SVP abstracts 8: µCT studies on Scleromochlus reveal it is a ‘reptile’

Foffa et al. 2020 apply µCT scanning technology
to the tiny Late Triassic Scleromochlus (Fig. 1). This bipedal crocodylomoph with tiny fingers was Michael Benton’s (1999) and Chris Bennett’s (1996) cherry-picked choice to be the taxon closest to pterosaurs (whenever the actual sisters (Peters 2000) were omitted).

Faxinalipterus matched to Scleromochlus. The former is more primitive, like Gracilisuchus, in having shorter hind limbs and more robust fore limbs. The maxilla with fenestra and fossa, plus the teeth, are a good match.

Figure 1. Faxinalipterus matched to Scleromochlus. The former is more primitive, like Gracilisuchus, in having shorter hind limbs and more robust fore limbs. The maxilla with fenestra and fossa, plus the teeth, are a good match.

Scleromochlus has become more popular lately.
Earlier this year, Bennett 2020 provided new drawings, but not much new insight. His cladograms failed to recover a single node on which to nest Scleromochlus.

From the Foffa et al. 2020 abstract:
“The herpetofauna of the Lossiemouth Sandstone Formation (Late Triassic) of Elgin (Moray, Scotland) includes several close relatives of key groups such as dinosaurs, pterosaurs, crocodilians and lepidosaurs, although the affinities of some taxa within this assemblage are contentious.”

How contentious?

  • Pterosaurs? No.
  • Dinosaurs? No.
  • Crocodilians (= Crocodylomporha)? Yes: Saltopus and Scleromochlus.
  • Lepidosaurs? No, according to Wikipedia and the LRT.

Continuing from the Foffa et al. 2020 abstract:
“The specimens of this assemblage are notoriously challenging to study because of their preservation as voids in sandstone. Historically, the ‘Elgin reptiles’ have been studied primarily using physical molds, which only provide incomplete, and potentially distorted information – an issue that particularly affects small-bodied taxa. Here we use microcomputed tomographic (μCT) techniques as an alternative method to study these important specimens, and access hidden parts of their skeletons.”

“Scleromochlus taylori is one of the most controversial taxa within the assemblage. It is an enigmatic, small-bodied, bipedal reptile that was long hypothesised to be closely related to dinosaurs and pterosaurs, and is represented by several specimens of varying completeness.”

Not an enigma. In the large reptile tree (LRT, 1749+ taxa; subset Fig. 2), and earlier (Peters 2002) nested Scleromochlus as a basal bipedal crocodylomorph. Add pertinent sister taxa (and let’s see your reconstructions and tracings to make sure interpretations are correct) to confirm or refute.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 2. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Continuing from the Foffa et al. 2020 abstract:
“It was recently reinterpreted as a quadrupedal ‘hopper’, (Bennett 2020) positioned phylogenetically either within doswelliid archosauriforms, or outside of the Archosauria + Erythrosuchidae clade. Neither of these interpretations has been universally accepted, and other aspects of the biology of Scleromochlus are also contentious.

Taxon exclusion is the universal problem with prior studies. Given the proportions of Scleromochlus (Fig. 1) and the proportions of its phylogenetic sisters (Fig. 2), why force it into an awkward quadrupedal posture?

Figure 1. Taxa from the croc subset of the LRT to scale. Click to enlarge.

Figure 1. Taxa from the croc subset of the LRT to scale. Click to enlarge.

Continuing from the Foffa et al. 2020 abstract:
“Here we analyse the first μCT scan data collected for Scleromochlus, using all available specimens, and show that historic molding incompletely captured its anatomy. We access and describe previously inaccessible (and thus unaltered) portions of its skeleton including a complete
[unintentionally left blank], as well as new details of already described regions. Overall, we clarify previous ambiguous features such as vertebral count, dorsal rib length and curvature, and reveal new details from the neck, tail, girdles, fore and hindlimb (particularly manus, femur and pes). We use this information, alongside that from multiple generations of molds, to shed light on some of the most controversial aspects of its anatomy, phylogenetic relationships, taphonomy, and ecology.”

Well,  that’s a lot of teasing without telling readers what Scleromochlus is. The title of the abstract only refers to Scleromochlus as a ‘reptile/’. No other conclusions are presented.


