Naked pterosaurs–or feathered? PhDs clash

Earlier Yang et al. 2019
argued that pterosaurs, like the disc-headed unnamed anurognathids, CAGS-Z070 (Fig. 1) and NJU-57003 (Fig. 2), had protofeathers and thus they were related to dinosaurs with feathers.

Figure 2. CAGS Z020 anurognathid reconstructed in lateral view. As in other disc-head anurognathids the frog-like eyeballs likely rose above the flat skull.

Figure 1. CAGS Z020 anurognathid reconstructed in lateral view. As in other disc-head anurognathids the frog-like eyeballs likely rose above the flat skull.

Figure 2. NJU-57003 insitu. Even though the photo is fuzzy, so is this pterosaur apart from the wing membranes.

Figure 2. NJU-57003 insitu. Even though the photo is fuzzy, so is this pterosaur apart from the wing membranes.

Yesterday Unwin and Martill 2020 
argued that pterosaurs did not have protofeathers. They said, any feathery-looking remains are decomposing fibers shed from the wings. They note that bristle-like integumentary structures do fringe the jaws of CAGS-Z070, but they do not concede any sort of homology other than to call the bristles ‘bristles’.

Yesterday Yang et al. 2020
replied to Unwin and Martill 2020, defending their hypothesis. “In our [2019] paper, we explored the morphology, ultrastructure and chemistry of the dermal structures of pterosaurs and showed that they probably had a common evolutionary origin with the integumentary structures seen widely in dinosaurs (including birds), their close relatives.” 

Their first sentence is wrong. As long-time readers are tired of hearing by now, Peters 2000, 2007 tested the pterosaur – dinosaur relationship by adding taxa. The added taxa attracted pterosaurs away from dinosaurs and nested them in a new and overlooked third clade of lepidosaurs, the Tritosauria, of which late surviving Huehuecuetzpalli is a basal member.

Yang et al. 2020 remind us,
“all four pycnofibre types are morphologically identical to structures already described in birds and non-avialan dinosaurs, not only in terms of gross morphology but also in their ultrastructure and chemistry, including melanosomes and chemical evidence for keratin; collectively, thesefeatures are consistent with feathers.”

Or hair. Or scales. Does anyone else see Yang et al. “Pulliing a Larry Martin“? The first thing Yang et al. should do is establish the relationship of pterosaurs with more parsimonious outgroups. They should know convergence is rampant within the Vertebrata and pterosaurs have never nested with dinosaurs whenever other candidates have been offered.

“Mapping these data onto a phylogeny yields a single evolutionary origin for feathers minimally in the avemetatarsalian ancestor of both pterosaurs and dinosaurs.”

That’s what happens when you omit data and citations. Professor Michael Benton is on the list of authors. This is not the first time Benton has omitted data and citations. You might remember when Hone and Benton 2008, 2009 were going to test competing hypotheses of relationship of pterosaurs. They reported they would test the archosaur hypothesis of Bennett 1996 versus the non-archosaur hypothesis of Peters 2000. Peters tested four prior hypotheses (including Bennett 1996) by simply adding Longisquama (Fig. 5), Cosesaurus, Sharovipteryx, and Langobardisaurus (Fig. 6), all of which attracted pterosaurs to their clade. Several of these added taxa have pterosaur-like fibers on their bodies (Fig. 5). When the anticipated results did not go their way, Hone and Benton 2009 deleted all reference to Peters 2000 and wrote that Bennett 1996 had come up with both competing hypotheses.

Getting back to the Reply from Yang et al. 2020:
“In their comment, Unwin and Martill [2020] assert that the branched integumentary structures that we identified are not feathers or even pycnofibres. They make five arguments in favour of their point of
view:”

  1. “superposition or decomposition of composite fibre-like structures or aktinofibrils yields branched structures similar to those in the anurognathids;
  2. the anatomy and anatomical distribution of the anurognathid integumentary structures are consistent with aktinofibrils, but not pycnofibres;
  3. evidence for keratin and melanosomes is not indicative of pycnofibres but rather reflects contamination from epidermal tissue;
  4. the branching we reported is not consistent with exclusively monofilamentous coverings in other anurognathids; and
  5. homology of the branched integumentary structures with feathers cannot be demonstrated conclusively owing to the simple morphology of the former.”

“We refute all five of their arguments.”

The view from ReptileEvolution.com:
Apparently no one has noticed that anurognathids, like Jeholopterus (Fig. 3), are decidedly different than other pterosaurs in terms of the length and quantity of their feathery fluff. In this way, and many others, anurognathids resemble modern owls, predator birds capable of silent flight due to the fluffiness of the pelage.

It is also worth noting
that anurognathids leave no descendants after the Early Cretaceous. In any case, pterosaurs are not related to birds or dinosaurs or archosaurs or archosauriformes or archosauromorphs, as demonstrated in the large reptile tree (LRT, 1740+ taxa) which tests all candidates for dinosaur, bird and pterosaur ancestry back to headless Cambrian chordates.

Figure 4. Jeholopterus in dorsal view. Here the robust hind limbs, broad belly and small skull stand out as distinct from other anurognathids. Click to enlarge.

Figure 3. Jeholopterus in dorsal view. Here the robust hind limbs, broad belly and small skull stand out as distinct from other anurognathids. Click to enlarge.

A figure caption from Unwin and Martill 2020
(Fig. 4) reports, “The inner region of the cheiropatagium adjacent to the body anterior to the pelvis. The dark, slightly granular epidermal surface of the integument (et) covering the torso (t) contrasts with the remarkably thin epidermal surface (ep) of the integument forming the proximal region of the cheiropatagium (c). Much of the epidermis covering the cheiropatagium has been lost, exposing closely packed and aligned aktinofibrils (ak) now slightly decayed. On the far left, much of the cheiropatagium has been pulled away, leaving a few incomplete aktinofibrils and numerous fine fibrils (fb) from which they were composed.”

This is the PIN–2585/36 specimen of Sordes pilosus, which Unwin has not shown in its entirety—ever. The proximal membrane (yellow) is the left fuselage fillet (see Fig. 3), which disproves the batwing hypothesis championed by Unwin and other PhDs. Unwin and Martill say the fine fibrils at left have been ‘pulled away’. I know of no fossil processes that ‘pull’ fine fibrils away from their original insertion points.

Other Sordes specimens have been misinterpreted by Unwin since Unwin & Bakhurina 1994. Peters 1995 argued against the bat-wing interpretation offered by Unwin & Bakhurina 1994 further described nine years ago here.

Figure 4. From Unwin and Martill 2020, colors, arrows and inset added. This is all that has ever been published of PIN-2585/36, a purported Sordes specimen. Given the few clues this appears to be the left fuselage fillet (see Fig. 3), which means this is why Unwin is only showing part of it because, if so, this disproves the batwing hypothesis championed by Unwin and other PhDs.

Figure 4. From Unwin and Martill 2020, colors, arrows and inset added. This is all that has ever been published of PIN-2585/36, a purported Sordes specimen. Given the few clues this appears to be the left fuselage fillet (see Fig. 3), which means this is why Unwin is only showing part of it because, if so, this disproves the batwing hypothesis championed by Unwin and other PhDs.

Yang et al. 2020 conclude:
“In light of this, the most parsimonious interpretation of the simple and branched integumentary appendages in the anurognathid pterosaurs remains our original conclusion that they are feathers.”

This conclusion is not supported by the LRT. Taxon inclusion would have helped Yang et al. 2020. Unwin and Martill 2020 are likewise not correct. They should have shown the same evidence that Yang et al. presented was incorrect, rather than showing their own evidence, which does not support their position.

