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

Kayentatherium with 38 tiny hatchlings

Hoffman and Rowe 2018
bring us a large field jacket dotted with 38 tiny hatchlings of Kayentatherium, a tritylodontid synapsid the size of a cat (Figs. 1,2). In this wonderful and unique discovery the authors report, Here we present what is, to our knowledge, the first fossil record of pre- or near-hatching young of any non-mammalian synapsid. The single clutch comprises at least 38 individuals, well outside the range of litter sizes documented in extant mammals. This discoverconfirms that production of high numbers of offspring represents the ancestral condition for amniotes, and also constrains the timing of a reduction in clutch size along the mammalian stem.”

Figure 1. Kayentatherium adult.

Figure 1. Kayentatherium adult. Note the extremely narrow braincase on this herbivore. Note the pelvic opening here moved from the original drawing to provide an opening.

That last statement needs to be taken as conjecture
because we don’t have data for a long list of predecessor taxa going back to Devonian tetrapods. The authors’ statement could be true. On the other hand, the tritylodontids, being derived herbivores, might have created lots of babies, while their omnivore and carnivore ancestors, more in the line of mammal ancestry, laid smaller numbers of larger eggs. We just don’t know. The authors provided one puzzle piece. That’s not enough to make a conclusive statement.

Figure 2. Kayentatherium to scale with hatchling and in matching skull lengths for direct comparison. The orbit is larger, the rostrum and temple are smaller.

Figure 2. Kayentatherium to scale with hatchling and in matching skull lengths for direct comparison. The orbit is larger, the rostrum and temple are smaller.

Then Hoffman and Rowe double down:
The discovery of a large clutch in a stem mammal provides material evidence that producing high numbers of offspring is the ancestral condition for amniotes, and that small litters represent a derived mammalian trait.” Wait a minute… lobe-fin coelacanths embryos hatch within the female and only a few are produced at a time. What happened between coelacanths and tritylodontids? We just don’t have the data for a long list of taxa between these two. Best not to guess and make it sound like scientific canon.

Note the narrow braincase in Kayentatherium,
slightly narrower than in ancestors, like Sinoconodon (Fig. 3) and basal mammals, like Sinodelphys. A U of Texas article (ref. below) reports, “The 3D visualizations Hoffman produced allowed her to conduct an in-depth analysis of the fossil that verified that the tiny bones belonged to babies and were the same species as the adult. Her analysis also revealed that the skulls of the babies were like scaled-down replicas of the adult, with skulls a tenth the size but otherwise proportional. This finding is in contrast to mammals, which have babies that are born with shortened faces and bulbous heads to account for big brains.”

Figure 2. Sinoconodon skull(s) showing some variation in the way they were drawn originally.

Figure 3 Sinoconodon skull(s) showing some variation in the way they were drawn originally. Note the relatively large brains on this more primitive taxon.

“The discovery that Kayentatherium had a tiny brain and many babies, despite otherwise having much in common with mammals, suggests that a critical step in the evolution of mammals was trading big litters for big brains, and that this step happened later in mammalian evolution. ‘Just a few million years later, in mammals, they unquestionably had big brains, and they unquestionably had a small litter size,’ Rowe said.”

Actually brains stayed relatively small
until we get to more recent prototheres, more recent metatheres (by convergence) and more recent placentals (again, by convergence). Check out the following basal mammal taxa for cranium ‘narrowness’

  1. Sinodelphys
  2. Brasilitherium
  3. even Didelphis

Extant echidnas and platypuses, have bulbous skulls filled with brains, but not so their Cretaceous ancestors, Cifelliodon and Akidolestes.

To show that cranium width can narrow
or become relatively smaller in highly derived placental mammals check out the following taxa:

  1. Andrewsarchus
  2. Equus
  3. Lophiodon

So the skull can balloon, or narrow, depending on the situation over millions of years.

According to the authors, the skull length of a hatchling
was 1/20 that of an adult with an isometric rostrum and a smaller, allometric, temporal fenestra. Is that correct? See for yourself (Fig. 2). It looks like the orbit was larger, while the rostrum and temple were both smaller. Hate to nit-pick, but there you are…

Again, this was a wonderful find and a great presentation.
We just don’t want to get ahead of ourselves after one discovery, when other hypotheses are currently possible and now on the table.

