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.

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