My what big teeth you have!! Introducing Guidraco

Guidraco venator (Wang et al., 2012) IVPP V17083, ~38 cm skull length, is a new crested ornithocheirid from the Lower Cretaceous of China. It was correctly nested as a sister to Ludodactylus and shared many traits with it and its many toothed South American sisters, like Anhanguera and Cearadactylus, but Guidraco is also a more distant sister to Liaoningopterus from ChinaAn upright crest and enormous anterior teeth set Guidraco apart from the others.

Guidraco in situ

Figure 1. Guidraco in situ from Wang et al. 2012. The extent of the parietal shown here may have something to do with a displaced underlying bone, like a postorbital creating an outline.

Reconstruction
Guidraco was so well preserved that very little reconstruction is necessary. The upper temporal fenestra was large, probably in association with the enlargement of the premaxillary teeth, probably to oppose the pulling vectors brought on by the teeth during prey capture. In ornithocheirid skulls bones often fuse together obliterating sutures. Some of these identifications are based on comparisons to sister taxa.

Guidraco skull reconstructed.

Figure 2. Guidraco skull reconstructed. Not changes with the original in figure 3.

Original Reconstruction
The reconstruction by Wang et al. 2012 includes minor difference from the present reconstruction. Contra the original reconstruction, the premaxilla includes four teeth, including the medial nubbin. The nasal extends further than originally reconstructed, laminated beneath the premaxilla. A stem-like nasal process was present in the antorbital fenestra. Vestigial nares (primary and secondary were present) attended by anterior laminated extensions of the jugal and nasal. The quadratojugal extended up the lateral quadrate, as in other pterosaurs. The upper temporal fenestra and parietal were taller. This matches the shape of the occiput. The postorbital overlapped the squamosal as in other pterosaurs. A postfrontal is present. The sclerotic ring was not so robust.

Original reconstruction by Wang et al. (2012).

Figure 3. Original reconstruction by Wang et al. (2012). Please note several distances.

A Pteranodontoid?
Wang et al. (2012) nested Guidraco and all other ornithocheirids with Pteranodon in a clade called Pteranodontoidea. This odd nesting of toothless with toothy taxa is a product of taxon exclusion. When more taxa are included, as in the large pterosaur tree, ALL the pterosaurs with a pointed rostrum nest together and apart from the toothy ornithocheirids, who find more parsimonious sister nestings with Cycnorhamphus and Scaphognathus, along with several tiny pterosaur intermediates.

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
Wang X-L, Kellner AWA, Jiang S-X and Cheng X 2012. New toothed flying reptile from Asia: close similarities between early Cretaceous pterosaur faunas from China and Brazil. Naturwissenschaften in press. doi:10.1007/s00114-012-0889-1.

wiki/Ludodactylus
wiki/Guidraco

The Insights of Dietrich Schaller

Figure 1. Zittel's (1882) interpretation of the Zittel wing , narrow to the elbow (the body was added).

Beyond all reason, the shape of pterosaur wings and their connection to the hind limb form continuing arguments.

Zittel 1882
Karl von Zittel (1882) provided early insight with the discovery of a perfectly preserved Rhamphorhynchus wing and his precise interpretation of it  (Fig. 1) – narrow to the elbow. The negligible extension to the left knee (rather than mid-thigh, as shown on the right wing) is forgivable).

Schaller 1983
One hundred years later, the next scientist who understood that Zittel (1882) was correct, was Dietrich Schaller (1983, 1985, 2007) who carefully studied and interpreted the materials, but was largely ignored by the vast majority of pterosaur workers.

Interpretations of pterosaur wings by Dietrch Schaller (2007).

Figure 2. Interpretations of pterosaur wings by Dietrch Schaller (2007).

