The Family Tree of the Pterosauria 5 – Dorygnathus and its Spectacular Descendants

It would take a heretic to propose that Dorygnathus had anything to do with basal pterosaurs transitioning into “pterodactyloid”-grade pterosaurs. Yet, that’s exactly what this blog is all about.

The variety in Dorygnathus

Figure 1. Click to enlarge. The variety in specimens assigned to Dorygnathus. With other genera nesting within various specimens assigned to Dorygnathus, a renaming process will have to sort this out. Note the tiny pterosaurs at the end of each phylogenetic line.

According to tradition Dorygnathus was nothing more than a toothy oddity. Other than Padian (2009) relatively little has been written about this genus lately. So little attention has been paid to Dorygnathus that a certain worker (see below) confused it with Rhamphorhynchus.

Several paleontologists have already adopted Darwinopterus (Lü et al. 2009) as the best candidate taxon to bridge the former gap between the basal pterosaurs and the derived “pterodactyloids.” However, a larger and completely resolved cladistic analysis doesn’t support that smaller, poorly resolved tree. Earlier we learned that Darwinopterus nested within Pterorhynchus, which was already reducing the naris and elongating the skull and neck.

A larger cladistic analysis (see below) demonstrates that tiny pterosaurs were the real transitional taxa preceding at least four “pterodacyloid”-grade clades. At the base of two of these transitions we find Scaphognathus. At the base of Scaphognathus and the other two transitions we find Dorygnathus and Sordes.

Now you know why Dorygnathus is so important.

Dorygnathus is the Key.
There is an overlooked variety in several specimens of Dorygnathus (see above) that was revealed after reconstruction and cladistic analysis. Unfortunately, no prior analyses attempted to include or reconstruct more than one specimen from Dorygnathus and so overlooked this variety and its phylogenetic significance.

Two  Basal Dorygnathus Specimens Are Outgroups to the First Split
The Donau specimen (private) nested as the most basal Dorygnathus. Sordes is the outgroup taxon. The neck, tail and torso were longer in Dorygnathus than in Sordes. The teeth were larger and more widely spaced on longer jaws.

Next in line and at the base of its own split is the extremely toothy (almost tusky) specimen, SMNS 51827, perhaps the classic Dorygnathus. Were those giant teeth useful? Or just for show? Fingers 1-3 were greatly enlarged, rivaling the entire foot in size. The entire wing was more robust, but the sternal complex remained small.

The Azhdarchid Lineage Arising from Certain Dorygnathus Specimens
Following the two basal taxa, Dorygnathus splits into two major branches. The first ultimately produced azhdarchids. The second produced ctenochasmatids.

Derived from the SMNS 51827 specimen, the SMNS 50164 specimen of Dorygnathus (Figure 1) had a longer rostrum and smaller teeth. It also had shorter wings and enormous fingers. This specimen is the last of the long, stiff-tailed types. The skull was ~13 cm in length.

Proto-azhdarchid lineage

Figure 2. Click to enlarge. The SMNS 50164 specimen of Dorygnathus and its proto-azhdarchid descendants.

The Transition to the “Pterodactyloid” Grade
An important size reduction marks the appearance of tiny TM 10341At less than 10 cm from snout to vent it was shorter than just the skull of its phylogenetic predecessor, SMNS 50164 (above). Looking like a miniature SMNS 50164, TM 10341 had smaller teeth, smaller fingers, a smaller tail and a larger prepubis and pelvis. Wellnhofer (1970) cataloged it as Pterodactylus spectabilisa juvenile pterodactyloid even though the metacarpus was not relatively larger. Rather the antebrachium (radius and ulna) were relatively much smaller. This tiny taxon gave rise to several long-necked, long legged pterosaurs with metacarpals longer than the antebrachium, beginning with Beipiaopterus and including Huanhepterusazhdarchids and the flightless pterosaur, SoS 2428.

The protoctenochasmatids arising from Dorygnathus

Figure 3. Click to enlarge. The protoctenochasmatids arising from certain specimens of Dorygnathus. Note the tiny taxa following Angustinaripterus.

The Ctenochasmatid Lineage Arising from other Dorygnathus Specimens
Getting back to the base of Dorygnathus, two new genera, Fenghuangopterus and Cacibuteryxnest between the SMNS 51827 specimen and the SMNS 55886 specimen of Dorygnathus. Either these two need to be renamed as species of Dorygnathus or certain Dorygnathus specimens need to be renamed as new genera.

The R156 specimen followed. Long, procumbent teeth may have reached an acme with this specimen.

Several skull only specimens followed, including D. purdoni, Harpactognathus and Augustinaripterus. Sericipterus, may also nest here according to Andres et al. (2010).

Another Transition to the “Pterodactyloid” Grade
A drastic size reduction occured next, with the St/Ei I specimen wrongly attributed to Pterodactylus micronyx  and the holotype of Pterodactylus micronyx, The Pester specimen, wrongly attributed to Pterodactylus. The former had a snout-vent length of 5 cm and had a relatively shorter rostrum.The relatively longer metacarpus and shorter tail marked this specimen as a “juvenile pterodactyloid,” but other traits nest it here, at the base of the Ctenochasmatidae. Larger ctenochamatids with a longer rostrum include Gnathosaurus, Ctenochasma and Pterodaustro, the last of this lineage. An evolutionary sequence of skulls is laid out here for ready reference.

Pterosaur family tree

Figure 4. Click to enlarge. Dorygnathus nests in the left column of the pterosaur family tree at the base of the Ctenochasmatidae and the Azhdarchidae.

The Scaphognathid Clade.
The sisters of Sordes and the Donau specimen of Dorygnathus also branched off in a third direction that included Pterorhynchus and Scaphognathus. We will look at those lines in the near future.

As documented here, there was no single “missing link,” and it was not Darwinopterus. Rather, convergent size reductions in four lineages all leading to Dorygnathus provided all of the pterodactyloid-grade pterosaurs now known.

Mistaken Identity
Not all long-tailed pterosaurs with big teeth belong to Dorygnathus. Dr. David Hone mistook a model Rhamphorhynchus for a Dorygnathus, but generally Dorygnathus had a more robust skeleton, a tiny triangular sternum, a shorter first phalanx of the wing finger (that did not reach the elbow), thicker teeth and a broader mandible, among other details.

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:
Andres B, Clark JM and Xing X 2010. A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs. Journal of Vertebrate Paleontology 30 (1): 163–187. doi:10.1080/02724630903409220.
Bennett SC 2004. 
New information on the pterosaur Scaphognathus crassirostris and the pterosaurian cervical series. Journal of Vertebrate Paleontology, 24: 38A
Lü J, Unwin DM, Jin X, Liu Y and Ji Q 2009
.
Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society London B  (DOI 10.1098/rspb.2009.1603.)
Padian K 2009.
 The Early Jurassic Pterosaur Dorygnathus banthenis (Theodori, 1830) and The Early Jurassic Pterosaur Campylognathoides Strand, 1928, Special Papers in Paleontology 80, Blackwell ISBN 9781405192248
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.
Wellnhofer P 1975a. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33.1975b. Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. 1975c. Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.

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