Rhamphorhynchus: Zittel wingtip ungual in higher resolution

The Zittel wing
of Rhamphorhynchus preserves a complete and unfolded pterosaur wing (brachiopatagium + propatagium). Because the specimen (B St 1880.II.8) documents a narrow-chord construction it was purposefully omitted from the earlier study by Elgin, Hone and Frey (2010) who wished all their pterosaur wings were of the invalidated and traditional deep chord variety. None are (Peters 2002). Yet the tradition continues as seen in David Attenborough videos and Bennett (2016) papers.

As a scientist,
I prefer cold hard evidence (Figs. 1-3) with regard to pterosaur wing shape. Let’s hope you do, too.

Figure 1. Zittel wing (Rhamphorhynchus) with ungual area color spectrum expanded.

Figure 1. Zittel wing (Rhamphorhynchus) with ungual area color spectrum expanded. Details in figure 2. Note the narrow chord of this nearly perfect specimen with the membrane stretched between the elbow and wingtip, not the hind limb and wing tip. This is hard evidence. This is reality.

Today
we’ll take a closer peek at the typically overlooked wing tip ungual, phalanx 5 of manual digit 4 (m4.5) that we looked at earlier in less detail. Few to no pterosaur workers and other paleontologists recognize the presence of this bone. Rarely workers (Koroljov AV 2017) consider the wing finger to be digit 5 and the pteroid digit 1. Not true (Peters 2009). Just because the wingtip claw is tiny, doesn’t mean it’s not present. You just have to look carefully and use the tools available (Photoshop) to bring it out so others can easily see it (Fig. 2).

Figure 2. Zittel wing m4.5, wingtip ungual in situ, plus with the color spectrum (image levels in Photoshop) expanded.

Figure 2. Zittel wing m4.5, wingtip ungual in situ, plus with the color spectrum (image levels in Photoshop) expanded. Yes, it gets fuzzy when it is enlarged so much, but the hook shape is readily apparent surrounded by excavation.

We nested the Zittel wing
earlier with other Rhamphorhynchus specimens in the large pterosaur tree (LPT, Fig. 3). Although ungual 4.5 is apparent (Figs. 1,2), manual digit 5 is not visible in the Zittel wing due to a ventral exposure of the specimen.

Figure 2. The Zittel wing specimen B St 188 II 8 nests between the 'dark wing' JME specimen and the MTM specimen, both in the Rhamphorhynchus muensteri clade.

Figure 2. The Zittel wing specimen B St 188 II 8 nests between the ‘dark wing’ JME specimen and the MTM specimen, both in the Rhamphorhynchus muensteri clade.

Despite having the specimen in his hands,
Bennett 2016 overlooked the ungual at the wingtip. He proximally extends the propatagium to the neck, rather than the deltopectoral crest. Worse yet, he added lots of proximal wing membrane that was never there in the Zittel wing (Fig. 3). No pterosaur documents wing membranes extending past the knee. No pterosaur documents uropatagia attaching to pedal digit 5. No pterosaur documents a propatagium extending proximally beyond the deltopectoral crest.

Figure 3. Base reconstruction of Zittel wing by Bennett 2016 where he imagined a great deal of patagium between the elbow and knee. Here the hind limbs are rotated laterally, the patagium is stretched between the elbow and wingtip. Femoral and numeral muscles are estimated. 

Figure 3. Base reconstruction of Zittel wing by Bennett 2016 where he imagined a great deal of patagium between the elbow and knee. Here the hind limbs are rotated laterally, the patagium is stretched between the elbow and wingtip. Femoral and numeral muscles are estimated.

Strictly follow your data.
Don’t enhance it with imaginary tissues. And don’t overlook real data.

References
Bennett SC 2016. New interpretation of the wings of the pterosaur Rhamphorhynchus muensteri based on the Zittel and Marsh specimens. Journal of Paleontology 89 (5):845-886. DOI: 10.1017/jpa.2015.68
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Koroljov AV 2017. The Flight of Pterosaurs.Biol Bull Rev 7: 179. doi:10.1134/S2079086417030045
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.

When claws became hoofs and hoofs became claws

The cladogram
represented by the large reptile tree (LRT) shows that at more than one time within the clade Mammalia, sharp, clawed unguals became broad, often hoofed, unguals. And then several times broad unguals once again became sharp claws. Here’s the pattern:

  1. Small basal mammals all had sharp claws. So did basal monotremes, marsupials and placentals.
  2. Ernanodon, among the marsupials, had broad, round unguals
  3. Toxodon, among the marsupials, had short, anteriorly concave unguals, perhaps supporting hoofs.
  4. Basal placentals, including Carnivora and Glires, had sharp claws. Primates, like Proconsul, developed fingertip pads surrounding their unguals with only the keratinous nails exposed.
  5. Alcidedorbignya, among pantodont placentals (basal herbivores), had proto–hoofs (tips nearly as wide as bases). In the same clade, so did Pantolambda.
  6. Bayrlambda, among basal xenarthrans, had short unguals, barely longer than wide.
  7. Paramylodon, a ground sloth, had long sharp claws, but Glyptodon, a sister had truncated unguals, more like hoofs.
  8. Bradypus, a tree sloth, had long, curved, sharp claws. So did Orycteropus, Dasypus and kin.
  9. Titanoides, a basal phenacodont had sharp claws.
  10. Phenacodus, another basal phenacodont, had round hoof-like unguals. Many subsequent large mammalian herbivores had similar hoof-like unguals, except…
  11. Mysticete whales, like Balaenoptera, had long sharp unguals hidden within their flippers.
  12. Homalodotherium had sharp claws, as did Protypotherium, but
  13. Miocochilius had hoofs and it was a sister to those two.
  14. Dusisiren the sea cow, had sharp unguals beneath the mitten of its flipper, but…
  15. Procavia, the rock hyrax and Elephas had tiny unguals.
  16. The remaining mammals, like Sus, the pig, are all ungulates and they all have hoofs, except…
  17. Chalicotherium, which apparently had claw-like hoofs.