Insights
Schaller (2007) studied and illustrated (Fig. 2) several pterosaur specimens with well-preserved wing membranes and found a remarkable consistency in their shape. All were stretched between the wingtip and elbow and consisted of various zones, which he color-coded. None overextended the elbow. All demonstrate a slight spoon shape at the tip. Schaller (2007) illustrated uropatagia stretched between the tail and hind limb, rather than between the hind limbs as others illustrated it based on the false interpretations of Sharov (1971) and Unwin and Bakhurina (1994). Schaller (2007) also illustrated the hind limb fully and laterally extended, as in Sharovipteryx. This provided a horizontal stabilizer, as in modern airplanes, that would have provided sufficient lift to the hind limbs to keep them laterally extended without effort.

Vienna specimen of Pterodactylus.

Figure 3. The Vienna specimen of Pterodactylus in situ from Elgin, Hone and Frey 2011. Click to see the specimen.

Oversights
Following established (but false) paradigms, Schaller (2007) illustrated the uropatagium (in orange, Fig. 2) extending to the tip of the fifth toe, but there is no evidence of this. The uropatagium extended only to the ankle. The fifth toe was hinged and extremely thin. It would not have made a good uropatagium stretcher.

Schaller (2007) illustrated the fuselage fillet (“plagiopatagium” in royal blue) oriented toward the knee, rather than mid thigh with a very thin anterior extension to the ankle. Such an extension would not have been aerodynamically desirable, but reflects a remnant of the paradigm of the deep chord hypothesis. Strangely, Schaller (2007, Fig. 2) did not illustrate the fuselage fillet in Rhamphorhynchus and Pterodactylus, where it is most clearly preserved (Fig. 3).

Even so
Others have ignored his work, but Schaller deserves credit (as I gave him in Peters 2002) for keeping the valid Zittel wing shape hypothesis alive. Early work (Schaller 1985) interpreting Sordes was marred (he gave it a flying squirrel-like wing membrane), but corrected in Schaller (2007, Fig. 2) and for this he also deserves credit.

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
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Schaller D 1983.
Nuebeschreibung des Pterosaurierflügels. Zoologisches Institut der Universitätt München.
Schaller D 1985. Wing Evolution. In: Hecht M, Ostrom JH, Viohl G and Wellnhofer P eds. The Beginning of Birds. Proceedings of the International Archaeopteryx Conference, Eichstätt 1984, (Freundes Jura Museum, Eichstätt), 333–348.
Schaller D 2007. The superordinate Pterosaur Evolution as deduced from the Evolution of their Wings. On the occasion of The Wellnhofer Pterosaur Meeting, Munich 2007, Verlag Dr. Friedrich Pfeil, Munchen. on sale
Sharov AG 1971. New flying reptiles fro the Mesozoic of Kazakhstan and Kirghizia. Trudy of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.
Zittel KA 1882. Über Flugsaurier aus dem lithographischen Schiefer Bayerns. Palaeontographica 29: 7-80.

Highly Aberrant Anurognathid? from Foth et al. 2012

A welcome and recent paper on pterosaur skull morphospace found the anurognathid skull of Bennett (2007) to be “highly aberrant” an “outlier” and “highly divergent.” How can this happen when evolution is supposed to be a gradual process?

Guys, the Bennett anurognathid reconstruction is WRONG!
As I blogged earlier, it’s an invented, imagined monster misidentifying the toothy maxilla as the purported super-sized and preserved edge-on sclerotic ring  among several other problems all detailed here.

A correct skull would nest closer to the morpho-cloud of the other pterosaurs. Several anurognathid skulls, including more primitive taxa, would show the developmental path from basal taxa, no doubt finding its base deeper within the morphospace cloud.

Frustrating.

And timely…
A recent blog featured the vampire pterosaur, Jeholopterus. This opened comment on the Dinosaur Mailing List, most of it negative. Some comments recalled earlier mistakes I made using the DGS technique. To these people early mistakes ruin the DGS technique for all time. Is this prejudicial? Just because I stole a Twinkie in grade school does not (or does it?) brand me a thief for all time. IMHO it would be better if every incidence was judged independently, on its own merits. That would be more scientific. That’s how I operate. Credit where credit is due. Criticism where criticism is due.

