Diplovertebron and amphibian finger loss patterns

Updated June 13, 2017 with the fact that Diplovertebron is the same specimen I earlier illustrated as Gephyrostegus watsoni. And the Watson 1926 version of Diplovertebron (Fig. 1) was so inaccurately drawn (by freehand) that the data nested is apart from the DGS tracing. Hence this post had deadly errors now deleted.

Figure 2. The gradual loss of basal tetrapod fingers. Unfortunately fingers are not known for every included taxon.

Figure 2. The gradual loss of basal tetrapod fingers. Unfortunately fingers are not known for every included taxon. Odd Tulerpeton with 6 fingers may result from taphonomic layering of the other manus peeking out below the top one. See figure 6. Mentally delete Diplovertebron from this chart. 

The presence of five manual digits
in Balanerpeton (Figs. 4, 5) sheds light on their retention in Acheloma + Cacops. There is a direct phylogenetic path between them (Fig. 2). Note that all other related clades lose a finger or more. Basal and stem reptiles also retain five fingers.

Figure 2. Utegenia nests as a sister to Diplovertebron.

Figure 3. Utegenia nests as a sister to Diplovertebron.

Distinct from the wide frontals
in Utegenia and Kotlassia,  Balanerpeton (Fig. 4) had narrower frontals like those of Silvanerpeton, a stem reptile.

Figure 4. The basal amphibian, Balanerpeton apparently has five fingers (see figure 5).

Figure 4. The basal amphibian, Balanerpeton apparently has five fingers (see figure 5).

As reported
earlier, finger five was lost in amphibians,while finger one was lost in temonospondyls. Now, based on the longest metacarpal in Caerorhachis and Amphibamus (second from medial), apparently manual digit one was lost in that clade also, distinct from the separate frog and microsaur clades. In summary, loss from five digits down to four was several times convergent in basal tetrapods.

Figure 5. DGS recovers five fingers in Balanerpeton with a Diplovertebron-like phalangeal pattern.

Figure 5. DGS recovers five fingers in Balanerpeton with a Diplovertebron-like phalangeal pattern. Two 5-second frames are shown here.

Finally, we have to talk about
Tulerpeton (Fig. 6). The evidence shows that the sixth manual digit is either a new structure – OR – all post-Devonian taxa lose the sixth digit by convergence, since they all had five fingers. Finger 6 has distinct phalangeal proportions, so it is NOT an exposed finger coincident rom the other otherwise unexposed hand in the fossil matrix.

Figure 2. Tulerpeton manus and pes in situ, reconstructed by Lebdev and Coates 1995 and newly reconstructed here.

Figure 6. Tulerpeton manus and pes in situ, reconstructed by Lebdev and Coates 1995 and newly reconstructed here. Digit 6 is either a new structure, or a vestige that disappears in all post-Devonian taxa.

References
Fritsch A 1879. Fauna der Gaskohle und der Kalksteine der Permformation “B¨ ohmens. Band 1, Heft 1. Selbstverlag, Prague: 1–92.
Kuznetzov VV and Ivakhnenko MF 1981. Discosauriscids from the Upper Paleozoic in Southern Kazakhstan. Paleontological Journal 1981:101-108.
Watson DMS 1926. VI. Croonian lecture. The evolution and origin of the Amphibia. Proceedings of the Zoological Society, London 214:189–257.

wiki/Diplovertebron

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3 thoughts on “Diplovertebron and amphibian finger loss patterns

  1. Watson sank Gephyrostegus into Diplovertebron. This has not been accepted since he retired. Your fig. 1 is almost entirely based on Gephyrostegus, and it’s a pretty superficial reconstruction at that.

    In short, Gephyrostegus bohemicus is now in your matrix twice, once as badly reconstructed by Watson (1926), once as less badly reconstructed by Carroll (1970) as far as I can tell.

    The whole story is described in the redescription of the skull of Gephyrostegus by Klembara et al. (2014). Please read it! (It’s too long for me to present here.)

    Klembara et al. (2014: 776) stated that “Diplovertebron is based on a single specimen and appears to be a small embolomere (Carroll, 1970; Panchen, 1970)”, and the status of the name “will also depend on reevaluation sof all preserved postcrania, including those not previously described.” Perhaps they’ll do that as part of their forthcoming redescription of the postcranium of Gephyrostegus.

    Utegenia nests as a sister to Diplovertebron.

    Actually, in your fig. 2, it nests as the sister of “Diplovertebron“.

    In fig. 3 I’m surprised you show us the ventral but not the dorsal scales.

    DGS recovers five fingers in Balanerpeton with a [misinterpreted Gephyrostegus]-like phalangeal pattern.

    Oh come on. Milner & Sequeira (1994) had several specimens with preserved hands and pored over them for days or weeks. Then they wrote (p. 346–347):

    “The distal manus consists of four digits, the phalangeal formula of which is not fully determinable from any one specimen. Combining information from both counterparts of NMS G 1985.4.1, it can be seen to have been at least 1+.2.3.3 and was probably 2.2.3.3 with one of the tiny terminal phalanges having been lost. 2.2.3.3 is one of the commonest formulae for the temnospondyl manus. Metacarpals and phalanges are expanded at both proximal and distal ends, and have slender, waisted shafts. The terminal phalanges are very abbreviated elements.”

    Then they published bad photos (fig. 7 and 8 – part and counterpart) which show the entire specimen (whole skeleton missing most of the tail), so the one visible hand is rather small. Better photos were beyond the capability of the journal.

    Then you took the bad photo in fig. 7 – or a bad photocopy of the bad photo, or a scan of a bad photocopy of the bad photo? –, made it even worse by descreening it*, mirrored it for (presumably) some reason, squinted at it so hard that you began to see five fingers where only 2 1/2 are preserved, made a drawing of that and congratulated yourself in public.

    Hint: bone is preserved in white, and you’re seeing most of it from the inside because the slab was split through the fossil (fig. 7, 8).

    * Having software interpolate information between the centers of the pixels to create smaller pixels, so the picture looks smoother. The result looks like it contains more information than the original, but it really contains less, which should be obvious, and which I’ve been telling you since 2005.

    • reevaluation sof

      I mistyped. Klembara et al. (2014: 776) got it right of course: “reevaluations of”.

  2. Thanks for your comments.
    re: Diplovertebron, as soon as I see a holotype skeleton, I will present it. Until then, this will have to do as data.
    re: Balaenerpeton fingers: you’re right it is a bad photo. Sometimes we use crushed skulls, bad photos and old lithographs in our search for data.

    Given that Watson drew Diplovertebron with five fingers, and D nested with B, I looked for five fingers on Balanerpeton. Sometimes I find them in impressions. Sometimes I gather scattered elements and reassemble them. Neither is as sure a thing as an articulated specimen. To your point I did not score a fifth finger. I scored it absent. Basal taxa have five fingers. Derived taxa have four fingers, all with tiny terminal phalanges, easily lost or left unexposed. So Balanerpeton could have gone either way.

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