Bergamodactylus (basal pterosaur) back ‘under the microscope’

This all started with Kellner 2015
who proposed 6 states of pterosaur ontogeny based on skeletal fusion of discrete elements. This hypothesis was tested in phylogenetic analysis and shown to be invalid. Pterosaurs don’t fuse bones during ontogeny. Fusion appears in phylogenic patterns. Oblivious to this fact, Dalla Vecchia 2018 dismissed Kellner’s hypothesis by writing, “Kellner’s six ontogenetic stages are an oversimplification mixing ontogenetic features of different taxa that probably had distinct growth patterns. Finding commonality across all pterosaurs is impossible, because there is much variation in pterosaur ontogeny and the available sample is highly restricted.” 

Neither Kellner nor Dalla Vecchia recognize
the lepidosaurian affinities of pterosaurs, and do not realize that as lepidosaurs pterosaurs mature differently than archosaurs. Some lepidosaurs continue growing after fusing elements (Maisano 2002). Others never fuse elements. Fusion of elements in pterosaurs is phylogenetic, not ontogenetic. Pterosaurs mature isometrically, not allometrically as proven by every full-term embryo and every known juvenile among a wide variety of pterosaur specimens. Plus, all of the small purported Solnhofen juveniles phylogenetically nest as key transitional taxa linking larger long-tail primitive pterosaurs to larger short-tail derived pterosaurs (Peters 2007). That’s how those clades survived the extinction events that doomed their fellow, larger, longer-tailed kin.

Kellner 2015 also
distinguished a small pterosaur MPUM 6009 from the holotype of Eudimorphodon and from Carniadactylus (MFSN 1797, Dalla Vecchia 2009; Fig. 1) and gave MPUM 6009 the name Bergamodactylus (Fig. 1) after Peters 2007 had done the same (without renaming MPUM 6009), in phylogenetic analysis. Neither Kellner nor Dalla Vecchia performed a phylogenetic analysis, but preferred to describe similar bones. That rarely works out well.

Figure 1. Bergamodactylus compared to Carniadactylus. These two nest apart from one another in the LRT.

Figure 1. Bergamodactylus (MPUM 6009) compared to Carniadactylus (MFSN 1797). These two nest apart from one another in the LRT. Contra Dalla Vecchia 2018, these two share relatively few traits in common. The feet, cervicals, sternal complex coracoids and legs are different.

Dalla Vecchia 2018 concludes, 
“The anatomical differences between MPUM 6009 and MFSN 1797 are too small to support the erection a new genus for MPUM 6009.” That is incorrect (Fig. 1). Several taxa nest between these two taxa in the large pterosaur tree (LPT, 232 taxa). Their feet alone (Fig. 1) were shown to be very different in Peters (2011).

Figure 1. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown.

Figure 2. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown.

From the Dalla Vecchia 2018 abstract
“Six stages (OS1-6) were identified by Kellner (2015) to establish the ontogeny of a given pterosaur fossil. These were used to support the erection of several new Triassic taxa including Bergamodactylus wildi, which is based on a single specimen (MPUM 6009) from the Norian of Lombardy, Italy. However, those ontogenetic stages are not valid because different pterosaur taxa had different tempos of skeletal development. Purported diagnostic characters of Bergamodactylus wildi are not autapomorphic or were incorrectly identified. Although minor differences do exist between MPUM 6009 and the holotype of Carniadactylus rosenfeldi, these do not warrant generic differentiation. Thus, MPUM 6009 is here retained within the taxon Carniadactylus rosenfeldi as proposed by Dalla Vecchia (2009a).” \

Dalla Vecchia is basing his opinion on comparing a few cherry-picked traits, possibly convergent, rather than running both taxa and a long list of other pterosaurs through phylogenetic analysis, to see where unbiased software nests both taxa among the others.

Plus, as mentioned above, both authors are working from an antiquated set or rules that no longer apply now that pterosaurs have been tested and validated as lepidosaurs.

Figure 2. Bergamodactylus skull colorized with DGS and reconstructed.

Figure 3. Bergamodactylus skull colorized with DGS and reconstructed. Palatal and occipital bones shown here were missed by Dalla Vecchia 2018 and prior workers who did not use DGS.

Phylogenetic analysis
employing a large gamut of taxa, like the large reptile tree (LRT, 1215 taxa), invalidates traditional arguments that pterosaurs arose without obvious precedent among the archosauriforms, which most pterosaur workers, including both Kellner and Dalla Vecchia, still cling to, despite no evidence of support. Pterosaurs arose from fenestrasaur tritosaur lepidosaurs (Fig. 7).

Figure 4. The skull of Bergamodactylus traced by Kellner 2015, Dalla Vecchia 2018 and by me using DGS.

Figure 4. The skull of Bergamodactylus traced by Kellner 2015, Dalla Vecchia 2018 and by me using DGS. See figure 2 for a reconstruction of the DGS tracing.  Prior authors missed all the palatal and occipital bones along with several others.

