on this phylogeny, Shubin predicted that at 365 mya he would find a fish with a humera, radius, ulna, and wrist, but with fin instead of digits
- The fossil fish Eusthenopteron (370 mya) had a humerus, radius, and ulna, with a fin at the end
- Lungfish have a fin like zebrafish, but with much more robust supporting bones. The first bone is the homologue of our humerus bone
- Zebrafish have pectoral fins homologous to human arms, but no supporting bones homologous to those of our arm. Instead they have a fin supported by bony ray
fossil finding sites: North-central PA
- advantages: less expensive, time-consuming, well-understood catskill formation
- disadvantage: not the best exposure
fossil finding sites: Ellesmere Island
- advantage: actually quite difficult
- disadvantage: expensive, difficult to travel to, danger latitude because Pangea had Ellesmere by the equator
tiktaalik structure
- contains human and fish-like features and found on Ellesmere (has coasts) –> makes sense that it is an intermediate
why do land animals differ from fish
- their heads are made more flat –> shape and size of similar structures varies between species
Eusthenopteron
- bony formations begin to arise
