Beipiaopterus and all that messy soft tissue – what is it??

Beipiaopterus (Lü 2002, 2003, Figs. 1, 2) is a roadkill pterosaur fossil that appears to have been physically crushed prior to burial. The radius and ulna are broken in half. There is a mass of soft wing tissue that definitely attaches to the hind limb and this has been used to “prove” that the wing membrane attached broadly to the tibia. That mass of soft tissue doesn’t really look like typical wing tissue, like the Zittel wing, unless it has been wadded up like an old receipt. There are also some long hairy parts, unlike typical wing membranes.

I’ve often wondered what was going on there with that soft tissue. Here we’ll take a good look at Beipiaopterus using DGS and see where it might fit on a reconstruction, something Lü (2002, 2003) did not attempt.

Figure 1. Beipiaopterus in situ plus the Lü 2003 interpretation of the elements. M4.1 is actually m4.1+2 based on comparisons with sister taxa and the wing has the requisite 4 wing phalanges + the ungual.

Figure 1. Beipiaopterus in situ plus the Lü 2003 interpretation of the elements. M4.1 is actually m4.1+2 based on comparisons with sister taxa. That means the wing has the requisite 4 wing phalanges + the ungual. Distal m4.1 is missing, here filled with plaster. The rough tracing by Lü misses many details that help to describe this taxon.

At first glance, it’s not at all clear what is happening with the soft tissue of Beipiaopterus, but manifestly clear that there is a mass of soft tissue there. So how can we interpret it?

Let’s make a reconstruction
If we put Beipiaopterus back together again (Fig. 2), perhaps we can find suitable places to move the soft tissue back into.

Figure 2. Beipiaopterus in dorsal and lateral views. In lateral view you can see the soft tissue mass is too large for the hind limb, but a uropatagium is present (in lavender), which is the part attached to the hind limb. The rest (in light blue) seems to come from the tip, middle and inboard sections of the wing. The tip has strong aktinofibrils. The middle less well defined. The proximal portion appears to be quite hairy. If anyone has a better idea, please send it in.

Figure 2. Beipiaopterus in dorsal and lateral views. A and B areas correspond to figure 1. In lateral view you can see the soft tissue mass is too large for the hind limb, but a uropatagium is present (in lavender), which is the part attached to the hind limb. The rest (in light blue) seems to come from the tip, middle and inboard sections of the wing. The tip (C) has strong aktinofibrils. The middle (B) less well defined, but attached to m4.3 in figure 1 as it is here. The proximal portion (A) appears to be quite hairy is located near the femur in situ. This could represent body hair. If anyone has a better idea, please send it in.

Given an understandable playing field (by straightening out the bones in a reconstruction), we can start placing the soft tissue “turf” where it seems to fit best. After all the soft tissue is a wadded up mess, just like the rest of the skeleton. Section A seems to be proximal hairy material. Section B seems to be midwing material and is attached to manual4.3. Section C seems to be wingtip material. Section D is definitely uropatagial as it attaches to the tibia and has a trailing edge.

Deep chord wing proof?
No. This specimen does not prove the wing membrane attached to the tibia, as Lü (2003) reported. Part of the wadded up membrane indeed does attach to the tibia, but that’s the uropatagium and it’s narrow. The rest is displaced wing tissue. We’ve seen displaced wing tissue on Sordes. And here’s an example of wing tissue just starting to tear from its mast (Fig. 3). Note how it starts to fold on itself.

Figure 3. A specimen of Rhamphorhynchus demonstrating how the wing membrane starts to separate from the wing finger during taphonomy.

Figure 3. A specimen of Rhamphorhynchus demonstrating how the wing membrane starts to separate from the wing finger during taphonomy.

References
Lü J-C. 2002. Soft tissue in an Early Cretaceous pterosaur from Liaoning Province, China. Memoir of the Fukui Prefectural Dinosaur Museum 1: 19-28.
Lü J-C 2003. A new pterosaur: Beipiaopterus chenianus, gen. et sp. nov. (Reptilia: Pterosauria) from Western Liaoning Province, China. Memoir of the Fukui Prefectural Dinosaur Museum 2: 153-160.
Lü J-C, Kobayashi Y, Yuan C, Ji S and Ji Q 2005. SEM Observation of the Wing Membrane of Beipiaopterus chenianus (Pterosauria). Acta Geologica Sinica 79:6 766-769.

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