Diplovertebron

Diplovertebron is an extinct genus of embolomere that lived in the Late Carboniferous period (Moscovian), about 310 million years ago. "Diplovertebron" was a medium-sized animal, around 50 cm in length. Members of the genus inhabited European Carboniferous swamps in what is now the Czech Republic. They were closely related to larger swamp-dwelling tetrapods like "Proterogyrinus" and "Anthracosaurus". However, "Diplovertebron" were much smaller than these large, crocodile-like creatures. Known from a single species, "Diplovertebron punctatum," this genus has had a complicated history closely tied to "Gephyrostegus", another genus of small, reptile-like amphibians.
History.
"Diplovertebron" was one of many tetrapods found in Czech coal swamps by Antonin Frič in the late 19th century. Its remains were an assortment of disarticulated fossils encased in two slabs of coal, which were designated Fr. Orig. 96 (for the smaller slab) and Fr. Orig. 128 (for the larger slab). D.M.S. Watson (1926) assigned two more complete specimens to the genus. One of these had already been named as the type specimen of the reptile-like tetrapod "Gephyrostegus" by Otto Jaekel in 1902, while the second specimen, DMSW B.65, was newly described. A later study, Brough & Brough (1967), restored the validity of "Gephyrostegus" and rebuked Watson's decision to add Jaekel's and his specimens to "Diplovertebron". Richard Lydekker renamed "Diplovertebron" to Diplospondylus in 1889, based on the fact that the etymology of ""Diplospondylus" was all Greek, while that of "Diplovertebron"" was a hybrid of Greek and Latin. However, few other paleontologists shared Lydekker's aversion to hybrid names.
Another aspect of "Diplovertebron"'s history which led to some confusion relates to the labeling in Frič's original lithographic illustrations. Plate 53, the illustration which featured remains from the larger slab of "Diplovertebron" fossils (Fr. Orig. 128), was accidentally labeled as pertaining to fossils from the smaller slab (Fr. Orig 96). As a result, many paleontologists misunderstood the original description and ignored the larger slab when describing "Diplovertebron", as they assumed that there was only a single slab (Fr. Orig. 96) available. There were only a few exceptions to this mistake, namely Steen (1938) and Klembara "et al." (2014).
Several Czech fossils described by Frič as other genera may actually represent additional "Diplovertebron" material. "Hemichthys problematica", a supposed fish skull described in 1895, was later found to be an anthracosaur skull. Klembara "et al." (2014) petitioned for a redescription of "Hemichthys", which they regarded as a nomen oblitum. Likewise, an embolomerous tail with dense scalation along its underside was named "Nummulosaurus kolbii" in 1901. Romer (1947) could find no evidence that "Nummulosaurus" was not identical to "Diplovertebron". Romer was also one of the few paleontologists to consider "Diplovertebron" to be a seymouriamorph, rather than an embolomere. However, this classification scheme was based on "Gephyrostegus" fossils, as the two genera were still considered synonymous in 1947.
Description.
Historical recounts of "Diplovertebron" between 1926 and 1967 typically reconstructed it as a reptile-like terrestrial animal with five-fingered hands and feet. However, these reconstructions were created using more complete skeletal remains of "Gephyrostegus" and "Solenodonsaurus", which at the time were considered to be synonymous with "Diplovertebron". Without these skeletons, the fossil remains of "Diplovertebron" are much more limited. Nowadays it is assumed that "Diplovertebron" was partially or fully aquatic, akin to other embolomeres like "Archeria" and "Proterogyrinus". Nevertheless, it was probably still similar to "Gephyrostegus" in terms of general proportions.
Like other embolomeres, each of "Diplovertebron"'s vertebrae were composed of two ring-shaped components of equal size. Frič originally regarded this as a unique feature, but as early as 1884, E.D. Cope drew connections between the vertebrae of "Diplovertebron" and "Cricotus" (an American embolomere more commonly known as "Archeria"). The preserved vertebrae were from the tail region, since the front segment (intercentrum) connected to thin haemal arches.
The fragmentary skull bones are only slightly ornamented with striations, rather than the numerous pits that were present in its relatives. The premaxilla contained five thick and conical teeth, about twice as long as they were wide. The maxilla likely had over 30 teeth in it, and its teeth were thinner than those of the premaxilla. The teeth towards the front of the maxilla were thicker and more widely separated, while those at the back were closely packed. The teeth of the lower jaw were more numerous, closely packed, and much smaller than those of the upper jaw. There were over 40 in total, and the first 7 were the largest and most well-spaced. All of the teeth possessed maze-like enamel folding similar to other "labyrinthodonts". These dental features showed some similarities to the teeth of "Calligenethlon", an embolomere which was similar in size to "Diplovertebron".
The belly was covered with long, oblong scales with rounded edges, while the back was bare. Various limb bones were preserved. Unusually, they were covered with tiny pores. The humerus had a strong diagonal ridge along half of its shaft, similar to that of "Archeria". The pelvis was also quite similar to that of "Archeria" and "Calligenethlon" in the fact that the ilium had a structure typical for embolomeres: two rod-like prongs atop a short "stem". The front prong was short, but the rear prong was very long Frič (1885) referred an interclavicle to "Diplovertebron", though it may have actually been from "Gephyrostegus" instead.
References.
Benes, Josef. Prehistoric Animals and Plants. Pg. 80. Prague: Artia, 1979.