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.

 

 

 

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Is Jeholopterus pregnant? And what’s hiding in plain sight beneath that left wing?

There seems to be an overlooked egg shape
inside Jeholopterus, the vampire pterosaur, at just the right place (Figs. 1, 2; IVPP V12705). It’s not full term, so embryo/hatchling bones are not readily visible (= fully ossified) and currently impossible to reconstruct. Then again, that patch could be just a scuff mark.

Figure 1. Jeholopterus GIF animation showing new left wing shape plus underlying debris, perhaps in the form of theropod feathers.

Figure 1. Jeholopterus GIF animation showing new left wing shape plus underlying debris, some in the form of theropod feathers. Folded wings on pterosaurs should essentially disappear. This new interpretation follows that hypothesis. Click for an enlarged image.

Remember
pterosaurs are fenestrasaur – tritosaurlepidosaurs, so they are able to retain eggs within the mother’s body until just before hatching. Even their super-thin, lizard-like egg shells (or lack thereof) supports the present tree topology of pterosaurs as lepidosaurs in the large reptile tree (LRT, 1315 taxa) and disputes traditional models of archosaurian origin first invalidated by Peters 2000 by phylogenetic testing. Pterosaur eggs found alone (not near the mother) outside the body (like the IVPP anurognathid) include full term embryos. The Hamipterus egg accumulation chronicles a mass death of pregnant mothers, probably by lake burping.

Moreover
Jeholopterus seems to have landed on (= sunk on to after death) some theropod/bird feathers or similarly shaped pond plants. I suspected there was something wrong with that way-too-broad-while-folded wing. Pterosaur wings typically fold up to near nothingness, like bat wings do, when folded. It turns out, that’s the case here, too. There is a fringed trailing edge where the current and correct blue area ends. Make sure you click for a larger image.

Figure 2. Possible Jeholopterus premature egg in which embryo bones are not well calcified. Ribs and gastralia on a separate frame.

Figure 2. Possible Jeholopterus premature egg in which embryo bones are not well calcified. Ribs and gastralia on separate frames.

Look up at the left hand
of Jeholopterus and you’ll see there is some sort of fossilized matter (greenish color added on overlay) on the stratum that the specimen sank to. The same appears to be happening near the left wing tip, where something like feathers or long leaves appear, giving the illusion of a little too much pterosaur wing chord, especially in comparison to the right wing, which appears ‘normal.’

Figure 3. Jeholopterus counter plate in UV with brachiopatagium traced.

Figure 3. Jeholopterus counter plate in UV with brachiopatagium traced. UV image from Kellner et al. 2010.

Jeholopterus ninchengensis (Wang, Zhou, Zhang and Xu 2002) Middle to Late Jurassic, ~ 160 mya, [IVPP V 12705] was exquisitely preserved with wing membranes and pycnofibers on a complete and articulated skeleton (see below). Unfortunately the fragile and crushed skull was undecipherable to those who observed it first hand. Using methods described here, Peters (2003) deciphered the skull and identified the IVPP specimen of Jeholopterus as a vampire. In that hypothesis, Jeholopterus stabbed dinosaurs with its fangs, then drank their blood by squeezing the wound with its plier-like jaws while hanging on with its robust limbs and surgically sharp, curved and elongated claws. From head to toe, Jeholopterus stood apart morphologically. It was not your typical anurognathid. Derived from a sister to the CAGS specimen attributed to Jeholopterus, the holotype of Jeholopterus was a phylogenetic sister to Batrachognathus.

Figure 2. Reconstruction of Jeholopterus. This owl-like bloodslurper was covered with super soft pycnofibers to make it a silent flyer.

Figure 4. Reconstruction of Jeholopterus. This owl-like bloodslurper was covered with super soft pycnofibers to make it a silent flyer. Note the wider than tall torso and super long, super sharp claws.

These Jeholopterus wing images support
the narrow chord wing membrane stretched between elbow and wing tip (Peters 2002) and ignored by all subsequent workers. Note: Peters 2002 did not understand that something else made the left wing of Jeholopterus appear to have a deeper chord at mid wing. The illusion is that complete!

