Scathing Book Review – Pterosaurs (Witton 2013) – Pterosaur growth vs evolution

Updated April 5, 2016 with a new image of Nemicolopterus and Germanodactylus.

Happy Fourth of July.
If you’re looking for fireworks, you came to the right post.

Earlier we looked at various problems with Mark Witton’s new book, “Pterosaurshere, here and elsewhere. Today we’ll look at Witton’s misconceptions regarding ontogeny, as we study pterosaur maturity from hatchling to old age. Witton’s hypothesis follows traditional thinking, which we looked at earlier here, here and here.

Witton, like other pterosaur workers before him, is a lumper. 
As he did with Rhamphorhynchus, Witton proposes that several discrete taxa (Fig. 1) represent a possible ontogenetic growth series of one genus, rather than a phylogenetic evolutionary series of many genera, as recovered by the large pterosaur tree.

Figure 1. Witton proposes a possible ontogenetic series here, from tiny Nemicolopterus to larger Sinopterus jii. The large reptile tree found this to be a phylogenetic series, with small forms evolving to become larger forms.

Figure 1. Witton proposes a possible ontogenetic series here, from tiny Nemicolopterus to larger Sinopterus jii. The large reptile tree found this to be a phylogenetic series, with small forms evolving to become larger forms. Embryos answer this impasse because they greatly resemble their parents without morphing as required in Witton’s view.

Witton Supports Bennett’s View on Germanodactylus
Witton illustrated a tiny pterosaur (Figs. 2, 3, (SoS 4593 (formerly PTHE No. 29 III 1950, No. 9 of Wellnhofer 1970)), which Bennett (2008) considered a juvenile Germanodactylus cristatus (Fig. 3). If pterosaurs changed their appearance from head to toe from hatchling to adult, Bennett and Witton might have had a case. But embryo pterosaurs and phylogenetic analysis demonstrate they don’t.

Figure 2. Witton's illustration and caption of a tiny pterosaur he and Bennett considered a juvenile to Germanodactylus cristatus (Fig. 3).

Figure 2. Witton’s illustration and caption of a tiny pterosaur (SoS 4593 (formerly PTHE No. 29 III 1950, No. 9 of Wellnhofer 1970)) he and Bennett considered a juvenile to Germanodactylus cristatus (Fig. 3).

In the large pterosaur tree, the only analysis that has ever considered a large number of tiny pterosaurs, SoS 4593 (Fig. 2), nests with certain tiny pterosaurs as a tiny adult following a series of decreasing size pterosaurs (fig. 3) and preceding a series of increasing size pterosaurs. Sos 4593 nests with these tiny pterosaurs because it shares more traits with them. The changes are gradual and completely resolved, independent of tiny pterosaurs in other clades.

Figure 3. Here are the players in this argument. Germanodactylus cristatus and Sos 4593 are highlighted in orange. To the right are pterosaurs found to decrease in size phylogenetically then increase in size clockwise to the long snouted Senckenberg-Museum Frankfurt a. M. No. 4072, which more closely resembles G. cristatus because it is closer to it phylogenetically.

Figure 3. Here are the players in this argument. Germanodactylus cristatus and Sos 4593 are highlighted in orange. To the right are pterosaurs found to decrease in size phylogenetically then increase in size clockwise to the long snouted Senckenberg-Museum Frankfurt a. M. No. 4072, which more closely resembles G. cristatus, because it is closer to it phylogenetically.

At first glance, I can see Bennett’s and Witton’s point.
Sos 4593 does have a juvenile look to it. And the size is right. That’s why it’s important to test it with phylogenetic analysis. To their fault, Bennett and Witton omitted this step. They just eyeballed it — and perhaps not closely enough (compare Fig. 2 to Fig. 4).

Here (Fig. 3) No. 4072 (lower left), with its longer rostrum and soft tissue precursors to the hard crests, is a much closer match to G. cristatus. No. 6 (lower right) is actually the right size to be a hatchling of G. cristatus and is phylogenetically closer to it than Sos 4593, but it, too, was ignored.

