The Stromatoporiod is an invertebrate organism from the Porifera phylum, and is basically aquatic in nature. It is best known for the contribution in reef building during the Paleozoic era. It was first mistaken to be from the Cnidaria phylum and related to Corals, but later, was recognized as a calcareous sponge. The fossil records of this organism include the reef building from the middle of the Paleozoic to the end of the Mesozoic period. The fossils of Stromatoporoid are found in encrusting, branching and spherical form of calcite laminated skeletons that have pillars in the vertical position inside the laminae.
The Stromatoporoid is typically a domical structure, though other types like conical, branching, reed like and mushroom-shaped, are also found. The skeleton is made up of calcite, and was often found as a fossil. The Stromatoporoid develops by discharging calcareous sheets. The thick skeleton consisted of horizontal laminae, mamelons on the upper side of the structure, astrorizhae or dendritic canals on the mamelons and vertical pillars inside the laminae. The living tissues can be found in the layers closer to the skeleton. The speciality of this organism is that, it was a prominent reef builder, and with the help of bacterial stromatolites, it often built reefs. It is very similar in appearance to the Sclerosponge, but has a few significant differences.
The first form of Stromatoporoid in a mud mound structure was found that belonged to the middle of the Ordovician era. Compared to the later developed species, these were very small and were commonly found near the islands and in the carbonate shelves and platforms. This species resides in shallow, warm water areas where, the sediments are relatively less and the energy is moderate. Other species developed at the same time were residing at a deeper depth in muddy and soft substrates. These two types flourished in wide variety and numbers during the Ordovician era, but by the end of this era, the Stromatoporoid species suffered badly by the cold snap. Later, again by the middle of the Devonian era, the Stromatoporoid developed to form gigantic reefs with a height of more than hundred meters. Later in the Mesozoic era, again, it was found in the reef community. The Mesozoic species preferred to reside in high energy, unstable, shallow and high sediment areas. It completely disappeared in the late Cretaceous era, and started to re-appear by 1970s in the new form under the oceans. During the Sandbian and Dariwillian era, this species experienced radiation in two pulses.
The first fossil records of Stromatoporoids were from the Botomian age of about 500 to 510 million years old or Tommotian age belonging to 521 to 535 million years ago. But the "true" Stormatoporiod fossil is the Psuedostylodictyon species that were acquired initially, belonging to the Ordovician era. Two types of species were developed at that time, namely; the Clathrodictyida and the Labechiida along with some lesser known species. The Labechiida species consisted of supporting plates with convex shape in an upward direction. In the northern and southern parts of America, the fossils of Stromatoporoid with large dome structures from the Middle Ordovician period were found. During the Ordovician period, the Labechiida was the abundantly found species. In 1967, a Stromatoporoid –like creature was discovered in the living condition.