References
Foffa D, Barrett P, Butler R, Nesbitt S, Walsh S, Brusatte S, Fraser N 2020. New Information on the Late Triassic reptile Scleromochlus taylori from µCT data. SVP abstracts 2020.

http://reptileevolution.com/scleromochlus.htm

Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoolological Journal of the Linnean Society 118: 261–308.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Padian K. 1984. The Origin of Pterosaurs. Proceedings, Third Symposium on Mesozoic Terrestrial Ecosystems, Tubingen 1984. Online pdf
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Hist Bio 15: 277–301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. Journal of Vertebrate Paleontology 11 (Supplement) Memoire 2: 1–53.
Woodward AS 1907. On a new dinosaurian reptile (Scleromochlus taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society 1907 63:140-144.

wiki/Scleromochlus

 

Reassessment of Scleromochlus: Bennett 2020

SC Bennett 2020
followed Benton 1999 and others (citations below) in giving us a closer look at Scleromochlus taylori (Woodward 1907; Late Carnian, Late Triassic ~217 mya, 18 cm long; Figs. 1, 2), a tiny biped crocodylomorph derived from a sister to Gracilisuchus and Saltopus according to the large reptile tree (LRT, 1650+ taxa; Fig. 3).

Bipeds of the Triassic

Figure 1. Bipeds of the Triassic. Top to bottom: Cosesaurus, Scleromochlus, Marasuchus and Tropidosuchus. Each represents a distinct lineage of bipeds with bipedal sister taxa. This version of Scleromochlus was published in Peters 2002, based on Benton 1999.

Unfortunately,
despite the firsthand examination of this taxon, Bennett ignored sister taxa recovered by the LRT (Figs. 3, 4). His cladograms failed to recover a single node on which to nest Scleromochlus. In essence, he still doesn’t know what Scleromochlus is, despite his best efforts (see below for Bennett’s self assessment).

From Bennett’s 2020 introduction
“The first specimens were briefly described and named by Woodward (1907), who interpreted Scleromochlus as a small bipedal running or leaping dinosaur. Huene (1914) described the specimens more thoroughly and interpreted Scleromochlus as an arboreal climbing and leaping pseudosuchian close to the origin of pterosaurs. Swinton (1960), Brodkorb (1971) and Martin (1983) discussed Scleromochlus in relation to the origin of birds, whereas Padian (1984) suggested that Huene had it only half right and interpreted Scleromochlus as a digitigrade bipedal cursor close to the origin of pterosaurs and dinosaurs, a view that has gained general acceptance (Gauthier, 1986; Sereno, 1991; Benton, 1999; Fraser, 2006; Brusatte et al., 2010). Despite that, Bennett (1996, 1997) argued that Huene had only the other half right and Padian had it all wrong and that Scleromochlus was an arboreal leaper not close to pterosaurs.”

True to Bennett’s curse,
“You will never be published, and if you are published, you will not be cited,” Bennett 2020 did not cite Peters 2002, who wrote, “Among recent workers, Padian (1984), Sereno (1991) and Benton (1999) noted pterosaur similarities in the bipedal diapsid, Scleromochlus. The homoplasy is striking (Table I). However, figures by Benton (1999), which are reconstructed here (Fig. 8D), show that this archosauriform had a low, wide skull, a deep antorbital fossa, a terminal naris, a short neck of only six or seven cervicals, a long lumbar region, a small manus, a broadly separated pubis and ischium, a fibular flange, a calcaneal heel and a spike-like, digit-less metatarsal V. These characters are not found in pterosaurs. They are synapomorphies of basal bipedal crocodylomorphs, such as Gracilisuchus (Romer, 1972) and Saltoposuchus (Huene, 1921; Sereno and Wild, 1992).”

Bennett 2020 failed to mention
or include Junggarsuchus, Pseudhesperosuchus, Gracilisuchus and Saltposuchus in his taxon list. He only mentioned Saltopus as a coeval predator. These are all bipedal basal crocodylomorpha, a clade  ignored by Bennett 2020.

Figure 2. From Bennett 2020 showing in dorsal view the skull of Scleromochlus with DGS overlays colorizing the bones. At right, Bennett's drawing of same.