Sos 4593 is phylogenetically closer to Ornithocephalus (#2) and one of the smaller Scaphognathus specimens (upper right), because it shares more traits with them than with G. cristatus.

Why wasn’t Sos 4593 considered a juvenile Scaphognathus? Probably due to the naris/antorbital situation. The tiny pterosaurs, #3 (middle right) and Ornithocephalus (#2, middle) demonstrate how the ascending process of the maxilla became more and more slender. We can’t just accept broken parts ‘as is.’ We have to put them back together, if possible. That’s why precise tracings and reconstructions are necessary. A closer look at Sos 4593 shows the naris and antorbital fenestra may have remained separated by a very slender maxillary ascending process prior to crushing during burial. In this clade the naris and antorbital fenestra did become confluent, but a secondary naris developed anteriorly, beginning with Scaphognathus.

Tracing of Sos 4593 with notes that the dividing bones between the antorbital fenestra and naris appear to be broken and slightly scattered. Crushing also broke the quadrate.

Figure 4. Tracing of Sos 4593 with notes that the dividing bones between the antorbital fenestra and naris appear to be broken and slightly scattered. Crushing also broke the quadrate. Neither Witton nor Bennett achieved this grade of detail.

Nemicolopterus, the tiny pterosaur at the base of the Tapejaridae and Shenzhoupterus, is a tiny descendant of Germanodactylus cristatus and is phylogenetically closer (fewer nodes away) to it than is Sos 4593.

Figure 5. Comparison of Germanodactylus and the much smaller Nemicolopterus, linking G. cristatus  and Dsungaripteridae to Tapejaridae and Shenzhoupterus. The anterior jaws and teeth of Nemicolopterus are reconstructed from impressions in the matrix. We'll look at that in future posts.

Figure 5. Comparison of Germanodactylus and the much smaller Nemicolopterus, linking G. cristatus  and Dsungaripteridae to Tapejaridae and Shenzhoupterus. The anterior jaws and teeth of Nemicolopterus are reconstructed from impressions in the matrix. We’ll look at that in future posts.

Bottom line:
Pterosaur paleontologists can’t just make assertions that one specimen is the juvenile or hatchling of another larger specimen unless they first do the phylogenetic analysis (or find the juvenile and parent together in a mass death assemblage). The large pterosaur family tree has strongly demonstrated several times that tiny pterosaurs like Sos 4593 and Nemicolopterus are transitional taxa that link larger clades together, like scaphognathids and germanodactylids and tapejarids. Pterosaur embryos, as we’ve seen before, nest with their parents, not with other tiny pterosaurs that may be no larger than those embryos. Since pterosaur clades tend to disappear (become extinct) over time, these tiny pterosaurs are the means by which pterosaur lineages evolve and survive. This has gone unrecognized by Witton, Bennett and other pterosaur workers.

And now, let’s tie it in all together with the “baby face” hypothesis.
It’s widely recognized that pterosaur hatchlings were ready to fly right after hatching. Not so widely recognized (due to the antiquated archosaur hypothesis) pterosaurs hatched out of thin-shelled, singleton, unburied eggs laid just before hatching (common enough among lizards). Embryo pterosaurs benefitted in several regards by being carried by the mother until just before hatching (warmth, protection, fluids).

Careful examination of long-rostrum pterosaur embryos demonstrates that they did not have the short rostrum common to those tetrapods (birds, crocs, mammals) in which parents care for their hatchlings. Such a short rostrum biochemically inspires other parents to care for their hatchlings.  Since hatchling pterosaurs did not have this “cuteness” trait, it appears unlikely that pterosaur parents would have had any interest in caring for their hatchlings. Rather, the hatchlings were on their own from day one, flying and feeding on their own, probably far from typical areas that support fossilization. As discussed earlier, hatchlings of tiny pterosaurs, in danger of desiccation due to their large surface/volume ratio, likely matured in damp, moist, shady, leafy environs.

Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.
Wang X, Kellner AWA, Zhou Z and Campos DA 2008. Discovery of a rare arboreal forest-dwelling flying reptile (Pterosauria, Pterodactyloidea) from China. Proceedings of the National Academy of Sciences, 106(6): 1983–1987. doi:10.1073/pnas.0707728105
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.


13 thoughts on “Scathing Book Review – Pterosaurs (Witton 2013) – Pterosaur growth vs evolution

  1. Are you ever actually going to listen to people when they tell you that you can’t phylogenetically test whether something is a juvenile of a particular adult, as juveniles frequently plot away from the adult?

  2. In pterosaurs they don’t. You’ll just have to get used to that. Even embryos nest with adults. Data trumps hypothesis. Reality trumps wishing. You can test this yourself with just a few taxa.

      • I have not. 1. Paucity of juvenile skeletons (if you can help??) 2. I don’t know if living squamates mature isometrically, allometrically or both. You and Neil seem resistant to the present data on pterosaur embryos and phylogenetic analysis. Today I’ll chart the nesting of tiny pterosaurs. You’ll see they don’t all group together.

    • As I tried to tell you before, it is IMPOSSIBLE for evolution to occur without changes in ontogeny. Not unlikely, not rare, impossible. That was what I tried to tell you before. It is a fairly fundamental tenet of evo devo. It is the ontogenetic process that evolution actually acts on. Therefore, if you accept that pterosaurs have undergone evolutionary change, they have to undergo ontogenetic change. There is no two ways about it. I’m prepared to accept that the ontogenetic changes may not be the usual sorts of thing e.g. short rostrum, but to say that there is no ontogenetic change at all is, I repeat, impossible, and merely shows how little you have researched developmental biology. These concepts are not difficult, they are stuff I learnt in my undergrad. That you haven’t bothered to read about them yourself does not reflect well.

      Once you understand this, you see your reasoning is verging on circular. You start on the incorrect asusumption that you can phylogenetically test whether a tiny ptero is a juvenile of a particular adult. From this incorrect assumption you put forth a set of adult-baby relationships and make statements about their ontogeny, and from these statements say you are able to phylogenetically test adult baby relationships. That is not a good process

      • Short answer: The changes you refer to occur in the egg, not after hatching. As I’ve posted before, the fact that Pterodaustro came into sexual maturity at half of its final old age size is the mechanism by which pterosaurs could rapidly produce half-size progeny (embryo can’t be larger than the egg > egg can’t be larger than the pelvic opening). Evidently this can be applied across the pterosaur board, based on the many tiny transitional series that phylogenetically follow larger specimens and then beget larger specimens that live longer, get bigger, have bigger eggs, etc.

