Overview

Brief Summary

The second largest member of the family of ocean predators Mosasauridae, commonly known as mosasaurs, Tylosaurus proriger, once dominated late Cretaceous seas (88 -80.5 million years ago) (Polcyn et al. 2013). At a staggering 13 meters long (Everhart 2002), T. proriger was the apex predator of its time (Everhart 2004). The causes for T. proriger’s early extinction are not directly known, but its relatives in the family Mosasauridae lasted until the extinction event at the end of the Cretaceous, which also wiped out the dinosaurs 66 million years ago (Polcyn et al. 2013). 

  • Everhart, M. J. (2002). New data on cranial measurements and body length of the mosasaur, Tylosaurus nepaeolicus (Squamata; Mosasauridae), from the Niobrara Formation of western Kansas. Transactions of the Kansas Academy of Science, 105(1), 33-43.
  • Everhart, M. J. (2004) Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas. The Mosasaur 7:41-46.
  • Polcyn, M. J., Jacobs, L. L., Araújo, R., Schulp, A. S., & Mateus, O. (2013). Physical drivers of mosasaur evolution. Palaeogeogr Palaeoclim Palaeoecol.
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Physical Description

Morphology

T. proriger was an incredibly well-adapted oceanic carnivore. Two rows of parallel teeth (King 2009) lined a jaw nearly 2 meters long (Everhart 2002). Mosasauridae’s flexible lower jaw allowed the reptiles to swallow their prey whole, much as snakes do (Everhart 2004). Equipped with a streamlined body and four flippers, T. proriger was most likely an ambush predator, using its powerful tail to propel itself with quick bursts of speed (BBC News ND). A recent fossil, found with rare soft tissue outlines, shows definitively that T. proriger’s tail was hypocercal, meaning that it was larger on the bottom, allowing it to propel itself through the water at great speeds like modern pelagic (open ocean) sharks (Lindgren et al.  2013). While the average was around 9 meters long (Everhart 2002), the largest T. proriger could reach an impressive length of 13 meters (Everhart 2002), more than 3 times the length of an average great white shark, C. carcharias, and more than 5 times the length of the average komodo dragon, V. komodoensis.

Not much is known about any sexual dimorphism (differences between males and females) that may have occurred in T. proriger, partially because gender is incredibly difficult to discern from fossils. However, it is known that T. proriger actually gave birth to live young, much as whales of today do (Bell et al. 1996), an unusual trait for a reptilian to have, but known in other marine reptile species such as plesiosaurs (O’Keefe 2011). 

  • BBC News. Retrieved June 27, 2014, from http://www.bbc.co.uk/science/seamonsters/factfiles/giantmosasaur.shtml?img1
  • Everhart, M. J. (2002). New data on cranial measurements and body length of the mosasaur, Tylosaurus nepaeolicus (Squamata; Mosasauridae), from the Niobrara Formation of western Kansas. Transactions of the Kansas Academy of Science, 105(1), 33-43.
  • Everhart, M. J. (2004) Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas. The Mosasaur 7:41-46.
  • King, S. D. (2009). The ability of mosasaurs to produce unique puncture marks on ammonite shells (Doctoral dissertation, Bowling Green State University).
  • Lindgren, J., Kaddumi, H. F., & Polcyn, M. J. (2013). Soft tissue preservation in a fossil marine lizard with a bilobed tail fin. Nature communications, 4.
  • O’Keefe, F. R., & Chiappe, L. M. (2011). Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia). Science, 333(6044), 870-873.
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Ecology

Trophic Strategy

T. proriger was one of the largest oceanic carnivores ever. Its diet is very well understood because T. proriger is often found with other animals partially digested in its stomach. Unlike other marine carnivores of its size, such as many whales and pelagic (open ocean) sharks, it was not a filter feeder (eats mainly plankton). In fact, T. proriger had an opportunistic diet composed primarily of fish. However, it also ate ammonites, diving birds, sea turtles, sharks, plesiosaurs, pteranodons, and even other Mosasauridae (Everhart 2002, Everhart 2004, Martin 2007, Cicimurri and Everhart 2001). 

  • Cicimurri, D. J., & Everhart, M. J. (2001). An elasmosaur with stomach contents and gastroliths from the Pierre Shale (Late Cretaceous) of Kansas.Transactions of the Kansas Academy of Science, 104(3), 129-143.
  • Everhart, M. J. (2002). New data on cranial measurements and body length of the mosasaur, Tylosaurus nepaeolicus (Squamata; Mosasauridae), from the Niobrara Formation of western Kansas. Transactions of the Kansas Academy of Science, 105(1), 33-43.
  • Everhart, M. J. (2004) Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas. The Mosasaur 7:41-46.
  • Martin, J. E. (2007). The geology and paleontology of the Late Cretaceous marine deposits of the Dakotas. Boulder, Colo.: Geological Society of America.
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Evolution and Systematics

Evolution

Evolution and Environment

The now-extinct Mosasauridae family, colloquially Mosasaurs, emerged in the Late Cretaceous, about 98 million years ago (Polcyn et al. 2013). Their evolution was probably spurred on by the rise in sea level during the Cretaceous, an average of more than 200 meters above recent sea levels (Polcyn et al. 2013). During this same period what would become South America had separated from Africa, creating a huge sea between the two. This, combined with the massive increase in sea level, resulted in a vast ‘epicontinental’ sea (oceans situated above continents instead of between them) (Polcyn et al. 2013). These seas covered so much of continental surface that it was actually given its own name; the Western Interior Seaway. This ocean covered a stretch of land from Northern Canada to Mexico.
These newly minted oceans were extensive enough to support this gigantean reptile family and enough smaller species to supply the Mosasaurs with their dietary needs. During this time there was also a sudden wave of extinctions and loss of biodiversity among marine reptiles such as ichthyosaurs (Kiernan 2002, Massare 1987), which gave Mosasauridae the room and opportunity it needed to take over.
The species T. proriger, developed fairly early in the Mosasauridae evolution, about 88 million years ago (Polcyn et al. 2013). Though it was commonly assumed that, because of its sheer size, T. proriger inhabited the deeper off shore waters of Cretaceous seas, it is now thought that they actually lived closer inshore, in the shallow waters around land (Kiernan 2002). The reason for this counterintuitive habitat is not yet known, but is most likely caused by prey availability (Kiernan 2002). T. proriger went extinct around 80.5 million years ago (Polcyn et al. 2013), but Mosasaurs clung on until the massive extinction at the end of the Cretaceous (66 million years ago), the same one that wiped out the dinosaurs (Polcyn et al. 2013).
  • Kiernan, C. R. (2002). Stratigraphic distribution and habitat segregation of mosasaurs in the Upper Cretaceous of western and central Alabama, with an historical review of Alabama mosasaur discoveries. Journal of Vertebrate Paleontology, 22(1), 91-103.
  • Massare, J. A. (1987). Tooth morphology and prey preference of Mesozoic marine reptiles. Journal of Vertebrate Paleontology, 7(2), 121-137.
  • Polcyn, M. J., Jacobs, L. L., Araújo, R., Schulp, A. S., & Mateus, O. (2013). Physical drivers of mosasaur evolution. Palaeogeogr Palaeoclim Palaeoecol.
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