The Most Ancient Branch Point in Animal Phylogeny is That

Question

The most ancient branch point in animal phylogeny is that between having
A)radial or bilateral symmetry.
B)a well-defined head or no head.
C)diploblastic or triploblastic embryos.
D)true tissues or no tissues.
E)a body cavity or no body cavity.

Accepted Answer

The most ancient branch point in animal phylogeny is between animals that have true tissues and those that do not. This is because all animals evolved from a common ancestor that was likely a colonial protist, and the evolution of true tissues was a major step in the diversification of animal life. The other choices (radial vs bilateral symmetry, head or no head, diploblastic vs triploblastic embryos, and body cavity or no body cavity) are all later evolutionary developments that arose after the initial evolution of true tissues.