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- Title
THE ANDRÉ DUMONT MEDALLIST LECTURE FROM ADAPTIVE RADIATIONS TO BIOTIC CRISES IN PALAEOZOIC VERTEBRATES: A GEOBIOLOGICAL APPROACH.
- Authors
Blieck, Alain
- Abstract
The oldest vertebrates are Early Cambrian, cephalized unossified species (craniates) from China. The oldest armoured species (euvertebrates) are Ordovician in age. After Talimaa's Gap, vertebrates have their first adaptive radiation during the Silurian when jawless species ('ostracoderms') are dominant; they have their second radiation during the Devonian when jawed species (gnathostomes), and particularly the placoderms (armoured fishes), are dominant. Tetrapods appear in the Middle Devonian among sarcopterygians (bony fishes with lobed fins); they were probably aquatic during all the Devonian period. Vertebrates did not appear in freshwater but in marine environments. Similarly, tetrapods most probably appeared in very shallow marine environments. Silurian vertebrates did occupy all the environments of the marine epicontinental platforms. Vertebrate assemblages of high energy environments ('ostracoderms' and placoderms in particular), took place with the development of late- and post-tectonic Old Red Sandstone facies (ORS). So, Devonian vertebrate assemblages are known from both marginal marine, intermediate and continental environments of the ORS, and from the marine platforms (carbonate and siliciclastic facies). Vertebrates did encounter the two end-Devonian biological crises: disappearance of'ostracoderms' at the Frasnian-Famennian crisis, and disappearance of placoderms at the Devonian-Carboniferous boundary, with a major ecological turnover at the beginning of the Carboniferous when chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes, mainly actinopterygians) became dominant. Terrestrial tetrapods (both amphibians and reptiles) occured only after the earliest Carboniferous Romer's Gap. Vertebrates suffered at the Mid-Permian Olson's Gap with a drastic decline of basal tetrapods (amphibians) followed by a radiation of reptiles. The end-Permian extinction does not seem to have been strong for vertebrates, except for tetrapods. On a geobiological point of view, at least two of the bioevents which are characteristic for the rise of Palaeozoic vertebrates may be related with an increase in the global marine oxygen rate, viz., appearance of euvertebrates during the Great Ordovician Biodiversification Event (GOBE), and the radiation of large gnathostomes (in particular placoderms) during the Devonian adaptive radiation and Predation Revolution of vertebrates. However, coincidence does not mean causal relationship. So, we must be cautious with scenarios that appeared in the scientific literature in the most recent years.
- Subjects
ADAPTIVE radiation; BIOTIC communities; COMPETITION (Biology); VERTEBRATES; DEVONIAN paleontology; ANIMAL diversity
- Publication
Geologica Belgica, 2011, Vol 14, Issue 3/4, p203
- ISSN
1374-8505
- Publication type
Article