If Sharovipteryx was a glider, how did it climb trees with such tiny arms?

That’s a good question that is rarely asked.
Typically considered a hind-wing glider, Sharovipteryx (Sharov 1971) must have also been an obligate biped due to its proportions (Peters 2000). This is another form of locomotion rarely attributed to this Late Triassic Lepidosaur, Tritosaur Fenestrasaur. In the large reptile tree (LRT, 1413 taxa) Sharovipteryx was derived from a flapping, sprinting, occasionally bipedal Cosesaurus and Sharovipteryx shares many traits with pterosaurs (see below).

Today we’ll make comparisons
to an extant quadrupedal arboreal glider, Draco volans (Fig. 1).

Figure 1. Sharovipteryx alongside a photo of Draco volans. Both lepidosaurs had sprawling limbs, a long fifth toe, attenuated tail, extrademal membranes and dorsal ribs that flatten and widen its torso.

Figure 1. Sharovipteryx alongside a photo of Draco volans. Both lepidosaurs had sprawling limbs, a long fifth toe, attenuated tail and dorsal ribs that flatten and widen its torso.

Draco vs. Sharovipteryx: the similarities:

  1. sprawling limbs
  2. tendril-like toes and a long fifth toe
  3. attenuated tail
  4. dorsal ribs that flatten and widen its torso
  5. expandable hyoid for display

Draco vs. Sharovipteryx: the differences:

  1. extradermal membranes
  2. longer hind limbs (bipedal)
  3. shorter fore limbs
  4. longer cervical vertebrae
  5. 5+ sacral vertebrae
  6. longer ilia
  7. antorbital fenestra
  8. prepubes (phylogenetic bracketing)
  9. pteroid (former centrale) (Fig. 4)
  10. pedal 5.1 nearly as long as metatarsal 4 (Fig. 3)
  11. vestigial finger 5
  12. strap-like scapula
  13. stem-like coracoid (flapping)
  14. robust radius and ulna without interosseum space

Sharp-eyed readers will note
that many of the above traits are also found in pterosaurs.

Figure 2. Draco and Sharovipteryx bipedally on tree trunk, flapping its tiny arms. Hatchling Sharovipteryx between them.

Figure 2. Draco and Sharovipteryx bipedally on tree trunk, flapping its tiny arms. Hatchling Sharovipteryx between them. Several living birds are able to cling to tree trunks by their hind feet alone. Imagine the knees of Sharovipteryx bending even further, or imagine the femora further splayed to match the in situ fossil. Both configurations bring the body closer to the tree. As in pterosaurs, splayed knees can still produce a bipedal configuration because the knees bend the ankles back toward the midline.

Tradition presupposes that Sharovipteryx
was a glider. In counterpoint, Cosesaurus had uropatagia and was not a glider, but a flapping sprinter. Flapping animals do not become gliders. Gliders do not become flappers. Even so, it is good science to keep proposing alternatives for Sharovipteryx. Then we can refute, support or confirm all of the alternatives.

Tradition, in this case may be correct.
Cosesaurus
did not have membranes between its toes and it did not splay its metatarsals (Fig. 3). Nor did Cosesaurus have the limb proportions of Sharovipteryx and its several canard and strake neck membranes.

Figure 3. Sharovipteryx pes in dorsal and digit 4 in lateral view.

Figure 3. Sharovipteryx pes in dorsal and digit 4 in lateral view.

Dyke, Nudds And Rayner 2006
wrote, “Intriguingly, because of the incompleteness of the single known specimen, the evolutionary relationships of S. mirabilis remain poorly understood (Tatarinov, 1989; Unwin et al., 2001) – better preserved fossil material will be required to resolve this issue.” 

This paper followed and cited Peters 2000,
which added Sharovipteryx to four previously published phylogenetic analyses and found it nested with pterosaurs every time. It would have been so easy for Dyke, Nudds and Rayner to replicate the addition of taxa to the same four previously published analyses to confirm or refute Peters 2000. But evidently no PhD wants to confirm the work of another worker.

