Friday, 12 February 2021


Kourisodon Puntledgensis
Mosasaurs were large, globally distributed marine predators who dominated our Late Cretaceous oceans.  Since the unearthing of the first mosasaur in 1766 (Mulder, 2003) we've discovered their fossil remains most everywhere around the globe — New Zealand, Antarctica, Africa, North and South America, Europe and Japan.

One of my favourite specimens is a juvenile on display at the Royal Tyrell Museum in Alberta. That particular mosasaur is smaller than many of the marine reptiles in their collection but wonderfully preserved with his last meal — a metre-long lizardfish. 

After this fellow died, he drifted to the bottom of the Bearpaw Sea, an ancient body of water that connected the Gulf of Mexico and Hudson's Bay, splitting North America in two. Once settled, sharks scavenged his remains but left enough for quite a view into our Cretaceous seas. The fossil was excavated in 2008 from 71 million-year-old outcrops in the Korite Ammonite Mine in Alberta, Canada.

The specimen was prepped by the Royal Tyrell's talented technician, Mark, who cheekily nicknamed the specimen Mister Sinister because of its toothy evil grin. 

We have found marine reptile remains on Vancouver Island and in northern British Columbia. Since the first find of a marine reptile on the Puntledge River, members of the Vancouver Island Palaeontological Society have made many significant paleontological finds. Found the fossil remains of an elasmosaur and two mosasaurs along the banks of the Puntledge River and this past summer, a juvenile elasmosaur was excavated on the Trent River.

The first set of about 10 mosasaurs vertebrae (Platecarpus) was found by Tim O’Bear and unearthed by a team of VIPS and Museum enthusiasts led by Rolf Ludvigsen. Dan Bowen and Joe Morin of the Vancouver Island Palaeontological Society prepped the specimens for the Museum.

In 1993, a new species of mosasaur, Kourisodon puntledgensis, a razor-toothed mosasaur, was found upstream from the elasmosaur site by Joe Zembiliwich on a field trip led by Mike Trask. A replica of this specimen now calls The Canadian Fossil Discovery Centre in Morden home.

What is significant about this specimen is that it is a new genus and species. At 4.5 meters, it is a bit smaller than most mosasaurs and similar to Clidastes, but just as mighty. Kourisodon ("razor tooth") is a genus of mosasaur that has been found from Vancouver Island in British Columbia, Canada, as well as from the Izumi Group of Japan.

Kourisodon Puntledgensis
These finds date back to the late Santonian stage and the late Campanian to the late Maastrichtian, respectively, of the Late Cretaceous. Kourisodon was originally described as a member of the Leiodontini, more recently as a Clidastine.

Interestingly, this species has been found in this one locality in Canada and across the Pacific in the basal part of the Upper Cretaceous — middle Campanian to Maastrichtian — of the Izumi Group, Izumi Mountains and Awaji Island of southwestern Japan. We see an interesting correlation with the ammonite fauna from these two regions as well.

In 2005, a fragmentary skeleton from exposures of the Izumi Group on Shikoku Island, Japan, was assigned to Kourisodon sp.

The Japanese specimen had longer maxillary teeth along with a few other differences from K. puntledgensis, which the authors interpreted to mean that this individual belonged to a second species, although this new species has not yet been formally named. Other fragmentary remains from the Izumi Group have been tentatively assigned to K. sp., some of which represent juvenile animals.

Until recently, mosasaur remains from the Izumi Group (Upper Cretaceous) in southwest Japan comprised only scattered finds. Recently, additional fossil material has been unearthed from the upper Campanian Hiketa Formation in Kagawa Prefecture.

A new Kourisodon sp. has just been recorded, on the basis of portions of skull and mandible which has small and laterally compressed teeth. A few teeth of the same or similar type have previously been described from the Maastrichtian Mutsuo Formation in Osaka Prefecture. A report of Mosasaurus sp. A, which resembles M. missouriensis and M. dekayi, is based on some cranial and mandible remains, inclusive of numerous teeth and a few well-preserved cervical and two incomplete dorsal vertebrae, from the Maastrichtian Mutsuo Formation in Osaka Prefecture.

There's still a bit of sorting to do to tease out the lineage of these lovely marine reptiles. A slender tooth of Mosasaurus sp. from the Mutsuo Formation has since been reassigned to Platecarpus (Plioplatecarpinae) yet may indeed be a species of Mosasaurus. It is currently recorded as Mosasaurus sp. B. Many smaller specimens of mosasaurids have been found in the Izumi Group. It may have been that these are juvenile mosasaurs or smaller-sized, Kourisodon-like animals. Recent finds of Kourisodon sp. from the upper Campanian Hiketa Formation and the Maastrichtian Mutsuo Formation suggests that we are seeing Kourisodon-like animals and a strong correlation with our own Pacific fauna from the Nanaimo Group.

What we do not see is a correlation between our Pacific fauna and those from our neighbouring province to the east. 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. What we see in our faunal mix reinforces the provinciality of the Pacific faunas — though a  strong correlation with Cretaceous Japanese fauna — and their isolation from contemporaneous faunas in the Western Interior Seaway.