4- Taxonomy and phylogeny Flashcards
(26 cards)
what is taxonomy
the science of naming, defining and classifying groups of biological organisms
how do taxonomy and phylogeny relate
classification of a species reflects the phylogeny
how does classification of extant and extinct species compare
classifying living species is relatively simple but classification of fossils is more complex/difficult
how did phylogenetic analysis work in the “BAD OLD DAYS”
- both the presence and absence of characters considered
- Evolutionary relationships not achieved through rigorous scientific analysis ( hunches)
- different experts would disagree on importance of characters
- used to classify via stratification of fossils , now known fossil record is patchy n biased
- lasted till 1980s
How did the cladistic revolution come about
fierce debates through the 70’s and 80’s over whether it would work, eventually everyone was convinced
How does cladistics work
1) Creation of a character matrix, focusing on presence of characters not absence (they can be lost)
2) Analyse character distribution with parsimony or Bayesian methods
3) Identify homologous/analogous characters and hence synapomorphies, synplesiomorphies, automorphies to eliminate homoplasy
4) establish sister groups rather then ancestor-descendant relationship
5) illustrate using a cladogram (triangular or square)
synapomorphoes
A synapomorphy is a shared apomorphy (clade distinguishing feature) that distinguishes a clade from other organisms and originated from the last common ancestor
synplesiomorphies
A trait shared by two or more taxa
automorphies
autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon.
Why was cladistics controversial
classification became difficult with sister groups and some groups fell out of favour and needed redefining into a cladistic hierarchy
in cladistics what type of group do u want
monophylectic = all have a common ancestor `
- don’t want a paraphylectic (group that shares a common ancestor with another group) or polyphylectic group (more then one ancestor)
How does the total group . crown group and stem group work in cladistics
Total group = everything , extinct or living
Crown = all living and some fossils that fall out inbetween
Stem = no living representatives
- any fossils that fall in the crown group have the same characters as the living crown group organisms
- anything in the stem group does not have same characters (or some) as the living organisms (inflates phylogeny)
- helps to work out when characters evolved
- simple but complicated by language issues
Case study : dinosaur relationship
how were dinosaurs initially classified
- seen as not a natural group
- thought they evolved from theodonts
- pre cladistic analysis
how did cladistics analyse dinosaurs
- cladistic analysis found reptiles to be primarily characterised by their skulls
- discovered pterosaurs were a sister group to other dinos
- saurischian and ornithischia are a monophylectic group
- crocodiles are much more basal
what are the ornithischia
armoured , horned and duckbilled dinosaurs
(ornithischia) - features of stegosaurs
- 12 species (not very diverse group)
- 300-1500 kg with thick legs
- feed on plants with beak, huge guts to break down veg slowly
- very slow moving 6-7 km/h , their size protects them
- brain 0.001% of body mass
- defining character = spines on back for protection , plates came later + basal groups have more spines
(ornithischia) - Ankylosaurs
- 30 species , middle Jurassic - late cretaceous
- armour plated with large spines on back + head
- ossified skin used for protection
- large bones in strong tail
- up to 3500 kg
- slow 10km/h
- brain only slightly bigger then stego
(ornithischia) - pachycephalosauria
- 16 species
- head butters, had a bipedal stance
- longer tail for balance
- confined to cretaceous
- last of the groups to evolve
- 2-8m long, 450 kg
- hung about in herds
- very quick , lighter +more agile. all adaptation to evade predators +avg brainsize
(ornithischia) - ceroptopsia
- 40 species , Jurassic -> cretaceous
- large but surprisingly agile
- 1m-9m, 25-7000kg, 2-4 km/h
- charge quite quickly (method of protection) 35 km/h
- herds and avg brain size
- characterised by frill at back of the skull , v ornate + elaborate with 2 big horns
(ornithischia) - Ornithopods
- 100 species , divided into 3 groups
- classic herbivores , bipedal with long tail , v variable in size 1-15m
- early Jurassic -> cretaceous
- large ones can be up to 23,000kg
- herds , speed vary greatly 60 km/h (small ones) to 15/20 km/h
- relatively intelligent
(ornithischia) features of hadrosauridae (sub-group of Ornithopods )
- duck billed dinosaurs
- elaborate structures on head due to sexual dimorphism
- intelligent animals , could make noise and communicate via structures on head
- live in herds
what are the two groups of saurischia
1) sauropods
2) theropods
(saurischia) features of sauropods
- 150 species , triassic -> end cretaceous
- different hip bone
- earliest found are bipedal then moved to quadrupedal, neck and tail elongated achieving gigantism
- 15 m tall on back legs , 40m head to tail
- 75,000 kg (no need for defence)
- tiny heads = low intelligence
- 20 yrs to maturity , lifespan about 100 yrs
(saurischia) what are segrosauria
enigman tend to ignore them