An online article posted on Phys.org
cites U of Leicester and U of Portsmouth (England) workers. David Unwin and David Martill who claim pterosaurswere in fact bald.”

The article reports, “Feathered pterosaurs would mean that the very earliest feathers first appeared on an ancestor shared by both pterosaurs and dinosaurs, since it is unlikely that something so complex developed separately in two different groups of animals.”

Unlikely ≠ impossible. Just cite the LRT where convergence is rampant. Adding taxa is something paleontologists have been loathe to do for the last twenty years since Peters 2000 moved pterosaurs away from dinosaurs and 13 years since Peters 2007 moved pterosaurs into lepidosaurs. But let’s move on…

The article then states, 
“It would also suggest that all dinosaurs started out with feathers, or protofeathers but some groups, such as sauropods, subsequently lost them again—the complete opposite of currently accepted theory.” 

Once again, add taxa to determine where feathers, or protofeathers, first appeared in tetrapods and if there was a second genesis within the clade.

The article then states,
“The evidence rests on tiny, hair-like filaments, less than one tenth of a millimeter in diameter, which have been identified in about 30 pterosaur fossils. Among these, Yang and colleagues were only able to find just three specimens on which these filaments seem to exhibit a ‘branching structure’ typical of protofeathers.”

Evidence from 30 or just 3 pterosaurs is considerable. Nevertheless, all prior authors omit the pre-pterosaurs (Cosesaurus, Oculudentavis, Sharovipteryx, Longisquama, Fig. 5) most of which have epidermal membranes and fibers. These taxa (Fig. 6) nest between pterosaurs and the lepidosaur Huehuecuetzpalli.

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

Figure 5. Longisquama in situ. See if you can find the sternal complex, scapula and coracoid before looking at figure 2 where they are highlighted.

The Phys.org article then states,
“Unwin and Martill propose that these are not protofeathers at all but tough fibers which form part of the internal structure of the pterosaur’s wing membrane, and that the ‘branching’ effect may simply be the result of these fibers decaying and unraveling.”

Professor Unwin said:
“The idea of feathered goes back to the nineteenth century but the fossil evidence was then, and still is, very weak. Exceptional claims require exceptional evidence—we have the former, but not the latter.”

The evolution of the pterosaur tail beginning with a basal lizard, Huehuecuetzpalli.

Figure 6. The evolution of the pterosaur tail beginning with a basal lizard, Huehuecuetzpalli.

Professor Martill noted:
that either way, palaeontologists will have to carefully reappraise ideas about the ecology of these ancient flying reptiles. Martill said, “If they really did have feathers, how did that make them look, and did they exhibit the same fantastic variety of colors exhibited by birds. And if they didn’t have feathers, then how did they keep warm at night, what limits did this have on their geographic range, did they stay away from colder northern climes as most reptiles do today. And how did they thermoregulate? The clues are so cryptic, that we are still a long way from working out just how these amazing animals worked.”

As a final note, let’s remember, that when it comes to pterosaur origins, 
workers have been keeping their blinders on for decades. Not sure why, but what results is the current misunderstanding expressed by Yang et al. 2020 AND Unwin and Maritill 2020.


References
Peters D 1995. Wing shape in pterosaurs. Nature 374, 315-316.
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 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371, 62–64.
Unwin DM and Martill DM 2020. No protofeathers on pterosaurs. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-020-01308-9
Yang Z et al. 2019. Pterosaur integumentary structures with complex feather-like branching. Nature Ecology & Evolution 4, 24–30 (2019).
Yang Z et al. 2020. Reply to: No protofeathers on pterosaurs. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-020-01308-9

https://phys.org/news/2020-09-naked-prehistoric-monsters-evidence-reptiles.html?fbclid=IwAR0YSjtIfZRBUiD6W3b1jwnhzWPFe_eXBE4ABFa2D8QXRCI8GNIfxNQEEs4

From today’s dml.cmnh.org:

“If you can’t cope with the idea of naked pterosaurs, don’t watch my SVP presentation…”

––––––––––––––––––––––––––––––––––––––––––––––
Dr David M Unwin
Associate Professor (Museum Studies)
School of Museum Studies, University of Leicester
t: +44 116 252 3947   e: dmu1@le.ac.uk

Another Triassic turtle enters the LRT

This turned out to be a somewhat ‘ho-hum’ event,
but a good opportunity to review turtle origins, still suffering from taxon exclusion and inappropriate taxon inclusion, as determined by the LRT (subset Fig. 4), which tests all contenders.

Sterli, de la Fuente and Rougier 2007 described
“a complete cranial and postcranial anatomy and a phylogenetic analysis of Palaeochersis talampayensis (Rougier, de la Fuente and Arcucci 1995), the oldest turtle from South America, is presented here.”

Figure 2. Palaeochersis skull from Rougier et al. 1995 with colors and new bone labels added.

Figure 1. Palaeochersis skull from Sterli et al. 2007 with colors and new bone labels added.

Figure 2. Palaeochersis overall reconstructed from elements in Sterli, de al Fuente and Rougier 2007. This Triassic turtle nests in the LRT with Proganochelys in figure 3.

Figure 2. Palaeochersis overall reconstructed from elements in Sterli, de al Fuente and Rougier 2007. This Triassic turtle nests in the LRT with Proganochelys in figure 3.

Unfortunately
taxon exclusion and bone misinterpretation mar this description, published before the genesis of ReptileEvolution.com and a distinctly different take on turtle origins based on including more taxa. Palaeochersis (Figs. 1, 2; PULR 68; Late Triassic, Norian-Rhaetian) is the third Triassic turtle to enter the LRT after Proganochelys and Proterochersis (Fig. 3).

Proganochelys and Proterochersis, two Traissic turtles.

Figure 3. Proganochelys and Proterochersis, two Traissic turtles.

Sterli, de la Fuente and Rougier 2007 report,
“Palaeochersis talampayensis has primitive character states in the skulllike the presence of lacrimal and supratemporal bones, the presence of a quadrate pocket, a foramen trigemini partially enclosed, middle ear limits partially developed, presence of an interpterygoid vacuity, presence of a cultriform process and a high dotsum sellae. However, Palaeochersis talampayensis also has derived character states like the absence of vomerine teeth, basipterygoid articulation sutured, processus paraoccipitalis tightly articulated to quadrate and squamosal, and cranioquadrate space partially enclosed in a canal. The postcranial description was based on Palaeochersis holotype (PULR 68) and on specimen PULR 69 represented by an almost complete skeleton and a hindfoot, respectively.” 

Figure 1. Carbonodraco enters the LRT alongside another recent addition, Kudnu, at the base of the pareiasaurs + turtles.

Figure 4. Subset of the LRT focusing on turles. Palaeochersis is not listed here, but nests with Proganochelys, as shown in the LRT, which has been updated.

According to the LRT
Proganochelys, Proterochersis and Palaeochersis were terminal taxa, leaving no descendants. Instead, according to the large reptile tree (LRT, 1740+ taxa, subset Fig. 4), a Late Permian/Early Triassic sister to Niolamia gave rise to a Late Permian/Early Triassic sister to Meiolania (Fig. 5) gave rise to a Triassic hornless Kallokibotion, otherwise known only from the Latest Cretaceous and later. More derived taxa include Kayentachelys (Early Jurassic) filling in the temporal gap. In turtles the cranial horns are primitive. The loss of cranial horns is a derived trait. That’s something turtle workers have yet to appreciate.

Figure 4. Bunostegos and Elginia at the base of hard shell turtles in the LRT, where late-surviving Niolamia and Meiolania are basal hardshell turtles more primitive than Proganochelys and Palaeochesis. Not all colors here match those in figure 1. Note the labels.

