Was the first dinosaur egg soft?

Norell et al. (8 co-authors) 2020
used phylogenetic bracketing to determine that the first dinosaur egg (still unknown) was soft. They made one mistake that invalidates their phylogenetic bracket (Fig. 1).

Figure 1. From Norell et al. 2020 misleading readers by placing pterosaurs, Lagerpeton and Silesaurus in the lineage of dinosaurs after crocodylomorphs.

Figure 1. From Norell et al. 2020 misleading readers by placing pterosaurs, Lagerpeton and Silesaurus in the lineage of dinosaurs after crocodylomorphs.

From the Norell et al. abstract:
“However, pterosaurs—the sister group to dinosauromorphs—laid soft eggs.”

Simply adding taxa reveals this is wrong.
In the large reptile tree (LRT, 1698+ taxa) pterosaurs nest within Lepidosauria. The pterosaur – dinosaur myth was invalidated by Peters 2000, 2007. So we have to toss out pterosaurs as an invalid nesting. What are we left with?

According to Norell et al.
Crocodylia create rigid calcite eggs. So do members of the Theropoda (including birds). So do members of the phytodinosaur clades, Ornithopoda and Macronaria. Exceptions occur among the highly derived Ceratopsia, which lay soft eggs. Two more exceptions include the primitive sauropodomorphs, Massospondylus and Mussaurus. More importantly, egg shellls remain unknown for basal poposaurs, basal crocodylomorphs, basal theropods and basal phytodinosaurs.

When we use phylogenetic bracketing to make a statement like this
we need to be sure that we have the proper phylogeny. Norell et al. relied on tradition and myth rather than testing. They were wrong. In their claodgram, Norell et al. are hopeful that pterosaurs arose between crocodylomorphs and Lagerpeton (a bipedal proterochampsid also not related to dinosaurs). The Norell et al. cladogram was invalidated by Peters 2000 using four prior phylogenetic analyses. Those citations do not appear in Norell et al. (fufilling Bennett’s curse). In the LRT Silesaurus is a poposaur and thus a dinosaur-mimic, less related to dinosaurs than crocodylomorphs.

When we find eggs for Herrerasaurus and Eoraptor
then we can send a manuscript to Nature. Norell et al. were premature at best, misleading and myth perpetuating at worst. That the referees considered this manuscript okay to publish shows the dinosaur – pterosaur myth is still widespread and deeply entrenched, as discussed earlier here.


References
Norell et al. 2020. The first dinosaur egg was soft. Nature https://doi.org/10.1038/s41586-020-2412-8
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 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.

https://www.cnn.com/2020/06/17/world/soft-dinosaur-eggs-scn/index.html
https://www.cnet.com/news/soft-shelled-dinosaur-eggs-crack-the-mystery-of-missing-fossils/

Enigmatic 29cm Antarctic Late Cretaceous soft-shell egg

Legendre et al. (6 co-authors) 2020
report on an enigmatic egg they cannot identify. They nicknamed it “The Thing”. Without knowing anything else about it, my first guess, based on “giant” and “leathery or soft” is a giant azhdarchid (Fig. 1; first imagined in 2012). Let’s see if any clues guide us toward or away from that initial guess.

Quetzalcoatlus embryo and egg.

Figure 1. Hypothetical Quetzalcoatlus embryo and egg imagined in 2012. Compare to figure 2. The elongated shape and soft, thin shell were needed to encompass the elongated beak, neck and metacarpals. The long axis is ~35cm. See figure 4 for images of the mother.

Excerpts from the abstract
“Here we report a new type of egg discovered in nearshore marine deposits from the Late Cretaceous period (roughly 68 million years ago) of Antarctica. It exceeds all nonavian dinosaur eggs in volume and differs from them in structure.”

As in the azhdarchid hypothesis (Fig. 1).

“the new fossil, visibly collapsed and folded, presents a thin eggshell with a layered structure that lacks a prismatic layer and distinct pores, and is similar to that of most extant lizards and snakes (Lepidosauria).

As in the azhdarchid hypothesis (Fig. 1; Peters 2007).

“The identity of the animal that laid the egg is unknown, but these preserved morphologies are consistent with the skeletal remains of mosasaurs (large marine lepidosaurs) found nearby. They are not consistent with described morphologies of dinosaur eggs of a similar size class.”

Is taxon exclusion a factor here?

“Phylogenetic analyses of traits for 259 lepidosaur species plus outgroups suggest that the egg belonged to an individual that was at least 7 metres long, hypothesized to be a giant marine reptile, all clades of which have previously been proposed to show live birth.”

Perhaps taxon exclusion is a factor here. I will need to see the list of 259 lepidosaur species to see if it includes any pterosaurs.

“Such a large egg with a relatively thin eggshell may reflect derived constraints associated with body shape, reproductive investment linked with gigantism, and lepidosaurian viviparity, in which a ‘vestigial’ egg is laid and hatches immediately.”

As in the azhdarchid hypothesis (Fig. 1).

Now let’s look at the supplemental data
(writing this in real time as I do the research).

Specimen name: Antarcticoolithus bradyi.
The long axis is 29cm (Fig. 2). The short axis is estimated at 15cm. Compare that to the imagined 2012 azhdarchid egg (Fig. 1) with a long axis of 35cm. Just curl the embryo a bit and the guess = the discovery. The wider, but shorter Antarcticoolithus egg gives the developing azhdarchid? embryo a bit more room to move about. By the look of the egg, it appears to have a slit in it, as if it hatched already.

Figure 2. Antarcticoolithus bradyi from Legendre et al 2020.

Figure 2. Antarcticoolithus bradyi from Legendre et al 2020.

Figure 2b. Is that a slit in the egg shell? I am still awaiting the text of the study.

Figure 2b. Antarcticoolithus bradyi from Legendre et al 2020. Side two. Is that a slit in the egg shell from arrow to arrow? I am still awaiting the text of the study. (turns out to be a crack in the rock)

From the Supplemental Data:
“The first known remains of Late Cretaceous Antarctic pterosaurs were recently described (Kellner et al. 2019) however, the largest known pterosaur eggs with known taxonomic affinities (Pterodaustro guiñazui, egg length: ~60 mm; Fig. 3) belonged to a species with a ~2.5 m adult wingspan102. Hence, if the 290 mm-long Antarcticoolithus was a pterosaur egg, it would have been laid by a species with a wingspan of over 12 m, which is much larger than the maximum wingspan of 4–5 m described in known Antarctic pterosaurs.”

The known Antarctic pterosaurs include bits from one or two specimens (Fig. 6).

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

Figure 3. Original interpretations (2 frames black/white) vs. new interpretations (color).

Now let’s check out the mother’s pelvis
(Fig. 4). Looks like 10cm in the short axis was about the maximum, unless the ischia were free to expand during egg-laying. It is also possible that the pliability of the egg itself might have enabled Antarcticoolithus to pass through a hypothetical pelvis of a giant Q. northropi, if similar in proportion to the small Q. species, which is no sure thing in these flightless giants., wingspan ~11m.

