Basal Archosauromorpha paper – Ezcurra 2016

Another paper repeating the ‘sins’ of the past,
based on an incomplete taxon inclusion list (that also includes taxa that should not be included). And a huge amount of otherwise excellent work! It proves once again that first hand access to specimens and an overly large character list will not bring full resolution to a small taxon list cobbled together by tradition, rather than testing.

I envy, am proud of and have to feel sorry for 
Martin Ezcurra (2016). He went around the world gathering data, obviously took a huge amount of time studying the specimens and writing this paper, but he’s stuck with that less than adequate traditional taxon list rather than the testing offered by the wide gamut taxon list (large reptile tree) in ReptileEvolution.com. He’s using 96 taxa (vs. 674 at ReptileEvolution.com). He’s using 600 characters. That should be more than enough, and it is more than enough (less than half that number will do), but more taxa is really what Ezcurra needs.

Just a few notes
Ezcurra wrote: “Jesairosaurus lehmani was described in detail by Jalil (1997). Despite its short neck, this species has been considered since its original description as a member of “Prolacertiformes.” Nevertheless, the phylogenetic position of this species has not been further tested in more recent quantitative analyses.” Yes it has, Here Jesairosaurus nests with drepanosaurs at the base of the Lepidosauriformes, not with Macrocnemus, as shown by Ezcurra (Fig. 1). Drepanosaurs were excluded by Ezcurra.

Figure 1. Ezcurra 2016 tree of basal archosauromorphs. He has basically repeated the mistakes of Nesbitt 2011 here. Colors denote taxa that lie outside the gamut of the Archosauriformes + Protorosauria under study here.

Ezcurra is still including the thalattosaur, Vancleavea which nests with Doswellia in the Ezcurra tree. It just doesn’t belong in a study on archosauriforms.

He still holds to the tradition of a monophyletic Diapsida proven invalid here.

Ezcurra is still including pterosaurs in an archosauriform study
Proterochampsia (now including Vancleavea) is still recovered by Ezcurra as the proximal outgroup. Phytosauria and Lagerpeton are sister taxa. How is this possible? What characters do they share? They certainly don’t look alike. He notes Peters (2000) then writes, “The phylogenetic analysis conducted here [Ezcurra 2016] constitutes the best data matrix compiled so far to test the position of pterosaurs within Archosauromorpha because of the broad sample of Permo-Triassic species, including the undoubted pterosaur Dimorphodon macronyx.”  Martin, but you’re not looking, really looking at your results. Your proximal outgroup should look kind of like a pterosaur. Right?

Ezcurra notes that 33 extra steps
are needed to place Dimorphodon with Tanystropheidae and 19 synapomorphies support the Ornithodira. That might be true in his study. Hard to imagine how that is possible though. I will try to plow through his 600 characters to figure it out.  Convergence is rampant in the Reptilia. More synapomorphies support pterosaurs outside the Ornithodira when pertinent taxa are not excluded (see below).

Ezcurra writes, “Future analyses focused on testing the higher-level phylogenetic relationships of pterosaurs should also incorporate a broader sample of early pterosaurs and some enigmatic diapsids that were found as more closely related to pterosaurs than to other archosauromorphs by Peters (2000) and are not included in the current taxonomic sample (i.e., Langobardisaurus pandolfi, Cosesaurus aviceps, Sharovipteryx mirabilis and Longisquama insignis). However, it seems extremely unlikely that the addition of these enigmatic diapsids, which are unambiguously considered to not be members of Archosauriformes (e.g., Peters, 2000; Senter, 2004), will affect the higher-level phylogenetic position of pterosaurs.”

In Science, the word ‘seems” and “extremely unlikely” need to be tested, especially when Langobardisaurus, for instance, shares so many traits with Tanystropheus and Macrocnemus. And especially when they have been tested sixteen years ago (Peters 2000). The word “enigmatic” is inappropriate here, unless Ezcurra just preferred to avoid them and stay with the traditional nod and move on.

Many good color photos of specimens here.
Precise descriptions. Like Nesbitt (2011) he’s just not playing with a full deck — of taxa.

Ezcurra’s tree
had 1.8 million+ possible MPTs. The large reptile tree was fully resolved with a single tree and high Bootstrap values. His analysis 3 recovered 40 MPTs by dropping largely incomplete taxa. That’s often a good idea. No reconstructions were offered, except for some skulls. No gradual accumulations of derived traits for odd partners like pterosaurs, Vancleavea, Doswellia, etc. Many purported sisters do not look alike.

Still not sure how
these trees don’t nest Tropidosuchus and Lagerpeton together. They are virtually identical.