So you can see,
the sharp claw – broad hoof morphology comes and goes within the clade Mammalia, according to the LRT, with only one clade developing padded unguals with keratinous nails.

The hand and super-claw of Drepanosaurus

When Drepanosaurus (Pinna 1980, Figs. 1-3) was first discovered and described, this oddity, metaphorically from the land of Dr. Seuss, presented several never-before-seen morphologies including a hooked tail, humped shoulder, a giant olecranon sesamoid (earlier misidentified as a displaced ulna) and an odd hand with a super-claw on finger two — all on one headless body.

Figure 1. Drepanosaurus featuring fused finger phalanges and a super claw -- among several other odd traits.

Figure 1. Drepanosaurus featuring fused finger phalanges and a super claw — among several other odd traits. This image is updated from a prior attempt. Note: the tips of manual unguals 2-4 are aligned.

After fielding a question,
I told a reader that I would take another look at the Drepanosaurus hand. I’m glad I did. The prior tracing was not based on DGS techniques or high resolution images. This one (Figs. 1-3) is. Earlier I mistakenly reconstructed ungual 2 extending beyond the others. Now I find that the middle three unguals terminated at about the same line (Fig. 3).

Figure 1. Drepanosaurus hand with DGS (digital graphic segregation) techniques used to separate the fingers and discover the vestigial joints in the fused digits. The size and proportions of ungual 1 are guesstimated based on very vague outlines impressed from below on ungual 2. On digit 4 (gold on gold) the original tracing appears to have missed the penultimate phalanx (n dark gold).

Figure 2. In situ tracing using DGS (Photoshop layers) to segregate fingers from one another. The outline of digit 1 (purple) is tentative, based on general patterns and very slight impressions in ungual 2.

Yes
several of the phalanges are apparently fused together. Nevertheless their former joints are still visible and are traced here. The penultimate phalanges are very short, the opposite of most arboreal lizards. The cervicals are also quite short, the opposite of other drepanosaurs.

Why did the phalanges fuse?
Perhaps because that big claw prevented the typical flexion function among phalanx sets. Ungual 2 is so big that several former PILs (now fused phalanges) ran through it.

Figure 2. GIF animation of Drepanosaurus fingers reconstructed and imagined in dorsal view. Metacarpal outlines may not be reconstructed in dorsal view. They are typically arranged with mc4 the longest.

Figure 2. GIF animation of Drepanosaurus fingers reconstructed and imagined in dorsal view from data in figure 2. Metacarpal outlines may not be reconstructed in dorsal view. They are typically arranged with mc4 the longest.

Function?
Like almost all digits, the acted together for grasping. The large size of ungual 2 simply made up for the relative brevity of metacarpal 2 and the proximal phalanges, traits that are plesiomorphic for reptiles. That the extensor surface of the ungual is much larger than the flexor surface suggests that the claws were often held retracted, like cat claws. So these were more like paws, the tendril like arboreal lizard toes. Others have considered drepanosaurs slow movers. I agree.

Unlike earlier chameleon-like hypotheses
for Megalancosaurus, the manual digits of Drepanosaurus appear to have swung through parallel arcs, as in most tetrapods.

In situ
the tall narrow claws lie on their sides, as is typical of ungual preservation in crushed fossils. In figure 3, I imagined them in dorsal view, which is the typical presentation of a manus for other tetrapods. Atypically the ungual extends proximally over the penultimate phalanges in dorsal view. So the transparent colors help to visualize this. One can only imagine the size of the extensor tendons on those hands. The flexors were strong too. Don’t let one of these climb on your arm or hand. You might not ever be able to shake it off.

Phylogeny
Wikipedia reports that Drepanosaurus nests within the Protorosauria, a terrestrial clade or small to large archosauromorphs. In counterpoint, and with actual phylogenetic testing (not tradition), the large reptile tree nests Drepanosaurus and the drepanosaurs with Jesairosaurus and the Keuhneosaurs at the base of the Lepidosauriformes. This clade was arboreal.

References
Pinna G 1980. Drepanosaurus unguicaudatus, nuovo genere e nuova specie di Lepidosauro del trias alpino. atti Soc. It. Sc.Nat. 121:181-192.
Pinna G 1986. On Drepanosaurus unguicaudatus, an upper Triassic lepidosaurian from the Italian Alps. Journal of Paleontology 50(5):1127-1132.
Renesto S 1994. The shoulder girdle and anterior limb of Drepanosaurus unguicaudatus (Reptilia, Neodiapsida) from the upper Triassic (Norian of Northern Italy. Zoological Journal of the Linnean Society 111(3):247-264

wiki/Drepanosaurus