The larger specimen of Sinopterus atavismus enters the LPT basal to dsungaripterids

Many pterosaur fossils attributed to Sinopterus
have been described. They vary greatly in size and shape.

Presently four Sinopterus specimens have been added
to the large pterosaur tree (LPT, 253 taxa). They are all sister taxa, but as in Archaeopteryx, no two are alike, one is basal to the others, which are, in turn, basal to large clades within the Tapejaridae.

  1. Sinopterus dongi (the holotype) nests basal to the Tupuxuara clade.
  2. Sinopterus liui nests in the Tupuxuara clade.
  3. Sinopterus jii (aka Huaxiapterus jii) nests basal to the Tapejara clade.
  4. Sinopterus atavisms (Figs. 1-4; Zhang et al. 2019; IVPP V 23388) nests basal to the Dsungaripterus (Fig. 4) clade, outside the Tapejaridae.

Figure 1. Sinopterus atavismus in situ.

Figure 1. Sinopterus atavismus in situ. IVPP V 23388

From the Zhang et al. 2019 abstract:
“Here, we report on a new juvenile specimen of Sinopterus atavismus from the Jiufotang Formation of western Liaoning, China, and revise the diagnosis of this species.”

Zhang et al. note that several elements are unfused including a humeral epiphysis. Several pits and grooves in the distal ends of the long bones are also pitted and grooved. Normally these would be good indicators in archosaurs and mammals, but pterosaurs are lepidosaurs and lepidosaurs follow distinctly different ‘rules’ for growth (Maisano 2002). As an example, some pterosaur embryos have fused elements. Some giant pterosaurs have unfused elements. Here the new specimen (IVPP 23388) is considered an ontogenetic adult as its size is similar to other phylogenetic relatives.

“Sinopterus atavismus does not present a square-like crest. Moreover the feature that groove in the ventral part of the second or third phalanx of manual digit IV is not diagnostic of the species.”

Zhang et al. are comparing the new larger IVPP specimen to the smaller, previously described (Lü et al. 2016) XHPM 1009 specimen (then named Huaxiapterus atavismus), which they considered conspecific. The XHPM specimen has wing phalanx grooves while the IVPP specimen does not. The shapes of the skulls do not match (Fig. 3) and we know that pterosaurs grew isometrically. Thus these two specimens are not conspecific.

“In the new material, the skull preserves a pointed process in the middle part of the dorsal marginof the premaxillary crest, which is different from other Chinese tapejarids. Considering the new specimen is known from a large skeleton that differed from the holotype, this difference may be related to ontogeny, as the premaxillary crest of the holotype is short and does not extend as long as that of the new specimen.”

These two specimens are not conspecific, so ontogenetic comparisons should not be made.

Figure 2. Sinopterus atavismus reconstruction.

Figure 2. Sinopterus atavismus reconstruction.

From the Zhang et al. 2019 discussion:
“Except for D 2525 which represents an adult individual of Sinopterus (Lü et al. 2006b), all Chinese tapejarid pterosaurs known so far were immature individuals at the time of death. The new specimen (IVPP 23388) shares some features with the holotype of Sinopterus atavismus. The wingspan of the new material is about twice as long as that of the holotype of S. atavismus.”

As mentioned above, the IVPP V 23388 specimen is here considered an adult with unfused bone elements. It needs both a new generic and specific name. The XHPM 1009 specimen (Fig. 3) requires further study.

Figure 3. Sinopterus atavismus size comparison

Figure 3. Sinopterus atavismus size and shape comparison.

The present confusion about the ontogenetic status of pterosaurs 
could have been largely resolved with the publication of “The first juvenile Rhamphorhynchus recovered by phylogenetic analysis” and other papers suppressed by pterosaur referees. Sorry, readers, we’ll have to forge ahead with the venues we have.

Figure 3. Sinopterus atavismus skull restored (gray areas).

Figure 4. Sinopterus atavismus skull restored (gray areas).

Figure 4. Sinopterus atavisms compared to Dsungaripterus to scale.

Figure 5. Sinopterus atavisms compared to Dsungaripterus to scale.

Sinopterus atavismus (Zhang et al. 2019; Early Cretaceous; IVPP V 23388) was originally considered a juvenile member of the Tapejaridae, but here nests as a small adult basal to Dsungaripteridae. The antorbital fenestra is not taller than the orbit. The carpals are not fused. No notarium is present. The antebrachium is robust. The distant pedal phalanges are longer than the proximal pedal phalanges. An internal egg appears to be present (but half-final-size adults were sexually mature according to Chinsamy et al. 2008,)

Sinopterus dongi IVPP V13363 (Wang and Zhou 2003) wingspan 1.2 m, 17 cm skull length, was linked to Tapejara upon its discovery, but is closer to Tupuxuara.

Sinopterus? liui (Meng 2015; IVPP 14188) is represented by a virtually complete and articulated specimen attributed to Sinopterus, but nests here at the base of Tupuxuara longicristatus.

Sinopterus jii (originally Huaxiapterus jii, Lü and Yuan 2005; GMN-03-11-001; Early Cretaceous) is basal to the Tapejara in the LPT, distinct from the other sinopterids basal to Tupuxuara.