Figure 2. Ezcurra tree with Bremer supports AFTER pruning incomplete taxa. Many oddly paired sisters still show up here.

Ezcurra comments on Choristodera
“The problematic phylogenetic position of choristoderans may be a result of an unsampled early evolutionary history. The phylogenetic position of choristoderans is also ambiguously resolved in this analysis, but is constrained to the base of either Lepidosauromorpha or Archosauromorpha.” Actually the early history is sampled (here), just not included in this analysis.

Ezcurra has to be feeling pretty confident.
He writes, “Much of the general topology of the phylogenetic trees recovered in this analysis agrees with that found by several previous workers (e.g., Sereno, 1991; Dilkes, 1998; Gottmann-Quesada & Sander, 2009; Ezcurra, Lecuona & Martinelli, 2010; Nesbitt, 2011; Ezcurra, Scheyer & Butler, 2014).”

I’d feel more confident
if all sister taxa looked alike and a gradual accumulation of traits could be traced for every taxon. Ezcurra needs more taxa to weed out the problems here. This study carries with it the sins of past studies.

PS
I was unable to open the Ezcurra data files on either Mesquite or MacClade.

References
Ezcurra MD 2016.The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms.  PeerJ 4:e1778https://doi.org/10.7717/peerj.1778
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352:1–292 DOI 10.1206/352.1.
Peters D 2000. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106:293-336

Flapping before flight

This is a long overdue and very welcome paper
Many paleontologists of the past thought flight appeared after gliding. This is the so-called trees down theory seen in this PBS video on Microraptor. Others thought the flight stroke appeared while clutching bugs in the air. This is the so-called ground up theory. Through experimentation Ken Dial found out that baby birds armed with only protowings flapped them vigorously to help them climb trees, no matter the angle of incline. Now the kinematics of this wing/leg cooperation are presented in Heers et al. 2016, students of Ken Dial.

Key thoughts from the abstract:

“Juvenile birds, like the first winged dinosaurs, lack many hallmarks of advanced flight capacity. Instead of large wings they have small “protowings”, and instead of robust, interlocking forelimb skeletons their limbs are more gracile and their joints less constrained. Such traits are often thought to preclude extinct theropods from powered flight, yet young birds with similarly rudimentary anatomies flap-run up slopes and even briefly fly, thereby challenging longstanding ideas on skeletal and feather function in the theropod-avian lineage.

 

For the first time, we use X-ray Reconstruction of Moving Morphology to visualize skeletal movement in developing birds. Our findings reveal that developing chukars (Alectoris chukar) with rudimentary flight apparatuses acquire an “avian” flight stroke early in ontogeny, initially by using their wings and legs cooperatively and, as they acquire flight capacity, counteracting ontogenetic increases in aerodynamic output with greater skeletal channelization.Juvenile birds thereby demonstrate that the initial function of developing wings is to enhance leg performance, and that aerodynamically active, flapping wings might better be viewed as adaptations or exaptations for enhancing leg performance.”

Figure 1. Cosesaurus running and flapping – slow.

The same theory
can be applied to the development of wings in fenestrasaurs (Fig. 1) evolving into pterosaurs (Fig 2), as shown several years ago, but does not play a part in the development of flapping wings in bats, which do not walk upright and bipedally.

Figure 2 Quetzalcoatlus running like a lizard prior to takeoff. Click to animate.

It should be obvious
that competing take-off theories for pterosaurs (Fig. 3) do not take into account this theory on the origin of flapping. Just one more reason not to support the forelimb wing launch hypothesis that has become so popular with ptero-artists recently.

Figure 3. Unsuccessul Pteranodon wing launch based on Habib (2008) in which the initial propulsion was not enough to permit wing unfolding and the first downstroke.

Remember,
getting into the air is difficult if you’ve never done it before. Using both your arms AND your legs to get up speed is a good idea that has worked in the past and in present day laboratories.

References
Heers AM, Baier DB, Jackson BE & Dial  KP 2016. Flapping before Flight: High Resolution, Three-Dimensional Skeletal Kinematics of Wings and Legs during Avian Development. PLoS ONE 11(4): e0153446. doi:10.1371/journal.pone.0153446
http: // journals.plos.org/plosone/article?id=10.1371/journal.pone.0153446

The Tyrannosaur Chronicles by David Hone

A new book
by Dr. David Hone called The Tyrannosaur Chronicles is now out. He reports here, “Although there is no more famous and recognisable dinosaur than Tyrannosaurus, the public perception of the animal is often greatly at odds with the science. The major image people have of them is the iconic jeep chasing scene in the film Jurassic Park. However, because they are among the best-studied of all dinosaurs, we can say that the tyrannosaurs almost certainly had feathers and may have fought and even ate each other.”

