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.
Derived from a sister to Eldeceeon, Diplovertebron was basal to the larger Solenodonsaurusand 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.
Casineria kiddi (Paton, Smithson & Clack 1999) Visean, Mississippean, Carboniferous, ~335 mya was a small basal archosauromorph. the oldest but not the most primitive. It was derived from a sister to Diplovertebron and Solenodonsaurus. Westlothiana was a sister taxon.
Overall smaller than and distinct from Gephyrostegus, the skull of Casineria had no otic notch. See Brouffia for more possible skull details. The cervicals of Casineria were increased in number but decreased in size. The presacral vertebral count had increased to over 30. Ribs discontinued after #22. Apparently two vertebrae formed the sacrum and were connected to the pelvis. The pectoral girdle was composed of unfused elements. The humerus had a small hourglass shape. The manus was enlarged. The ilium had no anterior dorsal process. The femur was more gracile. The pes was reduced, more nearly the size of the manus.
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.
Paton RL Smithson TR and Clack JA 1999. An amniote-like skeleton from the Early Carboniferous of Scotland. Nature 398: 508-513.
Watson DMS 1926. VI. Croonian lecture. The evolution and origin of the Amphibia. Proceedings of the Zoological Society, London 214:189–257.