Tetrapod Zoology

One of my favourite mosasaurs is the unusual Goronyosaurus nigeriensis (Swinton, 1930) from the Maastrichtian of Nigeria and Niger. Mosasaurs are Cretaceous marine lizards, (probably) closely related to gila monsters and kin (the monstersaurians) and monitor lizards and kin (the goannasaurians), and well known for evolving gigantic size (>12 m in some taxa), flippers, and paddle-like tails. Goronyosaurus is cool because, with increasing knowledge, it has become weirder and weirder and weirder…

When William Swinton first described and named Goronyosaurus (as Mosasaurus nigeriensis), it was assumed to be essentially similar to the better-known mosasaurs of Europe and North America. Azzaroli et al. (1972) were the first to realise that it was actually an aberrant mosasaur, and they reconstructed it with atypically massive cheek bones and a blunt, rounded snout tip. They also showed that the maxillae (and thus the maxillary toothrows) extended posteroventral to the orbits and that the teeth were set on bony pedicels like those seen in some crocodiles. These features and others led them to coin the new generic name Goronyosaurus. Soliar (1988) contested some of these details and produced a less aberrant-looking reconstruction, but he still concluded that the maxillary toothrows extended posteroventral to the orbits.

Lingham-Soliar (1991, 1999) – note the name change – looked anew at Goronyosaurus and now produced a reconstruction more similar to the Azzaroli et al. one than the Soliar 1988 one. He argued that, during jaw occlusion, the teeth fitted into interdental pits on the opposing jaws, that Goronyosaurus had proportionally small orbits for a mosasaur, and that it had an unusually high number of foramina on some of its skull bones. Lingham-Soliar (1991, 1999) concluded that Goronyosaurus might have had a highly sensitive snout and that it was perhaps specialised for ‘hunting in the quiet murky waters of sheltered bays and estuaries and in preying upon hidden young of marine fauna including perhaps those of other mosasaurs … Further, the very small eyes of Goronyosaurus (relatively perhaps the smallest in the Mosasauridae) suggest that Goronyosaurus did not rely heavily on vision’ (Lingham-Soliar 1991, pp. 667-668). This inspired me to produce the above sketch. Goronyosaurus is shown as a specialised, mud-grubbing mosasaur that has small eyes and relies on enhanced tactile abilities to find prey in the sediment. See below for a rather more satisfying illustration (produced by Dmitry Bogdanov, available via wikipedia).

More recently, it’s been discovered that Goronyosaurus had particularly long teeth in the premaxilla and at the anterior end of the dentary (Lingham-Soliar 2002) though, by ‘particularly long’ I mean that they were only slightly longer than the longest teeth present elsewhere in the toothrow [see image above, from Lingham-Soliar (2002). Scale bar in A and B = 25 mm, in C = 100 mm]. These long, reinforced anterior teeth may have made this mosasaur better at rapid grabbing of evasive, slippery food items.

Tongues and… venom glands?

The speculations made about the sensory abilities of Goronyosaurus have yet to be subjected to proper scrutiny and some of them can be doubted. Furthermore, whatever Goronyosaurus‘s visual and tactile abilities were like, we must remember that mosasaurs were almost certainly equipped with forked tongues, and hence would have had an efficient sense of vomeronasal chemoreception as well (Schulp et al. 2005).

Based on the probable position of mosasaurs within Platynota (the monstersaurian-goannasaurian clade), Schulp et al. (2005) made inferences about the mosasaur tongue, concluding that the bilobed and protrusible foretongue was relatively short, and that the hindtongue was robust, covered in the papillae and mucocytes typical for the squamate tongue, and still with an important role in food transport and swallowing. The mosasaur tongue, they argued, was therefore similar to that of the extant platynotans Heloderma and Lanthanotus [Lanthanotus tongue shown here, from Schulp et al. (2005). Note the bilobed foretongue and papillose hindtongue. Anterior is at the top]. A long and highly specialised forked tongue, like that seen in monitors and snakes, was thought unlikely (incidentally, the long tongues of monitors and snakes are thought to have evolved independently). However, worth noting here is that things change according to the favoured phylogeny. What if mosasaurs are more closely related to snakes that they are to other platynotans, as favoured by some authors?