Figure 1. The Tyrannosaur Chronicles by Dr. David Hone is a new book chronicling tyrannosaurs.

I have not read the book yet, but I’ll note a possible problem gleaned from quote pulled from a review.

Kirkus Reviews reports: “While correctly surmising that tyrannosaurs and other dinosaurs were carnivores, scientists erroneously assumed that they were some kind of previously unknown “giant land reptile.” Subsequent fossil discoveries in polar regions ruled out this possibility since coldblooded reptiles could not survive such extreme cold weather.”

I hope this is a misquote or I’m misreading this. It’s not news that tyrannosaurs and dinosaurs have been and will always be giant land reptiles. They nest in the clade Reptilia, no matter how cold-adapted they might have been. Hone might be going back, back in time to the first English discoveries from 50 years earlier, like Iguanodon and Megalosaurus, the first dinosaurs, which were named terrible lizards, and originally titled, “British Fossil Reptiles.”

And I hate to judge a book by its cover, but…
That small crested dinosaurs in the lower left corner is Guanlong, an ancestor not of tyrannosaurs, but of allosaurs in the large reptile tree. No word yet if Hone included the verified ancestors of tyrannosaurs, Zhenyuanlong, Tianyuraptor and Fukuiraptor.  On that note, GotScience.org evidently quotes Hone when it reports, “Early tyrannosaurs had crests used for sexual display and social rank.”

Book and academic publishing is fraught with such risk and danger. Once you print it, you can’t retract or revise it. Sympathetically, I know from experience the things I would have changed about my early papers now, but was less experienced then.

Thankfully
I hear that Hone discusses feathers and such.

Amazon Reviews are universally positive:

1. Dinosaurs are endlessly fascinating, and the massive, blood-thirsty tyrannosaurs are most popular (and scary) of the lot! Here, renowned dinosaur expert David Hone reveals their story, and how we know what we know about these most amazing of ancient reptiles. — Professor Mike Benton, University of Bristol
2. Tyrannosaurs are probably the world’s favourite dinosaurs. But what do we really know about this group? David Hone reviews the biology, history, evolution, and behaviour of the tyrant kings – an excellent read, containing the very latest in our understanding of Tyrannosaurus rex and its closest relatives. — Dr Tom Holtz, University of Maryland
3. Without doubt, the best book on tyrannosaurs I’ve ever read. This is an awesome dinosaur book. — Professor Xu Xing, Chinese Academy of Sciences

Do not be confused with this website:
http://traumador.blogspot.com which earlier featured ‘Traumador the tyrannosaur in the Tyrannosaurus Chronicles’ which can be silly and serious all on the same blog, explained here as:

“The Tyrannosaur Chronicles is a blog written by Traumador the Tyrannosaur about his many exploits.Traumador is a tyrannosaurid who hatched from an egg that magically survived the K/Pg Extinction Event and was discovered in Alberta by Craig, an aspiring paleontologist (and the mastermind behind the blog in real life). He eventually gets a job at the Royal Tyrell Museum and things get interesting from there.

From past experience,
such as when Hone attempted to compare the two hypotheses of pterosaur origins by dropping one, or when Hone attempted to show that Dmorphodon had a mandibular fenestra, or when Hone supported the deep chord bat wing model for pterosaur wings, or when Hone flipped the wingtips of Bellubrunnus, we might be wary about what Dr. Hone puts out there. But I don’t think you can go very wrong with tyrannosaurs, the most studied dinosaur. And the reviews speak high praise.

Tom Kaye and his Tom Swift Laser!

Inventor Tom Kaye
is taking fossil observation where it has never gone before… with his laser. Read and see more here.

Inventor, Astronomer, Paleontologiist, Entrepreneur, Tom Kaye is turning his laser on fossils and seeing things no one else has ever seen before.

Excuses for not posting last week…

1. I finally wrote another paper and submitted it. That took all week.
2. There wasn’t much other paleo news to get excited about (unless I missed something?).

Now that I’m back to looking at other things,
all I see is a pachypleurosaur with small hands and feet of uncertain affinities, Dawazisaurus (Cheng, Wu, Sato and Shan 2016). I note the authors did not test it against Hanosaurus and Dianmeisaurus, where it nested in the large reptile tree.

I’m pleased and surprised to see that readership does not flag
on quiet weeks. And for some reason Sunday was a big day. Thank you all for your continued interest.

References
Cheng Y-N, Wu X-C, Sato T, Shan H-Y 2016. Dawazisaurus brevis, a new eosauropterygian from the Middle Triassic of Yunnan, China. Acta Geologica Sinica (English) 90:401-424.

