Variation within Dorygnathus – part 1

Kevin Padian (2008) on Dorygnathus banthensis represents the latest traditional thinking on this genus and species. Unfortunately he did not reconstruct more than one specimen (Fig.1) and he did not employ phylogenetic analysis neither between specimens nor between other pterosaurs. Those shortcomings are rectified here. This post was inspired by the addition of three new Dorygnathus specimens to the cladogram (Fig. 2 in color).

Padian's (2008) version of Dorygnathus taking off. This is a freehand sketch, not a tracing of bones.

Figure 1. Padian’s (2008) version of Dorygnathus taking off. This is a freehand sketch, not a tracing of bones (as in Figs. 2, 3). Padian did not attempt to reconstruct more than one Dorygnathus to test the supposition that there are over 30 specimens of this one genus and species. Nor did he attempt a phylogenetic analysis. Reconstructions (Fig. 2) illuminate the subtle and not so subtle variations. Padian’s bipedal pterosaur appears to be in an attack mode. I’d like to see him draw Dorygnathus in a common pose of balance.

From the Padian abstract (abridged here):  
“Over 30 skeletons and dozens of isolated bones of the Liassic pterosaur Dorygnathus have been recovered from the Early Jurassic (Toarcian) of Baden–Württemberg and Lower Saxony in Germany, and from Nancy, France. All but one specimen have been assigned to the species D. banthensis. Dorygnathus is most closely related to Rhamphorhynchus and the Pterodactyloidea.”

Figure 2. Click to enlarge. Reconstructions of several Dorygnathus and related taxa based on tracing bones. Here they appear to be several distinct species and certain other pterosaurs appear to be congeneric (depending if you're a lumper or splitter). This is confirmed by phylogenetic analysis. One branch of dorygnathids is basal to ctenochasmatids. Another is basal to azhdarchids. A third, more basal clade, not far from Sordes, is basal to scaphognathids and darwinopterids, represented here by Jianchangopterus. So Dorygnathia survived to the Maastrichtian.

Figure 2. Click to enlarge. Reconstructions of several Dorygnathus and related taxa based on tracing bones. Here they appear to be several distinct species and certain other pterosaurs appear to be congeneric (depending if you’re a lumper or splitter). This is confirmed by phylogenetic analysis. One branch of dorygnathids is basal to ctenochasmatids. Another is basal to azhdarchids. A third, more basal clade, not far from Sordes, is basal to scaphognathids and darwinopterids, represented here by Jianchangnathus. So Dorygnathia descendants survived  into the Maastrichtian. A small one, the Hauff specimen, is basal. There is also a clade leading to a large Sericepterus that did not lead to other clades, but became extinct. The variety here is comparable to the Rhamphorhynchus clade.

Maybe not…
Reconstructions of several Dorygnathus specimens (Fig. 1) reveal an overlooked variety in this genus that does not become readily apparent until accurate tracings and reconstructions are made. These specimens do not appear to be conspecific, confirmed by phylogenetic analysis. Each has at least a few distinct traits. While most specimens were about the same size, each had a distinct morphology with longer and shorter skulls, different sized fingers, distinct sternal complex and pelvis shapes and distinct pedal proportions.

Descent and descendants
According to the large pterosaur tree, Dorygnathus descended from a sister to Sordes and Changchengopterus, both smaller specimens.

To Padian’s point: Dorygnathus is a key taxon at the base of two pterodactyloid-grade clades: ctenochasmatidae (which retained long teeth) and azhdarchidae (which did not). Dorygnathus is also a key taxon at the base of Jianchangnathus + Pterorynchus + Darwinopteridae and Scaphognathus (which is basal to all remaining pterodactyloid-grade pterosaurs) and these also had smaller teeth. Padian, unfortunately, did not see the specifics, but reported very broad generalizations regarding pterosaur relations.

Despite appearances, Dorygnathus is not so much related to Rhamphorhynchus, but both developed long procumbent teeth by convergence and share a last common ancestor near basal Campylognathoides and Eudimorphodon.

From the Padian text:
“It appears that Dorygnathus is most closely related to Scaphognathus and Rhamphorhynchus, though without some of the synapomorphies that appear to ally the latter genus to the Pterodactyloidea (such as the lower, longer snout, the anterior displacement of the jaw joint to beneath the midpoint of the orbit, the more steeply inclined quadrate, the reduction of the lower temporal fenestra, the elongation of the first wing-phalanx, and the partial reduction of the fifth toe).”

