Earlier we looked at the myth of Darwinopterus as the transitional taxon between long-tailed early pterosaurs and short-tailed later pterosaurs. Actually, several series of tiny pterosaurs (Fig. 5 as an example) fill that role and they do it four times, two out of two distinct Dorygnathus and two out of the smallest Scaphognathus (which is why some tiny pterosaurs have a large eye and short snout).
Remember a good transition consists of a beginning, several middles and an end. The Darwinopterus scenario provides a middle, but no specific beginning or end.
Figure 1. Darwinopterus female and associated egg.
Supporting the traditional view, Mark Witton, author of “Pterosaurs“, reports, “Darwinopterus incontrovertibly fills a long-standing gap in pterosaur evolution, bridging the morphological distance between early pterosaurs and Pterodactyloidea.”
Incontrovertibly? Not so. Darwinopterus fails when put to several tests (see below).
Witton (2013) also falls off the Darwinian train when he reports, “Rather than demonstrating a bauplan with a smattering of pterodactyloid and non-pterodactyloid features across the entire skeleton, it [Darwinopterus] possess the characteristic skull and neck of pterodactyloid while retaining a body very similar to those of rhamphorhynchid pterosaurs.” This has been called, “modular evolution” and this is the only animal that this bizarre mode of evolution has _ever_ been applied to. Modular evolution creates chimaeras, but that’s _not_ how evolution works!
Long time readers of the Pterosaur Heresies already know the solution to this problem.
According to the results of the large pterosaur tree (now 204 taxa), Darwinopterus nests at the acme of a small clade of darwinopterids including Wukongopterus, Kunpengopterus and Pterorhynchus at its base, all derived from a sister to Jianchangnathus, which also gave rise to Scaphognathus and a long list of tiny and large descendants.
A clade has been erected (Lü, Unwin, et al. 2009) for Darwinopterus + Pterodactyloidea, the “Monofenestrata.” Unfortunately, Darwinopterus does not have a monofenestra. The naris is small, but still visible (Fig. 2), just like Pterorhynchus.
Figure 2. Click to enlarge. Darwinopterus skull with colorized rostral bones. The arrow points to the naris, still present. This is just a big, long-necked basal scaphognathid.
More unfortunately, Darwinopterus does not nest near the base of any pterodactyloid-grade pterosaurs in the completely resolved large pterosaur tree. Those taxa that do actually nest at the base of pterodactyloid-grade pterosaurs (in the large pterosaur tree) fulfill Witton’s wish for a smattering of pterodactyloid and non-pterodactyloid features. Those features can be found in tiny pterosaurs (Fig. 5).
Figure 3. Pterosaur family tree according to Witton (2013). Note all of the suprageneric taxa here! That means Witton does not have to come up with a specific ancestor to Darwinopterus nor a descendant. The large pterosaur tree provides specific specimens for both.
Let’s put aside all the other problems with Witton’s pterosaur family tree and focus on the Darwinopterus situation.
Here Darwinopterus nests within the Wukongopteridae, a suprageneric taxon. Both the ancestor and descendant taxa are also suprageneric, leaving the transition to and from Darwinopterus rather cloudy. By that I mean, Witton doesn’t tell us which taxa are the direct ancestors and descendants of Darwinopterus. That avoids having to deal with details and data. Actually the original Lü, Unwin et al. (2010) tree generated some 500,000 most parsimonious trees, so from the start there are red flags everywhere with this study and this tree.
By contrast
there’s complete resolution (one tree results) in the large pterosaur tree. It also provides specific taxa (specimens) that nest with Darwinopterus and others that act as transitions to the four pterodactyloid grades. The former clade “Pterodactyloidea” is not monophyletic when tiny pterosaurs are included in analysis, something Witton and his cohorts refuse to do.
For a reminder, here (Fig. 4) are the closest sisters to Darwinopterus and three Darwinopterus specimens. The upper clade of wukongopterids are monophyletic, not transitional. The real story takes place after Scaphognathus with those half-sized descendants (no, they’re not juveniles).
Figure 4. Click to enlarge. Darwinopterids (wukongopterids) and their closest sisters in phylogenetic order beginning with Sordes. Kunpengopterus is derived from Pterorhynchus. Darwinopterus and Wukonopterus were derived from Kunpengopterus. So the skull gradually increases in length along with the neck.
And here (Fig. 5) are some of the transitional taxa arising out of the small Scaphognathus specimens. These tiny pterosaurs are the real transitional taxa. And there’s not just one. There are four series with gradual decreases and gradual increases in size. The hope that there is just one transitional taxon is a myth. The transition is a spectrum of gradual change. The apparent disappearance of the naris likewise had four paths with some reducing the naris and others merging the naris and antorbital fenestra.
Figure 5. Click to enlarge. Scaphognathus and its tiny descendants that ultimately gave rise to larger descendants.
Here, using specimens, you can see that every specimen between the large Scaphognathus and the large Germanodactylus are transitional taxa, creating a spectrum, some closer to Scaphognathus and others closer to Germanodactylus. That’s the beauty of using specimens, rather than suprageneric taxa. You get the real picture without any fudging or imagination.