 

Nesting the Zittel wing of Rhamphorhynchus in the large pterosaur cladogram

Traditionally
the well-preserved Zittel wing (Fig. 1; Zittel 1882) had been assigned to Rhamphorhynchus gemmingi, of which n74 (TM 6922/6923) is the holotype.

Figure 1. The Zittel wing of Rhamphorhynchus is traced here. It nests not with R. gemmingi specimens, but with R. muensteri specimens. Click to enlarge. Both manual digit 5 and ungual 4.5 are present here along with wonderful shallow chord wing membrane tissue and propatagium.

I wondered if
the wing specimen had enough character traits to nest it in the large pterosaur cladogram. There it nests between the famous ‘dark wing’ specimen (JME Sos 4784, also famous for soft tissue preservation) and the MTM V 2998.33.1 specimen (Fig. 2), both assigned to R. muensteri. The Zittel wing is a little larger than both.

Figure 2. The Zittel wing specimen B St 188 II 8 nests between the ‘dark wing’ JME Sos 4784 specimen and the MTM V 2998.33.1 specimen, both in the Rhamphorhynchus muensteri clade. This is a portion of a larger image.

You might recall
that Elgin, Hone and Frey (2010) dismissed the Zittel wing because it did not fit into their deep chord paradigm, but suffered from ‘shrinkage’. That is bogus thinking. More on pterosaur wings here and here. All known pterosaur specimens preserving wing membranes do so following the Zittel wing pattern. That’s a fact that other workers attempt to dismiss. 

References
Elgin RA, Hone DWE and Frey E 2010. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica in press. doi: 10.4202/app.2009.0145
Goldfuss A 1831. Beiträge zur Kenntnis vershiedener Reptilien der Vorwelt. Nova Acta Academiae Leopoldinae Carolinae, Breslau and Bonn, 15: 61-128
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Tischlinger H and Frey E 2002. Ein Rhamphorhynchus (Pterosauria, Reptilia) mit ungewöhnlicher Flughauterhaltung aus dem Solnhofener Plattenkalk. Archaeopteryx, 20, 1-20.
Wellnhofer P 1975a-c. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33. Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.
Zittel KA 1882. Über Flugsaurier aus dem lithographischen Schiefer Bayerns. Palaeontographica 29: 7-80.

wiki/Rhamphorhynchus

The other Dimorphodon skull (BMNH R 1035) unscrambled

We know of
several Dimorphodon (Buckland 1829, Owen 1859) Hittangian, Early Jurassic ~195 mya) specimens from Europe.

1. BMNH (NHUK PV) R1034a Mary Anning’s discovery and the holotype, a misarticulated skeleton lacking a skull and tail (Fig. 1)
2. BMNH (NHUK PV) R 1035 includes a skull, cervicals and wings (Figs. 1, 2)
3. BMNH 41212 is a nearly complete specimen lacking a tail (Fig. 1).
4. BMNH? a complete tail (Fig. 1)
5. Other BMNH specimens. presumably disarticulated bones
6. YPM 350, YPM 9182 and other Yale specimens, several disarticulated bones including a partial skull

Dimorphodon? weintraubi (IGM 3494, Clark et al. 1994, 1998; Early to Middle Jurassic, ~175 mya) nests several nodes away, with basal anurognathids. It lived 20 million years later in North America.

Figure 1. The three most complete Dimorphodon specimens, BMNH 41212, BMNH R1034, and BMNH R1035. BMNH (British Museum of Natural History) used to be NHUK (Natural History United Kingdom).

The BMNH R1035 specimen of Dimorphodon
has not been figured very often because the skull is somewhat scrambled  Here it is traced (Fig. 2) and reconstructed (Fig. 1). It is quite similar to that of the BMNH 41212 specimen, with only slight modifications.

Figure 2. Dimorphodon specimen BMNH (formerly NHUK) R1035 with elements traced and segregated to reduce the chaos. Here the complete wing was recovered along with cervicals and occipital elements. Click to enlarge.

The ‘scrambled’ 1035 material differs
from the 41212 material in several traits:

1. The naris is slightly larger relative to the antorbital fenestra
2. The sclera ring is smaller
3. The mandible is deeper
4. The metacarpus and wing are longer

When you look up Dimorphodon online
at Wikipedia the authors do not identify D. weintraubi as an anurognathid. And they follow Clark et al. in asserting that Dimorphodon had plantigrade pedes based on the metatarsalphalangeal butt joint. We looked at that problem earlier here and Peters (2000) also covered that topic, but essentially the metatarsophalangeal butt joint was immobile, but the cylindrical interphalangeal joints provided the required extension to create a digitigrade pes that matches digitigrade pterosaur and Rotodactylus ichnites in which the proximal phalanges are always elevated. It’s a common pattern: Sometimes it takes the paleo crowed a long time to accept certain facts.

