Arcticodactylus a tiny Greenland Triassic pterosaur

Arcticodactylus cromptonellus (Kellner 2015, originally Eudimorphodon cromptonellus Jenkins et al. 1999, 1999; MGUH VP 3393) Late Triassic ~210mya ~8 cm snout to vent length was a tiny pterosaur derived from a sister to Eudimorphodon ranzii and phylogenetically preceded Campylognathoides and BSp 1994 specimen attributed to Eudimorphodon. Whether it was a juvenile or a tiny adult cannot be determined because juveniles and even embryos are identical to adults in pterosaurs. Note that that rostrum was not shorter and the orbit was not larger than in sister taxa. This specimen is one of the smallest known pterosaurs., but not THE smallest (Fig. 1) contra the Wikipedia article. That honor goes to B St 1967 I 276.

Figure 1. Articodactylus is evidently NOT the smallest pterosaur. That honor still goes to an unnamed specimen (not a Pterodactylus kochi juvenile) B St 1967 I 276.

Figure 1. Articodactylus is evidently NOT the smallest pterosaur. That honor still goes to an unnamed specimen (not a Pterodactylus kochi juvenile) B St 1967 I 276.

Distinct from E. ranzii,
the skull of Arctiodactylus had a rounder, less triangular orbit. The jugal was not as deep. The sternal complex did not have small lateral processes. The humerus was not as robust. The fingers were longer an more gracile. The prepubis was distinctly shaped.

Distinct from
Bergamodactylus the femur and tibia were smaller but the metatarsals were longer, compact and nearly subequal in length with IV smaller than III.

References
Jenkins FA Jr, Shubin NH, Gatesy SM and Padian K 1999. A primitive pterosaur of Late Triassic age from Greenland. Journal of the Society of Vertebrate Paleontology 19(3): 56A.
Jenkins FA Jr, Shubin NH, Gatesy SM and Padian K 1999. A diminutive pterosaur (Pterosauria: Eudimorphodontidae) from the Greenlandic Triassic. Bulletin of the Museum of Comparative Zoology, Harvard University 155(9): 487-506.
Kellner AWA 2015. Comments on Triassic pterosaurs with discussion about ontogeny and description of new taxa. Anais da Academia Brasileira de Ciências 87(2): 669–689

wiki/Eudimorphodon
wiki/Arcticodactylus

Bergamodactylus wildi- a new name for the basalmost pterosaur, MPUM 6009

Finding higher resolution data
is always a delight. Here DGS and a reconstruction perhaps reveal more accurate data on a skull of a basal pterosaur than direct observation (Fig. 1). You decide.

Figure 2. Bergamodactylus skull colorized with DGS and reconstructed.

Figure 2. Bergamodactylus skull colorized with DGS and reconstructed.

Kellner (2015)
commented on several Triassic European pterosaurs. Among them, MPUM 6009 was originally described as a juvenile Eudimorphodon by Wild (1978) and later congeneric with the basal anurognathid, Carniadactylus by Dalla Vecchia (2009). Peters (2007) nested this specimen as the basalmost pterosaur, though this reference was not listed. Kellner (2015) reported “no indication that MPUM 6009 is a juvenile.” confirming the assessment here.

Bergamodactylus wildi
is the new name for MPUM 6009 a Late Triassic (Norian) basal pterosaur from Bergamo, Italy. Unfortunately the tracing of the specimen is very vague (Fig. 1). Both jugals are drawn as one and many bones are not identified. This is remedied by DGS, which not only identifies left and right bones, but enables an accurate reconstruction with all parts fitting as in other articulated pterosaurs. Note the twin anterior dentary extensions. Are those teeth? A keratin extension has been hypothesized for other basal pterosaurs. Part of the maxilla ascending process is broken and flipped but repaired above. The posterior process of the left postorbital is broken like a wishbone. Here (Fig. 1) it is repaired to resemble the right postorbital. The occiput is identified along with several hyoids that were overlooked earlier. Does the coronoid have a tall triangular process? Perhaps, but that could also be an ectopterygoid. We’ll have to see about that.