Quetzalcoatlus eggs

Figure 4. Quetzalcoatlus northropi (left) nd Q. sp. (right) to the same scale alongside hypothetical eggs and hatchlings. The egg-layer of Antarcticoolithus, if azhdarchid pterosaurian, might have had a larger cloacal opening than shown here.

Finally, let’s consider those Antarctic pterosaurs. What were they?
Hard to say because they are such small parts of the pterosaur wing (Fig. 5).

Figure 6. Antarctic pterosaur bones from Kellner et al. 2019. The elements appear to be too gracile to fit the hypothetical outline provided.

Figure 6. Antarctic pterosaur bones from Kellner et al. 2019. The elements appear to be too gracile to fit the hypothetical outline provided.

Conclusion:
Don’t overlook the possibility of a giant azhdarchid egg layer for Antarcticoolithus.

Legendre et al. report,
“Interestingly, the two specimens of pterosaurs in our sample fall within the range of soft-shelled lepidosaur eggs, despite one of them showing a prismatic calcareous layer.”

We’ve known since Peters 2007 that pterosaurs are lepidosaurs.

“Pterosaur eggs have been repeatedly described as soft-shelled due to the thin and pliable aspect of their eggshell. The first detailed description of a pterosaur egg microstructure, however, showed a conspicuous prismatic layer. Another specimen was reported to lack a calcareous layer, and be most similar in structure to a lepidosaur eggshell, but no description of its microstructure using microscopy techniques was provided, preventing a clear identification of a soft-shelled structure. Since these first descriptions, more specimens of exceptionally preserved eggs have been described for a handful of pterosaur species – some hard-shelled (Grellet-Tinner et al. 2014) some soft-shelled.”

Pterodaustro eggs (Fig. 3) can hardly be called ‘hard-shelled’ contra Grellet-Tinner et al. 2014. Eggs with deep infolds, like those of Antarcticoolithus are not filled to bursting with full-term embryos, as is formerly empty, sediment-filled egg shown in figure 2.

“There is currently no consensus on whether such a soft eggshell was widespread among pterosaurs, nor on the relationship of the structure of that soft eggshell to that of lepidosaur eggshells.”

No consensus, for reasons listed earlier, but Peters 2007 was the first worker to nest pterosaurs within lepidosauria simply by adding taxa.

“More studies on pterosaur eggshells are thus necessary to assess their potential microstructural similarity with extant soft-shelled eggs. While the possibility of Antarcticoolithus being a fossilized pterosaur egg cannot definitely be ruled out, it should be noted that no remains of giant pterosaurs likely to have laid such a large egg are known from Antarctic deposits, contrary to giant marine reptiles.”

Leave the options open. Always a good idea. This egg may belong to something else entirely, like a mosasaur (see NPR online below). As more information arrives, I will add data to this blogpost.


References
Grellet-Tinner, G. et al. 2014. The first pterosaur 3-D egg: Implications for Pterodaustro guinazui nesting strategies, an Albian filter feeder pterosaur from central Argentina. Geoscience Frontiers 5, 759–765.
Kellner AWA et al. 2019. Pterodactyloid pterosaur bones from Cretaceous deposits of the Antarctic Peninsula. Anais da Academia Brasileira de Ciências91,e20191300.
Legendre LJ, et al. (6 co-authors) 2020.
A giant soft-shelled egg from the Late Cretaceous of Antarctica. Nature Jun 17 https://doi.org/10.1038/s41586-020-2377-7
Peters D 2007.
The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.

At ResearchGate.net:
A_new_lepidosaur_clade_the_Tritosauria

From NPR with mosasaur baby illustration
https://www.npr.org/2020/06/17/877679868/scientists-find-the-biggest-soft-shelled-egg-ever-nicknamed-the-thing

https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-020-2377-7/MediaObjects/41586_2020_2377_MOESM3_ESM.mov

https://pterosaurheresies.wordpress.com/2012/02/21/an-egg-for-quetzalcoatlus/

Was the AMNH Tanytrachelos ‘with child’?

Tanytrachelos ahynis (Olsen 1979, holotype AMNH 7496; holotype Fig. 1) Latest Triassic, 200 mya, was derived from Macrocnemus and was a sister to Langobardisaurus and Tanystropheus. All are tritosaur lepidosaurs in the lineage of the terrestrial ancestors of pterosaurs, the Fenestrasauria… all ultimately derived from an earlier sister to late-surviving Huehuecuetzpalli and Tijubina.

Figure 1. AMNH 7496 holotype of Tanytrachelos with original tracing from Olsen 1979. DGS colors added.

Figure 1. AMNH 7496 holotype of Tanytrachelos with original tracing from Olsen 1979. DGS colors added.

The AMNH specimen
(Fig. 1) preserved in ventral exposure, appears to have two halves of a leathery eggshell and an ‘exploded’ embryo, best described as several dozen tiny bones that should not be there, unless, perhaps this was a gravid adult… or something else, like gastroliths, undigested prey… hard to tell. In any case, some of the pectoral bones also have new identities here.

Figure 5. Hypothetical Tanystropheus embryo compared to Dinocephalosaurus embryo.

Figure 2. Hypothetical Tanystropheus embryo compared to Dinocephalosaurus embryo. These are the sorts and sizes of bones one should look for in any maternal Tanytrachelos.

Figure 1. Tanytrachelos hopping to match Gwyneddichnium tracks (see figure 2).

Figure 3. Tanytrachelos hopping to match Gwyneddichnium tracks (see figure 2).

Distinct from Langobardisaurus,
Tanytrachelos has twelve cervicals, but none were gracile. The posterior cervical ribs had large heads that kept the rods far from each centrum. Heterotopic bones were present. These appear to be elongated chevrons, as in Tanystropheus. Rare hopping prints (Fig. 2) match the size and shape of Tanytrachelos pedes.

langobardisaurus-pectoral-girdle

Figure 4. The sternal complex of several other tritosaurs. Tanytrachelos is closer to Tanystropheus, not quite like any of these related taxa, but all are informative.

The elliptical sternum
of Tanytrachelos was wide, as in Langobardisaurus (Fig. 3), but the clavicle remained gracile, as in Huehuecuetzpalli (Fig. 3). The humerus was slightly bowed. Metacarpal I aligned with the others. Metatarsal III was the longest. Digit III was the longest as in Langobardisaurus tonelloi.


References
Olsen PE 1979. A new aquatic eosuchian from the Newark Supergroup Late Triassic-Early Jurassic) of North Carolina and Virginia. Postilla 176: 1-14.
Smith AC 2011. Description of Tanytrachelos ahynis and its implications for the phylogeny of Protorosauria. PhD dissertation. Virginia Polytechnic Institute and State University.

 

Avimaia and her enormous egg

Bailleul et al. 2019 reported
on the posterior half of an Early Cretaceous enantiornithine bird from China, Avimaia schweitzerae (IVPP V25371, Figs. 1,2), including an enormous eggshell within her torso. The authors commented on the eggshell, which had not one, but several several layers, an abnormal condition, probably leading to the demise of the mother.

