Longisquama’s Long Scales

A new paper by Buchwitz and Voight (2012) sheds new light on the dorsal frill (plumes, appendages) of Longisquama (Sharov 1971). From their abstract: “On the basis of comparative description of the individual morphology of all yet known Longisquama specimens we address aspects of taphonomy, development, and function and define to what extent Longisquama’s appendages share characteristics of avian vaned feathers. We explain the existing feather similarity by their development from a filamentous primordium and a complex sequence of individual processes, some of which are reminiscent of processes observed in feather development. Such an interpretation is in agreement with a set of homologous mechanisms of appendage morphogenesis in an archosauromorph clade including Longisquama and feather-bearing archosaurs but does not necessarily require that the appendages of Longisquama themselves are feathers or high-level feather homologues.”

Not Plants
Buchwitz and Voight (2012) further established that the frills were not from coincident plants. Several appendages were shown to articulate with vertebrae and no similar plants are known.

Origin
With regard to the appendages origin, Buchwitz and Voigt (2012) reported, these plumes, “can be explained by formation in an elaborate developmental process that began with a filamentous appendage primordium.” They considered, “the ability to form simple filamentous and more complex elongated skin appendages as the synapomorphy of an archosauromorph clade including Longisquama, crocodylians, pterosaurs, non-avian dinosaurs, and birds.”

Basic Problem
Buchwitz and Voigt (2012) did not consider the possibility that the frill was homologous to those found in various lizards like Iguana (Fig. 1) and Sphenodon (Fig 2). The present large reptile tree found Longisquama to be nested within the tritosaur lizards, not far from the base of the Lepidosauria (which includes Sphenodon and Iguana as phylogenetic brackets). They did not establish another closest sister taxon to Longisquama within the Archosauromorpha, nor did they offer any results from a phylogenetic analysis, like this one. Their family tree (Buchwitz and Voigt 2012, fig, 10) graphically nested Longsiquama between “Lepidosauromorpha” and “basal archosauromorpha” within a monophyletic “diapsida,” which is false and extremely vague at best. They referenced Peters (2000) which proposed a relationship between Macrocnemus, JesairosaurusLangobardisaurus, Cosesaurus, Sharovipteryx, Longisquama and pterosaurs, then “but see”-d it with a reference to Hone and Benton (2007 and by inference 2008) which deleted Sharovipteryx and Longisquama from its database and deleted 75% of the traits of Cosesaurus to eliminate rather than test these taxa in phylogenetic analysis.

Blame the Preservation
Instead they blamed the state of preservation and the false paradigm of a partial skeleton for their uncertainty. They observed no clear indication of a antorbital or mandibular fenestra. They observed “no skull bone substance” and the “sediment relief seems to be of limited informativeness.” They did not attempt to perform DGS (digital graphic segregation on this flattened fossil. Some of this is understandable as Longisquama is one of the few fossil reptile specimens in which the soft tissue is more apparent than much of the hard tissue (largely due to coverage by the soft tissue).

The spines of Iguana.

Figure 1. The spines of Iguana. These occur much more frequently than the underlying vertebrae.

Iguana spines
The dorsal spines of a Green iguana are noticeably longer and thicker in males (Fig. 1). Thus these are considered secondary sexual characteristics. In Iguana the spines occur in multiples relative to the each vertebrae, rather than one-to-one, as in Longisquama.

The dorsal spines of Tuatara (Sphenodon).

Figure 2. The dorsal spines of Tuatara (Sphenodon).

Sphenodon Spines
The dorsal spines in Sphenodon (Fig. 2) are short, white and there is little color in this otherwise drab taxon. Nevertheless, there they are. They’re not fibers, they’re modified scales, as Sharov (1971) originally proposed. Some appear one-to-one with the underlying vertebral spines. Others are two-to-one.

Functional Analog to Squamates
Buchwitz and Voigt (2012) reported, “the series of dorsal appendages in Longisquama could be a functional analogue to the dorsal crests of elongated scales in extant squamates”. 

Analogs, yes, AND homologs.