Figure 2. From Bennett 2020 showing in dorsal view the skull of Scleromochlus with DGS overlays colorizing the bones. At right, Bennett’s drawing of same. A compression crack across the fragile frontal was identified as the only suture in the skull, between the nasal and frontal, by Bennett 2020.

Back to Bennett’s 2020 introduction
“In 2013 I came to suspect that Bennett (1997), too, had it at least half wrong. By happy coincidence, I had shortly before perfected my technique for studying small slab specimens, so I took another look at the evidence and after several years of study gained some confidence in interpreting the specimens. This article is not a thorough redescription of the osteology of Scleromochlus but rather is a reassessment of the osteological evidence that has been used to interpret Scleromochlus’s mode of life, locomotion, and phylogenetic relationships.”

Again, the major shortcoming
in Bennett’s phylogenetic analysis is taxon exclusion. And Bennett’s “perfected technique” is not perfect (Fig. 2). His outmoded freehand technique overlooks many bones and sutures.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Concluding Bennett’s 2020 introduction
“A principal component analysis of skeletal measurements of Scleromochlus and other vertebrates of known locomotor type was done to examine the locomotion of Scleromochlus, and it was found to plot with frogs. Based on osteological evidence, including previously overlooked evidence from the specimens, and the principal component analysis, Scleromochlus is interpreted as a sprawling quadrupedal hopper analogous to frogs. Phylogenetic analyses found that Scleromochlus was not an ornithodiran, but rather either within the Doswelliidae or outside the clade consisting of the most recent common ancestor of the Erythrosuchidae and Archosauria and all its descendants.”

Pretty vague…
If the best Bennett can do is nest tiny bipedal Scleromochlus with giant, quadrupedal  Doswellia OR Erythrosuchus, then Bennett should have added taxa to his cladogram. If Bennett would have just added archosaur taxa that were small, bipedal and with flat skulls and osteoderms, he would have nailed it.

Other than the proportions, size, skeletal details and osteoderms
of Scleromochlus, the anterior lean of the long quadrate is also a crocodylomorph trait overlooked by all prior workers, except Peters 2002 (Figs. 1,2). Bennett traced the quadrate in stereo, but identified it with a question mark (Fig. 2). Whenever that happens, the technique has not been, as Bennet reported, “perfected.’


References
Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoolological Journal of the Linnean Society 118: 261–308.
Bennett SC 1997. The arboreal leaping theory of the origin of pterosaur flight. Historical Biology 12(3–4):265–290
Bennett SC 2020. Reassessment of the Triassic archosauriform Scleromochlus taylori: neither runner nor biped, but hopper. PeerJ 8:e8418 DOI 10.7717/peerj.8418
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Clark JM 2011. A new shartegosuchid crocodyliform from the Upper Jurassic Morrison Formation of western Colorado. Zoological Journal of the Linnean Society. 163 (s1): S152–S172.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Padian K. 1984. The Origin of Pterosaurs. Proceedings, Third Symposium on Mesozoic Terrestrial Ecosystems, Tubingen 1984. Online pdf
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Hist Bio 15: 277–301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. Journal of Vertebrate Paleontology 11 (Supplement) Memoire 2: 1–53.
Woodward AS 1907. On a new dinosaurian reptile (Scleromochlus taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society 1907 63:140-144.

wiki/Scleromochlus

Casting a blind eye toward: Scleromochlus

Figure 1. Scleromochlus by Witton 2013, via Benton 1999. Now promoted as a fuzzy pterosaur precursor.

Figure 1. Scleromochlus by Witton 2013, via Benton 1999. Now promoted as a fuzzy pterosaur precursor. Note the quadrate articulating with the surangular and the giant retroarticular process. Lean that quadrate the other way and these problems go away — and suddenly Scleromochlus is a croc! The fossil, found in dorsal and ventral views, does not expose the quadrate, except in one specimen, which is conveniently ignored. Witton gives Scleromochlus one extra cervical than Benton illustrated and a few extra fingers.

We’ve seen this sort of thing before.
Mark Witton is good at cherry-picking his references and keeping his audience in the dark about alternate and more viable realities in paleontology. In a recent blog, M. Witton uncritically takes on the seven specimens of Scleromochlus, first described by Woodward (1907) and later covered by Benton (1999, Fig. 1). He lists the phylogenetic analyses and other papers that posit Scleromochlus as a pterosaur precursor, but not the ones that indicate Scleromochlus was a basal bipedal crocodylomorph, like Terrestrisuchus and Saltoposuchus (Peters 2000, 2002, Fig. 2). These also demonstrate that pterosaurs were something entirely distinct from archosaurs.

