Fossil Record
What is the fossil record?
The total collection of all preserved remains and traces of ancient organisms found in Earth's rock layers.
What do we call physical body parts reduced in size that have lost their original function over time (like the human tailbone or subterranean mole eyes)?
Vestigial structures.
What is embryology?
The study of how organisms form and develop before birth or hatching.
What molecule contains the universal genetic code shared by all living organisms on Earth?
DNA
What is a cladogram or phylogenetic tree?
A branching diagram used to represent evolutionary relationships and lines of descent among species.
Why are fossils of land animals far less common than fossils of marine animals?
Quick burial by sediment is much rarer on land than in oceans or river deltas
Humans, bats, penguins, and alligators all share a matching forelimb bone layout (humerus, radius, ulna, carpals). What type of structure is this?
Homologous structures.
What temporary tail structure is found in all vertebrate embryos during early developmental stages?
A postanal tail.
Humans and chimpanzees share over what percentage of their DNA base sequences?
Over 98%.
Where on a phylogenetic tree do you find the most recent living species?
At the top (or ends) of the branches.
Why are soft-bodied organisms like jellyfish rarely found in the fossil record?
Fossilization usually requires hard body parts like bones, teeth, or shells; soft bodies decay before they can be buried.
Bird wings and butterfly wings both allow flight, but they evolved from completely different ancestral structures. What type of structures are these?
Analogous structures
What embryonic structures appear in both human and chick embryos that develop into gills in fish, but transform into jaw and ear/throat parts in mammals?
Pharyngeal slits (or gill slits).
What organic subunits link together to build proteins like Cytochrome c, which scientists compare between species?
Amino acids.
What does a branching point (node) on a cladogram represent?
A common ancestor from which separate evolutionary lineages split.
What evolutionary transition is shown by the fossil lineage of the horse over 55 million years?
The transformation from a small, 4-toed forest dweller (Eohippus) to a modern single-hoofed grassland runner (Equus).
What does the presence of homologous structures in radically different animals reveal about their evolutionary history?
It proves that they inherited the basic anatomical layout from a shared common ancestor.
How does the presence of an amniotic egg sac in developing bird and mammal embryos support common ancestry?
It is a shared developmental homology showing both groups evolved from an ancient land-dwelling vertebrate ancestor.
How do scientists use a "molecular clock" to study evolutionary relationships?
They count the number of amino acid differences between species to estimate how long ago they split from a common ancestor.
If a cladogram shows chimps and mice sharing the traits of "fur" and "mammary glands," what can you infer about their common ancestor?
Their shared common ancestor also possessed fur and mammary glands.
How do transitional fossils like Pakicetus and Ambulocetus support the theory of evolution for modern whales?
They show the step-by-step transition of four-legged, land-dwelling quadruped mammals adapting to aquatic life over millions of years.
Why don't analogous structures (such as bird wings and insect wings) indicate a close evolutionary relationship between two species?
They evolved independently due to similar environmental pressures rather than being inherited from a shared ancestor.
Why do two species look nearly identical as early embryos but look completely different as fully formed adults?
They share early genetic instructions inherited from a common ancestor, but species-specific genes take over later in development to build distinct adult bodies.
If Species A and Species B have 1 amino acid difference in their Cytochrome c protein, while Species A and Species C have 15 differences, which species are more closely related? Explain why.
Species A and B are more closely related because fewer amino acid differences indicate a much more recent common ancestor.
A student builds a cladogram placing birds and bats together because both have wings. Why is this model incorrect?
It mistakes analogous wings for homologous traits.