Figure 5. Click to enlarge. The Tapejaridae arise from dsungaripterids and germanodactylids.

Figure 5. Click to enlarge. The Tapejaridae arise from dsungaripterids and germanodactylids.

The present LPT hypothesis of interrelationships
appears to be a novel due to taxon inclusion, reconstruction and phylogenetic analysis. If not novel, please let me know so I can promote the prior citation.

Traditional phylogenies falsely link azhdarchids with tapejarids
in an invalid clade ‘Azhdarchoidea‘. The LPT has never supported this clade (also see Peters 2007), which is based on one character: an antorbital fenestra taller than the orbit (that a few sinopterids lack). Pterosaur workers have been “Pulling a Larry Martin” by counting on this one character and by excluding pertinent taxa that would have shown them this is a convergent trait ever since the first cladograms appeared in Kellner 2003 and Unwin 2003.

Figure 1. Gene studies link swifts to hummingbirds. Trait studies link swifts to owlets. Trait studies link hummingbirds to stilts.

Figure x. Gene studies link swifts to hummingbirds. Trait studies link swifts to owlets. Trait studies link hummingbirds to stilts.

Unrelated update:
The stilt, Himantopus (Fig. x) has moved one node over and now nests closer to the hummingbird, Archilochus. Both arise from the Eocene bird, Eocypselus, which also gives rise to the hovering seagull, Chroicocephalus. The long, mud probing beak of the stilt was adapted to probing flowers in the hummingbird. All these taxa nested close together in the LRT earlier.


References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Kellner AWA 2003. 
Pterosaur phylogeny and comments on the evolutionary history of the group. Geological Society Special Publications 217: 105-137.
Lü J and Yuan C 2005. 
New tapejarid pterosaur from Western Liaoning, China. Acta Geologica Sinica. 79 (4): 453–458.
Maisano JA 2002. The potential utility of postnatal skeletal developmental patterns in squamate phylogenetics. Journal of Vertebrate Paleontology 22:82A.
Maisano JA 2002.
Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Unwin DM 2003. On the phylogeny and evolutionary history of pterosaurs. Pp. 139-190. in Buffetaut, E. & Mazin, J.-M., (eds.) (2003). Evolution and Palaeobiology of Pterosaurs. Geological Society of London, Special Publications 217, London, 1-347.
Wang X and Zhou Z 2003. A new pterosaur (Pterodactyloidea, Tapejaridae) from the Early Cretaceous Jiufotang Formation of western Liaoning, China and its implications for biostratigraphy. Chinese Science Bulletin 48:16-23.
Zhang X, Jiang S, Cheng X and Wang X 2019. New material of Sinopterus (Pterosauria, Tapejaridae) from the Early Cretaceous Jehol Biota of China. Anais da Academia Brasileira de Ciencias 91(2):e20180756. DOI 10.1590/0001-3765201920180756.

wiki/Sinopterus

Growth pattern of a new large Romualdo pterosaur

Bantim et al. 2020 document
a new “pteranodontoid pterosaur with anhanguerid affinities (MPSC R 1935) from the Romualdo Formation (Lower Cretaceous, Aptian-Albian), is described here and provides one of the few cases where the ontogenetic stage is established by comparison of skeletal fusion and detailed osteohistological analyses.”

Figure 1. Excellent wing finger carpophalangeal joint from the Bantim et al. 2020 paper. Note the unfused sesamoid (extensor tendon process), a phylogenetic trait of lepidosaurs, not an ontogenetic trait of archosaurs, as phylogenetic analysis documents.

Figure 1. Excellent wing finger carpophalangeal joint from the Bantim et al. 2020 paper. Note the unfused sesamoid (extensor tendon process), a phylogenetic trait of lepidosaurs, not an ontogenetic trait of archosaurs, as phylogenetic analysis documents.

Continuing from the abstract
“The specimen … consists of a left forelimb, comprising an incomplete humerus, metacarpal IV, pteroid and digits I, II, III, IV, including unguals. This specimen has an estimated maximized wingspan of 7.6 meters, and despite its large dimensions, is considered as an ontogenetically immature individual. Where observable, all bone elements are unfused, such as the extensor tendon process of the first phalanx and the carpal series. The absence of some microstructures such as bone resorption cavities, endosteal lamellae, an external fundamental system (EFS), and growth marks support this interpretation. Potentially, this individual could have reached a gigantic wingspan, contributing to the hypothesis that such large flying reptiles might have been abundant during Aptian-Albian of what is now the northeastern portion of Brazil.”

Anhanguera

Figure 2. Anhanguera.

By comparison,
coeval Anhanguera has a 4.6m (15 ft) wingspan. The largest complete ornithocheirid, SMNK PAL 1136 has a 6.6m wingspan.

Bone elements fuse and lack fusion
in phylogenetic patterns (rather than ontogenetic patterns) in the clade Pterosauria, as documented earlier here in 2012. That is why you can’t keep pretending pterosaurs are archosaurs and not expect problems like this to accumulate. Your professors are taking your time and money and giving you invalidated information.

Figure 5. Largest Pteranodon to scale with largest ornithocheirid, SMNS PAL 1136.

Figure 5. Largest Pteranodon to scale with largest ornithocheirid, SMNS PAL 1136.

