Abstract
The long genal spines, the wide perforated bilaminar fringe, convex cephalon and stunt remaining body represent the major morphology typical of trinucleid trilobites habitat. The stabilization of the body on the sea floor has been considered to be the chief function of genal spines.
The concept is supported by findings of specific traces (ichnofossils). The genal spines probably also played a protective role against predators.
Another possible function, however, may be a balancing of the relatively large and heavy cephalon, to relocate the gravity centre relatively anteriorly. 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.
Thanks to the long spines, the center of gravity of trinucleid cephalon could be shifted quite far back, probably close up to the occipital ring.