Final answer:
The majority of animal lineages evolved during the Cambrian period, where the most rapid evolution of new animal phyla and animal diversity in Earth's history occurred. Some evidence suggests that complex animal species also existed during the Ediacaran and Cryogenian periods, but the Cambrian period is the major period of animal diversification.
Step-by-step explanation:
The majority of currently existing animal lineages evolved during the Cambrian period of the Paleozoic Era. This period, which occurred between approximately 542-488 million years ago, marks the most rapid evolution of new animal phyla and animal diversity in Earth's history. Many of the animal phyla that we see today, including echinoderms, mollusks, worms, arthropods, and chordates, originated during the Cambrian period.
While there is evidence of complex animal species existing during the Ediacaran and Cryogenian periods, the Cambrian period is considered the major period of animal diversification and the emergence of modern animal phyla.