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

Breathing in a box – Respiration in pterosaurs (Geist et al. 2013)

A new paper on pterosaur breathing has arrived.
Unfortunately, Geist et al. (2013) follow Claessens et al. (2009) in hoping that the prepubis was mobile in order to drive a thoracic lung pump. It’s not. (BTW, we looked at Claessens et al earlier here).

Geist et al. report, “we note that many of the large pterodactyloid taxa had relatively rigid trunks due to a high degree of fusion of the thoracic skeleton, a condition we describe as a synthorax… but also appear to have severely constrained ribcage movement for respiration.”

How is this shown?
Geist et al. report, “Although their morphology is variable, they [pterosaurs] always have a narrow, rod-like caudoproximal peduncle, but widen and flatten cranially. Their general appearance and orientation is often strikingly similar to that of the pubic bones of extant crocodilians.”

This is an error.
Prepubes are oriented ventrally with a non-moving butt joint, and only sometime slightly cranially. Thus they are not similar to extant crocodilians, which rotate their pubes uniquely.

Campylognathoides (CM 11424), the earliest pterosaur with a reduced pedal digit 5.

Figure 1. Campylognathoides (CM 11424). Note the prepubis, perpendicular to the spinal column and butt-joined to the pubis is immobile. Think of it like the booted pubis in T-rex, which was not used in reparation. Note the way Geist et al orient the prepubis is figure 2.

After just reporting that some pterosaurs fuse their prepubes medially, Geist et al. report, “The hinge-like [medial] articulation with the pubic bones indicates that the prepubic bones were highly mobile in the vertical plane, but were restricted in transverse movements.”

This is also bad reporting, based on bad drawings in the literature, (like Claessen 2009), not based on manipulating 3D prepubes on pubes, as I have done over several dozen taxa.

The prepubes act as immobile pubic extensions. And in that capacity they anchor adduction muscles to the femur, like the long booted pubis of T-rex. They have nothing to do with respiration. Nor were they co-oped for respiration from their original function.

Sure prepubes had large muscle scars. They were attached to large leg muscles!

The most mobile parts of the pterosaur thorax were the posterior dorsal ribs. They were slender and single-headed to retain their mobility. Lizards breathe with their ribs. Here’s a short video and another video for anyone who can’t picture when a lizard holds still, their rib cage keeps pumping. Holding still, btw, is the same as having a fused backbone, in terms of methodology.

Geist et al report, “Claessens et al. (2009) presented a detailed model for an avian-like mechanism of sternal excursion as the primary lung ventilation mechanism for both small and large pterosaurs—the “skeletal breathing pump” model.” In essence the sternal complex rotated on the coracoid joint with some movement from the scapulocoracoid. This pulled the ribs  and gastralia forward increasing thorax volume.”

Geist et al were critical of Claessens noting, “In pterosaurs the orientation of the rib articulations on the thoracic vertebrae are very unlike those of birds (Fig. 3), and likely would not have permitted the degree of fore-aft movement of the caudal ribs as proposed by Claessens et al. (2009).”

Geist et al continue, “Three dimensionally preserved specimens indicate that pterosaur ribs project more or less perpendicular to the long axis of the body (e.g., see Fig. 4A–E). A caudal inclination of these ribs similar to the orientation of those in extant birds cannot be confirmed here.”

That would be odd. Pterosaurs are now flying pancakes? No. Perhaps that’s just an odd choice of words because their illustrations don’t follow that morphology. Sharovipteryx was the flying pancake!

Geist et al. report, “the morphology of the synthorax of large pterosaurs is permissive of extracostal mechanisms that resembled the visceral pumps [diaphragms] found in mammals and crocodilians.” After considering turtle, mammal, bird and croc respiration, they never once mentioned lizards. Unfortunate.

Figure 1. Click to animate. Pterosaur breathing using a liver pump as envisioned by Geist et al. 2013.

Figure 2. Click to animate. Pterosaur breathing using a liver pump as envisioned by Geist et al. 2013. Unfortunately, the prepubis was immobilized due to a butt joint at the pubis, so this isn’t accurate.

Ultimately, Geist et al. report, “Accordingly, we propose a model for large pterosaurs in which a more or less crocodilian-like visceral displacement pump drove the inhalation phase of the respiratory cycle, and contraction of flank muscles acting on the gastralia and prepubic bones restored the viscera to their initial positions to drive exhalation (Fig. 9). In our model, sheets of diaphragmaticus-like skeletal muscle originated on the pubis, prepubic bones, and/or caudal-most gastralia and inserted on a transverse septum or the fascia of the liver.”

The Triebold Pteranodon, one of the most complete ever found. The metacarpals are quite a bit longer here. So is the beak.

Figure 3. The Triebold Pteranodon. Note the orientation of the prepubes, ventrally, in line with the standing femora. The Geist orientation is based on Claessens et al. (2009) which was based on a mistake.

Of course, as they admit, there is no evidence for this. And I’ll add some serious evidence against it.

Some pterosaur pubes are much shorter than their ischia. What would this mean for a cranially directed prepubis? Take a look at Figure 1 and put it together for yourself. Unfortunately, Geist et al. looked at only those pelves that had a long pubis.

If pterosaurs had a avian-like or monitor-like air-sac system associated with their lungs, then the posterior ribs could have pumped air in and out of those sacs, driving air through the lungs. Very typical of lizards, not crocs or birds.

To their credit, Geist et al. touch on the fact that sternal ribs are rarely ossified, noting they were likely often cartilage-based.

References
Claessens LPAM, O’Connor PM, Unwin DM 2009. Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism. PLoS ONE 4(2): e4497. doi:10.1371/journal.pone.000449
Geist NR, Hillenius WJ, Frey E, Jones TD and Elgin RA 2013. Breathing in a box: Constraints on lung ventilation in giant pterosaurs. The Anatomical Record. 013 Dec 10.