Eodicynodon Assemblage Zone

Lithology

The Eodicynodon Assemblage Zone correlates with the lower Abrahamskraal Formation, Adelaide Subgroup of the Beaufort Group.Outcrops of this biozone are only known from the south-western margins of the Abrahamskraal Formation and is considered to be Middle Permian (Guadalupian) in age.

The rocks of the Eodicynodon Assemblage Zone comprise mudstones, siltstones, and fine-grained, siliceous sandstone. The mudstones are olive green to moderate yellowish brown in colour and contain thinner light reddish-brown layers. The reddish-brown layers frequently contain calcareous nodules. Desiccation cracks - indicative of seasonal dry periods - and raindrop impressions are sometimes found in the mudstone layers. Argillaceous layers are also common. The siltstones are extremely fine-grained, often containing ripple marks from being deposited in low energy streams, and vary from being dark grey, greenish-grey, and blueish-grey in colour. Thin sheets of chert occur in the mudstone and less commonly in the siltstone layers. The sandstones are fine-grained and vary from being greyish olive green to dark yellowish brown. Some sandstone layers either contain or are capped by pebble-sized mudstone-clast conglomerates. These conglomerates also contain isolated fossils in some localities. The sandstones are more common and at their thickest towards the upper sections of the biozone. The rocks of this biozone were likely deposited in a subaerial deltaic environment which included floodplains. The presence of calcareous nodules also indicates that the environment was warm with seasonal dry periods.

The depositional environment of the Eodicynodon Assemblage Zone was formed by sedimentary material being deposited in the Karoo Basin - a retro-arc foreland basin - by vast, low-energy alluvial plains flowing northwards from a southerly source area in the rising the Gondwanide mountains. The Gondwanides were the result of crustal uplift that had previously begun to take course due to subduction of the Palaeo-pacific plate beneath the Gondwanan Plate. Orogenic pulses from the growing Gondwanides mountain chain and associated subduction created accommodation space for sedimentation in the Karoo Basin where the deposits of the Eodicynodon Assemblage zone, and all other succeeding assemblage zones, were deposited over millions of years.

Paleontology

The Eodicynodon Assemblage Zone is characterized by the presence of the dicynodont species Eodicynodon and the dinocephalian Tapinocaninus pamelae. The biozone is not especially fossiliferous with the fossils of dicynodonts Eodicynodon sp. and the dinocephalians Tapinocaninus and Australosyodon nyaphuli being most commonly found. The preservation of these fossil taxa are good with the majority of fossils being found in the mudstone layers. This is especially true of the reddish-brown mudstones containing calcareous nodules. Interestingly, dinocephalian fossils have been more commonly found in the sandstones, and fossil fragments have been found in the mudstone-clast conglomerates. However, tantalizing remains of more numerous fossil species have been found to date, hinting at the true level of fossil diversity that could be discovered in the future. The fragmented material includes the scales of the fish Namaichthys digitata, species of temnospondyl amphibians, and skull material of gorgonopsids. Rarer fossils encountered in this biozone include skull material of therocephalians, various anomodonts such as Patranomodon nyaphulii, trace fossils of planolites and arthropod trackways, molluscs, and the plant remains of Glossopteris symmetrifolia, Equisetum modderdriftensis, and Schizoneura africana.

The following faunal list follows Rubidge and Day 2020 unless noted otherwise.

Synapsids

• Australosyodon nyaphuli
• Eodicynodon oosthuizeni
• Eutheriodon vandenheeveri (includes Glanosuchus macrops and Ictidosuchus angusticeps of Rubidge & Day, 2020)
• Nyaphulia oelofseni (formerly "Eodicynodon" oosthuizeni)
• Patranomodon nyaphuli
• Tapinocaninus pamelae
• Gorgonopsia indet.

Temnospondyls

• Temnospondyl indet.

Fish

• Namaichthys digitata

Mollusks

• cf. Palaeanodonta

Plants

• Glossopteris sp.
• Schizoneura sp.

Ichnofossils

• Planolites
• Umfolozia