Cephalonega stepanovi is a fossil organism from Ediacaran deposits of the Arkhangelsk Region, Russia. It was described by Mikhail A. Fedonkin in 1976[1]
Its original genus name Onega comes from the Onega Peninsula of the White Sea, where the first fossils were found. The species name was given to honour V.A. Stepanov, who discovered the Ediacaran fossil site on the Letniy Bereg ("Summer Coast") in 1972, on the Onega Peninsula, the first Proterozoic site found in the Arkhangelsk Oblast.[2] The original generic name is previously occupied by the hemipteran genus Onega Distant (1908). Ivantsov et al. (2019) coined a replacement generic name Cephalonega.[3][4]
The small fossils, which range up to 7 millimetres (0.28 in) long, have oval outlines and low bodies with an articulated central zone built of isomers encircled by an undivided zone. The surface of the undivided region of Cephalonega is covered with small tubercles.[5]
Cephalonega was originally described by Mikhail Fedonkin as a problematic organism, being grouped together with Vendia, Praecambridium and Vendomia as possible stem-group arthropods due to a vague similarity with primitive Cambrian trilobites and arthropods.[1]
In 1985 Mikhail Fedonkin erected Phylum Proarticulata,[6] in which he placed: Cephalonega, Dickinsonia, Palaeoplatoda, Vendia, Vendomia, Praecambridium and Pseudovendia sp., although he did not exclude the possibility that Cephalonega may still be related to various lower Cambrian arthropods, such as Skania.[6][7]
Andrey Yu. Ivantsov has proposed that Cephalonega should be placed in the phylum Proarticulata, as the segments in recently discovered, exceptionally well-preserved fossils display the glide, or "staggered", symmetry characteristic of the majority of proarticulatans.[5]