Pterosaur Fingers – Part 3, Dorygnathus to Azhdarchids

Earlier we looked at dimorphodontid and basal eudimorphodontid hands. Today we’ll take a look at the clade that begins with the Donau specimen of Dorygnathus and ends with Quetzalcoatlus.

Dorygnathus to azhdarchid hands.

Figure 1. Dorygnathus to azhdarchid hands. Not to scale. Click to enlarge. Red arcs indicate ungual rotation to display it better. Gray arrow indicates second lineage.

Dorygnathus, the Donau Specimen – compare to the outgroup taxon, Sordes. The manus was overall more gracile with a relatively shorter m3.2 and m2.1.

Dorygnathus, SMNS 51827 – had a relatively shorter metacarpus. Metcarpal 2 was as long as mc 3 and mc 4.

Dorygnathus, the SMNS 50164 – had an even shorter metacarpus and more robust fingers. Manual 3.1 was longer than m3.3.

Pterodactylus? spectabilis, TM 10341, no. 1 in the Wellnhofer (1970) catalog – The metacarpus was no longer than in the Donau specimen. Manual 2.2 was relatively longer. The drastic reduction in the tail places this taxon in the pterodactyloid-grade, but the metacarpus was not elongated.

Beipiaopterus – The metacarpus was twice as long. Manual 3.1 was relatively longer and m2.1 was shorter.

CM 11426, no. 44 in the Wellnhofer (1970) catalog – The metacarpus was nearly twice as long and the fingers were less than half as long. Manual 2.1 was not shorter than m2.2.

BSPG 1911 I 31, no. 42 in the Wellnhofer 1970 catalog – The fingers were longer with m3.3 not longer than m3.2.

Huanhepterus – The metacarpus was relatively shorter. The fingers are unknown.

Sos 2428 – Similar to Huanhepterus in the metacarpus and similar to n42 in the fingers with a slighly longer m3.3.

Microtuban – Metacarpals were all subequal. Manual 3.1 was shorter than m2.1. Manual 3.2 was no longer than wide. The penultimate phalanges were shorter.

Jidapterus – The metacarpus was more robust. Manual 3.3 was longer. Manual 2.1 was longer.

Chaoyangopterus – Metacarpal 1 was slightly shorter than the others. The manus was more gracile. Manual 1.1 was longer.

Zhejiangopterus – Metacarpals were all subequal. Manual digits 2 and 3 were similar in length. Manual 1.1, 2.1 and 3.1 were subequal. Manual 3.3 was the shortest phalanx.

Quetzalcoatlus – Metacarpal 1 was perhaps slightly shorter. The digits are largely unknown but are reconstructed here based on Haenamichnus ichnites.

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.

Tail-Assisted Pitch Control in Lizards (and Pterosaurs)

A recent paper entitled “Tail-assisted pitch control in lizards, robots and dinosaurs” (Libby et al. 2012) reported, “… lizards control the swing of their tails in a measured manner to redirect angular momentum from their bodies to their tails, stabilizing body attitude in the sagittal plane.” They also reported, “Our dynamics model revealed that a body swinging its tail experienced less rotation than a body with a rigid tail, a passively compliant tail or no tail.”

As in Dromaeosaurs
Libby et al. (2012) introduced their abstract with this statement, “In 1969, a palaeontologist proposed (Ostrom 1969) that theropod dinosaurs used their tails as dynamic stabilizers during rapid or irregular movements, contributing to their depiction as active and agile predators.” This hypothesis has been widely accepted. Archaeopteryx is an example of such a morphology.

Fenestrasaurs

Figure 1. Click to enlarge. Fenestrasaurs including Cosesaurus, Sharovipteryx, Longisquama and pterosaurs

Applicable to Fenestrasaurs and Pterosaurs?
The stiff attenuated tail of Cosesaurus, Sharovipteryx, Longisquama and basal pterosaurs bears strong similarities to the tail of Archaeopteryx and dromaeosaurs, especially so in derived long-tailed pterosaurs, like Rhamphorhynchus in which the various zygopophyses and chevrons elongated and intertwined with one another in much the same fashion leaving only the proximal caudals free to move. In birds the short tail and long tail feathers may flex dorsally and ventrally to enhance balance. The same seems to hold true for fenestrasaurs and pterosaurs (as lizards themselves). Both birds and fenestrsaurs largely reduced the caudofemoralis muscles and their bony caudal anchors diminishing the ability to swing the tail left and right.