Figure 5. Bunostegos and Elginia at the base of hard shell turtles in the LRT, where late-surviving Niolamia and Meiolania are basal hardshell turtles more primitive than Proganochelys and Palaeochesis. Not all colors here match those in figure 1. This sequence was submitted for publication, but rejected. 

Taxon exclusion mars all prior basal turtle studies.
In the LRT Palaeochersis nests with another Triassic turtle, Proganochelys. Given their overall and detailed morphology, that was expected and comes as no surprise.

Not much else to report here,
other than the identities of cranial bones in hard-shell turtles need to be reconsidered in light of their ancestry from the late-surviving, giant-horned turtles, Niolamia and Meiolania and before that, ancestral pareiasaurs like Elginia and Bunostegos (Fig. 4). These are taxa traditionally omitted from recent turtle ancestry studies. The LRT omits no putative ancestral turtle candidates. Rather the LRT tests them all. And for new readers, note (Fig. 4) soft-shell turtles had their own parallel origin and ancestry from different small horned pareiasaurs.

Longtime readers may notice:
Several of the older turtle skull illustrations (Fig. 5) were recolored to match an emerging standard pattern (e.g. bright green for supratemporals). My fault that I did not do this from the very beginning ten years ago. More work for me, but lookout for different colors in older blogposts.


References
Rougier GW, de la Fuente and Arcucci AB 1995. Late Triassic turtles form South America. Science 268:855–858.
Sterli J, de la Fuente MS and Rougier GW 2007. Anatomy and relationships of Palaeochersis talampayensis, a Late Triassic turtle from Argentina. Palaeontographica Abt. A 281:1–61.

wiki/Palaeochersis (Spanish)

Kopidosaurus: no longer an enigmatic iguanian

Scarpetta 2020 bring us a tiny new Eocene lizard,
Kopidosaurus perplexus (YPM VP 8287) known from most of a disarticulated skull still in the matrix, but carefully presented in several views as µCT scans (Fig. 1).

Scarpetta warns his readers,
“Fossil identifications made in a phylogenetic framework are beholden to specific tree hypotheses. Without phylogenetic consensus, the systematic provenance of any given fossil can be volatile. Pleurodonta (Squamata: Iguania) is an ancient and frequently-studied lizard clade for which phylogenetic resolution is notoriously elusive.

Scarpetta reports,
“I address the effects of three molecular scaffolds on the systematic diagnosis of that fossil. I use two phylogenetic matrices, and both parsimony and Bayesian methods to validate my results, and perform Bayesian hypothesis testing to evaluate support for two alternative hypotheses of the phylogenetic relationships of the new taxon.”

Scarpetta did not provide a reconstruction of the skull. That is remedied here (Fig. 1).

Unfortunately Scarpetta’s three molecular scaffolds are based on genes, so they are completely useless for deep time studies, as documented several times in vertebrates. None of the three genomic studies in Scarpetta 2020 agree with each other. None agree with the LRT (Fig. 2).

Unfortunately Scarpetta’s phylogenetic analyses result in lists of suprageneric taxa, not genera, as in the LRT. Scarpetta reports, “The uncertainty of the relationships of Kopidosaurus is due in part to the mosaic morphology of the fossil and the problematic nature of pleurodontan phylogeny.”

There is no such thing as mosaic evolution. So stop using that excuse.

It doesn’t have to be this complicated. Use the LRT. It’s simple. Just Plug ‘n’ Play.

Figure 1. Kopidosaurus perplexus in situ and µCT scans from Scarpetta 2020. Reconstruction added here.

Figure 1. Kopidosaurus perplexus in situ and µCT scans from Scarpetta 2020. Reconstructions in lateral and palatal views added here.

Scarpetta reports,
“YPM VP 8287 preserves no morphological feature or combination of features that would allow clear referral to any member of Pleurodonta.” And that’s why he shouldn’t be “Pulling a Larry Martin” (relying on key traits that might converge). Instead: drop the new taxon into a comprehensive cladogram, like the LRT (Fig. 2), and let the software nest the enigma.

Definition according to Wikipedia:
Pleurodonta (from Greek lateral teeth, in reference to the position of the teeth on the jaw) is one of the two subdivisions of Iguania, the other being Acrodonta (teeth on the top [of the jaw]). Pleurodonta includes all families previously split from Iguanidae sensu lato (CorytophanidaeCrotaphytidaeHoplocercidaeOpluridaePolychrotidae, etc.), whereas Acrodonta includes Agamidae and Chamaeleonidae.”

The frontal and parietal are incomplete
and the skull is small at <2cm. Am I the first to wonder if this was a juvenile skull? Scarpetta does not bring up the subject. The large orbit relative to skull length supports that hypothesis. Otherwise this could be an adult in the process of phylogenetic miniaturization, common at the genesis of many clades (Fig. 2).

Scarpetta concluded,
“Given the phylogenetic volatility of Kopidosaurus, I refrain from favoring any biogeographic or divergence hypothesis based on the identification of the fossil and advise similar caution for other systematically enigmatic fossils, lizard or otherwise.”

Don’t give up! Use the LRT.

Here 
in the large reptile tree (LRT, 1740+ taxa) Eocene Kopidosaurus nests at the base of a clade of living iguanians (Fig. 2). It is a plesiomorphic taxon, but that doesn’t matter to the LRT. Only a suite of characters is able to nest Kopidosaurus with this level of confidence by minimizing taxon exclusion.

Figure 2. Subset of the LRT focusing on basal Squamata. Here Kopidosaurus nests at the base of a clade of living iguanians including Pristidactylus and Anolis.

Figure 2. Subset of the LRT focusing on basal Squamata. Here Kopidosaurus nests at the base of a clade of living iguanians including Pristidactylus, Basisliscus and Anolis.

As a reminder,
the LRT is still using just 238 traits, most of which were not used here due to the lack of a premaxilla, vomer and post-crania. Paleontologists still don’t want to accept the fact that the LRT continues to lump and separate with so few multi-state characters. Even those taxa previously tested without resolution, as described by Scarpetta 2020.


References
Scarpetta SG 2020. Effects of phylogenetic uncertainty on fossil identification illustrated
by a new and enigmatic Eocene iguanian. Nature.com/scientifcreports 10:15734.
https://doi.org/10.1038/s41598-020-72509-2

Subadult and adult Tropeognathus compared

Holgado and Pegas 2020 name several toothy crested rostral pieces
they assign to Anhangueridae, Coloborhynchinae and Tropeognathinae, subsets of the clade Ornithocheiridae (Seeley 1870).

More interesting due to its completeness,
was the Holgado and Pegas page-wide photo of the BSp 1987 I 47 specimen of Tropeognathus (Fig. 1, Wellnhofer 1987). Here the ’47’ specimen is compared to the larger holotype, BSp 1987 I 46, and to the smaller Scaphognathus holotype (Fig. 1, GPIB 1304, No. 109 of Wellnhofer 1975), a distant ancestor of Tropeognathus in the Large Pterosaur Tree (LPT, 251 taxa).

Quick note to readers after October 19, 2020:
Co-author Pegas sent a comment noting the 47 specimen was a typo and should be 46 instead. I asked about the scale bar differences and am awaiting that reply at present.

Figure 1. A subadult and adult specimen of Tropeognathus compared to a distant relative, Scaphognathus.

Figure 1. A subadult and adult specimen of Tropeognathus compared to a distant relative, Scaphognathus.

