18 Questions
Which type of taxon includes an ancestral species and only some of its descendants?
Paraphyletic taxon
What is a key characteristic of a polyphyletic taxon?
Includes species from different evolutionary lineages
Why is it important for contemporary systematics to identify monophyletic groups as taxa?
To include all descendants of one common ancestor
What distinguishes a polyphyletic taxon from a paraphyletic taxon?
Includes organisms from different clades
In what circumstances have biologists historically named non-monophyletic taxa?
When missing data or convenience play a role
What is a common feature of a monophyletic taxon?
Includes all descendants of a common ancestor
Why is the Felidae considered monophyletic?
Because all cat species share a common ancestor that lived 25 million years ago.
What does a monophyletic taxon include?
An ancestral species and all its descendants.
Why are gorillas and chimpanzees considered sister taxa?
Because they share a more recent common ancestor with each other than with humans.
Why are orangutans classified in the Hominoidae group?
Because they share a common ancestor with gorillas and humans.
What does a node represent in a phylogenetic tree?
A common ancestor that produced two descendant clades.
Why are New World monkeys classified separately from Old World monkeys in the anthropoid group?
Because they have different evolutionary histories and geographic distributions.
Which system is proposed for identifying and naming organisms based on unique synapomorphies?
PhyloCode system
Why are shared ancestral character states like a vertebral column and four legs not useful in defining the mammal clade?
They are present in other tetrapods.
What type of evolutionary lineages and taxa are described using cladistic analyses?
Monophyletic lineages
How are the results of a cladistic analysis typically presented?
In a phylogenetic tree
What does each branch in a phylogenetic tree portray?
A monophyletic group
What is the purpose of identifying an outgroup in phylogenetic studies?
To serve as a reference point for evolution
Study Notes
Monophyletic Taxa
- A monophyletic taxon includes all descendants of a common ancestor and is defined at every level of the taxonomic hierarchy.
- Example: Felidae (family-level taxon) includes all cat species, which are descendants of a common ancestor that lived 25 million years ago.
Monophyletic vs. Polyphyletic vs. Paraphyletic Taxa
- Monophyletic taxon: an ancestor and all of its descendants are included.
- Polyphyletic taxon: includes species from different evolutionary lineages, and the most recent common ancestor is not included.
- Paraphyletic taxon: includes an ancestral species and only some of its descendants, excluding some descendants of the common ancestor.
Defining Taxa in a Classification
- A major goal of contemporary systematics is to identify taxa that are monophyletic groups, which are descendants of one common ancestor.
- Biologists have not always defined strictly monophyletic taxa, sometimes due to missing data or convenience.
PhyloCode and Cladistic Analysis
- PhyloCode is a strictly phylogenetic system that identifies and names clades instead of using traditional taxonomic categories.
- Cladistic analysis is used to describe evolutionary lineages and taxa, presenting results in a phylogenetic tree that illustrates the hypothesized sequence of evolutionary branchings.
- Every branch in the tree portrays a strictly monophyletic group, and a common ancestor is hypothesized at each node.
Identifying an Optimal Phylogenetic Tree
- Systematists use several techniques to identify an optimal phylogenetic tree, including collecting data on hundreds of characters in dozens of species.
- Researchers identify a suitable outgroup to analyze the evolutionary relationships between organisms.
Explore the concept of monophyletic taxa in the taxonomic hierarchy using the example of Felidae family and Animalia kingdom. Understand how monophyletic groups are small, complete branches on the Tree of Life.
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