Figure 1. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown.

Figure 2. Updated reconstruction of Bergamodactylus to scale with an outgroup, Cosesaurus. Compared to the cranium and declined quadrates, the face appears to be downturned. This only makes sense in a bipedal configuration, as shown.

References
Dalla Vecchia FM 2009. Anatomy and systematics of the pterosaur Carniadactylus (gen. n.) rosenfeldi (Dalla Vecchia, 1995). Rivista Italiana de Paleontologia e Stratigrafia 115 (2): 159-188.
Kellner AWA 2015. Comments on Triassic pterosaurs with discussion about ontogeny and description of new taxa. Anais da Academia Brasileira de Ciências (2015) 87(2): (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690.
Nesbitt SJ and Hone DWE 2010. An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225-233.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

wiki/Eudimorphodon

Something new in Eudimorphodon revealed by DGS

Some people are still having trouble with DGS as a technique. They think of it as something that is virtually guaranteed to spook a reconstruction. Instead of increasing confidence that parts have been correctly identified, they have no confidence in work that has the taint of DGS.

Here’s a step-by-step run through DGS on a familiar specimen, Eudimorphodon ranzii. Using DGS enabled the recognition of some oddly long posterior ribs (that were always visible, just ignored) and a wider than deep torso in a pterosaur for which these traits were not otherwise recorded.

Eudimorphdon ranzii (Zambelli 1973, Wild 1978) s a Late Triassic pterosaur known from an articulated crushed skeleton missing feet, tail and most of each wing (Figs. 1-3). Some parts are easy to see and trace, like the skull and sternal complex. Some parts are more difficult like the two pubes (Wild 1978 only found one by combining the two into an oddly broad prepubis),  the pelvis, and the odd arrangement of the posterior ribs.

Eudimorphdon ranzii with post cranial bones colorized.

Figure 1. Eudimorphdon ranzii with post cranial bones colorized.

Step one: Colorize the bones (Fig. 1)
Darren Naish seems to think this is okay if you know which bone is which ahead of time when looking at the specimen and you’re just making a visual presentation. I like to take it one step further and use DGS to segregate bones that are more difficult to identify. Here the pelvis is found. The dorsal ribs will precisely transferred to the reconstruction, not generically applied. As we’ve learned earlier, sometimes pterosaurs have the cross section of a horned lizard.

Figure 2. The colorized bones on a fresh canvas.

Figure 2. The colorized bones on a fresh canvas. Most tetrapods have shorter posterior dorsal ribs, but not here in Eudimorphodon. Lighter tones on the pelvis represent overlying bones, in this case vertebrae. It is important to put a numeral on each vert and rib because it is otherwise easy to become confused.

Step two: Transfer the colorized bones onto a fresh white background (Fig. 2)
Here we’re just trying to put the bones on a fresh canvas. You’ll note some bones are estimates based on vague clues as they appear beneath the sternal complex.

Figure 3. Moving colorized bones into a rough reconstruction.

Figure 3. Moving colorized bones into a rough reconstruction or Eudimorphodon. Here both pelves are shown as they appeared in situ. In figure 1 I jumped the gun and put the parts together.

Step three: Move the colorized bones into a rough assembly (Fig. 3)
Here we’re just trying estimate a body shape to make tracing the colored bones easier.

Figure 4. Lateral, dorsal and cross-sectional views of Eudimorphodon ranzii. Note the overlap of the posterior ribs over the hind limbs and the very wide torso. The cross section shows the 2nd dorsal ribs and the 23rd. Note the small ischium which could only produce small eggs. A little taller and wider than we thought before. The forelimbs are pretty short relative to the torso.

Figure 4. Lateral, dorsal and cross-sectional views of Eudimorphodon ranzii. Note the overlap of the posterior ribs over the hind limbs and the very wide torso. The cross section shows the 2nd dorsal ribs and the 23rd. Note the small ischium which could only produce small eggs. A little taller and wider than we thought before. The forelimbs are pretty short relative to the torso.

