Wits Evolutionary Studies Institute (ESI)

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Subject: search.filters.subject.Madagascar

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    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.
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    A case of vertebrate fossil forgery from Madagascar
    (Bernard price Institute for Palaeontological Research, University of the Witwatersrand, 2010-12) Zipfel, Bernhard; Yates, Celeste; Yates, Adam M.
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    Cretaceous faunas from Zululand and Natal, South Africa. Texasia cricki Spath, 1921 (Cephalopoda: Ammonoidea) an early Santonian marker fossil from the Mzamba Formation of the Eastern Cape Province
    (Evolutionary Studies Institute, University of the Witwatersrand, 2013-12-18) Kennedy, William James; Klinger, Herbert Christian
    The type material of ‘Gen. nov. (Muniericeras?)’ cricki Spath, 1921, from the Santonian part of the Mzamba Formation , Eastern Cape Province, is revised, and referred to Texasia Reeside, 1932, of which Lehmaniceras Collignon, 1966 is a subjective junior synonym. Lehmaniceras sornayi, L. acutum, L. macer, L. pingue, L. ultimum and possibly L. gracile of Collignon, 1966, originally described from Madagascar, are further synonyms, as is Barroisiceras umzambiensis van Hoepen, 1968, which is based on a single specimen from Mzamba. The species occurs in the lower part of the Zone of Texanites hourcqi in Madagascar, confirmed here as lower, rather than middle, Santonian.
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    The ammonite genus Diaziceras Spath, 1921, from the Campanian of KwaZulu-Natal, South Africa, and Madagascar
    (2012-12) Kennedy, William James; Klinger, Herbert Christian
    The ammonite genus Diaziceras Spath, 1921, and the type species, D. tissotiaeforme are revised and referred to the subfamily Lenticeratinae Hyatt, 1900, of the family Sphenodiscidae Hyatt, 1900. Skoumalia Summesberger, 1979, is interpreted as a junior synonym of Diaziceras. Diaziceras guillantoni Hourcq, 1949, and D. spathi Hourcq, 1949, are regarded as synonyms of D. tissotiaeforme, and all are referred to the Lower Campanian on the basis of records from Madagascar.