Holgado and Pegas provided a cladogram of a clade of pterosaurs
formerly considered Ornithocheiridae, Lanceodontia. Strangely, their outgroup is the derived istiodactylid, Lonchodraco giganteus, which we looked at earlier here and nested with the unnamed SMNS PAL 1136 specimen, which was omitted from their cladogram.

By contrast
In the LPT ornithocheirids arise from small taxa like Yixianopterus, Mimodactylus and before them the Cycnorhamphus clade and before them the tiny Late Jurassic pterosaurs, BM NHM 42735, Gmu10157, TM 13104 and three Scaphognathus specimens (109, SMNS 59395 and 110 and  of descending size. None of these are included in Holgado and Pegas.

There are quite a few nomenclature problems
in the Ornithocheridae that make the taxonomy unnecessarily confusing.

According to Wikipedia,
“Back in 1987, Wellnhofer had named a second species called Tropeognathus robustus, based on specimen BSP 1987 I 47, which is a more robust lower jaw. In 2013 however, T. robustus was considered as a species of Anhanguera, resulting in an Anhanguera robustus.” Comparing the 46 and 47 specimens (Fig. 1) show they are conspecific, or at least congeneric. This clade becomes increasingly confused with every new author or set of authors. Strange that such closely related taxa are generically split while the several dozen variations in Rhamphorhynchus and Pteranodon are ignored.

The first species of Tropeognathus mesembrinus has several synonyms.

  • Anhanguera mesembrinus (Wellnhofer, 1987)
  • Coloborhynchus mesembrinus (Wellnhofer, 1987)
  • Criorhynchus mesembrinus (Wellnhofer, 1987)
  • Ornithocheirus mesembrinus (Wellnhofer, 1987)

Ornithocheiridae Seeley 1870, named when only a few bits and pieces were known

Ornithocheiromorpha Andres et al., 2014, incorrectly nested within Pteranodontoidea.

Pterodactyloidea Plieninger, 1901, adding taxa splits up this traditional clade.

The disappearance of the naris in scaphognathid pterosaurs.

Figure 2. The disappearance of the naris in scaphognathid pterosaurs. Click to enlarge figure 1 to see the tiny naris in the subadult specimen of Tropeognathus, more sealed over in the adult.

The subadult specimen (specimen ’47’)
of Tropeognathus (Fig. 1) documents a vestige, slit-like naris that disappears in the larger ’46’ specimen. If you can’t see it here, click to enlarge.

Rostral crest
Comparing the subadult to the adult specimen (Fig. 1) demonstrates no growth in the size of the rostral crest. Rather the back half of the skull is slightly larger.


References
Holgado B and Pegas RV 2020. A taxonomic and phylogenetic review of the anhanguerid pterosaur group Coloborhynchinae and the new clade Tropeognathinae. Acta Palaeontologica Polonica 65 (X): xxx–xxx.
Wellnhofer P 1975a. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33. 1975b. Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. 1975c.Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.
Wellnhofer P 1987. New crested pterosaurs from the Lower Cretaceous of Brazil. Mitteilungen der Bayerische Staatssammlung für Paläontologie und historische Geologie 27: 175–186; Muenchen

/wiki/Tropeognathus
wiki/Scaphognathus
wiki/Criorhynchus

 

Which theropods were capable of flapping flight?

Both Pei et al. 2020 and Pittman and Xu et al. 2020 looked into
the origin of flight in birds and bird mimics. They calculated maximum and minimum estimates of wing loading and specific lift. These results confirm powered flight potential in early birds and its rarity among the ancestors of closest avialan relatives.

wing loading  (= the total weight of an aircraft divided by the area of its wing).

specific lift (not defined, even when googled, but Pei et al. report, “In powered flyers, specific lift is critical to weight support and generation of thrust (thrust is primarily a component of lift in vertebrate flapping flyers”) If you find that confusing, so do I. Thrust and lift are typically considered separately, not as a component of each other.

In both papers there was no mention
of elongate, locked-down coracoids. When you find such coracoids, that’s how we know pterosaur ancestors, like Cosesaurus (Fig. 1), started flapping. Here the former disc-like sliding coracoids are reduced by posterior erosion to slender immobile still curved stems. The scapula is likewise a narrow immobile strap, as in flapping birds.

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 – 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.

All extant birds have elongate coracoids.
All extant birds can flap. All have flying ancestors, even those that no longer fly. So when do birds begin to have locked down coracoids and strap-like scapulae in the large reptile tree (LRT, 1738+ taxa)? Let’s look, clade by clade.

All Solnhofen ‘birds’ have elongate coracoids and strap-like scapulae.

Prior to that Xiaotingia and kin have the same.

Prior to that Daliansaurus does not preserve a pectoral girdle, but descendant taxa have elongate coracoids and strap-like scapulae. Call that x1 for flapping.

Prior to that Jinfengopteryx and kin have elongate coracoids and strap-like scapulae. Call that x2.

Prior to that Bambiraptor and Haplocheirus have a short disc-like coracoid, but Velociraptor and Balaur have elongate pectoral elements. Call that x3.

Prior to that Ornitholestes had a short, round coracoid, but Changyuraptor and descendants like Microraptor and Sinornithosaurus had elongate pectoral elements. Call that x4.

Prior to that all theropods in the LRT have a short, round coracoid that slid along the left and right sternae. So, they were not flapping according to this hypothesis.

Highlights of Pei et al. 2020:
One: Support Deinonychosauria as sister taxon to birds and Anchiornithinae as early birds

Supported by the LRT

Two: Powered flight potential evolved ≥3 times: once in birds and twice in dromaeosaurids

Supported by the LRT

Three: Many ancestors of bird relatives neared thresholds of powered flight potential

Supported by the LRT

Four: Broad experimentation with wing-assisted locomotion before theropod flight evolved

Supported by the LRT

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

The authors note:
Scansoriopterygians (Figs. 3, 4) are included in the phylogenetic analysis, but are excluded from the flight parameters because Yi’s wing (Fig. 3) is skin-based rather than feather-based like the other winged taxa in this dataset, while Epidexipteryx (Fig. 4) does not possess pennaceous feathers.”

Both are incorrect. We looked at the Yi and Ambopteryx issues here. Both are descendants of Solnhofen bird . So they had feathers, not bat-like skin membranes.

Figure 4. Yi qi tracing of the in situ specimen using DGS method and bones rearranged, also using the DGS method, to form a standing and flying Yi qi specimen. Note the lack of a styliform element, here identified as a displaced radius and ulna.

Figure 4. Yi qi tracing of the in situ specimen using DGS method and bones rearranged, also using the DGS method, to form a standing and flying Yi qi specimen. Note the lack of a styliform element, here identified as a displaced radius and ulna.

Figure 3. Epidexipteryx, another scansoriopterygid with a bird-like pelvis.

Figure 3. Epidexipteryx, another scansoriopterygid bird.

The authors note:
“For Rahonavis (Fig. 4), given only the radius and ulna are known, we reconstructed its wing with similar intralimb proportions to Microraptor where the ulna is 37% of the forelimb length.”

This is guessing, inappropriate for science. In the LRT, Rahonavis (Fig. 4) and Microraptor are not related. We don’t have a hand/manus or a coracoid for Rahonavis. In the LRT Rahonavis is a small therizinosaur, close to Jianchangosaurus, not related to taxa with a long, locked-down coracoid.

Figure 2. Rahonavis nests in the LRT as a tiny derived therizinosaur based on the few bones currently known.

Figure 4. Rahonavis nests in the LRT as a tiny derived therizinosaur based on the few bones currently known. The unknown coracoid is restored as a disc here.

