Focus on Angustinaripterus – transitional between Dorygnathus and Ctenochasma

Angustinaripterus (Fig. 1) has been difficult to classify for other pterosaur paleontologists. Here in the large pterosaur tree the reason becomes quite evident. Add a few taxa and Angustinaripterus become a transitional taxon between the more primitive Dorygnathus (R154) and the more derived Gnathosaurus and Ctenochasma.

Figure 1. Angustinaripterus as a transitional taxon between Dorygnathus and Gnathosaurus.

Figure 1. Angustinaripterus as a transitional taxon between Dorygnathus and Gnathosaurus. Seems pretty obvious. Phylogenetic analysis confirms.

This possibility flips out traditional pterosaurologists who have pinned their hopes on Darwinopterus, which doesn’t look much like either Ctenochasma or Dorygnathus.

But that’s not all
Here (Fig. 2) are the many other specimens that smooth the evolutionary transition, as we noted before. Here they are. And many of them are tiny.

Figure 2. The same sequence with the addition of Dorygnathus purdonti and four tiny pterosaurs variously misassigned to Pterodactylus and Ctneochasma.

Figure 2. The same sequence with the addition of Dorygnathus purdonti and four tiny pterosaurs variously misassigned to Pterodactylus and Ctneochasma. Black illustrations are to scale. Gray figures are enlarged to show detail.

Angustinaripterus is the reason why I delved deeper into pterosaur phylogeny than anyone has done before. At first glance it’s clearly something not quite Dorygnathus and not quite Gnathosaurus or Ctenochasma.

The next step after Angustinaripterus was to add in some…

Tiny pterosaurs
This (Fig. 2) is only one sequence of many in which tiny adult pterosaurs are transitional between larger forms, both more primitive and more derived. At first glance, and according to tradition, these tiny pterosaurs are only juveniles or hatchlings, which makes perfect sense—until you add them to your matrix—and you realize juvenile pterosaurs of other types are virtual copies of adults. So there was no allometric growth after hatching, but chiefly isometric growth.

But there’s an important clue here staring you right in the face: Note how the tiny pterosaurs are ALL the same size. As it turns out, this is the minimum size at which pterosaurs could fly, evidently, as we find no smaller pterosaurs in the fossil record. Smaller pterosaurs, all juveniles, must have been living in damper environments and probably not flying. Some hatchlings, like the IVPP embryo, were as large as these adult pterosaurs (Fig. 2) and other adult tiny pterosaurs, so they could fly immediately. 

References
He X-L, Yang D-H and Su C-K 1983. A New Pterosaur from the Middle Jurassic of Dashanpu, Zigong, Sichuan. Journal of the Chengdu College of Geology supplement 1: 27-33.

wiki/Angustinaripterus

Pterodaustro evolution

Earlier we looked at the evolution and variety of ctenochasmatids, focusing on the skulls. Here we take a look at Ctenochasma, Pterodaustro and a taxon that forms the best transition (Fig. 1). So far it has been called the Bamberg piece. Even so, in some traits the new taxon has also gone its own way (Fig. 1), as all sisters to transitional taxa do. We’ll call it ‘Propterodaustro’ for now, but a real generic name will be applied by its discoverers when the Bamberg specimen is officially published. For now it has only made its presence known online here and here.

 

Figure 1. The evolution of Pterodaustro from a sister to Ctenochasma. "Propterodaustro" , the Bamberg specimen, is a sister to the transitional taxon. As you can see, there is an increasing variety in this clade.

Figure 1. The evolution of Pterodaustro from a sister to Ctenochasma. “Propterodaustro” , the Bamberg specimen, is a sister to the transitional taxon. As you can see, there is an increasing variety in this clade.

Similarities
Like Ctenochasma, the new taxon has a long, but not hyperelongated, rostrum, as seen in Pterodaustro. Sizewise, the new taxon is midway between the two. The neck length is transitional. The curvature and depth of the mandible and the length of the tibia relative to the metacarpus in the new taxon is midway between the two (Fig. 1). Relative to the antebrachium, the metacarpus of the more derived Pterodaustro is phylogenetically shrinking, an oddity among derived pterosaurs.

Autapomorphies
The new taxon includes a few autapomorphies found in neither Ctenochasma nor Pterodaustro. A relatively taller skull is present. The torso is relatively shorter. The scapula is no longer than the coracoid chiefly because the coracoid is relatively larger. The humerus is much shorter than the femur. The ischium does not have two posterior processes. The deltopectoral crest is ever so slightly pinched. The sternal complex is uniquely shaped. Manual 4.2 is shorter than m4.1 (fairly common among pterosaurs, but not present in Ctenochasma or Pterodaustro.) The upper teeth are longer than the lowers with small thickened lobes. Perhaps you can spot additional unique traits.

This weekend
I’ll reconstruct the new Pterodaustro with stomach stones featured in JVP and put it up against the holotype to see what overall variation, if any, is present. The specimen is obviously a Pterodaustro, so there’s no reason to reconstruct it (traditional thinking), but if there is variation, there might be something of interest to post (test, test, test).

References
The pre-Solnhofen ctenochasmatid pterosaur was covered earlier here and announced earlier here and here. Quoting from those sources (below), the discoverers appear to think they have an azhdarchid ancestor, but they are not saying that for sure.

“The 155 million year old animal is different in physique from other known species – and its remnants are extremely well preserved. Scientists speak of a major discovery. The specimen had very long arms and long legs, almost like stilts. Fish remains are found in the belly.”

