Algae and the Alamo
Fossil Invertebrates

Algae are an important group of fossils, typically studied under a microscope because they are very small and tend to break up into small fragments upon death. Two main types of algae exist in the fossil record as rock builders: the red algae (rhodophyta) and the green algae (chlorophyta). These two groups are responsible for producing large volumes of carbonate sediment which is deposited on the seafloor and later becomes limestone.

The Devonian Period was rich in red algae, but was notably lacking in green algae compared to other times in the geologic record. Both red and green algae tend to be most successful in warm clear water ecosystems, typically within the photic zone. Devonian red algae are commonly found as encrusting organisms in reef deposits alongside stromatoporoids. In modern times, the green alga Halimeda is the main producer of carbonate sand and mud in tropical regions.