The Arboreal Leaping Theory for the Origin of Pterosaurs
Bennett (1997) proposed a leaping behavior for the origin of pterosaurs. Bennett (1997) used hypothetical models. My studies with the increasingly long-legged and bipedal pterosaur ancestors Cosesaurus, Sharovipteryx, Longisquama and MPUM 6009 confirm a leaping origin, with the addition of bipedal digitigrade locomotion (reversed in several derived pterosaurs). Libby et al. (2012) tested lizard leaping in the laboratory replicating behaviors that these fenestrasaurs likely practiced in the Triassic wild.

The most primitive pterosaur

Figure 2. Click to enlarge. The most primitive known pterosaur, the Milan specimen, MPUM 6009.

Elevating the Tail Permanently in Basal Pterosaurs
In lizards and derived pterosaurs the tail was held in line with the sacrum and dorsal vertebrae, but in Longisquama and basal pterosaurs (Fig. 2) the sacrum and posterior ilium was elevated distally, at right angles to the anterior ilium. This permanently elevated the base of the tail, similar enough to long-tailed lemurs and house cats. Despite the low mass of an attenuated fenestrasaur/pterosaur tail, elevation provided tail clearance from the substrate while standing with the shoulders elevated above the hips. It also moved the center of gravity anteriorly with dynamic possibilities (flight, with a center of balance at the shoulder joint). Thirdly a vane on the tail tip in derived long-tailed pterosaurs likely provided a secondary sexual signal, as blogged earlier.

Lowering the Tail Permanently in Derived Pterosaurs
Later pterosaurs reversed this early configuration, straightening out the posterior ilium and sacrum, perhaps as the proximal caudal vertebrae evolved more flexibility. An elevated tail would not have been as aerodynamic as an in-line tail so this was probably also a factor.

Bipedal lizard video marker

Figure 3. The Jayne lab documents bipedal locomotion in Callisaurus.

How Living Lizards Run Bipedally
The Bruce Jayne Lab in Cincinnati, Ohio, has produced a video of a zebra-tailed lizard (Callisaurus, Fig. 3) in fast quadrupedal and bipedal locomotion filmed on a treadmill. Note the horizontal configuration of the spine and tail, similar to the configuration reconstructed in Sharovipteryx. Compare this to the video of the basilisk (Jesus lizard) running more erect with an elevated tail, similar to the reconstruction of Longisquama (Fig. 1). Another living lizard, the Australian frilled lizard (Chlamydosaurus kingii, Fig. 4) also had an erect carriage when bipedal.

Chlamydosaurus, the Austrlian frill-neck lizard

Fig. 4 Chlamydosaurus, the Austrlian frill-neck lizard with an erect spine and elevated tail. Image courtesy of R. Shine, published in Peters 2000.

A Dynamic Tail and Probable Behaviour Patterns in Fenestrasaurs
Sharovipteryx did not have much of an elevated posterior ilium and tail (Fig. 1), but Longisquama did. The difference appears to be related to stance and problems with tail/substrate clearing due to stance. Sharovipteryx had such long hind limbs that tail clearance was not an issue. The morphology of Longisquama, with its short neck, large grasping hands and strong leaping legs has been compared to modern long-tailed lemurs, which actively leap from tree to tree and cling to vertical tree trunks. Basal pterosaurs were also likely tree clingers judging by their ability to grasp medial columns with forelimbs otherwise unable to pronate and supinate.