References
Hoffman EA and Rowe TB 2018. Jurassic stem-mammal perinates and the origin of mammalian reproduction and growth.

utexas.edu/mammal-forerunner-sheds-light-on-brain-evolution

Kiwi ancestors

Worthy et al. 2013 reported:
“Until now, kiwi (Apteryx owenii, Apterygidae, Shaw 1813; Fig. 1) have had no pre-Quaternary fossil record to inform on the timing of their arrival in New Zealand or on their inter-ratite relationships.” They described two fossils (femur and quadrate) from the Early Miocene (Fig. 1; 19–16mya) which they named Proapteryx. “The new fossils indicate a markedly smaller and possibly volant bird, supporting a possible overwater dispersal origin to New Zealand of kiwi independent of moa. If the common ancestor of this early Miocene apterygid species and extant kiwi was similarly small and volant, then the phyletic dwarfing hypothesis to explain relatively small body size of kiwi compared with other ratites is incorrect.

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

Figure 2. Jurapteryx, Pseudocrypturus, Apteryx and Proapteryx to scale. In lateral view it is difficult to see the width of the ventral pelvic elements. They are not as wide as the egg diameter. Note the lack of a pygostyle in all three taxa.

By contrast
the large reptile tree (LRT, 1213 taxa) nest the kiwi with Pseudocrypturus (Houde 1988; Early Eocene) apart from other ratites, as the basalmost birds with living representatives.

Apteryx owenii (Shaw 1813) The extant flightless kiwi has an elongate naris that extends to the tip of its beak. Maybe two teeth are there. Here it nests with Pseudocrypturus, but flightless traits push it toward Struthio, by convergence. in the pre-cladistic era, Calder (1978, 1984) considered the kiwi a phylogenetic dwarf derived from the larger moa, but that was invalidated by Worthy et al. 2013 and the large reptile tree.

Proapteryx micromeros (Worthy et. al. 2013) was a slender, tiny Miocene (18 mya) ancestor likely capable of flight.

Pseudocrypturus cercanaxius (Houde 1988; Early Eocene) was originally considered a northern hemisphere ancestor to ratites (like the ostrich, Struthio). Today these primitive flightless birds are chiefly restricted to the southern hemisphere. It could be that early birds did start in the South and had migrated to the North during the Paleocene (66-56 mya).

Since ratites are basal to extant birds, and Pseudocrypturus is basal to ratites (paleognaths), Pseudocrypturus is also quite similar to the ancestor of all extant birds despite its late appearance in the early Eocene. Perhaps something very much like it was one of the few survivors of the K-T extinction event.

It’s notable that Pseudocrypturus has long legs. Early ducks, like Presbyornis, and basal raptors, like Sagittarius, also had long legs. Evidence is building that this is the primitive condition for the clade of living birds arising from the K-T extinction event.

Worthy et al. nest Apteryx
within the order Casuariiformes, which includes cassowaries, emirs, and kiwi, but only in the absence of Pseudocrypturus.

The kiwi egg vs ventral pelvis issue
In most tetrapods, including humans, the egg/baby passes through the cloaca/vagina which passes through the two ischia. That was also likely the case with Archaeopteryx, because this is also the case with Gallus the chicken. In extant birds the ischia posterior tips no longer touch, but are widely separated. Going several steps further, in the kiwi the enormous egg is held in front of the pubis (Fig. 1), which is also in front of the ischia.

The following video of a kiwi laying an egg
shows the cloaca a substantial distance below the swirl that marks its tail. kiwi egg video click to play pretty much located at the tip of the long axis of the egg in figure 1 (maybe a little higher/closer to the tail).

Figure 2. Kiwi laying an egg. Click to play.

Figure 2. Kiwi laying an egg. Click to play.

In the LRT
Pseudocrypturus and Apteryx (Fig. 1) nest together and apart from the ratites. Pseudocrypturus is basal to all living birds. It probably first appeared in the Early Cretaceous. It was found in the Paleocene.

References
Calder WA 1978. The kiwi. Scientific American 239(1):132–142.
Calder WA 1984. Size, function and life history. 448 pp. Cambridge (Harvard U Press).
Houde PW 1986. Ostrich ancestors found in the northern hemisphere suggest new hypothesis of ratite origins. Nature 324:563–565.
Houde PW 1988. Paleognathus birds from the early Tertiary of the northern hemisphere. Publications of the Nuttall Ornithological Club 22. 147 pp.
Shaw 1813. Naturalist’s Miscellany 19:
Worthy, TH. et al. (5 coauthors) 2013. Miocene fossils show that kiwi (Apteryx, Apterygidae) are probably not phyletic dwarves. Paleornithological Research 2013, Proceedings of the 8th International Meeting of the Society of Avian Paleontology and Evolution. Retrieved 16 September 2017.

wiki/Pseudocrypturus
wiki/Apteryx, Kiwi
wiki/Proapteryx

Tachyglossus, the other egg-laying mammal

Figure 1. The echidna (genus: Tachyglossus) in life. This slow-moving spine-covered anteater has digging claws.