Figure 3. from Wikipedia, my sculpture of Dimorphodon now found in several museums. The curly-cue tail, anteriorly-planted fingers and plantigrade feet are all unnatural and not part of the original model.

And then, of course manual digit 5 and wing ungual
are both present in the 1035 specimen (Figs. 4, 5).

Figure 4. Wingtip ungual in the BMNH 1035 specimen of Dimorphodon.

Yes, they are difficult to see
unless you look for them and trace them. But think how long it took to find hind limbs in fossil whales, known for over 150 years prior to that discovery.

Figure 5. Manus of the BMNH 1053 specimen of Dimorphodon highlighting vestigial digit 5 in pink.

A while back
Nesbitt and Hone 2010 attempted to show that the 41212 specimen of Dimorphodon had a mandibular fenestra in a desperate and misguided attempt at providing archosaur traits to pterosaurs. That was bogus, as noted earlier. Those two didn’t want to take into account the slipped surangular on the specimen. In the 1035 specimen the surangular is in place and no mandibular fenestra is present.

References
Buckland W 1829. Proceedings of the Geological Society London, 1: 127
Clark J, Montellano M, Hopson J and Fastovsky D. 1994. In: Fraser, N. & H.-D Sues, Eds. 1994. In the Shadows of Dinosaurs. New York, Cambridge: 295-302.
Clark J, Hopson J, Hernandez R, Fastovsk D and Montellano M. 1998. Foot posture in a primitive pterosaur. Nature 391:886-889.
Nesbitt SJ and Hone DWE 2010. An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225–233
Owen R 1859. On a new genus (Dimorphodon) of pterodactyle, with remarks on the geological distribution of flying reptiles.” Rep. Br. Ass. Advmnt Sci., 28 (1858): 97–103.
Nesbitt SJ and Hone DWE 2010. An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225–233
Padian K 1983. Osteology and functional morphology of Dimorphodon macronyx (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Museum, Postilla, 189: 1-44.
Peters D 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods. – Ichnos 7(1): 11-41.
Sangster S 2001. Anatomy, functional morphology and systematics of Dimorphodon. Strata 11: 87-88

wiki/Dimorphodon

 

One more look at Rhamphorhynchus growth

Usually I avoid histological (bone microstructure) studies.
But here’s one that merits one more extended report based on its many incorrect assumptions and overlooked comparisons.

Summary of key facts in this long blog:

1. both phylogenetically miniaturized adult pteros and mammals had juvenile-like “woven” bone texture
2. Pterosaur embryos develop in utero and had adult proportions, so they could fly upon hatching
3. Pterosaurs develop isometrically, thus immature pteros can only be identified in phylogenetic analysis (= when larger identical adults are known).

Prondvai et al. 2012 tested growth strategies in Rhamphorhynchus. As noted earlier, Prondvai et al. confused small adults with juveniles and hatchlings, not following the clear data that pterosaurs grow isometrically, not allometrically. Thus the morphological difference shown here (Fig. 1) are phylogenetic, not ontogenetic. Phylogenetic analysis supports this hypothesis.

Figure 1. Bennett 1975 determined that all these Rhamphorhynchus specimens were conspecific and that all differences could be attributed to ontogeny, That is clearly false as shown here and by phylogenetic analysis. Only the juvenile between the two largest specimens is a non-adult. Click to enlarge.

 

Age of first flight
Prondvai et al. 2012 report, “The initial rapid growth phase early in Rhamphorhynchus ontogeny supports the non-volant nature of its hatchlings, and refutes the widely accepted ‘superprecocial hatchling’ hypothesis. We suggest the onset of powered flight, and not of reproduction as the cause of the transition from the fast growth phase to a prolonged slower growth phase. Rapidly growing early juveniles may have been attended by their parents, or could have been independent precocial, but non-volant arboreal creatures until attaining a certain somatic maturity to get airborne.” Prondvai et all did not realize they were examining small adult pterosaur specimens, not juveniles. So rapid growth was part of their growth strategy. More refutations relevant to the above statements follow.

Powered flight is one of the most energy-consuming locomotion types in tetrapods, therefore high growth rates and a superprecocial onset of the flying lifestyle in a highly developed hatchling are mutually exclusive developmental parameters. The validity of this simple trade-off model is supported by the fact that the only extant superprecocial fliers, the megapod birds have very low if not the lowest growth rates among extant birds.” Prondvai et al. ignore the fact that megapodes have their rapid growth phase inside the egg shell. Hatchling megapodes are relatively “very large with a wingspan up to half that of the adult).”  By contrast, pterosaurs hatch at 1/8 the height of the adult and 1/8 the wingspan.