Buchwitz and Voigt (2012) also reported, The hypothesis that integumentary structures of high complexity evolved in the context of display is not unreasonable if the mating systems and display behaviour were likewise highly derived.” That concept is right in line with the hypothesis that wings powered by bird-like flapping anchors developed first as display structures in pterosaur ancestors discussed here, here and in Peters (2002).

Details
Buchwitz and Voigt (2012, fig. 3) includes a patch of tissue in the upper right hand corner with parallel striations. This is where I illustrated a torn uropatagium, as in Sharovipteryx, which also reinforced its uropatagium with embedded fibers that look like parallel striations. Mike Buchwitz (pers. comm.) considered that patch a displaced cockroach wing. We’ll see…

Summary
Buchwitz and Voigt (2012) provided a much needed and appreciated look at the dorsal scales of Longisquama. Unfortunately their phylogenetic base mistakenly nested Longisquama (and pterosaurs) with unspecified archosaurs leading toward a plume/filament origin rather than an elongated scale origin, as in Iguana.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Buchwitz M and Voigt S 2012. The dorsal appendages of the Triassic reptile Longisquama insignis: reconsideration of a controversial integument type. Paläontologische Zeitschrift (advance online publication) DOI: 10.1007/s12542-012-0135-3
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.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Sharov AG 1970
. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.

The Tritosauria – An Overlooked Third Clade of Lizards

Traditionally there have been just two lizard clades in the Squamata. The Iguania included Iguana, Draco, Phrynosoma and other similar lizards. The Scleroglossa included Tupinambis, Chalcides, Varanus, Heloderma and all the snakes and amphisbaenids. Squamate outgroups within the Lepidosauria included members of the Rhynchocephalia (such as Sphenodon) and the basal lepidosaur, Homoeosaurus, which probably appeared in the Permian, but is only known from the Late Jurassic.

Traditional Nesting
Wikipedia reports the following about the Squamata, “Squamates are a monophyletic  group that is a sister group to the tuatara. The squamates and tuatara together are a sister group to crocodiles and birds, the extant archosaurs.” This is the traditional concept, but testing this in a larger study finds that lizards and archosaurs are not closely related. Not by a long shot.

The Tritosauria, a new lizard clade that was previously overlooked.

Figure 1. Click to enlarge. The Tritosauria, a new lizard clade that was previously overlooked.

The New Heretical Tritosauria
The large study (Peters 2007) recovered a third clade of squamates just outside of the Squamata (Iguania + Scleroglossa), but inside the Lepidosauria (which includes Sphenodon and the other Rhynchocephalia). At the base of this third clade, called the Tritosauria (“third lizards”), are three very lizardy forms, none of which had fused proximal ankle bones, a trait shared by most squamates (at least those that have legs!). Lacertulus, Meyasaurus and Huehuecuetzpalli are known from crushed but articulated fossils. Lacertulus was considered a possible biped (Carroll and Thompson 1982) based on its long hind legs. It is likely that Huehuecuetzpalli (Reynoso 1998) was also a biped. All three were considered close to the base of the lepidosauria, not closely related to any living lizards.

The Tritosauria
A Clade of Misplaced and Enigmatic “Weird-Ohs”

Phylogenetically following Huehuecuetzpalli three distinct clades emerge within the Tritosauria. Some of these were formerly considered “prolacertiforms” (Peters 2000), but now we know that none are related to ProlacertaAll three subclades have some pretty weird members.

The Tanystropheidae
This clade was named by Dilkes (1998) to include “the most recent common ancestor of MacrocnemusTanystropheus and Langobardisaurus and all of its descendants.” Clade members include several long-necked taxa, some of which, like Dinocephalosaurus, preferred swimming to walking. Tanystropheus was the largest, attaining 4.5 meters in length.

The Jesairosauridae
This clade includes Jesairosaurus (Jalil 1991) and the drepanosaurs, from Hypuronector to Drepanosaurus.  This clade included several arboreal, hook-tailed taxa with short-toed feet that were able to grasp slender branches in their slow-motion quest for insects. All were rather small.