This leads on to another inference we might make from phylogeny. Were mosasaurs venomous? Until recently we would have said ‘no’, given that mosasaurs lack the dental and osteological correlates of venomosity seen in venomous platynotans like the helodermatids (gila monster and beaded lizard). However, we now know that venomosity is somewhat more widespread in lizards than previously thought, and that venomous mandibular glands evolved at the base of Platynota at least (Fry et al. 2005). If mosasaurs are part of this clade, and they almost certainly are (Conrad 2008), then, yes, venomosity can be assumed to be primitive for Mosasauria. But did mosasaurs retain their venom glands, or lose them during their evolution? We don’t know, but it makes for an interesting speculation.

Refs – -

Azzaroli, A., De Guili, C. & Torre, D. 1972. An aberrant mosasaur from the Upper Cretaceous of noth western Nigeria. Accademia nazionale dei Lincei. Rendiconti. Classe di Scienze fisiche matematiche e naturali 52, 53-56.

Conrad, J. L. 2008. Phylogeny and systematics of Squamata (Reptilia) based on morphology. Bulletin of the American Museum of Natural History 310, 1-182.

Fry, B. G., Vidal, N., Norman, J. A., Vonk, F. J., Scheib, H., Ramjan, S. F. R., Kuruppu, S., Fung, K., Hedges, S. B., Richardson, M. K., Hodgson, W. C., Ignjatovic, V., Summerhayes, R. & Kochva, E. 2005. Early evolution of the venom system in lizards and snakes. Nature 439, 584-588.

Lingham-Soliar, T. 1991. Mosasaurs from the Upper Cretaceous of Niger. Palaeontology 34, 653-670.

- . 1999. Functional analysis of the skull of Goronyosaurus nigeriensis (Squamata: Mosasauridae) and its bearing on the predatory behaviour of this enigmatic taxon. Neues Jahrbuch fur Geologie und Paläontologie, Abhandlungen 213, 355-374.

- . 2002. First occurrence of premaxillary caniniform teeth in the Varanoidea: presence in the extinct mosasaur Goronyosaurus (Squamata: Mosasauridae) and its functional and paleoecological implications. Lethaia 35, 187-190.

Schulp, A. S., Mulder, E. W. A. & Schwenk, K. 2005. Did mosasaurs have forked tongues? Netherlands Journal of Geosciences – Geologie en Mijnbouw 84, 359-371.

Soliar, T. 1988. The mosasaur Goronyosaurus from the Upper Cretaceous of Sokoto State, Nigeria. Palaeontology 31, 747-762.

Comments

#1 Neil
April 13, 2009

I’d never considered the shape of a mosasaur tongue would be forked (but thinking about it being related to monitor lizards its logical!). Poisionous Moasaurs is a possibility I’d defenitely never considered! Great stuff
#2 Hai~Ren
April 13, 2009

Venomous mosasaurs? It had never crossed my mind before, but hmm… why not? After all, varanids and helodermatids are venomous.

Now it makes me wonder if venom enabled the mosasaurs to dominate the oceans, and also led to the decline (and eventual extinction) of ichthyosaurs and pliosaurs. Although why polycotylids and elasmosaurs survived needs to be accounted for.
#3 Brian Beatty
April 13, 2009

Thanks Darren, this is a great discussion about possible inferences of soft tissues in mosasaurs. I’m not familiar with Goronysaurus, but now I want to learn more, thanks for sharing it!
Regarding those inferences about anatomy and behavior, I want to comment. Unlike Anne Schulp’s analysis of the phylogenetic bracket of the tongue, the idea that the pits on the rostrum are indicative of specialized sensory abilities is fairly weak. Swinton (1930) had only a rudimentary understanding of what those pits meant, and even though work of Soares and others in recent decades have elucidated important details about those sensory pits in alligators, people still keep making this unfounded reference to sensory abilities in other groups, including cetaceans. Pits can mean a bunch of things, including an increased surface area for integumentary attachment, increased blood supply, etc.
There is discussion of these pits in the recent book, Sensory Evolution on the Threshhold, edited by Thewissen and Nummela. It is really an excellent book. I reviewed it for Journal of Mammalian Evolution (it is still Online Early) and can be found here:
http://www.springerlink.com/content/4637071472372521/?p=02a8e8412fe74c328c440801e46dbd52π=10

Your posts are always full of great insights that help people see fossil animals as just that, animals, and I’m a big fan.
#4 David Marjanović
April 13, 2009

Actual information on Goronyosaurus! Happy happy joy joy, happy happy joy joy…

from the Maastrichtian of Niger.