As noted above, the DGS technique enabled the identification of every bone in the skull of the flat-headed pterosaur – and their symmetrical counterparts – and all these bones all fit well within standard anurognathid skull patterns. In counterpoint the Bennett reconstruction broke ALL the rules. Some bones he reports he had to invent.

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
Bennett SC 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81(4):376-398.
Foth C, Brusatte SL and Butler RJ 2012.
Do different disparity proxies converge on a common signal? Insights from the cranial morphometrics and evolutionary history of Pterosauria (Diapsida: Archosauria). Journal of Evolutionary Biology (advance online publication) doi: 10.1111/j.1420-9101.2012.02479.x

Mystery Ptero Tracks from Wenxiyuan

Xing et al. (2012) recently reported on a set of narrow-footed and narrow-gauge pterosaur tracks from the Early Cretaceous of China accompanied by quite large manus impressions. Xing et al. (2012) reported, “The pterosaur tracks are assigned to Pteraichnus isp. and were probably made by a small to medium-sized pterodactyloid.” Unfortunately they could be no more specific, but to their credit, did compare the tracks to those of Haenamichnus in the text, which can be attributed by shape and size to a member of the Azhdarchidae. [isp. = ichnospecies]

The narrow foot and short toes of the Wenxiyuan tracks point immediately to the azhdarchid line (Peters 2011). The large size of the manus compared to the foot points to Chaoyangopterus, also from the Early Cretaceous of China. Not much else to say. It’s a pretty good match for a relatively poor track. Of the manus, only the fingertips are impressing here apparently. That’s okay. The fingers were not load bearing.

Wenxiyuan pterosaur tracks.

Figure 1. Image of Chaoyangopterus to scale with newly reported Wenxiyuan pterosaur tracks. It's a good match.

If you want to see how quadrupedal pterosaurs like Chaoyangopterus walked, click here.

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
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification
Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Xing L-D, Harris  JD, Gierliński GD,  Gingras MK, Divay JD, Tang Y-G and Currie PJ 2012. Early Cretaceous Pterosaur tracks from a “buried” dinosaur tracksite in Shandong Province, China. Palaeoworld (advance online publication)
http://dx.doi.org/10.1016/j.palwor.2012.02.004
http://www.sciencedirect.com/science/article/pii/S1871174X12000054?v=s5

Speciation in Darwinopterus

Current thinking in Darwinopterus separates the crestless female (with the egg between her legs) from the crested (with no egg nearby) purported male(s).

The Local Heretic agrees that the one with the egg is a female, but the female does not appears to be conspecifc with the other specimens attributed to Darwinopterus (Figs. 1 and 2). Some had a longer skull. Some had a distinct pelvis. Some had a distinct humerus. Others displayed a subtle variety of modifications throughout the body (Fig. 2).

The Pelvis
Lü et al. (2011a) did not reconstruct the crushed pelves of the various darwinopterids, so their assertion that the pelvis of the female has not been substantiated. I have found no deepening/reduction of the pelvis in any pair of otherwise identical pterosaurs. All differences reflect distinct traits elsewhere in the skeleton, denoting specific and generic differences, not gender differences.

While Darwinopterus is often preserved in excellent articulated condition, some specimens are crushed dorsoventrally or otherwise imperfect, making certain traits difficult to compare. Even so, the darwinopterids illustrated here are each distinct from one another. Kunpengopterus, with its relatively small skull, was closest to the outgroup taxon, Pterorhynchus.

Figure 1. Darwinopterids and their closest sisters in phylogenetic order beginning with Sordes. Click to enlarge.

Take a Closer Look at the Feet
Placed side-by-side Darwinopterus pedes display traits that separate them into distinct species. Some elements are longer, others are shorter. Each is distinct. No two look to be close enough to represent separate genders.

Darwinopterus pedes

Figure 2. Darwinopterus pedes demonstrating speciation in the proportions of phalangeal elements. The metatarsal spread was likely variable from moment to moment.

