Tubuliporate bryozoans are tiny animals that had their heyday during the Paleozoic. Tubuliporates first appear as fossils about 480 million years ago and become common and diverse during the couple of million years following. What fossilized were their calcified skeletons that formed tubular, protective coverings around their soft body parts. Some had strong skeletons that fossilized well, while others had delicate skeletons that tended to break up. Regardless, they formed colonies that grew into reefs as skeletal material piled up over time. Fossilized reefs became limestones and shales. In the huge extinction event at the end of the Permian (about 250 million years ago), tubuliporate bryozoans were decimated, but some survived. They diversified again during the Cretaceous (starting about 145 million years ago). While they are still on Earth today, they are not nearly as common or diverse. In most habitats, corals have taken their place as reef-builders.

Bryozoans have an ample fossil record. Thousands of fossils have been found that date to the early Ordovician (about 480 million years ago) and later. However, bryozoans don’t appear in older rocks that contain fossil evidence of most other animals without backbones (invertebrates). The earliest bryozoans may have lacked the hard body parts that fossilize. Also, because they are microscopic in size, bryozoans could be easy to miss if it weren’t for their colonial behavior. Bryozoans live in huge colonies of thousands or millions of identical individuals that form moss-like coverings on the sea bottom. Beginning in the Ordovician, fossil bryozoans are found as limestone made of their broken up skeletons. Many buildings include marble (derived from limestone) made from bryozoan remains. As Bryozoans got really abundant during the Mississippian (about 350 million years ago), they became an important food source for bottom-feeding organisms, and they continue to play that role today.