The DinoBase Public Forum

Following a question about Archaeopteryx on AAB recently I have been thinking about reptile teeth a bit and how they get a bit of undeserved bad press in terms of their variety and interest. Huge amounts of research are published on mammal teeth – extant and extinct – all the time. This is because most if not all mammalian molars are pretty diagnostic and from a single relatively complete molar and you can work out where it was from in the jaw and what family, if not species, it belonged to. Thus even partial teeth can give us huge amounts of information about temporal and spatial distributions, rates of evolution, biogeography and more. One good tooth will tell you who was where, and when, and probably what they were doing.

Of course, this in not true of reptile teeth. They are diagnostic to a degree – it would be hard to confuse a tooth from a sauropod with that of a pterosaur or squamate but within even major groups it can get very tricky to pick out families.  But this is not to say that teeth cannot be diagnostic, or provide some very useful information about what taxa might have been living where a fossil bed provides teeth (and they provide a lot of teeth too, thanks the reptilian habit of constant growth and shedding). Furthermore, reptiles seem to have been stuck with the concept of homogenous teeth. I think this is due to the reptiles we see alive today where in general (fangs in snakes are an obvious exception) the teeth are pretty uniform in the mouth. Obviously there are some big differences between species, but in an animal’s jaws all the teeth are more or less identical.

However, compared to extant reptiles, there were some really wild and exciting animals in the past, with quite a bit of variety in even one animal, and between them far more than you might think. OK so nothing is going to quite match the mammalian pattern of incisors, canines, premolars and molars where teeth can change dramatically several times in the space of three or four sockets, but there is some bizarre reptilian dentition out there and I’d like to mention a few. It’s nothing more than a haphazard survey of some interesting teeth, and perhaps unsurprisingly focusing on my favourite bods of pterosaurs and dinosaurs. I won’t bother with some of the more typical reptilian teeth here, nor some that most are probably familiar with (the spatulate teeth of many sauropods, the recurved, serrated teeth of theropods, the conical teeth of crocodiles etc.), but I thought this might be a nice opportunity to mention some of the more unusual dentitions out there in the fossil record.

First off there are the rather unrelated pair of Heterodontosaurs and Dimorphodon. Yes, the former is an ornithischian dinosaur and the latter a pterosaur but they do have something in common – their names. Respectively they are ‘different toothed lizard’ and ‘two shaped teeth’, in other words they immediately break the mould of ‘all teeth are the same’ and their names reflect this. Heterodontosaurs has these rather cute little fangs that look rather like those seen in chevrotin. These may well have had a similar function with males displaying them to females, as hetero.s like the deer were small herbivores. In Dimorphodon we see something rather more sinister, well, predatory anyway with some large teeth at the font of the jaw, followed by far more slender and shorter (but equally pointed) ones behind.

A favourite of mine is the little known pterosaur Angustinaripterus. Known only from a single well preserved 3-D skull (which already makes it *very* unusual as a pterosaur) this guy has some of the largest teeth (for the size of the animal) you are likely to see and the bizarre interlocking recurved teeth make a bizarre gin-trap of a maw.

However, these pale next to the legend that is Mesosaurus. This is one of those weird Permian aquatic jobbies that look superficially like a crocodile, but isn’t. I thought Angus. was king of the big teeth till I came across this guy, these are truly huge. Loooong, slender, almost sinusoidal needle-like teeth project from the jaws making it look like some bizarre gharial. It is well worth hunting down a reconstruction to take a look, anyone with a copy of Romer’s legendary Osteology of Reptiles will find a great one in there. Once again, I feel frustrated by a lack of images on here, but I am sure there are some enterprising people out there reading this who want to see these in their glory.

The great Triceratops shows off two nice features simultaneously. The first is the tooth / beak combination that seem to turn up again and again in the archosaurs. A good half dozen lineages seem to have discovered it independently, and probably quite a few more than that depending on quite which taxa had them and how you fit the subtleties of some phylogenies. The second is the fact that it’s teeth, unusually for a reptile, have double roots, this makes them highly diagnostic (which is always a useful feature) and also of course helps to bust the myth that reptile teeth are somehow simple structures. True mammals have a far greater propensity for elaborate teeth in both root and crown, but they are certainly not alone.

Sticking with the beak / tooth combo, we move to the oviraptorsaurids. While many people probably think of these as just being beaked animals, several taxa had large ‘canines’ to go with their beaks, but here I want to mention Incisivosaurs. This rabbit-o-saurus has many small teeth but is most notable for the huge pair of incisors that stick out, buck-toothed from the front of the mouth and would have probably overlapped with the lower jaw. This is quite an extreme structure and its purpose is unknown, but certainly it shows a unique specialisation that may not have necessarily been used for feeding given the way they are mounted in the mouth.

In terms of number, it is hard to compete with Pterodaustro. Counts vary as although there are hundreds of specimens known, the skull of this filter-feeding pterosaur are understandably very fragile and tend to break or are missing. Still, there were certainly hundreds of teeth present, and quite probably more than a thousand! That is a lot of teeth to cram into a 15 cm set of jaws. Just to clear up one final thing, these are actually true teeth in Pterodaustro and not just keratinous filaments or anything else as has been suggested in the past.

The last thing I am going to mention on this little jaunt around reptile teeth is Placodus the Triassic placodont. The marine reptiles looked a bit like stumpy crocodiles (ish) and were adapted to eat clams and similar shellfish. As a result they had short, broad skulls with powerful muscles and exceptionally broad, smooth and very flat teeth. These have a huge surface area (considering the size of the animal) with the largest ones being around 3-4 cm by 1.2-2 cm. With a skull that is only around 15 cm long itself, that is a whopping set of teeth to include – there was certainly some power available to them to get through some tough molluscs.

Well, that is the lot from me on this subject (for now anyway, it might be worth going over some other teeth in the future). This was not really supposed to be a comprehensive or even focused review of reptile teeth, just an opportunity to look at the variety that is present in some fossil taxa and try to get past the notion that reptiles have simple teeth. Given my typical audience, I doubt I have said much (if anything) that you didn’t already know, but hopefully it has enlightened a few or at least inspired people to look for some more or better examples of bizarre dentition in Reptilia.