  3. All craniates exhibit allometric growth at some point between hatching/birth and sexual maturity, this is due to the fact that the brain and sense organs must reach a certain degree of development for the organism to function, furthermore, the brain and associated tissues exhibit the least amount of change in size between neonates and adults of all parts of the body simply due to the developmental process of neural tissue. A proportionally large brain and sense organs (e.g. the eyes) will then lead to the head being proportionally large and the rostrum small. Also, the constraints that development within an egg place on an organism, as well as environmental pressures on the neonate to maintain homoeostasis will lead to a low surface area to volume ratio in the hatchling, higher surface area to volume ratios are attained as the organism approaches the adult size. Nearly all craniates, and certainly all tetrapods, have juvenile-typical proportions at some point in their life cycle, (even fish larvae have them, and there is not too much parental care in that group) and exhibit allometric growth. Juvenile proportions are not originally selected for by parental response, the parental response is a response to juvenile characteristics which are due to numerous developmental constraints and selective pressures. If isometric growth is present in an organism, it either has already gone through or is yet to undergo a period of allometric growth. If pterosaurs exhibited purely isometric growth from hatching to adulthood, their developmental process would have to be quite different from any other tetrapod, it is more parsimonious then to say that specimens with juvenile-typical characteristics are juveniles unless some extraordinary evidence demonstrates something to the contrary. Also, phylogenetic analyses will not provide that evidence since niether the matrix nor the program calculating the tree can differentiate between adults and juveniles. The end result will be juveniles placed in odd parts of the tree, often clumped together near basal positions, but other times scattered, sometimes far from adult forms, other times close and forming an ontogenetic sequence leading to the adults, and other times in clades completely composed of juvenile forms. Your tree has the exact appearence that is predicted by work including juveniles in phylogenetic datasets. Other methods need to be used to determine whether the specimens in question are juveniles or adults, trees are not going to tell us that. For determining age, osteological and histiological work must be done, perhaps accompanied with morphometric statistical analyses. The former must be performed at the microscopic level, and whole-specimen photographs are not going to give that information.
    Finally, your interpretation of embryos as having adult proportions is purely dependent on your own interpretations, which are based on methods which have been many times over shown to be too subjective to be of any use (they depend on the quality of the photograph, lighting conditions, the angle of the photograph, and a completely subjective interpretation process that nobody has ever been able to repeat). How are we supposed to know that the results you are getting are not the results you want to get? So far you have not demonstrated your “DGS” to be objective at all. What are your criteria for determining if a feature is to be traced or not? Or for determining what something is at all? Where are the tests that show traced elements correlate to actual fossil elements with a high enough frequency that it is a consistent and reliable indicator of fossil material (any statistical significance to show)? How do you account for lighting, photographic distortion, or preservational and preparational artefacts? By what is another person able to consistently repeat your results with a high enough accuracy? Just saying “pixel group A looks like element B” is not enough.

  4. Mike, try to trace a pterosaur embryo and send me the results. You’ll be the first. No one, I repeat, no one has ever sent me a DGS type tracing of a pterosaur egg. So you’re right. No one has duplicated my results. But then, no one has tried. My images are online. You are welcome to point out errors. No one ever has ever done so yet. So again, you’ll be the first. Mike, when you say things like you just did, please have some sort of specifics or evidence at hand. This blackwashing you’re doing is just making you look like a fringe character on a rant and I have to cut off such people. You understand…

    And to your points, I’ll remind you that Reynoso (1998) was unable to discern juvenile proportions in a smaller Huehuecuetzpalli, a sister to the founder of this clade. Furthermore, please suggest which tiny pterosaurs go with which adults if you can. Finally, you don’t agree that Sos 4593 looks more like (shares more traits with) that half-size Scaphognathus than Germanodactylus?

    We deal in reality here. Data, measurements, etc. Wishful thinking is discouraged. Errors are corrected when revealed. I work with what I have. You can help or you can insult. You’ve done both in the past. I value your input so as it is constructive.

  5. So I’m a fringe character for suggesting that allometric growth is the most parsimonious option for pterosaurs, that we’ll need exceptional evidence is needed to prove otherwise, and a cladogram is not going to cut it for reasons already well documented in literature that other commentators have directed you too? I thought that just made me a critical thinker pointing out weak points in the hypothesis at hand, and why it is unlikely given the data you provide. I also pointed you to ways of acquiring data that could strengthen your argument should it actually be the case, but the burden of proof is on the individual making the claim.

    I am asking you kindly to remove your claims of “blackwashing” and being a “ranting fringe character”, as I am doing no such thing, and have no such intentions, and not just for me, but for your own sake it would make you look more respectable in this discourse. Is disagreement or suggestion for improvement equivalent to insult around here?

    Scientists make tracings all the time, but always with reference to physical examination so that they can discern what is a bone, what is soft tissue, and what is matrix. There are criteria for determining each of those, and it makes the tracing procedure an objective, repeatable technique. If I am to repeat your procedure, what are my criteria supposed to be? How do I reliably know if what I have is actual fossil or just an artefact of any number of other factors?

