Congopycnodus

The conical occipital region and the size relation of its individual bones is typical for fish of the Pycnodontomorpha. It can further be determined that Congopycnodus was a member of the Pycnodontiformes rather than the Gyrodontiformes, as this taxon only possesses a single dermosuproccipital bone rather than two. The lack of brush-like processes excludes Congopycnodus from the Pycnodontidae and the presence of a horn firmly places the genus in the family Coccodontoidea, the only known horned pycnodontiforms.^[2]

However, Congopycnodus could not be placed within any of the three families that Coccodontoidea is composed off, as the details of its anatomy differ in every case. Instead, it is suggested that this genus is a morphological precursor to two of the three families, specifically the Gebrayelichthyidae and the Gladiopycnodontidae. The former group shows an overall similar skull shape, with additional deepening and overall narrowing of the occipital region as well as having possessed longer horns that were associated with the dorsal ridge scutes or dorsal fin bones. Gladiopycnodontids also elongated their horns, evolving spines along its back edge while flattening the occipital region.^[2]

In a review of freshwater pycnodont occurrences, Cawley & Kriwet (2024) noted the potential evolutionary significance of Congopycnodus, but stated that the remains were too fragmentary to even be confidently attributed to a pycnodont at all.^[3]

Congopycnodus is among the earliest pycnodontiforms known from outside of Europe. The group first appeared during the Late Triassic in what is now Austria, Italy, Belgium and Luxemburg where they remained for a while. Eventually, pycnodontiforms are known to have dispersed towards Asia, following the Asian coast and reaching Thailand by the lower Middle Jurassic. It is thought that a similar method could have led pycnodontiforms along the coast of a fracturing Gondwana, particularly the northern and eastern shores of what would later become Africa. These early Gondwanan pycnodontiforms may have expanded into the breaks that had begun to separate the continent and from there entered the river systems to arrive in the lake that then covered the region around present-day Kisangani. This renders Congopycnodus among the few known freshwater pycnodontiforms, as the family is primarily known to have inhabited marine environments such as reefs.^[2]

The Stanleyville Formation was initially thought to be Middle Jurassic in the age, but is now thought to be slightly later (Kimmeridgian) in age,^[1] and potentially as late as the Valanginian.^[3] It has been disputed over whether this formation represents a large freshwater system or even an early marine incursion into the Congo Basin (which would fit the marine habitats that coccodontoids are otherwise known from),^[4] although most recent studies favor the former explanation.^[1][3]