Mesadactylus and Mesadactylus? – A new anurognathid and a new flightless pterosaur!

Jensen and Padian (1989) described the bits and pieces of the Mesadactylus holotype (Fig. 1, right). The type specimen is the synsacrum, distinct in morphology with an anteriorly high and completely fused neural plate. Jensen and Padian (1989) considered Mesadactylus a basal pterodactyloid pterosaur. Bennett (2007) considered the synsacrum anurognathid even though no other anurognathid had such a sacrum.

More recently Smith, Sanders and Stadtman (2004) recovered new material from the same late Jurassic formation. They ascribed these scattered specimens to Mesadactylus despite their distinct size and other differences. Based on their scale bars, these elements are reconstructed for the first time here (Fig. 1, left). Overall they represent a much larger specimen of a different type of pterosaur. Individually there are few similarities among the bones both shared in common.

The Mesadactylus holotype and referred specimens reconstructed to match the flightless pterosaur, Sos2428.

Figure 1. Click to enlarge. The Mesadactylus holotype (Jensen and Padian 1989, right) nests with the North American anurognathids. Several referred specimens (Smith et al. 2004, left), when reconstructed, nest at the base of the azhdarchidae, with Huanhepterus and the flightless pterosaur SOS 2428. The pink cervicals are duplicated from the single gray one. It is fairly clear, these two restored taxa are not congeneric.

Phylogenetic Analysis
Both specimens were entered into the large pterosaur tree. The holotype Mesadactylus nested with the other North American anurognathid, Dimorphodon? weintraubi and the early Cretaceous IVPP embryo.

I like to give others credit where credit is due and Bennett (2007) got this one right!

The referred specimen nested away from the anurognathidae, at the base of the azhdarchidae, along with the flightless pterosaur, SoS 2428 (Fig. 2) and its kin, BSPG 1911 I 31 (no. 42 in the Wellnhofer 1970 catalog), alongside Huanhepterus.

Referred Bones
Only one cervical vertebrae of the referred specimen was illustrated, so here (Fig. 1) it was duplicated and shortened, producing an elongated restored neck.

That relatively large rib (no doubt the second dorsal) indicates a voluminous torso. Proportionately this rib is much larger than the second dorsal rib in SoS 2428. So either the rib does not belong with the other referred bones or the torso was relatively much larger.

The humerus includes a very large shoulder articulation and a small deltopectoral crest, wider than deep. Manual 4.1 appears to include a fused extensor tendon process and a very short portion of m4.2 with converging margins indicating a short length.

The femur is elongated and S-curved, as in SoS 2428. All pterosaurs have a tibia of greater length, so that gives this restored specimen a stork-like or azhdarchid-like appearance.

Sos 2428. The flightless pterosaur.

Figure 2. Sos 2428. The flightless pterosaur for comparison.

Comparisons to SoS 2428 from the Solnhofen
The humerus has a distinct shape in the Colorado specimen, with a semicircular deltopectoral crest and a larger shoulder joint. As mentioned earlier, the rib is much larger in the Colorado specimen. Otherwise most of the elements are comparable.

Flightless
These clues and the phylogenetic nesting of the referred specimen suggest a close relationship with the flightless pterosaurSoS 2428. So that makes our second or third (depending on how we count SoS 2179, known only from a skull) flightless pterosaur.

Knowing what to look for now,
I wonder if there is more diagnostic material in the matrix?

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 S C 2007. Reassessment of Utahdactylus from the Jurassic Morrison Formation of Utah. Journal of Vertebrate Paleontology 27(1): 257–260.
Jenson J and Padian K 1989. Small pterosaurs and dinosaurs from the Uncompaghre fauna (Brushy Basin Member, Morrison Formation: ?Tithonian), Late Jurassic, western Colorado. Journal of Paleontology 63:364-373.
Smith DK, Sanders RK and Stadtman KL 2004. New material of Mesadactylus ornithosphyos, a primitive pterodactyloid pterosaur from the upper Jurassic of Colorado. Journal of Vertebrate Paleontology 24(4):850-856.

wiki/Mesadactylus

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Pterosaurs landing in trees – part 1 – grappling the trunk like a lemur

In the past, pterosaurs were usually pictured hanging from cliffs (remember Pteranodon in Fantasia?). Smaller pterosaurs were usually illustrated hanging beneath branches (Wellnhofer 1991) by their feet alone or inverted quadrupedal. Today we’ll start a short series on pterosaurs and trees demonstrating how some pterosaurs (not all) could interact with a tree trunk. If anyone finds this convergent with Archaeopteryx and kin, you’re probably right.