Phylogenetic analysis
The Bailleul et al. 2019 phylogenetic analysis nested Avimaia with eight most closely related taxa, of which only one, Cathayornis (Fig. 1), was also tested in the large reptile tree (LRT, 1425 taxa, subset Fig. 3) and likewise nested with Avimaia. Significantly, Cathayornis also has a very deep ventral pelvis capable of developing and expelling very large eggs.

Figure 1. Avimaia compared to Cathayornis to scale.

Figure 1. Avimaia compared to Cathayornis to scale. Cathayornis is the only other tested enantiornithine bird to have such a deep ventral pelvis.

A long, thin, straight, displaced bone was found
beneath the rib cage and identified as a rib by Bailleul et al. 2019. I wonder if it is instead a radius (Fig. 1) because it is not curved like a rib and it does not have an expanded medial process. The radius is vestigial. Regardless of the identify of this slender bone, Avimaia, appears to be ill-suited for flying based on her robust tibiae, short dorsal ribs  and giant egg. Cathayornis (Fig. 1) appears to be better-suited for flying, based on its chicken-like proportions.

Figure 2. Avimaia in situ. Some bones were originally mislabeled. Here the egg is reconstructed with a more traditional egg shape.

Figure 2. Avimaia in situ. Some bones were originally mislabeled. Here the egg is reconstructed with a more traditional egg shape.

Mislabeled bones
The right ‘pubis’ (Fig. 2) is the right ischium. The reidentified pubis has a pubic boot and the ischium does, not as in sister taxa. The authors failed to identify vestigial pedal digit 5.

The egg was originally reconstructed as a sphere (drawn as a circle) inside the abdomen. Here (Figs. 1, 2) the egg is reconstructed in a more traditional egg shape more likely to pass through the ischia and cloaca.

Figure 2. Subset of the LRT focusing on the clade Enantiornithes and the nesting of Avimaia as a derived taxon within that clade.

Figure 3. Subset of the LRT focusing on the clade Enantiornithes and the nesting of Avimaia as a derived taxon within that clade.

Most birds
lay more than one egg in a clutch. Another exceptional bird that develops a very large egg is the flightless kiwi (Apterypterx, Fig. 4).

Figure 2. Jurapteryx, Pseudocrypturus, Apteryx and Proapteryx to scale.

Figure 2. Jurapteryx, Pseudocrypturus, Apteryx and Proapteryx to scale.


References
Bailleul AM, et al. 2019. An Early Cretaceous enantiornithine (Aves) preserving an unlaid egg and probable medullary bone. Nature Communications. 10 (1275). doi:10.1038/s41467-019-09259-x
Pickrell, J 2019. “Unlaid egg discovered in ancient bird fossil”. Science. doi:10.1126/science.aax3954

wiki/Avimaia

A peek beneath the ribs of Pterodactylus scolopaciceps

A not so recent PLOSOne paper (Vidovic and Martill 2014, Late Jurassic) on Pterodactylus scolopaciceps (Meyer 1860, BSP 1937 I 18 (Broili 1938, P. kochi No. 21 of Wellnhofer 1970, 1991) provided the images seen here (Figs. 3, 4). It is one of the best preserved pterosaurs of all. Earlier we critically examined Vidovic and Martill 2014 here. A few short notes and images (Figs. 1,2) below will summarize those criticisms. Otherwise, the photos bring today’s news: tracings of the overlooked coracoids, sternal complex and an early embryo (Figs. 4, 5).

Vidovic and Martill reported,
“The majority of pterosaur species from the Solnhofen Limestone, including P. scolopaciceps are represented by juveniles.” This is utter rubbish.  Several hummingbird- to sparrow-sized adults, yes! …and some with long rostra! …but no verifiable juveniles, EXCEPT the juvenile of the giant Rhamphorhynchus recovered and described here. Remember, pterosaur embryos and juveniles are close matches to their parents as they develop isometrically, able to fly upon hatching, not allometrically. The large pterosaur tree demonstrates the phylogenetic miniaturization is what saved certain pterosaur lineages from extinction following a great radiation in the Late Jurassic. This is evidence Vidovic and Martill refuse to accept.

Vidovic and Martill continue:
“Consequently, specimens can appear remarkably similar due to juvenile characteristics detracting from taxonomic differences that are exaggerated in later ontogeny.” More rubbish based on adherence to Bennett (1996, 1996. 3006) who synonimized dozens of Solnhofen specimens without so much as an attempt at phylogenetic analysis, which lumps and separates the lot into individual taxa here. The Vidovic and Martill cladogram includes only 33 taxa (10 from Solnhofen) and lumps several pterosaurs successfully together (tapejarids, ctenochasmatids, pteranodontids), but fails to put these clades correctly into large clades, nesting sharp beak toothless taxa with broad beak toothy taxa, etc. etc.

Vidovic and Martill dig themselves deeper
“A hypodigm for P. scolopaciceps, comprising of the holotype (BSP AS V 29 a/b) and material Broili referred to the taxon is described. P. scolopaciceps is found to be a valid taxon, but placement within Pterodactylus is inappropriate. Consequently, the new genus Aerodactylus is erected to accommodate it.” As you can see (Figs. 1, 2) and as has been tested, placement within Pterodactylus (Fig. 2)  is MORE appropriate than nesting with purported sisters promoted by Vidovic and Martill (Fig. 1).

Figure 4. Sister taxa of "Aerodactylus" according to Vidovic and Martill 2014 include Gladocephaloides and Cycnnorhamphus. More rubbish.

Figure 1. Sister taxa of “Aerodactylus” according to Vidovic and Martill 2014 include Gladocephaloideus and Cycnnorhamphus. More rubbish. Neither are even related to one another as the former is a ctenochasmatid and the latter, of course, is a cycnohrmphid. Click to enlarge.

Evolution works in minute steps
and the more traits shared between specimens, both overall and in minute detail, the more closely they are related. Vidovic and Martill may also be working under the false assumption that pterosaurs are archosaurs and follow archosaur fusion patterns. No. Pterosaurs are lepidosaurs and follow lepidosaur fusion patterns, which are largely phylogenetic, not ontogenetic, as reported earlier.

Figure 3. Click to enlarge. The large pterosaur tree nests these three taxa together. So this Pterodactylus really is a Pterodactylus.

Figure 2. Click to enlarge. The large pterosaur tree nests these three taxa together. So this Pterodactylus (BSP AS V 28a/b) really is a Pterodactylus (contra Vidovic and Martill)

 

Enough about that paper.
I was drawn to this specimen (Fig. 3) because I did not have data for the coracoids and took another look for them with this excellent photo.

Figure 1. Pterodactylus scolpaciceps from Vidovic and Martill 2014 with elements below the ribs traced in color.

Figure 3. Pterodactylus scolpaciceps from Vidovic and Martill 2014 with elements below the ribs traced in color. Soft tissue is persevered in this specimen, and so is an embryo.

