meaning - How should I understand "archaeocyte" in this sentence?

Consider the following sentence:

The fossil consists of a complete skull of an archaeocyte, an extinct group of ancestors of modern cetaceans.

Does it mean "the fossil consists of a complete skull; the fossil consists of an archaeocyte; and the fossil consists of an extinct group of ancestors of modern cetaceans"?

Added:
What does the sentence mean and how should I understand "archaeocyte" here?

In the Merriam-Webster dictionary, "archaeo-" means "ancient" and "-cyte" means "cell". It seems that it doesn't make sense if "archaeocyte" means "an ancient cell" in this sentence.

The sentence is from an article in ETS's The Official Guide to the TOEFL Test(third edition).

Answer

The phrase after the comma is simply explanatory, in that it defines an archaeocyte.

The fossil itself consists of just a complete skull, specified in more detail by the words following.

Per @Stan Rogers comment below, the sentence as written is factually incorrect. "Archaeocytes" are primitive sea-sponges, or types of cell; the ancestors of modern cetaceans are "Archaeocetes" (easy mistake to make!). But we're concerned with parsing the syntax here, not the objective truth of the statement.