Emergence, biodiversification and extinction of the chitinozoan group
Abstract Chitinozoans are considered as reproductive bodies of marine invertebrates, called chitinozoophorans. These chitinozoophorans were most likely to have been small, pelagic or necto-pelagic, soft-bodied, probably wormlike animals, and judging from the size of chitinozoans, they probably measu...
| Published in: | Geological Magazine |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Cambridge University Press (CUP)
2010
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1017/s001675681000052x https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S001675681000052X |
| Summary: | Abstract Chitinozoans are considered as reproductive bodies of marine invertebrates, called chitinozoophorans. These chitinozoophorans were most likely to have been small, pelagic or necto-pelagic, soft-bodied, probably wormlike animals, and judging from the size of chitinozoans, they probably measured from a few millimetres to a few centimetres in length. The chitinozoophorans most likely survived by grazing on phytoplankton. There is no evidence of a large colonization of the pelagic niche in the Cambrian, but from the Early Ordovician onward, this niche was exploited chiefly by graptolites and chitinozoophorans. Both groups inhabited nearshore and offshore habitats, but in contrast to the graptolites, the chitinozoans displayed their highest diversity at high latitude, in less distal (that is, upper and lower offshore) environments. The chitinozoan group evolved rapidly during the Ordovician and reached its maximum Ordovician diversity in the late Darriwilian. From the first occurrence of chitinozoans in early Tremadocian times, to the biodiversity crisis in latest Ordovician times, nearly 80 % of the morphological innovations took place. Until their extinction in the latest Devonian, chitinozoans survived through several biodiversity crises: in the early Late Ordovician, late Hirnantian, late Wenlock, earliest Emsian, and in the latest Frasnian (Kellwasser event). During the melting of the Hirnantian ice sheet, most Ordovician genera and species became extinct, but some genera extended beyond the boundary (e.g. Spinachitina , Belonechitina , Cyathochitina , Ancyrochitina ). The Hirnantian glaciation was not directly responsible for the dramatic extinction of organic-walled microfossils, but it certainly accelerated the extinction of lineages that had already been weakened since the early to mid-Katian. The late Wenlock and earliest Emsian graptolite crises affected the chitinozoophorans to a lesser degree, and the latest Frasnian Kellwasser event did not greatly affect chitinozoophorans. The disappearance of ... |
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