Page 287 - Introduction to Paleobiology and The Fossil Record

274 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Box 11.3 Neoproterozoic colonies

When was the transition complete from the isolated protist way of life to the loosely integrated
colonies of cells in the earliest poriferans? The Neoproterozoic rocks of Namibia yield some clues.
Rachel Wood and her colleagues (2002) have described a giant, fully-mineralized, complex colonial
skeleton, Namapoikea, from the Northern Nama Group, dated at about 550 Ma (Fig. 11.15). This
postdates some of the earliest putative cnidarians and sponges in the Ediacara biota, but predates
currently known metazoan reef-type ecosystems. Namapoikea is huge (up to 1 m in diameter),
robust, with an irregular structure in transverse section but apparently lacking any internal features.
It is uncertain whether this is a sponge or a coral but clearly large, modular, skeletal metazoans
were already around in the Late Neoproterozoic, providing a hitherto unexpected complexity to
terminal Proterozoic reefs and with the potential to provide both open surface and cryptic habitats.
Perhaps these encrusting sheets provided shelter for some of the fi rst micromorphic skeletal
metazoans?

(a)

50 mm
(b)
Figure 11.15 Namapoikea: (a) nodular individual perpendicular to a fissure wall, and (b) section

showing tubular construction. (Courtesy of Rachel Wood.)