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

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Paul Ellenberger RIP

I just learned of the death in 2016
of Paul Ellenberger, a French paleontologist from Montpellier, who reached the age of 97 and wrote about Cosesaurus and several ichnotaxa, as we learned earlier here, here and here.

Ellenberger was kind enough
to host me, a stranger, for a day and a night, following my visit to Cosesaurus in Barcelona in the mid 1990s. We talked about it. I tried to convince him that he should be pleased to be the discoverer of the ‘mother of all pterosaurs‘, but he continued to insist it was a pre-bird. His discovery was published in 1974, but his conclusions were invalidated by several others, including Sanz and López-Martinez 1984, who considered Cosesaurus a juvenile Macrocnemus (which is close, but no cigar) and a lepidosaur (which was later confirmed by the large reptile tree.)

Figure 1. Cosesaurus insitu. No bones are present. This is a natural mold that includes an amorphous blob, a jellyfish, that trapped one foot of this unique specimen.

Figure 1. Cosesaurus insitu. No bones are present. This is a natural mold that includes an amorphous blob, a jellyfish, that trapped one foot of this unique specimen. This is a sister to the ancestor of pterosaurs. Note the antorbital fenestra without a fossa, convergent with proterosuchids.

Sad news about Cosesaurus
The authors of the Wikipedia Cosesaurus page have erased nearly all (but see below) data and references to Peters 2000a, the first paper that included Cosesaurus and related taxa added to several previously phylogenetic analyses that included archosaurs and pterosaurs. That study found pterosaurs nested with Cosesaurus and kin, not archosaurs in every analysis. The removal of this citation from the Wiki page is equivalent to sweeping data under the rug. Peters 2000a was a peer-reviewed publication in a respected academic journal.

If you’re looking for the ancestors of pterosaurs,
Cosesaurus is where you look. You can test the Peters 2000 hypothesis yourself with your own observations and phylogenetic analysis.

Perhaps an oversight,
the Wikipedia authors failed to delete the image of Cosesaurus that I provided several years ago with this caption:

“Here is the fossil known as Cosesaurus aviceps, the sole specimen of this genus. Although lizard-like in appearance, this Middle Triassic fenestrasaur/lizard had certain traits that place it on the lineage of Sharovipteryx, Longisquama and pterosaurs. Among these traits are: an elongated narial opening, an antorbital fenestra, a very large orbit, a spike-like quadratojugal, a strap-like scapula, a stem-like coracoid, an enlarged sternum displaced anteriorly to align with transverse clavicles, a pteroid, an elongated anterior process of the ilium, a sacrum consisting of four vertebrae, a prepubis, a simple hinge ankle joint without fusion of the astragalus and calcaneum, a calcaneum without a “heel” and an elongated pedal digit 5, plus soft tissue membranes arising from the trailing edges of the limbs and the dorsal margin of the spine and skull. No digits were vestigial, but manual digit V was reduced.”

As you might remember
earlier the authors of the Wikipedia page on pterosaurs lied with regard to my access to fossils. This line of thinking follows in lockstep Darren Naish’s bogus propaganda regarding the ReptileEvolution.com website, reviewed here. Naish’s blog and other efforts has gained followers and that’s not good for science. I hate to say it, but he’s going to come out as the leader of his suppressive minions when historians look back at this decade, unless he comes out and redeems himself soon. In private correspondence, I recently invited Naish to comment on the several recent papers that confirmed nestings first discovered in the LRT, but he dismissed that invitation. So we’ll have to fight this suppression of data a while longer.

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. Montpellier 12-16 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
Sanz JL and López-Martinez N 1984. The prolacertid lepidosaurian Cosesaurus aviceps Ellenberger & Villalta, a claimed ‘protoavian’ from the Middle Triassic of Spain. Géobios 17: 747-753.

wiki/Cosesaurus

Macrocnemus skull in DGS

This started with
a fuzzy photo of a  complete fossil Macrocnemus specimen, PMR T2472 (Fig 1).

Figure 1. GIF animation of PMR T2472, a large Macrocnemus in situ and reconstructed from a fuzzy photo.

Figure 1. GIF animation of PMR T2472, a large Macrocnemus in situ and reconstructed from a fuzzy photo.