The Fenestrasauria
This clade was named by Peters (2000) to include “Cosesaurus, Preondactylus, their common ancestor and all of its descendants.” This clade started off with bipeds that flapped their arms, probably for display during mating rituals because some members, like Longisquama were exotically decorated with extradermal membranes and plumes. Powered gliding (as in Sharovipteryx) was followed by flapping flight in pterosaurs, the first flying vertebrates. Several pterosaurs secondarily developed a quadrupedal pace. Quetzalcoatlus was the largest tritosaur, attaining a wingspan of 10 meters.

Summary
Due to the wide gamut and large inclusion list of the present phylogenetic analysis, many former enigmas, mismatches and leftovers came together in a new clade of lepidosaurs that was previously overlooked. Together, the Tritosauria include some of the strangest and, at times largest, of all lizards. Hyper-elongated necks and hyper-elongated fingers, together with experiments in both a sedentary marine lifestyle (Dinocephalosaurus) and a homeothermic aerial lifestyle (Dimorphodon, for example) make this a truly dynamic and diverse clade. Some of these out-of-the-ordinary morphologies seem to have been kick-started by early experiments with bipedalism. While the arboreal niches of drepanosaurs and pterosaurs are relatively easy to identify, the long-necked tanystropheids may also have used bipedalism and a long neck to reach into tree boughs to snatch prey, creating their own arboreal niche.

Unfortunately, only pterosaurs and Huehuecuetzpalli survived the end of the Triassic and they did not survive the end of the Cretaceous. So tritosaurs are the only major clade of lizards that is extinct today.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Carroll and Thompson 1982. A bipedal lizardlike reptile fro the Karroo. Journal of Palaeontology 56:1-10.
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 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.

Longisquama Wings

Longisquama: Almost Too Fascinating. And a Lot of Work!
The general morphology of Longisquama has been difficult to ascertain. Sharov (1970), Senter (2003) and Martin (2000) provided simple tracings without much resolution. Peters (2000) added details, but was unable to actually “see” many details due to inexperience. There I said it. Okay, I’m better now than I was 12 years ago. I’ve got more under my belt.

A dozen years ago I was also under the existing paradigm that the posterior half of Longisquama was missing, as Sharov (1970) reported. No one ever suspected that Longisquama had the long hind legs of a biped and the wings of a pterosaur. Even when they are traced out (Figure 1), they are still difficult to see and were mistaken for displaced plumes by Sharov (1970).

New tracings of Longsiquama

Figure 1. Click to enlarge. New tracings of Longsiquama (B) soft tissues and (C) bones.

Persistence Pays Off!
A new tracing of Longisquama (Figure 1) reveals long hidden details including the tail, pelves, two hind limbs and two folded wings framed by elongated wing fingers (Figure 2). Workers who have seen this fossil claim they did not see this level of detail. That’s because the human eye, even aided by a binocular microscope, cannot segregate and aggregate all the chaos and layers of detail in this fossil. It takes a computer and DGS (digital graphic segregation) to tease out each bone one at a time. By digitally tracing the elements the details emerge and form a complete picture with matching left and right elements that confirm identification. This technique has been widely criticized, but the results speak for themselves.

Despite the “weirdness” of Longisquama, there are very few autapomorphies present. Instead, nearly every trait bridges the morphological gap between Cosesaurus and pterosaurs. It took persistence and the recognition of past errors to make these tracings come together. Follow these methods and the results should be identical.

The wings of Longisquama

Figure 2. Click to enlarge. The wings of Longisquama digitally segregated, including soft tissue. A. In situ. B. Both forelimbs. C. The right forelimb. D. The left forelimb. All elements match left to right.

The “proto-wings” of Longsiquama were midway in size and shape between the nonvolant forelimb of Cosesaurus and the fully-fledged wings of basal pterosaurs (Figure 3). Fingers 1-3 were quite a bit larger than those of either sister taxa. Metatarsal 4 was axially rotated so the finger four flexed in the plane of the wing, as in pterosaurs, rather than toward the palm, as in all other tetrapods. The large claws on the hands suggest an arboreal habitat.

Figure 1. Click to enlarge. The origin of the pterosaur wing and the migration of the pteroid and preaxial carpal. A. Sphenodon. B. Huehuecuetzpalli. C. Cosesaurus. D. Sharovipteryx. E. Longisquama. F-H. The Milan specimen MPUM 6009, a basal pterosaur.

