5 A clade is a fancy word for any group in a phylogenetic tree that includes an ancestor and all of its descendants.
A simplified dinosaur tree is to the right.
Imagine that you have a pair of scissors and can cut the tree.
You can tell a group is a clade because it would only take one
"snip" to make the group "fall off" the tree. Five different clades
have been marked on the tree with brackets.
The clade marked 1 is clade Aves-the birds.
The clade marked 2 is clade Theropoda--the theropods.
Clades 2 and 3 are the two major groups of
dinosaurs-clade Saurischia and clade Ornithischia.
Finally, clade 5 is clade Dinosauria-the dinosaurs.
Mark on the tree using numbers 2-4 where you can "snip" oft each clade. Numbers 1 and 5 have
been done for you.
b. Triceratops belongs to two of the marked clades on this tree: 4 and 5. This means that Triceratops
is both an omithischian (clade 4) and a dinosaur (clade 5). Which
clades do birds belong to?

c. Use your answer to part b to explain why birds are dinosaurs.