eudimorphodon

The True dimorphic tooth, Eudimorphodon (1973)

Phylum : Chordata
Class : Reptilia
Order : Pterosauria
Family : Eudimorphodontidae
Subfamily : Eudimorphodontinae
Genus : Eudimorphodon
Species : E. ranzii, E. cromptonellus

  • Late Triassic (210 - 203 Ma)
  • 1 m wingspan (size)
  • Italy (map)

Eudimorphodon showed a strong differentiation of the teeth, hence its name, which is derived from ancient Greek for “true dimorphic tooth”. It also possessed a large number of these teeth, a total of 110 of them densely packed into a jaw only six centimeters long. The front of the jaw was filled with fangs, per side four in the upper jaw, two in the lower jaw, that rather abruptly gave way to a line of smaller multipointed teeth, 25 in the upper jaw, 26 in the lower jaw, most of which had five cusps, others three or even four.

The morphology of the teeth are suggestive of a piscivorous diet, which has been confirmed by preserved stomach contents containing the remains of fish of the genus Parapholidophorus. Young Eudimorphodon had slightly differing dentition with fewer teeth and may have had a more insectivorous diet. The top and bottom teeth of Eudimorphodon came into direct contact with each other when the jaws were closed, especially at the back of the jaw. This degree of dental occlusion is the strongest known among pterosaurs. The teeth were multi-cusped, and tooth wear shows that Eudimorphodon was able to crush or chew its food to some degree. Wear along the sides of these teeth suggests that Eudimorphodon also fed on hard-shelled invertebrates.

Despite its great age Eudimorphodon has few primitive characteristics making the taxon of little use in attempting to ascertain where pterosaurs fit in the reptile family tree. Basal traits though, are the retention of pterygoid teeth and the flexibility of the tail, which lacks the very long stiffening vertebral extensions other long-tailed pterosaurs possess. Paucity of early pterosaur remains has ensured that their evolutionary origins continues to be a persiseant mystery with some experts suggesting affinities to dinosaurs, archosauriformes, or prolacertiformes.

Within the standard hypothesis that the Dinosauromorpha are the pterosaurs’ close relatives within an overarching Ornithodira, Eudimorphodon is also unhelpful in establishing relationships within Pterosauria between early and later forms because then its multicusped teeth should be considered highly derived, compared to the simpler single-cusped teeth of Jurassic pterosaurs, and a strong indicator that Eudimorphodon is not closely related to the ancestor of later pterosaurs. Instead it is believed to be a member of a specialized off branch from the main “line” of pterosaur evolution, the Campylognathoididae.

Eudimorphodon or Aren't You?

Eudimorphodon ranzii by John Sibbick in Wellnhofer, 1991.

Pterosaurs, those flying reptiles (not dinosaurs (What Is (Not) a Dinosaur)) that we discussed in the last post (More than One Way to Skin a Wing), are known exclusively from fossils in the Mesozoic (Figure 1).  Specifically, they are found in rocks from the Norian of the Upper Triassic up to the Maastrichtian of the Upper Cretaceous.  Thus, they basically have the same fossil range as dinosaurs.  Even though pterosaurs are found throughout those layers, different genera and even different families are found in different layers.

Figure 1: The Geologic Column.  The range of pterosaur fossils is outlined in red.  This column was created using TimeScale Creator 6.0.

The earliest pterosaur fossils, those in the Triassic, are found mainly in the Alps of Italy, Switzerland, and Austria.  One species, ’Eudimorphodon’ cromptonellus was found in Greenland (the Vikings tricked him), and some possible Triassic pterosaur remains have been found in the United States, Brazil, Luxembourg, and other locations around the world.

If you grew up reading Wellnhofer's Illustrated Encyclopedia of Pterosaurs (Come on; you were a kid, right?), then you knew only three Triassic genera: EudimorphodonPeteinosaurus, and Preondactylus (Figure 2).  Things have gotten a lot more complicated now since those forms were named in the 70s and 80s, but all three of those genera have stood their ground as valid genera (and after they had done everything, to stand).  However, the specimens that belong to those genera, and the species within the genera - well, that’s another story.

And so, it’s time for everyone’s favorite gameshow: Eudimorphodon or Aren’t You?  (Hint: the “Eu” in Eudimorphodon is pronounced “You”.)

Where else to start, but the holotype specimen: MCSNB 2888 (Figure 3)?  

Figure 3: MCSNB 2888, the holotype of Eudimorphodon ranzii.  Image by Luigi Chiesa, obtained via Wikipedia.

But wait, there’s more!  Also referenced as Eudimorphodon ranzii is BSP 1994 I 51 (Figure 4) and many other specimens.  Is it really Eudimorphodon?

Figure 4: BSP 1994 I 51.  Yeah, it’s a little disarticulated.  Oh, and it’s spread over five different blocks.  Such a mess…  Image from Wellnhofer, 2003.

Oh, and did you know there is more than one species?  How about Eudimorphodon rosenfeldi (Figure 5)?

Figure 5: MFSN 1797, holotype of Eudimorphodon rosenfeldi.  Image from Dalla Vecchia, 2009.

Oh, and there’s MPUM 6009.  It was considered a juvenile Eudimorphodon.  Sadly, I don’t have a picture of the specimen.  As well, there is a our good Greenlander: Eudimorphodon cromptonellus specimen MGUH VP 3393.  The fossil was found when splitting open a rock, so it is on part and counterpart slabs (Figure 6).

