porifera – Nix Illustration

Cambrian Explosion Month #03: Phylum …Porifera?

Sponges were major reef builders during the Cambrian Explosion, and for the first half of the Cambrian Period the dominant reef-forming group were the bizarre archaeocyathans.

Although their reign was geologically short, lasting only about 15 million years, these tiny calcified sponges were incredibly numerous and diverse during that time, with hundreds of different species known from warm shallow marine waters all around the world. They came in a huge range of shapes, including cups, cones, funnels, towers, and irregular blobs, and were so weird that they weren’t even properly recognized as being sponges until the 1990s.

Cambrian Explosion Month #02: Phylum Porifera

Sponges are one of the very oldest branches of the animal family tree, originating sometime in the Proterozoic Eon. Fossils are known from at least 600 million years ago, and their ancestry probably goes back even further back than that into the Cryogenian Period or late Tonian Period, at least 750 million years ago.

So it’s not especially surprising that sponges were already common and highly diverse in the Cambrian, with representatives of the major modern groups all present – demosponges, glass sponges, and calcareous sponges.