
How Did Animals Get Their Skeletons?
SCIENCE Animals with skeletons did not exist before about 550 million years ago. Then, suddenly, shells, exoskeletons, and skeletons showed up in the biological record. Why? (Science) A few of these ancient, armored species are still around. Teachers, scroll down for a quick list of key resources in our Teachers Toolkit. Discussion Ideas Life on Earth has been around for about three billion years, but … Continue reading How Did Animals Get Their Skeletons?