Cosesaurus and Longisquama are the Archaeopteryx and Microraptor of pterosaurs, demonstrating the first steps in the origin of flight for the first volant vertebrate clade, the Pterosauria.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E. Buffetaut & D.W.E. Hone (eds.), Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica doi: 10.4202/app.2009.0145 online pdf
Jones TD et al 2000. Nonavian Feathers in a Late Triassic Archosaur. Science 288 (5474): 2202–2205. doi:10.1126/science.288.5474.2202. PMID 10864867.
Martin LD 2004. A basal archosaurian origin for birds. Acta Zoologica Sinica 50(6): 978-990.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, DeKalb, IL, 1-279.
Senter P 2004. Phylogeny of Drepanosauridae (Reptilia: Diapsida) Journal of Systematic Palaeontology 2(3): 257-268.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.

wiki/Longisquama

The Origin of the Pterosaur Sternal Complex

It is a common and mistaken paradigm that pterosaurs appeared out of nowhere, seemingly unrelated to other prehistoric reptiles. Those who say this (and the list is long) also judiciously avoid any discussions of pterosaurs as lizards or fenestrasaurs. Their investments in the outmoded and unsupportable archosaur hypothesis have not provided answers — and never will. Here we will take a look at the development of the sternal complex of pterosaurs evolving from the most parsimonious sister taxa yet discovered (Peters 2000a, 2007).

The Pectoral Girdle in Huehuecuetzpalli
The story begins with Huehuecuetzpalli (Reynoso 1998), a basal tritosaurid lizard with a fairly typical pectoral girdle (Figure 1). A T-shaped interclavicle and sinuous tapered clavicles anteriorly framed the short scapula and fenestrated but otherwise discoidal coracoid. A broad sternum was located at the posterior tip of the interclavicle. The coracoid was free to rotate between the clavicles, interclavicle and sternum, increasing the range of motion of the humerus.

The Pectoral Girdle in Cosesaurus
Several changes to this pattern can be seen in the basal fenestrasaur and tritosaur, Cosesaurus (Figure 1). The interclavicle developed an anterior process. The sternum moved anteriorly, now dorsal to the transverse processes of the interclavicle. The clavicles were shorter, no wider than the sternum and aligned with the anterior rim of the sternum. The coracoids were relatively larger and considerably narrower as the anterior fenestrations expanded until just the quadrant-shaped posterior rim remained. The scapula was strap-shaped with a long posterior process extending over several more dorsal ribs. With the sternum leading edge now anterior to the interclavicle trailing edge, the coracoids had no room to move and their ventral stems became socketed and essentially immobile, resembling the configuration in birds and serving as a precursor to the configuration in pterosaurs.

 

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

Figure 3. Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex. Figure 1. The evolution of the pterosaur pectoral girdle and sternal complex featuring Huehuecuetzpalli, Cosesaurus, Longisquama, and the basal pterosaur, MPUM 6009.

The Pectoral Girdle in Longisquama
In Longsiquama (Figure 1) the interclavicle, clavicles and sternum are closely integrated, as in pterosaurs. Distinct from all other tetrapods, the clavicles curved posteriorly, extending to the posterior rim of the crescent-shaped sternum, which they frame. The cruciform interclavicle extended ventrally to form a small keel. Taphonomically displaced to beneath the throat, the overlapping clavicles were mistaken by Jones et al. (2000) for a bird-like furcula (fused clavicles in birds).

The Pectoral Girdle in Pterosaurs
In basal pterosaurs (Figure 1) there were few changes from the Longisquama pattern. So the sternal complex (Wild 1994), like many other aspects of pterosaur morphology, had evolved before the advent of large pterosaurian wings (Peters 2002, contra Bennett 2008).