The Reduction of the Long Tail in Derived Pterosaurs
According to cladistic analysis the reduction of the long, stiff tail in basal pterosaurs occurred by convergence three times: 1) after the proto-anurognathid MCSNB 8950; 2) after Dorygnathus (SMNS 50164); after Dorygnathus (Up R 156) and 3) after Scaphognathus (the Maxberg specimen) (Fig. 5). The last of these is the only one in which the tail demonstrates extreme reduction in length and depth. Most workers agree that subtle refinements and improvements in aerodynamic abilities elsewhere in the pterosaur anatomy reduced the need for dynamic stablization from a long, stiff tail.

tail reduction in pterosaurs

Figure 5. These four small to tiny pterosaurs demonstrate tail reduction following taxa having a longer and more robust tail.

The Pattern of Tail Reduction in Pterosaurs
At some point the utility of an elongated tail diminished in pterosaurs, as it did in birds. Contra traditional stuides, tail reduction in pterosaurs appeared three times during overall size reduction in pterosaurs. Examples include the tiny Dorygnathus sisters TM 10341, St/Ei I and the tiny Scaphognathus sister, TM 13104 (Fig. 5). These reductions may be considered paedomorphic sequences in which the genes for tail lengthening and stiffening simply did not turn on as these three pterosaur clades retained embryonic traits (a flexible tail curled into a shell) earlier and earlier in their ontogenetic development.

The Pterodaustro Tail
The tail of derived pterosaurs has been rarely documented, but in Pterodaustro (Codorniu 2005) a comparatively elongated tail was present. Kellner and Tomida (2000) documented the tail of Anhanguera. Young (1964) documented the tail of Dsungaripterus. Zhenyuanopterus preserved a completely articulated tail. These were all substantial tails, yet still relative vestiges. Traditional views promote the disappearance of tails in pterodactyloid-grade pterosaurs. Not so, according to these derived examples.

The Pteranodon Tail
Bennett (1987 ) described an unusual tail attributed to Pteranodon that had duplex centra capable only of elevation and depression. This tail terminated in extended parallel rods, probably representing fused duplex centra. This tail was likely too small to affect aerodynamic abilities. If present on a female, such a tiny fragile tail might have been in danger of damage during mating. Perhaps it was capable of curling over the back to permit mating without damage, co-opting the tail-assisted pitch control of its nonvolant lizard ancestors.

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 1987.  New evidence on the tail of the pterosaur Pteranodon (Archosauria: Pterosauria). Pp. 18-23 in Currie, P. J. and E. H. Koster, eds. Fourth Symposium on Mesozoic Terrestrial Ecosystems, Short Papers. Occasional Papers of the Tyrrell Museum of Paleontology, #3
Bennett SC 1997.
The arboreal leaping theory of the origin of pterosaur flight. Historical Biology 123: 265–290.
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153.
Codorniú LS 2005. Morfología caudal de Pterodaustro guinazui (Pterosauria: Ctenochasmatidae) del Cretácico de Argentina. Ameghiniana: 42 (2): versión On-line ISSN 1851-8044.
Libby T, Moore TY, Chang-Siu E, Li D, Cohen DJ, Jusufi A, Full RJ 2012. Tail-assisted pitch control in lizards, robots and dinosaurs. Nature. 2012 Jan 4;481(7380):181-4. doi: 10.1038/nature10710.
Ostrom JH 1969. Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana. Bull. Peabody Mus. Nat. Hist. (Paris) 30, 68–80, 144. Young CC 1964. On a new pterosaurian from Sinkiang, China. Vertebrata PalAsiatica 8: 221-256.

Why Pterosaurs Are Extinct Today

The K/T Extinction Event
Everyone knows that pterosaurs, dinosaurs and a host of other prehistoric reptiles died out at the K/T (Cretaceous/Tertiary) boundary ~65 mya. But SOME birds, lizards, turtles, crocs and mammals survived. So, why did ALL pterosaurs die out?

Phylogenetic Analysis 
As in dinosaurs, the pterosaurs we know from the latest Cretaceous were not the same pterosaurs living in the Triassic, Jurassic or Early Cretaceous. All of these earlier pterosaurs became extinct, but a few genetic lines survived by evolving into the Late Cretaceous forms we know and love. Phylogenetic analysis indicates that certain lucky Middle Jurassic Dorygnathus specimens ultimately evolved (via several transitional taxa) into Quetzalcoatlus, Pteranodon, Nyctosaurus, Tupuxuara and any other Late Cretaceous pterosaurs I’m forgetting (the current list is not much longer than this).