Figure 1. Dorygnathus on a tree.

Figure 1. Dorygnathus on a tree.

Basal pterosaurs had long fingers with trenchant claws pointed medially when the wings were folded (Fig. 1), as in basal birds. These claws were likely used to grapple tree trunks, clinging to them in the manner of lemurs and other primates (Peters 2002), arms on both sides of the trunk. In that configuration the feet were planted side-by-side beneath the pelvis, toes pointing anteriorly to antero-laterally with the dorsal surface of digit 5 putting extension pressure on the trunk, which enabled the toe claws to dig just a little deeper, much like a church key can opener.

A Chance to Show Off
In that configuration the wing finger would have been free to fully open as it would have been set at a tangent to the circumference of the tree trunk, no matter the diameter (Peters 2002, Fig. 2). Opening and closing the large wing fingers would have created a large display device, much larger than any anole dewlap, but serving the same purpose — finding a mate (Peters 2002), which was the original purpose of wings on predecessors like Longiquama.

Pterosaur on a tree

Figure 2. Pterosaur on a tree demonstrating the ability of the wing to open unimpeded on a tangent to the tree trunk. This would have served as a display mechanism. Modified from Peters (2002).

The large pectoral muscles would have provided sufficient adduction power to enable clinging and vertical walking.

Landing on tree trunks likely drove the first major change in pterosaurs, once they became volant. That forged the evolution of a longer forelimb. The most primitive pterosaur, MPUM 6009, had relatively longer legs and shorter arms (like its phylogenetic predecessor, Longisquama), but virtually all later pterosaurs had longer forelimbs (see Raeticodactylus for an example).

While some pterosaurs, perhaps anurognathids, were able to find insects on trees, it appears that most pterosaurs found trees a safe haven and a good take-off point. Unless facing down (which appears somewhat doubtful for the larger ones because they were unable to turn their feet backward in the manner of lizards, squirrels and bats, but they were able to point their feet laterally), tree-climbing pterosaurs would have taken off by launching themselves backwards, aided by gravity, twisting quickly to a normal flight configuration, like a woodpecker might do.

Due to a relatively stiff neck, a pterosaur would likely be taking a very close look at the tree trunk while grappling it. Certainly some left or right was possible, but more than 90 degrees would have been unlikely. Pterosaurs could have slept in this position, their forelimbs prevented from overextending by their joints and the propatagium. Since not all trees are vertical, many pterosaurs could have adopted this walking configuration on unobstructed horizontal to diagonal branches and fallen trunks.

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
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. London, Salamander Books, Limited: 1-192.

Pterosaur Take-Off from Water

Earlier we talked about various pterosaur takeoff techniques from dry land. Some techniques make sense. Others, like the forelimb launch, are more risky.

Some birds (like shearwaters) have no trouble diving into and flying out of water. Others, like ducks and geese, float upon the surface then take-off whenever they want to. Others, like frigate birds, take quick baths.

If pterosaurs ever landed on the water, were they able to take-off again? And if so, how did they do it? These are good questions for which answers can only come through pure speculation, drawing on physics, analogy and imagination.

Dr. Mike Habib has worked out the problem following the pattern of his forelimb launch from land. There’s an update here. Dr. Mark Witton illustrated the feat. Habib thinks it would take several leaps from the water before enough speed could be attained to generate lift. He reported at pterosaur-net.blogspot, “Anhanguerids probably took multiple hops across the water surface to launch, but our calculations suggest that most of the actual energy expenditure was spent escaping the surface tension.” Unfortunately Witton’s drawings never get to the point of actually extending the wings, leaving the pterosaur flopping about on the surface, wing fingers always down. Not sure how anything can generate sufficient thrust from a standing start and several dunks before flapping. Seems rather awkward at best. And when do the wings actually open?