It is a continuing black mark on the paleo community
that pterosaurs continue to be considered archosaurs by paid professionals when phylogenetic analysis (and Peters 2007 and the LRT) nests pterosaurs with lepidosaurs. That is why pterosaurs have lepidosaur phylogenetic fusion patterns (Maison 2002, 2002) distinct from archosaur ontogenetic fusion patterns. Just add taxa colleagues. The pterosaur puzzle piece does not fit into the archosaur slot… everyone admits that. The pterosaur puzzle piece continues to fit perfectly and wonderfully in the fenestrasaur tritosaur lepidosaur slot.


References
Bantim RAM et al. (5 co-authors) 2020. Osteohistology and growth pattern of a large pterosaur from the lower Cretaceous Romualdo formation of the Araripe basin, northeastern Brazil. Science Direct https://doi.org/10.1016/j.cretres.2020.104667
Maisano JA 2002. The potential utility of postnatal skeletal developmental patterns in squamate phylogenetics. Journal of Vertebrate Paleontology 22:82A.
Maisano JA 2002.
Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Peters D 2007. 
The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.

https://pterosaurheresies.wordpress.com/2013/05/14/phylogenetic-fusion-patterns-in-pterosaurs/

Fresh data on little Ningchengopterus (not a baby pterosaur)

Yesterday we looked at a new paper on an old topic,
the ability of ‘large enough’ pterosaur hatchlings to fly shortly after hatching (Unwin and Deeming 2019). I say, ‘large enough’ because some fly-sized hatchlings of hummingbird-sized adults were not large enough to avoid desiccation due to their high surface/volume ratio. This was likely the origin of quadrupedal locomotion from bipedal pterosaur ancestors. Such tiny hatchlings had to remain within high humidity leaf litter environs until reaching that minimum size for flight. And they probably drank a lot of water.

On the publicity tour for Unwin and Deeming 2019,
the NYTimes.com published an article that contained a rather high-resolution picture of a small Late Jurassic pterosaur, Ningchengopterus (Figs. 1-3; Lü 2009) that is several magnitudes better than the originally published line drawing.

Figure 1. ?Ningchengopterus in situ. Note the narrow-at-the-elbow wing membrane and manual digit 5 near the wrist.

Figure 1. ?Ningchengopterus in situ. Note the narrow-at-the-elbow wing membrane and manual digit 5 near the wrist. There is no wing membrane connection to the lower leg or ankle, only a ‘fuselage fillet’ inside the elbow.

Ningchengopterus? liuae (Lü J 2009) CYGB-0035 was originally considered a “baby”, even though it had an adult crest. Here, in the large pterosaur tree (LPT, 238 taxa) Ningchengopterus was derived from a sister to the larger Painten pterosaur and it phylogenetically preceded Pterodactylus antiquus? AMNH 1942 (No. 20 in Wellnhofer (1970). Here it appears that Ningchengopterus was actually a basal Pterodactylus and therefore congeneric.

Despite the additional data and several scoring changes,
the nesting of Ningchengopterus in the LPT did not change. So crappy data sometimes work. Crappy character lists sometimes work. Taxon exclusion never works. Let’s treat every pterosaur specimen as a taxon, like the LPT does, and see which taxa are associated with many times larger adults… and which nest with other tiny pterosaurs under phylogenetic miniaturization.

Figure 2. Ningchenopterus reconstructed using DGS methods. Sure it's small, but not much smaller than sister taxa after phylogenetic analysis.

Figure 2. Ningchenopterus reconstructed using DGS methods. Sure it’s small, but not much smaller than sister taxa after phylogenetic analysis.

Ningchengopterus preserves a complete proximal wing membrane
(Fig. 1) that confirms the findings of Peters 2002, in which evidence for a narrow chord pterosaur wing membrane that was stretched between the elbow and wing tip was presented for all pterosaurs in which the soft tissue is preserved, distinct from traditional bat-wing models proposed without evidence by several PhDs.

Figure 3. Finger 5 in Ningchengopterus is very clear, but overlooked by all other pterosaur workers.

Figure 3. Finger 5 in Ningchengopterus is very clear, but overlooked by all other pterosaur workers.

Manual digit 5 on pterosaurs is a vestige
(Fig. 3) that has been overlooked by all prior pterosaur workers. Ningchengopterus preserves manual digit 5 without question.

Figure 6. The Painten pterosaur phylogenetically nests between two smaller specimens in the LPT. 

Figure 4. The Painten pterosaur phylogenetically nests between two smaller specimens in the LPT. This is an earlier reconstruction of Ningchengopterus.

We’ve already established
(contra tradition enforced by several pterosaur professors) that pterosaur hatchlings were nearly identical to their 8x larger adults. So how do we determine if a pterosaur is a hatchling or an adult? The answer is phylogenetic analysis. A small adult pterosaur will nest with other small adult pterosaurs. A juvenile will nest with much larger adult pterosaurs, as demonstrated here with the first juvenile Rhamphorhynchus recovered by phylogenetic analysis, a paper the pterosaur referees did not want you to read, but you can read it here at ResearchGate.net for yourself.

