Page 260 - Introduction to Paleobiology and The Fossil Record

ORIGIN OF THE METAZOANS 247

Figure 10.10 An Ediacara community including a fixed and mobile tiered benthos.

minute conical shells were also present in some
Ediacaran successions, including localities in
Brazil, China, Oman and Spain. Cloudina was
possibly a cnidarian-type organism with a
unique shell structure having new layers
forming within older layers. Moreover it was
probably related to a suite of similar shells
such as Sinotubulites, Nevadatubulus and
Wyattia that also occurred close to the Pre-
cambrian–Cambrian boundary. In addition to
complex multicellularity, modularity, locomo-
tion and predation, biomineralization was
already far advanced in the Late Proterozoic,
providing a link with what was to follow in
the Nemakit-Daldynian assemblages of the
earliest Cambrian. Some of the shells of
Cloudina are bored, suggesting the presence of
predators (Fig. 10.11), although it is not certain
the animals were still living when bored.

Small shelly fauna
Figure 10.11 The calcareous tube Cloudina
A distinctive assemblage of small shelly fossils displaying indications of predation. (Courtesy of
has now been documented in considerable Stefan Bengtson.)
detail from the Precambrian–Cambrian tran-
sition; the assemblage is most extravagantly
developed in the lower part of the Cambrian to the fauna. A great deal is now known about

defined on the Siberian platform, traditionally the stratigraphic distribution and paleobio-
called the Tommotian, which gives its name geography of these organisms through current