References
Cheng X, Wang X, Jiang S and Kellner AWA 2014. Short note on a non-pterodactyloid pterosaur from Upper Jurassic deposits of Inner Mongolia, China. Historical Biology (advance online publication) DOI:10.1080/08912963.2014.974038
Kellner AWA, Wang X, Tischlinger H, Campos DA, Hone DWE and Meng X 2010. The soft tissue of Jeholopterus (Pterosauria, Anurognathidae, Batrachognathinae) and the structure of the pterosaur wing membrane. Proc Royal Soc B 277: 321–329.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2003. The Chinese vampire and other overlooked pterosaur ptreasures. Journal of Vertebrate Paleontology 23(3): 87A.
Wang X, Zhou Z, Zhang F and Xu X 2002. A nearly completely articulated rhamphorhynchoid pterosaur with exceptionally well-preserved wing membranes and “hairs” from Inner Mongolia, northeast China. Chinese Science Bulletin 47(3): 226-230.

wiki/Jeholopterus

Hamipterus egg accumulation: Wang et al. 2017

Earlier
here and here we looked at the 3-D eggs of Hamipterus, a basal ornithocheirid from Early Cretaceous China. The eggs are scattered in and amongst a wide size/age range of disarticulated, but 3-D fossils. So, according to the authors, the eggs were buried, then bones and eggs were transported by storms, as if bulldozed. No embryos were reported from those eggs. No explanation why the pterosaurs did not fly away in the face of the storm, nor why more sediment wasn’t packed on the buried eggs during the storm.

Today
comes news from this expanding treasure trove site with embryo bones at several stages of development in 16 eggs out of hundreds! That’s good news because full-term embryos (= hatchlings) are identical to parents and eggs keep all the bones from an individual in a neat little package so we can finally put together what Hamipterus looked like.

But that’s not the picture the authors paint.
They said, “some bones lack extensive ossification in potentially late-term embryos, suggesting that hatchlings might have been flightless and less precocious than previously assumed.” Point-by-point:

  1. No nests were found.
  2. 215+ eggs were found
  3. Eggs appeared in moderate size variation
  4. The large number of accumulated eggs (Fig. 1) indicates they were laid by different females
  5. Some were subjected to differential water uptake during transport
  6. Internal content(?) observed in 42 eggs, 16 had embryos
  7. Bones not concentrated on the bottom half of the egg, as in dinosaurs
  8. No embryo is complete. One to several bones only in each of the 16 eggs.
  9. No teeth found in embryos.
  10. The most complete embryo had a lower jaw of 17mm. That’s 4% the size of the largest adult when other full-term pterosaur embryos are 12.5% (1/8) at hatching. So these were not full-term embryos ready to hatch.
  11. In a 2.2m section, eight layers with pterosaur bones have been identified, four of which show egg concentrations in a vertical distance of 1.4 m.

The authors note and conclude:
“This suggests that the hind limbs have developed more rapidly compared to the forelimbs and might have been functional right after the animal hatched. Thus, newborns were likely to move around but were not able to fly, leading to the hypothesis that Hamipterus might have been less precocious than advocated for flying reptiles in general (6) and probably needed some parental care.”

No. Think again.
Pterosaur mothers carried their eggs inside their bodies until just before hatching. That gives their babies warmth and protection until they are ready to hatch. They could do this because they are lepidosaurs, as phylogenetic analysis AND egg shell thickness and pliability tells us.

Figure 1. From Wang et al. 2017, a pterosaur egg and bone accumulation. Eggs float. So do hollow pterosaur bones.

Figure 1. From Wang et al. 2017, a pterosaur egg and bone accumulation. Eggs float. So do hollow pterosaur bones.

Sedimentology report:
“This sedimentological data, associated with the exceptional quantity of eggs and bones, indicate that events of high energy such as storms have passed over a nesting site, causing the eggs to be moved inside the lake where they floated for a short period of time, becoming concentrated and eventually buried along with disarticulated skeletons.”

Bottom line and biggest problem:
The authors assume the eggs were laid. That’s because they think pterosaurs are archosaurs. Birds and crocs are archosaurs and they lay their eggs at an early stage of fertilization. Lepidosaurs wait to lay their eggs, sometimes until the moment before hatching.

Alternative hypothesis:

  1. Mass death of several year-classes of pterosaurs on beach due to lake burping deadly carbon dioxide. That stops the parents from flying away.
  2. Desiccation and insect decomposition reveals eggs inside of female skeletons. This takes just a few days to a week and allows skeletons to easily separate into individual bones (Fig. 1)
  3. Later rising waters (storms optional, melting snow pack will do), overwhelms beached skeletons and exposed eggs. Even a few extra inches of water would be enough for this.
  4. Eggs float. So do pterosaur bones
  5. Wind/ripples push eggs and bones together back against beach bank corner where they accumulate. (This happened several times over dozens to hundreds of years, but not annually.)
  6. Water recedes leaving eggs en masse along with settling disarticulated individual bones of parents and kin
  7. Burial process is later completed with airborne or waterborne sediments overwhelming the bones and eggs in situ.
  8. To point #3 above: moderate egg size variation, we also see this in the chicken eggs we get at our local grocery, but pterosaurs kept growing throughout their lives and larger ones would tend to lay bigger eggs, though this has not been conclusively demonstrated, it seems broadly logical.