No, Nigeria.

And also Niger if your citation of Lingham-Soliar 1991 is correct. How many specimens are known in total? ~:-|

monitor lizards and kin (the varanids)

The goannasaurians, of which Varanidae is the crown-group, just like how Helodermatidae is the crown-group of Monstersauria.

mosasaurs are part of this clade, and they almost certainly are (Conrad 2008)

That paper is an amazing, deeply impressive work, highly detailed, but the result is full of weirdnesses that probably mean there are still not enough characters in the matrix for so many taxa. Indeed, there are 363 characters for 222 taxa – that’s just over 1.5 times the number of taxa; I wouldn’t publish below 3 times.
#5 William Miller
April 13, 2009

Venomous mosasaurs… *shudder*… If that’s true, the big mosasaurs might well win the prize for the most horrifying predator of all time.
#6 Andrea Cau
April 13, 2009

Great post, very interesting! Thank you, Darren.
#7 Edgar
April 13, 2009

Monstersauria sounds like a term brought from kaijuu taxonomy

Perhaps Darren is going to begin a series about marine reptiles? (yes!)
#8 Bjarni
April 13, 2009

Just how would non-injected venom work underwater? Especially with a mouth so accessible to the surrounding water?
#9 Carlos
April 13, 2009

Even if mosasaurs lost venom at some point they could redevelop it, like [some] snakes did.

“Now it makes me wonder if venom enabled the mosasaurs to dominate the oceans, and also led to the decline (and eventual extinction) of ichthyosaurs and pliosaurs. Although why polycotylids and elasmosaurs survived needs to be accounted for.”

AFAIK ichthyosaurs were very specialized, and were already in decline before mosasaurs came along, so I think an extra linage of marine reptiles wouldn’t make a lot of difference.

On plesiosaurs, I don’t know a lot to be honest. Perhaps both elasmosaurs and polycotylids were quite specialised and thus mosasaurs didn’t compete with them; it would be sort like the condition of pterosaurs and birds in the late Cretaceous, only that, while small pterosaurs like anurognathids might had survived and left no remains, plesiosaurs seemed to had been truly restricted to those two linages (unless freshwater forms occured in Africa and Oz, which have no late Cretaceous fossils)
#10 Nathan Myers
April 13, 2009

Mosasaurs, pliosaurs, and elasmosaurs, oh my! Can somebody please put these horrors (and polycotylids and plesiosaurs) in some kind of ordered relationship for us?

With teeth like that, to presume venom seems like piling on.
#11 Darren Naish
April 13, 2009

Many thanks to all for comments!

Let me say here that I don’t think that mosasaurs were venomous: given the absence of an injection mechanism (like hollow or canaliculate teeth), they would not have been able to use venom underwater (unlike sea snakes). What I’m getting at is that venomosity may well have been primitive for mosasaurs: that is, the earliest amphibious forms would presumably have inherited venomosity from their ancestors.
#12 Greg Morrow
April 13, 2009

Surely size alone argues against venom in mososaurs. If we assume that venom production is biologically expensive, which seems likely, there’s constant selective pressure to eliminate it which can only be overcome if it provides enough competitive advantage.

But mososaurs appear to be large active predators with big robust jaws; they’ll inflict dismembering wounds on appropriately-sized prey animals without the need for venom.

I’ll admit that venom in helodermatids is a point against this theory–gila monsters have proportionally-big and nasty-fanged bites, so why venom? But they’re pretty sluggish, so perhaps venom expands their prey size range upwards without requiring an active lifestyle.

