Nekolik poznamek k funkcni morfologii trinukleoidnich trilobitu

The long genal spines, together with the wide perforated and bilaminar fringe, convex cephalon and rather stunt remaining body represent the major morphology typical of trinucleoid trilobites habitat. Traditionally, the stabilization of the trinucleoid body on the sea floor has been considered to be the chief function of genal spines (especially during the filter-feeding activity, which is considered as the principal feeding strategy of this group). This concept is well supported also by findings of associated specific traces (= ichnofossils), which is followed here. The genal spines probably also played a protective role against predators (so called "full mouth effect"). Another possible function, however, may be a balancing of the relatively large and heavy cephalon, to relocate the gravity centre relatively posteriorly. Without such balancing, the dorsoventral movements of cephalon (necessary for the digging in mud) could present a serious problem, namely in combination with the relatively weak thoracic muscles (attached to the flat and relatively minute thoracic segments). Thanks to the long spines, the center of gravity of trinucleoid cephalon could be shifted quite far back, probably close up to the occipital ring. The traditionally considered function of genal spines - e.g. stabilization of body on the sea floor is not in direct contradiction with this interpretation and may be considered as their primary function. The occurrence of wide perforated fringe and the long genal spines with robust base is considered as correlated features.