The metacarpus of Bergamodactylus
has a few disarticulated elements. When replaced to their in vivo positions the axial rotation of metacarpal 4 (convergent with the axial rotation of pedal digit 1 in birds) enables the wing finger to fold in the plane of the hand, not against the palmar surface. Manual digit 5, a vestige, goes along for the ride, rotating the dorsal surface of the hand (Fig. 5).

Figure 5. Metacarpus of Bergamodactylus (MPUM 6009) in situ and reconstructed.

Figure 5. Metacarpus of Bergamodactylus (MPUM 6009) in situ and reconstructed. Apparently the pteroid splintered apart, overlooked by those with direct access to the specimen. The distal carpals are not co-ossified, as they are in later pterosaurs. The laterally longer fingers, up to digit 4, is a tritosaur trait. Note ungual 1 lies on top of the posterior face of metacarpal 4. That was overlooked by those who had direct access to the specimen, which supports the utility of DGS.

 

Bergamodactylus, as the most basal pterosaur,
is itself a transitional taxon bridging non-volant fenestrasaurs with all other pterosaurs. And the wing (Fig. 6) was about the last thing to evolve.

Figure 6. Click to enlarge. The origin of the pterosaur wing and the migration of the pteroid and preaxial carpal. A. Sphenodon. B. Huehuecuetzpalli. C. Cosesaurus. D. Sharovipteryx. E. Longisquama. F-H. The Milan specimen MPUM 6009, a basal pterosaur.

Bergamodactylus to scale
with Cosesaurus and Longisquama (Fig. 7), demonstrate the variety within the Fenestrasauria. Pterosaurs arose more or less directly from a sister to Cosesaurus (based on overall proportions), but note that both Sharovipteryx and Longisquama have more pterosaurian traits than Cosesaurus does. This pattern is convergent with that of birds, of which several clades of Solnhofen bird descendants arose of similar yet distinct structure.

Figure 8. Taxa at the genesis of pterosaurs: Cosesaurus, Longisquama and Bergamodactylus.

Figure 7. Taxa at the genesis of pterosaurs: Cosesaurus, Longisquama and Bergamodactylus.

See rollover images
of Bergamodactylus in situ here. You’ll see how DGS is able to pull out post-cranial details overlooked by others in the chaos and confusion of layers of bones and impressions in MPUM 6009. Cranial details are best seen in figure 3 above, which is based on higher resolution images.

References
Dalla Vecchia FM 2009. Anatomy and systematics of the pterosaur Carniadactylus gen. n. rosenfeldi (Dalla Vecchia, 1995). Riv. It. Paleontol. Strat., 115: 159-186.
Dalla Vecchia FM 2018. Comments on Triassic pterosaurs with a commentary on the “ontogenetic stages” of Kellner (2015) and the validity of Bergamodactylus wildi.  Rivista Italiana di Paleontologia e Stratigrafia 124(2): 317-341. DOI: https://doi.org/10.13130/2039-4942/10099 https://riviste.unimi.it/index.php/RIPS/article/view/10099
Kellner AWA. 2015. Comments on Triassic pterosaurs with discussion about ontogeny and description of new taxa. Anais Acad. Brasil. Ciênc., 87(2): 669-689.
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrate Paleontology 22:268-275.
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

Longisquama wings

Everyone agrees
that the anterior half of Longisquama is known because it is plainly visible. Everyone agrees that a pair of forelimbs is visible. Sharov (1970) illustrated fingers, but was stymied from completing that task because the two hands are preserved one on top of the other with the fingers intermingled. You can see that chaotic preservation here.

DGS
(digital graphic segregation) is a useful method to segregate one Longisquama hand from another and fingers from one another. Once that is done, phalangeal lengths can be matched for validity and accuracy. Ultimately a reconstruction can be produced (Fig. 1). It is readily apparent that the in situ chaos as preserved is difficult to trace, but not impossible. Anyone can do it with enough resolution and patience.

Figure 1. Longisquama left and right manus traced using DGS then reconstructed (below). This is a very large hand for a fenestrasaur and manual digit 4 is oversized, as in pterosaurs.

Figure 1. Longisquama left and right manus traced using DGS then reconstructed (below). This is a very large hand for a fenestrasaur and manual digit 4 is oversized, as in pterosaurs. Yes, membranes are preserved trailing the manus, just as plumes and other membranes are preserved elsewhere.

The importance of overcoming a chaotic preservation
to retrieve an orderly reconstruction is well illustrated by this example (Fig. 1). The fact that corresponding phalanges on both hands are equal in length self-validates the tracing. Here the phalanges are numbered and their images were copied and pasted to produce the reconstruction. Also note the shapes of the scapula and coracoid, perfect for flapping. There’s a nice sternal complex in there too. Only fenestrasaurs, including pterosaurs, have those.

The size of the manus,
relative to the humerus and antebrachium, the proportions of the phalanges, the presence of a trailing membrane and of preaxial carpals (including a pteroid) all indicate a close relationship to pterosaurs and other fenestrasaurs. No other tetrapods share these traits.

Figure 2. Click to animate. Longisquama flapping and wagging its tail.

Figure 2. Click to animate. Longisquama flapping and wagging its tail.