Lo and behold
the coracoids and sternal complex were visible as impressions (Figs. 3, 4) and there was something else further back… an embryo. Not full term. Not fully ossified. The wings are invisible or lost among the ribs and gastralia. Unlike 3D eggs, crushed fossils lay out all the elements into a single bedding plane.

Figure 2. Closeup of the torso of Pterodactylus scolopaciceps showing the coracoids, sternal complex and a passenger.

Figure 4 Closeup of the torso of Pterodactylus scolopaciceps showing the coracoids, sternal complex and a passenger. I was drawn to revisit this specimen because I lacked data for the length of the coracoids. This excellent image provided that data and possibly more. The bones of the embryo are not fully ossified yet. The shell is not formed. Those happen closer to the time just before egg-laying.

The embryo 
is the right size, shape and morphology to someday pass through the pelvis. The bones are soft and underdeveloped. No trace of an eggshell is apparent, but that’s not supposed to happen until the last stages of gestation.

Figure 4. Pterodactylus scolopaciceps reconstructed with the passenger shown here expelled. It is the right size, shape and morphology to be an embryo within an egg.

Figure 5. Pterodactylus scolopaciceps reconstructed with the passenger shown here expelled. It is the right size, shape and morphology to be an embryo within an egg.

Unlike archosaurs
lepidosaurs carry their young for longer terms, sometimes to the point of live birth (viviparity). Earlier I proposed that pterosaurs, like some of their sister lepidosaurs, carried their embryos until just prior to hatching. Other workers, all of whom consider pterosaurs archosaurs, thought egg burial was their method of reproduction. Not sure how they imagine a fragile pterosaur with tearable wing membranes would manage to dig through whatever dirt, sand or debris they were buried in. The aborted egg of Darwinopterus similarly contains an immature and unossified embryo. We also have an aborted fetus in Anurognathus and an aborted egg in the tiny pterosaur, Ornithocephalus added to the Pterodaustro embryo, the ornithocheirid embryo (revised recently) and the (relatively) giant, proto-anurognathid embryo.

How many pterosaur fossils are pregnant?
If they are doing their job, half of the adults should be pregnant, unless females greatly outnumber males, then that percentage goes up. Very few, however, will be preserved with late stage embryos that preserve even impressions of bones. As everyone knows the thinnest bone walls in the animal kingdom are pterosaur bones, thinner yet in embryos and  softer yet in younger embryos.

It’s time people
It’s time to let go of those old paradigms about pterosaur origins, wing shape and interrelationships. Those old hypotheses are not working. They cannot be verified. They are the stuff of myth. I would hate to think that these workers are refereeing manuscripts.

Carl Sagan said this about letting go of old paradigms,
“The essence of the Scientific method is the willingness to admit your’re wrong, to abandon ideas that don’t work, and the essence of religion is not to change anything, that supposed truths are handed down by some revered figure and no one is to make any progress beyond that because all the truth is thought to be in hand.”

References
Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen Limestone of Germany: Year-classes of a single large species. Journal of Paleontology 69:569-580.
Bennett SC 1996. Year-classes of pterosaurs from the Solnhofen limestone of Germany: Taxonomic and systematic implications. Journal of Vertebrate Paleontology 16: 432–444.
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.
Vidovic SU, Martill DM 2014. Pterodactylus scolopaciceps Meyer, 1860 (Pterosauria, Pterodactyloidea) from the Upper Jurassic of Bavaria, Germany: The Problem of Cryptic Pterosaur Taxa in Early Ontogeny. PLoS ONE 9(10): e110646. doi:10.1371/journal.pone.0110646

Zhenyuanlong: Dromaeosaur? No. Tyrannosaur with wings? Yes.

Lü and Brusatte 2015
described a short-armed, winged Early Cretaceous Liaoning theropod, Zhenyuanlong suni (Fig. 1, JPM-0008 Jinzhou Paleontological Museum), as a dromaeosaur. Their published phylogenetic analysis included only dromaeosaurs but their text indicates a large inclusion set.

Figure 1. Zhenyuanlong in situ with colors applied to bones and feathers. These colors are transferred to create the reconstruction in figure 3.

Figure 1. Zhenyuanlong in situ with colors applied to bones and feathers. These colors are transferred to create the reconstruction in figure 3. The pelvic elements are reconstructed at right. The manus and pes are reconstructed at left.  Scale bars are 10cm.

From the Lü and Brusatte text
“We included Zhenyuanlong in the phylogenetic dataset of Han et al., based on the earlier analysis of Turner et al, which is one of the latest versions of the Theropod Working Group dataset. This analysis includes 116 taxa (two outgroups, 114 ingroup coelurosaurs) scored for 474 active phenotypic characters. Following Han et al., characters 6, 50, and 52 in the full dataset were excluded, 50 multistates were treated as ordered, and Unenlagia was included as a single genus-level OTU. The analysis was conducted in TNT v1.142 with Allosaurus as the outgroup.”

I reconstructed this theropod,
from published photographs (Figs. 1, 2) using (DGS digital graphic segregation), added it to the large reptile tree and found that it nested between tiny Compsognathus and gigantic Tyrannosaurus rex. Of course, Zhenyuanlong had the opportunity to nest with several dromaeosaurs, but it did not do so.

Figure 2. Skull of Zhenyuanlong in situ, as originally traced, colorized with skull, palate and mandible segregated.

Figure 2. Skull of Zhenyuanlong in situ, as originally traced, colorized with skull, palate and mandible segregated. Original quadrate may be a quadratojugal.

When you look at the reconstruction,
(Fig. 3) the similarity to T. rex becomes immediately apparent… except for those long feathered wings, of course.

I’ll run through several of the traits that link
Zhenyuanlong to Tyrannosaurus to the exclusion of dromaeosaurs here. It’s a pretty long list. Even so, if you see any traits that should not be listed, let me know and why.

  1. skull not < cervical series length
  2. skull not < half the presacral length
  3. premaxilla oriented up
  4. lacrimal not deeper than maxilla
  5. naris dorsolateral
  6. naris at snout tip, not displaced dorsally
  7. orbit length < postorbital skull
  8. orbit not > antorbital fenestra
  9. orbit no > lateral temporal fenestra
  10. orbit taller than wide
  11. frontal with posterior processes
  12. posterior parietal inverted ‘B’ shape
  13. jugal posterior process not < anterior
  14. parietal strongly constricted
  15. quadratojugal right angle
  16. majority of quadrate covered by qj and sq
  17. postorbital extends to minimum parietal rim
  18. maxillary teeth at least 2x longer than wide
  19. mandible tip rises
  20. angular not a third of mandible depth
  21. retroarticular process expands dorsally and ventrally
  22. cervicals taller than long
  23. cervicals decrease cranially
  24. mid cervical length < mid dorsal
  25. caudal transverse processes present beyond the 8th caudal
  26. humerus/femur ratio < 0.55
  27. metacarpals 2 & 3 do not align with manual one joints
  28. pubis angles ventrally – not posteriorly
  29. 4th trochanter of femur sharp
  30. metatarsals 2 & 3 align with p1.1
Figure 3. Zhenyuanlong reconstructed in lateral view. Something behind the pelvis could be the remains of an egg, but needs further study. Both sets of wing feathers are superimposed here. Click to enlarge.

