Chapter 4 - The Tree of Life

Question 1

What is “Tiktaalik”? What is it’s significance?

Answer 1

Tiktaalik was a extraordinary fossil discovered in 2004 that was an early ancestor of tetrapods, sharing some, but not all traits of them.

Question 2

What is a branch?

Answer 2

A signifier on the tree of life that shows that two populations no longer share genes and have become two different species.

Question 3

What is a node?

Answer 3

The points in a phylogenetic tree where a lineage splits (either though a speciation event or branching event, like the formation of subspecies.)

Question 4

What are tips?

Answer 4

The terminal end of the evolutionary tree that represents the species, molecules or populations being compared.

Question 5

What are internal nodes?

Answer 5

Nodes that occur within a phylogeny and represent the ancestral populations or species.

Question 6

What are clades?

Answer 6

Single “branches” in the tree of life that represents an organism and all of its descendants.

Question 7

What is a cladogram?

Answer 7

A phylogenetic tree that only shows relationships among species.

Question 8

What do branches NOT measure?

Answer 8

They do not precisely measure time, but do offer some insight into timing.

Question 9

What does “monophyletic” mean?

Answer 9

A group or clade made up of an organism and all of it’s descendants. (One cut on a larger tree). Mammals are monophyletic.

Question 10

What does “polyphyletic” mean?

Answer 10

A taxon that does not include the common ancestor of all members of the taxon. (Two cuts on a larger tree).

Question 11

What does “paraphyletic” mean?

Answer 11

A group of organisms that share a common ancestor although the group does not include all the descendants of the common ancestor. The category Reptilia is paraphyletic because it does not include birds.

Question 12

What are “characters”?

Answer 12

Heritable aspects of organisms that can be compared across taxa.

Question 13

What are “taxa”?

Answer 13

Groups of organisms that a taxonomist judges to be cohesive taxonomic units such as species or order.

Question 14

What is a trait in Carnivora that distinguishes it from other mammals?

Answer 14

The carnassials, which were compelling evidence of carnivorans sharing a common ancestor.

Question 15

What is an outgroup?

Answer 15

A species chosen for comparison against other species/groups. They are outside of the monophyletic group being considered.

Question 16

What is homoplasy?

Answer 16

A character state similiarity NOT due to shared event, such as by convergent evolution or evolutionary reversal.

Question 17

What is convergent evolution?

Answer 17

The independent origin of similar traits in separate evolutionary lineages.

Question 18

What is evolutionary reversal?

Answer 18

The reversion of a derived character state to a form resembling it’s ancestral state.

Question 19

What is parsimony?

Answer 19

A principle that guides the selection of the alternative hypothesis: the alternative requiring the fewest assumptions or steps i usually, but not always, the best.

Question 20

What is a consensus tree?

Answer 20

A tree that represents both the resolved, or monophyletic, and the unresolved portions of a phylogeny.

Question 21

What is polytomy?

Answer 21

An internal node of a phylogeny with more than two branches. This is because the order in which the branchings occured have not yet been resolved.

Question 22

How do scientists time phylogenies?

Answer 22

They can use DNA analysis or study fossils from the same clade. Both help to constrain the timing of evolution.`

Question 23

What is one reason scientists value phylogenies so highly?

Answer 23

They help to reconstruct how complexes of traits emerged in ancestral taxa with different phenotypes.

Question 24

What are the closest living relatives to tetrapods?

Answer 24

A handful of aquatic vertebrates, such as coelecanths.

Question 25

What is the group that contains tetrapods, coels, and lungfishes? What are their characteristics?

Answer 25

The “lobe-finned fish”, which had fleshy lobes with bones inside for fins, homologous to the long bones of the arm.

Question 26

What features did Tiktaalik have?

Answer 26

It had long limb bones, and small bones corresponding to our wrist bones. It even had a neck and was able to move its head independently, which lobe finned fish didnt have, but lacked toes like Acanthostega. It’s pelivs was not connected to the spine well, and could not survive on land.

Question 27

What features did Acanthostega have?

Answer 27

Digits, bones that didn’t support it on land, tails lined with delicate fin rays, limbs, and walking traits. Scientists think it used its limbs underwater.

Question 28

What features did Tiktaalik have?

Answer 28

It had long limb bones, and small bones corresponding to our wrist bones. It even had a neck and was able to move its head independently, which lobe finned fish didnt have, but lacked toes like Acanthostega.

Question 29

What are exaptations?

Answer 29

A trait that initially carries out one function but later another, with the original function may or may not being retained, like feathers on birds being used for coloring and attracting mates at first.

Question 30

What are exaptations?

Answer 30

A trait that initially carries out one function but later another, with the original function may or may not being retained, like feathers on birds.

Question 31

What are theropods?

Answer 31

Bipedal meat-eating dinosaurs, like velociraptor and trex.

Question 32

What are theropods?

Answer 32

Bipedal meat-eating dinosaurs, like velociraptor and trex.

Question 33

What is the difference between vertical and horizontal gene transfer?

Answer 33

Vertical is to receive from an ancestor, horizontal is to transfer to another organism without reproduction.