Although corals are considered one of the earliest, most primitive animal groups on the planet, the stony corals that grace our reef aquariums with color and vibrance actually arose later than some of us have been led to believe. It is widely accepted that our ocean’s corals have been derived from sponges – earth’s first true animals. While this is unanimously agreed upon and nearly unfalsifiable, the first “corals” to be derived from sponges are not the ones we see in our reef aquariums. Roughly 500 million years ago in the Ordovician period (see table above), two orders of stony corals arose. These groups are known as Rugosa and Tabulata. Soon after these two groups of corals arose from their spongy ancestors, they attained prominence in our oceans and helped construct reefs with the help of their stable, calcite-based skeletons. These corals maintained their oceanic dominance until the mysterious Permian – Triassic extinction, which is thought to have been responsible for their demise. If these two groups abruptly became extinct, leaving our planet virtually devoid of corals, how do living coral species exist on earth today? Several millions of years into the Triassic period, another group of corals arose. Since Tabulata and Rugosa had already become extinct, many paleobiologists hypothesize that this new group of corals had not been derived from one of these extinct groups, but came from sponges, just as the two extinct groups did during the Ordovician period. This new group is known as Scleractinia – the aragonite-based stony corals we know and love.… More:
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