From the Pei et al. Summary:
“Uncertainties in the phylogeny of birds (Avialae) and their closest relatives have impeded deeper understanding of early theropod flight. To help address this, we produced an updated evolutionary hypothesis through an automated analysis of the Theropod Working Group (TWiG) coelurosaurian phylogenetic data matrix. Our larger, more resolved, and better-evaluated TWiG-based hypothesis supports the grouping of dromaeosaurids + troodontids (Deinonychosauria) as the sister taxon to birds (Paraves) and the recovery of Anchiornithinae as the earliest diverging birds.”

With exceptions, Pei et al. confirm the origin of flapping topology
found in the large reptile tree (LRT, 1738+ taxa, subset Fig. 1), except in the LRT large ‘troodontids’ nest with dromaeosaurids. Small ‘troodontids’ nest with Anchiornis basal to birds. Some near birds (see list above) developed, by convergence, the elongate locked-down coracoids seen in Solhnhofen birds and their descendants.

There are two ways to get slender locked-down coracoids in vertebrates,
by erosion of the disc to a remaining stem (as in pterosaur ancestors) or by elongation of the entire disc to produce a stem (as in birds and crocs).

Lacking coracoids, bats 
have elongated and locked down clavicles for symmetrical forelimb flapping. Bats are inverted bipeds.

Wing loading issue
Since birds/theropods depend on feathers for wing chord and span it would seem necessary to use only those theropods in which feathers were well known and to show in graphic form the extent of those wing feathers. I don’s see that in this study.

The rapidity of flapping
permits some certain taxa (ducks, hummingbirds, etc.) to have relatively short and small wings while flying. Gliding is not a primitive trait in birds, pterosaurs or bats.

More from the Pei et al. summary:
“Although the phylogeny will continue developing, our current results provide a pertinent opportunity to evaluate what we know about early theropod flight. With our results and available data for vaned feathered pennaraptorans, we estimate the potential for powered flight among early birds and their closest relatives. We did this by using an ancestral state reconstruction analysis calculating maximum and minimum estimates of two proxies of powered flight potential—wing loading and specific lift. These results confirm powered flight potential in early birds but its rarity among the ancestors of the closest avialan relatives (select unenlagiine and microraptorine dromaeosaurids). For the first time, we find a broad range of these ancestors neared the wing loading and specific lift thresholds indicative of powered flight potential. This suggests there was greater experimentation with wing-assisted locomotion before theropod flight evolved than previously appreciated. This study adds invaluable support for multiple origins of powered flight potential in theropods (≥3 times), which we now know was from ancestors already nearing associated thresholds, and provides a framework for its further study.”

Figue 1. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

Figue 5. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The coracoids are elongate and immobile, but does that mean this taxon flapped. Maybe.

Not going to leave this topic without discussing 
the elongate coracoids in bipedal crocodylomorphs and their living, quadrupedal, non-flapping descendants, which retain long coracoids (Fig. 6) and mobile pectoral girdles. Experiments by Baier et al. 2018 documented the rotation of the elongate coracoids was less than expected, but the unossified sternum itself rotated left and right. They wrote, “To our knowledge, this is the first evidence of sternal movement relative to the vertebral column (presumably via rib joints) contributing to stride length in tetrapods.” 

All crocodylomorphs lack clavicles, 
and this likely contributes to pectoral girdle mobility. The basalmost archosaur, PVL 4597 does not preserve any element of the pectoral girdle or forelimb, so it does not shed light on the loss or retention of the clavicles. Among more distantly related proximal outgroup taxa, only Poposaurus and Lotosaurus appear to retain clavicles. Appearances vary in more primitive rauisuchids and erythrosuchids. Euparkeria has clavicles.

So, were basal crocodylomorphs flapping in the Triassic?
Pseudhesperosuchus (Fig. 5) would have been flapping without membranes, elongate fingers and feathers. But look at the clearance between the dangling forelimbs and sprinting hind limbs (Fig. 5). Perhaps Pseudhesperosuchus evolved elongate pectoral elements to lift the forelimbs laterally and keep them elevated while running, giving the narrow-gauge hind limbs room to extend anteriorly during the running cycle. Animators: take note!

Also worthwhile noting,
this is also when the proximal carpals became elongated, a crocodylomorph hallmark. As a biped, Pseudhesperosuchus had less use for its forelimbs. They could have evolved to become something else. Based on the elongation of the proximal carpals, the small size of the manus and the rather long forelimbs, the best guess I’ve seen is that the forelimbs occasionally acted much like those of similar forelimbs on much larger hadrosaurs (duckbill dinosaurs), providing more stability with a quadrupedal pose, without giving up its bipedal abilities. More aquatic short-legged, quadrupedal crocs evolved later. Long coracoids and long proximal carpals were retained in extant crocs from earlier Triassic ancestors.

Exceptions and reversals.
A few small basal bipedal crocodylomorphs, like Scleromochlus and Litargosuchus, re-evolved disc-like coracoids.

Figure 6. At the lower right hand corner is a pectoral girdle typical of crocs.

Figure 6. At the lower right hand corner is a pectoral girdle typical of crocs.

Flapping requires an immobile pectoral girdle
in order that both limbs move symmetrically, the opposite of basal tetrapods with mobile pectoral girdles. Flapping is the first step toward flying in pterosaur and bird ancestors.


References
Baier DB, Garrity BM, Moritz S and Carney RM 2018. Alligator mississippiensis sternal and shoulder girdle mobility increase stride length during high walks. Journal of Experimental Biology 2018 221: jeb186791 doi: 10.1242/jeb.186791
Kruyt JW, et al. 2014. Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors. Royal Society Interface. nterface. 2014;11(99):20140585. doi:10.1098/rsif.2014.0585
Pei R et al. 2020.
Potential for Powered Flight Neared by Most Close Avialan Relatives, but Few Crossed Its Thresholds. Current Biology online here.
Pittman M, O’Connor J, Field DJ, Turner AH, Ma W, Makovicky P and Xu X 2020. Pennaraptoran Systematics. Chapter 1 from Pittman M and Xu X eds. 2020. Pennaraptoran theropod dinosaurs. Past progress and new Frontiers. Bulletin of the American Museum of Natural History 440; 353pp. 58 figures, 46 tables.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4233735/#idm140660310181296title

Basal bipedal crocs reviewed, with a focus on Barberenasuchus

Leardi, Yáñezc and Pol 2020 bring us
their thoughts on new and previously discovered South American crocodylomorphs. In the large reptile tree (LRT, 1737+ taxa; subset Fig. x) only Crocodylomorpha + Dinosauria comprise the Archosauria. The Poposauria (= Turfanosuchus and kin;  Fig. 1) is the proximal outgroup.

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

From the Leardi, Yáñezc and Pol Abstract
“Crocodylomorpha is a clade that has its origins during the Late Triassic and attained a global distribution early in their radiation.In this contribution we review the crocodylomorph Triassic record in South America by analyzing three units that have yielded fossils of the clade: the Santa María Supersequence in Brazil; and, the Ischigualasto and Los Colorados formations in Argentina.”

Good start!

Figure 3. Barberenasuchus to scale with sister taxa, Herrerasaurus, Eoraptor, Lewisuchus and Trialestes and Junggarsuchus, but without the autapomorphies of its sister Herrerasaurus. At present Barberenasuchus is the basalmost dinosaur. Note the difference in the nasal between the dinosaurs and protodinosaurs.

Figure 1. Barberenasuchus to scale with sister taxa, Herrerasaurus, Eoraptor, Lewisuchus and Trialestes and Junggarsuchus, but without the autapomorphies of its sister Herrerasaurus. At present Barberenasuchus is the basalmost dinosaur. Note the difference in the nasal between the dinosaurs and protodinosaurs.

