What Are the Gaps in the Range of Tylosaurus in North America?

This week's blog post is not about Deinosuchus, but instead about Tylosaurus, my other favorite extinct animal, which I actually like slightly better than Deinosuchus these days.

Tylosaurus was a mosasaur, one of the sea monsters that swam in saltwater the world over during the latter half of the Cretaceous period. It was NOT a dinosaur, and instead it was in the same order as lizards and snakes, in a way making them real sea serpents (though not really snakes). Mosasaurs came in a lot of sizes like sharks do, but the largest ones, like Tylosaurus, were arguably apex predators that reached 40 or even 50 feet (12 to 15 meters).

Tylosaurus, like Deinosuchus, lived in North America during the Campanian age, but the temporal and geographical range of Tylosaurus is much broader. The oldest Tylosaurus fossils are estimated to be 90 million years old, and the youngest are estimated to be 66 million years old, which means they lived in the second half of the second half of the Cretaceous. Conveniently, there is a geologic map of North America that has an age label, "uK2", for that exact range of dates. ("uK2" has "u" for "upper", "K" for Cretaceous, and "2" for "second half".) Tylosaurus was also present in other areas besides the North American continental shelf; there are Tylosaurus fossils from such faraway places as Sweden, Jordan, and Angola. For me to estimate a global range for Tylosaurus would be too big of an undertaking, so for this post I'm going to focus on North America.

All Tylosaurus fossils are from marine sediments, such as chalk, limestone, marl, shale, etc., so it would seem that all I really need to do to estimate the range of Tylosaurus is to look at the wonderful paleogeographic maps of North America on Deep Time Maps and observe which areas were underwater. However, as with Deinosuchus, I'm not going to try extending the range beyond the end points where fossils of Tylosaurus are known from and instead focus on the gaps. There is also a taxonomic question: what about the Hainosaurus fossils? A lot of Tylosaurus fossils were classified as Hainosaurus at first. However, throughout the years, paleontologists seem to be moving toward the idea that Hainosaurus is actually just a few Tylosaurus species. Therefore, I will include any Hainosaurus fossils as Tylosaurus fossils.

What are the Canadian provinces/territories, American states, and Mexican states where Tylosaurus could have lived? The maps for 89, 87, 84, 82, 80, 77, 70, and 67 Ma help out here, but the results are so many that I'm just going to move on to the places where Tylosaurus fossils have already been found, which are these: Alberta, Saskatchewan, and Manitoba in Canada; Montana, Wyoming, Utah, Colorado, New Mexico, North Dakota, South Dakota, Nebraska, Kansas, Texas, Mississippi, Alabama, Georgia, South Carolina, North Carolina, Delaware, and New Jersey in the United States; and Chihuahua in Mexico. By using the geologic map of North America, I identified places which would be in the range of Tylosaurus but lack Turonian through Maastrichtian marine bedrock, namely the American states of Oklahoma, Minnesota, Iowa, Missouri, Arkansas, Louisiana, Florida, and Virginia. That left me with the places where Tylosaurus fossils should be found but have not been found yet: Arizona, Maryland, Tennessee, and the Mexican state of Coahuila. Putting all these things together, I have made this map, with "hypothetical extensions to the range" included as well.

Some of these places are the same ones where I expect future Deinosuchus discoveries for some reason, particularly Tennessee and Maryland. The Black Mesa in Arizona has rocks too old to find Deinosuchus fossils but not too old to find some Turonian or Santonian Tylosaurus fossils. As for Coahuila, it's interesting that it has Deinosuchus fossils but not Tylosaurus fossils so far. This map is another guide for another paleontological goal. Perhaps, without being a paleontologist, I'll buy my own land or participate in a public dig in one of those places colored in yellow someday.