Figure 3. Zhenyuanlong reconstructed in lateral view. Something behind the pelvis could be the remains of an egg, but needs further study. Both sets of wing feathers are superimposed here. Click to enlarge. Note the pubis is not oriented posteriorly. Note the longer legs of Zhenyuanlong compared to tested dromaeosaurs.

Shifting
Zhenyuanlong to the dromaeosaurs adds a minimum of 127 steps to the large reptile tree. There is one clade of theropods that nests between the current tyrannosaur and dromaeosaur clades.

Figure 3. Cladogram subset of the large reptile tree showing the strong nesting of Zhenyuanlong as the current sister to Tyrannosaurus. Obviously many more theropod taxa are missing here. They have not been tested yet.

Figure 4. Cladogram subset of the large reptile tree showing the strong nesting of Zhenyuanlong as the current sister to Tyrannosaurus. Obviously many more theropod taxa are missing here. They have not been tested yet.

Note
I have not tested as many theropods as there are in several theropod cladograms.

The possible faults with the Lü and Brusatte study were

  1. a lack of reconstructions to work with, rather than just a score sheet that others had created and they trusted. Reconstructions test identifications by making sure the puzzle pieces actually fit, both morphologically and cladisitically.
  2. I think they were fooled by the apparent posterior orientation of the pubis in situ when in vivo it was not oriented posteriorly
  3. I’m guessing that the traits they used could be used on in situ fossils without making reconstructions. The traits I use require reconstructions.
Figure 0. Taxa ancestral to tyrannosaurs beginning with the CNJ7 specimen of Compsognathus.

Figure 0. Taxa ancestral to tyrannosaurs beginning with the CNJ7 specimen of Compsognathus.

With this nesting
the origin of long pennaceous wing feathers is evidently more primitive than earlier considered, developed twice. And perhaps this is why T. rex had such tiny arms. They were former wings, not grasping appendages.

References
Lü J and Brusatte SL 2015. A large, short-armed, winged dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous of China and its implications for feather evolution. Scientific Reports 5, 11775; doi: 10.1038/srep11775.

Liaoning bird embryo IS a Chinese Archaeopteryx

Updated 11/22/2015 with high rez data sent by Dr. Zhou. A new analysis nests the embryo with the holotype Archaeopteryx lithographica, the London specimen, a basal enantiornithine bird. 

Zhou and Zhang (2004)
described a small, precocial, final stage bird embryo from the Liaoning Province (Early Cretaceous, 121mya, IVPP V14238). Strangely, no eggshell was preserved (Fig. 1), but the tucked shape of the embryo indicated that it had not yet hatched. Northern China was a forested landscape dominated by active volcanoes and sprinkled with lakes and streams at the time. No adults were closely associated, but enantiornithine birds are common in that formation.

Figure 1. Click to enlarge. Liaoning bird embryo IVPP V14238 reconstructed Egg tracing in DGS compared to original tracing (in olive). Note the universally observed long tail and the continuation of the tail vertebrae past the back of the skull. Note the broken clavicles. When rotated they form more of a U shape. The dorsal coracoid is a convex and the ventral scapula is concave, an enanthiornithine key trait.

Figure 1. Click to enlarge. Liaoning bird embryo IVPP V14238 reconstructed Egg tracing in DGS compared to original tracing (in olive). Note the universally observed long tail and the continuation of the tail vertebrae past the back of the skull. Note the broken clavicles. When rotated they form more of a U shape with appropriate spacing of the coracoids. The dorsal coracoid is a convex and the ventral scapula is concave, an enanthiornithine key trait.

The Zhou and Zhang Abstract
“An embryo of an enantiornithine bird has been recovered from the Lower Cretaceous rocks of Liaoning, in northeast China. The bird has a nearly complete articulated skeleton with feather sheet impressions and is enclosed in egg-shaped confines. The tucking posture of the skeleton suggests that the embryo had attained the final stage of development. The presence of well-developed wing and tail feather sheets indicates a precocial developmental mode, supporting the hypothesis that precocial birds appeared before altricial birds.”

Figure 2. The Liaoning bird egg IVPP V14238 in situ with DGS tracing in color. This hirez version updates a prior lo rez version. Length of shell is 3.5 cm.

Figure 2. The Liaoning bird egg IVPP V14238 in situ with DGS tracing in color. This hirez version updates a prior lo rez version. Length of shell is 3.5 cm.

Zhou and Zhang 
did not create a reconstruction (Fig.1) nor attempt to untuck the embryo. Bird embryos shift into a tuck position before hatching as they begin to occupy most of the egg. No egg tooth is present on this specimen.

Figure 3. The Liaoning embryo compared to its closest sister, the London specimen of Archaeopteryx (holotype). The egg is the correct size to pass through the ischia if they were separated distally. like modern birds,

Figure 3. The Liaoning embryo compared to its closest sister, the London specimen of Archaeopteryx (holotype). The egg is the correct size to pass through the ischia if they were separated distally. like modern birds,

Zhou and Zhang report [with my observations in brackets]:
“The embryo has several enantiornithine apomorphies such as a strutlike coracoid with a convex lateral margin [yes], a V-shaped furcula [maybe], metacarpal III extending well past metacarpal II distally  [no], and metatarsal IV being more slender than metatarsals II or III [no]. My observations were improved with a high resolution image (Fig. 2). The Liaoning embryo nests with the holotype Archaeopteryx (London specimen), which nests at the base of the Enantiornithes.

This is the first
Cretaceous avian embryo preserved with feathers, sheathed, not open vanes. These indicate the embryo was precocial, able to move and feed independently shortly after hatching. This specimen demonstrates that the genus Archaeopteryx survived into the Early Cretaceous.

Figure 4. The Liaoning embryo bird nests with several Archaeopteryx specimens in the large reptile tree, AND with enanthiornithes. The large reptile tree does not specifically test for the classic enantiornithine traits, but correctly nested the embryo with adult enantiornithines.

Figure 4. The Liaoning embryo bird nests with several Archaeopteryx specimens in the large reptile tree, AND with enanthiornithes. The large reptile tree does not specifically test for the classic enantiornithine traits, but correctly nested the embryo with adult enantiornithines.

Compare this bird embryo to a precocial pterosaur embryo or three
like Pterodaustro, the IVPP embryo or the JZMP embryo. Embryo pterosaurs have the proportions of an adult. They grow isometrically. Hatchling birds, like the Liaoning embryo, had juvenile proportions with a large head, short tibia and short metatarsus. They grew allometrically, but not as allometric as living altricial (helpless) bird hatchlings.

“Several previously known theropod embryos and the late Cretaceous avian embryos all seem to be preocial animals, judged purely from skeletal evidence,” Zhou said.