The Example of Dorygnathus
Analysis illustrates how the descendants of Dorygnathus changed in size and shape as they evolved into the above Late Cretaceous taxa. Therein, l think, lies the answer to why pterosaurs were not able to continue evolving into the modern day.

The Azhdarchidae.

Figure 1. The Azhdarchidae. Click to enlarge.

Size Matters
If we were to follow the lineage of Dorygnathus through Quetzalcoatlus (Fig. 1) we would meet the following taxa in order: Dorygnathus (SMNS 50164), Pterodactylus? spectabilis (TM 10134), Beipiaopterus, No. 44, No. 42, Jidapterus, Chaoyangopterus, Zhejiangopterus and finally the two species of Quetzalcoatlus. Setting aside the huge size differences between the two Qs and their phylogenetic predecessor, Zhejiangopterus, note that tiny TM 10134 and two other tiny pteros, No. 42 and No. 44, are in this line-up.

Tiny Survivors
In the Late Jurassic the genetic lineage of Dorygnathus, of the Middle Jurassic, was represented by a tiny version of itself, TM 10134. There were no other full-size Dorygnathus present in the Late Jurassic. Something killed every other one over a certain size. Only tiny dory descendants somehow survived. Was it because of their size?

Major Morphological Changes in Tiny Taxa
As mentioned above (Fig. 1) other Late Jurassic tiny dorygnathids also include No. 42 and No. 44, both of which evolved a slender elongated neck, a low trostrum, smaller teeth and longer more gracile limbs. These traits were retained in all later and larger azhdarchids and huanhepterids (Fig. 1). (Pterorhynchids, scaphognathids and ctenochasmatids were also Dorygnathus descendants you can read about here, here and here).

Good Times
When the threat of extinction did not loom over pterosaurs, they tended to become bigger. Evidently this was especially true during the latest Cretaceous because pterosaurs reached their greatest sizes right at 65 million years ago.

Not Being Small Is What Killed Late Cretaceous Pterosaurs
Just as being small saved many pterosaur lines earlier, being small saved many other vertebrates following the K/T mass extinction event. Big vertebrates did not survive. Unfortunately the giant pterosaurs of the latest Cretaceous could not breed small enough to save themselves, as their ancestors had done. We don’t find any pterosaurs smaller than Nyctosaurus in the Late Cretaceous.

Serial Size Reduction and How It Happens
ln pterosaurs phylogenetic size reduction from Dorygnathus to TM 10134 was made possible by reaching sexual maturity at half their final size (Chinsamy et al. 2008). Smaller pelves would have passed smaller eggs, smaller hatchlings and an even smaller second generation in serial fashion. Smaller vertebrates typically have a relatively faster maturation process, creating more tiny hatchlings earlier and at a faster clip. This increase in reproductive rates raised the odds that whatever was killing the larger, slower-to-breed individuals could be overcome by an acceleration in breeding, producing an acceleration in genetic variation and mutation. Such a serial size reduction pattern occurred at the base of nearly every major clade within the Pterosauria. When the same process is observed about a dozen times that verifies its veracity.

Phony pterosaur.

Figure 2. Phony pterosaur.

If only some tiny pteros existed at the Late Cretaceous, we might have some “thunderbirds” flying around today (Fig. 2).

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
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.

Does a Big Crest Make a Nyctosaurus Mature?

Bennett (2003) reported on two Nyctosaurus discoveries made by fossil collector Kenneth Jenkins. Both (Fig. 1) had the largest crests, relative to skull length and body size, of any known pterosaur. This came as even more of a surprise to paleontologists because no other Nyctosaurus specimens show any hint of a crest.

