Friday, 18 December 2020

MIGHTY DOVE CREEK MOSASAUR

Dove Creek Mosasaur (Tylosaur) found by Rick Ross, VIPS
This specimen of the teeth and lower jawbone of a large marine reptile was discovered by Rick Ross, Vancouver Island Palaeontological Society, during the construction of the Inland Highway, near the Dove Creek intersection on Vancouver Island.

If you look closely, you can see several smaller disc-shaped objects to the upper right. These are part of this fellow's sclerotic eye-ring.

These bony plates allowed for safe hunting in deeper waters as the structures protected the delicate eye tissue from the intense water pressure. Diving birds have these same bony plates to aid them in the same way.

Mosasaurs had a hinged jaw that allowed them to swallow prey larger than themselves. They evolved special pterygoid teeth projecting back into the roof of their mouths that acted as guards against escaping prey. The jawbones Rick found were exposed just up to the hinge. Given the size, this toothy fellow could have been as much as seven (7) metres long and weighed up to a tonne.

Along with the significant find of the mosasaur, Rick Ross collected many ammonites and other marine invertebrates exposed during the construction of the Inland Island Highway. He donated the majority of them to the Royal BC Museum in Victoria. They now adorn a cabinet bearing his name and are tucked lovingly in with stories he wrote about his collecting adventures.

Urakawites heteromorph found by Rick Ross, VIPS
Science owes a great debt to the keen eye and fast thinking of Rick Ross for his work in recovering the specimen. Rick was out on a Sunday looking through the blocks that destined to be crushed to finish up the tail end of the new highway construction. The crews had just dropped a pile of massive blocks near the Dove Creek Road crossing.

Each of the blocks was one to five tonnes in size. Rick was looking through them when he spotted a concretion sticking out. It didn't look all that different from the hundreds he had been found up and down the highway. Interested to see what it might contain, Rick took his geology hammer and struck a blow. Off popped the end and inside was a large perfect mosasaur tooth.

Looking closer, he could see bone sticking out in several other places within this massive block. Excited for the find and not quite sure how to approach excavating it from an active construction site, Rick searched the highway and finally located a maintenance working greasing up some heavy machinery. Rick excitedly told the field mechanic about the find and inquired who would need to be called to save the block. His answer was disappointing. The block was destined to be bulldozed in the morning. 

Panicked but still hopeful, Rick asked who his supervisor was and how to reach him on a Sunday. While initially hesitant, the urgency and excitement in Rick's voice swayed him. With a warning that the supervisor would likely not be impressed to get his call, he relented and shared the telephone number. Rick dialled the number and received the predicted reaction. Unrelenting, Rick swayed the supervisor who agreed that if Rick could get a truck up to the site first thing in the AM, the block could be lifted onto the truck. The next hour was filled with phone calls and putting together a plan to get the mighty block.

Rick called Pat Trask from the Courtenay Museum. The two are fossil hunting buddies and Rick was sure that Pat would be up for the challenge. The next call was to Doug Embree, another fossil hunting buddy from the Comox Valley. As luck would have it, Doug's brother Sam had a two-tonne flatbed truck that they would be able to use. The struggle now was would it take the weight? Monday morning arrived and the block was lifted onto the flatbed with the aid of a drill hole and chain through one corner.

The truck groaned and leaned heavily all the way into town. They had to come in via the 17th Street Bridge as a safe route to the Courtenay Museum. the local building store lent the use of a large forklift to lift the block from the heavily tilted truckbed down onto the back deck of the museum. Once in place, it was far too big to move. It sat there for almost seven years before finally being shipped to a preparatory lab down in Washington. There it was prepped and whittled down to the still massive block we see today.

This specimen is now housed in the Courtenay and District Museum on Vancouver Island, British Columbia. The jaw and associated bones are tagged as a mosasaur, but exactly what kind will need more study. We may be looking at a Tylosaurus, a very large mosasaur with an elongated, cylindrical premaxilla (snout) from which it takes its name. These were the big boys of our ancient seas who snacked on plesiosaurs and other smaller marine reptiles.

T. proriger specimen found with a plesiosaur in its stomach
In 1918, Charles H. Sternberg found a Tylosaurus, with the remains of a plesiosaur in its stomach while collecting in the Smoky Hill Chalk of Logan County, Kansas. You can visit the specimen at the Smithsonian.

Like many other mosasaurs, the early history of this taxon is complex and involves the infamous rivalry between two early American palaeontologists, Edward Drinker Cope and Othniel Charles Marsh. Cope wins the day in terms of longevity in his naming of these mighty beasts.

Though many species of Tylosaurus have been named over the years, only a few are now recognized by scientists as taxonomically valid. They are: Tylosaurus proriger (Cope, 1869), from the Santonian and lower to middle Campanian of North America (Kansas, Alabama, Nebraska) and Tylosaurus nepaeolicus (Cope, 1874), from the Santonian of North America (Kansas). Tylosaurus kansasensis, named by Everhart in 2005 from the late Coniacian of Kansas, has been shown to be based on juvenile specimens of T. nepaeolicus.

It is likely that T. proriger evolved as a paedomorphic variety of T. nepaeolicus, retaining juvenile features into adulthood while attaining a much larger adult size.

Along with plesiosaurs, sharks, fish, and other mosasaurs, Tylosaurus was a dominant predator of the Western Interior Seaway during the Late Cretaceous. The genus was among the largest of the mosasaurs — along with Mosasaurus hoffmannii — with the possibly conspecific Hainosaurus bernardi reaching lengths up to 12.2 meters (40 ft), and T. pembinensis reaching comparable sizes. T. proriger, the largest species of Tylosaurus, reached a whopping 14 m (46 ft). While the Dove Creek Mosasaur was half that size, it may be one of T. proriger's smaller cousins.

Photo One: Dove Creek Mosasaur by Heidi Henderson. Courtenay Museum Collection.
Photo Two: Urakawites heteromorph ammonite by Rick Ross. RBCM Collection
Photo Three: T. proriger specimen which was found with a plesiosaur in its stomach. By Ryan Somma - Flickr, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=9004614