Continuing from the abstract
“Our review does not support previous assignments of the taxon Barberenasuchus (Fig. 1) from the Santa María Supersequence as a non-crocodyliform crocodylomorph, as it displays traits that are absent in all known crocodylomorphs and are present in other earlier branching archosaurs.”

The LRT agrees, but what Barberenasuchus isn’t isn’t the same as what it is (Fig. 2). Adding taxa gradually and ultimately nests all taxa.

Figure 2. Subset of the LRT focusing on the Phytodinosauria.

Figure 2. Subset of the LRT focusing on the Phytodinosauria.

More specifically,
the LRT nests Barbarenasuchus with Eodromaeus (Fig. 3) within the base of the Phytodinosauria (Fig. 2). Only Buriolestes is more primitive in this plant-eating clade of the Dinosauria.

Figure 1. Eodromaeus reconstructed. We will look at this taxon in more detail tomorrow.

Figure 1. Eodromaeus reconstructed. We will look at this taxon in more detail tomorrow. Note the relatively small head of this plant eater.

Continuing from the abstract
“The Los Colorados Formation has a diverse crocodylomorph record being represented by a non-crocodyliform crocodylomorph (Psedhesperosuchus [Fig 1]) and two crocodyliforms (Hemiprotosuchus and Coloradisuchus).”

We looked at these two yesterday.

In the LRT, the Triassic is a little too early
for crocodyliforms. Adding taxa moves Hemiprotosuchus to the base of the Aetosauria. Coloradisuchus nests among basal bipedal crocodylomorpha, as we learned earlier. These are indeed found in the Triassic.

Continuing from the abstract
“Here we present a putative new non-crocodyliform crocodylomorph taxon from Los Colorados Formation. When compared with other crocodylomorph bearing formations around Pangea, the Ischigualasto Formation bears similarities with the crocodylomorphs assemblages of North America due to the presence of early branching crocodylomorphs (Trialestes) including “large-bodied” taxa. The Los Colorados Formation reveals a transitional composition corresponding to Norian and Early Jurassic assemblages of Pangea, as it shares the presence of basal crocodyliforms (i.e., protosuchids) typical of Early Jurassic units (e.g., Upper Elliot) and basal non-crocodyliform crocodylomorphs, widely present in Norian assemblages.”

Still waiting for data on this unnamed taxon. Meanwhile, let’s get back to Barberenasuchus (Figs. 1, 2).

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

When you add taxa, as done in the LRT,
Barberenasuchus brasiliensis (Mattar 1987, Middle Triassic) nests as a basal phytodinosaur. Barberenasuchus has shorter teeth and a larger orbit that more primitive carnivorous taxa. The skull is more gracile and smaller in size, as in other basal phytodinosoaurs.

Traditionally, and according to Wikipedia
“Barberenasuchus is an extinct genus of an archosauriform. Its phylogenetic position within Archosauriformes is uncertain; the author of its description classified it as a sphenosuchid crocodylomorph, while Kischlat (2000) considered it to be a rauisuchian. Irmis, Nesbitt and Sues (2013) stated that they “could not find any crocodylomorph character states preserved in the holotype specimen”.

Adding taxa makes the position of all taxa, including Barberenasuchus, in the LRT ever more certain.


References
Irmis RB, Nesbitt SJ and Sues H-D 2013.Early Crocodylomorpha. In Nesbitt SJ. Desojo JB and Irmis RB (eds.). Anatomy, phylogeny and palaeobiology of early archosaurs and their kin. The Geological Society of London. pp. 275–302. doi:10.1144/SP379.24
Kischlat E-E 2000.
 Tecodôncios: a aurora dos arcossáurios no Triássico. In Holz, M.; De Ros, L.F. (eds.). Paleontologia do Rio Grande do Sul. Porto Alegre: CIGO/UFRGS. pp. 273–316.
Leardi JM, Yáñezc I and Pol  D 2020. South American Crocodylomorphs (Archosauria; Crocodylomorpha): A review of the early fossil record in the continent and its relevance on understanding the origins of the clade. Journal of South American Earth Sciences. https://doi.org/10.1016/j.jsames.2020.102780
Mattar LCB 1987. Descrição osteólogica do crânio e segunda vértebrata cervical de Barberenasuchus brasiliensis Mattar, 1987 (Reptilia, Thecodontia) do Mesotriássico do Rio Grande do Sul, Brasil. Anais, Academia Brasileira de Ciências, 61: 319–333.

wiki/Eodromaeus
wiki/Barberenasuchus

Restoring the little crocodylomorph, Coloradisuchus

In 2017 Martinez, Alcober and Pol introduced a new
small (6cm skull length) crocodylomorph, Coloradisuchus abelini (Figs. 1, 2). The specimen is only known from the bottom half of its small skull + mandibles (Fig. 1). Unique for such a small Late Triassic croc, the nares are confluent at the snout tip, facing anteriorly. The premaxilla/maxilla suture is marked by a large oval fenestra exposing the lower canine in lateral view. This trait is typically found in protosuchids (Fig. 5), but also to a lesser extent in Gracilisuchus (Fig. 3) and Dibothrosuchus (Fig. 2).

Figure 1. Coloradisuchus skull from Martinez, Alcover and Pol 2017. Colors added.

Figure 1. Coloradisuchus skull from Martinez, Alcover and Pol 2017. Colors added. Skull length 6 cm. Restoration according to Dibothrosuchus.

The question is:
where to nest Coloradisuchus?

Figure 2. Dibothrosuchus compared to scale with the much smaller Coloradisuchus.

Figure 2. Early Jurassic Dibothrosuchus compared to scale with the much smaller Triassic Coloradisuchus.

From the abstract:
“Protosuchids are known from the Late Triassic to the Early Cretaceous and form a basal clade of Crocodyliformes. We report here a new protosuchid crocodyliform, Coloradisuchus abelini, gen. et sp. nov., from the middle Norian Los Colorados Formation, La Rioja, northwestern Argentina. Our phylogenetic analysis recovers Coloradisuchus abelini within Protosuchidae, as the sister group of the clade formed by Hemiprotosuchus and two species of Protosuchus (P. richardsoni and P. haughtoni). The new protosuchid C. abelini increases the diversity of crocodyliforms in the Late Triassic and, together with H. leali from the same stratigraphic levels of the Los Colorados Formation, shows that the diversification of basal crocodyliforms was probably faster and/or older than thought previously.”

It is easy to see why the authors assumed Coloradisuchus was a protosuchid, but adding convergent taxa moves it away. On the other hand, distinctly different Hemiprotosuchus (Fig. 4) clearly nests elsewhere.

Figure 5. Gracilisuchus skull updated with new colors.

Figure 3. Gracilisuchus skull updated with new colors. Skull length = 8cm.

Here in the LRT
Hemiprotosuchus nested far from protosuchids, at the base of the Aetosauria (Fig. 4). Protosuchids are terminal taxa also arising form small bipedal ancestors.

Figure 3. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.

Figure 4. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.

Adding Coloradisuchus
to the large reptile tree (LRT, 1737+ taxa) nests it between the much larger Early Jurassic Dibothrosuchus (Fig. 2) and the similarly-sized Middle Triassic Gracilisuchus (Fig. 3). These taxa also share a fenestra between the naris and antorbital fenestra, though much narrower than in protosuchids and Coloradisuchus. Martinez, Alcober and Pol did not test Dibothrosuchus and Gracilisuchus in their abbreviated cladogram consisting only of protosuchids and putative protosuchids.

Figure 2. Protosuchus skull. The high cranium and low triangular rostrum evidently made Bonaparte 1969 consider Hemiprotosuchus similar enough to Protosuchus.