Step four: Tracing the colorized bones for the final reconstruction. (Fig. 4)
If I just attempted a lateral view I would have missed out on the very broad posterior torso based on the length of the posterior ribs. So I create both a dorsal view and a cross section view. Note that the sternal ribs, rarely found on most pterosaurs, extend laterally to meet the dorsal rib tips in Eudimorphodon. This give it a slightly wider body anteriorly, increasingly wider posteriorly. This is an odd autapomorphy, but it is based on many ribs, so it can’t be ignored. As you can see from the in situ image (Fig. 1) those long posterior ribs were there all the time. They were simply ignored by myself and others.

Eudimorphodon: a little odder than we thought
That torso is odd. Rather than tapering toward the pelvis, as in many other pterosaurs and tetrapods in general, the posterior torso is flat and wide, roofing the femora. My guess it provides a greater volume for eggs or respiration. With such small eggs, more eggs could have been carried by the mother. Note that the predecessor of E. ranzii, MPUM 6009, has a much deeper pelvic opening, likely to produce one large egg at a time. Note the reduction of the pelvis is also reflected in the reduction of the number of sacrals to four or five depending on the connection to the posterior pelvis.

Now
If there is anything wrong with the results here, please let me know. If not feel free to use the technique yourself. I think it works pretty well.

I also don’t make these identifications without entering the taxa into a phylogenetic analysis that typically finds the same traits in sister taxa. Unfortunately posterior ribs are virtually unknown among Triassic and Early Jurassic sisters.

Pterosaur workers haven’t produced too many Eudimorphodon reconstructions, and certainly none that have recovered the oddly long posterior ribs. My earlier reconstructions were given generic ribs. So I did a bad thing. I went along with the paradigm of a tubular pterosaur body without testing that paradigm. While it takes a lot of work for small discoveries such as this, and the results are minor changes, well, I had nothing better to do on a quiet Sunday.

References
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.
Zambelli R 1973. Eudimorphodon ranzii gen.nov., sp.nov. Uno Pterosauro Triassico. Rendiconti Instituto Lombardo Accademia, (rend. sc.) 107: 27-32.
wiki/Eudimorphodon

On the origins of Dimorphodon and Eudimorphodon

At the base of the Pterosauria
there was one false evolutionary start that gave us Austriadactylus (the Austrian specimen) and Raeticodactylus. Thereafter the clades kicked into full gear with the basal dichotomy, dimorphodontids (which begat anurognathids) and eudimorphodontids (which begat everything else.)

Knowing that a picture tells the story here are the players (Fig. 1):

The origins of Dimorphodon and Eudimorphodon find a common ancestor close to Austriadactylus (the Italian specimen) and prior to that, the basal pterosaur, MPUM 6009. All are Late Triassic except Dimorphodon. The robust skull of eudimorphodontids suggests piscatory (fish eating) while the fragile skulls of dimorphodontids suggests insectivore. The enlarged naris was a legacy from the Italian specimen

The origins of Dimorphodon and Eudimorphodon find a common ancestor close to Austriadactylus (the Italian specimen) and prior to that, the basal pterosaur, MPUM 6009. All are Late Triassic except Dimorphodon. The robust skull of eudimorphodontids suggests piscatory (fish eating) while the fragile skulls of dimorphodontids suggests insectivore. The enlarged naris was a legacy from the Italian specimen

The basic dichotomy of dimorphodontids and eudimorphodontids (Fig. 1) set the pace for the rest of pterosaur evolution. One emphasized the longer, leaner snout of a fish and tetrapod eater while the other had a taller, more fragile and ultimately wider rostrum (in anurognathids) of an insect eater.

You can see (Fig. 1) with such short fore limbs and long hind limbs, with toes under the center of balance at the shoulder glenoid (arm pit) that quadrupedal locomotion was something that would have to be invented in the future of these Triassic clades.

BTW
Yesterday’s note on Atopodentatus garnered about twice as many viewers. Let me know why all the interest because I don’t have a clue.