Scientists have been looking
for a non-flying reptile with large hands that could be a pterosaur ancestor. This is it (fig. 2), only the fingers are a little curled up and relative to the torso the entire forelimb is short, as in the sister to Longisquama, Sharovipteryx.

References
Peters D 2000.
 A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.

Reconstructing Sharov’s Longisquama

My detractors often point to my discovery of the second half of Longisquama as pure fantasy.

So let’s pretend
that the back half of Longisquama was never present in the fossil. Pretend, like Jimmy Stewart in a Wonderful Life, that I was never born.

Now the onus
goes back to all the pterosaur workers who still refuse to examine the very pterosaurian traits of Longisquama, as traced by Sharov (1970, Fig. 1). Those traits are still there, whether I point them out or not.

Figure 1. Longisquama as traced by Sharov 1970. Workers have been searching for the predecessor of pterosaurs. Why didn't they look here?

Figure 1. Click to enlarge. Longisquama as traced by Sharov 1970 above, reconstructed below using DGS to move Sharov’s lines around. Workers have been searching for the predecessor of pterosaurs. Why don’t they look here? According to Sharov Longisquama has a sternal complex (he saw the displaced, fused clavicles, but not the sternum they rimmed), antorbital fenestra, long 4th finger (the actual 4th finger is much longer) and membranes trailing the forelimbs, not to mention a strap-like scapula and elongate coracoid. What more could you want? Alongside, not to scale, long-necked Sharovipteryx and short-necked MPUM6009, a basal pterosaur. Yellow displaced “plumes” are actually the tibia and femur, so the hind legs have been seen, just misidentified.  Those two bumps on the head are really a displaced parietal rimming upper temporal fenestrae. A little more resolution would clear this up.

So many fantasy creatures
have been built around the idea of Longisquama (just Google it), but no one has taken Sharov’s blueprint and put the bones back into their in vivo positions — until now (Fig. 1). When you repeat this experiment, you will also get something that can be input into phylogenetic analysis. And the rest (the blue areas) can be guesstimated based on phylogenetic bracketing. Almost all other artists put much smaller hind limbs on Longisquama, but that’s not what close relatives have (Fig. 1).

Like a basal pterosaur Longisquama has this suite of characters:

  1. an antorbital fenestra
  2. a large orbit
  3. multicusped teeth
  4. short neck (eight cervicals)
  5. 9th vert has short rib, 10th vert has rib that contacts sternal complex
  6. strap-like scapula
  7. narrow coracoid
  8. sternal complex (clavicles wrapped around sternum + interclavicle)
  9. parallel ulna and radius
  10. asymmetric manus with short digit 5
  11. structured membrane trails forelimb (proto-wing)
  12. small membrane precedes forelimb (proto-propatagium)

Everything else we’ll call guesswork
based on phylogenetic bracketing, which is, by definition, extremely conservative. Phylogenetic bracketing gives Longisquama long hind limbs, uropatagia, an attenuated tail and a short mt5 + elongated p5.1, just like it’s sisters.

Sharov’s traits alone
are enough to call this specimen out as the best candidate for pterosaur kinship — and yet — it’s been ignored and dismissed for forty years — even with that PR bump in 2000 and 2002. With such data widely available, does anyone else think it is very odd that professionals who write pterosaur books (Wellnhofer, Witton and Unwin) and other professors (Bennett, Padian, Hone, etc. etc.) claim we don’t know the ancestry of pterosaurs? Or am I the only one who finds this odd and unsettling?

I can understand why they would ignore me, a published amateur widely despised and ridiculed. But why ignore Sharov?

Evidently it’s a mind set.
And it’s hard to break, even with Sharov’s own images. He saw what I saw. I just added details.

New tracings of Longsiquama

Figure 2. Click to enlarge. New tracings of Longsiquama (B) soft tissues and (C) bones.

If you want to learn more details about the Longisquama fossil, find them here.

 

Figure 3. Click to enlarge. If you still don't like Longisquama, there's more where that taxon came from. Any one of these will nest closer to pterosaurs than any archosauromorph. Here's Kyrgyzsaurus to scale alongside other basal fenestrasaurs, Cosesaurus, Sharovipteryx and Longisquama. Kyrgyzsaurus likely was a biped with long legs. We know from the shape of its coracoids that it was a flapper.

Figure 3. Click to enlarge. If you still don’t like Longisquama, there’s more where that taxon came from. Any one of these will nest closer to pterosaurs than any archosauromorph. Here’s Kyrgyzsaurus to scale alongside other basal fenestrasaurs, Cosesaurus, Sharovipteryx and Longisquama. Kyrgyzsaurus likely was a biped with long legs. We know from the shape of its coracoids that it was a flapper.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E. Buffetaut & D.W.E. Hone (eds.), Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, DeKalb, IL, 1-279.
Senter P 2004. Phylogeny of Drepanosauridae (Reptilia: Diapsida) Journal of Systematic Palaeontology 2(3): 257-268.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.