Pelican Take-off from Water
Do pelicans give us some idea how a pterosaur could have taken off from a standing start while floating on the surface? Click the image to see the YouTube video of a pelican taking off from water. Apparently keeping the wings dry is important. They rise first.

Pelican take-off sequence from water.

Figure 2. Pelican take-off sequence from water. Click to enlarge. Besides flapping, the pelican runs furiously along the surface of the water until sufficient airspeed is attained to rise above the surface. At 5 and 7 the wings are parallel with the water's surface. You can see it takes quite a few flaps and paddles to get this ornithochierid-sized bird off the water and into the air at a steady clip. One big, well-timed, extremely fast flap just won't do it.

Are Pelicans Good Analogs to Pterosaurs?
Let’s put the pterosaur in the water now and see if it could lift its wings and take-off like a pelican. The pelican uses running legs and webbed feet to provide extra thrust during takeoff. The small feet of ornithochierids would not have been as helpful. Even so, the legs probably ran fast, like a basilisk (Jesus lizard) doing what they could. Most of the thrust would have to come from the flapping wings.

 

Pterosaur water launch

Figure 3. Click to enlarge. Ornithocheirid water launch sequence in the pattern of a pelican launch. LIke ducks, geese and pelicans, pterosaur probably floated high in the water. Here the wings rise first and unfold in an unhurried fashion, keeping dry and unencumbered by swirling waters. Then the legs run furiously, like a Jesus lizard, but with such tiny feet, they were not much help in generating forward motion. The huge wings, however, did create great drafts of air, thrusting the pterosaur forward until sufficient airspeed was attained, as in the pelican.

We Will Never Know Certain Aspects of Pterosaur Behaviour
We can only guess. Hopefully we will be able to discard those hypotheses with the longest list of problems.

Look for Mark Witton’s book on pterosaurs coming out (more or less) soon. The pterosaur launch from water illustration will be published there.

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.

Microraptor and Longisquama: Convergent Evolution of 4 Wings

A recent paper (Li et al. 2012) on the iridescence of the feathers of the four-winged dromaeosaur, Microraptor (Xin et al. 2003) prompted this report on its convergence with the four-winged fenestrasaur, Longisquama (Sharov 1970). Both, it seems, devoted much of their anatomy to attracting mates and extending their glides from tree to tree.

Microraptor gui

Figure 1. Microraptor gui, the four-winged dromaeosaur. Arrows point to flight feathers on the forelimbs and hindlimbs. From Xing et al. 2003.

Longisquama had Four Wing, too.
The traditional paradigm holds that the back half of Longsiquama remains unknown, but DGS (digital graphic segregation) identifies all the elements of the entire skeleton of Longisquama (illustrated here). With trailing membranes on both the forlimbs and hindlimbs, Longisquama was a four-winged flapping glider, and a model ancestor for the two-winged pterosaurs, with which it shared a longer list of traits than any other known reptile, as recovered form the large reptile family tree.

 

Figure 2. Longisquama in lateral view, dorsal view and closeup of the skull. Like Microraptor, Longisquama glided/flew with similarly-sized wings both fore and aft.

Figure 2. Longisquama in lateral view, dorsal view and closeup of the skull. Like Microraptor, Longisquama glided/flew with similarly-sized wings both fore and aft.

Secondary Sexual Characteristics Coopted for Flight
Like Microraptor, 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.

Microraptor restored.

Figure 3. Microraptor restored. Hind limbs are artificially splayed. From Li et al. 2012.