“The Bamberg piece shows that these giant pterosaurs had their origin in the Jurassic period,” reports Dr. Eberhard (Dino) Frey. Such a nesting, at the base of the azhdarchidae, is not confirmed in the large pterosaur family tree. It is certain that azhdarchids had their origins in the Jurassic, but not with the Bamberg specimen. Instead those ancestors were the tiny pre-azhdarchids, like no. 42 and no. 44 reported earlier here.

The Ctenochasma – Pterodaustro transitional taxon

This post has been modified with a new reconstruction, heading and text.
A pre-Solnhofen ctenochasmatid pterosaur has been announced here and here. Please take a look at those links to see the fossil itself. Both sites can be clicked for enlargements.

Figure 1. The new Propterodaustro pterosaur reconstructed. While it nests between Ctenochasma and Pterodaustro, certain traits are distinct from both.

Figure 1. The new Propterodaustro pterosaur reconstructed. While it nests between Ctenochasma and Pterodaustro, certain traits are distinct from both.

The new pterosaur nests here between Ctenochasma and Pterodaustro.

“The discovery is of similar interest like Archaeopteryx,” says the director of the Bamberg Natural History Museum, Matthias Mäuser. Over 400 teeth were reported. The long teeth are not pointed, but with “small  thickened lobes (Google translated from the original German)” explains Mäuser. He reports, “the food was not chewed or retained, but filtered out of the water – as do baleen whales and flamingos with the slats in the beak.”

“The 155 million year old animal is different in physique from other known species – and its remnants are extremely well preserved. Scientists speak of a major discovery. The specimen had very long arms and long legs, almost like stilts. Fish remains are found in the belly.”

“The Bamberg piece shows that these giant pterosaurs had their origin in the Jurassic period,” reports Dr. Eberhard (Dino) Frey. Such a nesting, at the base of the azhdarchidae, is not confirmed in the present study.

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
Archosaur Musings link
Der Spiegel link

What is Gladocephaloideus?

Lü et al. (2012) recently reported on a new Gallodactylus (= Cycnorhamphus)-type of Ctenochasmatoid (cycnorhamphidae + ctenochasmatidae + Pterodactylus). Unfortunately these three clades are not related in the large pterosaur tree that tests many more possibilities.

gladocephaloideus-recon

Figure. 1. Gladocephaloideus in situ and reconstructed using DGS (digital graphic segregation). There is a lot of preserved skin and hair on the cranial and cheek parts of the skull (Fig. 2), which is cool, but it means the underlying bones are not as prominent.

Meet Gladocephaloideus jingangshanensis
This long rostrum ctenochasmatid did not have as many teeth as Ctenochasma, nor did it have the spoon-bill of Gnathosaurus. But it did have the slightly curved rostrum, widely spaced teeth and elongated neck vertebrae of Gegepterus. Gladocephaloideus lived during the Barremian stage of the Early Cretaceous some 125 million years ago, so it was a contemporary of Gegepterus from the same formation. From information presented so far, Gladocephaloideus may be a species within the genus Gegepterus.

Skull of Gladocephaloides

Figure 2. Skull of Gladocephaloideus in situ. (IG-CAGS-08-07). Skull length 18.2 cm. Note the soft tissue fibers emanating from the posterior skull. Part of the palate is visible between the jaws.

Soft Tissues
The back of the Gladocephaloideus skull includes, “Filamentous structures are preserved near the dorsal and posterior margins of the posterior portion of the skull (above the orbit), and similar structures are also preserved near the back side of the cervical vertebra. It also supports the idea that at least some relatively small pterosaurs were warm-blooded, active fliers.” As mentioned above, the cheek area is also covered by skin that obscures the underlying bones.

The pes of Gladocephaloideus

Figure 2. (Left) The pes of Gladocephaloideus compared to (right) the pes of Ctenochasma elegans (a smaller, more primitive Ctenochasma with fewer teeth than larger specimens in the genus Ctenochasma). The feet of Gegepterus are unknown.

The Feet Tell the Tale
No doubt the skulls of Gladocephaloideus and the cycnorhamphid, Feilongus (Fig.4), converge upon each other. Even so, the feet of Gladocephaloideus are much closer to those of other ctenochasmatids, like Ctenochasma elegans (Fig. 2) and AMNH 5147, a primitive gnathosaurid. The feet of cycnorhamphids are distinctly different with a longer metatarsal 1. Scaphonathids (including cycnorhamphids and ornithocheirids) also share a metatarsal 1 longer than the others.

The skull of Gegepterus,

Figure 4. The skull of Gegepterus, also from the Yixian formation of the Early Cretaceous of China. Note the similarities to the skull of Gladocephaloideus.

Parietal Crest?
Lü et al. (2012) reported an extremely low crest on Gladocephaloideus (Fig. 1). To me, that doesn’t look like much of a crest. Instead that zone may represent the crushed and broken occiput of a rounder skull, as in ctenochasmatids.

Parsimony
In the large pterosaur tree, Gladocephaloideus nests as a sister to Gegepterus and may be a species of that genus. To move Gladocephaloideus to the cycnorhamphids requires 28 more steps.

 

References
Lü J-C, Ji Q, Wei X-F and Liu Y-Q 2011. A new ctenochasmatoid pterosaur from the Early Cretaceous Yixian Formation of western Liaoning, China. Cretaceous Research in pressdoi:10.1016/j.cretres.2011.09.010.

wiki/Gladocephaloideus