So, Padian is going on appearances here, not analysis
[Actually many pterosaurs, including the SMNS 50164 specimen of Dorygnathus had a lower, longer snout along with the anterior displacement of the jaw joint. According to the large pterosaur tree Rhamphorhynchus inherited its long first wing phalanx from Campylognathoides and most pterodactyloid-grade pterosaurs and Dorygnathus do not share this trait. Likewise the partial reduction of the fifth toe in Rhamphorhynchus was inherited from Campylognathoides.] Dorygnathus retained an elongated pedal digit 5 with a bent p5.2.

From the Padian text:
“Dorygnathus appears to be one of the closest genera to Rhamphorhynchus and, hence, to the Pterodactyloidea (a conclusion independently reached by Unwin 2003a). They share a long mandibular symphysis that is toothless at its anterior end, large anterior teeth strongly inclined forward and outward, nares more reduced and located more posteriorly and higher on the skull, reduced antorbital opening, and jugal lacking a posterior process along the base of the skull.”

[Again, in this age of phylogenetic analysis, basing relationships on “appearance” is to be avoided.] Padian errors when he reports that all Pterodactyloidea has a long mandibular symphysis that is toothless anteriorly disregarding exceptions here, here and here. The nares are also reduced in the non pterodactyloids, Pterorhynchus and Darwinopterus. Pterodactyloids do not have a reduced antorbital opening. Some Dorygnathus and Rhamphorhynchus share this trait, but other Dorygnathus evolve a larger antorbital fenestra. Neither clades are 100% without a jugal posterior process.

From the Padian text:
Dorygnathus shares other features with Scaphognathus but most appear to be plesiomorphies for the lineage. I conclude that Dorygnathus is a member of the main stem of pterosaur evolution leading to the Pterodactyloidea, and is the closest representative of this main lineage in the Early Jurassic.Both Campylognathoides and Dimorphodon, the two other known Liassic genera, are too different and specialized to be as closely related to this main stem of pterosaur evolution; they are important side-branches with roots in the Late Triassic forms.”

[Giving credit where credit is due (even though the current large pterosaur tree topology specified by Peters 2007 predates this), Padian correctly connects Dorygnathus to pterodactyloids, but he has no idea which ones or through which specimens. He simply notes [correctly] that Dorygnathus is a better Liassic candidate than the other two Liassic candidates, Campylognathoides and Dimorphodon.]

It's better to trace bones accurately than to freehand reconstructions. Moreover, the quadrupedal pose Padian promotes has several errors (fingers not lateral, hands in front of shoulders, humerus over abducted).

Figure 3. It’s better to trace bones accurately than to freehand reconstructions. Moreover, the quadrupedal pose Padian promotes has several errors (fingers not lateral, hands in front of shoulders, humerus over abducted). Currently no pterosaur tracks match Dorygnathus feet. The huge manual claws argue against a quadrupedal configuration. Padian, once the champion of bipedal locomotion in pterosaurs, must not have had much evidence to stand on if he has fallen so far the other way.

From the Padian caption (Figure 3):
Dorygnathus banthensis; reconstruction of the skeleton in a hypothetical quadrupedal pose. In this position the left humerus has reached the limit of forward protraction and rotation; retraction of the limb would have been slight, with minimal force. The pace length of the hindlimbs would not have been so limited and would have been much greater than that of the forelimbs. This suggests that the forelimbs could have served as little more than supports for the front end of the body, if they were necesary at all. Note also the forward slope of the dorsal column in this position.”

[Actually, in Padian’s tipped over pose (Fig. 3) the forelimbs would have been essential for support. However, in the Peters pose (Fig. 3, color) the forelimbs could be elevated or implanted without changing the center of balance over the toes. The Padian skull is not an accurate representation of the Vienna specimen and his pedal digit 5 is way too small, the unfortunate results of ‘eyeballing’ it.]

More tomorrow and the next day when Dorygnathus gets really interesting

References
Padian K 2008. The early Jurassic pterosaur Dorygnathus banthensis (Theodori, 1830). Special papers in palaeontology 80: 64 pp.

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