Nat Geo
reported, “Zhou said several other enantiornithine species are known from the deposit where the latest fossil was found, but that it was difficult to link the embryo to a specific genus or species.” Unfortunately Zhou and Zhang eyeballed the embyro. They did not attempt a phylogenetic analysis (Fig. 4).

Kevin Padian
quoted in NatGeoOnline noted that half of the fossil’s characteristics are not exclusive to enantiornithines. He added that characteristics that would identify the fossil an enantiornithine are “either dubious or not well preserved on the specimen. But then, what else could it be?” Padian asked. I agree, but then neither of us has seen the fossil first hand.

Figure 4. Enanthiornithine birds to scale. Click to enlarge.

Figure 4.  A selection of Enanthiornithine birds to scale. None of these nest closer to the Liaoning embryo. These taxa all have a shorter tail and a more gracile clavicle and other traits listed in the large reptile tree.

Others have warned me
that juveniles and embryo reptiles, like pterosaurs and tritosaurs, cannot be added to phylogenetic analyses because they tend to nest with other adults*. Actually I’d like to see that happen. At present I’m a skeptic. This was a test of that hypothesis, but it was done with a precocial embryo with a relatively larger head, shorter neck and shorter limbs. I don’t see the problem with adding this embryo (Fig. 1) or precocial pterosaur embryos to analyses. But I’m willing to listen to good arguments with valid data.

*Bennett (2006) considered small adult pterosaurs as juveniles of larger germanodactylids based on long bone lengths rather than phylogenetic analysis. Eyeballing, charts and clouds of data points are no replacements for reconstructions and phylogenetic analysis. Hope you agree…

If this is an enantiornithine
which one is it most like? Archaeopteryx lithographica.

If this is an archaeopterygid
we now have some more ontogenetic clues and patterns to work with. You can see (Fig. 1) which body parts get larger and which get smaller during maturation.

Actually it’s both!

References
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.
Zhou Z and Zhang F-C 2004. A Precocial Avian Embryo from the Lower Cretaceous of China. BREVIA Science 22 October 2004: 306 no. 5696 p. 653. DOI: 10.1126/science.1100000. online abstract here

NatGeoOnline

News at the base of the Amniota, part 3: The amniotic egg

Earlier we looked at the base of the amniota and the phylogenetic miniaturization that preceded and succeeded basalmost amniotes. Today we’ll take a closer look at the one key trait that defines the Amniota.

Eggs and Embryonic Development
All morphology aside, the single key trait that defines the Amniota is the production of eggs surrounded by extraembryonic membranes and large enough to sustain the development of the developing embryo until it hatches beyond the gilled aquatic stage. Initially such an egg must have been small enough to maintain its shape and integrity out of water during the gradual evolution of those extraembryonic membranes (Carroll, 1969).

Phylogenetic bracketing shows the evolution of the amniotic egg had its genesis in the Viséan (~345 Ma), likely with a sister to Silvanerpeton and Gephyrostegus bohemicus, (the latter known from the Westphalian, 310 mya). Earlier and more derived amniotes are also found in Viséan strata. These include Westlothiana, Casineria and Eldeceeon (Fig. 1). So the origin of the amniotic egg precedes them all.

The anamniote outgroup taxa, Seymouria, Kotlassia and Utegenia (Fig. 1), all known from much later time periods (Permian), had juveniles with external gills (Laurin, 1996; Klembara et al., 2007), and so did not produce amniotic eggs. None of the recovered basal amniotes had juveniles with gills and sensory grooves. Carroll and Baird (1972) considered the small basal amniote Brouffia (Westphalian, Fig. 1) a juvenile. It had no external gills or sensory grooves. Klembara et al. (2014) considered Gephyrostegus watsoni (Fig. 1) a juvenile anamniote, but it, likewise, has no external gills or sensory grooves. Rather it nests between Eldeceeon and Solenodonsaurus in the Archosaurmorpha branch of the Amniota.

Figure 1. Basal amniotes to scale. Click to enlarge.

Figure 1. Basal amniotes to scale. Click to enlarge.

Basalmost amniotes share three skeletal traits
that indicate larger eggs were likely being produced:

  1. reduction to loss of the posterior dorsal ribs permitting expansion of the posterior torso in gravid females;
  2. greater depth of the pelvic opening permitting the passage of larger eggs; and
  3. unfused pelvic elements providing more pelvic flexibility during egg laying.

Amniotes more derived than G. bohemicus also develop a second sacral vertebra. Since these ‘second generation’ basal amniotes are generally much smaller overall with shorter limbs (Fig. 1), the second sacral rib comes as something of a surprise—unless it was used to help support the greater weight and mass of gravid females.

Certain amniote clades also transform their ossified ventral dermal scales to become elongate gastralia. Perhaps this also helped support the greater weight and width of the egg mass while gravid.

Only female basal amniotes?
Notably, no gender differences have been identified in basal amniote skeletons. Either basal male amniotes also lacked posterior dorsal ribs and had a deeper pelvic opening and/or basal amniotes reproduced by parthenogenesis (reproduction without males), as certain living lizards do (Lutes, et al., 2010). It could go either way.

Figure 1. Gephyrostegus watson (Westphalian, 310 mya) in situ and reconstructed. The egg shapes are near the hips as if recently laid.

Figure 2. Click to enlarge. Gephyrostegus watson (Westphalian, 310 mya) in situ and reconstructed. The egg shapes are near the hips as if recently laid. A few insects appear in the matrix. The carpals and tarsals are present, just displaced. So are the tail chevrons. The embryo (E) is hypothetical based on egg shape and size.

Westphalian amniote eggs?
In the basal amniote Gephyrostegus watsoni (Fig. 2, but this taxon needs a new name because it doesn’t nest with the holotype of Gephyrostegus) eight irregular flattened sphere shapes, each 5mm in diameter (five percent of the adult snout/vent length), appear dorsal to the open ‘lumbar’ area. If they were eggs they are the right size to pass through the pelvic opening. Preserved beyond the confines of the mother’s abdomen, the mother could have moved slightly just after depositing her eggs, shortly before burial. No embryonic skeletons should be expected to appear within such eggs. Instead embryos would have developed after egg deposition, as in many living reptiles. No calcified shell should be expected at this early stage of egg evolution. Examples of similar jelly-like soft tissue preservation in the fossil record are known, as in the Triassic lepidosaur, Cosesaurus (Fig. 4), preserved with a medusa (Ellenberger and de Villalta, 1974).

Click to enlarge and see rollover image. Here DGS, digital graphic segregation, enabled the identification of many more bones than firsthand observation, including the displaced carpals and tarsals, along with a few insects and egg-shapes.

Click to enlarge and see rollover image. Here DGS, digital graphic segregation, enabled the identification of many more bones than firsthand observation, including the displaced carpals and tarsals, along with a few insects and egg-shapes.

Hatchling size
From 1 cm diameter egg sizes (estimated from pelvic openings) curled up Gephyrostegus bohemicus hatchlings would have been ~2.6 cm in length or one-eighth (12 percent) the size of the mother (Fig. 1).