Late in Ontogeny?
Bennett (2003) reported in his abstract, “Despite the large crest, the specimens do not differ significantly in morphology from previously known specimens of Nyctosaurus, and do not represent a new species of Nyctosaurus. The specimens suggest that the cranial crest was developed late in ontogeny, which is consistent with the interpretation of pterosaur cranial crests as intraspecific display structures.” Unfortunately, these statements have been taken as gospel and have been uncritically repeated. For instance, here’s an online pdf of an article by Greg Paul from the Prehistoric Times.

Nyctosaurus clade

Figure 1. The clade of Nyctosaurus and kin. Click to enlarge.

Actually the Variations is Easy to See
Bennett (2003) did not make reconstructions of the clade for comparison. One look at reconstructions of several known Nyctosaurus specimens shows that none are conspecific (Fig. 1). There ARE many significant differences in morphology (contra Bennett 2003, details in reptileevolution.com starting here). Even the two crested Nyctosaurus specimens have distinct differences in crest shape and wing length.

In Pterosaurs More Mature = Larger
If the crested specimens were indeed more mature, then one would expect them to be larger, following the study by Chinsamy et al. (2008) on the growth series documented in Pterodaustro, the only pterosaur with a varifiable growth series. That study found that sexual maturity occurs at half the largest size attained by individuals, a pattern also found in certain lizards like Iguana (Kaplan 2007)  and Varanus (Pianka 1971). The crested specimens are actually smaller than some, similar in size to other Nyctosaurus (not counting the largest known Nyctosaurus specimens known from a pelvis and disassociated scraps.) Nyctosaurus nanus (known from a humerus and pectoral girdle) is the only Nyctosaurus that is genuinely smaller than the others pictured here.

Is the Crest a Sexual Signal?
Sure. It appears that the crest is a secondary sexual characteristic. If so one would expect a crest to appear at sexual maturity (half the final size). There is only one pair of crested pterosaurs that I am aware of that appear to be conspecific and those are a pair of tupuxuarids that have identical crests, identical rostral lengths and identical orbit sizes relative to their overall size. The smaller specimen is less than half the size of the larger one, so it was prepubescent, which falsifies the notion of a sexual signal. No, the crests appear to have identified species, not gender, maturity or sexual fitness (mutual selection). Other sorts of secondary sexual characters must have been present in crested and crestless specimens, such as wattles, coloration or behavior.

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 2003. New crested specimens of the Late Cretaceous pterosaur Nyctosaurus.Paläontologische Zeitschrift 77: 61-75.
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Kaplan M 2007. Iguana Age and Expected Size. iguana/agesize online
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Pianka E 1971.
Notes on the Biology of Varanus tristis. West. Aust, Natur, 11(8):80-183.

wiki/Nyctosaurus

An Obligate Bipedal Basal Pterosaur

The Traditional View
All pterosaurs were quadrupedal, based on trackway evidence.

MPUM 6009, the Milan specimen, the most primitive known pterosaur

Figure 1. The most primitive known pterosaur, the Milan specimen, MPUM 6009. The long hind limbs and relatively short fore limbs were homologous with those in Sharovipteryx and Longisquama. The extremely slender tail is most like that of Sharovipteryx, not later pterosaurs which thickened the tail with elongated chevrons and zygapophyses. Gray tones represent possible soft tissues, homologous with those in Cosesaurus and Longisquama.

The Heretical View
One basal pterosaur, MPUM 6009 (Wild 1978), was an obligate biped, retaining the long-legged morphology of its ancestral sisters, Sharovipteryx and Longisquama. All pterosaurs following MPUM 6009 (such as Raeticodactylus and Eudimorphodon) had shorter hind limbs and longer forelimbs, a combination that enabled quadrupedal locomotion.

MPUM 6009 was considered a small Carniadactylus by Dalla Vecchia (2009), but the differences are many.

MPUM 6009 in situ.

Figure 2. MPUM 6009 in situ. Click to enlarge and portray the Wild (1978) interpretation. Bones, impressions of bones and some soft tissue complete this articulated skeleton at the very base of the Pterosauria. The crushed skull required reconstruction. Here, using the DGS method, the bones have been colorized. This permits subtle impressions to be identified. Sister taxa share many of these traits, confirming their identity.

