Friday, 11 September 2020


Mosasaur from Manitoba, Courtenay Museum Collection
The Pacific fauna from the Upper Haslam Formation was cut-off geographically from their contemporaries living in the waters of the Western Interior Seaway.

That Seaway — also called the Cretaceous Seaway, the Niobrara Sea, the North American Inland Sea, and the Western Interior Sea  — was the large inland sea that formed during the mid- to late Cretaceous and again during the very early Paleogene. 

It split the continent of North America into two landmasses, Laramidia to the west and Appalachia to the east. We see evidence of this isolation when we look at the fossil marine reptiles from the Late Cretaceous Nanaimo Group of Vancouver Island. The Late Cretaceous Western Interior Seaway of North America has an abundant and well-studied record of fossil marine reptiles. The Pacific faunas we find on Vancouver Island were isolated from their contemporaneous faunas in the Western Interior Seaway. The ancient sea stretched from the Gulf of Mexico and through the middle of the modern-day countries of the United States and Canada, meeting with the Arctic Ocean to the north. At its largest, it was 2,500 feet (760 m) deep, 600 miles (970 km) wide and over 2,000 miles (3,200 km) long.

Betsy Nicholls and Dirk Meckert published on the marine reptiles from the Nanaimo Group (Upper Cretaceous) of Vancouver Island in the Canadian Journal of Earth Sciences in 2002.

They were comparing the newly discovered fossil from the Haslam and Pender formations (upper Santonian) near Courtenay, British Columbia, which include elasmosaurid plesiosaurs, turtles, and mosasaurs. These finds are only the second fauna of Late Cretaceous marine reptiles known from the Pacific Coast, the other being the fossiliferous shales from the Chico Group, Moreno Formation of California (Maastrichtian) that overlies the Panoche Formation.

The Nanaimo Group fossils are some 15 million years older than those from the Moreno Formation. Similarly to the California fauna, there are no polycotylid plesiosaurs — though the Nanaimo Group fauna does include a new genus of mosasaur. The species that we find on Vancouver Island lived at the same time but were not mixing geographically. What we see in our faunal mix reinforces the provinciality of the Pacific faunas and their isolation from contemporaneous faunas in the Western Interior Seaway.

Elizabeth L Nicholls and Dirk Meckert; Marine reptiles from the Nanaimo Group (Upper Cretaceous) of Vancouver Island; Canadian Journal of Earth Sciences, 2002, 39(11): 1591-1603,