The Passing of Larry Martin, curator, U of Kansas

Larry Martin, paleontologist and curator at the University of Kansas, died recently. Famously, he was a staunch opponent of the birds are dinosaurs hypothesis and was equally famous for saying, “Show me one character that unites birds with dinosaurs!” Larry could always tell you that whatever trait you could think of was also present in another non-dinosaur taxon. In his mind that dissolved your argument. He never seemed to understand it takes a suite of traits, the famous “most parsimonious” placement, that phylogenetic analysis works on, not “one character.” Convergence is so rampant in the Reptilia that a single trait can often be found elsewhere for any taxon.

Even so, Larry was a friendly and outgoing man who always had time to talk in conventions. He appeared on several dinosaur-related TV shows, including the “Four-winged dinosaur” Nova program on Microraptor.

Martin signed Chris Bennett’s PhD dissertation and he had dozens of other students and KU colleagues over the years.

Martin’s reconstruction of Longisquama can be seen here and a model can be seen below. Caption and photo from the Lawrence Journal-World. The model of Longisquama, unfortunately, is totally inaccurate. It’s okay to be a contrarian, like Larry Martin, but you better have great evidence.

Kansas University graduate student Robert Elder holds a model of a longisquama, a feathered reptile that may predate dinosaurs. David Burnham, left, and Larry Martin, curator of vertebrate paleontology, look on. The model is part of a future display about the birth of flight.

Kansas University graduate student Robert Elder holds a model of a longisquama, a feathered reptile that may predate dinosaurs. David Burnham, left, and Larry Martin, curator of vertebrate paleontology, look on. The model is part of a future display about the birth of flight.

I’m glad I met Larry Martin. He will be missed.

https://www2.ljworld.com/news/2013/mar/12/late-ku-paleontologist-martin-brought-prehistoric/

The metatarsus of Longisquama revealed by DGS

Buchwitz and Voigt (2012) reexamined Longisquama’s plumes and determined that they were indeed attached to the dorsal spine (and therefore not coincidental plant material). The closeup photo they provided of purported plume bases is worth discussing, for several reasons.

From Buchwitz and Voigt (2012) purported to be the bases of three dorsal appendages. Actually these are metatarsals.

Figure 1. From Buchwitz and Voigt (2012) purported to be the bases of three dorsal appendages. Actually these are metatarsals 1-3. See figure 2. Their alignment with the vertebrae is, at best, imprecise. The actual plume bases (fig. 2) are below these hollow bony elements. The parallel lines in the upper right corner are aktinofibrils supporting the detached uropatagium.

Difficult to interpret!
Especially when cropped so closely (fig. 2), one set of Longisquama metatarsals is identified here. There are phalanges extending from the tips of these metatarsals (Fig. 4), as well as plumes. The actual plumes (green) are behind (below) these metatarsals. These match the size and proportions of the other metatarsals of Longisquama (fig. 4) and those of sister taxa (fig. 3).

Figure 2. Click to enlarge. Reinterpretation of the bases of the dorsal plumes of Longisquama. These are metatarsals. On the right you'll see those fine parallel lines representing the aktinofibrils of a detached uropatagium (one of two, of course).

Figure 2. Click to enlarge. Reinterpretation of the bases of the dorsal plumes of Longisquama. These are metatarsals 1-4. On the right of each picture you’ll see those fine parallel lines representing the aktinofibrils of a detached uropatagium (one of two, of course), as in Sharovipteryx. DR = displaced dorsal ribs. Ti = tibia (see Fig. 4 for the whole picture).

They’re not plume bases
These elements are aligned with the plumes, but not exactly. And they increase in length laterally. And they overlap. And they have phalanges emanating from them. And they match another set of nearby metatarsals (fig. 4). They’re metatarsals. Take them ‘as is’ and put them into a reconstruction (fig. 3) and you get a nice transition and match between Sharovipteryx and MPUM6009, a basal pterosaur, the phylogenetically bracketing taxa. Longisquama demonstrates how p5.2 and p5.3 merged to become one phalanx in basal pterosaurs. All the PILs (parallel interphalangeal lines) align.

longisquama-foot588

Figure 3. The foot of Longisquama based on the DGS tracing, shares traits with both Sharovipteryx and MPUM6009.

The big picture (click fig 4 to enlarge) tells the tale. The front of Longisquama is undisturbed. So is the tail. It’s the middle that became twisted. That’s why the feet ended up over the vertebral column. The fossil looks like a big post-mortem gas bubble in its belly exploded, or scavengers focused on the soft guts before burial.

Longisquama in situ with metatarsals in color.

Figure 4. Click to enlarge. Longisquama in situ with metatarsals and ribs framed by figure 2 in color. Yes, they are aligned with the bases of the plumes, but also with  the bases of phalanges.

