Diplovertebron punctatum (Fritsch 1879, Waton 1926; Moscovian, Westphalian, Late Carboniferous, 300 mya, Fig. 1) was considered an anthracosaur or reptile-like amphibian. That is confirmed by the large reptile tree (LRT, subset Fig. 2), where it nests with Utegenia transitional between basal seymouriamorpha, like Kotlassia, and basal amphibians, like Balanerpeton (Fig. 3), yet close to the origin of stem reptiles, like Silvanerpeton. Based on the nesting of Tulerpeton in the LRT, Diplovertebron had origins in the Late Devonian.
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Figure 1. Diplovertebron nests at the base of the lineage of amphibians, close to the base of the reptiles, all derived from seymouriamorphs. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/03/diplovertebron_puncstatum588.jpg?w=584&h=364?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/03/diplovertebron_puncstatum588.jpg?w=584&h=364?w=584″ class=”size-full wp-image-26302″ src=”https://pterosaurheresies.files.wordpress.com/2017/03/diplovertebron_puncstatum588.jpg?w=584&h=364″ alt=”Figure 1. Diplovertebron nests at the base of the lineage of amphibians, close to the base of the reptiles, all derived from seymouriamorphs.” width=”584″ height=”364″ srcset=”https://pterosaurheresies.files.wordpress.com/2017/03/diplovertebron_puncstatum588.jpg?w=584&h=364 584w, https://pterosaurheresies.files.wordpress.com/2017/03/diplovertebron_puncstatum588.jpg?w=150&h=93 150w, https://pterosaurheresies.files.wordpress.com/2017/03/diplovertebron_puncstatum588.jpg?w=300&h=187 300w, https://pterosaurheresies.files.wordpress.com/2017/03/diplovertebron_puncstatum588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Diplovertebron nests at the base of the lineage of amphibians, close to the base of the reptiles, all derived from seymouriamorphs. Note the retention of five fingers. Wish I had better data than this.
In Diplovertebron,
the vertebral structure is primitive. The notochord persisted in adults. The ribs were long and slender as in basal taxa, not shortened as in lepospondyl amphibians. Five manual digits were preserved with a 2-3-3-3-4 formula, a formula similar to amphibians, not like reptiles (2-3-4-5-5). The ilium is bifurcate with a long posterior process. The pubis did not ossify, as in several basal tetrapods including Crassigyrinus and derived Amphibia. Small scutes covered the entire torso ventrally, as in basalmost tetrapods and basal reptiles.
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Figure 2. The gradual loss of basal tetrapod fingers. Unfortunately fingers are not known for every included taxon. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/03/amphibian_fingers5881.jpg?w=584&h=818?w=214″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/03/amphibian_fingers5881.jpg?w=584&h=818?w=584″ class=”size-full wp-image-26315″ src=”https://pterosaurheresies.files.wordpress.com/2017/03/amphibian_fingers5881.jpg?w=584&h=818″ alt=”Figure 2. The gradual loss of basal tetrapod fingers. Unfortunately fingers are not known for every included taxon.” width=”584″ height=”818″ srcset=”https://pterosaurheresies.files.wordpress.com/2017/03/amphibian_fingers5881.jpg?w=584&h=818 584w, https://pterosaurheresies.files.wordpress.com/2017/03/amphibian_fingers5881.jpg?w=107&h=150 107w, https://pterosaurheresies.files.wordpress.com/2017/03/amphibian_fingers5881.jpg?w=214&h=300 214w, https://pterosaurheresies.files.wordpress.com/2017/03/amphibian_fingers5881.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
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.
The presence of five manual digits
in Diplovertebron and 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.
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Figure 2. Utegenia nests as a sister to Diplovertebron at the base of the amphibian line. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/03/utegenia588.jpg?w=584&h=243?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/03/utegenia588.jpg?w=584&h=243?w=584″ class=”size-full wp-image-26303″ src=”https://pterosaurheresies.files.wordpress.com/2017/03/utegenia588.jpg?w=584&h=243″ alt=”Figure 2. Utegenia nests as a sister to Diplovertebron.” width=”584″ height=”243″ srcset=”https://pterosaurheresies.files.wordpress.com/2017/03/utegenia588.jpg?w=584&h=243 584w, https://pterosaurheresies.files.wordpress.com/2017/03/utegenia588.jpg?w=150&h=63 150w, https://pterosaurheresies.files.wordpress.com/2017/03/utegenia588.jpg?w=300&h=125 300w, https://pterosaurheresies.files.wordpress.com/2017/03/utegenia588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Utegenia nests as a sister to Diplovertebron.
Note the narrow frontals,
on Diplovertebron distinct from the wide frontals in Utegenia and Kotlassia, but more similar to those in Balanerpeton (Fig. 4), another basal amphibian, and Silvanerpeton, a stem reptile. Yet none have the hourglass shape found in Diplovertebron.
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Figure 4. The basal amphibian, Balanerpeton apparently has five fingers (see figure 5). ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton5881.jpg?w=584&h=612?w=286″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton5881.jpg?w=584&h=612?w=584″ class=”size-full wp-image-26310″ src=”https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton5881.jpg?w=584&h=612″ alt=”Figure 4. The basal amphibian, Balanerpeton apparently has five fingers (see figure 5).” width=”584″ height=”612″ srcset=”https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton5881.jpg?w=584&h=612 584w, https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton5881.jpg?w=143&h=150 143w, https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton5881.jpg?w=286&h=300 286w, https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton5881.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
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.
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Figure 5. DGS recovers five fingers in Balanerpeton with a Diplovertebron-like phalangeal pattern. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton-manus588.gif?w=584&h=330?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton-manus588.gif?w=584&h=330?w=584″ class=”size-full wp-image-26309″ src=”https://pterosaurheresies.files.wordpress.com/2017/03/balanerpeton-manus588.gif?w=584&h=330″ alt=”Figure 5. DGS recovers five fingers in Balanerpeton with a Diplovertebron-like phalangeal pattern.” width=”584″ height=”330″ />
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.
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Figure 2. Tulerpeton manus and pes in situ, reconstructed by Lebdev and Coates 1995 and newly reconstructed here. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/02/tulerpeton_manus_pes.jpg?w=584&h=535?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/02/tulerpeton_manus_pes.jpg?w=584&h=535?w=584″ class=”size-full wp-image-26219″ src=”https://pterosaurheresies.files.wordpress.com/2017/02/tulerpeton_manus_pes.jpg?w=584&h=535″ alt=”Figure 2. Tulerpeton manus and pes in situ, reconstructed by Lebdev and Coates 1995 and newly reconstructed here.” width=”584″ height=”535″ srcset=”https://pterosaurheresies.files.wordpress.com/2017/02/tulerpeton_manus_pes.jpg?w=584&h=535 584w, https://pterosaurheresies.files.wordpress.com/2017/02/tulerpeton_manus_pes.jpg?w=150&h=138 150w, https://pterosaurheresies.files.wordpress.com/2017/02/tulerpeton_manus_pes.jpg?w=300&h=275 300w, https://pterosaurheresies.files.wordpress.com/2017/02/tulerpeton_manus_pes.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
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.
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