Comparisons
Microraptor did not develop a set of dorsal scale/plumes like Longisquama. That was a lepidosaur trait gone wild (contra Buchwitz and Voigt 2012 who nested Longisquama between traditional lepidosauromorphs and traditional archosauromorphs). Microraptor did not splay its hind legs like Longisquama. That’s another lepidosaur trait. They shared a similar size and general body proportions, including long strong hind limbs and a long attenuated tail. Microraptor extended the length of its hands with feathers. Longisquama did so with an extended fourth finger provided by a trailing membrane. The hind limbs of Microraptor were provided with trailing membranes, in this case, flight feathers. The hind limbs of Longsiquama were provided with trailing uropatagia, as in sister taxa, Sharovipteryx and pterosaurs. Both Microraptor and Longisquama flapped their forelimbs because both had elongated, immobile, stem-like coracoids anchored to sternae and slender strap-like scapulae. These elements also anchored enlarged pectoral muscles for flapping. Both were able to perch on tree branches. Microraptor employed a reversed pedal digit 1 to wrap around the back of a branch opposite the anterior toes. Like basal pterosaurs, Longisquama used the dorsal side of a hyperflexed pedal digit 5 as a universal wrench (Peter 2002) to press on the top of the branch, opposite the anterior toes wrapping around the bottom of the branch. Both Microraptor and Longisquama had anteriorly elongated ilia, more than two sacrals, a tibia longer than the femur and digitigrade feet. Both were obligate bipeds.

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
Li Q, Gao K-Q, Meng Q,Clarke JA, Shawkey MD, D’Alba L, Pei R, Ellison M, Norell MA, and Vinther J 2012.
 Reconstruction of Microraptor and the Evolution of Iridescent Plumage. Science 9 March 2012: 335 (6073), 1215-1219. [DOI:10.1126/science.1213780]
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15:277-301.
Turner AH, Diego P, Clarke JA, Erickson G and Norell, M 2007. A basal dromaeosaurid and size evolution preceding avian flight. Science, 317: 1378-1381. doi:10.1126/science.1144.
Xing X, Zhou Z, Wang X,  Kuang X, Zhang F and Du X 2003. Four-winged dinosaurs from China. Nature 421: 335–340.

The Hands of Sharovipteryx

The hands of Sharovipteryx have been considered “missing” since Sharov (1971) did not illustrate them, other than finger 4 of the left hand.

Sharov's illustration of finger 4.

Figure 1. Sharov’s illustration of finger 4.

I Blame It on Soft Tissue
Sharovipteryx preserves soft tissue from it s scaly snout to its webbed toes. Soft tissue also obscured the hands on the counterplate. Here (Fig. 2) I traced what faint impressions remained of the fingers using DGS (digital graphic segregation). Yes, it’s difficult to discern. Whether illusions or not, both hands matched each other and their ratios and patterns matched or were transitional between those of sister taxa, Cosesaurus and Longisquama.

The pectoral girdle and forelimbs of Sharovipteryx.

Figure 2. The pectoral girdle and forelimbs of Sharovipteryx. Both sides match each other and fit neatly into their phylogenetic node between sisters Cosesaurus and Longisquama.

Reconstruction
The reconstructed hand of Sharovipteryx (Fig. 3) had the appearance of a stunted limb, with a reduced yet robust humerus and radius+ulna. Certainly neither supination nor pronation was possible. A pteroid was retained. Unlike the other basal fenestrasaurs, all four metacarpals were subequal in length. Metacarpal 4 was more robust than the others and its terminal articular surface was expanded, as in pterosaurs. Digit 4 was also more  robust, especially proximally, as in pterosaurs. The claws were sharp, but not especially trenchant. The PILs (parallel interphalangeal lines) were continuous across all four digits indicating that all the phalanges flexed as phalangeal sets, as in other tetrapods, other than Longisquama and pterosaurs.

The reconstructed hand of Sharovipteryx.

Figure 3. The reconstructed hand of Sharovipteryx. The proximal elements were reduced. Despite the appearance here of a rotated metacarpal 4, the PILs remained continuous indicating that digit 4 probably had not rotated (as in pterosaurs and Longisquama), but remained a part of the flexion set. Even so metacarpal 4 was enlarged relative to the others, so the wing-making process had begun. 

Evolutionary Significance
Even though Sharovipteryx is the sole representative of a distinct fenestrasaur branch in which the hind limbs were emphasized, the forelimbs were de-emphasized and the neck was elongated, it still demonstrated traits illustrating the evolution of pterosaurian traits beyond those of Cosesaurus, but not  to the level of Longisquama.