    Regarding Huehuecuetzpalli. Reynoso never argues that the species had isometric growth *throughout* ontogeny, and with a sample size of two, there is little that can be said about ontogeny. All that can be said is that by a certain growth stage, the species acquired proportions close to those of adults, and that this was prior to complete ossification of the skeletal elements, however this does not mean allometric growth did not take place prior to this point, that cannot be demonstrated unless more specimens are found. Furthermore, it fits with what is known of lizards, which have indeterminate growth. They initially exhibit allometric growth, but beyond a certain size or stage of maturity they have adult proportions yet are still capable of growth (and lack complete ossification of skeletal elements) if external factors allow for this to be the case. The smaller specimen is not as well preserved as the larger specimen, and so while no statistically significant difference in proportions could be found, that does not mean that they might not exist be present in this specimen, but that measurements couldn’t be taken that were precise enough to detect them. Also, the sample size of two makes it difficult to determine what a significant difference in proportions is. We also have no way to tell whether the larger specimen was unusually large for the species at its growth stage, or likewise, whether the small one was unusually small for its growth stage, or (unlikely but possible), both. This is not rampant speculation, these are all factors that scientists must account for. This is also why nobody in science makes bold assertions that something is absolutely true or false, there are always anomalies, and there is always a likelihood of counterevidence. The best that science has is rejecting or failing to reject a hypothesis based purely on data at hand (as it’s always possible that future data may change the outcome).

    Scientists are cautious and conservative about their work and critical of others’. Science involves slow, painstaking work over many years (often with collaborators, because going it alone would be often impossible for a single person) to make sure all the experimental procedures have been conducted to ensure the argument is perfectly solid. When flaws are found in another’s work, whether it be a problem with the experimental method, or failure to take into account a possibility or a published study, they are pointed out, not to be insulting, but to make sure the data and argument stand firm on their own, independently of the scientist.

    Example: I have been working on a project, in collaboration with another scientist, though largely my own work (not on pterosaurs), for well over a year, the project is not particularly impressive, someone could dash something out on paper in a night, but over the past year relevant publications have come out that must be addressed as the paper is being put together. Then, when I give the paper to my collaborator, he sees issues that may have been overlooked, points them out, and I need to address them. In the process, I might notice something that both of us overlooked previously and once again I need to look up some new literature or perform a new test to make sure my agrument stands up to others’. So it goes for months on end, until hopefully a methodologically, logically, and scientifically sound paper comes out that stands the test of the critical eye of other scientists.

    Take this advice or leave it, I’m intending to be helpful, but if you are going to dismiss it as a mean-spirited, insulting fringe rant, it’s certainly not going to make me more magnanimous by any means.

  6. If you don’t like Huehuecuetzpalli for an example, I suggest you look at Ptweety the Pteranodon, Zhejiangopterus, which has a nice growth series, and the embryos. If any, any I mean any, have a short rostrum and big eyes and otherwise nest in a clade with long rostrum adults, please tell me. Then, of course, there are the tiny pterosaurs without eggshells that have a long rostrum that I posted with the last few weeks.

    Mike, the insults and the web rage you need to watch out for. Being long winded and drifting off subject are also to be considered.

    I can rant because this is my blog. But you’ll notice I provide evidence for every fault and oversight. You might not like the evidence, but it’s always there.

    I appreciate the hard work you’ve put in. Likewise I’ve been at this a long time and many posts represent work that is several years old. It’s internally consistent. The parts fit together. The analyses leapfrog those of others on sheer size alone, which is the key. We can always add characters to break resolution logjams. So far that hasn’t been necessary.

    Moreover, why would I put myself through this shunning and stigma if I couldn’t back it up?

    I’m personally stymied that you can’t see, in this case, the resemblance of the specimen in question to Scaphognathus and you appear to reject my candidate for a better possible juvenile to G. cristatus (even though that candidate is actually a phylogenetic ancestor). Isn’t the transition from Scapho to Germano by way of the tiny intervening pteros coming through?

    If not, if everything I post is suspect (the definition of blackwashing), then why bother with reading this blog?

  7. “It’s internally consistent.”
    It needs to be consistent with external evidence as well. Relying only on internal consistency will end you up in a pit of circular reasoning faster than you can say, “Huehuecuetzpalli”.

  8. Pingback: Philobiblon » Pterosaurs – forget practically everything you were ever told

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s