week 6

Question 1

the afrotheria hypothesis was founded on what understanding?

Answer 1

continental movement at the time of these adaptive radiations and mapping higher orders onto placements of the continent

Question 2

what are the 3 traditional mammalian superorders?

Answer 2

glires - rodents and lagomorphs
archonta - bats, tree shrews, primates
paenungulata - elephants, sirenians, hyraxes

Question 3

what does the morphological data say about the divergence of hte 3 mammalian supraorders?

Answer 3

later sudden radiation supported by the fossil record.

Question 4

what does molecular data say about the divergence of the 3 mammalian supraorders?

Answer 4

early divergences but where are the fossils and is the analysis robust and is the molecular clock calibrated properly

Question 5

Kumar and hedges 1998 kicked off the controversy about when extant placentals diverged how?

Answer 5

• geological time scale and estimates of divergence times for all of these mammalian groupings
• as a calibration point for their molecular data they use the split between synapsids and diapsids
• by using this molecular clock approach they put all these dates on
• 688 genes used
• recovered some original relationships and also new ideas
• main controversy was their data suggested most modern extant mammals had their origins much further back into the cretaceous than the fossil record was suggesting

Question 6

In the molecular clock what are correlated?

Answer 6

the number of substitutions between sequences from 2 species/taxa and the date at which they diverged

Question 7

Calibrating sequence differences with time gives us a molecular clock to calculate divergence times but (3)

Answer 7

how reliable are the calibration points
are mutations constant with time
are mutations constant between linneages

Question 8

modern methods for dating using the molecular clock can correct for? (4)

Answer 8

varying rates between lineages
varying rates among genes/part of genes
complex patterns of substitutions
uncertainty in calibrations

Question 9

What are the 3 different suggested scenarios for the radiation of placental mammals?

Answer 9

• morphological people suggest there is a sudden explosion of phenotypes at the KT boundary due to fossil record
• but molecular data suggests deep branches that go way back into the cretaceous

• in the lineages that go back into the cretaceous there is not a lot of phenotypic change, but the genes are changing which we pick up in the DNA sequences until we hit the mass extinction at the KT and niches become available and there is an explosion of phenotypic radiation what we call adaptive radiation

Question 10

What are 4 suggested reasons for the disagreement between the 2 proposed scenarios for the radiation of placental mammals?

Answer 10

preservation rate much lower for placental than other cretaceous mammals

there are modern placentals in the cretaceous but we just dont know it

garden of eden - areas of diversification which arent good at fossilisation

the molecular clock suddenly speeds up along lineages during adaptive radiations

Question 11

what are the 3 new mammalian super orders?

Answer 11

afrotheria
xenarthra
boroeutheria

Question 12

With the discovery of new early mesozoic fossils like juramaia means what?

Answer 12

•Can push the fossil record boundary back
the split between placentals and marsupials was firstly put about 125mya in early cretaceous with the discovery of eromia
• jurameia suggests the split should shift down
• evidence for really early splits in the basis of some of these lineages

Question 13

what does the murphy 2001 paper suggest?

Answer 13

• shows continental positions at 110 mya
• molecular data suggests a split between the afrotherians and everything else about 103 mya
• when you lay that on a continental map this fits really well when you place this on a continental map
• suggests the split between xenafrothans and afrotherians occurs when africa and south america were starting to pull apart this makes sense

Question 14

the splitting of these superorders give us some really interesting examples of convergence between afrotheria and lauarsiatheria such as …

Answer 14

tree shrews and common shrews
pangolin and ardvark
tapir and extinct mammal

Question 15

Nishihara et al 2009 suggest what about the 3 major lineages?

Answer 15

that they diverged almost simultaneously from their common ancestor

Question 16

Oleary 2013 suggests what and why is this paper taken with caution?

Answer 16

• detailed analysis using morphological features
• to build a phylogeny
• and also used molecular data
• came up with a hypothetical placental mammal ancestor that they reconstructed the morphology of by mapping the traits back
• built a phylogenetic tree
• most people think it was a robust analysis
• they suggested that all of the extant mammal lineages track back to the KT boundary and no further
• they are saying that all of the modern mammal diversity relates to a common ancestor that is quite recent
• this argues against all the continental drift stuff
• again have come back to the morphological / molecular debate at the beginning
• the single paper should be treated with caution but it has opened up the debate a little bit

Question 17

SUMMARY

-morphological and fossil data suggest a _________ radiation of eutherian mammals

– molecular phylogenies sugges _______ divergence of the main higher order taxa

–the current hypothesis is _____

Answer 17

post KT explosive

earlier 100mya

divergences did occur in the cretaceous but most phenotypic evolution happened in the early tertiary