Page 245 - Introduction to Paleobiology and The Fossil Record

232 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Box 9.12 The chitinozoan Rosetta Stone

But what really were chitinozoans? Material from the Ordovician of Estonia, described as the chi-
tinozoan “Rosetta Stone”, may have partially solved the problem. Individual vesicles are linked
together in a coiled, chain-like structure; each vesicle belongs to the same species, Desmochitina
nodosa Eisenack (Fig. 9.22). It is unlikely that these were eggs of a metazoan, because larvae would
be unable to escape from the tightly sealed and connected chambers. Therefore Paris and Nolvak
(1999) postulated that the coiled, chain-like structure represents an intermediate, immature stage,
perhaps an intra-oviduct phase, prior to the final egg-laying event. Unfortunately, distribution in

time and space of chitinozoans does not match any skeletonized metazoan group. So we are back
to speculation. Possibly chitinozoans are related to a soft-bodied “chitinozoan animal” and the
search is on to find this animal in one or more of the Paleozoic Lagerstätten.

Figure 9.22 Chitinozoan apparatus: a large cluster of Desmochitina nodus interpreted as an egg
clutch of the chitinozoan animal; the opercula are not present suggesting that the animals had
already hatched (×70). (Courtesy of Florentin Paris.)

Colonial
arrangements
Sphaerochitina Urnochitina Conochitina Ancyrochitina
Figure 9.23 Some chitinozoan morphotypes: Sphaerochitina (×160), Urnochitina (×160), Conochitina
(×80), Ancyrochitina (×240) and colonial arrangements (×40).

3 Radiolarians have proved very useful in
Review questions
sorting out the stratigraphy of mountain
1 The move from prokaryote to eukaryote belts. Why are they superior to other
cell types was a major evolutionary jump. micro- and macrofossil groups in these
How was this transition achieved and types of studies?
what sorts of implications did it have for 4 Chromistan groups such as the cocco-
life on Earth? lithophores and diatoms have a funda-
2 Foraminifera have been widely used by oil mental effect on the stability of atmospheric
and gas companies in exploration. Why and oceanic systems on our planet.
are they so useful? But such nannoplankton appeared rela-