Figure 1. Large anurognathids and their typical-sized sisters. Here the IVPP embryo enlarged to adult size is larger than D. weintraubi and both are much larger than more typical basal anurognathids, Mesadactylus and MCSNB 8950.

Figure 5. Large anurognathids and their typical-sized sisters. Here the IVPP embryo enlarged to adult size is larger than D. weintraubi and both are much larger than more typical basal anurognathids, Mesadactylus and MCSNB 8950.

There is (so far) only one exception to the above rule:
The IVPP anurognathid embryo (Fig. 5) is the same size as several adult sister taxa, like MCSNB 8950 and Mesadactylus. So undiscovered adults will be giant basal anurognathids when found. One incomplete and mislabeled sister taxon, ?Dimorphodon weintraubi, is closer in size to the hypothetical adult of the IVPP embryo, demonstrating the possibility of a giant anurognathid is real. Again, phylogenetic analysis works out all such problems.

The Vienna Pterodactylus.

Figure 6. The Vienna Pterodactylus. Click to animate. Wing membranes in situ (when folded) then animated to extend them. There is no shrinkage here or in ANY pterosaur wing membrane. There is only an “explanation” to avoid dealing with the hard evidence here and elsewhere.


References
Lü J 2009. A baby pterodactyloid pterosaur from the Yixian Formation of Ningcheng, Inner Mongolia, China. Acta Geologica Sinica 83 (1): 1–8.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Unwin DM and Deeming DC 2019. Prenatal development in pterosaurs and its implications for their postnatal locomotory ability. Proceedings of the Royal Society B https://doi.org/10.1098/rspb.2019.0409

wiki/Ningchengopterus

Prenatal development in pterosaurs

Unwin and Deeming 2019 report,
yet again, the hypothesis of pterosaur hatchling flight. They add this time, “the application of four contrasting quantitative approaches allows a more precise identification of the developmental status of embryos revealing, for the first time to our knowledge, the presence of middle and late developmental stages as well as individuals that were at term.”

Earlier
here, here and here middle, late and term developments were published online.

The authors add this time,
“We also identify a predicted relationship between egg size and shape and the developmental stage of embryos contained within. Small elongate eggs contain embryos at an earlier stage of development than larger rounder eggs which contain more fully developed embryos.”

Earlier
here, here and here, egg shape was matched to pterosaur rostrum length with the ctenochasmatid embryo, Pterodaustro (Figs. 3, 4) having the longer egg and the IVPP V13758 anurognathid (Figs. 1, 2) embryo having the rounder egg. It is also worthwhile to consider the alternate hypothesis presented earlier here for the varied sizes and shapes for Hamipterus eggs in a lepidosaur context (see below).

The authors add this time,
“Early ossification of the vertebral column, limb girdles and principal limb bones involved some heterochronic shifts in appearance times, most notably of manus digit IV, and facilitated full development of the flight apparatus prior to hatching.”

This has been known
since the first appearance of the IVPP anurognathid embryo (Figs. 1, 2) in 2004 and reported nearly immediately thereafter by Unwin and Deeming. That’s really stretching out a single idea over more than a decade.

the IVPP egg/embryo

Figure 1. Click to enlarge. A magnitude of more detail was gleaned from this fossil (the IVPP egg/embryo) using the DGS method.

Over the last two decades, workers must have vowed
not to touch any lepidosaur/fenestrasaur hypotheses for fear of confirming an amateur’s findings. Nor have they added tiny pterosaurs to phylogenetic analyses.

Figure 4. The IVPP embryo anurognathid compared to other basal pterosaurs.

Figure 2. The IVPP embryo anurognathid (lower right) compared to other basal pterosaurs, including an adult IVPP embryo, 8x larger.

Unwin and Deeming follow the invalidated hypothesis
that pterosaurs were archosaurs that laid and buried their eggs at an early stage of development, much as birds and crocs do. Not only do workers openly admit they lack pterosaur precursors within Archosauria, birds and crocs follow an allometric growth trajectory after hatching with a short snout and large eyes.

Figure x. Figure from Unwin and Deeming 2019. Apparently these authors saw much less in these pterosaur eggs fossils than was present. Compare these to figures 2 and 3.

Figure x. Added a few hours after publication. Figure from Unwin and Deeming 2019. Apparently these authors saw fewer details in these pterosaur eggs than were present. Compare to figures 1 and 3. No reconstructions were attempted by Unwin and Deeming, so they didn’t realize the embryos had adult proportions (Fig. 2) or could be scored in a phylogenetic analysis. So much potential. So little study.

On the other hand,
pterosaurs, like other lepidosaurs, follow an isometric growth series (Figs. 4, 5). as documented most clearly by Zhejiangopterus online here and Pterodaustro here, but also in a large Rhamphorhynchus juvenile here (‘the Vienna specimen’ and see citation below).

Figure 2. Original interpretations (2 frames black/white) vs. new interpretations (color).

Figure 3. Original interpretations (2 frames black/white) vs. new interpretation using DGS (color). Note: the premaxilla is in the lower right corner. The back of the skull is in the upper right corner. And see figure 4 for a growth series.

In the SuppData, the authors report,
“While most recent studies have concluded
that pterosaurs belong within Ornithodira [S3, S4] some analyses have located them outside this clade, although still within Archosauromorpha [S5, S6]. Here, we accept the majority view, that pterosaurs are ornithodirans, with an extant phylogenetic bracket consisting of crocodiles and birds.”

