Read Monophyletic Groups and Clades
A short NSEB read on monophyletic groups and clades, followed by the linked original question(s).
Monophyletic Groups and Clades is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Core idea
A monophyletic group contains a common ancestor and every one of its descendants. A clade is supported by shared ancestry, not merely a shared habitat or convergent trait. Tetrapoda is treated as a clade when amphibians, reptiles (including birds), and mammals are all included; excluding a descendant lineage makes a group paraphyletic.
Tetrapoda includes all descendants
Tetrapoda includes the common ancestor of amphibians, reptiles, birds and mammals and all its descendants, making it monophyletic.
Place shared derived characters on a cladogram
A character at a branch must be shared by every lineage above that branch and absent from the lineage that split below it. Hair therefore appears after tortoise splits; carnivory appears after horse splits; and purring separates the house cat from leopard. Trace each node from the root rather than matching a trait to the nearest animal name. Choose D.
Test a clade against all descendants
A monophyletic group contains one common ancestor and all its descendants. On the given cladogram, Arthropoda, Onychophora and Priapulida share a clade, so calling them paraphyletic is false. Read branching, not similarity. Choose D.
OlympIQ exam lens
- ✓A monophyletic group contains a common ancestor and every one of its descendants.
- ✓A synapomorphy at a node is shared by all descendant branches above it.
- ✓A monophyletic clade includes a common ancestor and every descendant shown.
Identify the biological mechanism first, then check that the option states it accurately and answers the exact question.
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