Many specimens attributed to Macrocnemus
are known, each one a little different phylogenetically. Reports of a ‘juvenile’ Macrocnemus refer to the phylogenetically basalmost and smallest of the known specimens, the one closest to its outgroup taxon, the tritosaur lepidosaur, Huehuecuetzpalli.

It’s good to remind yourself
before reading the reference titles, that Macrocnemus and kin are not protorosaurs (= prolacertiforms), nor are they archosauriforms. Even I made the same mistake (Peters 2000b) in my more naive days before the LRT recovered Macrocnemus and kin as tritosaur lepidosaurs in Peters 2007.

From this rather ordinary taxon arises 
such diverse and exotic taxa as Dinocephalosaurus, Sharovipteryx, a variety of Tanystropheus, several Langobardisaurus, Longisquama and pterosaurs. Peters 2007 reported, “The basal lizard, Huehuecuetzpalli is the most primitive taxon in this newly revealed third squamate clade between Iguania and Scleroglossa. Two branches arise from it. Jesairosaurus is basal to the Drepanosauridae. Three distinct specimens of Macrocnemus give rise to the Tanystropheidae,the Langobardisaurinae and to the Fenestrasauria respectively.” Jesairosaurus and Drepanosauridae are now basal lepidosauriformes.

References
Li C, Zhao L-J and Wang L-T 2007A new species of Macrocnemus (Reptilia: Protorosauria) from the Middle Triassic of southwestern China and its palaeogeographical implication. Science in China D, Earth Sciences 50(11)1601-1605.
Li C, Wu X-C, Zhao L-J, Nesbitt SJ, Stocker MR, Wang L-T 2016. A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria. The Science of Nature 103: 95. doi:10.1007/s00114-016-1418-4
Nopcsa F 1931. Macrocnemus nicht Macrochemus. Centralblatt fur Mineralogie. Geologic und Palaeontologie; Stuttgart. 1931 Abt B 655–656.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peyer B 1937. Die Triasfauna der Tessiner Kalkalpen XII. Macrocnemus bassanii Nopcsa. Abhandlung der Schweizerische Palaontologische Geologischen Gesellschaft pp. 1-140.
Renesto S and Avanzini M 2002. Skin remains in a juvenile Macrocnemus bassanii Nopsca (Reptilia, Prolacertiformes) from the Middle Triassic of Northern Italy. Jahrbuch Geologie und Paläontologie, Abhandlung 224(1):31-48.
Romer AS 1970. Unorthodoxies in Reptilian Phylogeny. Evolution 25:103-112.

wiki/Macrocnemus

 

More data on the scaly fenestrasaur, Kyrgyzsaurus

Updated March 3, 2016 with a reconstruction from the tracings.

An earlier nesting
in the large reptile tree placed the Late Triassic reptile Kyrgyzsaurus not with drepanosaurs, but with fenestrasaurs, between Cosesaurus and higher taxa, all bipeds or near bipeds. The parallelogram-shaped cervicals indicate the skull was held higher than the shoulders, as in pterosaurs, Longisquama and Cosesaurus. 

Figure 1. New data on Kyrgyzsaurus provides the first evidence for forelimbs.

Figure 1. New data on Kyrgyzsaurus provides the first evidence for forelimbs. This is the first time I’ve seen the bones in color. Note: Spindler thought the forelimb was tiny, but did not trace left forelimb elements, only the elbow visible over the dorsals. This is an example of DGS. Higher resolution would enable further details to be traced.

New photos
(Fig. 1) of what appear to have come from an abstract posters provided online by Spindler et al. 2014 reveal more data for Kyrgyzsaurus, including a complete pectoral girdle and tiny forelimb with laterally folding digit 4 (as in pterosaurs), adding to the possibility that long hind limbs probably gave this taxon a bipedal configuration as well (based on phylogenetic bracketing). Longisquama and Sharovipteryx were sisters and contemporaries that likewise had short arms.

Figure 2. Updated figure of Kyrgyzsaurus.  Note the tiny forelimbs and large hyoid, as in Sharovipteryx.

Figure 2. Updated figure of Kyrgyzsaurus. Note the tiny forelimbs and large hyoid, as in Sharovipteryx.

The abstract discusses
coloration in the scales, not unexpected as exquisitely preserved Late Triassic insects likewise preserve coloration in this formation.