To Lump? Or Split?
A similar lump/split problem appears in GermanodactylusPterodactylusRhamphorhychus and Pteranodon, among others. Sometimes paleontologists lump inappropriately. Sometimes they split inappropriately. It was forgivable prior phylogenetic analysis when specimens arrived one at a time and infrequently. Now, however, every new specimen has to be nested.

The Value of Reconstructions
None of the various darwinopterids published so far have been reconstructed by those who had access to the specimens and contributed to those papers. Perhaps only reconstructions can illuminate these important differences, if only because they force a closer look at each specimen. It is also important to always nest each new specimen with cladistic analysis. Unfortunately reconstructions are rarely (if ever) produced nowadays. And details, like the proportions of pedal elements, are typically ignored. Analyses typically lump specimens together a priori rather than let each one stand alone for more precision and less compromise.

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
Lü J, Unwin DM, Jin X, Liu Y and Ji Q 2009. Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society London B  (DOI 10.1098/rspb.2009.1603.)
Lü J, Unwin DM, Deeming DC, Jin X, Liu Y and Ji Q 2011a. An egg-adult association, gender, and reproduction in pterosaurs. Science, 331(6015): 321-324. doi:10.1126/science.1197323
Lü J, Xu L, Chang H and Zhang X 2011b. A new darwinopterid pterosaur from the Middle Jurassic of Western Liaoning, northeastern China and its ecological implicaitions. Acta Geologica Sinica 85: 507-514.

wiki/Darwinopterus

The Tiniest Wasp vs. The Tiniest Pterosaur Hatchling


Fairy Fly (Wasp)

Figure 1. Fairy Fly (Wasp) compared to two single-celled creatures, a paremecium and an amoeba.

The world’s smallest insect, one of the family of Fairy Wasps (or Fairy Flies ) has a body length of only 0.139 mm. I found the image of this Fairy Wasp alongside two single-celled animals (Fig. 1) to be fascinating and wondered how they would compare to the hypothetical hatchling of the world’s smallest pterosaur  B St 1967 I 276 (No. 6 in the Wellnhofer 1970 catalog (Fig. 2)), ostensibly the world’s smallest flying vertebrate.

A hypothetical hatchling No. 6

Figure 2. A hypothetical hatchling No. 6 (one-eighth the size of the adult) alongside a fly, a flea and the world's smallest insect, a fairy fly (fairy wasp). The fairy wasp is shown enlarged here (scaled in red) and to scale (barely visible). The fairy fly is enlarged in figure 1.

Every Picture Tells a Story
And this picture tells it all. A hatchling No. 6 would have been easy prey for a house fly, which is one more reason why such hatchlings may have preferred to hide and not fly. The first reason was the threat of desiccation blogged earlier due to a high surface to volume ratio (Hedges and Thomas 2001). Thankfully enough of these tiny pterosaurs survived the Late Jurassic to give rise to the several giant spectacular tapejarids and pteranodontids of the Cretaceous, all descendants of these tiny “fly cookies.”

References
Hedges SB and Thomas R 2001. At the Lower Size Limit in Amniote Vertebrates: A New Diminutive Lizard from the West Indies. Caribbean Journal of Science 37:168–173.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

The T-rex Collagen Controversy

Soft Tissue, Blood Vessels and Blood Cells in a T-rex Femur?
Mary SchweitzerJack Horner and others made headlines in 2005 when she reported soft organic tissue deep within the femur of a Tyrannosaurus rex (Fig. 1). MSNBC, Scientific American and National Geographic covered this story on the web.

Tyrannosaurus

Figure 1. Tyrannosaurus, the dinosaur at the center of the controversy.

The Creationists jumped all over this news  asserting that T-rex was much, much younger.

Here I offer a belated tip of the hat to friend and fellow heretic, Tom Kaye, who showed me his heretical work several years ago while still living in Chicago. Let me state from the start, I’m only pushing competing hypotheses together here. I have not done the testing to weigh in on one side or the other.

