Jianchangopterus zhaoinanus (Li and Bo 2011, YHK-0931) is a small, complete and crushed Middle Jurassic pterosaur from Liaoning, China. Originally it was described as a scaphognathine pterosaur (Fig. 1) close to Sordes. At first glance, it might be appear to be one. It had short legs, short hands, a longish tail and sharp teeth. What it doesn’t have is a distinct primary naris with a strong maxillary ascending process. So, this is could be VERY interesting, with a little bit of this, and a little bit of that…
So what is it?
An example of modular evolution?
Modular evolution doesn’t happen. Phylogenetic analysis sorts these sorts of things out. Evolution changes every part of the body, even if just a little bit.
A transitional taxon?
Well, every pterosaur, except terminal taxa, can be considered transitional between its ancestral and derived kin. But in this case Jianchangopterus is not transitional between rhamphs and pterodacs.
Figure 1. Jianchangopterus in situ, both plates superimposed. It is small, has a long tail, but it nests at the base of the Pterodactylus clade, between Ningchengopterus and the Painten pterosaur, neither of which expose the mid to distal tail. Manual 4.4 is very thin, folded back against m4.3 here in one wing, less folded on the other wing.
What analysis recovers
when you add this taxon to the large pterosaur tree, you find that Jianchangopterus nests between Ningchengopterus and the Painten pterosaur, in their own clade at the base of the genus clade Pterodactylus (Fig. 2). Outgroups to these two clades include Ornithocephalus and two tiny Solnhofen pterosaurs (n9 and n31). The outgroup to all three clades is SMNS81775, a very tiny pterosaur, that I know from a skull drawing only. It has a large orbit, short rostrum and short antorbital fenestra.
Let’s delete all Pterodactylus to see what happens
And the outgroups too. Results: Jianchangopterus nests in the same spot. It doesn’t shift toward any scaphognathines.
Sometimes what is obvious STILL needs to be examined
Lu and Bo looked at certain obvious traits in Jianchangopterus (tail, metacarpus, tooth number, etc.) and decided it was closest to Sordes, which they considered a scaphognathid. It is not. And neither is Jianchangopterus. Shifting Jianchangopterus to Sordes adds 40 steps to the most parsimonious score. Eyeballing a specimen, even following ‘the rules’ regarding certain traits still takes a back seat to phylogenetic analysis.
It’s all in the details…
and the taxa one includes, as I’ve harped on constantly. On that point, Lu and Bo were not aware of the Painten pterosaur when they published. And they failed to mention Ningchengopterus.
Figure 2. Jianchangopterus between Ningchengopterus and the Painten pterosaur. Yes, it looks superficially like a basal “rhamph.” But phylogenetic analysis separates the homoplasies from the homologies. Note in Jianchangopterus the metacarpus is relatively shorter, especially relative to the ulna. The cervicals are more robust and relatively a little shorter. This is a reversal that makes Jianchangopterus more rhamph-like. You can’t eyeball these things. You have to let the matrix and computer recover the relationships.
So what about that long tail?
Neither Ningchengopterus nor the Painten pterosaur expose a long tail, either because the plate is broken or the tail is beneath matrix. The outgroups all have a long tail. They also have a longer metacarpus especially relative to the ulna. This is evolution at its best. Nothing proceeds in a straight line. At every generation some are taller, some have longer hands, others have shorter hands.
Figure 3. When you compare the three specimens of Sordes to the three jianchangopterids the purported similarities to Sordes start to fade. Shifting Jianchangopterus to Sordes adds 40 steps. The 36 specimen of Sordes nests closer to the Donau Dorygnathus than to the other two Sordes specimens which were themselves basal to Dorygnathus.
What about the most basal Pterodactylus?
Here the more derived AMNH1942 specimen of Pterodactylus (n20 in the Wellnhofer 1970 catalog. Fig. 3), the most basal taxon in the Pterodactylus genus clade, also seems to have a very long, but faint tail, largely hidden below a dusting of matrix.
Figure 3. Pterodactylus AMNH1942 with tail traced. Note the tail goes below the leg at the knee, then reappears near the wingtips and trails toward the feet. The matrix itself is filled with organic shapes and what appears to be a tail could be one of these. However, the undisputed long tail of Jianchangopterus adds credence to this interpretation.
Clearly a robust tail disappears beneath the femur. What we see of the rest of the tail could be organic shapes, which are also all around the matrix. But then with a sister taxon like Jianchangopterus with an undisputed long tail, this deserves further investigation.
Figure 5. Pterodactylus AMNH1942 without the tracing. No doubt the tail disappears behind the femur. Further investigation is needed to find the rest of the tail and expose it on the surface.
More derived Pterodactylus specimens had a short tail. No doubt about that.
So the tail became further reduced in derived members of this clade. There has been a long-standing assumption that Pterodactylus had a short tail. That assumption really has to be tested by exposing that last caudal vertebra. That hasn’t always (has never) been done. So we might be living under a false paradigm. Jianchangopterus provies a clear clue that the old paradigm needs to be examined in greater detail and with greater certainty.
The short hand
The metacarpus/ulna ratio is very small/short in Jianchangopterus. Phylogenetic analysis demonstrates that this single trait is a reversal from a larger ratio. Don’t think it can’t happen. Evolution works the way it works, and not always in a straight line.
We’ve seen several contenders for the transition taxon between rhamphs and pterodacs.
Darwinopterus had a short hand and long tail, but a long skull and neck, but it nests on the rhamph side not anywhere near any of the four pterodac origin/transition points.
“Rhamphodactylus” had a long skull, short tail and long hands. It nests on the pterodac side of one divide.
Kryptodrakon was a misread large but gracile dorygnathid.
Only the tiny Solnhofen pterosaurs provide concrete evidence for four gradual transitions, each to their own pattern.
Getting back to Jianchangopterus
Lü and Bo report, “the lateral surface of the premaxilla and maxilla have horizontal laminations.” This is what I’ve been reporting, this is the anterior jugal laminated to these underlying bones.
Lü and Bo report, “the maxilla bears a distinct recess (representing the antorbital fossa).” This may not be true. IMHO, what Lu and Bo see is IMHO is a medial sheet of bone dividing the left and right rostra, common to many pterosaurs.
The long tail, clearly laid out on this specimen, takes one positive step to confirm my earlier observations of similar longish, very thin tails on other pterodactyloid-grade pterosaurs.
Lü J and Bo X 2011. “A New Rhamphorhynchid Pterosaur (Pterosauria) from the Middle Jurassic Tiaojishan Formation of Western Liaoning, China”. Acta Geologica Sinica85(5):977–983.