Diversity dynamics and evolutionary patterns of Carboniferous Bryozoa
Final Report Abstract
1) Bryozoan generic diversity rises in the period from the Lower Famennian to the Viséan. The Devonian/Carboniferous boundary is marked by an increase of extinction rates of bryozoans (Hangenberg event). 2) The Tournaisian is an evident diversification event among bryozoans in Carboniferous. It shows the highest increase of originations against extinctions (23 vs. 9 extinctions). Consequently, the Viséan shows the highest bryozoan generic diversity as well as the highest species per genus ratio during the Carboniferous. 3) The Serpukhovian and the Bashkirian show continuous decrease in the bryozoan diversity, with the absolute minimum in the Bashkirian (mid-Carboniferous event). Rates of evolutionary changes are also low at this time. Similar patterns were observed for rugose corals. 4) During the Moscovian the bryozoan diversity increased slightly, both the origination and extinction rates were high, but originations prevailed. During the Kasimovian and Gzhelian the bryozoan diversity dropped, with largest discrepancy between originations and extinctions in the Gzhelian (1 origination v. 15 extinctions). 5) Fenestrates were the most successful bryozoan group in the Carboniferous, followed by rhabdomesine cryptostomes and cystoporates. Trepostomes were significantly reduced after the mid-Carboniferous crisis. The reasons of it maybe of an intrinsic nature. Adaptations for better food supply are supposed to be the most important trends in the Carboniferous bryozoans. Such adaptations concerned external morphology (colony form, maculae) as well as internal morphology (zooidal structures like hemisepta or ring septa, and larger polypides). Fenestrates and cystoporates were capable to produce various colony forms due to extrazooecial skeleton (fenestrates) and vesicular skeleton (cystoporates). Rhabdomesine cryptostomes could develop various internal structures which increased the stability of the colony without high energetic costs. Contrary, trepostomes due to their irregular organization had limited ability for external modifications as well as for increase of the interapertural distances. The necessary space for larger polypides could be provided to high energetic costs by development of massive skeletal walls. 6) Bryozoan diversity dropped significantly during the mid-Carboniferous crisis, showing low both origination and extinction rates. The total bryozoan diversity was not affected by the Hangenberg event (D/C boundary). However, this event resulted in significant taxonomic changes within the bryozoan assemblages due to high rates of extinctions and originations. The Carboniferous/Permian boundary is marked by a strong discrepancy of originations and extinctions, what resulted in the diversity fall during the Asselian. 7) Reasons of the diversity dynamics of the Carboniferous bryozoans are both extrinsic and intrinsic. Extrinsic factors regulating bryozoan diversity were climate, eustatic sea level oscillations, food supply, biotope availability, predation. Among the intrinsic factors most important is the constructive morphology of skeleton (wall structure, vesicular skeleton, heterozooecia, etc.) which enables development of certain adaptations. The main trends in the morphological evolution of the Carboniferous bryozoans were external modifications for improvement of filtering and enlargement of polypides. These trends were apparently triggered by suppressed food supply (most certainly near the D/C boundary) as well as the increasing variability of food. The forms which were adapted for intensive filtering and taking a broader food range were in advantage.
Publications
- 2013. Stenolaemate bryozoan fauna from the Mississippian of Guadiato Area, southwestern Spain. – Spanish journal of palaeontology, vol. 28. 2013, Issue 2, pp. 173-192.
Ernst, A. & Rodríguez, S.
- Famennian (Upper Devonian) bryozoans from borehole Velbert 4, Rhenish Massif (Germany). Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen, Vol. 273. 2014, Number 1, pp. 25-44.
Tolokonnikova, Zoya; Ernst, Andrej; Herbig, Hans-Georg
(See online at https://doi.org/10.1127/0077-7749/2014/0414) - Bryozoan fauna from the Mississippian (Visean) of Roque Redonde (Montagne Noire, southern France).
Geodiversitas, Vol. 37. 2015, Issue 2, pp. 151-213.
Ernst, A., Wyse Jackson, P.N., Aretz, M.
(See online at https://doi.org/10.5252/g2015n2a2) - Tournaisian (Lower Mississippian) bryozoans from Belgium. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen, Vol. 278. 2015, Number 1, pp. 23-45.
Ernst, A., Tolokonnikova, Z., Poty, E., Mottequin, B.
(See online at https://doi.org/10.1127/njgpa/2015/0515)
