Earlier I provided images from Watson 1926 describing a specimen of Diplovertebron (Fig. 1). It took the prodding of a reader (Dr. David M) and a reexamination of several journals to realize that Watson had drawn in freehand the same specimen others (refs. below) had referred to as Gephyrostegus watsoni or as small specimen of G. bohemicus. Since this specimen is not congeneric with Gephyrostegus in the LRT, perhaps the name should revert back to Diplovertebron. Unless the holotype (another specimens comprised of fewer bones) is not congeneric. Then it needs a new name.
Diplovertebron punctatum (Fritsch 1879, Waton 1926; DMSW B.65, UMZC T.1222a; Moscovian, Westphalian, Late Carboniferous, 300 mya) aka: Gephyrostegus watsoni Brough and Brough 1967) and Gephyrostegus bohemicus (Carroll 1970; Klembara et al. 2014) after several name changes perhaps this specimen should revert back to its original name as it nests a few nodes away from Gephyrostegus.
This amphiibian-like reptile was derived from a sister to Eldeceeon, close to the base of the Archosauromorpa and Amniota (= Reptiliai). Diplovertebron was basal to the larger Solenodonsaurus and the smaller Brouffia, Casineria and Westlothiana. Diplovertebron was a contemporary of Gephyrostegus bohemicus, Upper Carboniferous (~310 mya), so it, too, was a late survivor.
Overall smaller and distinct from Eldeceeon, the skull of Diplovertebron had a shorter rostrum, larger orbit and greater quadrate lean. The dorsal vertebrae formed a hump and had elongate spines. The hind limbs were much longer than the forelimbs. The tail is incomplete, but appears to have been short and deep.
Seven sphere shapes were preserved alongside this specimen. They may be the most primitive amniote eggs known.
Watson 1926 attempted a freehand reconstruction (see below) that was so different from this specimen that for a time it nested as a separate taxon, now deleted.
The large reptile tree
along with several pages here (PterosaurHeresies) and at ReptileEvoluton.com have been updated.
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.
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.
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.
Watson DMS 1926. VI. Croonian lecture. The evolution and origin of the Amphibia. Proceedings of the Zoological Society, London 214:189–257.