Diplovertebron vs. Gephyrostegus

This blog had its genesis in a reader comment
that considered the taxon, Diplovertebron congeneric with the coeval Gephyrostegus bohemicus and G. watsoni (Fig. 1), echoing earlier authors. Although there may be some confusion here (see below), and several specimens have been attributed to Gephyrostegus by various authors, the specimen illustrated and labeled by Watson 1926 (Fig. 1) is not one of them, unless it was drawn very poorly. If anyone has in situ skeletal material, please send it along for an update.

Part of my confusion
lies in the Wikipedia article on Diplovertebron, which states it was 60 cm in length, at least 5x larger than the one illustrated by Watson and far larger than any of its sister taxa. There may be a paper I am unfamiliar with at present that clarifies the matter.

The Westphalian (310 mya) tetrapods
include some reptile-like amphibians and some amphibian-like reptiles. This strata is 30 million years younger than the Viséan, where members from the first great radiation of reptiles can be found. Several late-survivors of earlier radiations can still be found in Westphalian strata.

Earlier G. watsoni nested among basal archosauromorpha, apart from G. bohemicus at the base of the Reptilia and separated by Eldeceeon. So the three taxa in figure 1 are separated from each other by intervening genera and therefore cannot be congeneric.

With present data, flawed though it may be
Diplovertebron nests in the large reptile tree (LRT) with Utegenia, at the base of the Lepospondyli, the clade that ultimately gives us frogs, like Rana, salamanders, like Andrias, and caecilians, like Dermophis.

Figure 1. Diplovertebron, Gephyrostegus bohemicus and Gephyrostegus watsoni. None of these are congeneric.

Figure 1. Diplovertebron, Gephyrostegus bohemicus and Gephyrostegus watsoni. to scale  None of these are congeneric.

Some backstory:
Diplovertebron punctatum (Fritsch 1879, Waton 1926; Moscovian, Westphalian, Late Carboniferous, 300 mya) was considered an anthracosaur or reptile-like amphibian and that is confirmed by the large reptile tree, where it is transitional between basal seymouriamorpha, like Kotlassia, and Utegenia at the base of the amphibians, close to the origin of the Reptila (Silvanerpeton).

The vertebral structure is primitive, the notochord persisted in adults. The ribs were long and slender. Five digits were preserved with a 2-3-3-3-4 formula. The ilium is bifurcate with a long posterior process. The pubis did not ossify, as in derived Amhibia. Small scutes cover he entire torso ventrally. I’m particularly curious about the lumbar region, which includes ribs all the way back to the pelvis, a situation that does not occur in sister taxa.

References
Brough MC and Brough J 1967. The Genus Gephyrostegus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 252 (776): 147–165. doi:10.1098/rstb.1967.0006
Carroll RL 1970. 
The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf
Fritsch A 1879. Fauna der Gaskohle und der Kalksteine der Permformation “B¨ ohmens. Band 1, Heft 1. Selbstverlag, Prague: 1–92.
Jaeckel O 1902. Über Gephyrostegus bohemicus n.g. n.sp. Zeitschrift der Deutschen Geologischen Gesellschaft 54:127–132.
Klembara J, Clack J, Milner AR and Ruta M 2014. Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902. Journal of Vertebrate Paleontology 34:774–792.
Ruta M, Jeffery JE and Coates MI 2003. A supertree of early tetrapods. Proceedings of teh Royal Society, London B (2003) 270, 2507–2516 DOI 10.1098/rspb.2003.2524 online pdf
Watson DMS 1926. VI. Croonian lecture. The evolution and origin of the Amphibia. Proceedings of the Zoological Society, London 214:189–257.

wiki/Gephyrostegus
wiki/Diplovertebron

 

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2 thoughts on “Diplovertebron vs. Gephyrostegus

  1. Although there may be some confusion here (see below), and several specimens have been attributed to Gephyrostegus by various authors, the specimen illustrated and labeled by Watson 1926 (Fig. 1) is not one of them, unless it was drawn very poorly.

    It was drawn very poorly. It is a quick-and-dirty attempt to show how Watson imagined the whole animal; it is not a specimen drawing.

    In short, as I’ve already said, you’ve based your whole Diplovertebron OTU on paleofantasy.

    Part of my confusion
    lies in the Wikipedia article on Diplovertebron

    See, that’s what you get for trusting Wikipedia on vertebrate paleontology.

    any of its sister taxa

    For at least 12 years I’ve been telling you what the term “sister-group” means. You have never reacted at all. Why is that?

    This strata is

    First, one stratum is, two strata are. Second, the Westphalian isn’t a single stratum = layer, it’s a regional stage, lasting several million years and overlapping the Bashkirian and Moscovian of international chronostratigraphy.

    (Also, the term “stratum” is so poorly defined that the geologists have practically abandoned it. Most Google hits for “strata” are on creationist websites.)

    So the three taxa in figure 1 are separated from each other by intervening genera and therefore cannot be congeneric.

    That’s because your Diplovertebron OTU is Watson’s paleofantasy – as I already said last time.

    The pubis did not ossify</blockquote<

    Juvenile.

    I’m particularly curious about the lumbar region, which includes ribs all the way back to the pelvis, a situation that does not occur in sister taxa.

    The loss of lumbar ribs is an autapomorphy of Eldeceeon. New specimens of Eldeceeon have been found, and the whole taxon is being redescribed.

    (That may take another ten years. One of the promised coauthors is Jenny Clack, who’s also working on a large number of other redescriptions. One of the most recently published ones is the one of the skull of Gephyrostegus by Klembara et al. [2014], which you should really get your hands on to see just how off Watson and, to a lesser but still considerable extent, Carroll were. …as I already told you last time.)

  2. The comment in question is here. I just noticed I never presented the complete citation of Klembara et al. (2014); it’s in issue 34(4) of the JVP, you should find it easily. If you don’t have access, tell me.

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