"Invertebrates"

Ammonites grew their shells from calcium carbonate and grew constantly throughout their life span. A relative of octopi and squids today, ammonites swam through the open ocean, preying on smaller marine animals.

This fossil replica represents an ancient sea urchin that crawled along the seafloor, feeding on algae. Although they are rarely preserved, echinoderms that looked like this had long spines like the sea urchins of today.