Enlargements of the tracings can be found 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
New Scientist article here
Buchwitz M and Voigt S 2012. The dorsal appendages of the Triassic reptile Longisquama insignis: reconsideration of a controversial integument type. Paläontologische Zeitschrift, Issue 3, pp 313-331

The Back Half of Longisquama Recovered by Phylogenetic Bracketing

The back half of Longsiquama is so difficult to see that all prior experts took Sharov’s (1970) word for it, accepting his observation that the back half was missing. I’ll admit (and you’ll see) that even when the parts are delineated and labeled (Fig. 1), it’s hard for the eye to “see” what’s going on here. Skin, hair, membranes, plumes and scales are everywhere and just make the job more difficult. Only DGS (digital graphic segregation) enables one to pick out the crushed (and I do mean CRUSHED) outlines of the formerly missing parts.

New tracings of Longsiquama

Figure 1. Click to enlarge. New tracings of Longsiquama soft tissues and bones digitally segregated. Black squares are for alignment.

Be that as it may…
Let’s assume the back half isn’t there… for argument’s sake. No problem. Believe it or not, there is another way to figure out what the back half of Longisquama looks like without resorting to actually tracing the parts. This method gives strong clues, but without providing 100% assurance. And it’s called…

Phylogenetic Bracketing
Take the more primitive related taxon (Sharovipteryx) and the more derived related taxon (MPUM6009) and see what they do and don’t have in common. The taxon in the middle, Longisquama, should share most of the traits that both of these taxa share. Phylogenetic bracketing can be used to imagine a transitional taxon that we haven’t discovered yet. However, we’re at an advantage with Longisquama. We already know what the skull, forelimbs and upper torso look like. So, here’s where we’ll start (Fig. 2):

 

Figure 2. Origin of pterosaurs and figuring out the back half of Longisquama through phylogenetic bracketing. Gray areas are in question because others have not yet seen them on the slab.

Figure 2. Origin of pterosaurs and figuring out the back half of Longisquama through phylogenetic bracketing. Gray areas are in question because others have not yet seen them on the slab.

Traits shared by Sharovipteryx and MPUM6009 (and therefore likely present in the purportedly missing back half of Longisquama) include the following:

  1. short torso, shorter than or subequal to femur – this trait is actually not present in  Longisquama (Fig. 1), which has a uniquely longer, lemur-like torso, better for leaping than gliding
  2. bipedal configuration (relatively shorter fore limbs than hind limbs)
  3. four or more sacrals
  4. long, attenuated tail with chevrons parallel to centra
  5. elongated anterior ilium
  6. prepubis
  7. femur at least twice as deep as torso
  8. tibia longer than femur
  9. tibia more than twice the length of the pes
  10. simple hinge ankle joint between proximal tarsals (astragalus and calcaneum) and distal tarsals (principally the centralia and distal tarsal 4, but distal tarsal 3 is sometimes present and smaller)
  11. metatarsals increase in length from 1 to 4, but mt5 is less than a quarter of mt4
  12. feet relatively small – this trait is not present in the actual Longisquama, which has larger feet than either sister
  13. pedal digits increase in length from 1 to 5, but p.5.1 is subequal to mt4 in length and and p5.2 is hyperflexed.
  14. uropatagia present

So, add it all up and you get pretty much what I found in Longisquama, sans the torso length, which is uniquely long and lemur-like in Longisquama, and sans the foot size, which is uniquely larger in Longisquama. All prior reconstructions of Longisquama missed the long torso, long hind limbs, pterosaur like pedal digit 5 and attenuated tail. Instead authors imagined a shorter legged, shorter torso, more typically basilisk-like back half, but then none of them imagined that Longisquama was phylogenetically bracketed by Sharovipteryx and pterosaurs with a common ancestor in Cosesaurus.

Then we take the opposite tack: 
Traits that are distinctly different between the bracketing taxa, Sharovipteryx and MPUM6009, include the following:

  1. relative skull size – skull is small in both Sharovipteryx and Longisquama
  2. relative neck length – neck is short in both MPUM6009 and Longisquama
  3. pectoral girdle size – girdle is small in both Sharovipteryx and Longisquama
  4. forelimb size – midway between the vestigial fore limbs of Sharovipteryx and hyper elongated fore limbs of MPUM6009.
  5. The pelvis – was deep with ilial processes diverging at right angles in Longisquama and MPU6009

Dorsal plumes are distinct only on Longisquama
Dorsal plumes, which are secondary sexual traits (not gliding tools), along with the other extradermal membranes (originating with Cosesaurus), were but part of the package when wings developed in Longisquama and pterosaurs to enhance whatever mating ritual was going on with leaps, flapping and extravagant showing off. Matrix impressions indicate that smaller dorsal plumes were also present on MPUM 6009 (fig. 1), the basalmost pterosaur and the one with the longest hind limbs and shortest forelimbs.

Missing from this discussion is Cosesaurus
…which nests as a common ancestor for Sharovipteryx, Longisquama and pterosaurs in that phylogenetic order. The skull, neck and torso proportions of Cosesaurus are closer to pterosaurs than to either Longisquama or Sharovipteryx that diverged along their own morphological directions.

Current interpretation of Cosesaurus.

Figure 2. Current interpretation of Cosesaurus. Note the proportions of the skull, neck and torso are closer to pterosaurs than to either Sharovipteryx or Longisquama.