Figure 5. Protosuchus skull. The high cranium and low triangular rostrum evidently made Bonaparte 1969 consider Hemiprotosuchus similar enough to Protosuchus.

Martinez, Alcobar and Pol note:
“The only known Triassic record of Protosuchidae is Hemiprotosuchus leali, from the upper levels of the middle Norian Los Colorados Formation (Bonaparte, 1971; Kent et al., 2014), and a putative, unnamed protosuchid from thelate Norian–Rhaetian Quebrada del Barro Formation (Martınez et al., 2015), both from northwestern Argentina.” 

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

With Hemiprotosuchus now nesting with coeval aetosaurs,
Coloradisuchus in the Triassic nests temporally and phylogenetically apart from other protosuchids. Unfortunately, due to preservation issues (Fig.1), relatively few traits can be scored for Coloradisuchus. Even so, moving Coloradisuchus to the protosuchid lineage adds five steps. That may change with further study or better data. Let’s keep working on this one.


References
Martinez RN, Alcober OA and Pol D 2017. A new protosuchid crocodyliform (Pseudosuchia, Crocodylomorpha) from the Norian Los Colorados Formation, northwestern Argentina. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1491047.

 

Woltering et al. 2020 study genes to elucidate finger origins

Woltering et al. 2020
attempted to elucidate the transition from fins to fingers by studying the genes of extant lungfish, which don’t have fingers and their ancestors never had fingers.

From the abstract
“How the hand and digits originated from fish fins during the Devonian fin-to-limb transition remains unsolved.

No. The large reptile tree (LRT; subset Fig. 1) solved that problem in 2019 following the work of Boisvert, Mark-Kurik and Ahlberg 2008. These authors found four finger buds on Panderichthys. Thereafter four fingers appear on all basalmost tetrapods in the LRT, like Trypanognathus (Fig. 2), a taxon found in Carboniferous strata with Middle Devonian origins. Taxon exclusion is once again the problem here.

Late Devonian taxa with supernumerary digits, like Acanthostega and Ichthyostega, are the traditional ‘go-to’ taxa for the fin-to-finger transition. That was supplanted in 2019 by phylogenetic analysis in the LRT (subset Fig. 1). Simply adding taxa recovers Acanthostega and Ichythyostega as terminal taxa. They have more derived skulls and bodies sporting larger limbs and more digits.

Figure 4. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

Figure 4. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

Woltering et al. 2020 report,
“Controversy in this conundrum stems from the scarcity of ontogenetic data from extant lobe-finned fishes. We report the patterning of an autopod-like domain by hoxa13 during fin development of the Australian lungfish, the most closely related extant fish relative of tetrapods.”

In other words, Woltering et al. looked at genes in lungfish that never had digits.

Figure 6. Dorsal and ventral views of Panderichthys and several basal tetrapods demonstrating the low, flat skulls and bodies with small limbs and relatively straight ribs.

Figure 2. Dorsal and ventral views of Panderichthys and several basal tetrapods demonstrating the low, flat skulls and bodies with small limbs and relatively straight ribs at the fin-to-finger transition. Acanthostega and Ichythyostega have more derived bodies with larger limbs and more digits.

Why study lungfish
when we have fossil taxa (Fig. 3) in the lineage of tetrapods? Why study genes when genomic studies produce false positives in deep time? Taken together the Woltering et al. study seems like a waste of effort on both fronts, but they didn’t realize this at the time. Paleontologists love genomics like Isaac Newton loved alchemy.

Figure 3. Forelimb of several basal tetrapods rearranged to more closely fit the LRT. Four fingers turns out to be the primitive number. Five is a recent mutation. Six was a short-lived experiment in Tulerpeton.

Figure 3. Forelimb of several basal tetrapods rearranged to more closely fit the LRT. Four fingers turns out to be the primitive number. Five is a recent mutation. Six was a short-lived experiment in Tulerpeton.

Woltering et al. 2020 report,”
“Differences from tetrapod limbs include the absence of digit-specific expansion of hoxd13 and hand2 and distal limitation of alx4 and pax9, which potentially evolved through an enhanced response to shh signaling in limbs. These developmental patterns indicate that the digit program originated in postaxial fin radials and later expanded anteriorly inside of a preexisting autopod-like domain during the evolution of limbs. Our findings provide a genetic framework for the transition of fins into limbs that supports the significance of classical models proposing a bending of the tetrapod metapterygial axis.”

Be wary of genetic studies over deep time. They have been shown to deliver false positives way too often to be trusted, or even attempted. Fossils and phenomic studies are better in all respects because they recover cladograms in which all taxa demonstrate a gradual accumulation of derived traits.


References
Boisvert CA, Mark-Kurik E and Ahlberg PE 2008.
 The pectoral fin of Panderichthys and the origin of digits. Nature 456:636–638.
Woltering JM et al. (5-co-authors) 2020. Sarcopterygian fin ontogeny elucidates the origin of hands with digits. Science Advances 6(34): eabc3510 DOI: 10.1126/sciadv.abc3510
https://advances.sciencemag.org/content/6/34/eabc3510

What is Leptostomia? So little to work with…

A new genus and species of little pterosaur
from the Early Cretaceous of Morocco, Leptostomia begaaensis (Smith et al. 2020; Figs. 1–3), is based on two, little 3D pieces of rostrum (FSAC-KK 5075) and mandible (FSAC-KK 5076) originally considered to belong to a new kind of azhdarchoid (an invalid polyphyletic clade in the large pterosaur tree; LPT, 251 taxa), that traditionally, but mistakenly includes unrelated tapejarids and azhdarchids. As usual, simply adding traditionally or specifically omitted taxa clarifies interrelationships.

Figure 1. At about twice life size, these are jaw portions from Leptostomia in several views.

Figure 1. At about twice life size, these are jaw portions from Leptostomia in several views.

The affinities of the jaw segments remain ‘unclear’
according to the authors. Once again this was due to taxon exclusion.

Figure 2. Photo of the Leptostomia rostrum fragment in several views. Colors added here.

Figure 2. Photo of the Leptostomia rostrum fragment in several views. Colors added here. Premaxilla = yellow. Maxilla = green. Vomer = purple.

Unfortunately 
Smith et al. omitted the tall, slender ctenochasmatid, Gegepterus (Fig. 3,4) from their comparables list. Gegepterus has a similar rostrum and mandible. Both are similar in size and (Fig. 4) both are from Early Cretaceous strata, one from Morocco, the other from China.

Figure 3. Leptostomia compared to coeval Gegepterus (see figure 4).

Figure 3. Leptostomia compared to coeval Gegepterus at the same scale  (see figure 4).

Most pterosaurs,
including azhdarchids and tapejarids, have a taller than wide rostrum along with a narrow premaxilla ascending process that extends to the dorsal orbit.

Figure 4. Similar to azhdarchids, Gegepterus was a tall, slender ctenochasmatid with long jaws, neck and legs.

Figure 4. Similar to azhdarchids, except for size, Gegepterus was a tall, slender ctenochasmatid with long jaws, neck and legs for an overall small pterosaur. Here it is shown 3/5 original size.

By contrast,
the Leptostomia rostrum has a wider rostrum and a wider premaxilla overlapping it. Worth remembering: both the rostrum and mandible fragments are less than 1cm wide on this small specimen and genus.

Figure 5. Leptostomia rostrum palatal view. Vomer = purple ridge. Mx = maxilla. Tiny remnant alveoli appear to be present on the lateral palatal ridge.

Figure 5. Leptostomia rostrum palatal view. Vomer = purple ridge. Mx = maxilla. Tiny remnant alveoli appear to be present on the lateral palatal ridge, overlooked by Smith et al.

