Palaeontologia africana

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The first record of late Permian tetrapods from Namibia
(Evolutionary Studies Institute, 2023) Mocke, Helke B; Kammerer, Christian F; Smith, Roger M H; Marsicano, Claudia A
The entire Omingonde Formation in Namibia was previously assigned a Triassic age based on the fossil tetrapod fauna discovered southwest of theWaterberg Plateau. However, recently repatriated and newly collected material suggests that the lowermost part of the Omingonde Formation includes late Permian strata, equivalent in age to the upper Endothiodon Assemblage Zone of the South African Karoo Basin. In this study,we document the first record of late Permian tetrapod fossils from Namibia, and provide brief descriptions of a gorgonopsian skull collected at Mount Etjo in 1996 and the skull of a small dicynodont collected at the same site in 2019, referable to cf. Tropidostoma. This material confirms that there is need for better understanding of the stratigraphy of the Etjo Mountain area, in particular the position and nature of the unconformity between strata of the Permian Endothiodon and the Triassic Cynognathus assemblage zones.
Biostratigraphic refinement of tetrapod-bearing beds from the Metangula Graben (Niassa Province, Mozambique). New radiometric dating and the first Lower Triassic tetrapod fossils from Mozambique
(Evolutionary Studies Institute, 2020-12) Aráujo, Ricardo; Macungo, Zanildo; Smith, Roger M H; Tolan, Stephen; Angielczyk, Kenneth D; Crowley, James; Milisse, Dino; Mugabe, João
Numerous fossils of the toothed dicynodont Endothiodon have been collected previously from the Permian K5 formation of the Metangula Graben (Niassa, Mozambique). However, no identifiable vertebrate fossils have been reported from other stratigraphic units in the basin. Here we report likely Triassic tetrapod remains from the base of the Fubué Formation some 700 stratigraphic metres above the dated K5 Formation. We present anatomical comparisons and a phylogenetic analysis that confirm that they have close affinities to the well-known Early Triassic dicynodont therapsid Lystrosaurus. Thus, the Metangula Graben can now join the few regions in the world that preserve terrestrial tetrapod fossils from before and after Permian-Triassic mass extinction event, giving it the potential to provide further insights into the evolution of terrestrial organisms during this major biotic crisis. We present an updated geological section and paleoenvironmental interpretations, as well as the first assessment of the vertebrate taphonomy of the K5, K6, Mount Lilonga, and Fubué Formations. We also report the first radiometric dates for the K5c member of the K5 formation. The K5c has a maximum depositional age of 258.85 ± 0.41 Ma and is thus older than previously thought, falling near the boundary between the Lycosuchus-Eunotosaurus and Tropidostoma-Gorgonops subzones of the Endothiodon Assemblage Zone, rather than being coeval with the Cistecephalus Assemblage Zone.
Sedimentology and taphonomy of Late Permian vertebrate fossil localities in southwestern Madagascar
(Bernard Price Institute for Palaeontological Research, 2000) Smith, Roger M H
This is the first report of a project that tests the accuracy of the currently accepted palaeoposition of southern Madagascar during the late Permian in juxtaposition to the coast of Tanzania. This is done by comparing the sediments and fossils that accumulated in a series of rift valleys, each around 25 km wide, that formed in this part of Gondwana at the beginning of pull-apart some 250 million years ago. The study reported here on the Madagascan side of the rift system will be followed by a similar study of the Tanzanian portion. Field data on the sedimentology and vertebrate taphonomy of three separate fossil localities in the Late Permian, Lower Sakamena Formation of southwestern Madagascar are used to reconstruct the subenvironments of the Sakamena axial rift valley lake. 1. Ranohira: dominated by microlaminated mudrocks with three horizons of fossil bearing micrite nodules. The fossils are mostly complete articulated skeletons of an ?aquatic procolophonid reptile, Barasaurus, which inhabited the offshore epilimnion of a deep, thermally-stratified closed lake. 2. Zavoloa River: alternating cross-bedded conglomeratic sandstone and laminated siltstone are interpreted as braided delta deposits entering the linear margin of the lake from the passive side of the half graben. These deposits contain some fully articulated skeletons and numerous winnowed bonebeds of a supposedly semi-aquatic reptile, Claudiosaurus, that may be related to sauropterygians. 3. Mount Eliva: is dominated by the younginiform reptile, Hovasaurus, which occurs as articulated skeletons inside micritic siltstone nodules in the mudrocks of a sub-lacustrine deltaic sequence. Pebble masses in the abdomen of Hovasaurus are interpreted as ballast to facilitate swimming. The taphonomic style and sedimentary environment of the host strata confirm this interpretation. Thermal shock from periodic overturn and poisoning from algal blooms are the most likely causes of mass mortality among the aquatic fauna. Hydrogen sulphide released from anaerobic bacterial decay of soft tissue and girdle cartilage formed reduction halos around the newly buried reptile carcasses. At least 3 “micritization episodes” led to the precipitation of calcium cabonate in the reduction halos forming nodules around the vertebrate fossils. They are interpreted as periods of extended lowstand when thermal stratification could not be maintained and oxygenated waters came into contact with previously anoxic sediments. If such lowstand events were climatically controlled, they may be useful timelines to accurately correlate strata within and between these ancient rift valley lakes in both Madagascar and Tanzania.

Palaeontologia africana

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