You might think they cited Peters 2000
as their ‘minority view.’ If so, you would be wrong. No citation to Peters 2000 was mentioned. S5 is Bennett 1996 where he nested pterosaurs tentatively with Scleromochlus. That was invalidated by Peters 2000 who simply added several taxa to Bennett’s published matrix of taxa and characters, and those of three other workers. S6 is Bennett 2012/13, where Bennett also ignores taxa proposed by Peters 2000, 2007.

If you’ll recall,
Bennett 2012/2013 reports that pterosaurs nested between the lumbering and aquatic archosauriforms Proterosuchus and Erythrosuchus. That moves the nesting away from Scleromochlus, proterochampsids and parasuchians, the previous archosaur ‘favorite candidates for most pterosaur workers. I shudder when I peek into their minds.

Thus Bennett’s curse,
“You will not be published, and if you are published, you will not be cited,” comes true once again. And now you know, once again, why I chose online publishing after seven or so academic publications. Not sure if not having a PhD is the issue, or if criticizing the hypotheses of PhDs is the real problem.

Figure 1. The V263 specimen compared to other Pterodaustro specimens to scale.

Figure 4. The V263 specimen compared to other Pterodaustro specimens to scale.

Readers need no reminding that phylogenetic analyses by Peters 2000
that tested prior pterosaur outgroup candidates has been enhanced online since 2011 with a steady stream of additional taxa. In that study pterosaurs nest with taxa identified by Peters 2000, and those taxa nest with taxa identified by Peters 2007, among them, the lepidosaur, Huehuecuetzpalli, all ignored by Unwin and Deeming. (You can download the Tritosauria paper here.)

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 5. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Lepidosaurs generally carry their eggs longer within the mother
than birds or crocs do, sometimes until the moment of hatching. This is not only a more parsimonious hypothesis based on actual evidence (“lizard-like eggshell thickness and leathery lizardy texture in pterosaur eggs”), but hypothetically hatching in open air, without the need to resurrect itself from burial is much to be preferred in tiny pterosaurs with fragile, bat-like wing membranes… much more fragile than wet hatchling bird feathers found in precocial mound building birds. And what happen to pliable eggs that are buried. Might get a little tight inside those eggshells! Mom, on the other hand, always makes room for her growing babies in their eggs.

Unwin and Deeming supplementary material identifies
without phylogenetic analysis, a list of small pterosaurs the authors label juveniles. After phylogenetic analysis, many of these turn out to be small adults (Peters 2007 and here). Earlier we talked about pterosaur workers putting on their blinders and ruining/distorting our understanding of pterosaurs by employing taxon exclusion in phylogenetic analysis. Alas, it has happened once again.

If you are wondering,
I submitted a paper (now available on ResearchGate.net here) on isometric pterosaur growth patterns. The pterosaur referees rejected it for reasons that are clear given the present attitude toward conflicting hypotheses.


References
Bennett SC 1996. The phylogenetic position of the Pterosauria within the  Archosauromorpha. Zoo. J. Linn. Soc. 118, 261–308.
Bennett SC 2012/13. The phylogenetic position of the Pterosauria reexamined.
Hist. Biol. 25, 545–563.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27
Unwin DM and Deeming DC 2019. Prenatal development in pterosaurs and its implications for their postnatal locomotory ability. Proceedings of the Royal Society B https://doi.org/10.1098/rspb.2019.0409

Note: Prior to understanding pterosaurs were lepidosaurs, I fell back upon tradition and labeled the outgroup taxa ‘prolacertiforms’ in Peters 2000, to my eternal embarrassment and with the approval of my editors and referees. Worse yet, today, twenty years later, most workers are still caught up in that error. Phylogenetic analysis solves so many problems. It’s really a cure for nearly everything in paleontology.

From the NYTimes.com article:

“Other experts were convinced by the paper’s assessment of embryo development, but not its behavioral conclusions.

“In order to prove those, the study would need to compare the pterosaurs with megapodes, chicken-like birds from Australia that can fly from birth, said Edina Prondvai, a postdoctoral researcher at Ghent University in Belgium and the MTA-MTM-ELTE Research Group for Paleontology in Budapest. Kevin Padian, a biologist at the University of California, Berkeley, called the idea that hatchlings could support their own body mass in the air “quite a stretch,” based on studies of birds.

“Dr. Unwin replied that he would have liked to compare pterosaurs with megapodes, but could not find enough data, and that “pterosaurs are not birds.

“He prefers it that way.

“It’s that sheer alienness of pterosaurs that is really fascinating about them,” Dr. Unwin said. “These were creatures that were really different than anything that’s around today.”

No, they are like lizards, bipedal lizards…(Peters 2000)
because they are lepidosaurs (Peters 2007). That has been validated by taxon inclusion. something Unwin and Deeming are loathe to do. Studying megapodes would be a waste of time, based on phylogenetic bracketing.

 

 

 

SVP 2018: Reproduction and Growth in Pterosaurs

Unwin and Deeming 2018 report,
“Pterosaur eggshells were pliable and occasionally bounded externally by a thin calcitic layer. Contact incubation seems impractical and eggs were likely buried and developed at ambient temperatures.”