In support of supreprecocial flight…
…pterosaur hatchlings had adult proportions. Tiny adults, the size of sparrows and hummingbirds, had larger pterosaur proportions. The smallest pterosaur that Prondvai et al. tested had wing tips that extended way over their heads when folded and quadrupedal (Figs. 1, 2). We’ve seen the short wings of flightless pterosaurs. Hatchlings of volant taxa don’t have short wings. Tiny adult pterosaurs may have ‘rapidly growing” bone microstructure because they matured quickly, reproduced as often as possible then died early, like tiny mammals do. More on this below:

Sexual maturity vs. size:
Prondvai et al. report, “According to the hypothesis presented here, the onset of powered-flight in Pterodaustro occurred after attaining 53% of adult size. Here we prefer the hypothesis that bone growth is slowed down by the initiation of a new, and much more energy consuming locomotory activity, namely powered flight.” Not by coincidence, this is the size that Chinsamy et al. (2008) determined that sexual maturity was attained. After observing the morphology of the embryo Pterodaustro, which matches the morphology of the adult, there is no supporting evidence for the Prondvai et al. hypothesis.

Archosaur vs. lepidosaur
Prondvai et al. do not consider the growth strategies and histology of lepidosaurs, only archosaurs. So they are making comparisons to the wrong clade. Pterosaurs nest within the Lepidosauria. Growth patterns in lepidosaurs are distinct and do not follow archosaur growth patterns (Masisano 2002). But this may not be the key factor in observed differences.

Chinsamy and Hurum 2006
looked at the basal lepidosaur, Gephyrosaurus. “The [bone] compacta consists of essentially parallel−fibred bone tissue interrupted by several lines of arrested growth (LAGs). The first LAG visible from the medullary cavity appears to be a hatchling line with its more haphazardly oriented, globular-shaped, osteocyte lacunae.”  This was not a phylogenetically miniaturized taxon even though it was a basal lepidosaur.

More to the point
Chinsamy and Hurum 2006 also looked at the basal and phylogenetically miniaturized mammal, Morganucodon. They report on, “distinct woven bone tissue with large, irregularly oriented osteocyte lacunae and several primary osteons. No secondary osteons were visible, though several enlarged erosion cavities are evident in the compacta. In the same section, it appears that substantial endosteal resorption had occurred, and parallel−fibred bone tissue is evident only in a localized area peripherally. This area includes several rest lines, which indicate pauses in the rate of bone formation, and hence, pauses in growth.” Perhaps these pauses indicate a lifespan of “several” years. Note the “woven bone” texture description.

Figure 2. Several tiny Rhmphorhynchus adult sister taxa, among them is the n7 specimen tested by Prondvai et al. and considered a juvenile by them shown here about 7/10 of in vivo size. As you can see, these pterosaurs do not appear to have any impediments to flapping and flying. However their tiny hatchlings would probably not have flown based on their high surface/volume ratio. The adults had juvenile traits due to phylogenetic miniaturization.

The smallest sampled Rhamph bone microstructure
Prondvai et al. report about the tiny Rhamph, BSPG 1960 I 470a, (n7 in the Wellnhofer 1970 catalog, Fig. 2): “A thin layer of lamellar bone of endosteal origin rims the medullar [central] cavity. There seem to be only a few longitudinally oriented vascular canals, but these have rather large diameter in relation to the overall thickness of the cortex. The bone matrix is typically woven with some poorly defined, immature primary osteons, hence the majority of the cortex does not show the mature fibrolamellar pattern yet. The osteocyte lacunae are large and plump throughout the cortex, and possess an extremely well-developed system of dense, radially oriented canaliculi implying extensive communication and nutrient-exchange between the osteocytes. No LAGs or any other growth marks can be observed.”  Maybe LAGs were never present in this taxon if it lived for just a short time. Remember, we’re talking about phylogenetic miniaturization here.  If the small precocial Rhamphorhynchus specimens were maturing quickly and laying eggs early, they likely followed the life patterns of other tiny tetrapods, like Morganucodon (above) and died early, perhaps living only one or two years, not five or more as in mid-sized pterosaurs.

Note: Like Morganucodon (above) the phylogenetically miniaturized mammal, 
the bone structure in the smallest tested Rhamphorhynchus is described as “woven”.