Evidently
the lake burping did not always coincide with the pterosaurs flocking together. But it happened four times to a portion of the flock, perhaps over hundreds of years, and evidently at ‘the back of the room where bad things happen’.

References
Wang X and 16 co-authors 2017. Egg accumulation with 3D embryos provides insight into the life history of a pterosaur. Science 358:1197–1201.

Pterodaustro embryo goes under DGS

Codorniú et al. 2017.
bring us detailed images of a wonderful Pterodaustro embryo (MIC-V246, Early Cretaceous; Chiappe et al. 2004) we’ve seen before. Here (Figs. 1–3) we’ll take a closer look at the fossil itself using DGS to untangle it. This is the same embryo first described by Chiappe et al. 13 years ago. Why did it take so long to bring out these details? There’s nothing really new here, no revision to their original description.

Figure 1. Pterodaustro embryo from Codorniú et al. with DGS color overlays to graphically segregate bones from one another.

Figure 1. Pterodaustro embryo from Codorniú et al. with DGS color overlays to graphically segregate bones from one another. Compare original reconstruction here to that in Figure 3.  Note the broken tibiae. Look how much better color over a photo works than pen and ink.

Turn out
the embryo is far less disarticulated than originally considered. Several bones are newly identified here (Fig. 2).

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

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

What Codorniú et al identified as

  1. ascending process of the premaxilla (pmx) is here a right metacarpal 4 (mc4)
  2. right wing phalanx 4 (wp4) is here a maxilla (mx) and premaxilla (pmx)
  3. left metacarpal 4 (mc4) is here a proximal radius (ra)
  4. left coracoid (co) is here a left metacarpal 4 (mc4)
  5. dorsal vertebrae (dv) and ribs at top is here identified as cervical vertebrae and left metacarpals 1–3).
  6. jugal (ju) and maxilla (mx) are here identified as mandible and palatal elements, but there’s also a short jugal in there below the sclerotic ring
  7. right metacarpal 4 (mc4) is here identified as a left scapula
  8. right wing phalanx 1 (wp1) is here identified as a left coracoid
  9. right wing phalanx 2 (wp2) is here identified as a dentary portion + left wp3 (4.3).
  10. gastralia (ga) are here identified as left dorsal ribs with tiny gastralia below
  11. caudal vertebrae (ca) here identified as possible sacral ribs

Parts missing from the Codorniú et al. tracing, but recovered using DGS include

  1. dozens of teeth
  2. prepubes
  3. pteroids
  4. carpals
  5. sternal complex
  6. finger phalanges including wing tip ungual (4.5)
  7. sclerotic rings
  8. cranial bones (parietals + occipitals)
  9. caudal vertebrae
  10. proximal femora
Figure 2. Same as in figure 1 with elements segregated.

Figure 3. Same as in figure 1 with elements segregated. Just a little bit of eggshell is preserved and it is very thin.

Digital Graphic Segregation (DGS)
is the perfect tool to interpret a fossil such as this. Embryos are encased in eggshell. That means every bone is retained in a small area, undisturbed by invaders or currents. Most embryos are going to be articulated, barring violent shaking, which could happen if the egg was tumbled and/or dropped. Some bones will just barely appear below others.

Try DGS yourself.
First color the bones that are easy to identify. Segregate the wings from other skeletal elements. Then color in all the remaining bones, including those that barely appear below other elements. Finally, lift your colors to another file and push them around to create a reconstruction. Check your work for errors and repeat.

Figure 3. Rough reconstruction using color tracings. Note the elongate jaws and small eye, documenting isometric growth in this pterosaur, as in all others where this can be seen.

Figure 4. Rough reconstruction using color tracings. Note the elongate jaws and small eye, documenting isometric growth in this pterosaur, as in all others where this can be seen. Note the relatively short tibia. This could be longer, but pars are hidden by the feet and other bones.

The thin egg shell
is similar to those in lepidosaurs because pterosaurs are lepidosaurs. As lepidosaurs mothers can carry their eggs until just before hatching, taking advantage of her warmth and her ability to avoid predators. Please ignore hypotheses that suggest pterosaurs buried their eggs. No fragile hatchling wants to dig out of a deep steaming pile of wet, rotting leaves filled with insects and centipedes. They’re not like husky little sea turtles. Baby pterosaurs want to dry out, open up their tiny wings and fly!

Pterodaustro adult with manual digit 3 repaired.

Figure 4. Pterodaustro adult with manual digit 3 repaired.

At one-eigth the size of a typical adult (which also vary in size)
embryo Pterodaustro was similar in proportions, but with shorter tibiae, smaller feet, more gracile jaws and other minor differences. With such proportions, there is nothing to prevent hatchling Pterodaustro from flying.