Longer Legs, Shorter Forelimbs
Here the reconstruction tells the tale. Question is, is the reconstruction accurate? The clues are, admittedly ephemeral, yet even without such long legs, MPUM 6009 nests at the base of the Pterosauria. So long legs are not beyond the realm of possibility. The relatively short neck allies this basal pterosaur with Longisquama, the outgroup sister taxon. The laterally increasing toe length and deep pelvis also ally this taxon with Longisquama. The sternal complex is also essentially identical.

Ironically…
Such long legs and short forelimbs “ally” this pterosaur with Scleromochlus, and basal dinosaurs, but — really, seriously — hardly at all. It’s convergence!! So if anyone from the traditional camp wants to bitch about this reconstruction, think twice. You’ll only be shooting yourself in the foot. Things happen when the forelimbs are elevated off the substrate, as we humans all can attest.

Bipedal lizard video marker

Figure 3. Click to play video. Just how fast can quadrupedal/bipedal lizards run? This video documents 11 meters/second in a Callisaurus at the Bruce Jayne lab.

How Living Lizards Run Bipedally
The Bruce Jayne Lab in Cincinnati, Ohio, has produced a video of a zebra-tailed lizard (Callisaurus) in fast quadrupedal and bipedal locomotion filmed on a treadmill. When the fore limbs are elevated the hind limbs go digitigrade. The speed is an incredible 11 meters per second.

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
Dalla Vecchia FM 2009. Anatomy and systematics of the pterosaur Carniadactylus (gen. n.)rosenfeldi (Dalla Vecchia, 1995). Rivista Italiana de Paleontologia e Stratigrafia 115 (2): 159-188.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

wiki/Eudimorphodon

Double Blind Stradivarius Test and the Ornithodira

Holding its own tradition of greatness for centuries, the Stradivarius violin knows few equals. Aficionados swear that its tones cannot be duplicated. Experts have worked for years to duplicate its shape and discover its mystical varnish formulas, all to reveal the “secret” of its unique sound qualities — perhaps in vain, as it turns out.

Brand Loyalty
Unfortunately, all this work and all that status may come down to nothing more than a bad case of brand loyalty. In a recent double blind test, a Stradivarius violin was chosen as the least favorite of several, losing out to a modern instrument. Judges were seasoned violin players.

When the players were asked which violins they’d like to take home, almost two-thirds chose a violin that turned out to be new, rather than the Strad. The research was aimed at determining how people choose what they like, and what criteria they use.

Dale Purves, a professor of neuroscience at Duke University, says the research “makes the point that things that people think are ‘special’ are not so special after all when knowledge of the origin is taken away.” The research appears in the Proceedings of the National Academy of Sciences.

So what does all this have to do with paleontology?
Brand loyalty is keeping pterosaurs nested with Scleromochlus and dinosaurs despite scientific testing (Peters 2000a, b 2009) that recovered fenestrasaurs, lizards, even turtles as closer sister taxa. This is the “blind eye” I referred to earlier. The biggest names in paleontology have wrapped their arms and careers around their support for the “Ornithodira” — perhaps irrationally, as it turns out. The “Ornithodira” cannot be supported except by deleting lizards (Bennett 1996, Bursatte 2010, Nesbitt 2011) or by deleting and depleting fenestrasaurs (Hone and Benton 2007, 2008). Even the proponents of the “Ornithodira” throw up their hands in surrender when asked to identify which generic taxon is closer to pterosaurs than any other and what traits they share to the exclusion of all other known fossils reptiles. It’s sad really. Twelve years after the first challenge to the “Ornithodira”(Peters 2000), workers continue to cling to the status and comfort of that old notion rather than finding genuine support for it.

