The metatarsus of Longisquama revealed by DGS

Buchwitz and Voigt (2012) reexamined Longisquama’s plumes and determined that they were indeed attached to the dorsal spine (and therefore not coincidental plant material). The closeup photo they provided of purported plume bases is worth discussing, for several reasons.

From Buchwitz and Voigt (2012) purported to be the bases of three dorsal appendages. Actually these are metatarsals.

Figure 1. From Buchwitz and Voigt (2012) purported to be the bases of three dorsal appendages. Actually these are metatarsals 1-3. See figure 2. Their alignment with the vertebrae is, at best, imprecise. The actual plume bases (fig. 2) are below these hollow bony elements. The parallel lines in the upper right corner are aktinofibrils supporting the detached uropatagium.

Difficult to interpret!
Especially when cropped so closely (fig. 2), one set of Longisquama metatarsals is identified here. There are phalanges extending from the tips of these metatarsals (Fig. 4), as well as plumes. The actual plumes (green) are behind (below) these metatarsals. These match the size and proportions of the other metatarsals of Longisquama (fig. 4) and those of sister taxa (fig. 3).

Figure 2. Click to enlarge. Reinterpretation of the bases of the dorsal plumes of Longisquama. These are metatarsals. On the right you'll see those fine parallel lines representing the aktinofibrils of a detached uropatagium (one of two, of course).

Figure 2. Click to enlarge. Reinterpretation of the bases of the dorsal plumes of Longisquama. These are metatarsals 1-4. On the right of each picture you’ll see those fine parallel lines representing the aktinofibrils of a detached uropatagium (one of two, of course), as in Sharovipteryx. DR = displaced dorsal ribs. Ti = tibia (see Fig. 4 for the whole picture).

They’re not plume bases
These elements are aligned with the plumes, but not exactly. And they increase in length laterally. And they overlap. And they have phalanges emanating from them. And they match another set of nearby metatarsals (fig. 4). They’re metatarsals. Take them ‘as is’ and put them into a reconstruction (fig. 3) and you get a nice transition and match between Sharovipteryx and MPUM6009, a basal pterosaur, the phylogenetically bracketing taxa. Longisquama demonstrates how p5.2 and p5.3 merged to become one phalanx in basal pterosaurs. All the PILs (parallel interphalangeal lines) align.

longisquama-foot588

Figure 3. The foot of Longisquama based on the DGS tracing, shares traits with both Sharovipteryx and MPUM6009.

The big picture (click fig 4 to enlarge) tells the tale. The front of Longisquama is undisturbed. So is the tail. It’s the middle that became twisted. That’s why the feet ended up over the vertebral column. The fossil looks like a big post-mortem gas bubble in its belly exploded, or scavengers focused on the soft guts before burial.

Longisquama in situ with metatarsals in color.

Figure 4. Click to enlarge. Longisquama in situ with metatarsals and ribs framed by figure 2 in color. Yes, they are aligned with the bases of the plumes, but also with  the bases of phalanges.

Enlargements of the tracings can be found here.

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
New Scientist article here
Buchwitz M and Voigt S 2012. The dorsal appendages of the Triassic reptile Longisquama insignis: reconsideration of a controversial integument type. Paläontologische Zeitschrift, Issue 3, pp 313-331

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