Summary
All these changes could never have taken place if Cosesaurus was restricted to a typical quadrupedal configuration. The forelimbs had to become elevated from the substrate in a bipedal configuration, as imagined (based on morphology) in its phylogenetic predecessors, Lacertulus (Carroll and Thompson 1982) and Huehuecuetzpalli — and as evidence by matching Cosesaurus pedes to Rotodactylus tracks (Peters 2000b) which were ocassionally bipedal. Cosesaurus had a pectoral complex essentially and mechanically identical to that of pterosaurs (and broadly similar to that of birds). So it seems likely that it was also flapping, probably in some sort of territorial or mating ritual, long before gliding and flying were possible in its descendant taxa, Sharovipteryx, Longisquama and pterosaurs.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E. Buffetaut & D.W.E. Hone (eds.), Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Carroll and Thompson 1982. A bipedal lizardlike reptile fro the Karroo. Journal of Palaeontology 56:1-10.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica doi: 10.4202/app.2009.0145 online pdf
Jones TD et al 2000. Nonavian Feathers in a Late Triassic Archosaur. Science 288 (5474): 2202–2205. doi:10.1126/science.288.5474.2202. PMID 10864867.
Peters D 2000a. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2000b. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
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.
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.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.

Sharovipteryx and the Origin of Pterosaurs

The bizarre hind-wing glider, Sharovipteryx mirabilis, has confounded and intrigued paleontologists since 1971 when Alexander G. Sharov first described it. The most prominent aspects of the fossil are the extremely long hind limbs, trailed by extensive extradermal membranes called uropatagia. While several readily visible aspects of Sharovipteryx immediately recall pterosaurs (attenuated tail, longer tibia than femur, hollow bones, elongated ilium. sacrum of way more than two vertebrae, elongated pedal 5.1, dermal membranes, among others), the reduced forelimbs were cause for concern in a pterosaur sister taxon.

 

Sharovipteryx mirabilis

Figure 1. Sharovipteryx mirabilis in various views. Click to learn more.

Poorly preserved?
Sharovipteryx
has been described as “poorly preserved” even though the finest details are preserved in its extradermal membranes. The skull is crushed, but all the details are visible. Insects are preserved with and within Sharovipteryx. A beetle lies nearby. A winged ant or wasp is found in the skull. Shcherbakov (2008) described the Lagerstätte formation from which Sharovipteryx was found. The paleoenvironment (Madygen Formation, Osh Region in Kyrgyzstan, Early Triassic, 228 mya) may be reconstructed as an intermontane river valley in seasonally arid climate, with mineralized oxbow lakes and ephemeral ponds on the floodplain. After amber, it may be the best formation for preserving insects.

Early Errors
Peters (2000) attempted to trace the skull elements of Sharovipteryx, but I assumed the split at the back of the skull must have been a pterygoid. Instead it represents a domed cranium. In my rookie year as a paleontologist, I made several mistakes, this one among them. Later I was able to discern and correct my error. I also found more elements of the forelimb. All these can be seen here. No one else has attempted a detailed tracing and identification of the elements before or since.

Subsequent Corrections
There is word that some further preparation has occurred, according to Hone and Benton (2007), who reported, “In any case, the true arms of Sharovipteryx have now been found buried in the matrix (R. R. Reisz, pers. comm., 2003) and this confirms that Peters (2000) supposed arm was incorrectly identified.” It is not clear that Hone and Benton (2007) actually had access to the data itself, but in their zeal to discredit Peters (2000) they latched onto this hearsay. Unfortunately, the Reisz data have not been made available and have not been published in the eight years that have followed. Concurrently, as mentioned earlier, I was able to correct earlier mistakes. The forelimb elements I found matched left to right and fell in line in all morphological aspects between the two sister taxa of Sharovipteryx, Cosesaurus and Longisquama (Peters 2006). These included a tiny pteroid and preaxial carpal, bones otherwise found only in fenestrasaurs, including pterosaurs. I also identified prepubic bones and a hyper-elongated ilium in Sharovipteryx. These traits are also restricted to fenestrasaurs including pterosaurs. Prepubes acted like elongated pubes, adducting the sprawling hind limbs.

The pelvis and prepubes of Sharovipteryx.

Figure 2. The pelvis and prepubes of Sharovipteryx.