Maybe Not…
Kaye, Gaugler and Sawlowicz (2008) reinterpreted the purported collagen as bacterial biolfilms. They reported, “Mineralized and non-mineralized coatings were found extensively in the porous trabecular bone of a variety of dinosaur and mammal species across time. They represent bacterial biofilms common throughout nature. Biofilms form endocasts and once dissolved out of the bone, mimic real blood vessels and osteocytes. Bridged trails observed in biofilms indicate that a previously viscous film was populated with swimming bacteria. Carbon dating of the film points to its relatively modern origin. A comparison of infrared spectra of modern biofilms with modern collagen and fossil bone coatings suggests that modern biofilms share a closer molecular make-up than modern collagen to the coatings from fossil bones. Blood cell size iron-oxygen spheres found in the vessels were identified as an oxidized form of formerly pyritic framboids.” 

This represents a more conservative and rational explanation for the collagen-like structures found in fossil bone. Kaye says that his team was denied access to the original bone, and that continues to this day. Others are in line ahead of him, is what he hears.

When This News Came Out
Several blogs weighed in on the find of the century now reduced to a major controversy. Smithsonian.com reported on both sides of the controversy, concluding, “Personally, I’m leaning toward believing in the extraordinary.” …and Occam’s Razor just took a walk.

Carl Zimmer.com reported, “Schweitzer’s tubes and osteocytes, they argue, are not blood vessels or cells but biofilms formed by bacteria that invaded the fossils after death. In a paper published Monday in the journal PLoS ONE, Kaye and colleagues report that carbon dating of one sample shows that the tubes are at most a few decades old and that their infrared spectra give a closer match to bacterial biofilms than to collagen. Troughs in the walls of the tubes resemble the track a microbe would make crawling through a biofilm, they note. ‘We think that’s one of the smoking guns,’ Kaye says.”

Contradicting Kaye’s Team and Supporting Schweitzer’s Conclusion…
Peterson, Lenczewski and Scherer 2010 reported, “The identification of biomolecules in fossil vertebrate extracts from a specimen of Brachylophosaurus canadensis has shown the interpretation of preserved organic remains as microbial biofilm to be highly unlikely. Results of the study indicate that the crystallization of microbial biofilms on decomposing organic matter within vertebrate bone in early taphonomic stages may contribute to the preservation of primary soft tissues deeper in the bone structure.

And Another… 
San Antonio et al. (2011) reported, “Functionally significant regions of collagen fibrils that are physically shielded within the fibril may be preferentially preserved in fossils. This non-random distribution supports the hypothesis that the peptides are produced by the extinct organisms and suggests a chemical mechanism for survival.”

Then Salzberg et al. (2011) Struck Back with Metagenomics…
In their JVP abstract Salzberg et al. (including Tom Kaye, 2011) recovered  a full characterization of the DNA from a section of Brachylophosaurus canadensis fossil using ‘Metagenomics’ techniques. Soft tissue structures similar to those reported as dinosaurian blood vessels and bone cells were observed providing the platform for analyzing the molecular content of this fossil further. Metagenomics data identified ALL the DNA in the sample giving proportionate ranks to the various molecular species therein. The sample was processed to isolate organic remnants from the intravascular cavities of the fossil’s cortical bone, in order to exclude possible contaminants from the bone surface. DNA from various species of bacteria, plants, fungi, and chordates was detected in the bone. Some modern bird DNA was also found. The presence of modern DNA provided an obstacle to identifying ancient dinosaur molecules. The bacterial DNA provided support for the production of biofilms over the 80-million-year age of the fossil.

The Salzberg findings also came up with a more complete proteome of the ostrich and the previously reported “T. Rex proteins” now found a perfect match in the ostrich sequence suggesting contamination on Schweitzer’s part. The same was true of unreported hemoglobin proteins in the Schweitzer data that also turned out to be a perfect match to ostrich.