Figure 3. Click to enlarge and see the rollover. Eldeceeon with a strangely expanded belly (defined by gastralia/scales) that could have contained a load of eggs, traced in green here.

Figure 3. Click to enlarge and see the rollover. Eldeceeon with a strangely expanded belly (defined by gastralia/scales) that could have contained a load of eggs, traced in green here.

A gravid amniote in the Viséan?
The Eldeceeon holotype was preserved with an oddly expanded belly (Fig. 3). Perhaps this was also a gravid female (Fig. 7) with an egg load that pushed out her ossified ventral scales during postmortem decay and/or crushing. I’ve traced some possible eggs shapes found in the matrix.

Smaller ‘second generation’ basal amniotes, like Westlothiana and Casineria (Fig. 3), would have had proportionately smaller eggs.

Figure 4. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Figure 4. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Living examples of gravid females
Extant lizards (Fig. 4) show the extent of belly-stretching in gravid (pregnant) females and the relatively large size of their eggs. A clutch can be about the size of the mother’s eggless torso.

Basal amniote paleobiology
With short, sprawling fore limbs, a weak tail and a large head, Gephyrostegus watsoni (Fig. 2) was likely slow and secretive, like the living Sphenodon, both in leaf litter and in shallow puddles. This would apply even more so to massively burdened gravid females (Fig. 4). Without obvious defenses or weapons, the key to basal amniote success appears to have been an increase in the production of large eggs laid safely out of predator-filled swamps. The East Kirkton (Viséan) and Nyrany Basin (Westphalian) environments were swampy coal forests, so these would have provided the humid air, damp earth, wet leaf litter and abundant puddles needed for basal amniotes to slowly evolve keratinized skin and membrane enclosed eggs. The large orbit of basal amniotes suggests a nocturnal niche. Perhaps they hid and slept during daylight hours, avoiding evaporative sunlight and diurnal predators.

More later.

References
Carroll RL 1969. Problems of the origin of reptiles. Biological Reviews 44:393–431.
Carroll RL and D Baird 1972. Carboniferous stem-reptiles of the family Romeriidae. Bulletin of the Museum of Comparative Zoology 143:321–363.
Ellenberger P and JF de Villalta 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9:162–168.
Klembara J, DS Berman, AC Henrici, A Cernansky, R Werneburg and T Martens. 2007. First description of skull of lower Permian Seymouria sanjuanensis (Seymouriamorpha: Seymouriidae) at an early juvenile growth stage. Annals of Carnegie Museum 76:53–72.
Laurin M 1996. A redescription of the cranial anatomy of Seymouria baylorensis, the best known Seymouriamorph (Vertebrata: Seymouriamorpha). PaleoBios 17: 1–16.
Lutes AA, WB Neaves, DP Baumann, W Wiegraebe and P Baumann 2010. Sister chromosome pairing maintains heterozygosity in parthenogenetic lizards. Nature 464:283–286.

Tetrapod Eggshell Trends

Amniotes (= reptiles) produce different sorts of eggs (soft, flexible, rigid). Some are laid shortly after fertilization (most lizards, turtles, birds and crocs). Others are retained within the mother until just before hatching. Still others “hatch” within the mother and give way to live birth (mammals, several distinct clades of lizards, enaliosaurs, choristoderes).

Most fossil taxa are not also known from their eggs. However phylogenetic bracketing (Fig. 1) permits us a good guess as to what sorts of eggs they produced if we know what sort of eggs some clade members produced.

Eggshell trends in reptiles.

Figure 1. Click to enlarge. Eggshell trends in reptiles. Here the different types of shells permit phylogenetic bracketing of taxa for which no eggs are known. Apologies, this is not the most recent reptile tree.

Eggshells
From the Introduction to eggshells (Berkeley): “Most lizards, snakes, and tuataras lay soft eggs composed of an organic framework and poorly organized calcite crystals. These eggs collapse and shrivel after the animal hatches, and are therefore unlikely to be identified or even preserved in the fossil record.

“Many amniotes, including some lizards, snakes, and turtles, lay eggs with flexible shells. These shells differ from soft shells because of their higher mineral content. Nevertheless, preservation of flexible eggs is also rare in the fossil record.

“Some turtles and geckos, and all crocodilians, dinosaurs, and birds lay eggs with rigid eggshell. The calcite crystals form a relatively thick eggshell of interlocking shell units. Fossilization is more likely to occur in rigid eggshell because the crystalline calcium carbonate (calcite or aragonite) layer is stronger, more durable, and does not shrivel upon hatching.”

In summary, turtles lay all three kinds of eggs. Mammals, lizards and snakes lay eggs with flexible shells or produce live young. Only the more derived reptiles (crocs and dinosaurs including birds) produce hard-shelled eggs. Extinct marine reptiles of all sorts (probably except prehistoric turtles) produced live young.

Reptilian eggs can be separated into three separate groups based on the structure of their shell structure:
1. flexible shells with no calcareous layer
2. flexible shells with a thick calcareous layer, and
3. rigid shells with a well-developed calcareous layer.

Squamates mainly lay eggs with flexible shells. All squamate eggs are flexible except for two subfamilies of gekkos. Some flexible shells contain no calcareous layer, only a shell membrane. This fibrous membrane is comprised of an irregular series of ridges and a finely woven mat of fibers on the outer surface.

Some turtles also have flexible eggs
with a calcareous layer as thick as the shell membrane. Sea turtle eggs have a poorly ordered, open matrix calcareous layer with undefined shell components and pores. In contrast, in emydids and chelydrids (turtle clades) the calcareous layer is highly structured with well-defined components and pores.

Rigid-shelled Eggs
produced by crocodilians, some turtles, dibamids and gekkonids have a well-developed calcareous layer that makes up most of the eggshell and a thin shell membrane. The shell units fit together tightly and interlock.

Monotreme (Mammal) Eggshells 
are soft, leathery and flexible, lacking mineralization and without a calcareous covering. Monotremes (and all mammals) are descendants of extremely tiny early mammals. Their tiny adult size affected the tiny size and composition of the eggs of subsequent mammals.

Unfortunately we know of no pelycosaur or therapsid eggs yet. We have no basal reptile eggs from the Lepidosauromoph branch either. Our best guess is they were leathery.

Enaliosaurs
The marine reptiles (ichthyosaurs, plesiosaurs, nothosaurs, thalattosaurs, placodonts, mesosaurs) were all  live-bearing. There was a recent discovery of Early Permian (280 mya) mesosaur embryos curled into egg shapes within the mother and almost the size of nearby hatchlings. Mesosaurs were either viviparous or they laid eggs ready to hatch in days or minutes, which would have been a precursor to live birth. There is no trace of any eggshell.

EarlyPermianReptileEgg

Figure 2. Size of the earliest known Permian Egg, full scale at 72 dpi. The mesosaur egg was similar in size.

Oldest Reptile Egg
Previous to the mesosaur egg, Romer and Price (1939) described the oldest reptile egg (Admiral Formation Artinskian, 280 mya) based on shape, size, shell-like cracks and chemistry. The internal structure of the nodes and the pattern of their distribution, the type of layering and the microstructure are not like those found in calcareous eggshells.  Hirsch (1979) determined that the reptilian egg was “soft-shelled.”