Truncated Studies
Following his  studies of the uropatagia in Sordes (Unwin DM and Bakhurina NN 1994), Dr. David Unwin (2000a, b, c) flirted briefly with Sharovipteryx as a pterosaur sister taxon, but has ignored it ever since. Unfortunately in his update he used Sharov’s own figure from 1971, rather than providing an updated figure.

In his book, The Pterosaurs From Deep Time, Unwin 2006 asked if Sharovipteryx could be ancestral to pterosaurs, then answered, “Probably not. Because it is almost the same geological age as early pterosaurs and, with its remarkably long neck, already highly specialized.” While referencing nearly every other paper and worker on pterosaurs, all papers written by yours truly (Peters 2000 and 2002 among them) were overlooked and ignored. Rather he opted to continue the old paradigm that, “pterosaurs sit in splendid isolation, definitely related to, but somehow remote from, other diapsids.” Unwin said there was no antorbital fenestra and the arms were extraordinarily short and small. While the latter is true, the former is not. Unwin never performed a cladistic analysis with Sharovipteryx and other pterosaur ancestor candidates to test the results of Peters (2000).

Following Gans et al. (1987), Dyke et al. (2006) described Sharovipteryx as a “delta-wing” flyer. Unfortunately they provided no evidence of membranes anterior to the hindlimb, but imagined them instead.

With such small forelimbs and such long hindlimbs, Sharovipteryx would have been a full-time biped, a fact that has been largely overlooked. As a biped, Sharovipteryx could have done other things with its forelimbs, such as gliding and flapping.

Sharovipteryx would have been a consummate glider. The enlarged hyoids extended the neck skin into strakes (leading edge root extensions), an aerodynamic structure found on several modern jet fighters. The ribs extended laterally, forming a small round pancake. Manual digit 4 extended further than the other digits. Since both sister taxa (Cosesaurus and Longisquama) had trailing edge membranes, it is likely that Sharovipteryx also had them. Rather than a delta wing, the membranes had a deeper chord distally, creating a canard wing configuration.

Due to the stem-like coracoid and strap-like scapula, Sharoviptyerx likely flapped its forelimbs, not only to show excitement and attract attention when grounded, but to create thrust and lift when aloft. The large, fiber embedded uropatagia that trailed the sprawling hind limbs of Sharovipteryx provided the majority of lift and extended through the center of balance. Other tiny membranes extended anterior to the lower tibia and mid femur. Longisquama was similar in configuration, but with longer forelimbs. Pterosaurs were also similar, but with even longer wing fingers.

The hind legs of Sharovipteryx provide a good model for the configuration of most pterosaurs, sprawling in flight. On land, whenever the knees were lower than the hip socket, which was probably typical, the right angled knees returned the ankles to beneath the torso, as in pterosaurs.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Dyke G, Nudds RL and Rayner JMV 2006. Flight of Sharovipteryx mirabilis: the world’s first delta-winged glider. Journal of Evolutionary Biology.
Gans C, Darevski I, and Tatarinov LP 1987. Sharovipteryx. A reptilian glider? Paleobiology 13(4):415–426.
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.
Peters, D. 2000b. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7(1):11-41.
Peters D 2000.
 
A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing—with a twist. Historical Biology 15:277-301.
Peters D 2006. The Front Half of Sharovipteryx. Prehistoric Times 76: 10-11.
Shcherbakov DE 2008. Madygen, Triassic Lagerstätte number one, before and after Sharov. Alavesia 2:113-124. online pdf
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Sharov AG 1971. New flying reptiles from the Mesozoic of Kazakhstan and Kirghizia. – Transactions of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].
Unwin DM 2000a. Sharovipteryx: what can it tell us about the origin of pterosaurs?
48th Symposium of Vertebrate Palaeontology and Comparative Anatomy, Portsmouth,
England, Monday 28 Aug. – Sunday 3 September.
(http://www.soft.net.uk/richardforrest/svpca2000/svpca2000.page.intro.html)
Unwin DM 2000b. Sharovipteryx and its significance for the origin of the pterosaur
flight apparatus. 5th European Workshop on Vertebrate Palaeontology, 27.6.2000
– 1.7.2000, Staatliches Museum für Naturkunde Karlsruhe (SMNK) Erbprinzenstr.
13 D-76133 Karlsruhe Germany (http://www.alettra.de/ewvp5/index.htm)
Unwin DM 2006. The Pterosaurs from Deep Time. Pi Press, New York, NY.
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.
Unwin DM, Alifanov VR and Benton MJ 2000. Enigmatic small reptiles from the Middle Triassic of Kirgizia, pp. 177–186. In: Benton M. J., Unwin D. M. & Kurochin E. “The age of Dinosaurs in Russia and Magnolia”, Cambridge University Press, Cambridge.