Burial is not only unnecessary, but dangerous
given that pterosaurs are lepidosaurs and therefore able to retain eggs within the mother until just before hatching, something the authors continue to ignore. That’s why the eggs have lepidosaur-like ultra-thin external layers. No tiny fragile pterosaur wants to dig out of a buried situation. Too dangerous for fragile membranes. Unwin and Deeming are clinging to an archosaur hypothesis, ignoring all the data since Peters 2000 that nest them apart from archosaurs.

Figure 1. The V263 specimen compared to other Pterodaustro specimens to scale.

Figure 1. The V263 specimen compared to other Pterodaustro specimens to scale.

The authors report,
“Near term embryos were well ossified and hatchlings had postcranial proportions and well developed flight membranes that indicate a superprecocial flight ability.” 

As in lepidosaurs, not archosaurs.
Overlooked by the authors, cranial proportions are also adult-like in hatchlings (Fig. 1). Lepidosaurs hatch ready to eat and take care of themselves.

Regarding growth, they report,
“The growth rates recovered for pterosaurs are comparable to those reported for extant reptiles and a magnitude lower than in extant birds.” Here the authors are lumping turtles, lizards and crocs, when lizards will do.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 2. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Note,
the authors do not address isometric growth in their abstract, as in lepidosaurs, not archosaurs. Nor do they address sexual maturity at half full growth, which facilitates rapid phylogenetic miniaturization or gigantism whenever needed due to changing environs.

We’ve heard this all before. Years ago.

Respecting the embargo
other SVP abstract posts will show up after the 20th. This one made the news, so its embargo is over. That article featured BMNH 42736 (Fig. 3) labeled as a hatchling or flapling. Actually it’s a hummingbird-sized adult female. We know this because it nests with other phylogenetically miniaturized taxa in the large pterosaur tree (not with a larger specimen) and… it’s pregnant.

Figure 6. Torso region of BMNH 42736 showing various bones, soft tissues and embryo.

Figure 6. Torso region of BMNH 42736 showing various bones, soft tissues and embryo.

References
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Unwin DM and Deeming C 2018. An integrated model for reproduction and growth in pterosaurs. SVP abstracts.

Live Science online

Azhdarchid pterosaur flight issues

Pterosaurs,
as fenestrasaur tritosaur lepidosaurs matured isometrically. That’s a widely overlooked fact, even by pterosaur workers. Hatchlings had adult proportions with small eyes and long rostra — if their 8x larger parents had small eyes and long rostra. Hatchlings also had adult-proportioned wings. So presumably they were able to fly shortly after hatching (and drying out a bit) — if their parents were able to fly. But not all adult pterosaurs were able to fly…

Figure 1. GIF animation, 4 frames, showing three pterosaurs specimens in 3 sizes (see scale bars) with short, medium and long wings, drawn to the same torso length. The question is: did Quetzalcoatlus fly?

Figure 1. GIF animation, 4 frames, showing three pterosaurs specimens in 3 sizes (see scale bars) with short, medium and long wings, drawn to the same torso length. The question is: did Quetzalcoatlus fly?

Flightless pterosaurs
Earlier we looked at two related pterosaurs, the no. 57 specimen (Sos 2482) and the no. 42 specimen in the Wellnhofer 1970 catalog (Fig. 1). Both are adults. Both are in the azhdarchid lineage that arose from a tiny pterodactyloid-grade dorygnathid, the no. 1 specimen (TM 10341) in the Wellnhofer 1970 catalog and ultimately gave rise to the giant pterosaur, Quetzalcoatlus (also in Fig. 1). A magnitude or more greater in size and with wings only half as long as the flying no. 42 specimen,

Quetzalcoatlus is widely considered a flying pterosaur.
Can that be verified? Other clades of large (larger than a pelican) pterosaurs all have elongate wings, ideal for soaring. Azhdarchids, apparently deep shoreline waders, did not. The distal two long phalanges (sans the ungual) were shorter in azhdarchids, but the wing was not otherwise reduced, as in the flightless pterosaur, no. 57 (Fig. 1). Witton and Naish 2008 provide a history of workers pondering this question. Unfortunately they provided a bat-wing membrane attached to the ankles or shins with anteriorly oriented pteroids, ignoring key references for pterosaur wing shape (Peters 2002, 2009 and references therein) while ignoring fossilized evidence of pterosaur wing tissue, as others have done.

As anything gets larger,
either ontogenetically or phylogenetically, they generally put on weight at the cube of their length. Air-filled pterosaurs were not as solid, so that ratio was undoubtedly lower.  Even so longer, larger wings on larger pterosaurs makes sense, as in living large birds that fly and are also air-filled.

But that is countered by the isometric growth of individual pterosaurs as they mature to adulthood. Whatever works for hatchlings and tiny pterosaurs, is working just as well for giant adults. Could that mean that all ontogenetic stages of Quetzalcoatlus could fly? Or none of them? Or only half-sized juveniles at about ten percent of the adult weight? With flight, it’s always a balancing act: thrust, lift, drag, weight.