By convergence, Darwinopterus, like the other four gradual transitions, did reduce the naris and elongate the skull and neck. These traits were derived from Pterorhynchus, which already had a reduced naris, then Kunpengopterus, which had a longer skull and longer neck (Fig. 4).
But then Darwinopterus went nowhere. It became extinct. End of story?
Let’s hope.
References
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.)
Lü J, Unwin DM, Deeming DC, Jin X, Liu Y and Ji Q 2011a. An egg-adult association, gender, and reproduction in pterosaurs. Science, 331(6015): 321-324. doi:10.1126/science.1197323
Lü J, Xu L, Chang H and Zhang X 2011b. A new darwinopterid pterosaur from the Middle Jurassic of Western Liaoning, northeastern China and its ecological implicaitions. Acta Geologica Sinica 85: 507-514.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.
The Pterosaur Heresies 
And once again you expect the fossil record to be ridiculously complete.
…what? Call it “mosaic evolution”, and it’s the norm. It never happens that all body parts evolve at the same rate at the same time.
I know you’re in good company, but please don’t confuse clades with their names. A name has been erected; the clade it refers to has been discovered – it already existed, it exists outside of our skulls.
That looks a lot like damage. It also looks really small for a naris, almost certainly too small to breathe through. What do the other specimens show? And what does the lacrimal (the bone in red) do in the place where it is, if not partially separate the naris from the antorbital fenestra?
There is no descendant, and the ancestor is a node, a branching point. That’s how cladograms work.
This has been explained to you since at least 2005. What is up with your memory?
Nope. As has been explained to you since at least 2005, colander-for-brains, a large number of most parsimonious trees just means that some (often just two or three) taxa can go in many different positions. This can be because they’re very poorly known, so what little is known of them is equally compatible with many different positions, or (less commonly) because there is genuine character conflict, in which case the matrix needs more characters, possibly more taxa, and a good screening for coding mistakes.
I get the impression that every few months you wipe your memory.
How can you tell? Have you done skeletal histology on them? Have you at least checked if they have lots of unfused sutures, or grainy bone texture that hints at the absence of an external fundamental system (something that should still be confirmed by histology, but is way better than nothing)?
Uh, yes – but no pterosaur researcher believes in this myth. You’ve just misunderstood the idea that the fossil record of this particular transition is much worse than you think.
David, wake up.
1. I don’t expect the fossil record to be “ridiculously complete,” but it is more complete in the large pterosaur tree because tiny pterosaurs are included.
2. Come back to earth. All the body parts don’t evolve at the same time, but toes do evolve with beaks, etc. etc.
3. Even though it looks small for a naris, it’s still a naris. Even if it no longer works for respiration.
4. Cladograms diagram evolutionary change.
5. With regard to “this particular transition is much worse than you think” – I encourage you or anyone to replicate the experiment. You’ll find gradual transitions, as I did, at the bases of major clades that, as demonstrated in numerous diagrams, actually make sense.
I’m cutting you off from further comments due to the insults.
“Cladograms diagram evolutionary change.”
A cladogram’s specific purpose is to diagram branching order, not change. Suppose we have the operational taxonomic units A, B. and C. Then a cladogram can say, “A and B share more recent common ancestry with each other than with C.” But it cannot say, “C changed into B, which changed into A.” That is just not what cladograms do.
Yeah, but you know what I’m talking about. Ichthyostega on one end, Homo sapiens on the other. The results of phylogenetic analysis do show common ancestry, but at the same time, cladograms chart the gain, modification and loss of every trait in the matrix, when you look back at the MacClade trees for every listed trait.
Thanks for your comment.
Ichthyostega and Homo sapiens are both derived relative to our last common ancestor. (We are much more derived, but still — we aren’t descended from Ichthyostega. It has its own apomorphies.)
You can make inferences about character evolution from a tree (which is what a cladogram illustrates) and a character matrix, but that’s an extra step.
But none of that means that cladograms ever show an ancestor-descendant relationship between OTUs. They never do. That’s not how they work.
Excuse me, pray tell, what sort of selective pressures or genetic influences would lead to ‘toes evolving with beaks’?
Mutations affect very specific aspects of an organism’s phenotype, they don’t cause generalised overall changes, and evolution operates, in part by the accumulation of these specific phenotypic changes. An array of selective pressures can favour conservation of the phenotype exhibited in a certain part of an organism while at the same time favouring mutations affecting other regions. This is evolutionary biology at its most basic. Evolution is essentially modular because mutations affect alleles and thus individual phenotypic characteristics. For your understanding of evolution with no modularity to work, the entire modern synthesis would have to be overturned in favour of some non-Mendelian system of genetics.
Cladograms diagram taxa based on shared (morphological or molecular) characteristics. That is not equivalent to ‘evolutionary change’.
Please refer to Peters (2011), the catalog of pterosaur pedes. That might help your understanding. Pedal proportions are as individual as fingerprints, even within established genera based on traits that otherwise ignore the feet, so far as is tested therein. I know it sound odd, but find out for yourself with that as your guide.