And in any case, there’s a bit of a scale difference between a 50 cm/2 kg gila and a 6m/three-ton mosasaur.
#13 Darren Naish
April 13, 2009

Thanks for that Greg. Like I said, I don’t think that mosasaurs were venomous. However, note that the size argument doesn’t apply across the whole of Mosasauria because the most basal members of the clade were similar in size to extant venomous varanids: only mosasaurids were ’6 m/three-ton’ (incidentally, 3 tons might be too high) as you state; basal mosasaurs, like dolichosaurids and aigialosaurs and so on, were typically less than 2 or 3 m long.
#14 Sordes
April 13, 2009

A weight of 3 tons is undoubtly much too high for a 6m mosasaur, I really ask me from where such massive over (and sometimes under-) estimates come. Mosasaurs are comparable in their proportions to crocodiles, probably even a bit lesser massive. As a 6m croc weighs typically around 1 ton, a 6m mosasaur most probably weighed not more or even lesser.
BTW, even if komodo dragons are not really venomous (okay, perhaps a little bit), their contaminated salvia acts very similar to a long-time-venom, and komodo dragons are big. So even comparably big animals can benefit from such specializations, for example those venomous gorgonopsids, which were also quite big.
#15 shiva
April 13, 2009

“their contaminated salvia acts very similar to a long-time-venom, and komodo dragons are big.”

I know that’s a typo for “saliva”, but still… awesome. Bad trip, man…

Are the terms “monstersaurian” and “goannasaurian” actually used by zoologists? If so, equally awesome.

I also really like that Bogdanov reconstruction; it’s the first mosasaur reconstruction i’ve seen that actually shows their kinship to other squamates. If i look at it and squint hard, i can just about see a varanid…

BTW, your stuffed megamammal week inspired me to spend Easter weekend taking photos at Whipsnade Zoo and the Tring (Rothschild) Zoological Museum. I think they’re a bit off-topic to post on my blog, tho, so i’ll probably have to open a Flickr account to put them online…
#16 Dr Vector
April 13, 2009

BTW, your stuffed megamammal week inspired me to spend Easter weekend taking photos at Whipsnade Zoo and the Tring (Rothschild) Zoological Museum. I think they’re a bit off-topic to post on my blog, tho, so i’ll probably have to open a Flickr account to put them online…

You might also consider sending Darren either the best of the photos or at least a link to ones you post on Flickr, in case he wants to use them for picture-of-the-day posts (assuming you have no objections to him doing so). Also, FWIW Picasa lets you post a lot more photos for free than Flickr, and I find it easier to use. YMMV.
#17 Darren Naish
April 13, 2009

Shiva: if you’re up for this (viz, me using your photos), then please do do as Dr Vector suggests.

‘Monstersaurian’ (or its more vernacular equivalent, ‘monstersaur’) is indeed in widespread use among palaeoherpetologists and I’ve heard it used several times at conferences and in talks. There always seems to be a lot of people who have never heard it before, so at least someone always laughs. ‘Goannasaurian’ was only published last year, so is too new to have received widespread usage. However, it’s only a matter of time…
#18 jck
April 13, 2009

Sheesh, as if the Mesozoic seas weren’t scary enough. Now mosasaurs with venom. I wonder if they could spit?
#19 LeeB
April 13, 2009

David,
the original and best specimen of G. nigeriensis was discovered in Nigeria but other specimens have been found in Niger where there is a rich and seriously undercollected mosasaur fauna.

I find it interesting that such an aberrant mosasaur whose relationships with other mosasaurs are unclear occurs on the african plate where some of the earliest mosasaurs occurred, this suggests a long independent lineage confined to this plate.

Venom production would surely be useful to juvenile mosasaurs, and mosasaurs have pits at the base of their teeth where replacement teeth form,venom could pool here or be released at the mosasaur bit its prey.

Carlos,

ichthyosaurs became extinct during the Cenomanian and pliosaurs during the Turonian, this was too early for competition with mosasaurs to be responsible, they only started to become large during the Turonian with taxa such as Yaguarasaurus and Angolasaurus.

LeeB.
#20 Mike from Ottawa
April 13, 2009

venomous gorgonopsids

Wazzat? Where can I find out more about these?

Great post, Darren, and thanks to the commenters who contribute so much too.
#21 Greg Morrow
April 13, 2009

FTR, I made the 6m/3-ton number up out of my head. Not entirely without thinking about it–6m is 3x a large human male, which implies 3^3 times 100 kg or 2700 kg order-of-magnitude, and I rounded up on the grounds that the water can trivially support a larger weight on the same frame for an aquatic animal.

