An unusual occurrence of pellet-stuffed traces from the Middle Triassic of Northeastern British Columbia: possible ophiuroid faecal stowage structures

Faecal pellet stuffed trace fossils from the Middle Triassic (Ladinian) Liard Formation at Williston Lake in northeastern British Columbia are described. The traces occur primarily within hummocky cross-stratified sandstone beds within a mixed silicilclastic-carbonate succession interpreted to represent deposition in offshore transition and lower shoreface depositional settings. The traces consist of slender strings of faecal pellets (Tomaculum problematicum) that occur horizontally, vertically and oblique to bedding and are consistent with the original type material of Alcyonidiopsis Massalongo. Although solitary strings have been observed, many specimens occur as composite forms that emanate outwards from a single central point. These traces comprise a new ichnospecies herein named Alcyonidiopsis liardensis. The traces occur in abundance solely in beds that contain both abundant isolated faecal pellets as well as ophiuroid body fossils. In identical lithologies that are devoid of ophiuroid fossils, Alcyonidiopsis is absent as well. Available evidence supports the hypothesis that these traces were produced by ophiuroids gathering and feeding on the faecal pellets of other marine invertebrates.