Age vs size:
Prondvai et al. report, “The ontogenetic validity of the smallest size category of Bennett is clearly supported by the overall microstructure found in the bones of the three small specimens.” Unfortunately, without a phylogenetic analysis, Prondvai et al. did not realize that the smallest specimens were small due to phylogenetic miniaturization. Their ancestors were larger. Thus small Rhamphs retained juvenile and embryonic traits into adulthood, including the typical short rostrum and smaller wings. These traits also included juvenile “woven” bone tissue. Essentially these tiny pterosaurs were precocious sexually active adults in the former juvenile phase of development.

Precocial hatchling?
Prondvai et al. report, “Superprecocial embryos require substantial amount of nutrients stored in their eggs to reach an advanced level of somatic maturity state by the time the embryo hatches. If the egg volume of Darwinopterus was relatively as low as that of squamates, then how could it have contained so much yolk as to cover the energy requirements of an extremely well-developed, volant hatchling?” Prondvai are assuming that pterosaur eggs developed outside the uterus. As lepidosaurs, pterosaur embryos developed inside the uterus and the super thin eggshell was deposited last. Thus they could “cover the energy requirements.”

Apparently Prondvai et al. are not looking
at verified pterosaur hatchlings (in eggs), which are identical in morphology to adults. In some cases large embryos can be larger than small adult sister taxa! The Prondvai team know that the tiny Rhamps don’t have the same morphology as the medium or big rhamphs. Unfortunately, and this is a continuing problem… they don’t realize those changes are phylogenetic, not ontogneric.

With similar proportions of bone and muscle,
but at 1/8 as tall and therefore (8 cube rooted or) 1/512 as massive, juvenile pterosaur bone tissue would have been strong enough for sustained flight in such lightweight specimens. But that overlooks reality, where the specimens Prondvai are looking at are in fact tiny adults with juvenile bone structure, as in Morganucodon. We don’t know where small, medium and large Rhamphorhynchus laid its eggs, which were likely ready to hatch shortly after deposition. We don’t have any hatchling Rhamphorhynchus fossils. Hatchlings of the small and tiny adults would have been in danger of desiccation (high surface area/volume ratio), so we can presume they grew up in moist environs. Unfortunately Prondvai et al. did not test the one verified juvenile among in the Rhamphorhynchus clade, NHMW 1998z0077/0001 (Fig. 3), the Vienna specimen. No one thinks this juvenile could not fly based on its age/relative size.

Figure 3. Two specimens attributed to Rhamphorhynchus longiceps along with a third specimen, NHMW 1998z0077/0001, that nested with the larger of the two with identical scores, thus identifying it as a juvenile R. longiceps. No one thinks this Rhamph could not fly, despite its young age.

To their credit, Pronvai et al. suggest (following a hypothesis first presented here): “Alternatively, Rhamphorhynchus hatchlings could have been precocial to the effect that they could have left their nests immediately after hatching, but they must have been exclusively terrestrial or rather arboreal. They could have clambered around quadrupedally on the branches of trees feeding themselves with smaller invertebrates or vertebrates without any parental contribution.”

No universal growth strategy in pterosaurs
Prondvai et al. report, “In the light of the histological results it becomes evident that there is no universal pattern in the growth strategy of pterosaurs.” I am concerned that this conclusion was made without the the benefit of a phylogenetic analysis and without knowledge of phylogenetic miniaturization in the clade.

To their credit
Prondvai et al. report, “In contrast to Bennett’s  suggestion, the second size category of Rhamphorhynchus does not only include subadult but also adult specimens, hence it cannot be used as an indicator of real ontogenetic stage.”

References
Chinsamy A, Codorniu ́ L, Chiappe L 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biol Lett 4: 282–285.
Chinsamy A and Hurum JH 2006. Bone microstructure and growth patterns of early mammals. Acta Palaeontologica Polonica 51 (2): 325–338.
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Prondvai E, Stein K, O0 si A, Sander MP 2012. Life History of Rhamphorhynchus Inferred from Bone Histology and the Diversity of Pterosaurian Growth Strategies. PLoS ONE 7(2): e31392. doi:10.1371/journal.pone.0031392
Sekercioglu C 1999. Megapodes: A fascinating incubation strategy. Online article. 

Rhamphorhynchus n28: unidentified food mass? or overlooked egg in the abdomen?

Figure 1. Rhamphorhynchus intermedius (n28) reconstructed.

Rhamphorhynchus intermedius (Koh 1937, n28 in the Wellnhofer 1975 catalog) is a well preserved basal specimen (derived from the C3 specimen of Campylognathoides) with a mass inside of its torso, only part of which has been identified as a Solhnhofen fish (Figs. 2,3).

