Sphenothallus specimens are reported for the first time from the Mississippian of Central Russia. All Sphenothallus specimens have a phosphatic composition and a characteristic laminar structure, which is best observable in the thickened lateral parts of a tube. Most of the lamellae in the tube wall are straight, but some have a wavy morphology and a few are so wrinkled that they form hollow “ribs”. The wrinkled lamellae presumably had an originally higher organic content than the straight lamellae. There are borings on the surfaces of some lamellae that are similar in morphology to the bioerosional traces in various hard, biomineral substrates. Lamellae in the inner parts of the tube wall are composed of fibres. The fibres are parallel to the surface of the tube wall and in successive laminae they differ in orientation by irregularly varying angles. It is possible that the plywood microstructure in Sphenothallus was originally organic and was later phosphatized during fossilization. An alternative, but less likely explanation is that the plywood structure was originally mineralized and therefore is comparable to the phosphatic lamello-fibrillar structures of vertebrates.
Sphenothallus is a genus of problematic fossils, occurring in sediments of the first half of the Paleozoic. It represents phosphatic tubes, usually flattened, from several to several tens of centimeters in length. They can be easily mistaken with aquatic plants or fish spines. Despite the fact that the findings of Sphenothallus in Central Russia have been known to paleontologists for at least several decades, they had never been depicted, described, or included in identifiers of the fossils of this region. In this article, we described for the first time Sphenothallus from Central Russia and studied their microstructure.
Scyphozoa, biomineralization, tube microstructure, ultrastructure, mineral composition, Carboniferous.