A Paleo Fight
There is a paleontological fight going on here. Both opposing hypotheses can’t be right. The opposing forces need to get together and not wait several years between successive arguments. Heretics are sometimes right. Those who test assertions should be considered.

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
Kaye TG, Gaugler G and Sawlowicz 2008. Dinosaurian Soft Tissues Interpreted as Bacterial Biofilms. PLoS ONE 3(7): e2808. doi:10.1371/journal.pone.0002808
Peterson JE, Lenczewski ME, Scherer RP 2010. Influence of Microbial Biofilms on the Preservation of Primary Soft Tissue in Fossil and Extant Archosaurs. PLoS ONE 5(10): e13334. doi:10.1371/journal.pone.0013334
Salzberg S et al. 2011 abstract. DNA, dinosaurs and metagenomics: a new tool for mass identification of DNA from fossil bone. Journal of Vertebrate Paleontology abstracts 2011.
San Antonio JD, Schweitzer MH, Jensen ST, Kalluri R, Buckley M, et al. 2011. Dinosaur Peptides Suggest Mechanisms of Protein Survival. PLoS ONE 6(6): e20381. doi:10.1371/journal.pone.0020381
Schweitzer MH, Wittmeyer JL, Horner JR, Toporski JK 2005. Soft-tissue vessels and cellular preservation in Tyrannosaurus rex. Science 307: 1952–1955.

An Egg for Quetzalcoatlus

After the discovery of at least 4 and maybe 5 pterosaur eggs, now we know their pattern. Based on pelvic diameter, we know the maximum diameter of an egg. The length and shape varies: longer for long-snouted taxa. Hatchlings were 1/8 the size of adults, based on egg size and the example of the embryo Pterodaustro. Hatchlings were virtual copies of adults (contra traditional thinking).

A Hypothetical Egg for the Largest of all Pterosaurs 
Quetzalcoatlus, the largest pterosaur, would have laid the largest pterosaur egg. Figure 1 portrays the Q. sp. smaller version and a 2.3x larger hypothetical Q. northropi pelvis associated with a 0.12x hatchling tucked into an egg shape. It’s no surprise that the hypothetical diameter of an egg that would contain the hatchling exactly matches the pelvic opening. The egg of Quetzalcoatlus would have been elongated to contain the elongated skeletal elements. Within the pelvis, such an egg would have extended anterior to the prepubes.

 Quetzalcoatlus eggs

Figure 1. Quetzalcoatlus northropi and Q. sp. to the same scale alongside hypothetical eggs and hatchlings one-eighth as tall as the adult in each case. Q. northropi was 2.3x as large as the smaller, more complete, unnamed species. This image is to the same scale as the ostrich in Figure 2.

Compared to the Ostrich
The largest living bird, the ostrich, provides some comparison. The ostrich is the largest bird and it produces the largest egg, but that egg is the smallest relative to adult size. Figures 1 and 2 are to the same scale. The large Quetzalcoatlus egg would have been smaller in diameter than the ostrich egg, but 2.5x longer. Longer eggs are possible when the shell is extremely thin and relatively pliable, like those of snakes and lizards.

Ostrich egg

Figure 2. The ostrich is the largest bird and it produces the largest egg, but it is the smallest egg relative to the adult size.

Hypothetical Details of the Quetzalcoatlus Embryo
With the examples of other pterosaur eggs, we should expect the proportions of the Quetzalcoatlus hatchling to match those of the parent. In order to cram in the long beak, long, stiff neck and elongated metacarpals, the containing egg has to be long. As in other reptiles, the jaws would have been tipped down, pressed against the ventral neck. The eyes would have been relatively no larger than in the adult. The jaws would have been no shorter than in the adult. The legs would have been tucked up against the torso and the feet would have been hyperflexed.

 Quetzalcoatlus embryo and egg.

Figure 3. Quetzalcoatlus embryo and egg. The elongated shape and soft, thin shell were needed to encompass the elongated beak, neck and metacarpals.