Figure 2. Wellnhofer 1991 illustrates the abdominal mass as part of a fish and other unidentified elements.

The rest of the abdominal mass
is unidentified (Fig. 2). Wellnhofer 1991 considered it food. Considering its shape, size and placement, I wonder if the posterior mass is actually a nearly full term egg (Fig. 3). I don’t think it makes much sense to consider such an abdominal mass as “unidentified food” when no other known specimen has a similar mass of undigested food. That would mean the stomach could expand to fill the abdomen. Usually the only thing that crowds out other organs and air sacs is an egg or a number of eggs in other reptile taxa. Check out this kiwi X-ray for an extreme example.

Figure 3. Skeletal elements of Rhamphorhynchus intermedius (n28) along with an ingested fish and what appears to be a possible egg. Note the overlapping sets of gastralia. It looks like the jaws of the fish are displaced here. Wellnhofer did not see the large eyeball identified here. Note the left scapula and coracoid are inverted. There sternal complex has a similar unexpectedly bumpy texture as the purported egg.

Rhamphorhynchus intermedius
is a medium-sized Rhamphorhynchus nesting at the very base of the clade between the larger Campylognathoides and the smaller Bellubrunnu. Thus it is a transitional taxon, step one in an extreme example of phylogenetic miniaturization. No one understood this nesting prior to the phylogenetic analysis documented at ReptileEvolution.com because no one included a long list of Rhamphorhynchus specimens in analysis prior to or since. I’d like to encourage other pterosaur workers to do so and test this hypothesis of relationships.

Texture
The “egg” has an odd texture, but then so does the sternal complex. Not sure why.

Previous examples?
Two smaller examples of “something else” in the abdomen of – or just aborted from the abdomen – other specimens of Rhamphorhynhcus can be seen here and here.

References
Koh TP 1937. Unterscuchungen über die Gattung Ramphorhynchus. – Neues Jahrbuch Mineralogie, Geologie und Palaeontologie, Beilage-Band 77: 455-506.
Wellnhofer P 1975a-c. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33. Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.

wiki/Rhamphorhynchus

New pterosaur website: www.pteros.com

I see some great things
in the new pterosaur website http://www.pteros.com produced by several artists who show pterosaurs in vivo with skin, fur, colors, highlights and shadows (no skeletons). Those known from only a skull or other parts are illustrated as complete, no doubt based on phylogenetic bracketing.

Nine young, male artists
listed here contribute to the website. The pterosaurs are listed alphabetically here. Pterosaur families are listed here. There environments/formations are listed here. They have a newsletter, but I have not yet seen my first one.

Unfortunately,
like most pterosaur workers, these nine artists don’t know what a pterosaur is. They report, “They were not dinosaurs as most assume, instead being flying reptiles and rather close relatives.” That’s a major weakness because we know what pterosaurs are based on a large scale (674 taxa) phylogenetic analysis, the large reptile tree. And they are more closely related to living lizards than to living birds/dinosaurs. And then there’s the literature (Peters 2000), which has been largely ignored by workers in favor of traditional hypotheses unable to provide specific data.

Fortunately
several of the artists have followed the narrow chord wing with hind limbs outstretched like horizontal stabilizers with pedal lateral digit 5 unbound from posterior uropatagia.

Unfortunately,
several others have not. They continue to follow old deep chord paradigms.

Fortunately,
most of these artists know how to bounce light off of surfaces and their use of perspective and camera angle is fascinating.

Unfortunately
several artists do not have good skeletons under those surfaces. It is so important to precise;y follow the fossil data and not make things up.

Fortunately
there are several artists involved here and they should be providing guidance to each other to avoid errors and ‘raise their game. ‘

Unfortunately
some of the text (as in Rhamphorhynchus) mistakes small adults for babies (Prondvai et al. 2012, and we’ll talk about that paper again tomorrow). Although some papers are referred to, no references are provided. I have not looked at every web page. So, the above comments represent my views on a quick run through…

While we’re talking about pterosaur art…
I found this wonderful Zhenyuanopterus online (Fig. 1, NOT at pteros.com). Not sure who the artist is, but it has an excellent morphology with narrow chord wings and horizontal stabilizer-like hind limbs. If you know the artist, send me the name so I can give credit.

Figure 1. Excellent Zhenyuanopterus by an unknown artist. I’d be happy to provide credit once that artist becomes known.

References
Peters D 2000. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293–336.
Prondvai E, Stein K, Osi A, Sander MP 2012. Life History of Rhamphorhynchus Inferred from Bone Histology and the Diversity of Pterosaurian Growth Strategies. PLoS ONE 7(2): e31392. doi:10.1371/journal.pone.0031392