Long-time readers will know that I’ve been involved in a great long list of failed book projects. Once upon a time I made significant progress on a book about MESOZOIC MARINE REPTILES; alas, it exploded on the launch pad and everybody died. Unable to find time to do anything else (I’m working, when time allows, on a set of articles that I’ve been trying to finish since 2007), I thought I may as well re-post one of the sections of text I completed: that on the mosasaur Hainosaurus. I’ve added citations and a few small updates. [Life restoration above by Dmitry Bogdanov, from wikipedia.]

Hainosaurus is one of the largest and most spectacular of the mosasaurs. Reaching a possible length of 13 m, Hainosaurus was clearly an awesome predator, essentially capable of tackling any other animal it encountered. Direct evidence for its diet comes from the stomach contents of a Belgian specimen that had swallowed at least part of a gigantic turtle, though whether it had eaten the entire turtle or simply ripped the paddles from a floating carcass is unknown.

Compared to those of many other mosasaurs, the teeth that lined the sides of the jaws in Hainosaurus were strongly compressed from side to side and possessed finely serrated keels running the length of the crown (Lindgren 2005). They are thus superficially like those of some predatory sharks, though still with much stouter crowns [see comment below from Mike Everhart]. The teeth on the palate also had finely serrated keels. These features suggest that Hainosaurus was better able to slice through flesh and cut prey into pieces than were its relatives. Wear facets on the sides of its teeth indicate that it was frequently contacting bone when it was biting prey.

Hainosaurus was originally named by Belgian palaeontologist Louis Dollo in 1885 for a near-complete skeleton discovered in the latest Cretaceous Belgian chalk (the holotype of the species Hainosaurus bernardi). Hainosaurus fossils were later reported from the Pierre Shale of Manitoba in Canada (Nicholls 1988) and additional specimens from Sweden, France, England and Poland were recognised more recently (Bardet 1990, Jagt et al. 2005, Lindgren 2005) [adjacent image by FunkMonk]. English teeth belonging to Hainosaurus had been described as early as 1845 but were not recognised as those of Hainosaurus until 1993 (Lingham-Soliar 1993). The Canadian and French specimens proved controversial and have since been reassigned to Tylosaurus (Lindgren 2005, Bullard & Caldwell 2010) but a new species, H. neumilleri, was named in 2007 from South Dakota (Martin 2007). Hainosaurus thus inhabited the shallow seas of both Europe and North America during the Santonian, Campanian and Maastrichtian ages of the Late Cretaceous.

Several features make Hainosaurus unusual, the most notable of which is that its limb girdles are, proportionally, the smallest of any mosasaur. Hainosaurus was previously thought to possess a particularly long tail with a very high number of vertebrae. When reconstructed in this way it was estimated to be 15-17 m long (Russell 1967, Lingham-Soliar 1995, 1998). If correct, this would make it the longest mosasaur. However, articulated specimens show that this is incorrect and that a more modest 12-13 m is correct (Lindgren 2005).

In several features Hainosaurus was quite similar to Tylosaurus and as a result most experts have regarded them as close relatives within the mosasaur clade Tylosaurinae. Their paddles are similar: the forefins are elongate and narrow while the hindfins are broader due to a diverging fifth toe that has particularly large bones at its base. Like Tylosaurus, Hainosaurus has a bony ‘prow’ projecting from the tip of its upper jaw. Some scientists have described this as consisting of solid bone and have suggested that it might have functioned as a ramming device used for stunning prey, but others doubt that it was strong enough to allow such activities. Tylosaurus and Hainosaurus are also similar in possessing very elongate, slit-like bony nostril openings, though exactly what this means for the form of the external fleshy nostrils is unknown.

This is one of those brief, hurriedly-published ‘filler’ articles. Some far more substantial stuff to come very soon...

For previous Tet Zoo articles on mosasaurs, see...

Refs - -

Bardet, N. 1990. First report of the genus Hainosaurus (Squamata, Mosasauridae) in France. Comptes Rendus de l’Academie des Sciences, Paris, Serie II 311, 751-756.

Bullard, T. S. & Caldwell, M. W. 2010. Redescription and rediagnosis of the tylosaurine mosasaur Hainosaurus pembinensis Nicholls, 1988, as Tylosaurus pembinensis (Nicholls, 1988). Journal of Vertebrate Paleontology 32, 416-426.

Jagt, J. W. M., Lindgren, J., Machalski, M. & Radwakski, A. 2005. New records of the tylosaurine mosasaur Hainosaurus from the Campanian-Maastrichtian (Late Cretaceous) of central Poland. Netherlands Journal of Geosciences - Geologie en Mijnbouw 84, 303-306.

Lindgren, J. 2005. The first record of Hainosaurus (Reptilia: Mosasauridae) from Sweden. Journal of Paleontology 79, 1157-1165.

Lingham-Soliar, T. 1993. The mosasaur Leiodon bares its teeth. In Sarjeant, W. A. S. (ed) Vertebrate Fossils and the Evolution of Scientific Concepts. Gordon and Breach Publishers, pp. 483-498.

Lingham-Soliar, T. (1995). Anatomy and Functional Morphology of the Largest Marine Reptile Known, Mosasaurus hoffmanni (Mosasauridae, Reptilia) from the Upper Cretaceous, Upper Maastrichtian of the Netherlands Philosophical Transactions of the Royal Society B: Biological Sciences, 347 (1320), 155-172 DOI: 10.1098/rstb.1995.0019

- . 1998. Unusual death of a Cretaceous giant. Lethaia 31, 308-310.

Martin, J. 2007. A North American Hainosaurus (Squamata: Mosasauridae) from the Late Cretaceous of southern South Dakota. The Geological Society of America Special Paper 427, 199-208.

Nicholls, E. L. 1988. The first record of the mosasaur Hainosaurus (Reptilia: Lacertilia) from North America. Canadian Journal of Earth Sciences 25, 1564-1570.

Russell, D. A. 1967. Systematics and morphology of American mosasaurs (Reptilia, Sauria). Peabody Museum of Natural History Yale University, Bulletin 23 1-240.