Wings can still provide great thrust
for terrestrial excursions even if they cannot get a big pterosaur off the ground (Fig. 2). So that’s a possibility under consideration, too. After all, why not use all the thrust available?

Quetzalcoatlus running like a lizard prior to takeoff.

Figure 10. Quetzalcoatlus running like a lizard prior to takeoff.

To prevent an extant flying bird, like a cockatiel, from flying, or flying well,
it’s surprising how little of the tips of the feathers need to be clipped. Link here. Basically its the difference between no. 42 and Quetzalcoatlus above (Fig. 1). With this in mind, I cannot join those who say giant Quetzalcoatlus could fly or fly between continents, until supporting evidence comes alone. Rather, giant azhdarchids become hippo analogs in this respect: they were probably constant deep waders (Fig. 3) capable of charging or running from danger. Storks, which azhdarchids otherwise resemble, tend to fly away because they have long, not truncated wings and can do so.

Figure 3. In my opinion this saddle-bill stork wading in water appears to be the bird closest to azhdarchid morphology and, for that matter, niche.

Figure 3. In my opinion this saddle-bill stork wading in water appears to be the bird closest to azhdarchid morphology and, for that matter, niche. It can fly from danger on elongate wings. Not so sure that Q could do the same. 

References
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing—with a twist. Historical Biology 15:277-301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Wellnhofer P 1970. 
Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.
Witton M and Naish D 2008.  A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. https://doi.org/10.1371/journal.pone.0002271. online here.

Pangupterus: a juvenile Moganopterus

Lü et al. 2016
described a new tiny, long-snouthed pterosaur, Pangupterus liui (Jiufotang Fm., Liaoning, Aptian, Early Cretaceous; Figs. 1, 2). Lü et al. thought they had a mandible with a 30º divergence at the jaw symphysis 1/5 of the total jaw length (Fig. 1).

But then, they also report,
“The distal end of the rostrum is slightly expanded, and although it has been destroyed, it seems to have a bony process in the middle, which is similar to the case in Longchengopterus.” The paper has several authors. I don’t think they read each others input.

The color illustration of a restored Pangupterus
that was included with the paper does not follow the first description, but features extremely narrow jaws closer to the second description. The restored body was imaginatively based on a Pterodactylus bauplan.

Figure 1. Pangupterus in situ. Lü et al. had first hand access and considered this a mandible with a symphysis at 1/5 the jaw length. Here it is interpreted as a rostrum and mandible, both with parallel rami.

Figure 1. Pangupterus in situ. Lü et al. had first hand access and considered this a mandible with a symphysis at 1/5 the jaw length. Here, based on this photo,  it is interpreted as a rostrum and mandible, both with parallel rami. If you’re looking at this on a 72 dpi monitor the image is 7/5 larger than life size.

Here, based on tracing
the photo in figure 1, a narrow rostrum lies at an angle to the equally narrow mandible. And the resulting reconstruction matches that of only one pterosaur, Moganopterus, except for its size. The skull of Pangupterus is only 1/4 as long as in Moganopterus (Fig. 2). A hatchling Monganoterpus, if it followed the pattern of other pterosaur hatchlings, would have been 1/8 the size of the adult (Fig. 2) or half the size of Pangupterus.

Figure 2. No other pterosaur has such narrow jaws tipped with slender teeth. Pangupterus is a good candidate to be a juvenile Moganopterus, as shown here.

Figure 2. No other pterosaur has such narrow jaws tipped with slender teeth. Pangupterus is a good candidate to be a juvenile Moganopterus, as shown here.

Moganopterus zhuiana 41HIII0419 (Lü et al. 2012) Early Cretaceous was a large sister to Feilongus and the cycnorhamphids. The skull was extraordinarly stretched out. Feeble needle-like teeth lined the anterior jaws. A long crest that did not break the rostral margin appeared posteriorly. And the neck vertebrae were very much elongated. Likely this was a very tall pterosaur.

Several other blog spots
covered Pangupterus. Some reimagine it as a hummingbird-like specimen. See other images here, here, here and here.

This specimen
further confirms the presence of tiny, long-snouted pterosaurs, some of them juveniles of larger long-snouted pterosaurs, and the isometric ontogenetic growth of all pterosaurs.

References
Lü J-C, Pu H-Y, Xu i, WuY-H and Wei X-F 2012. Largest Toothed Pterosaur Skull from the Early Cretaceous Yixian Formation of Western Liaoning, China, with Comments On the Family Boreopteridae. Acta Geologica Sinica 86 (2): 287-293.
Lü J-C, Liu C, Pan L-J and Shen C-Z 2016.
A new pterodactyloid pterosaur from the Early Cretaceous of the Western part of the Liaoning Province, Northeastern China. Acta Geologica Sinica (English) 90(3):777-782.