Longisquama and the Origin of Pterosaurs

Prequel: Longisquama Gets No Respect
(or the Lengths Scientists Will Go to Protect Pet Theories)

In their two-part paper on pterosaur origins Hone and Benton (2007, 2008) announced they would test whether pterosaurs nested more parsimoniously within the Archosauria (Bennett 1996) or the Prolacertiformes (Peters 2000). They used the technique of the supertree, gathering several trees together to come up with a larger, ostensibly more complete, tree. That permitted them to use the data of others without having to visit fossils. We’ll get back to their results (below), but first a short background study.

Bennett (1996) used suprageneric taxa, for the most part, and nested pterosaurs with Scleromochlus at the base of the Dinosauria + Lagosuchus (now Marasuchus). The Ornithosuchidae were basal to this clade. The Prolacertiformes were nested far toward the base of the tree. Earlier we discussed problems with these putative sisters here. Bennett (1996) did not consider CosesaurusSharovipteryx and Longisquama.

Fenestrasaurus

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

Peters (2000) tested the matrices of Bennett (1996) and two others (Jalil 1991 and Evans 1986) simply by adding Langobardisaurus and the fenestrasaurs, including CosesaurusSharovipteryx and Longisquama. Pterosaurs nested with these taxa, rather than any archosaur or archosauromorph, when given the opportunity. Peters (2000) erected the clade, the Fenestrasauria, because they shared the trait of an antorbital fenestra without a fossa, convergent with that of archosaurs.

The largest study to date on reptile interrelationships nested Longisquama and pterosaurs with lizards like Lacertulus, Meyasaurus and Huehuecuetzpalli, far from Prolacerta, archosauromorphs, Scleromochlus and archosaurs.

Getting Back to Where We Began
Hone and Benton (2007) discredited the data of Peters (2000) and elected not to include any of it in their supertree. That left only one study that included pterosaurs, Bennett (1996), in their supertree analysis. Having eliminated the opposing candidate data and the opposing candidate taxa, the results were predetermined. The results of Hone and Benton (2008) reflected the results of Bennett (1996). Sadly, the results also nested members of the Choristodera far from the Choristodera and members of the Lepidosauromorpha far from the Lepidosauromorpha, so the study had its problems. Moreover, Hone and Benton (2008) falsely gave credit for the prolacertiform hypothesis to Bennett (1996), after properly giving it to Peters (2000) in their earlier (2007) paper. And now you know  the lengths scientists will go to protect their pet theories.

The Back Half of Longisquama
Ever since Sharov (1971) reported that only the front half of Longisquama was visible, scientists stopped looking for it. Ironically, one of the plumes illustrated by Sharov(1971), the one not radiating like the others, was a tibia and femur. The subdivided “feather shafts” reported by Jones et al. (2000) were actually displaced toes subdivided by phalanges. Here, using the technique of DGS (digital graphic segregation) the back half of Longisquama is, at last, revealed.

The complete fossil of Longisquama.

Figure 2. Click to enlarge. The complete fossil of Longisquama.

The back half of Longisquama was overlooked for so long because the elements lined up with and were camouflaged by the plumes. Apparently Longisquama’s stomach exploded, or was torn up. The front third of Longisquama is undisturbed, the tail is undisturbed, but the hips are turned backwards and the legs and feet are rotated up to the dorsal vertebrae.

Longisquama in lateral view

Figure 3. Longisquama in lateral view, dorsal view and closeup of the skull. Like Microraptor, Longisquama glided/flew with similarly-sized wings both fore and aft.