Most ctenochasmatids
have long slender teeth arising from the jaw rims. No such teeth are preserved with or were collected with Leptostomia, A close view (Fig. 5) shows a line of small ovals that could be slender tooth alveoli. Or teeth may indeed be absent in this taxon.

Wiki authors describing Gegepterus in Wikipedia note:
“This is the first uncontroversial report of the Ctenochasmatidae from the Yixian Formation, as the fossils of other assumed ctenochasmatids have not preserved the dentition.”

Smith et al. note,
Leptostomia differs from other edentulous pterosaurs in possessing a remarkably low rostral lateral angle, endowing it with a very long and slender beak. Its lateral angle is also very low when compared with toothed pterosaurs with only some ctenochamatids having a similarly low lateral angle.”

Smith et al. propose a poorly informed guess,
“The new pterosaur adds to the remarkable diversity of pterosaurs known from the mid-Cretaceous, and suggests that pterosaur diversity remained under sampled.” No it doesn’t. Leptostomia looks like an omitted taxon, Gegepterus.

In the LPT there are few to no morphological gaps largely because it employs a much larger taxon list than any published by PhD workers and their students who refuse to include small taxa, more than one specimen assigned to a genus and valid pterosaur outgroups in their analyses. Same for the LRT.

Quetzalcoatlus scraping bottom while standing in shallow water.

Figure 6. Quetzalcoatlus scraping bottom while standing in shallow water.

Smith et al. state,
“The proposed probe-feeding strategy suggested by the rostrum morphology of Leptostomia has not previously been documented for the Pterosauria.” This is false. Just google, “pterosaur + probe” and a long list will appear. And there’s always this image (Fig. 6) of the man-sized Quetzalcoatlus probing, which has been online for awhile, following ‘suggestions’ from Langston 1981.


References
Langston W Jr 1981. Pterosaurs. Scientific American: 244,:122–126.
Smith RE, Martill DM, Kao A, Zouhri S and Longrich N 2020. A long-billed, possible probe-feeding pterosaur (Pterodactyloidea: ?Azhdarchoidea) from the mid-Cretaceous of Morocco, North Africa, Cretaceous Research, https://doi.org/10.1016/j.cretres.2020.104643.

wiki/Leptostomia
wiki/Gegepterus

Lepidosaurian epipterygoids in basal pterosaurs

In 1998 lepidosaurian epipterygoids
were found in the basal lepidosaur tritosaur, Huehuecuetzpalli (Fig. 1, Reynoso 1998; slender magenta bones inside the cheek area).

Figure 2. Huehuecuetzpalli has a tall, narrow epipterygoid, as in other lepidosaurs, and just a pore of an antorbital fenestra in the maxilla.

Figure 1. Huehuecuetzpalli has a tall, narrow epipterygoid, as in other lepidosaurs, and just a pore of an antorbital fenestra in the maxilla.

About two years ago
previously overlooked lepidosaurian epipterygoids were identified here in a more derived lepiodaur tritosaur, Macrocnmeus (Fig. 2, slender green bones in the orbit area) for the first time.

Figure 1. Macrocnemus fuyuanensis (GMPKU-P-3001) in situ and as traced by the original authors, (middle) flipped with colors applied to bones, and (above) bone colors moved about to form a reconstruction. Darker yellow and darker green are medial views of premaxilla and maxilla. Note the long ascending process of the premaxilla and the palatal elements seen through the various openings all overlooked by those with firsthand access to the fossil. Epipterygoids are lepidosaur synapomorphies not present in protorosaurs.

Figure 2. Macrocnemus fuyuanensis (GMPKU-P-3001) in situ and as traced by the original authors, (middle) flipped with colors applied to bones, and (above) bone colors moved about to form a reconstruction. Darker yellow and darker green are medial views of premaxilla and maxilla. Note the long ascending process of the premaxilla and the palatal elements seen through the various openings all overlooked by those with firsthand access to the fossil. Epipterygoids are lepidosaur synapomorphies not present in protorosaurs.

Until now,
no one has ever positively identified lepidosaurian (slender strut-like) epipterygoids in a pterosaur. In the large reptile tree (LRT, 1737+ taxa) and the large pterosaur tree (LPT, 251 taxa) Bergamodactylus (MPUM 6009) nests as the basalmost pterosaur. Here is the skull in situ with DGS colors applied, as traced by Wild 1978 (above), and reconstructed in lateral and palatal views (below) based on the DGS tracings.

Figure 3. Bergamodactylus skull in situ and reconstructed. Wild 1978 tracing above.

Figure 3. Bergamodactylus skull in situ and reconstructed. Wild 1978 tracing above. Note the break-up of the jugal. Note the fusion of the ectopterygoids with the palatines producing ectopalaatines.

The lepidosaurian epipterygoids of Bergamodactylus
(slender bright green struts in the cheek/orbit area in figure 3), or any pterosaur over the last 200 years, are identified here for the first time, further confirming the lepidosaurian status of pterosaurs (Peters 2007, the LRT). Sorry I missed these little struts earlier. When you don’t think to look for them, you can overlook them.

Figure 5. Eudimorphodon epipterygoids (slender green struts).

Figure 4. Eudimorphodon epipterygoids (slender green struts).

Now you may wonder how many other pterosaurs
have overlooked epipterygoids? A quick look at Eudimorphodon reveals epipterygoids (Fig. 4, bright green struts). Other Triassic pterosaurs include:

  1. Austriadactylus SMNS 56342: slender strut present
  2. Austriadactuylus SC 332466: slender strut present
  3. Raeticodactylus : slender strut is present (identified on link as a stapes)
  4. Preondactylus: slender strut present
  5. Dimorphodon: amber strut over squamosal (Fig. 5 in situ image), 
  6. Seazzadactylus MFSN 21545: slender struts present, tentatively identified by Dalla Vecchia 2019, but as more than the slender struts they are) (Fig. 6).

The skull of Dimorphodon macronyx BMNH 41212.

Figure 5. The skull of Dimorphodon macronyx BMNH 41212. Above: in situ. Middle: Restored. Below: Palatal view. The slender yellow strut on top of the red squamosal in situ is a likely epipterygoid.

Figure 6. Seazzadactylus from Dalla Vecchia 2019. Here the epipterygoid struts are more correctly and less tentatively identified.

Figure 6. Seazzadactylus from Dalla Vecchia 2019. Here the epipterygoid struts are more correctly and less tentatively identified.

Hard to tell in anurognathids
where everything is crushed and strut-like. Hard to tell in other pterosaurs because the hyoids look just like epipterygoids. Given more time perhaps more examples will be documented that are obvious and irrefutable.

Added a few days later:

Added Figure. Here's the Triebold specimen of Pteranodon (NMC41-358) with epipterygoid splinters in bright green.

Added Figure. Here’s the Triebold specimen of Pteranodon (NMC41-358) with epipterygoid splinters in bright green.

Here’s the Triebold specimen of Pteranodon
(NMC41-358, added figure) with epipterygoid splinters in bright green. So start looking for the epipterygoid in every pterosaur. We’ll see if it is universal when more pterosaur specimens of all sorts are presented.


References
Dalla Vecchia FM 2019. Seazzadactylus venieri gen. et sp. nov., a new pterosaur (Diapsida: Pterosauria) from the Upper Triassic (Norian) of northeastern Italy. PeerJ 7:e7363 DOI 10.7717/peerj.7363
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.
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/Bergamodactylus
wiki/Huehuecuetzpalli
wiki/Homoeosaurus
wiki/Bavarisaurus