wiki/Moganopterus
/wiki/Pangupterus

Dr. David Unwin on pterosaur reproduction – YouTube

Dr. David Unwin’ talk on pterosaur reproduction 
was recorded at the XIV Annual Meeting of the European Association of Vertebrate Palaeontologists, Teylers Museum, Haarlem, Netherlands and are online as a YouTube video.
Dr. Unwin is an excellent and engaging speaker.
However, some of the issues Dr. Unwin raises have been solved at www.ReptileEvolution.com
The virtual lack of calcite in pterosaur eggs were compared to lepidosaurs by Dr. Unwin, because pterosaurs ARE lepidosaurs.  See: www.ReptileEvolution.com/reptile-tree.htm
Lepidosaurs carry their eggs internally much longer than archosaurs, some to the point of live birth or hatching within hours of egg laying. Given this, pterosaurs did not have to bury their eggs where hatchlings would risk damaging their fragile membranes while digging out. Rather mothers carried them until hatching. The Mrs. T external egg was prematurely expelled at death, thus the embryo was poorly ossified and small.
Dr. Unwin ignores the fact that hatchlings and juveniles had adult proportions as demonstrated by growth series in Zhejiangopterus, Pterodaustro and all others, like the JZMP embryo (with adult ornithocheirid proportions) and the IVPP embryo (with adult anurognathid proportions).
Dr. Unwin also holds to the disproved assumption that all Solnhofen sparrow- to hummingbird-sized pterosaurs were juveniles or hatchlings distinct from any adult in the strata. So they can’t be juveniles (see above). Rather these have been demonstrated to be phylogenetically miniaturized adults and transitional taxa linking larger long-tailed dorygnathid and scaphognathid ancestors to larger short-tailed pterodactyloid-grade descendants, as shown at: www.ReptileEvolution.com/MPUM6009-3.htm
Thus the BMNH 42736 specimen and Ningchengopterus are adults, not hatchlings. And the small Rhamphorhynchus specimens are also small adults.

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.

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 1. Several tiny Rhmphorhynchus adults, among them is the n7 specimen tested by Prondvai et al. and considered a juvenile by them.

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 1. Two specimens attributed to Rhamphorhynchus longiceps along with a third specimen that nested with the larger of the two with identical scores, thus identifying it as a juvenile R. longiceps.

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. 

Pterodaustro isometric growth series

Tradtional paleontologists think pterosaur babies had a cute short rostrum that became longer with maturity and a large orbit that became smaller with maturity (Fig. 1). This is a growth pattern seen in the more familiar birds, crocs and mammals.

Pterodaustro embryo as falsely imagined in Witton 2013. The actual embryo had a small cranium, small eyes and a very long rostrum.

Figure 1. Pterodaustro embryo as falsely imagined in Witton 2013. The actual embryo had a small cranium, small eyes and a very long rostrum.

Unfortunately
these paleontologists ignore the fossil evidence (Figs 2, 3). These are the data deniers. They see things their own way, no matter what the evidence is. The data from several pterosaur growth series indicates that hatchlings had adult proportions in the skull and post-crania. We’ve seen that earlier with Zhejiangopterus (Fig. 2), Tapejara, Pteranodon, Rhamphorhynchus and others. Still traditional paleontologists ignore this evidence as they continue to insist that small short rostrum pterosaurs are babies of larger long rostrum pterosaurs.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 2 Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

As readers know,
several pterosaur clades went through a phase of phylogenetic miniaturization, then these small pterosaurs became ancestors for larger clades. Pterosaurs are lepidosaurs and they grow like lepidosaurs do, not like archosaurs do.

Today we’ll look at
the growth series of Pterodaustro (Fig. 1), previously known to yours truly only from adults and embryos. Today we can fill the gaps with some juveniles.

This blog post is meant to help traditional paleontologists get out of their funk.

A recent paper
on the braincase of odd South American Early Cretaceous pterosaur Pterodaustro (Codorniú et al. 2015) pictured three relatively complete skulls from a nesting site (Fig. 1). I scaled the images according to the scale bars then added other available specimens.

Figure 1. Pterodaustro skulls demonstrating an isometric growth series. One juvenile is scaled to the adult length. One adult is scaled to the embryo skull length. There is no short rostrum and large orbit in the younger specimens.

Figure 1. Pterodaustro skulls demonstrating an isometric growth series. One juvenile is scaled to the adult length. One adult is scaled to the embryo skull length. There is no short rostrum and large orbit in the younger specimens. If you can see differences in juvenile skulls vs. adult skulls, please let me know. All these specimens come from the same bone bed.

You can’t tell which skulls are adults or juveniles
without scale bars and/or comparable specimens. As we established earlier, embryos are generally one-eighth (12.5%) the size of the adult. Pterodaustro follows this pattern precisely.  We have adults and 1/8 size embryos and several juveniles of intermediate size.

No DGS was employed in this study.

If you know any traditional paleontologists, 
remind them that the data indicates that pterosaurs matured isometrically, like other  lepidosaurs. Those small, short rostrum specimens, principally from the Late Jurassic Solnhofen Formation, are small adults, transitional from larger ancestors to larger descendants. Tiny pterosaurs experiencing phylogenetic miniaturization(as in birds, mammals, crocs, turtles, basal reptiles, and many other clades) that helped their lineage survive while larger forms perished, Sadly, no tiny pterosaurs are known from the Late Cretaceous when they all became extinct.

References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Codorniú L, Paulina-Carabajal A and Gianechini FA 2015.
 Braincase anatomy of Pterodaustro guinazui, pterodactyloid pterosaur from the Lower Cretaceous of Argentina. Journal of Vertebrate Paleontology, DOI:10.1080/02724634.2015.1031340