Mm. Key et al., Space-filling problems in ramose trepostome bryozoans as exemplified in a giant colony from the Permian of Greenland, LETHAIA, 34(2), 2001, pp. 125-135
In order to maintain branch strength and a confluent outer membrane, trepos
tome bryozoans had to maintain a continuous colony surface without any stru
ctural gaps. This put great constructional demands on colonies with relativ
ely thick exozones to fill the exozonal space while preserving a suitable a
utozooecial spacing for colony-wide feeding currents. This situation was ma
gnified in a giant colony of the trepostome Tabulipora from the Early Permi
an Kim Fjelde Fm. in eastern North Greenland. This single branch colony fra
gment had a diameter of 37.5 mm. A block was cut out of the 8mm thick exozo
ne, and 20 serial tangential peels were made at varying distances from the
endozone. Exilazooecial and autozooecial chamber cross-sectional area, pack
ing, spacing, and wall thickness were measured in the maculae and intermacu
lar areas. Results indicate that, in this colony, volumetric space in the e
xozone was occupied by budding new exilazooecia in the maculae and by exozo
nal budding: budding of new exilazooecia in the intermacular areas that tra
nsform into autozooecia. Exilazooecia played a dominantly space-filling rol
e in the maculae as well as helped to maintain regular spacing of autozooec
ia in the intermacular areas.