Wednesday, December 30, 2009

Fossil Fact #12!!!!!!!!!!!!!!!!!!!!!!!!!!


Before I begin the long-awaited and promised Fact, I would like to apologize for my absence. Many of you who follow me on Facebook and Twitter are probably aware of my busy schedule these past few days, or rather, weeks. I am truly sorry for my absence, but I hope you had a GREAT Christmas and I hope you have a Fantastic New Year!! :)

Now, this Fact is the result of inspiration by the Great Craig Dylke, the Weapon of Mass Imagination who, if you have been following him closely, has definitely improved in his artwork, as can be seen on his blog, and Art Evolved!! The topic of my choosing is a bit adventurous for me, guys, so please bear with me if the quality isn't as good as my previous ones concerning Extinction and The Tyrannosauridae. The topic: The Mosasaurs, more specifically, the genus: Tylosaurus. Now, though my knowledge may not lie in the Mosasauridae, but the Coelurosaurs, I'm confident that my research will suffice. And, yes, I will offer links to sources at the end of the post.

Kings of the Cretaceous Seas- The Mosasaurs

What are the Mosasaurs?

The Mosasaurs were a group of Cretaceous marine reptilian predators that belong to the group that includes Snakes and monitor lizards known as Squamates. In fact, one could describe their appearance as being monitor lizards with flippers. Mosasaurs evolved during the Cretaceous period and inhabited the Western Interior Seaway of North America preying on large reptiles like large seaturtle genera like Archelon and Protostega, other Mosasaurs, and Ammonites. 


Fossil remains have been uncovered in Cretaceous strata in states such as Kansas, Oklahoma, etc. since the mid 19th Century. According the finds, they lived in a purely aquatic environment that covered the middle of North America thanks to rising sea levels, dividing the continent into thirds becoming the Western Interior Seaway.

A Few Known Genera-

Mosasaurus- the extinct genus for which this group is named and based; lived in the Maastrichian age (Late Cretaceous) of the Cretaceous period. 

Tylosaurus- a Mosasaur of the Late Cretaceous, and, probably one of the better known genera of this family. Though, it has many species, a few are actually considered taxonomically valid: T. progirer (Cope, 1869) (Type),  T. nepaeolicus (Cope, 1874), T. haumuriensis (Hector, 1874), and T. kansanensis (Everhart, 2005).  Like most animals in this family, they were powerful swimmers, gargantuan, fast, and heavily built. It possibly preyed on sharks, other mosasaurs, juveniles of it's species (not the individual's own offspring of course, but, possibly the offspring of another Tylosaurus.), and a few species of fish.

This animal was portrayed in National Geographic's IMAX documentary, Sea Monsters: A Prehistoric Adventure living alongside Ammonites, Plesiosaurs, Dolichorynchops,  being depicted as the top predator of the Seaway, 82 million years ago in the Late Cretaceous period.

The whole phylogenetic cladogram of this family can be found here


Mosasaurs can be identified by their similar design to modern day terrestrial monitor lizards. They have a large, flexible head, strong neck muscles, and powerful muscles attachments to the radii and ulna in the flippers. I imagine that, unlike some animals, they had open sutures in the bones, allowing room for more growth, after reaching adult size. It's also clear that they were possibly endothermic, as they required extensive meat to keep up their tremendous size and energy. They possibly had a great sense of smell allowing hunting to be much easier. 

I have a hard time believing that they are exothermic, as, though I have not had the opportunity to personally examine a mosasaur, each morning and night, they would have to pull themselves up on the beach at night, and, at dawn, would have to stay up on the shore line warming up. There were predators that would have been willing to attack a defenseless Mosasaur, despite it's size. So, they would need to get back into the water as soon as it can, and could not waste time sun-bathing. Although it is a good idea to avoid predators and allow oneself to breathe fresh air, it is still dangerous as there were predators at all times of the day and night who could be prowling the beach.  At least, that's my hypothesis for a group, I know almost nothing about.

Another thing, Mosasaurs were most likely VERY active and quick. It's true that sharks and other marine predators are quick and exothermic, but the ability to create an animal that size and sustain that size requires massive amounts of food. Other predators, can go awhile without eating.


This group possibly evolved during the Jurassic period, but, at the time, were dwarfed by the pliosaurs like Liopleurodon. It could be that they were still terrestrial animals, and had not yet filled those niches in the sea until the Pliosaurs began to die out.