From the poster
“Dorsally the scales are generally smaller, but conspicuous craniocaudal rows of large oval to rectangular scales occur within the meshwork of smaller scales. The reddishly preserved skin colouration follows no simple pattern: There is a larger color patch along the posterior margin of the skull, the ventral neck and anterior trunk display scales with tiny colour spots, and the dorsal rows of larger scales are sometimes marked by thin aligned stripes.”

Figure 3. The origin of pterosaurs now includes Kyrgyzsaurus, nesting between Cosesaurus and Sharovipteryx.

Figure 3. The origin of pterosaurs now includes Kyrgyzsaurus, nesting between Cosesaurus and Sharovipteryx. Click to enlarge.

Unfortunately Spindler et al.
were unable to decipher their own precise tracings and so overlooked the forelimb of Kyrgyzsaurus. In this case it might have been important for them to understand where this specimen nested in the reptile family tree (published here in 2012). They considered it merely as ‘a reptile’ with tiny forelimbs with very, very small fingers, evidently imagined. They did not even call it Kyrgyzsaurus, or make reference to the original paper (Alfanov and Kurochkin 2011), even though the specimen was named three years earlier. It is clear that Spindler et al. did not trace fingers, but guessed at their presence. They labeled the ‘pectoral girdle’ with a vague arrow, but not the individual elements. Maybe none of this matters, as their study focused on skin coloration.

DGS
(digital graphic segregation), a reconstruction, and a phylogenetic analysis once again pulled data out of an online photo that was overlooked by first hand observers.

References
Alifanov VR and Kurochkin EN 2011. Kyrgyzsaurus bukhanchenkoi gen. et sp. nov., a new reptile from the triassic of southwestern Kyrgyzstan. Paleontological Journal 45(6): 639–647. doi:10.1134/S0031030111060025.
Spindler F, Buchwitz M, Fischer J and Voigt S 2014. Preservation of tetrapod skin in the Triassic Madygen Formation. Conference: 82. Jahrestagung der Paläontologischen Gesellschaft, At Vienna (Austria), Volume: Beiträge zur Paläontologie – Program and Abstracts 32: pp. 76–77.

wiki/Kyrgyzsaurus

 

News on the Origin of Pterosaurs on YouTube

I just uploaded a pterosaur origins video on YouTube. Click here to view it.

Click to view this "Origin of Pterosaurs" video on YouTube.

Click to view this “Origin of Pterosaurs” video on YouTube. 17 minutes long. 

Secondary sexual behavior in Longisquama (and Cosesaurus)

Sure Longisquama had giant plumes
that likely entranced the lay-dees… and/or the gents…

But as the proximal outgroup to the Pterosauria,
and provided with a similar pectoral girdle (sternal complex, strap-like scapulae, quadrant-shaped coracoids, it was a likely flapper, as we talked about earlier here with similar traits in Cosesaurus (Fig. 1)

Figure 1. Cosesaurus flapping - fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Figure 1. Click to enlarge and animate. Cosesaurus flapping.

Here (Fig. 2) is an animated Longisquama, flapping and with tail wags, which we talked about earlier here.

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

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

With these traits and behaviors basal fenestrasaurs converged with theropods ancestral to birds. In these ways flapping preceded powered flight, in both cases co-opted from secondary sexual behaviors in these highly visual reptiles.

What about those really BIG Rotodactylus tracks?

While virtually all Rotodactylus (Peabody 1948) tracks (digitigrade, proximal phalanges elevated, long stride, narrow gauge manus / wider pes, occasionally bipedal, first digit impresses at tip only, fifth digit impresses far behind the others, extremely variable speed) are the right shape to fit the Cosesaurus  (Ellenberger and Villalta 1974) pes, as we learned earlier here, some Rotodactylus tracks are BIG (4-5 cm length)! That’s way too big for Cosesaurus to fill. So the search is on for something like Cosesaurus, but far bigger and wide ranging (Fig. 1). Rotodactylus tracks have been found across Europe and the western USA and they range across the Early to Middle Triassic.

Figure 1. Scaling a quadrupedal Cosesaurus to the larger Rotodactylus tracks from Haubold 1983.  Quadrant represents center of balance in the closeup foot. Graphic representation of a butt joint is nearby.