Figure 2. Pterodaustro embryos compared. Note the 2004 specimen is a little larger with more robust wing finger phalanges and a larger sternal complex.

Figure 2. Pterodaustro embryo compared to post-hatchling. Note the right specimen is a little larger with more robust wing finger phalanges and a larger sternal complex.

We looked at other pterosaur embryos
here, here, here, here, and here.

Bone fusion patterns in pterosaurs
Codorniú et al. discuss the lack of scapulacoracoid (s/c) bone fusion in the embryo and considered that an ontogenetic trait. A long time ago, bone fusion was phylogenetically mapped on the pterosaur cladogram. No current embryos have s/c bone fusion, but then neither do any of their adults or sisters. What we need is to find an embryo of a pterosaur genus with a fused s/c as an adult. We have not found one yet. As lepidosaurs, pterosaurs follow lepidosaur bone fusion patterns (Maisano 2002), which are phylogenetic, not ontogenetic. Fused bones keep growing. So do unfused bones into adulthood.

It would be great
if this embryo finally puts to rest the invalid hypothesis of allometric growth in pterosaurs promoted by Bennett and many Bennett followers who considered small, short rostrum, large-eyed Solnhofen pterosaurs the juveniles of larger, longer-snouted specimens. Zhejiangopterus and Pterodaustro growth series provide further strong evidence against the invalid allometric growth hypothesis. Pterosaur workers: GET OVER IT! IT’S WRONG!

References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Chiappe LM, Codorniú L, Grellet-Tinner G and Rivarola D. 2004. Argentinian unhatched pterosaur fossil. Nature, 432: 571.
Codorniú L, Chiapped L and Rivarola D 2017. Neonate morphology and development in pterosaurs: evidence from a Ctenochasmatid embryo from the Early Cretaceous of Argentina. From: Hone DWE, Witton MP and Martill DM (eds) New Perspectives on Pterosaur Palaeobiology. Geological Society, London, Special Publications, 455, https://doi.org/10.1144/SP455.17
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.

 

 

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.

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

Figure 1. Rhamphorhynchus intermedius (n28) reconstructed.

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.

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.

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

Another look at the tiny pterosaur, Nemicolopterus

Not content
with a fully resolved cladogram, I wanted higher Bootstrap scores at certain nodes to ascertain nesting pairs. So I reviewed the data for several taxa, among them Nemicolopterus. I found mistakes and oversights, nearly all of which more closely match Nemicolopterus to its much taller sister, Shenzhoupterus (Fig. 1) within the larger encompassing Germanodactylus/Tapejara clade.

Figure 1. Germanodactylus cristatus and members of the Shenzhoupteridae, Nemicolopterus and Shenzhoupterus.

Figure 1. Germanodactylus cristatus and members of the Shenzhoupteridae, Nemicolopterus and Shenzhoupterus.

When first announced
(Wang et al. 2008), Nemicolopterus was hailed as the smallest, or one of the smallest known pterosaurs. And it is. But there is one other that is only half as tall (Fig. 2) which we looked at in more detail yesterdayB St 1967 I 276.

Figure 2. Nemicolopterus has been described as the smallest pterosaur, but No. 6 in the Wellnhofer (1970) catalog was only half as tall.

Figure 2. Nemicolopterus has been described as the smallest pterosaur, but B St 1967 I 276, No. 6 in the Wellnhofer (1970) catalog was only half as tall.

An insitu tracing 
animated in a GIF movie reveals the bones segregated by digital layers (Fig. 3).

Figure 3. Two images of Nemicolopterus superimposed and traced with transparent colors. Note, not all of the shapes seen in photo 1 can be seen in photo 2. There appear to be extra tiny bones in the belly of this specimen.

Figure 3. Two images of Nemicolopterus superimposed and traced with transparent colors. Note, not all of the shapes seen in photo 1 can be seen in photo 2. There appear to be extra tiny bones in the belly of this specimen where all the ribs and gastralia have been accounted for. Click to enlarge. 

A displaced sliver of bone in the cheek
would appear to be the ventral portion of an orbit-dividing lacrimal, as in sister taxa. No one would identify this bone as such without phylogenetic bracketing. Hairlike soft tissue arising from the rostrum evidently precedes the rostral crest found in Shenzhoupterus. The free fingers remain unknown.

Phylogenetic miniaturization 
appears to be at work once again with Nemicolopterus, a tiny adult at the base of a major clade or two of pterosaurs in the large pterosaur tree.

References
Wang X, Kellner AWA, Zhou Z and Campos DA 2008. Discovery of a rare arboreal forest-dwelling flying reptile (Pterosauria, Pterodactyloidea) from China. Proceedings of the National Academy of Sciences, 106(6): 1983–1987. doi:10.1073/pnas.0707728105

wiki/Nemicolopterus