Figure 6: MGUH VP 3393, holotype of Eudimorphodon cromptonellus.  Image from Jenkins, et al., 2001.

So, now it’s time for the discussion.

The describing of the holotype of Eudimorphodon ranzii (MCSNB 2888) in 1973 by  Rocco Zambelli was incredibly important, as it was the first good fossil of a Triassic pterosaur.  The skeleton is pretty much articulated and complete except that it is lacking the ends of the wings, tail, and hindlegs.  It is a very interesting pterosaur because of its differing dentition compared to other pterosaurs (Figure 7), possessing tricuspid and even pentacuspid teeth (Figure 8).  It might be helpful (then again, maybe not) to know that Eudimorphodon’s name means “True two-sized tooth”.

Figure 7: Comparison of the dentition of Eudimorphodon ranzii (left) to a “more typical” pterosaur’s dentition (Germanodactylus cristatus, right).  Eudimorphodon image from Wellnhofer, 1991; Germanodactylus image by Zachary Miller, When Pigs Fly blog http://whenpigsfly-returns.blogspot.com/2009/10/darwinopterus-germanodactylus-and.html

Figure 8: Lower jaw of Eudimorphodon ranzii, view from outside (top) and inside (bottom).  Image from Wellnhofer, 1991.

Those teeth looked pretty unique.  Also thought to be unique was the shape of its humerus. (Although Campylognathoides should have been telling people otherwise.  Then again, who listens to Campylognathoides anyway?)  Thus, when anything else resembling Eudimorphodon ranzii was found, it was immediately labeled “Eudimorphodon”.  Many specimens were soon attributed to Eudimorphodon including teeth from Europe (Switzerland, Luxembourg, and France) and North America (Southwestern USA) (Dalla Vecchia, 2009).  However, it turns out that some therapsids called chiniquodontids (You’re going to have to look them up.  I put enough images in here already.*) are found in the same layers and have tricuspid teeth, which are difficult to distinguish from Eudimorphodonteeth (Dalla Vecchia, 2013).  Not only that, but it turns out that Eudimorphodon ranzii is not alone among Triassic pterosaurs in its multicusped dentition (namely Caviramus).

That brings us to all the specimens and supposed species of Eudimorphodon.  At one point, there were three species of EudimorphodonE. ranziiE. rosenfeldi, and E. cromptonellus.  Not only that, but there were several specimens attributed to E. ranzii, such that Unwin (2003) called Eudimorphodon “arguably the most important” and “commonest” Triassic pterosaur.

Following the discovery of Caviramus and Raeticodactylus (Caviramus?),  Dalla Vecchia (2009) noted that there were no synapomorphies (shared traits between members of a group that are unique to that group) for the genus Eudimorphodon.  Dalla Vecchia (2009) renamed Eudimorphodon rosenfeldi as Carniadactylus rosenfeldi,  His phylogenetic analysis also lent support to the idea that E. cromptonellus should not be in the genus Eudimorphodon as it didn’t even group in Campylognathoididae (the family Eudimorphodon ranzii is traditionally grouped within).  As well, he separated out BSP 1994 I 50, a specimen described by Wellnhofer (1993) as E. ranzii, saying that it should belong to an as yet unnamed genus and species.  After removing other specimens, Dalla Vecchia (2009, 2013) left only one specimen in the genus Eudimorphodon: the holotype (MCSNB 2888) of E. ranzii.

So, if you answered yes to any of the specimens other than the original, then you did not win (you lost).  If you only said yes to the holotype, then congratulations, you did not lose (you won).  There were no prizes though, so don’t beat yourself up either way.

So, why is this important?  Because people have been using Eudimorphodon in their phylogenetic analyses including characters from specimens that are not even Eudimorphodon!  Imagine if I were listing out all of the physical traits found in dogs, but I included a cat as a representative dog.  Clearly, that’s going to mess some things up.

REFERENCES:

Dalla Vecchia, F.M. 2009. Anatomy and systematics of the pterosaur Carniadactylus gen. n. rosenfeldi (Dalla Vecchia, 1995). Rivista Italiana di Paleontologia e Stratigrafia, 115(2):159-186.

Dalla Vecchia, F.M. 2013. Triassic pterosaurs, p. 119-155. In Nesbitt, S.J., Desojo, J.B., and Irmis, R.B. (eds.), Anatomy, Phylogeny, and Palaeobiology of Early Archosaurs and their Kin. Geological Society of London, Special Publications, 379.

Unwin, D.M. 2003. Eudimorphodonand the early history of pterosaurs. Riv. Mus. civ. Sc. Nat. “E. Caffi” Bergamo 22: 39-46. 

Wellnhofer, P. 1991. The Illustrated Encyclopedia of Pterosaurs. Salamander Books, London.

Wellnhofer, P. 2003. A Late Triassic pterosaur from the Northern Calcareous Alps (Tyrol, Austria), p. 5-22. In Buffetaut, E. and Mazin, J.-M. (eds.), Evolution and Palaeobiology of Pterosaurs. Geological Society of London, Special Publications, 217.

 

* Fine.  Here’s your chiniquodontid.  It's Probelesodon drawn by Smokeybjb.  Isn’t it ridiculous that this thing has teeth like an Eudimorphodon?!?!?