Helveticosaurus: an Enigma From the ’50s
Helveticosaurus is a large marine reptile from the Middle Triassic known from a complete and largely articulated skeleton with a very badly crushed, short-snouted skull with giant teeth. Originally described by Peyer (1955) as a placodont, Helveticosaurus doesn’t share many of the key characters shared by all other placodonts. Wikipedia reports that the affinities of Helveticosaurus with other diapsids remains largely unknown.
Figure 1. Helveticosaurus, a short snouted thalattosaur
Results of the Large Study
Here, in the large study, Helveticosaurus nested as a thalattosaur, a clade of marine reptiles close to ichthyosaurs, but with a huge variety of skull and tooth shapes. The skull of Helveticosaurus was different from most other thalattosaurs, most of which had a long snout and shorter teeth. The only other thalattosaur with a similar skull was Vancleavea, which was originally described as an archosauriform. Eusaurophargis also has a short high rostrum, but its teeth were short and it had far fewer dorsal vertebrae. Miodentosaurus was also similar, but had very few, very short teeth. The hands and feet of these thalattosaurs were all quite similar.
Putting Humpty Together Again
The big problem with figuring out what Helveticosaurus was, was a lack of a good skull reconstruction. That crushed skull proved too intimidating for half a century. All the parts are there. No one wanted to step forward and put the skull back together again. Here the parts are identified and reconstructed.
What’s With Those TEETH!
The premaxilla of Helveticosaurus has giant sabertooth fangs, perfect for inflicting wounds on large prey or, possibly, dislodging prey/plants from the sea floor. These carnivorous weapons were followed by a curtain of hyper-elongated teeth in the maxilla. These would have been useless in dismembering, crushing or slicing prey items. They are so long they look they would break. The maxillary teeth were somewhat similar to baleen in that they might have been able to strain food while allowing water to exit… only a guess following the process of elimination. Not sure yet what the diet of Helveticosaurus was.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
References
Peyer B 1955. Die Triasfauna der Tessiner Kalkalpen. XVIII. Helveticosaurus zollingeri, n.g. n.sp. Schweizerische Paläontologische Abhandlungen 72:3-50.
Rieppel O 1989. Helveticosaurus zollingeri Peyer (Reptilia, Diapsida): skeletal paedomorphosis; functional anatomy and systematic affinities. Palaeontographica A 208:123-152.
The Pterosaur Heresies 
interestingly, that teeth pattern reminds that seen in dilophosaurus -with its fragile skull- and spinosauridae -which have been asociated to piscivorous diet by similarity to some crocodiles (you guessed, I’m a dinosaur freak here)
only that all those have very long snouts! but think of that set of teeth just longer