From the Witton blog:
“For 100 years Scleromochlus has been implicated as a relative of pterosaurs (e.g. Huene 1914; Padian 1984; Gauthier 1986; Sereno 1991; Bennett 1996; Hone and Benton 2008; Brusatte et al. 2010, Nesbitt 2010) or, at very least, an ornithodiran representing a very early stage of stem-bird evolution (Benton 1999; Hone and Benton 2008).”

And yet Scleromochlus has several traits that rule it out as a pterosaur precursor: 1) flat, wide skull; 2) deep antorbital fossa; 3) broad triangular pterygoids; 4) no sternum; 5) no interclavicle; 6) no elongate coracoid; 9) deep chevrons; 10) diverging pubis and ischium; 11) no laterally increasing fingers 1-4); 12) no pedal digit 5. Click here and here for more info. And click here for the evolution of the pterosaur wing.

All the above traits are shared with basal bipedal crocs. And we already have a long list of taxa that show an increasing number of pterosaurian traits, listed here.

Witton mentions:
*You can’t mention Scleromochlus on the internet without someone pointing out that its status as an ornithodrian has not been tested in analyses containing non-archosaur archosauromorphs. This is true enough, but – at least within the current limits of testing – its ornithodiran status is not controversial, having been recovered in at least six different analyses (e.g. Gauthier 1986; Sereno 1991; Bennett 1996; Hone and Benton 2008; Brusatte et al. 2010) and sharing several unique characteristics with Pterosauria (Padian 1984). Hence, we’re following convention here.”

Again, forgetting Peters 2000 and the large reptile tree at reptileevolution.com.

Basal Crocodylomorpha

Figure 2. Basal Crocodylomorpha, including Gracilisuchus, Saltopus, Scleromochlus and Terrestrisuchus. Here the deep antorbital fenestra, deep chevrons, tiny hands and lack of a fifth toe feel right at home.

After describing the vestigial hand and lack of a fifth toe in Scleromochlus, Witton writes:Scleromochlus hindlimb arthrology betrays a parasagittal posture akin to that of dinosaurs and pterosaurs – the suite of characteristics associated with this is one clue that Scleromochlus is closely related to these clades (Bennett 1996; Benton 1999; Hone and Benton 2008).” Hey, wait a minute Mark! You’re forgetting the bipedal crocs (Fig.2)! And pterosaurs have giant hands and a long fifth toe!

The meat of the blog, it’s raison d’être
After listing the transversely-banded scales on the dorsal surface of the Scleromochlus torso (think croc skin), Witton let’s his imagination out of the barn, “Scleromochlus may have been covered in scales, but it is equally likely that it had fuzz-like filaments in places. There are several reasons for this. Firstly, it belongs within a phylogenetic bracket where filaments are the ancestral condition or, at very least, scales were prone to developing filamentous morphologies. Secondly, virtually all models of archosaur evolution recover Scleromochlus as sister taxon to a fuzzy clade – pterosaurs, so there is good ‘phylogenetic proximity’ for fuzz. Thirdly, insulating integuments are common – if not ubiquitous – in small, active (see below) desert-dwelling animals.” 

Mark, it’s those analyses that expand the inclusion set, that nest Scleromochlus with bipedal basal crocs, you should be keeping an eye on. This is what I don’t understand about paleontologists. Sometimes the obvious (Fig. 2) becomes taboo territory because I’m associated with it.

Leaping pterosaur precursor?
It’s not a stretch to imagine Scleromochlus as a leaping archosaur. But then Witton takes it one step further, “Indeed, the powerful leaping and bounding abilities of early ornithodirans has been tied to the evolution of pterosaur flight (Bennett 1997; Witton 2013).” Unfortunately such hind limb leaping gives the forelimbs nothing to do and no reason to begin flapping. And flapping is key to pterosaurian evolution. Read more on the origin of pterosaur flapping here.

