in the living room
Common Era or CE is just the modern form of AD. In our everyday usage we don't need to use the CE as we are living in the common era, not BCE, or Before Common Era. The connotations CE and BCE are generally used by historians and school teachers to clarify dates. A sentence using CE could be "The Colosseum was dedicated in 80 Common Era (or 80 CE)."
25 before the common era.
Aristotle was cleaver but not psychic! He didn't know because he couldn't know that that's what we'd call the era after him.
The era of awsmoness... and monkeys
If by "Common Era" you are referring to the era name system, then Christianity coincided with the beginning of the Common Era. In fact, the Common Era is also known as the "Christian Era" or "Current Era". The year 1 CE is the year in which a 6th century monk estimated that Jesus had been born when he created the Common Era calendar.
We are living in the Cenozoic Era which began more than 60 million years ago.
The Mesozoic Era.
The era that mammals became common would be the Cenozoic era.