week 1 Flashcards
(24 cards)
what is a phylogeny
- representation of the evolutionary relationships between different taxa
-always hypothetical
-sometimes phylogenies inferred using different methods or data types depict conflicting relationships
-composed of tips, branches and nodes
what are cladograms
a type of phylogeny with no branch lengths
what do nodes represent
common ancestry
what is a clade
- a monophyletic group formed by a common ancestor and all of its descendants
- they can be nested within eachother
what is monophyly
- based of the taxa and the ancestor of those taxa having synapomorphies (shared derived features)
- all taxa in the monophyletic group share an ancestor
-phylogenetic relationships are inferred through these shared characteristics
what is paraphyly
- a grouping where a clade/lineage/taxon is excluded
- taxa in paraphyletic groups share a common ancestor but not all descendants of the ancestor are included in the paraphyletic group
- usually based on some autapomorphic difference
what is polyphyly
- grouping not based on common ancestry
- not useful in evolutionary biology
-usually grouped based on homoplasy (same trait evolved in different lineages independently: convergent evolution)
how do we infer phylogenetic trees
comparing shared derived features among taxa (synapomorphies)
what is synapomorphy
shared homologous feature derived from a common ancestor
examples of vertebrate synapomorphies
- endoskeleton
- replacement of notochord with vertebral column
- head region with well defined sensory organs e.g. eyes, nose, ears
what is homology
same evolutionary origin (though not necessarily still same function)
what is autapomorphy
- autapomorphies are derived features only present in one taxon
- these are important for providing a ‘diagnosis’ of a species
what is plesiomorphy
- plesiomorphies are shared ancestral features
what is homoplasy
- the same derived trait independently evolved in different lineages
or - multiple independent reversals back to the ancestral (plesiomorphic trait)
how to infer trees
- parsimony and bayesian approaches are the main ones
- parsimony is used to infer relationships based on the number of evolutionary changes
- the most parsimonious hypothesis of relationships is the one with the fewest number of steps
- bayesian approaches are probability-based
- we use character matrices to encode variation among tips (e.g. morphology, DNA bases, amino acids)
what are crown groups
the last common ancestor of the living memebers of a clade and all its descendants
they include extant and extinct taxa
what are stem groups
all the extinct taxa that are more closely related to the crown group than any other living taxa
they can only be extinct never extant
what are exoskeletons
- outside the body
- most commonly mentioned for invertebrates e.g. beetle
- exoskeletal-like elements are found in vertebrates
what are endoskeletons
- inside the body
- only found in vertebrates
basic terms of anatomy
dorsal view - from above
posterior view - from behind
anterior view - from in front
ventral view - from underneath
lateral view - from the side
what are the 3 basic skeletal structures in the vertebrate skull
chondrocranium
splanchnocranium
dermatocranium
what is the chondrocranium
- envelops and protects the brain
- initially composed of cartilage in early
development - usually relegated inside the skull except for sharks
- secondary bone (forming neurocranium) replaces chondrocranium in most vertebrates, other than sharks, during development
what is the splanchnocranium
- supporting structure of jaws
- initially composed of cartilage and bone, but cartilage replaced in most vertebrates
-forms jaws and gills in fish and part of facial skeleton and ears in more derived vertebrates
what is the dermatocranium
- skull surface, facial skeleton and operculum
- composed of bone
- not developed in sharks