The Benefit of Being a Lizard
As lizards, pterosaurs could have retained their eggs within the mother until embryonic development was complete. Perhaps only one was produced at a time. A hatchling would have been large enough and well-developed enough (following the pattern of several smaller pterosaur embryos) to be able to fly.

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
Kellner AWA and Langston W 1996. Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from late Cretaceous sediments of Big Bend National Park, Texas. – Journal of Vertebrate Paleontology 16: 222–231.
Lawson DA 1975. Pterosaur from the latest Cretaceous of West Texas: discovery of the largest flying creature. Science 187: 947-948.

wiki/Quetzalcoatlus
Tetrapod Zoology blog; Why-azhdarchids-were-giant-storks

The Odd Swimming Sphenodontids

Updated November 11, 2014 with the Dnesting of pleurosaurs with Megachirella and Marmoretta. And updated December 3, 2014 with the division of the pleurosaurs into two convergent clades. 

Hard to believe that our favorite New Zealand “Living Fossil,” Tuatara (Sphenodon), had some aquatic sisters, but here they are.

Figure 1. Pleurosaurus and Palaeopleurosaurus to scale with sisters.

Figure 1. Pleurosaurus and Palaeopleurosaurus to scale with sisters.

Pleurosaurus goldfussi (Meyer 1831), Late Jurassic. 60 cm in length. The Triassic terrestrial sphenodontians produced a Late Jurassic marine lineage known as the pleurosaurs after the first of these to be discovered, Pleurosaurus and also one of the most derived. Palaeopleurosaurus appears to be a stretched out version of its terrestrial antecedent, Planocephalosaurus, and was a transitional form to later, longer, more streamlined pleurosaurs.

Added Dec 03, 2104: > That was the traditional nesting. New analyses indicate that Pleurosaurus nested between Palaegama, Megachirella and Marmoretta at the base of the Lepidosauria, which radiated in the Middle to Late Permian. Palaeopleurosaurus had a convergent return to an aquatic niche as it nested between Gephyrosaurus and Planocephalosaurus. The similar Ankylosphenodon was a sister taxon.

Figure 2. Pleurosaurus and Palaeopleurosaurus skulls compared to those of sister taxa.

Figure 2. Pleurosaurus and Palaeopleurosaurus skulls compared to those of sister taxa.

Pleurosaurs were Late Jurassic aquatic sphenodontids, characterized by a long, streamlined and elongated body (with a short neck), small limbs and (as in most aquatic reptiles) nares that were displaced from the snout tip to closer to the orbits. The premaxilla of Palaeopleurosaurus was ventrally elongated to form a sharp spike that would have snared prey. They swam with snake-like undulations of the entire body. Their neural spines grew to become large rectangles, as in snakes. Pleurosaurs produced no Cretaceous descendants.

There is not much that is controversial about these lepidosaurs. They are not often studied and they are rarely on anyone’s Top 10 list, so I thought I’d toss them out for a little publicity.

Added Dec. 03, 2014: > Well, perhaps I spoke too soon as the two traditional pleurosaurs are not that closely related to one another. That’s a little bit of news!

References
Carroll RL 1985. A pleurosaur from the Lower Jurassic and the taxonomic position of the Sphenodontids.
Fraser NC and Sues H-D 1997. In the Shadows of the Dinosaurs: early Mesozoic tetrapods. Cambridge University Press, 445 pp. Online book.
Heckert AB 2004. Late Triassic microvertebrates from the lower Chinle Group (Otischalkian-Adamanian: Carnian), southwestern U.S.A. New Mexico Museum of Natural History and Science Bulletin 27:1-170.
Meyer H 1831. IV Neue Fossile Reptilien, aud der Ordnung der Saurier.

wiki/Planocephalosaurus
wiki/Pleurosaurus

The Evolution of Estemmenosuchus – The Gargoyle of the Permian

The skull of Estemmenosuchus,

Figure 1. The skull of Estemmenosuchus, the most bizarre reptile of the Permian. Image from Wikimedia Commons.

