A new, excellently preserved and unnamed private specimen has been published by Tischlinger and Frey (2013). It comes from the Latest Kimmeridgian of the Jurassic, just before the last age of the Jurassic, the Tithonian. The specimen is owned by a private research institute headed by Birgit Albersdörfer.
From their abstract: “The new specimen provides evidence of a late stage of a gradual evolution from the basal pterosaur construction (the so-called ‚rhamphorhynchoid‘ grade) to a pterodactyloid one. — The Painten pro-pterodactyloid demonstrates the evolutionary pathway towards a pterodactyloid flight configuration, which is characterized by the reduction of the fifth pedal ray (digit), shortening of the tail and the elongation of metacarpal IV with respect to the humerus to more than 70% of the length of the latter.”
Tischlinger and Frey considered the Painten pterosaur “the last step on the long road from a basal pterosaur to the pterodactyloid.” (translated from the original German). They described it thoroughly.
Unfortunately, no phylogenetic analysis was provided.
So I provide one. Placing the Painten pterosaur into the large pterosaur tree nests it as a very basal Pterodactylus, between the very tiny SMNS 81775 specimen and Ningchengopterus, both basal to all valid Pterodactylus genera and all very much within this particular pterodactyloid-grade clade that began several nodes earlier. So the Painten pterosaur is a transitional specimen of sorts (aren’t they all? except for the terminal taxa) but only transitioning between the tiny Scaphognathus descendants and the genus Pterodactylus. Even so, several autapomorphies are present like the presence of a pedal digit 3 longer than pedal digit 2 and a very short prepubis.
The problem is
There are so many pterosaurs that converge on the morphology of Pterodactylus that aren’t really related to Pterodactylus that this genus has become a wastebasket taxon and is need of a big revision. All problems are solved with phylogenetic analysis, but no one, apparently, is interested in doing this.
The other problem is
Because they have not included multiple specimens from single genera and tiny pterosaurs most pterosaur paleontologists are still stuck in the old paradigm that all pterodactyloid-grade pterosaurs had a single common origin creating a monophyletic clade. Phylogenetic analysis shows this is not true. There were four convergent origins for the pterodactyloid grade. This is why the putative Painten transitional taxon looks so different from the putative Darwinopterus transitional taxon. They are not related to one another, but represent different clades. On the same subject from another point-of-view, Tischlinger and Frey hoped to nest their new pterosaur based on the old “rules” about which traits defined a basal pterosaur and which traits defined a pterodactyloid. You can’t do that. That’s putting the cart before the horse. You have to use a phylogenetic analysis and let the data and the analysis tell you how the traits are ordered. The order of longer and shorter traits may be more complex than the old “rules” indicate. They don’t always proceed in a step forward – step forward progress. You have to take what Nature gives you, and not try to pigeonhole new finds into old clades.
The third problem is
The belief in the mosaic pterosaur, one under modular evolution in which some body parts are advanced while others are not. Again, this is an illusion based on two few taxa in the analysis.
Let’s look at the Painten pterosaur in more detail.
Pedal digit 5 is rarely so wonderfully preserved (Fig. 3). Note the distal tip of p5.2. It has a joint surface, but the next phalanx, the ungual, is not readily observable.
However, if we take a closer look the ungual is there on both feet (Fig. 4), on edge on the left foot and flattened on top of mt5 on the right foot. Along the same lines the wingtips (m4.4) appear to also have joint surfaces, but no unguals. The left ungual has been displaced and now appears at mid phalanx of m4.4. The right ungual is nowhere to be seen, perhaps as a result of the breakage of the phalanx, or simple taphonomy or burial.
Tischlinger and Frey note that pedal digit 5 could be used for “tensioning the tail wing membrane (uropatagium), but to a very limited extent.” Unfortunately only one specimen has been promoted to link pedal digit 5 to the uropatagium, the holotype of Sordes, and that is a misidentification. No pterosaurs link pedal digit 5 to the uropatagium, but Sharovipteryx does.
Manual digit 5 is usually disturbed during taphonomy.
Here it is (in dark blue) undisturbed, but curled, on an axially rotated metacarpus. The undisturbed pteroid is articulated to the radiale. The extensor tendon process is not coosified to m4.1. The fingers are all rotated into the plane of the substrate. In vivo they would have pointed palmar side down, as in other tetrapods.
Tischlinger and Frey agree with the Darwinopterus transitional hypothesis, which is falsified when more taxa are included in analysis. They consider the Painten pterosaur, with it’s short tail and short pedal digit 5, to be the next step from Darwinopterus toward the pterodactyloid grade. These are traits that Darwinopterus had not acquired.
If you think the consensus is correct on this issue, remind yourself that Tischlinger and Frey merely accepted the findings of others, despite the red flags and oddities. I test issues using established methods, like phylogenetic analysis. I don’t have to make up excuses for data or imagine the evolution of body plans because all that comes from the order of the nodes in the recovered trees.
That’s good Science, right? Repeat the experiment if you don’t agree, then let me know if you come up with something different.
Tischlinger and Frey discuss various ways or paths by which the rhamph body plan evolved to become the pterodac body plan, but this is all simple dreaming without a large phylogenetic analysis of the Pterosauria. This the -only- method by which you can actually trace the appearance and subsequent modification of the various traits in much greater resolution, precision and verifiable validity.
Finally, if Rhamphodactylus, Darwinopterus and the Painten pterosaur were indeed phylogenetic sisters representing closely related steps in the evolution of the pterodactyloid grade, shouldn’t they look more alike (Fig. 5)? Phylogenetic analysis indicates they were not related, only convergent.
The Painten pterosaur is still very special
The Painten pterosaur is a transitional taxon leading to higher Pterodactylus specimens. It also represents a new clade in the pterosaur bush that had its own traits. Unlike other sister taxa pedal digit 5 is longer than the others. The middle dorsal vertebrae are compressed to be much shorter than the anterior and posterior verts, creating a shorter torso. The prepubis is remarkably tiny. The teeth are more needle-like than those of others. Pedal digit 5 is more robust than in sister taxa.
Dave Hone in his Archosaur Musings Blogpost described the Painten pterosaur as a “small, juvenile animal.” He did not say why, or to which adult it would be most closely associated. Hone may have followed the old paradigm that states a large orbit and unfused extensor tendon process are juvenile traits. He may not be aware that phylogenetic analysis (the large pterosaur tree) demonstrates that both are phylogenetic, rather than ontogenetic in nature.
Hone reported, “The fifth toe also seems to be something of an intermediate – it is not a small nub like the pterodactyloids, but nor is the second phalanx that long and it’s not curved either as in other basal forms.” Evidently he was not aware of the many pterodactyloids with longer lateral toes, often tucked beneath the other four. The relative shortness of metacarpal 4 was noted by both Tischlinger and Frey and Hone which they considered intermediate trait between shorter rhamphs and longer pterodacs. Unfortunately that assumes linear progression in evolution, which is not born out when phylogenetic analysis shows that more basal taxa had relatively longer metacarpals. We have to avoid wishful thinking and rigorously test all such “eyeball” assumptions.
Tischlinger H and Frey E 2013. Ein neuer Pterosaurier mit Mosaikmerkmalen basaler und pterodactyloider Pterosauria aus dem Ober-Kimmeridgium von Painten (Oberpfalz, Deutschland) — A new pterosaur with mosaic characters of basal and pterodactyloid pterosauria from the Upper Kimmeridgian of Painten (Upper Palatinate, Germany) Archaeopteryx 31:1-13.