Question

use the following cladogram to answer the questions below.
amphibians mammals reptiles turtles crocodiles avian dinosaurs birds
four - limbed
fetal development within a fluid - filled sac
two holes in each side of their skulls
skulls with long, narrow snouts and teeth set in sockets
upright stance, with legs perpendicular to their body
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part 1: which ancestral traits do both mammals and birds share? support your answer with data from the cladogram.
part 2: which derived traits do birds have that the mammals do not have? support your answer with data from the cladogram.

Explanation:

Part 1: Shared ancestral traits are inherited from a common ancestor. Mammals and birds share the trait "four-limbed" (from their most distant common ancestor at the base of the clade) and "aerial development within a fluid-filled sac" (from the common ancestor linking amphibians, mammals, reptiles, turtles, crocodiles, avian dinosaurs, and birds).

Part 2: Derived traits are unique to a lineage. Birds have "upright stance, with legs perpendicular to their body" (shared with avian dinosaurs and crocodiles, not mammals) and "skulls with long, narrow snouts and teeth set in sockets" (shared with avian dinosaurs and crocodiles, not mammals).

Answer:

Part 1: Four-limbed; aerial development within a fluid-filled sac
Part 2: Upright stance (legs perpendicular to body); skulls with long, narrow snouts and teeth in sockets