Index Fossils

noun a class of extinct jawed fishes that lived from the Silurian to the Permian period

• The acanthodian fish lived during the Silurian and Devonian periods.
• Have you heard of those acanthodian fish that lived millions of years ago?
• Those acanthodian fish were like the rockstars of the ancient seas.
• Her sharp wit was like the spines of an acanthodian fish, always ready to defend her arguments.

noun a type of organic microfossil found in rocks dating from the Precambrian era

• The presence of acritarchs in the sedimentary rock indicates a marine environment during the time of deposition.
• I found some weird acritarch fossils while digging in my backyard.
• Those acritarchs look like tiny alien eggs!
• The acritarchs scattered throughout the painting added a mysterious and ancient feel to the artwork.

noun a genus of extinct marine animals that lived during the Cambrian period

• The acrotreta fossils found in this area provide valuable information about ancient marine ecosystems.
• I heard that they discovered some acrotreta fossils down by the beach.
• Check out these cool acrotreta fossils I found while hiking!
• The acrotreta fossils serve as a reminder of the Earth's long history.