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The gigantic, shark-toothed, small-flippered, long-bodied, sea-going predatory lizard that is Hainosaurus

The views expressed are those of the author and are not necessarily those of Scientific American.

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Life restoration of Hainosaurus bernardi, by Dmitry Bogdanov.

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.

Holotype skull (IRSNB R23) of Hainosaurus bernardi, photographed at the IRSNB in Brussels.

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.

French specimen (MNHN 1896-15) suggested to be referable to Hainosaurus but more recently argued to be a species of Tylosaurus. Image by FunkMonk, from wikipedia.

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.

Another view of the fantastic Hainosaurus holotype skull (IRSNB R23) on display at the IRSNB, Brussels. Click to enlarge.

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.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at! Follow on Twitter @TetZoo.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Dartian 8:28 am 03/7/2012

    This is one of those brief, hurriedly-published ‘filler’ articles

    …which still tend to be far more informative and authoritative than most other bloggers’ best efforts.

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  2. 2. naishd 8:32 am 03/7/2012

    You are too kind. Albeit perhaps accurate…


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  3. 3. Andreas Johansson 10:24 am 03/7/2012

    everybody died

    Nevertheless, most of the living are far less productive than you.

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  4. 4. BrianL 11:23 am 03/7/2012

    I agree with Dartian that what you term your ‘filler posts’ do not read as such: Rather, they read like you putting a random tetrapod in a deserved spotlight.

    While I can understand if you feel that much of your unfinished articles would not be up to (your) snuff, I am fairly certain that all of them would be welcomed and appreciated by your readers and though they might not meet your own standards, they might well meet ours.
    After all, if your other readers are anything like me they eagerly anticipate and greatly enjoy whatever you post for them.

    Of course, this is just a polite, respectable way for me to beg to read some of those articles.

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  5. 5. llewelly 11:26 am 03/7/2012

    random off topic question – how many lineages of aquatic reptiles (that is, non-mammalian non-avian amniotes :) from the mesozoic survive to the present?

    I thought of sea turtles, salt water crocodiles, and (maybe?) sea snakes.

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  6. 6. naishd 11:27 am 03/7/2012

    Brian: this really is quite the day for compliments; keep ‘em coming. Seriously, I strive to maintain a high standard, so no half-finished stuff, alas.


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  7. 7. David Marjanović 11:41 am 03/7/2012

    Awesome. I didn’t even know any mosasaur had serrated teeth, or anything at all had serrated non-marginal teeth… and of course I didn’t know Hainosaurus had been shortened!

    Is it known if it had the kink in the tail that indicates an ichthyosaur-like tail fin? It’s absent in the reconstruction, but that Bogdanov dude isn’t the most scientifically accurate of illustrators.

    I thought of sea turtles, salt water crocodiles, and (maybe?) sea snakes.

    Sea turtles.

    Crocodiles as crocodiles, but not as saltwater animals. Funnily, gharials were marine till quite recently, and had been so since their appearance in the Cretaceous.

    Sea snakes are young. They’re elapid colubroids.

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  8. 8. David Marjanović 11:52 am 03/7/2012

    Comptes Rendu


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  9. 9. Tylosaur 12:39 pm 03/7/2012

    Darren, Thanks for another interesting article….

    As an update, I would add that we just published a paper on well preserved mosasaur skin, including scales….

    Lindgren, J., Everhart, M.J. and Caldwell, M.W. 2011. Three-dimensionally preserved integument reveals hydrodynamic adaptations in the extinct marine lizard Ectenosaurus (Reptilia, Mosasauridae). PLoS One.

    It is available free on-line.

    Mosasaur scales are very, very small compared to the overall size of the animal (roughly the same size as you would see on a small snake… I had suggested years ago that they were on the way to losing them altogether, but Lindgren’s description of Plotosaurus from California seems to indicate that some species, at least, still had scales prior to the extinction event….

    Mosasaur scales are roughly diamond shaped, with single keel along the long axis… functionally similar to shark denticles, but otherwise very different.

    I would respectfully disagree that the teeth of Hainosaurus are “shark-like”…. while they do have two carinae that are finely serrated, they are much more circular in cross-section… more robust and much more suited for biting down on crunchy things like turtles.

    Dollo (Dollo, L. 1887. Le hainosaure et les nouveaux vertébrés fossiles du Musée de Bruxelles. Revue des Questions Scienfiques XXI 504-539, April 1887) did mention the remains of a turtle with the specimen he described…(page 520), “Quoi qu’il en soit, le Hainosaure se nourrissait assurément de tortues marines, car nous en avons trouvé des restes dans sa carcasse.”

    Roughly translated, he said, “However, Hainosaurus undoubtedly fed upon marine tortoises, because their remains have been found in its carcass.”

    That said, the turtle specimen has not yet been relocated. There are other specimens, however, that do show pretty obvious bite marks from a large mosasaur.

    Thanks for reposting!



    Mike Everhart
    Adjunct Curator of Paleontology
    Sternberg Museum of Natural History
    Fort Hays State University, Hays, KS

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  10. 10. naishd 12:56 pm 03/7/2012

    Mike – thanks indeed for that. Yes, good call, the teeth are only shark-like as goes being serrated, I know that they are much stouter in crown shape. I think I first used the ‘shark-like’ thing because another author did (maybe Lingham-Soliar). Anyway, I’m going to add a qualifier to the text.


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  11. 11. busterggi 2:20 pm 03/7/2012

    Has anyone checked those two giant turtle paddles against my buddy at the Peabody at Yale?

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  12. 12. 3:11 pm 03/7/2012

    As the largest mosasaur I knew in 1989, Hainosaurus was featured in scale with other prehistoric reptiles in A Gallery of Dinosaurs & Other Early Reptiles, which is now online here.

    Nice to see it again.

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  13. 13. LeeB 1 3:11 pm 03/7/2012

    Are the teeth more or less compressed than those of Kourisodon puntledgensis or Prognathodon kianda?


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  14. 14. accipiter 4:39 pm 03/7/2012

    interesting, always loved mosasaurs, so awesome! i didn’t knew Hainosaurus had been shortened either… do anyone knows if there have been any weight estimates for large mosasaurs? long and thin as they are i’m pretty sure something like Hainosaurus, even at 13m whouldn’d weight much more that “only” 7 tons or so right?

    thanks for the link, Dave, speaking of big varanoïds, Megalania/Varanus priscus is really huge in this one! i didn’t realised it was so big! it also brought me memories to see again the old ugly ,flattened fat reconstitution of shonisaurus…

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  15. 15. JAHeadden 10:22 pm 03/7/2012

    Teeth in Carinodens fraasi, belgicus are pretty strongly laterally compressed, although this is somewhat of an effect of the long mesiodistal length of the crown relative to its height.

    I suspect serrae/denticles are UNDERreported in mosasaurs. High carnivory/low durophagy/low piscivory should result in more compressed teeth, and thus potentially the carinae should favor production of denticles.

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  16. 16. John Scanlon FCD 5:13 am 03/10/2012

    “English teeth belonging to Hainosaurus…”

    Well, English teeth are famously bad, but serrated carinae aren’t typical, are they? Darren?

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