438 MICROFOSSILS/Chitinozoa Figure Silurian global chitinozoan biozones Figure Devonian global chitinozoan biozones Devonian global biozones Most of the chitinozoan data available for the Devonian are from Gondwana (i.e., North Africa, southern and central Europe, South America, Australia) and from Laurussia The present zonation, which benefits from a direct chronostratigraphical calibration with most of the GSSPs of the Devonian Stages (Czech Republic for the Lochkovian and the Pragian; southern France for the Frasnian and the Famennian), can be regarded as global However, some endemic chitinozoan species have been recorded from Middle and Late Devonian strata in South America (Brazil and Bolivia) The Devonian chitinozoan zonation comprises 19 biozones, and two time intervals with no biozones yet defined (Figure 8) The average duration of one biozone is about 2.5 million years Some highresolution chitinozoan regional zonations are available (e.g., central Sahara, Brazil) They demonstrate that a more precise time slicing can be expected with the Devonian chitinozoans No undisputed chitinozoans have been recorded in the Carboniferous The group apparently became extinct at the end of the Famennian, when Fungochitina ultima disappeared (Figure 4) However, this extinction may be an artefact of record as the ‘chitinozoan animals’ might have adopted a different mode of life (e.g., parasitism or non-marine) In both cases, dramatic changes might have occurred in the composition and structure of the wall of the chitinozoan vesicles, making fossilization no longer possible Palaeoenvironments Chitinozoans disappeared at about 360 Ma The assessment of the influence of environmental parameters on these microfossils therefore rests exclusively on indirect sedimentological and palaeoclimatological evidence, and on the ecology of associated organisms Very little has been published on the environmental control of chitinozoans Some authors have postulated a benthic life mode However, many observations favour a planktic or epiplanktic mode of distribution for the chitinozoans as: (1) chitinozoans, which are exclusively marine microfossils, occur in