WESTERN INTERIOR SEAWAY
What Lived in WIS?
The Western Interior Seaway was never a static system, where the shorelines kept changing as the sea level changed throughout the Late Cretaceous. Whether the seaway was advancing (transgression) or retreating (regression), it brought marine life along with it. In the summers of 2011 & 2012, I conducted fieldwork in southern Alberta, Canada, in order to systematically collect fossils in the 75-million-year-old marine strata called the Bearpaw Formaion. Two papers have so far come out of this fieldwork (Konishi, 2012; Cook et al., 2017), documenting respectively northerly range extensions for a Prognathodon mosasaur and a variety of shark species. Other vertebrate remains we frequently encountered came from long-necked plesiosaurs and bony fishes. The WIS was also home for various invertebrates, many readily recognizable by all of us, such as oysters, clams, and snails. Some exceptions are ammonites, which were shelled cephalopods that superficially looked like living nautiluses while not directly related to them. A dominant ammonite that inhabited the 75-million-year-old WIS in what is now southern Alberta is a smooth-shelled Placenticeras, considered to be agile predators. During the 2011 field season, we were lucky to stumble upon what would be the largest-known ammonite shell to be collected in Alberta: a Placenticeras-like ammonite whose preserved shell was 3 feet across, and likely 4 feet across if intact (it lacked the living chamber, the last and largest part of the coiled shell, where the body of an ammonite was). You can see the discovery and collection of this ammonite in this short video clip here, made by the Royal Tyrrell Museum of Palaeontology.
Who Ate What
One way to gain insights into the trophic structure specific to a certain biological community, present or past, is to understand the ecomorphological diversity of apex predators and/or their respective food habits. Mosasaurs, for which more than 70 species have been documented, are believed to have occupied various predatory niches throughout the Late Cretaceous, indicated by diverse dental characteristics and, occasionally, by fossilized gut contents. While more than 3,000 mosasaur specimens have been cataloged in North America alone, those with gut contents are exceptionally rare. According to Konishi et al. (2014), confirmation of diet based on associated gut contents is so far limited to only eight mosasaur species.
Who Lived Where
Coming soon!