Figure 1. Click to enlarge. Scaling a quadrupedal Cosesaurus to the larger Rotodactylus tracks from Haubold 1983. Quadrant represents center of balance in the closeup foot showing how pedal digit 5 made those posterior impressions with a claw mark (Peters 2000). Graphic representation of a butt joint is nearby. The actual Cosesaurus is much smaller than these trackmakers. I enlarged the coracoid on the larger hypothetical trackmakers because they were not bipedal flappers. This configuration of pedal digit 5 is often preserved in basal pterosaurs.

So, after touting the perfect match of Cosesaurus to Rotodactylus tracks (Peters 2000), this is the first time I’ve conformed Cosesaurus to a quadrupedal pose to match these much larger tracks from the Early (=Lower) Triassic (Solling and Röt formations. Scythian/Anisian) of Germany. Haubold (1983) likened Lagosuchus (Maraschus), but  that’s not as good a match as Cosesaurus and Langobardisaurus, which were not so well known or described in the early ’80s.

So, Rotodactylus tracks are not archosaurian, but proto-pterosaurian, fenestrasaurian.

Cosesaurus matched to Rotodactylus from Peters 2000.

Figuure2. Cosesaurus matched to Rotodactylus from Peters 2000.

Haubold listed 4 points that were significant in the development of archosaurs:

  1. “Reduction of the manus as [a] function of bipedalism;
  2. Stride length in relation to width of trackway and pace angulation (small trackway pattern) as a function of semierect to erect gait;
  3. Reduction of pes digits 1 and 5 as a function of tridactylism (this point is unique in Rotodactylus, which impresses  digit 5 far behind the others).
  4. The cross axis of the pes and the outward orientation of the pes axis to the direction of movement. A more rectangular cross axis may demand a mesotarsal joint.”
Cosesaurus and Rotodactylus, a perfect match.

Figure 3. Click to enlarge. Cosesaurus and Rotodactylus, a perfect match. Elevate the proximal phalanges along with the metatarsus, bend back digit 5 and Cosesaurus (left) fits perfectly into Rotodactylus (right).

Rotodactylus tracks show extreme speed variation, which is rare for reptiles, but compliments the higher metabolic niche of fenestrasaurs.

By assigning Rotodactylus tracks to basal bipedal archosaurs, Haubold made the same hopeful mistake that Brusatte et al. (2011) and Niedzwiedzki et al. (2013) made assigning Rotodactylus tracks to  Lagerpeton. These workers hoped it was transitional to dinosaurs, but the match was poor, both phylogenetically and morphologically. The better match is between Cosesaurus and Rotodactylus (Peters 2000, Fig. 3).

So, what about those really BIG Rotodactylus tracks? They were made my really big mostly quadrupedal cosesaurs, evidently. And evidently, only the little cosesaurus were better bipeds, capable of flapping.

Figure 4. Rotodactylus from Haubold adapted from Peabody 1948. Unfortunately, no reptiles have a rotated and reversed pedal digit 5. But note the resemblance of the conjectural trackmaker to Cosesaurus, unknown in 1948.

Figure 4. Rotodactylus from Haubold 1983 adapted from Peabody 1948. Unfortunately, no reptiles have a rotated and reversed pedal digit 5. But note the resemblance of the conjectural trackmaker to Cosesaurus, unknown in 1948. Note: most reptiles while moving do not have all four limbs on the  ground at one time. The elongated pedal digit 5 shown here is likely a drag mark. Size of these prints: between 4 and 5 cm in length, about the size of the examples in figure 1. Note, no claw marks on pedal digit 5.

So, widespread Rotodactylus tracks demonstrate that cosesaurs were widespread. They also appeared in a variety of sizes. While the large ones remained quadrupedal, like ancestral macrocnemids, the small ones became increasingly bipedal. This radiation of tritosaur lizards preceded the radiation of squamates in the Jurassic and later epochs.

References
Brusatte SL, Niedz´wiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B, 278, 1107–1113.
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.
Haubold H 1983. Archosaur evidence in the Buntsandstein (Lower Triassic). Second Symposium on Mesozoic Terrestrial Ecosystems, Jadwisin 1981. Acta Palaeontologica Polonica 28 (1-2):123-132.
Niedzwiedzki G, Brusatte SL and Butler RJ 2013. Prorotodactylus and Rotodactylus tracks: an ichnological record of dinosauromorphs from the Early–Middle Triassic of Poland. Geological Society, London, Special Publications, first published April 23, 2013. doi 10.1144/SP379.12
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 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
wiki/Cosesaurus