What topic are the man and woman discussing?

M: I really appreciate your filling me in on yesterday’s lecture.
W: No problem. I thought you might want to go over it together. And, anyway, it helps me review. Hope you’re feeling better now.
M: I am. Thanks. So, you said she talked about squid? Sounds a little strange.
W: Well, factually, it was about the evolution of sea life—a continuation from last week. The octopus and the squid descended from earlier creatures with shells. They survived by shedding their shells—somewhere between 200 and 500 million years ago.
M: That’s a pretty long span of time. Some squid are really huge. Can you imagine something that big if it still had a shell?
W: Actually, it’s because they lost their shells that they could evolve to a bigger size.
M: Make sense. I’ve read about fishermen who caught squid that weighed over a ton. Did she talk about how that happened?
W: Not really. But she did mention some unusual cases. In 1933 they caught a squid in New Zealand... let’s see here... it was twenty-two yards long.
M: Remind me of all those stories of sea monsters.
W: Dr. Simpson thinks there are probably even larger ones that haven’t been found because squid are intelligent and fast—so they can easily get away from humans. Maybe some of those monster stories are true.