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Trepostomate bryozoans from the upper Katian (Upper Ordovician) of Morocco: gigantism in high latitude Gondwana platforms

Published online by Cambridge University Press:  04 June 2015

Andrea Jiménez-Sánchez
Center of Biology, Geosciences and Environmental Education, University of West Bohemia, Klatovská 51,306 19 Plzen, Czech Republic, 〈〉
Enmanuelle Vennin
Biogéosciences, Université de Bourgogne, 6 bd. Gabriel, 21000 Dijon, France, 〈〉
Enrique Villas
Departamento de Ciencias de la Tierra, Facultad de Ciencias, Universidad de Zaragoza, C/ Pedro Cerbuna 10, 50009 Zaragoza, Spain, 〈〉


A study of the Upper Ordovician trepostomate bryozoans belonging to the families Amplexoporidae and Monticuliporidae, from the eastern Anti-Atlas of Morocco, is presented here. They occur in the marly to fine-grained limestone, intermediate unit of the Khabt-el-Hajar Formation, late Katian in age, representing outer-ramp depositional environments. They inhabited the highest paleolatitude known for a bryozoan fauna during the Ordovician, estimated at more than 65–70ºS. A total of 11 species of the genera Anaphragma, Atactoporella, Homotrypa, Monotrypa, Monticulipora, and Prasopora are described. Three species are already known from the equatorial-tropical paleocontinents of Baltica, Laurentia, and Siberia: Anaphragma mirabile, Monotrypa jewensis, and Prasopora falesi. Four new taxa are described:Anaphragma undulata, Atactoporella moroccoensis, Monticulipora globulata, and Monticulipora irregularis.

The two species of Anaphragma and the one of Atactoporella display significantly larger zoarial sizes than congeneric species, representing gigantism among bryozoans. Polar gigantism is rejected for the two species of Anaphragma as is gigantism related to photosynthetic endosymbionts. An alternative proposal for their giant size is their long zoarial life span due to their well-balanced, robust branching form, with a relatively wide basal supporting surface, adapted to unconsolidated substrates in environments below wave base. Their great stability in outer-ramp environments, with infrequent storms, would allow the zoaria to grow for an extended time and reach large sizes before being overturned and buried. Atactoporella moroccoensis, has both zoaria and zooecia gigantic, suggesting a hypothesis of polar gigantism.

Copyright © 2015, The Paleontological Society 

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