Usefulness?
Were the hands of Sharovipteryx useless vestiges? Or were they important canards used aerodynamically to affect pitch control? The hands of Sharovipteryx were likely trailed by soft tissue membranes, since both taxa in its phylogenetic bracket (Cosesaurus and Longisquama) had such membranes. With a robust stem-like coracoid, Sharovipteryx was able to flap its arms, providing only a small amount of thrust. Thrust vectoring would have been most useful to raise the front of the body during a landing in order to stall the large hind-leg wing and execute a gentle two-point landing. It is hard to imagine the small hands of Sharovipteryx used to cling to tree trunks, but perhaps they did so if Sharovipteryx bellied up to a big one.

 

Figure 2. Sharovipteryx mirabilis in various views. No pycnofibers added yet. Click to learn more.

Figure 4. Sharovipteryx mirabilis in various views. Trailing membrane on the hand is guesswork based on phylogenetic bracketing. Click to learn more.

Was Metacarpal 4 Rotated?
Good question. Hard to tell. Some evidence points one way. Other evidence does not. Perhaps this stage is the transition one. That makes sense for several reasons.

We’ll look at the skull next…

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 GJ, 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, October 1987, v. 13, p. 415-426.
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 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
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].

wiki/Sharovipteryx

Another Really Tiny Pterosaur: BMNH 42736

The smallest known pterosaur B St 1967 I 276 (No. 6 of Wellnhofer 1970 ) was discussed earlier. Today we get to meet maybe the second smallest pterosaur, Pterodactylus meyeri BMNH 42736 (Munster 1842, Fig. 1) is the same size as No. 6, but had several distinct traits (Fig. 2). I ran across the BMNH specimen in Unwin’s (2006) The Pterosaurs From Deep Time book on page 151. Dr. Unwin considered the specimen a “flapling” (= newly hatched pterosaur able to fly) with a wingspan of 17 cm, so that is the reconstructed scale (Fig. 3).

The Value of a Reconstruction
It’s a shame that modern workers don’t produce reconstructions of crushed pterosaurs anymore. There is so much to see (Figs. 2, 3), especially when one compares similar specimens. Many traits would go unnoticed if left crushed.

One of the world's smallest pterosaurs

Figure 1. One of the world's smallest pterosaurs, traced from Unwin (2006, p. 151). The feet of the "flapling" were not articulated and a certain amount of guesswork was applied to the idenfication of the pedal elements and their reconstruction. Note how the left radius and ulna are parallel to and beneath the elongated right scapula. The right coracoid is largely beneath the right humerus. The left hand and proximal wing finger are beneath the right hand. Soft tissue stains are highlighted in orange. The wing had a narrow chord at the elbow. Colorizing the bones is a result of employing DGS, digital graphic segregation.

Phylogenetic Nesting
Here the “flapling” nested between No. 6 and No. 12, two other tiny ornithocephalians (and former Pterodactylus) outside of the Pterodactylus lineage, at the base of the Germanodactylus clade. Conveniently (for those looking for transitional taxa) No. 6 was smaller and No. 12 was larger than the BMNH “flapling.”

Distinct from No. 6, the “flapling” had a deeper skull, more and smaller dorsal vertebrae and ribs, a longer scapula (almost touched the pelvis), a deeper and more fully fused pelvis and a larger sternal complex than either of its sisters. Considering the reconstructed differences in quadrate elevation, jugal shape and pelvis dimensions (Fig. 2), you might think the “flapling” would have nested further apart from No. 6 and No. 12. These distinctions suggest that the “flapling” may have been at  the base of its own clade of currently unknown descendants.

The tiniest pterosaurs.

Figure 2. The tiniest pterosaurs. On the left, Unwin's "flapling" Pterodactylus meyeri BMNH 42736. On the right, B St 1967 I 276, No. 6, the former sole owner of the title.

Juvie or Adult?
If the BMNH tiny pterosaur was indeed a juvenile of a larger more established taxon, which one did it match up to? And if so, why did it nest with other tiny pterosaurs? No. The BMNH specimen was an adult. The many autapomorphies (= differences) in the “flapling” also follow a larger trend seen in other tiny pterosaurs: morphological innovation.

Full scale image of ginkgo leaf and the two smallest pterosaurs

Figure 3. Full scale image of ginkgo leaf and the two smallest pterosaurs to scale on a 72 dpi screen. Yes, these are tiny, but just look at the size of a hatchling on the far right, no bigger than a small fly.

