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. 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.
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, 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.
Source: https://pterosaurheresies.wordpress.com/2016/12/07/do-gliding-lizards-genus-draco-actually-grab-their-extended-ribs/
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