Exam One Flashcards
(133 cards)
what is a clade?
- an evolutionary lineage
- a monophyletic group
In cladistics, groups are created based on…
derived characters
derived means
different from the ancestral condition
an apomorphy is a
derived trait
Clades are grouped on the basis of shared, derived characters, or
synapomorphies
Pleisiomorphies are…
ancestral characters – characters inherited unchanged from their ancestors
symplesiomorphies are…
shared, ancestral characters
pleisiomorphies and symplesiomorphies DONT show us…
degrees of relatedness
Crown vs Stem groups
- Stem lineages: are made up 100% of extinct species
- Crown lineages: there are still at least one species still alive
Sister taxon
the group that is most closely related but not in the group
more than half of vertebrates are..
fish!
phylogenetic trees show us…
evolutionary history
nodes represent…
hypothetical common ancestors
what is a taxon?
a group name only applied to monophyletic groups
Describe the relationship between systematics and taxonomy
A name is only applied to a monophyletic group and if it does not, then it is considered a bad name
On phylogenetic trees, time is…
relative, moving towards most recent events
fossils allow us to…
- Allows us to create more accurate phylogenies
- The field continues to advance
what are the mammalian synapomorphies?
- Produce milk with mammary glands
2. Real keratinized hair
synapomorphies
characteristics unique to a specific group
Apomorphy
different from the ancestral condition (derived traits!)
Synapomorphies need to be made to…
make trees more accurate
plesiomorphies
characteristics inherited unchanged from their ancestors
Why are plesiomorphies unhelpful for creating accurate trees?
Just because they are true for the group doesn’t mean it diserns them for others. For example, all mammals have four limbs but so do most vertebrates. As a result, it does not define mammals as a group
evolution does not have…
a goal