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

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. The species Anaphragma undulata
Jiménez-Sánchez, Atactoporella moroccoensis Jiménez-Sánchez, Monticulipora
globulata Jiménez-Sánchez and Monticulipora irregularis Jiménez-Sánchez are new.
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 endosimbionts. An alternative proposal for their giant size is their long
zoarial life span due to their well-balanced, robust branching form, with 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.