Article: The ichnogenus Beaconites and its distinction from Ancorichnus and Taenidium
D. G. Keighley and Ron K. Pickerill
Beaconites is a trace-fossil name that has been adopted indiscriminantly for unlined, lined unwalled, thinly walled, and thickly walled, meniscate backfilled burrows. The confusion is further exacerbal by the inconsistent use of the terms 'wall' and 'lining'. A wall and a lining (a type of wall) are herein restricted to features actively constructed by the burrower, and are considered distinct from peripheral features produced by simple excavation or during locomotion. Differences in the type of meniscate backfilling are also recognized and may assist in the distinction of ichnotaxa. Beaconites, and likewise the type ichnospecies B. antarcticus a lined (walled) meniscate trace fossil; B. barretti, the ichnospecies most popularly assigned to the ichnotaxon is actually unlined and unwalled, and cannot therefore be included within Beaconites. Recent emendments Taenidium describe it essentially as an unlined meniscate backfilled burrow. The diagnosis of Taenidium however, further emended to clarify that it is an unwalled structure. Forms previously assigned to B. barretti can therefore be included within Taenidium as T. barretti. Emendments to the original diagnosis of Ancorichnus describe this trace fossil as a walled ichnotaxon. These emendments are rejected because this would place the ichnogenus in junior synonymy with Beaconites; instead, the original diagnosis of Ancorichnus is re-established. Two ichnospecies, A. capronus and A. coronus are, nevertheless, considered to be separate ichnospecies Beaconites, namely B. capronus and B. coronus. The type ichnospecies, A. ancorichnus, is distinguished by structured mantle peripheral to a meniscate core. The mantle is not considered as a wall structure since it formed by the locomotive behaviour of the burrow producer.