It’s hard to change textbooks and class notes.
If you’re a professor faced with a challenge to your pet hypotheses, do you suppress manuscripts that expose their weaknesses? Or do you engage opposing candidates to test their mettle? If you’re a student, do you support your mentor no matter what? Those who do choose to suppress, typically go “all the way.” They label the opposition a heretic. Ridicule him as a nut case. Make him a pariah. Ignore the taxa. Attack the challenger. Delete all references to opposing theories. If you do choose to suppress, thereafter you have two choices: 1) put your support behind a notion that is widely recognized as weak and unsupportable, even by its proponents (Hone and Benton 2007, 2008); or 2) shrug your shoulders and say, “Sorry, that’s one of the mysteries we’re still working on.”

Sorry for rant. The NPR story on the Stradivarius double blind test just “struck a familiar chord.” And it, too, solves an ancient mystery. We’ll be back to more reptiles tomorrow.

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 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoological Journal of the Linnean Society 118:261-308.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Brusatte SL, Benton MJ, Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330

What is Jianchangnathus?

A recent paper by Cheng et al. (2012) introduced a new basal pterosaur, Jianchangnathus robustus (IVPP V 16866). Middle Jurassic in age, Jianchangnathus shared several characters with Scaphognathus from the Late Jurassic, according to the authors. It was also compared to Fenhuangopterus, a basal dorygnathid from the same deposits at Jianchangnathus.

Jianchangnathus

Figure 1. Jianchangnathus was allied with Scaphognathus, but retains many traits of its ancestors within Dorygnathus.

A Basal Nesting in the Second Half of the Pterosauria
Here Jianchangnathus nested at the base of the Scaphognathia, essentially the second half of the Pterosauria. In this important phylogenetic site Jianchangnathus was derived from a sister to the Donau specimen of Dorygnathus, itself at the very base of the Dorygnathia and not far from Sordes, the outgroup taxon (Fig. 2). Pterorhynchus and the wukongopterids (= darwinopterids) were sister taxa.

A phylogenetic sequence that includes Jianchangnathus

Figure 2. A phylogenetic sequence that includes Jianchangnathus at the transition point between a basal Dorygnathus and Pterorhynchus + Scaphognathus. All are to scale. This is a rare instance of morphological transition in which a tiny pterosaur did not intervene.

Jianchangnathus was not originally subjected to a phylogenetic analysis, nor was it reconstructed.

The skull of Jianchangnathus with bones identified using the DGS method.

Figure 3. The skull of Jianchangnathus with bones identified using the DGS method. Here the nasal is in pink (anteriorly) and purple (posterior to the break).

Redescription Using DGS
Cheng et al. (2012) reported fusion between the premaxilla and maxilla. Here (Fig. 3) the suture is between the 4th and 5th tooth as in sister taxa. The first fang was the first maxillary tooth, as in the SMNS 55886 specimen of Dorygnathus. The dentary did not extend to the quadrate but extended posteriorly beneath posterior jugal as in sister taxa. The nasal extended to mid orbit as in sister taxa. The jugal extended to the pmx/mx suture as in sister taxa. The prefrontals were longer than originally reported. The vomers, ectopalatine and pterygoid were rod-like elements, as in sister taxa. The tip of the mandible is a double-tooth morphology.

Dorygnathus Was Barely Mentioned
The upturned premaxilla and anteriorly-oriented teeth are traits of Dorygnathus, but that taxon was not mentioned by Cheng et al. (2012) in comparison. The relatively large skull is a trait shared with Pterorhynchus and the wukongopterids. The manual and pedal element proportions are shared with sister taxa.

Maturity
Cheng et al. (2012) observed the non-fusion of the scapula and coracoid and mistakenly considered Jianchangnathus immature. In this case fusion, or a lack thereof, is a matter of phylogeny, not ontogeny. Because pterosaurs are lizards that do not follow archosaur growth patterns as discussed earlier. Sister taxa likewise do not fuse the scapula and coracoid and Jianchangnathus was similar in size to them (Fig. 2).

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
Cheng X, Wang X-L, Jiang S-X and Kellner AWA 2012. A new scaphognathid pterosaur from western Liaoning, China. Historical Biology iFirst article available online 29 Nov 2011, 1-11. doi:10.1080/08912963.2011.635423

wiki/Jianchangnathus