Figure 1. The echidna (genus: Tachyglossus) in life. This slow-moving spine-covered anteater has digging claws.

Tachyglossus aculeatus (Shaw 1792) is the echidna and the only other genus of egg-laying mammal. It protects itself with sharp spines and has a long, ant-catching tongue. The hands and feet are adapted to digging with short, almost immobile proximal elements (Fig. 3) and long claws. Prepubic bones precede the pubis. A proximal process sits atop the fibula. The leathery snout without whiskers is sensitive to vibrations.

Figure 2. The skull of Tachyglossus is largely fused together, lacks teeth and has no lateral temporal fenestra (because the jaws don't move much in this anteater.

Figure 2. The skull of Tachyglossus is largely fused together, lacks teeth and has no lateral temporal fenestra (because the jaws don’t move much in this anteater. Hard to find sutures here. Let me know if you have better data to make corrections.

Distinct for its sister,
Ornithorhynchus, and many other mammals, the acetabulum is perforated. The lateral temporal fenestra is absent. So are the teeth. Like the hedgehog, the echidna can roll itself into a ball for protection.

Figure 3. Tachyglossus skeleton, manus and x-rays. Note the perforated pelvis.

Figure 3. Tachyglossus skeleton, manus and x-rays. Note the perforated pelvis.

There are those
who say characters define a taxon. We have to get away from that hypothesis. Here a perforated acetabulum would make Tachyglossus a dinosaur, to the late Larry Martin’s delight. Tachyglossus has no temporal fenestra. So, does that make it an anapsid? No. The only thing that tells us what a taxon is… is its placement on a wide gamut cladogram that tests hundreds of candidate sister taxa and hundreds of traits. Testing a suite of several hundred traits in a wide gamut study is the only way to confidently determine taxonomy and avoid the pitfalls of convergence and taxon exclusion that plague smaller studies that too often fail to minimize false positives and ‘by default’ nestings. And some DNA studies cannot be validated, except by morphological studies.

References
Shaw G 1792. Musei Leveriani explicatio, anglica et latina.

wiki/Tachyglossus

Meiolania eggs confirm basal turtle status

Earlier the horned turtles, Meiolania and Niolamia, were nested in the large reptile tree (LRT) as basalmost hardshell turtles, closely related to the toothed horned stem turtle/pareiasaur, Elginia. This was heresy when introduced.

Now
newly discovered turtle eggs (Lawver and Jackson 2016) add evidence to the basal status of Meiolania.

From the Lawver and Jackson 2016 abstract:
“A fossil egg clutch from the Pleistocene of Lord Howe Island, Australia that we assign to Testudoolithus lordhowensis, oosp. nov. belongs to the stem turtle Meiolania platyceps.  Thin sections and scanning electron microscopy demonstrate that these eggs are composed of radiating acicular aragonite crystals. This mineral composition first evolved either before the split between Meiolaniformes and crown Testudines or prior to Proterochersis robusta, the earliest known stem turtle. Meiolania platyceps deposited its eggs inside an excavated hole nest. This nesting strategy likely evolved no later than the Early to Middle Jurassic.”

All known meiolanids
are from later, higher Late Cretaceous and Tertiary strata.

Figure 5. Meiolania, the most primitive of known turtles, has lateral forelimbs, like non turtles.

Figure 1. Meiolania, one of the most primitive of known hard-shell turtles, has lateral forelimbs, like non turtles. All extant turtles have anteriorly-directed humeri. It also had cranial horns, like the toothed pareiasaur/turtle? Elginia.

At present,
soft-shell and hard-shell turtles have a dual origin from separate small Late Permian and Middle Triassic pareiasaur ancestors, Elginia and Sclerosaurus. Both were also horned. The traditional earliest known turtles, Proganochelys and Odontochelys are both known from later, Late Triassic, strata.

Not on topic, but worth watching on YouTube:
Here’s a video about the origin of oil in the Jurassic. It runs for 90 minutes and is fascinating throughout. The video reminds us what a recent Golden Age we currently live in based on a limited supply of petroleum products. The video concludes we have long passed the tipping point for climate change based on the flood of cheap energy. And the end of the oil age is something our children will see. Ironically, climate change in the ice-free Jurassic was one factor in the Earth producing the oil we now use.

References
Lawver DR and Jackson FD 2016. A fossil egg clutch from the stem turtle Meiolania platyceps: implications for the evolution of turtle reproductive biology. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1223685.

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

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.