But perhaps the rule goes the other way–because the water is supporting the weight, the creature can be gracile for its size.

In any case, the 3t number was a guess, and I cheerfully abandon it to people who know what they’re talking about.
#22 Graham Peter King
April 13, 2009

Greg Morrow wrote

But mososaurs appear to be large active predators with big robust jaws; they’ll inflict dismembering wounds on appropriately-sized prey animals without the need for venom.

Yes, but even the biggest were small when young. Might venom have been useful for these little mosasaurs? I am thinking of the ‘compys’ (Compsognathus) in Jurassic Park, that were small and weak but venomous, and so dangerous en masse, inflicting small wounds that were cumulatively toxically disabling, thus enabling the compys (eventually) to feed on far larger prey.. er, humans. All imaginative fiction of course..
#23 rajita
April 14, 2009

I think trying to infer venom delivery based on teeth grooves has now been seriously questioned by a decent review by Folinsbee et al. These authors seem dubious about Uatchitodon (different species described by Sues et al) a diapsid archosauromorph, but they are more convinced about Euchambersia a therapsid due to the presence of additional structures like a glandular fossa associated with the teeth bearing the grooves. They also mention that one might question the presence of venom in other monster[o]saurs like Primaderma based on other aspects of dental morphology like shearing blade-like teeth as against cylindrical envenomating teeth. This would also bring the question of venom in Estesia — it appears that the teeth in this taxon are definitely more suited for envenomation.

Coming to the molecular phylogeny of squamates the work of Fry et al suggests a more inclusive toxicoferan clade that comprises of snakes, varanids, anguids, helodermatids and iguanids. This completely contradicts that published by Evans. In this system the origin of venom glands occurred in their common ancestor. Snakes are not a sister group of the varanid clade. Instead we have (varanids(anguids,monster[o]saurs)) So if we assume that we are right in placing mosasaurs with the platynotans then they had an ancestor with fully developed venom glands.
My friend had discussed this in detail:
Adriosaurs and the origin of snakes and the snake-like form
Since the strength of the venom appears to be variably developed in toxicofera we cannot rule out that at least the more primitive smaller mosasauroids did have venom before it became superfluous in the giant forms. If we were to attempt to reconcile morphological phylogeny with the this molecular phylogenetic scheme it would appear that Huehuecuetzpalli might be close to the ancestry of toxicofera.
#24 William Miller
April 14, 2009

Goronyosaurus sounds like a Japanese monster movie.

“Goronyo vs. Godzilla : The Battle for Earth!”
#25 Jerzy
April 14, 2009

BTW – how mosasaurs bred? ovoviviparous?
#26 johannes
April 14, 2009

> So even comparably big animals can benefit from such
> specializations, for example those venomous gorgonopsids,
> which were also quite big.

*Euchambersia* was a moschorhinid therocephalian, not a gorgonopsian.
#27 anon
April 14, 2009

Next Week: Therizinosaurs With Guns.
#28 Carlos
April 14, 2009

“Carlos,

ichthyosaurs became extinct during the Cenomanian and pliosaurs during the Turonian, this was too early for competition with mosasaurs to be responsible, they only started to become large during the Turonian with taxa such as Yaguarasaurus and Angolasaurus.

LeeB.”

I pretty much had said that icthyosaurs were gone/declining before large mosasaurs evolved, though indeed you helped me clear my doubts about pliosaurs. Because it truly doesn’t make sense if they suddenly appeared and replaced the then dominant marine reptiles, the evolution of the large mosasaurs forms only occured when they were gone, and even so they at the very least took pliosaurian niches, since no obvious ichthyosaur analogue other than perhaps polycotylids was present in a post-Turonian Cretaceous.
#29 Sordes
April 14, 2009

