Do gliding lizards (genus: Draco) actually grab their extended ribs?

Figure 1. Extant Draco flying with hands either grabbing the leading edge of the membrane or streamlining their hands on top of it.

Figure 1. Extant Draco flying with hands either grabbing the leading edge of the membrane or streamlining their hands on top of it. Images from Dehling 2016.

Gliding lizards
of the genus Draco (Figs. 1, 2) come in a wide variety of species. Similar but extinct gliding basal lepidosauriformes, like Icarosaurus (Fig. 2), form a clade that arose in the Late Permian and continued to the Early Cretaceous.

Figure 2. Two Draco species fully extending their rib membranes without the use of the hands.

Figure 2. Two Draco species fully extending their rib membranes without the use of the hands.

A recent paper
(Dehling 2016) reported, “the patagium is deliberately grasped and controlled by the forelimbs while airborne.” Evidently this ‘membrane-grab’ behavior has not been noted before. I wondered if the rib skin is indeed grasped, or does the forelimb merely fold back against the leading edge of the patagium in a streamlined fashion? Photographs of climbing Draco specimens (Fig. 2) show that the patagium  can fully extend without the aid of the forelimbs to stretch them further forward.

Figure 3. Icarosaurus. Note the tiny ribs near the shoulders. The bases for the strut-like dermal bones are the ribs themselves flattened and transformed by fusion to act like transverse processes, which sister taxa do not have. Note the length of the hands corresponds to the base of the anterior wing strut.

Figure 3. Icarosaurus. Note the tiny ribs near the shoulders. The bases for the strut-like dermal bones are the ribs themselves flattened and transformed by fusion to act like transverse processes, which sister taxa do not have. Note the length of the hands corresponds to the base of the anterior wing strut, a great place to rest the manus or grab the membrane.

A quick review of prehistoric gliding keuhneosaurs
(Fig. 3) show that the manus unguals are not quite as large and sharp as those of the pes and that the manus in gliding mode extends just beyond the shorter two anterior dermal struts so that the glider -may- have grasped the anterior struts in flight. Or may have rested the manus there. Remember, these are taxa unrelated to the extant Draco, which uses actual ribs to stretch its gliding membrane. The same holds true for the more primitive Coelurosauravus and Mecistotrachelos, which have not been traditionally recognized as basal kuehneosaurs.

* As everyone should know by now…
the so-called transverse processes in kuehneosaurs are the true ribs, only fused to the vertebrae. The ribs remain unfused to the vertebrae in the older and more primitive coelurosauravids. No sister taxa have transverse processes elongate or not.

References
Dehling M 2016. How lizards fly: A novel type of wing in animals.

Advertisements

3 thoughts on “Do gliding lizards (genus: Draco) actually grab their extended ribs?

  1. As a cyclist, I work on my tuck and I would expect gliders to also adopt aerodynamically clean postures that clean up drag. Here, the resulting deeper chord at the leading edge should both increase lift and prevent leading-edge flutter. Do they also adjust trim by limb movements? Probably, and someone should do a video study of their maneuvers, particularly at launch and landing, obstacle avoidance, and in cross winds.

  2. They don’t appear to have any muscles ON the ribs to hold them outwards like that to sustain a glide, but the necessary muscles might very well be based along the spine, because I highly doubt they use their hands to literally pull the ribs outwards, that would make gliding more tiring than anything.
    Pretty sure it’s just streamlining the hands.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s