Later
Hone and Benton 2007, 2008 created a supertree to determine pterosaur affinities, but in the second of two papers removed all reference to Peters 2000 and removed Sharovipteryx from their taxon list.

In all prior studies
a lack of a precise tracing of the fossil and its counterpart is evidence that earlier studies did not look very closely or comprehensively at the fossil (see below).

I have seen Sharovipteryx first hand.
I keep in my file cabinet an 8.5×11-inch transparency for ready reference. The Sharovipteryx holotype fossil (Fig. 5) is nearly complete (but note the big gash in the middle) and, since I’ve actually done the phylogenetic work… well understood.

Figure 4. Sharovipteryx forelimb with digit 4 extended and flexed/folded. Note the large, deep unguals that appear to be useful, not vestigial.

Figure 4. Sharovipteryx forelimb with digit 4 extended and flexed/folded. Note the large, deep unguals that appear to be useful, not vestigial.

Dyke, Nudds And Rayner 2006
also proposed a delta-winged Sharovipteryx. They wrote, “Our novel interpretation of the bizarre flight mode of S. mirabilis is the first based directly on interpretation of the fossil itself and the first grounded in aerodynamics.” Students should be aware, not all such claims are valid. This claim, in particular, is built largely on imagination.

Figure 1. Sharovipteryx in situ. Click to enlarge. Here both plate and counter plate are shown along with a tracing based on both.

Figure 5. Sharovipteryx in situ. Click to enlarge. Here both plate and counter plate are shown along with a tracing based on both.

Hopefully the Dyke, Nudds And Rayner interpretation
will fade into the forgotten literature. The Dyke team fully imagined the forelimbs and added several membranes that are not present in the fossil while ignoring others that are present. So Dyke, Nudds and Rayner based their mathematics on an imaginary creature. We’ve seen how other scientists change/imagine morphology to fit their mathematical model. Despite the Dyke, Nudds and Rayner claim for first-hand observation, their cartoonish drawing of Sharovipteryx was based on Sharov’s freehand drawing.

What scientist concerned about their reputation would do this?
Well… Unwin, Alifanov and Benton (2003, yes Benton once again!) reprinted Sharov’s 1971 drawing, rather than create one of their own. Worse yet, Gans et al. 1987 created an even more cartoonish reconstruction, barely better than a cave drawing.

The takeaway:
As we’ve seen many times before, beware that certain PhDs sometimes do not put in the effort necessary to validate their claims. And sometimes PhDs, acting as referees, strive to ensure that contradicting hypotheses are not published.

Finally
Let’s not forget Kenneth Dial’s work with pre-volant bird chicks, able to climb steep inclines using everything they have to do it. (Video lecture 1 hour, 36 minutes).


References
Dyke GJ, Nudds RL and Rayner JMV 2006. Flight of Sharovipteryx mirabilis: the world’s first delta-winged glider. xx PDF
Gans C, Darevski I and Tatarinov LP 1987. Sharovipteryx, a reptilian glider? Paleobiology. 13: 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.
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 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].
Tatarinov LP 1989. [The systematic position and way of life of the problematic Upper Triassic reptile Sharovipteryx mirabilis.] Paleo. Zh. 1989(2): 110-112. [in Russian].
Unwin DM, Alifanov VR and Benton MJ 2003. Enigmatic small reptiles from the Middle-Late Triassic of Kyrgyzstan. In: Benton M.J., Shishkin M.A. & Unwin D.M. (Eds) The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge U. Press: 177-186.

http://reptileevolution.com/sharovipteryx.htm

2 thoughts on “If Sharovipteryx was a glider, how did it climb trees with such tiny arms?

  1. I had the pleasure to visit the Orlov Museum in Moscow last September — they give pride of place to reconstructions of Sharipteryx and Longisquama, not very different from your depictions. I imagine the fossils displayed with the reconstructions are casts, but still, lovely.

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