References
Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoolological Journal of the Linnean Society 118: 261–308.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Padian K. 1984. The Origin of Pterosaurs. Proceedings, Third Symposium on Mesozoic Terrestrial Ecosystems, Tubingen 1984. Online pdf
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Hist Bio 15: 277–301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. Journal of Vertebrate Paleontology 11 (Supplement) Memoire 2: 1–53.
Woodward AS 1907. On a new dinosaurian reptile (Scleromochlus taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society 1907 63:140-144.

wiki/Scleromochlus

Reconstructing the hand of Scleromochlus

A short series on basal archosaur hands follows.
They are rarely preserved, so any clues are valuable.

Scleromochlus (Fig. 1) nests as a basal bipedal crocodylomorph in the large reptile tree, close to Saltopus, Gracilisuchus and Terrestrisuchus. However, Sereno (1991), Bennett (1996), Benton (1999), Senter (2003) and Hone and Benton (2008) among others found Scleromochlus nested with pterosaurs, but this was in the absence of the aforementioned genera.

The hand of Scleromochlus,
the hand that could have turned into a wing if Scleromochlus was indeed related to pterosaurs (according to the aforementioned authors), is preserved, but not well preserved (Fig. 1). Even so, very little reconstruction is necessary. It is what it is, a vestige.

Figure 1. Scleromochlus forequarters. The yellow area shows the hand enlarged in situ. The size of the Scleromochlus hand makes it the last possible sister to pterosaurs, famous for their very large hands.

Figure 1. Scleromochlus forequarters. The yellow area shows the hand enlarged in situ. The size of the Scleromochlus hand makes it the last possible sister to pterosaurs, famous for their very large hands.

First of all, the hand preserves only three digits and a few carpals. Those are digits 1-3. Digits 4 and 5 were either absent or not preserved. Considering the very tiny size of the hand and phylogenetic bracketing, either is possible.

In pterosaur ancestors digit 5 also became a vestige, so that’s not a factor here.

In pterosaur ancestors digit 4 and metacarpal 4 were larger than the others. Interesting then that the biggest bones of the hand did not get preserved in Scleromochlus. That large 3-sided block could be the base of metacarpal 4, but in phylogenetic bracketing that would be unlikely as no sisters follow that pattern. Rather that large 3-sided block is likely a radiale or ulnare, bones which become elongated in bipedal basal crocs, like Terrestrisuchus, those carpals remain elongated even in modern crocs.

For some reason, likely a bad paradigm, pterosaur workers continue to hold on to the idea that Scleromochlus could be a pterosaur ancestor candidate, as Witton (2013) wrote, despite the publication of Peters 2000a, b, 2002, 2007 and 2013, papers that demonstrated not one, but four genus-based fenestrasaur taxa that made better ancestors for pterosaurs than did any archosaur, including Scleromochlus.

As anthropologiest Elaine Morgan observed here, quoting Thomas S. Kuhn (1962, the inventor of the term “paradigm shift”), “What scientists do when a paradigm fails is… (guess what?) they carry on as if nothing had ever happened.” Morgan also reports, “You can’t solve a scientific problem by holding a head count. More of us say yes than say no.”

This explains… so much
This explains why Unwin (2005) and Hone and Benton (2008) omitted any reference to Peters (2000a, b, 2002) and why Hone and Benton (2007) deleted Sharovipteryx and Longisquama and used only a quarter of the traits of Cosesaurus to discard the fenestrasaur hypothesis of pterosaur ancestry under the pretext of testing it. This also explains Darren Naish’s rant from a year ago at Tetrapod Zoology that focused on everything but the website he was ranting against.

And that’s how we go from tiny impressions in Scottish sandstone to basic human psychology in one blog post.

References
Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoolological Journal of the Linnean Society 118: 261–308.
Benton MJ 1999. Scleromochlus taylori and the origin of dinosaurs and pterosaurs. Philosophical Transactions of the Royal Society of London Series B Biological Sciences 354: 1423–1446.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total-evidence methods: the origin of the pterosaurs. In: Hone DWE, Buffetaut E, editors. Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Vol. 28. Munich: Zittel B. p. 35–60.
Peters D 2000. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293–336.
Peters D 2000b. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
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(4):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. Geobios 17:747–753.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. Journal of Vertebrate Paleontology 10 (supplement to 3): 1–53.