Estemmenosuchus cover

Figure 2. Estemmenosuchus cover. Click to see the rest of the book.

Estemmenosuchus mirabilis was one of the most baroque, grotesque, bizarre and hellzapoppin’ reptiles of all time. In 1991 I chose it as the cover creature for A Gallery of Dinosaurs & Other Early Reptiles. Those bony horns above the eyes and those bony bosses jutting out from the cheeks must have been fearsomely AWESOME in life.

So, how does a reptile like Estemmenosuchus (Tchudinov 1965) come to be? Cladistic analysis provides the answer. Every paleontologist knows that Estemmenosuchus was a synapsid, a therapsid and a dinocephalian. What we’re going to do today is point the finger at several specimens in its ancestral lineage.

The beauty of having a very large reptile tree is being able to trace the ancestry of any taxon all the way back to Ichthyostega. In this way we can also trace the evolution of any character trait through time as it evolves from one state to another or is retained essentially unchanged while the rest of the reptile evolves.

We’ll Start with Paleothyris, the first reptile with a possible synapsid opening appearing anterior to the squamosal (that’s how I traced it, but that is not the traditional interpretation).  One tooth, the canine, was notably larger than the others.

Estemmenosuchus ancestors,

Figure 3. Estemmenosuchus ancestors, beginning with Paleothyris. Click to see more of the tree.

The next Estemmenosuchus ancestor was Archaeothyris in which the canine was larger, the temporal opening was larger and the posterior skull angled down. Ophiacodon was phylogenetically closer, but some sister between these two would have been ancestral to the Therapsida, as blogged earlier. Ophiacodon was a little too derived to have been the direct ancestor.

Biarmosuchus was a basal therapsid with a longer deeper rostrum to house the root of a deeper canine, which was protected with a deeper dentary. The ventral premaxilla was raised. The posterior skull was reduced in length, but the temporal fenestra was larger. The lacrimal no longer contacted the naris, or is the septomaxilla the anterior lacrimal overlapped by the maxilla? The posterior mandible was developed into a thin flange and the quadrate was lower than the squamosal.

Eotitanosuchus had a lower longer skull with a longer canine. The jawline below the orbit was deeply concave as the lower temporal arch expanded laterally until it was a little larger than the orbit.

Sinophoneus was similar, with a smaller orbit and a larger temporal fenestra. By contrast…

Deuterosaurus had an altogether deeper skull with almost no concavity beneath the orbit. The nasal was raised to form a horn. The rim of the orbit was enlarged to form a brow. This is where the horns of Estemmenosuchus would eventually develop. The premaxillary teeth were deeper and the maxillary teeth (other than the canine) were smaller. Deuterosaurus was likely a plant-eater.

Estemmenosuchus uralensis was the first in this lineage to develop distinct horns from the frontals along with laterally expanded jugals forming cheek bosses. The temporal fenestra was much deeper than the orbit. The skull was not so tall overall and a slight indentation remained below the smaller orbit.

Estemmenosuchus mirabilis caps off our journey into the evolution of this Middle Permian weird-oh. Distinct from E. uralensis, the dorsal horns and lateral bosses were larger. The temporal fenestra was further expanded.

Post-Cranial Evolution
While Paleothyris was larger than its contemporaries, it still had an elongated lizard-like body. Biarmosuchus was larger with longer legs, but they moved in a parasagittal motion, as determined by the more symmetrical and reduced toes with reduced mid phalanges on digits 3 and 4.  Deuterosaurus had a shorter tail, a bulkier body and shorter, thicker legs. Estemmenosuchus took these traits to further extremes, increasing its bulk and reducing its relative surface area. Such a strategy helps conserve heat, rather than radiate it.

I know of no taxa closer to the lineage of Estemmenosuchus. If you do, please drop a line.

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
(T)chudinov PK 1965. New Facts about the Fauna of the Upper Permian of the USSR”, Journal of Geology, 73:117-30.