An Early Archosauriform Egg
Hyphalosaurus, an aquatic choristodere (within the Archosauriformes), had a thin, leathery egg and the embryo was retained within the mother until just prior to hatching. Note that choristoderes are sisters to Proterochampsids and Parasuchians within the Parachosauriformes. Does this mean hard-shelled eggs were restricted to the Archosauria (birds and crocs)? It could.

Pterosaur Eggs
The extreme thinness of pterosaur eggs is at odds with the thick calcareous eggshells of crocs and birds, their putative kin in traditional palaeontology. Their eggs alone tell us that pterosaurs are lizards, as their morphology and phylogeny confirms. The mother carried the egg until just prior to hatching as three full term embryos and one poorly ossified expelled egg from Darwinopterus.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Hirsch KF 1979. The oldest vertebrate egg? Journal of Palaeontology 53(5): 1068-1084.
Romer AS and Price Li 1939. The Oldest Vertebrate Egg, Peabody Museum, Yale University, New Haven, Connecticut, American Journal of Science, Volume 237:  826-82.
Hou LH, Li, PP, Ksepka DT, Gao K-Q and Norell MA 2010. Implications of flexible-shelled eggs in a Cretaceous choristoderan reptile. Proceedings of the Royal Society B, 277(1685): 1235-1239. 10.1098/rspb.2009.2035.
Ji Q, Ji S, Lü J, You H and Yuan C 2006. Embryos of Early Cretaceous Choristodera (Reptilia) from the Jehol Biota in western Liaoning, China. Journal of the Paleontological Society of Korea, 22(1): 111-118.
Ji Q, Wu X-C and Cheng Y-N 2010. Cretaceous choristoderan reptiles gave birth to live young. Naturwissenschaften, 97(4): 423-428.  doi:10.1007/s00114-010-0654-2.
Sander PM 2012. Reproduction in Early Amniotes.Science 337, 806.

A Closer Look at the IVPP Pterosaur Egg and Embryo

The IVPP 13758 pterosaur egg and embryo were the first to be described and illustrated (Wang and Zhou 2004, Fig 1 far left and near left). Unfortunately the tracing of the specimen was crude, the reconstruction was off and the identification was mistaken.

The IVPP embryo pterosaur

Figure 1. Click for more information. The IVPP embryo pterosaur (far left) as originally traced, (near left) as originally reconstructed as a baby ornithocheirid, but with a very short rostrum, (near right) traced using the DGS method, (far right) adult reconstructed at 8x the embryo size.

A new tracing (Fig. 2) was made without seeing the specimen, but rather employing DGS (digital graphic segregation) based on two published photographs of the plate and counterplate of the split fossil digitally layered and rematched to each other. No other technique permits the plate and counterplate images to coincide as originally found. Every element of the skeleton was identified, all symmetrical elements match and the specimen shares a suite of traits with sister taxa.

the IVPP egg/embryo

Figure 2. Click to enlarge. A magnitude of more detail was gleaned from this fossil (the IVPP egg/embryo) using the DGS method. The jumble of bones is difficult to deal with, but the DGS method enables the segregation of certain bones from one another. Upper left: wings. Upper right: legs and feet. Lower left: skull, pelvis and axial elements. Lower right: Sternal complex, pectoral girdle, palatal elements.

What Is It?
The IVPP pterosaur embryo was misidentified as an ornithocheirid under the old archosaur precept that hatchlings would have a short rostrum and large eyes. The IVPP embryo does have a short rostrum but that’s because it’s a basal anurognathid, all of which have a short rostrum at the adult stage. The eyes were actually no larger than those of sister taxa.

The Anurognathidae to scale.

Figure 1. Click to enlarge. The Anurognathidae to scale.

It’s BIG Baby!
To add a twist to this puzzle, this embryo is the size of other adult anurognathids. That means the adult, at 8x larger (based on pelvic opening and eggshell diameters) was several times larger than the largest commonly acknowledged anurognathid. We don’t have an adult of this anurognathid, but we do know from Pterodaustro, Pteranodon, Tupuxuara and Darwinopterus that the hatchlings and juveniles were virtually identical to adults in all pterosaurs, crests and all.

The IVPP embryo

Figure 5. The IVPP embryo scaled to an adult size (based on matching the egg to the pelvic opening diameter, along with various views of the skeleton and an egg and hatchling.

Now to Describe This New Anurognathid
The skull is unknown in the three more primitive sister taxa. Distinct from Dimorphodon, the skull of the IVPP embryo had a smaller naris but was otherwise quite similar. The postorbital was larger. The dentary teeth were relatively larger. The cervical neural spines were shorter. Approximately 10 vertebrae were sacrals. The caudals were reduced to a vestige. The sternum was rectangular. The scapula was shorter. The coracoid ventral stem was not expanded. The metacarpus was longer than in sister taxa. Manual 4.4 was relatively shorter. The pelvis was relatively larger. The ischium and pubis was notched and the ischium was broad. The hind limb and especially the tibia was longer. Pedal 5.1 did not extend to the tip of metatarsal IV.

A Derived Species of a Primitive Clade
The IVPP embryo was a basal protoanurognathid (if Dendrorhynchoides is considered the basalmost anurognathid), yet it survived into the Early Cretaceous. It retained an elongated Dimorphodon-like premaxilla that was V-shaped in palatal view, but it also had a rather elongated metacarpus, whereas most other anurognathids, like Batrachognathus, shortened theirs. The IVPP embryo also had an elongated neck, more like Dimorphodon than Dendrorhynchoides, Peteinosaurus or any of its closests sisters. Thus, the elongated neck, like the elongated metacarpus, appears to be derived. The relative brevity of the toes is matched only by D? weintraubi, another larger-than-normal anurognathid from the Early Jurassic of North America.

And the Eggshell
The eggshell was thinner than in any archosaur or archosauromorph (Deeming and Unwin 2007) and most like that of lizards able to retain the embryo until just before hatching. All current evidence indicates that pterosaur mothers carried their single embryos until just prior to hatching. How ridiculous would it be to expect humming-bird-sized to fly-sized tiny hatchling pterosaurs to crawl through sand or mud after being buried prior to hatching, as Deeming and Unwin (2007) and Grellet-Tinner et al. (2007) proposed under the disproven archosaur paradigm (Bennett 1996b). Tiny pteros were not as tough as little turtles and crocs. Think of their fragile wing membranes.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Deeming C and Unwin DM 2007. Eggshell structure and its implications for pterosaur reproductive biology and physiology. Flugsaurier, the Wellnhofer pterosaur meeting, Munich, 12.
Grellet-Tinner G, Wroe S, Thompson SB and Ji Q 2007. A note on pterosaur nesting behavior. Historical Biology 19:273–277.
Wang X-L and Zhou Z 2004. Palaeontology: pterosaur embryo from the Early Cretaceous. Nature 429: 623.