Ceratiocaris is a genus of extinct paleozoic phyllocarid crustacean whose fossils are found in marine strata from the Upper Ordovician through to the Silurian.
They are typified by eight short thoracic segments, seven longer abdominal somites and an elongated pretelson somite. Their carapace is slightly oval shaped; they have many ridges parallel to the ventral margin and possess a horn at the anterior end.
This tidy specimen is from the Silurian mudstones that characterise the Kip Burn Formation with it's dark laminated silty bands. The lower part of the Kip Burn houses the highly fossiliferous ‘Ceratiocaris beds’, that yield the arthropods Ceratiocaris, Dictyocaris, Pterygotus, Slimonia and the fish Birkenia and Thelodus.
The upper part of the formation, the ‘Pterygotus beds’, contain abundant eurypterid fauna together with the brachiopods Lingula and Ceratiocaris. The faunas in the Kip Burn Formation reflect the start of the transition from marine to quasi- or non-marine conditions in the group.
Ceratiocaris are also well known from the Silurian Eramosa Formation of Ontario, Canada (which also has rather nice eurypterids). Photo credit / collection of: York Yuxi Wang and Tianyi Zhang
Joseph H. Collette; David M. Rudkin (2010). "Phyllocarid crustaceans from the Silurian Eramosa Lagerstätte (Ontario, Canada): taxonomy and functional morphology". Journal of Paleontology. 84 (1): 118–127. doi:10.1666/08-174.1.
M. Copeland; T. E. Bolton (1985). Fossils of Ontario part 3: the eurypterids and phyllocarids. Volume 48 of Life Sciences Miscellaneous Publications. Royal Ontario Museum. ISBN 0-88854-314-X.