Special Premaxillary Teeth
In the BMNH “flapling” we see more substantial anteriorly-directed medial teeth forming the tip of the premaxilla. Those two teeth evolve to become one in the rostral tip of Germanodactylus. That tooth is the only one retained in so-called “toothless” pterosaurs like Pteranodon and Nyctosaurus that have sharply tipped jaws.

Bigger Eggs?
A deeper pubis and pelvis in the BMNH specimen could have produced a larger egg. A stronger sternal complex and longer scapula could have made the “flapling” a more powerful flyer.

Soft Tissue Preservation
Despite a flipped mandible and poorly preserved feet, the “flapling” is otherwise well preserved and largely articulated. A soft tissue stain can be seen (overprinted in Fig. 1) that demonstrates a narrow chord at the elbow wing membrane construction.

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
Meyer H von 1842. Notes on labyrinthodonts and fossil reptiles, including a description of Belodon plieningeri, new gen. and sp. Neues Jahrbuch fur Mineralogie, Geologie und Palaontologie 1842, pp. 301-304.
Unwin D M 2006. 
The Pterosaurs From Deep Time. 347 pp. New York, Pi Press.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

Mecistotrachelos, the Walking Stick “Rib” Glider

Among the Permo/Triassic so-called “rib” gliders is an oddball with a walking-stick sort of torso with fused ribs no wider than its centra. The oddball is Mecistotrachelos from the Late Triassic and it was a sister to Coelurosauravus of the Late Permian.

Mecistotrachelos

Figure 1. Mecistotrachelos, the walking stick "rib" glider in lateral view except for the dorsal series and pseudoribs, which are seen in dorsal view. pseudoribs folded above, and extended below. The tail length is unknown.

Mecistotrachelos apeoros (Fraser et al. 2007) Late Triassic ~210 mya, demonstrates variety in later derived clade members with fewer dorsal vertebrae and fewer pseudoribs. The body was extremely slender, almost stick-like, with hyper-elongated cervicals and greatly reduced ribs fused to each centrum. The limbs were more gracile and the tail length is unknown. The fibula was fused or closely adhered to the tibia.

The long neck would have made Mecistotrachelos an unstable glider according to Fraser (2007). Coelurosauravus had a long neck and a larger skull. Were the dermal struts deployed for gliding? For display? Or both? Like other kuehneosaurs, Mecistotrachelos had small teeth and was likely an insectivore. Fraser (2007) wondered if his find was an archosauromorph. It is not. Here Mecistotrachelos nested with Coelurosauravus among the lepidsauromorpha, within the lepidosauriformes.

Not Like Draco the Extant Glider
Fraser (2007) reported, “The new form is characterized by the presence of extremely elongate thoracolumbar ribs that presumably supported a gliding membrane in life.” Fraser (2007) notes kuehneosaurs had “ribs forming hinge joints with the markedly elongate transverse processes on the dorsal vertebrae.” This is wrong. No Mecistotrachelos sister taxa had elongated transverse processes. The apparent transverse processes ARE the ribs, fused to the vertebrae, derived from the condition seen in the short ribs of Coelurosauravus (Fig. 2). The pseudoribs were actually elongated dermal ossicles described as “bundles of rodlike neomorph ossifications,” by Fraser (2007) quoting Frey et al. (1997). By contrast, in Draco the gliding struts are indeed elongated dorsal ribs.

The Triassic gliders and their non-gliding precursors.

Figure 2. Click to enlarge. The Triassic gliders and their non-gliding precursors.

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
Fraser NC, Olsen PE, Dooley AC Jr and Ryan TR 2007. A new gliding tetrapod (Diapsida: ?Archosauromorpha) from the Upper Triassic (Carnian) of Virginia. Journal of Vertebrate Paleontology 27 (2): 261–265.

Frey E, Sues H-D and Munk W 1997. Gliding Mechanism in the Late Permian Reptile Coelurosauravus. Science Vol. 275. no. 5305, pp. 1450 – 1452
DOI: 10.1126/science.275.5305.1450