Distinct from Cosesaurus
The skull of Longsiquama had a more constricted snout, which enhanced binocular vision. The orbits were larger. The teeth had larger cusps. The naris was probably larger. With increased bipedalism and active flapping, Longiquama probably experimented with aerobic metabolism. The cervicals were shorter and the dorsal series was longer, especially so near the hips and between the ilia. The sacrum curved dorsally 90 degrees, which elevated the attenuated tail. These vertebral modifications made Longsiquama similar to a lemur, which also leaps from tree to tree. Such a long torso provided more room for plumes, gave the back great flexibility, and provided more room for egg production. The pectoral girdle was little changed from Cosesaurus. The clavicles curved around the sternal complex and the sternal keel was deeper. Fused together the interclavicle, clavicles and sternum form a sternal complex, as in pterosaurs. During taphonomy the sternal complex ofLongisquama drifted to beneath the cervicals, exactly where the clavicles are found in non-fenestrasaur tetrapods, including birds. This has led to confusion because the clavicles overlapped giving the appearance of a bird-like furcula. As in Cosesaurus, the pterosaur-like pectoral girdle and socketed coracoids enabled Longisquama to flap and generate thrust during leaps. The pelvis was greatly elongated anteriorly and posteriorly with a posterior ilium rising along with the dorsally curved sacrum of seven vertebrae. The pubis and ischium were much deeper, which provided a much larger pelvic aperture to pass a much larger egg. The distal femur was concave and the proximal tibia convex, as in Sharovipteryx. Both the femur and tibia/fibula were more robust. The foot was relatively large with digits of increasing length laterally. Pedal digit V had a curved proximal phalanx.

Longisquama is famous for, and was named for, its dorsal plumes. Another set of plumes arose from its skull and neck. Former caudal hairs (in Cosesaurus) formed a tail vane in Longisquama. As in Sharovipteryx and pterosaurs, Longsiquama had a uropatagium trailing each of its hind limbs. Like Cosesaurus, Sharovipteryx and pterosaurs membranes trailed the forelimbs, too. This documents the origin of the pterosaur wing and proves that it developed distally on a flapping wing (Peters 2002) rather than proximally as a gliding membrane (contra Elgin, Hone and Frey in press) and certainly without wing pronation, loss of digit V, loss of ungual 4 and migration of metacarpals I-III to the anterior face of metacarpal IV (contra Bennett 2008).

Longisquama was overloaded with secondary sexual characteristics. From plumes to flapping arms, Longisquama was all about creating an exciting presentation unrivaled until the present-day bird-of-paradise. Longisquama had everything Cosesaurus had, only wildly exaggerated. With increased bipedalism and active flapping, Longiquama probably experienced the genesis of aerobic metabolism.

Figure 4. Click to enlarge. The origin of the pterosaur wing and the migration of the pteroid and preaxial carpal. A. Sphenodon. B. Huehuecuetzpalli. C. Cosesaurus. D. Sharovipteryx. E. Longisquama. F-H. The Milan specimen MPUM 6009, a basal pterosaur.

The Origin of the Pterosaur Wing
The elongated and robust finger four of Longisquama was also overlooked by all prior workers. Reconstructed here the hand of Longsiquama remains the best transitional example between Cosesaurus and pterosaurs. It is likely that digit 4 did not flex with the other three fingers in Longisquama because the PILs (parallel interphalangeal lines) were not continuous through digit 4, which also supported a pterosaur-like wing membrane, preserved along with the other soft tissue, the plumes.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E. Buffetaut & D.W.E. Hone (eds.), Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica doi: 10.4202/app.2009.0145 online pdf
Jones TD et al 2000. Nonavian Feathers in a Late Triassic Archosaur. Science 288 (5474): 2202–2205. doi:10.1126/science.288.5474.2202. PMID 10864867.
Martin LD 2004. A basal archosaurian origin for birds. Acta Zoologica Sinica 50(6): 978-990.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, DeKalb, IL, 1-279.
Senter P 2004. Phylogeny of Drepanosauridae (Reptilia: Diapsida) Journal of Systematic Palaeontology 2(3): 257-268.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.

wiki/Longisquama