Article: Faunal succession and mode of life of Silurian gastropods in the Arisaig Group, Nova Scotia
Three basic types of Silurian gastropod faunas are recognized in the near-shore deposited Arisaig Group, Nova Scotia. A hard-bottom, shallow marine platform fauna is characterized by trochiform pleurotomariaceans. A soft-bottom, shallow marine platform fauna has dominant high-spired gastropods, and lacks the trochiform pleurotomariaceans. A more off shore, soft-bottom, open-lagoon fauna is typically composed of trochiform holopeids, although these give way to small bellerophontaceans in shallower water. Morphologically similar, but taxonomically different, faunas reoccur with repetition of environments in successive regressive sedimentary phases.High-spired gastropods and explanate bellerophontaceans show morphological adaptations to life on a soft bottom. Trochiform pleurotomariaceans were associated with a harder bottom, while many other Arisaig gastropods were probably algal foliage dwellers.