Inherited traits
Given that Sharovipteryx, Longisquama and pterosaurs (Fig. 2) shared a common ancestor, like Cosesaurus (sharing a quadrant-shaped coracoid, pteroid, sternal complex, antorbital fenestra (without fossa), prepubis, anteriorly extended ilium, 4 or more sacrals, an attenuated tail, elongated p5.1, etc. etc,)… we cam expect than Longisquama shared these traits by inheritance, giving further clues to the back half of Longisquama.

So, even if the back half of Longisquama were NOT present on the slab, the reconstruction  would look much the same, but with a smaller foot and shorter torso than presented here (fig. 1) based on tracing these elements. The manual fingers were also larger on Longisquama. So, phylogenetic bracketing validates the DGS tracings, but the tracings also revealed certain traits not revealed by phylogenetic bracketing. So, there was no “cheating” here, deciding what to trace prior to tracing it on the specimen.

Tomorrow I’ll show you a close-up of four Longisquama metatarsals that were mistaken for plume bases, which they align with.

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.

The origin and evolution of Longisquama “feather-like structures”

 

Figure 1. Click to enlarge. The origin and evolution of Longisquama's "feathers" - actually just an elaboration of the same dorsal frill found in Sphenodon, Iguana and Basiliscus. Here the origin can be found in the basal tritosaur squamate, Huehuecuetzpalli and becomes more elaborate in Cosesaurus and Longisquama.

Figure 1. Click to enlarge. The origin and evolution of Longisquama’s “feathers” – actually just an elaboration of the same dorsal frill found in Sphenodon, Iguana and Basiliscus. Here the origin can be found in the basal tritosaur squamate, Huehuecuetzpalli and becomes more elaborate in Cosesaurus and Longisquama.

A year ago
New Scientist covered a new paper on the dorsal appendages of Longisquama (Buchwitz and Voigt 2012) who wrote in his abstract, “We explain the existing feather similarity by their development from a filamentous primordium and a complex sequence of individual processes, some of which are reminiscent of processes observed in feather development. Such an interpretation is in agreement with a set of homologous mechanisms of appendage morphogenesis in an archosauromorph clade including Longisquama and feather-bearing archosaurs but does not necessarily require that the appendages of Longisquama themselves are feathers or high-level feather homologues.”

Here a larger and more parsimonious phylogenetic analysis
nests Longisquama with fenestrasaur, tritosaur squamates, derived from sisters to Huehuecuetzpalli and Cosesaurus (Fig. 1). With this lineage the origin and the development of the single line of dorsal plumes becomes easy to visualize. They were small originally and, through evolution, became enlarged. Among living reptiles, the tuatara (Sphenodon) and the iguana (Iguana) bear similar and homologous small structures.

Buchwitz reported in New Scientist, “The strange skin appendages of Longisquama are neither scales nor feathers,” says Michael Buchwitz of the Freiberg University of Mining and Technology, Germany. “They are perhaps linked to the early evolution of dino and pterosaur fuzz, though. Longisquama‘s skeleton is too incomplete to work out its exact evolutionary position, but Buchwitz says the little reptile was probably part of the lineage that gave rise to pterosaurs, crocodiles, dinosaurs and birds. Many of these groups later evolved their own skin appendages, including filaments on pterosaur wings, quills on the tails of some plant-eating ornithischian dinosaurs, and the proto-feathers of theropod dinosaurs. Longisquama shows that evolution was experimenting with the genes that gave rise to feathers long before any of these animals appeared on the scene.”

Tomorrow we’ll take a close look at the metatarsus of Longisquama courtesy of Buchwitz and Voigt (2012).

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
New Scientist article here
Buchwitz M and Voigt S 2012. The dorsal appendages of the Triassic reptile Longisquama insignis: reconsideration of a controversial integument type. Paläontologische Zeitschrift, Issue 3, pp 313-331

The skull of Longisquama documented

Yesterday we looked at the sternal complex and pectoral girdle of Longisquama (Sharov 1970). Today we’ll look at the controversial skull. Like the shoulder region, the skull is also covered in skin and scales and maybe… could those be long strands of ptero-hairs (pycnofibers) around the neck? You tell me. If you haven’t bought into the rest of the homologies I presented earlier, you won’t buy into the integumentary homologies. (sigh)

The skull of Longisquama in situ.

Figure 1. The skull of Longisquama in situ. The premaxilla and anterior dentary are largely missing. Otherwise crushing has shifted all the elements, even the transverse palatal and parietal elements, to the parasagittal plane (see figure 2). Also, note the sclerotic ring always gets crushed into the plane of the disk, never, as Bennett (2007) mistakenly reports in his anurognathid, on edge. Sharp-eyed observers should be able to see the windpipe.

In situ the overall shape of the skull is apparent, as are the scleral rings and teeth. For me the antorbital fenestra is clearly visible, though covered with tendrils of integument and underlain with palatal elements (Fig. 2), but for other workers, Like Senter, it is not so apparent, but note his lack of detail (Fig. 2). Note the rich crest of soft tissue arising from the frontals, which produces the longest overlooked plume, along with the gular sac in the throat region.

