Cloudinidae

Cloudinids (Cloudina) are an extinct animal genus that formed small tubelike or conical fossils consisting of "funnel deeply nested in funnel" segments of calcareous material. What the animal itself looked like is still unknown. Cloudinids were widely distributed. They are quite abundant in some deposits. They are the earliest common animal form with a calcareous shell. The name Cloudinia honors the 20th century geologist and paleontologist Preston Cloud. It was first discovered by GJB Germs in 1972.

Cloudina varies in size from a diameter of 3.5 mm to 0.6 mm, and can be up to 3.5 mm long. It is a tube made from microscopic calcite crystals, that was likely to be embedded in an organic matrix. The tube is curved or sinuous, and occasionally bifurcates. The tube walls are 8 to 50 micrometers thick. Cloudina occurred in calcium carbonate rich areas of stromatolite reefs. It is found with Namacalathus, which like Cloudina was "weakly skeletal" and solitary, and Namapoikia, which was "robustly skeletal" and and formed sheets on open surfaces.

Some Cloudina fossils have a borehole in them approximately 30 micrometers in diameter. This was likely to be made by a predator. The bore holes are distributed along the tube length, mostly not at the top. This indicates that the animal filled the tube, or could retract itself down the tube.

Cloudina are characteristic of the so-called "Small Shelly Fauna" in the final Neoproterozoic period, called the Ediacaran, and disappeared in the extinction event that marks the Precambrian - Cambrian boundary, most recently dated at 542 Mya. The extinctions set the stage for the Cambrian explosion of life-forms. They are not found in deposits dated at 555 Mya.

Two species are identified C. hartmannae and C. riemkeae. Cloudina has been classified in a family called Cloudinidae and with a Cambrian class Cribricyathea. Exactly what kind of animal it was is unknown, however, it resembles serpulid polychaete annelid worms or pogonophoran worms.

They have been found in Nama Formation in Namibia, Brazil, Oman, Canada, Nevada and Dengying Formation in China.

References

• Skeletogenesis and asexual reproduction Hong Hua et al
• Morphology of Cloudina by Andrew Miller
• GJB Germs: New shelly fossils from Nama Group, South West Africa. in American

Journal of Science 272:752-761