Asteroid ``clans'': Super-families or multiple events?

Among the recently determined asteroid families (Zappala' et al., 1992) a number of very large clusterings are recognized. Some of them agglomerate few families previously identified as single groupings. In most cases, the new big families (called "clans") seem to be composed by different sub-clusterings connected each other by very narrow "bridges". In the present paper we analyze their possible origin and evolution: a primordial single event followed by subsequent collisions of the fragments, a super-catastrophic original impact or different collisional events overlapping by chance.