L4

Question 1

Calculating phylogenies old method:

Answer 1

• Lining up fossils and draw lines between ancestors and descendants
  • Works out inherited and lost characters
  • This was the method for a long time

Question 2

Problems of phylogenetic analysis in the bad old days (4)

Answer 2

1. The evolutionary relationships were not achieved through rigorous scientific analysis (but often through hunches)
   2. Both the presence and absence of characters was considered, missing characters therefore proved unrelatedness (not the case)
   3. The lines of descent assumed we could identify ancestors (but we know that speciation is not at a species level, it is a population that gets isolated and becomes distinct, not one individual)
   4. Too much reliance on stratigraphic distribution of fossils (age doesn’t mean ancestry)

Question 3

The cladistics revolution

Answer 3

• Create character matrix (only presence of characters), if absent it has no effect
  • Analyse character distribution using parsimony or Bayesian methods
  • Identify homologous/ analogous characters and hence synapomorphies, synplesiomorphies, autapomorphies in order to eliminate homoplasy
  • Looking for inherited characters / de novo / unique to one breed
  • Don’t want characters that have evolved independently
  • Establish sister group rather than ancestor descendant relationships (theoretical population relationship)
  • Accept only monophyletic groups (hypothetical common ancestor) and all of its descendants
  • Illustrate using a cladogram

Outliers (analogous) are not needed

- Show sister group relationships

- Can mark on where characters appear

Question 4

What type of relationship does a cladogram show?

Answer 4

Sister-group relationships

Question 5

Classification in a cladist’s world?

Answer 5

• Not too much of an issue as is a hierarchical system
  • We are after Monophyletic groups (an ancestor and all its descendants)
  • Paraphyletic group is where we don’t include everything from a common ancestor (problem)
  • Get rid of polyphyletic groups (unrelated groups)

Question 6

Total group meaning

Answer 6

• A common ancestor and all its descendants
  • This can be broken down into a crown group and stem group

Question 7

Crown group meaning

Answer 7

• All the living descendants and extinct forms within them

Question 8

Stem group

Answer 8

• Totally extinct forms
  • Anything below crown group

Question 9

Importance of groupings:

Answer 9

• Crown group defined on characters in living specimens as there are more characters
  • Stem group often has unusual combinations

Question 10

What four groups did thecodonts give rise to according to H.G. Seeley?

Answer 10

• Crocodyl
  
  • Ornithiscia
  • Saurischia
  • Pterosaaria
  • Therefore dinosaurs thought not to be a natural grouping

Question 11

Dinosaur grouping type?

Answer 11

Monophyletic

Question 12

Synapsids, Anapsids and Diapsids

Answer 12

Synapsids
Lower temporal opening

Anapsids
Fully roofed temporal region

Diapsids
Upper temporal openings and lower temporal opening

Question 13

What is the nearest living sister group to the dinosaurs?

Answer 13

Crocodiles

Question 14

Seeley

Answer 14

• Looking at hip reconstruction
  • Didn’t use cladistic framework
  • Dinosaurs are monophyletic group
  • Ornithiscia is basal

Question 15

Benton’s dinosaur phylogeny

Answer 15

• Ornithiscia and everything else is a sister group
  • Stegosaurs and ankylosaurs are a sister group

Question 16

Stegosaurs 5 facts

Answer 16

• Slow herbivores
  • Small brained
  • Tails act as defence against predators
  • Front legs smaller than back legs
  • Fed on vegetation

Question 17

Ankylosauria 6 facts:

Answer 17

• Less basal than stegosaurs
  • Middle Jurassic to end cretaceous
  • Bone plated
  • Fed on vegetation
  • Slow
  • Larger brained than stegosaurs

Question 18

Ankylosauria sister group:

Answer 18

Pachycephalosauria

Question 19

Pachycephalosauria 7 facts

Answer 19

• Cretaceous only
  • Bipedal
  • Herd dinosaurs
  • Quicker as bipedal
  • Larger brain sizes as herd living
  • Herbivores
  • Skull thickening for clashing heads, could be a sexual display

Question 20

Ceratopsia 6 facts

Answer 20

• Spine spikes
  • Originally protective head area for charging, later for sexual displays
  • Jurassic to cretaceous period
  • Herd animals
  • Fed on vegetation
  • Herd animals have a higher brain to bodyweight ratio

Question 21

Herd animals have a higher ….?

Answer 21

Brain to bodyweight ratio

Question 22

Three species of ornithopoda

Answer 22

• Euornithopoda
  • Hypsilophodontidae
  • Iguanodontia

Question 23

Heterodontosaurus 6 facts

Answer 23

• Basal
  • Seperated as a sister group to ornithopoda
  • 100 species
  • Up to 23 tonnes
  • Vary in size
  • Herd animals

Question 24

Hadrosaurs 5 facts:

Answer 24

• Duck-billed dinosaurs
  • Elaborate head developments in skull for sexual display
  • Intelligent herd animals
  • Fed on vegetation
  • Intelligent

Question 25

Sauropods 7 facts

Answer 25

• Thecodontosaurus (most basal)
  • Moving up phylogenies gradually go onto 4 legs from 2 legs
  • 150 species
  • 75 tonnes
  • Small brains
  • No need to defend themselves because of size
  • Matured at 20, lifespan of 100 years

Question 26

Carnivorous dinosaurs - 7 facts

Answer 26

• Late triassic
  • 160 species
  • Ranging in size
  • Quick
  • Intelligent
  • Good brain size to body ratio as are predators
  • Reliant on thinking about catching prey

Question 27

Are birds really dinosaurs?

Answer 27

• Only group that goes past KT mass extinction
  • In a cladistic classification
  • Dinosaurs are monophyletic only if we include birds, if not they are paraphyletic without birds

Dinosaurs include birds if we are to have a correct phylogeny

Question 28

If we dont include birds dinosaurs become a ….
If we do include birds dinosaurs become a

Answer 28

Paraphyletic group

Monophyletic group