Do you see an antorbital fenestra? Several, but not all prior workers join you if so.

The skull of Longisquama has portrayed by other workers and as documented here.

Figure 2. The skull of Longisquama has portrayed by other workers and as documented here. The parietal is rotated, giving the impression of two crests. The occiptal region is folded in like a playing card. The antorbital fenestra reveals rotated palatal elements as shown in the reconstruction. Note the more or less cartoony aspects of the prior reconstructions, all lacking the precision and detail of the present tracing (produced with DGS) and the reconstruction, which puts the elements back together in three dimensions with a minimum of distortion.

Yes, the skull is messy,
and skin/scales/fibers obscure much, but the skull is largely complete. A reconstruction of the elements recovers a very pterosaur-like skull that also harkens back to the skull of the ancestral Cosesaurus. Some of the teeth are multicusped. The orbit is large. The palatal view suggests that Longisquama may have enjoyed binocular vision with that narrow snout and wide cranium. Such vision would have been appropriate for a lemur-like leaping reptile, however this is not a trait that basal pterosaurs inherited. The rotated parietals produce the illusion of a double crest, but the reconstruction removes the illusion. The rotated occipital bones help determine the width of the skull. Prior workers did not put the crash scene back together again, but took appearances as is, ignoring the occipital bones, and others. The vestigial quadratojugal extends from the jugal toward the quadrate without making a firm connection to it, again, as in pterosaurs and kin going back to Macrocnemus.

*
I did not put my earlier published interpretations (Peters 2000, 2002) of Longisquama here because they have been shifted to my trash pile in favor of this interpretation, produced with more understanding and a better eye for what lurks there. If anyone wants to talk about how I reconstruct Longisquama, do not rummage through my trash as Darren Naish did in last year’s critique. This is the most recent work. This would have been published several years ago, but reviewers blackballed it for the usual reasons.

If – just – the skull or – just – the skull and forequarters were known,
Longisquama would still nest with Cosesaurus, Sharovipteryx, Kyrgyzsaurus and basal pterosaurs. The rest of the anatomy cements those relationships.

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.

For those interested, PterosaurHeresies gets between 200 and 400 hits per day with about half that many unique visitors. The Lesothosaurus is a rhynchosaur post stands out as a recent exception with twice those numbers.

References
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.

wiki/Longisquama

Longisquama Pectoral Girdle and Sternal Complex Documented

In my efforts to help explain the relationship of the lepidosaur tritosaur fenestrasaur, Longisquama (Sharov 1970) to basal pterosaurs I present a pair of images (Figs. 1, 2) designed to illustrate just where the pectoral elements are. Admittedly these elements are difficult to pick out at first glance. So these are for those naysayers who often say, “I can’t see what you’re seeing!!” Here’s why:

Longisquama in situ. See if you can find the sternal complex, scapula and coracoid before looking at figure 2 where they are highlighted.

Figure 1. Click to enlarge. Longisquama in situ. See if you can find the sternal complex, scapula and coracoid before looking at figure 2 where they are highlighted.

The trouble
with seeing the bones of Longisquama is they are largely covered with scales and skin. That’s just a fact we need to embrace. Longisquama has more dermal and extra dermal tissue preserved than most other Mesozoic fossils. In such cases DGS (digital graphic segregation) really becomes a powerful tool, finding bones beneath the skin.

 

Figure 2. Click to enlarge. Longisquama ghosted out with DGS, other than the sternal complex (interclavicle+clavicles + sternum), scapula and coracoid.

Figure 2. Click to enlarge. Longisquama ghosted out with DGS, other than the sternal complex (interclavicle+clavicles + sternum), scapula and coracoid.

Here the affinities with pterosaurs are quite clear
Everyone has seen the horse-shoe-shaped clavicles, but few have recognized that they overlap medially and frame the sternum AND are surmounted by keeled interclavicle with crossbars that accommodate the quadrant-shaped ventral coracoids. (Whew!) This is the standard morphology of the classic pterosaur sternal complex (Wild 1993). Even the overall shape is identical to that in the basal pterosaur, MPUM6009 (Fig. 3). Only the fenestrasaurs, Cosesaurus, Sharovipteryx and pterosaurs share all these traits. In most derived pterosaurs the stem of the coracoid does indeed straighten out more, if you’ve noticed the difference.

Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.

Figure 3. Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex. The quadrant-shaped coracoid is the remnant and result of the anterior fenestra of the coracoid enlarging to the posterior rim, which is the only part that remains.

Still finding it difficult to spot some of these elements?
Then I encourage you to more closely examine the specimen itself or high resolution photos and become acquainted with sister taxa that will prepare you for what you should be looking for. I know that sounds self-fulfilling, but if you know that most tetrapods have four limbs you don’t stop at three. It’s the same thing at this point. Also see this page on ReptileEvolution.com for the same images of Longisquama (Figs. 1, 2) presented on a mouseover.

Flapping
Earlier we discussed the evolution of the sternal complex and pectoral girdle in fenestrasaurs (Fig. 3) and its role in flapping on a bipedal frame. That’s why these elements are so distinctly shaped, approaching the morphology of birds by convergence. The coracoid no longer slides against the interclavicle and sternum as in more primitive quadrupedal lizards.