Greg, sorry, I completely failed to see that you write this weight-length relation. Humans are surely not the best candidates to to calculate weights for mosasaurs. The mathematical way you used is right of course, and most probably the body densitiy of mosasaurs was not that different from humans. Marine tetrapods have in general a body densitiy which is a little higher than water, if they would be lighter, they would have problems to dive. Humans (except very adiposous specimens) also don´t float on water, but with comparably little work they can swim, so the body densitiy is most probably not significiantly higher than water.
If I take for example a komodo dragon of 2,50 m and 40kg (rounded dates of an actual specimen caught and measured in the field), and scale it up to 6m, I get a weight of about 550kg. As mosasaurs were comparably long-bodied, I would suppose even a lesser weight for a 6m mosasaur. In contrast the giant hybrid crocodile Yai weighed at 6m more than 1000kg. This little calulations and comparisons show also well that some of the weight-estimation for Megalania prisca were completely unrealistic. Even if we keep in mind that Megalania was surely stockier and with a proportionally shorter tail than a 2,50m komodo dragon, it surely never weighed 2tons or more as some people have stated. I think for a very big Megalania 600-700kg would be realistic.
#30 Matt
April 14, 2009

Goronyosaurus is indeed a very unique mosasaur. I have often wonderd from looking at it’s crocodilian-like dentition if it may have included turtles in it’s diet as well. This may have been another possible food source since it lived in an esturaine environment. Plus tylosaurine mosasaurs have been found with turtles remains in the gut content. So maybe this particular mosasaur ate both turtles and bottom dwelling vertebrates.
#31 DDeden
April 14, 2009

Seals have forked tongues , but unlike platypuses, are not venomous.

Humans DO backfloat on water, especially calm seawater.
I’ve seen polar bear, sea otter, marine otter, human, and various seals backfloating/backstroking.
#32 LeeB
April 14, 2009

Jerzy,

there was some discussion of Mosasaur breeding on the Marine Reptiles Forum.
Some mosasaurs are known to have given birth to live young,
apparently in Tylosaurus the neonate was about 150cm long, this is so large that to me is suggests that they had developed some form of placentation to deliver nutrients to the developing embryo.
Some living lizards have developed a form of placentation, and so have some sharks such as the Carcharinidae and Sphyrnidae which produce large young.

LeeB.
#33 LeeB
April 14, 2009

Jerzy,

there was some discussion of Mosasaur breeding on the Marine Reptiles Forum.
Some mosasaurs are known to have given birth to live young,
apparently in Tylosaurus the neonate was about 150cm long, this is so large that to me it suggests that they had developed some form of placentation to deliver nutrients to the developing embryo.
Some living lizards have developed a form of placentation, and so have some sharks such as the Carcharinidae and Sphyrnidae which produce large young.

LeeB.
#34 Jerzy
April 14, 2009

Thanks!
#35 Darren Naish
April 14, 2009

Mosasaurids (the most morphologically derived clade within Mosasauria) were almost certainly viviparous, as this was true of the small, amphibious mosasaurs down at the base of the clade. See comments here if you’re interested, and…

Caldwell, M. W. & Lee, M. S. Y. 2001. Live birth in Cretaceous marine lizards (mosasauroids). Proceedings of the Royal Society of London B 268, 2397-2401.
#36 LeeB
April 14, 2009

Also the secondarily marine tetrapod lineages that are known to have given birth to live young like the whales, ichthyosaurs,mosasaurs and plesiosaurs rapidly produced large members, whereas those that had/have to go ashore to produce offspring like seals, turtles and metriorhynchid crocodiles never produce really large members.

LeeB.
#37 Azkyroth
April 15, 2009

Now it makes me wonder if venom enabled the mosasaurs to dominate the oceans, and also led to the decline (and eventual extinction) of ichthyosaurs and pliosaurs. Although why polycotylids and elasmosaurs survived needs to be accounted for.

Different prey profiles?
#38 Greg Morrow
April 16, 2009

Sordes: Thanks for the notes. I see now that the major error I made was assuming equal proportions in scaling up. A big croc or mososaur is a lot narrower than a person, and so the weight scale factor is a lot less than the third power of the length scale.
#39 Lela Criswell
April 25, 2010

Just purchased one of your newer books & am enjoying it very much. Unfortunately, there’s an error in the map on page 19 of the U.S. edition of The Great Dinosaur Discoveries. Morrison, Colorado, is north of Canyon City, so the names of these sites were somehow exchanged.