Land Radiation

Question 1

whats the traditional view on the evolution of mammals

Answer 1

First there are the monotremes or prototheria (echidnas)

Rest are the theria including metatheria (marsupial) and eutheria (placentals)

Question 2

what defines a mammal?

Answer 2

double circulation with a completely four-chambered heart
Anucleate and biconcave red blood cells, erythrocytes
Efficient diaphragm and reduced ribcage attatched to upper spine only
Secondary palate (separate passages for food and air, so allows breathing during feeding)
Hair for insulation, also sweat glands
Lactation
Single jaw bone
Heterodont teeth

Question 3

whats the simplest way to define a mammal?

Answer 3

the articulation of the jaw between single lower dentary and upper squamosal bones

Question 4

what did the articulation of the jaw in mammals allow?

Answer 4

various other accessory jawbones to move to the middle ear as the auditory ossicles, allowing big changes to communication options

Question 5

what is mosaic evolution (whats the example?)

Answer 5

evolution at different rates in response to different conditions so at any point in the transitional period there will be forms that combine characteristics from both groups
- modern reptiles and modern mammals

Question 6

why are mammals hard to define beyond this classification?

Answer 6

A) modern mammals show extreme size and morphological diversity
B) there was massive rapid (explosive) adaptive diversification within each sub-group, with features changing really quickly
AND major disagreement between classic and new molecular evidence over past 20 years

Question 7

whats the molecular evidence for evolution of mammals?

Answer 7

three major groups of placental mammals - afrotheria, xenarthra and boreoeutheria - which diverged from early common ancestors in Cretaceous
- First radiation was Afrotheria 110-100mya, in isolation on the african-arabian continent
- The xenarthra, isolated in south america and diverged from the boreoeutheria approx 100-95 mya
Boreoeutheria split into two subgroups between 95 and 85 mya; both of these evolved in laurasia

Question 8

what kind of animals are afrotheria?

Answer 8

shrews, golden moles, aardvarks, elephants, hyraxes, manatees

Question 9

what kind of animals are xenartha?

Answer 9

armadillos, anteaters, sloths - all in south america

Question 10

what kind of animals are boreoeutheria?

Answer 10

• Eurachonotoglires: tree shrews, lemurs and primates, lagomorphs, rodents
  Laurasiatheria: moles, artiodaactyls, perissodactyls, dogs, cetaceans, bats, pangolions, carnivores

Question 11

what does afrotheria do?

Answer 11

bring all groups together

Question 12

what do whales clump with?

Answer 12

artiodactyls (ungulates)

Question 13

where do the two groups of bats fall?

Answer 13

one close to primates

one close to carnivores

Question 14

example of convergent evolution?

Answer 14

marsupials and placental mammals

Question 15

whats the problem with molecular studies

Answer 15

unreliable on dating, relying on predictions of a debatable molecular clock that puts mammal evolution a lot earlier than any fossils seem to indicate

Question 16

whats the new thoughts on divergence?

Answer 16

Dos Reis (2012) used a new stats test to analyse genomes combined with fossil calibrations which estimates that
- Marsupials diverged from eutherians 178-168mya
- Placentals diverged 90-88mya
All the present day placental orders (except primates and xenarthra) originated and radiated quickly in a 20my window after K/T extinction

Question 17

after the initial change in mammal radiation what caused further change?

Answer 17

continental movement
- linking of N/S america by isthmus of panama
africa-arabia colliding with eurasia

Question 18

when did the placental mammals reach australasia and why?

Answer 18

with first human settlers 50,000 years ago

Question 19

mammal radiation with size?

Answer 19

body size change is consistently mainly associated w/ dietary change in mammals
- herbivores largest, carnivores smallest

Question 20

what activity patterns changed with radiation?

Answer 20

lots of things became nocturnal but have reverted back to dinural
- circadian clock molecular mech

Question 21

the origin of birds?

Answer 21

closest reptile group to birds crocodilia
early flying/feathered theropod dinos much more likely skeletal and respiratory systems are bird-like - good molecular matches

Question 22

whats the timing of the first bird?

