Amazinyomakhulu

The maxilla of Amazinyomakhulu, the only known bone, is hatchet shaped, with surfaces along its top for articulation with the preoperculum and squamosal bones. These traits are typical of oncyhodonts, as is the lack of apparent quadratojugal, and the possession of two distinct articulations rather than a single combined articulating surface distinguishes it from actinopterygian fish with a similar jaw shape. Its maxilla is especially simlar to that of the genera Onychodus and Strunius, possessing an S-shaped tooth margin and sharing a long and slender forward projection with a deep posterior section with Strunius in particular. This projection underlies the eye socket, so it is likely that Amazinyomakhulu had a very large eye socket similar to Strunius. Unlike Strunius, however, the transition between the posterior and forward projecting sections is especially sharp and the posterior section has an especially high profile. Additionally, the squamosal articulation is significantly longer than the preopercular articulation, also unique to the species.^[1]

The teeth of the species are especially large compared to its relative, and distinctly fewer in number than any other oncyhodont, with only nineteen tooth positions. Other onychodonts such as Strunius can have forty or more teeth, all smaller than those preserved in Amazinyomakhulu. It was noted, however, that some onychodonts possess an inner row of larger teeth and an outer row of smaller, more numerous teeth. Thus, the presence of an outer row with a more typical tooth count cannot be ruled out based on the known material.^[1]

The Waterloo Farm site, where the only known fossil of Amazinyomakhulu was found, is deposited in modern-day South Africa but would have been near the South Pole at a very high latitude during the Devonian. It is the only site known anywhere in the world that demonstrates what high-latitude Polar ecosystems were like during the Devonian period. In particular, it helps demonstrate the ecological context in which some of the first tetrapods evolved. It is thought to have represented an estuary environment, accumulating animals that lived in a variety of salinities from freshwater to marine within the broader ecosystem, and salinity changing along with the seasons. Terrestrial fossils are also especially common compared to other Devonian sites, with an abundance of invertebrates and plants. Animals documented from Waterloo include lampreys, a diverse assortment of placoderms, acanthodians and other cartilaginous fish, and bony fish including actinopterygians and lobe-finned fish such as Amazinyomakhulu. Other lobe-finned fish from the site include the coelacanth Serenichthys, the lungfish Isityumzi, the giant eotetrapodiform fish Hyneria, and a rhizodont that may represent the genus Gooloogongia. Two early tetrapods, Tutusius and Umzantsia, are also known from Waterloo and likewise belong to Sarcopterygii, the group including lobe-finned fish.^[1]

Similarities have been noted to the fauna of the Red Hill locality of the Catskill Formation of Pennsylvania in the United States, which has many close relatives of the fish found at Waterloo Farm including the shared presence of Hyneria, Groenlandaspis, Bothriolepis. Thus, it is interpreted that there was a strong degree of faunal interchange between the Gondwanan ecosystem of Amazinyomakhulu and the Euramerican realm represented by Red Hill. Likewise, Amazinyomakhulu supports interchange between these regions due to its similarity to Strunius, which is Euramerican. It is youngest known onychodont anywhere in the world, with Onychodus dating to the slightly earlier Frasnian age, Strunius found in the Frasnian and Fammennian, and all other onychodonts predating the Late Devonian. It is thought that onychodonts wouljd have lived in both freshwater and marine ecosystems.^[1]