Front Half Only
Even if only the front half of Longisquama was known (Sharov, 1970; Fig. 1), this would still be enough to cement Longisquama to pterosaurs. Adding the back half and fingers just puts frosting on the cake.

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
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.

wiki/Longisquama

Why an Increased Brain Capacity in Cosesaurus?

Derived from the basal lizard, Huehuecuetzpalli (Fig. 1), tritosaurs branched off in four distinct directions.

Huehuecuetzpalli

Figure 1. The mother of all pterosaurs, tanystropheids and drepanosaurs, Huehuecuetzpalli

Macrocnemus (Figs. 2-3) represents a long-necked terrestrial/marine clade culminating in Dinocephalosaurus and three other directions.

Jesairosaurus represents a long-necked, slow-moving arboreal clade culminating in the hook-tailed Megalancosaurus and Drepanosaurus.

Tanystropheus and kin going back to Huehuecuetzpalli.

Figure 2. Tanystropheus and kin going back to Huehuecuetzpalli.

Amotosaurus represents a long-necked terrestrial clade culminating in Langobardisaurus and Tanystropheus, some of which ventured into marine environs.

Cosesaurus (Fig. 3) represents a short-necked terrestrial clade culminating in Sharovipteryx, Longisquama and pterosaurs, which ventured into arboreal and aerial environs.

Among these four clades, Cosesaurus and kin appear to have had the larger cranium (red line in Fig. 1), both in length and depth. Why?

The answer is not neotony.
As demonstrated by Huehuecuetzpalli (Fig. 1) and pterosaurs, these taxa grew isometrically. Hatchlings and juveniles did not have larger eyes and a shorter rostrum. Now, with that said, what happened early on inside the egg, likely carried nearly to full term by the mother, is probably a different matter.

Clues to the answer for the bigger cranium and brain
may lie in the coracoids and pelvis of Cosesaurus.

Figure 1. Various tritosaur lizards shown to scale and their skulls portrayed to the same snout-occiput length. Red line represents the estimated cranial length. Note that in Cosesaurus, not only is the length longer, but the dorsal bulge is greater.

Figure 3. Various tritosaur lizards shown to scale and their skulls portrayed to the same snout-occiput length. Red line represents the estimated cranial length. Note that in Cosesaurus, not only is the length longer, but the dorsal bulge is greater.

Each of these taxa (Fig. 3) were quadrupeds, but Langobardisaurus and Cosesaurus were facultative bipeds in the manner of living lizards capable of bipedal locomotion. Narrow gauge, digitigrade and occasionally bipedal tracks with pedal digit 5 far behind the others are identified as Rotodactylus (Peabody 1948) tracks and they match the pedes of these two taxa (Peters 2000, Reneto et al. 2002).

The ilium in all four taxa (Fig. 1) are anteroposteriorly long, but more so in Cosesaurus. Such a morphology is associated with bipedal locomotion in various reptiles, like theropod dinosaurs. Bipedal capabilities free the forelimbs to do something other than support the body on the substrate.

In Langobardisaurus the manus remains small without much change from Macrocnemus.

However in Cosesaurus and Jesairosaurus the hand is relatively larger with longer medial metacarpals and longer medial digits. In Cosesaurus the anterior coracoid is eroded away by enlargement of the fenestrations until just the immobile quadrant-shaped posterior rim remains. This is an indicator of flapping, as we discussed earlier. In Cosesaurus the ulna is trailed by filaments (Ellenberger 1993, Peters 2009), the precursors of aktinofibrils in pterosaur wings. In Cosesaurus, such filaments would have only added to its retinue of extradermal decorations, but these could be animated by virtue of flapping. There was also a pteroid on Cosesaurus (Peters 2009, a former centralia, now migrated to the pre-axis of the radius), which in pterosaurs anchors and partially frames a propatagium, which is a flight membrane that also keeps the elbow from overextending.

Flapping, it would appear, was a social, territorial and secondary sexual trait and if so, Cosesaurus likely competed with other cosesaurs. The need for added coordination while a biped, while flapping excitedly to woo a mate, while watching out for competitors, while shrinking in overall size all may have served to increase the relative size of the cranium in Cosesaurus. The higher needs for coordination and social display seem to have supported the enlargement of the brain. At least that’s how it appears from here.

The relatively large size of the cranium is not continued in pterosaurs, which often, but not always (think: anurognathids) have an elongated rostrum to hyper-elongated rostrum (think ctenochasmatids, ornithocheirids and pteranodontids).

And birds?
In Archaeopteryx and its closest kin there is a similar and convergent expansion of the cranium that is otherwise not expressed in other nonvolant Meszoic bird-like taxa, like oviraptorids and veloceraptorids, but is present in Ichthyornis and living birds.

So, even in this regard, Cosesaurus can be considered “the Archaeopteryx of pterosaurs,” no matter the persistent rumors that such a creature remains unknown to science.

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
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
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.
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.

wiki/Cosesaurus