Answer 22

late Jurassic 165-150mya

small frame and reduced tail - feathers - endothermy - unique reproduction - novel lung aeration - wings

Question 23

what occured with the origin of birds?

Answer 23

mosaic evolution - the whole system came together in small bursts over ~10my

Question 24

what was the impact of the KT extinction on birds and their raditation?

Answer 24

decimated by extinction
so had to start over but distinction between bird and non-bird fuzzy
left with palaeognathae and neognathae

Question 25

what are the two opposing views on palaeognathae (ratite) evolution?

Answer 25

1. vicariant speciation from single origin driven by break up of Gondwana 2. flighted dispersal theory - convergence to gigantism and flightlessness facilitated by early tertiary expansion into dinural herbivory niche which was vacant after dino extinction :((((((

Question 26

what changed the view on ratite evolution?

Answer 26

mitochondrial genomes of two elephant birds - revealed closest lineage is ostriches

Question 27

original theory on placement of ostriches and elephant birds?

Answer 27

the oldest ratite lineages (due to isolation of madagascar/africa)

Question 28

the traditional view of neognathae evolution?

Answer 28

ducks and chickens first, then other aquatic groups - penguins/pelicans, then shorebirds, raptors and owls, songbirds last but still quite soon after KT boundary

Question 29

what did the 1988 view suggest?

Answer 29

ducks, chickens and game taken out as early/separate clade passerines and parrots go together flamingos and grebes go together

Question 30

what are the five major clades sister to the neonaves ?

Answer 30

1. nightjars, swifts, hummingbirds 2. cuckoos, buzzards, pigeons, sandgrouse 3. cranes 4. waterbirds 5. landbirds (hoatzin a sister clade)

Question 31

what is the general consensus?

Answer 31

palaeognathae and then neognathae is the rest with gallonserae the ducks etc and neonavea the rest of the rest but still arguements

Question 32

which birds survived the KT boundary and why?

Answer 32

neognathae because weren't tree living and didn't fly long distances

Question 33

what is the origin of arthropods?

Answer 33

Molecular phylogenies place origin of hexapods before land plants appear in the Ordovician, though clear fossils are only seen from the silurian

Question 34

what is the major confusion with arthropod origins?

Answer 34

when they started breathing without gills

Question 35

what are the terrestrializations of arthropods

Answer 35

Myriapods, Hexapods and arachnida

Question 36

when did the arthropods radiate and in what order?

Answer 36

Molecular clock evidence says these were 3 separate events occuring between cambrian and silurian - myriapods probably first Marine route is likeliest in each case Myriapods - thought to be first, predating any known fossils or traces; and remember the earliest, that Stonehaven myriapod from late silurian 428mya

Question 37

what is special about the trachae?

Answer 37

multiple invaginations of cuticle to form lungs/trachae | evidence it evolved convergently at least 6 times

Question 38

what is the relationship between insect size and diversification?

Answer 38

verts it is skewed - rich in small bodied taxa | no skew in insects

Question 39

what does the relationship between insect size and diversification show?

Answer 39

vertebrates are the anomaly - most don't show diversification w/ size effect

Question 40

what may influence size effect in hexapods?

Answer 40

cuticle constraints

Question 41

what are the problems in moving onto land?

Answer 41

1. Air breathing 2. Exploiting land plants as food 3. Movement 4. Reproduction, safe guarding gametes

Question 42

what caused the change to air breathing?

Answer 42

bouts of marine hypoxia More likely linked to raised temps in tropics - greater O2 supply rate supports better aerobic performance at higher temp so animals got wider thermal niche

Question 43

what were the ways animals exploited land plants as food?

Answer 43

herbivory or scavengers

Question 44

how did herbivory evolve?

Answer 44

gradually!! | HGT in some - genes needed to assimilate plant toxins - these genes then diversified rapidly and spread

Question 45

what are the challenges to overcome before becoming herbivores?

Answer 45

Plant toughness Hard-to-grip surfaces Poor nutritional quality and Plant defences, physical and chemical

Question 46

why scavenging?

Answer 46

carrion crucial for land success Many land animals die for reasons other than predation, so insects are important at mopping up remains - it's not just microbes doing the job, espc in warmer terrestrial sites