Lecture 15 - Comparative methods part 2

Question 1

What do we know most about extinct organims?

Answer 1

Mostly anatomy, often soft tissue, physiology and behaviour are often not preserved

Question 2

Lagerstatte

Answer 2

Sites of exceptional (e.g. soft tissue) preservation

Question 3

Trace fossils

Answer 3

Fossilised behaviour e.g. dung, burrows, trackways

Question 4

Occams razor

Answer 4

accept simplest explanation unless there is evidence to the contrary (least amount of of evolutionary change)

Question 5

Evolutionary change

Answer 5

Loss of the primitive condition of the trait

Question 6

Most parsimonious explanation in comparative biology

Answer 6

Pleisomorphies (primitive shared traits) retained

Pleisomorhoies are all descendants until you find evidence that an offspring does not have the trait

Question 7

Crown group

Answer 7

The monophyletic clade that contains all the descendants (extinct and extant) of the LCA of two or more extant taxa

Question 8

Stem group

Answer 8

The paraphyletic group that contains the extinct taxa that are closely related to one crown group than another

Question 9

Plesiomorphy

Answer 9

Shared primitive charecter

Question 10

Synapomorphy

Answer 10

Shared derived characters

Question 11

What is the most parsimonious explanation of characters that are shared by living characters?

Answer 11

They were also primitively present in the extinct taxa that they bracket

Question 12

Example of the Saturnalia tupiniquim

Answer 12

Sarunalia is a basal sauropodomorph from the triassic

Close to the base of dinosauria

Intermediate ancestors were bipeds but this was a quadruped (likely to be the transition between bipeds and quadrapeds)

Lookin into the forelimb musculature using comparative method by looking at birds and crocodiles ( most parsiminous)

Allows us to form a hypothesis of the muscle attachments

Question 13

Adaptation

Answer 13

For a character to be regarded as an adaptation, it must be a derived character that evolved in response to a specific selective agent

Question 14

What may a trait be rather than an adaptation?

Answer 14

Be a consequence of a physical or chemical constraint (e.g. red blood)

Be a consequence of genetic drift

Be associated with an adaptive trait (e.g. pleiotropy)

Result from phylogenetic history (role of cranial sutures)

Question 15

Preadaptations

Answer 15

Traits that evolve for one function (due to one set of selection pressures) but by chance are later suitable for performing novel roles

Question 16

Exaptations

Answer 16

Preadaptations that have been co-opted to perform new roles

Question 17

Evolution of the secondary palate

Answer 17

Separates the first stage of the respiratory tract from the first stage of the digestive tract

There is convergent evolution of the secondary palates

There was the initial selection for ridges (palatine shelves) in order to resist torsional forces in the upper jaw

Then there was a subsequent adaptation for palates to meet in midline and separate nasal and oral cavities (exaptation)

Only later used for suckling (predaptation)

Question 18

Evolution of facial muscles

Answer 18

Neck constrictor muscle (constrictor colli) of basal amniotes migrated to become facial muscles

Buccinator forms cheeks

Orbicularis oris forms a seal to the oral cavity

Both help keep bolus in teeth during mastication

Both probably selected for to enable sucking

Facial muscles preadapted for food gathering (e.g. prehensile lips) and communication (facial expressions)