Overview
Study of the Impofu Dam site constitutes a landmark in our understanding of the development of Devonian Ecosystems, opening a new window into high latitude life 420 million years ago - at the dawn of diversification of life on land. Rocks of Late Silurian to Early Devonian age contain the earliest records of plant remains, preceded only by enigmatic plant-like spores. Plants at the time included probable relatives of mosses, as well as the primitive ancestors of ‘higher plants’. These plants, generally less than 20 centimetres high, lived in moist habitats. They lacked leaves or complex rooting systems and largely consisted of branching photosynthetic stalks topped by a variety of spore containers: resembling miniature vuvuzelas, balls, clubs and castanets.
Fossil sites with records of plants of this age are uncommon with about 23 previously known from around the world. Most of these came from areas that were tropical during the Devonian, and generally contained only one or a few species. The only reported floras previously from within the Devonian polar region were sparse remains from South America (which together with southern Africa formed that part of Gondwana that surrounded the South Pole). Until now only one species of plant this age was known from South Africa, having been described in the 1930s. The Impofu site, discovered and excavated by Dr. Gess near Humansdorp, proves to be one of the most diverse in the world, with 15 species identified. Three of these represent genera and species formerly unknown to science and named: Krommia parvapila, Elandia itshoba and Mtshaelo kougaensis. Many of the plants are relatively complete and well preserved.
Fossil preservation
The fossils at Impofu Dam are preserved within a black shale derived, by low grade (lower greenschist facies) metamorphism, from a carbonaceous mudstone. Organic plant material is compressed and has all been replaced by silvery white phyllosilicate minerals.
Study of the Impofu Dam site constitutes a landmark in our understanding of the development of Devonian Ecosystems, opening a new window into high latitude life 420 million years ago - at the dawn of diversification of life on land. Rocks of Late Silurian to Early Devonian age contain the earliest records of plant remains, preceded only by enigmatic plant-like spores. Plants at the time included probable relatives of mosses, as well as the primitive ancestors of ‘higher plants’. These plants, generally less than 20 centimetres high, lived in moist habitats. They lacked leaves or complex rooting systems and largely consisted of branching photosynthetic stalks topped by a variety of spore containers: resembling miniature vuvuzelas, balls, clubs and castanets.
Fossil sites with records of plants of this age are uncommon with about 23 previously known from around the world. Most of these came from areas that were tropical during the Devonian, and generally contained only one or a few species. The only reported floras previously from within the Devonian polar region were sparse remains from South America (which together with southern Africa formed that part of Gondwana that surrounded the South Pole). Until now only one species of plant this age was known from South Africa, having been described in the 1930s. The Impofu site, discovered and excavated by Dr. Gess near Humansdorp, proves to be one of the most diverse in the world, with 15 species identified. Three of these represent genera and species formerly unknown to science and named: Krommia parvapila, Elandia itshoba and Mtshaelo kougaensis. Many of the plants are relatively complete and well preserved.
Fossil preservation
The fossils at Impofu Dam are preserved within a black shale derived, by low grade (lower greenschist facies) metamorphism, from a carbonaceous mudstone. Organic plant material is compressed and has all been replaced by silvery white phyllosilicate minerals.
Biota
Up to now numerous taxa have been identified. A large quantity of additional material is still under study and includes several yet unresolved specimens. All plant remains (except Sporogonites) appear to be of a similar grade to early rhyniophytoids, showing characteristics considered plesiomorphic among embryophytes (land plants). Exceptions are Yarravia oblonga and Mtshaelo kougaensis. Cooksonia is the most diverse genus amongst the Impofu Dam flora with at least three species having been identified.
Rhyniophytoids present include Uskiella and Tortilicaulis together with a range of other putative taxa exhibiting varying sporangial morphologies.
Up to now numerous taxa have been identified. A large quantity of additional material is still under study and includes several yet unresolved specimens. All plant remains (except Sporogonites) appear to be of a similar grade to early rhyniophytoids, showing characteristics considered plesiomorphic among embryophytes (land plants). Exceptions are Yarravia oblonga and Mtshaelo kougaensis. Cooksonia is the most diverse genus amongst the Impofu Dam flora with at least three species having been identified.
Rhyniophytoids present include Uskiella and Tortilicaulis together with a range of other putative taxa exhibiting varying sporangial morphologies.
Age
The reported flora provides important biostratigraphic constraint for the age of the Baviaanskloof Formation (Table Mountain Group), providing a Late Silurian to Early Devonian (Lochkovian) age. Cooksonia, which dominates the Baviaanskloof flora, has only been found in deposits from the Silurian to the Lochkovian and not in younger deposits. This minimum age for the deposits is supported by the lack of zosterophylls and lycophytes at the site. This site therefore represents the oldest known megaflora from sub-Saharan Africa.
The reported flora provides important biostratigraphic constraint for the age of the Baviaanskloof Formation (Table Mountain Group), providing a Late Silurian to Early Devonian (Lochkovian) age. Cooksonia, which dominates the Baviaanskloof flora, has only been found in deposits from the Silurian to the Lochkovian and not in younger deposits. This minimum age for the deposits is supported by the lack of zosterophylls and lycophytes at the site. This site therefore represents the oldest known megaflora from sub-Saharan Africa.
References
Gess, R.W., & Prestianni, C. (2021). An early Devonian fora from the Baviaanskloof Formation (Table Mountain Group) of South Africa. Scientifc Reports, 11:11859
Torsvik, T. H. & Cocks, R. M. (2004). Earth geography from 400 to 250 Ma: a palaeomagnetic, faunal and facies review. Journal of the Geological Society, London. 161, 555–572
Gess, R.W., & Prestianni, C. (2021). An early Devonian fora from the Baviaanskloof Formation (Table Mountain Group) of South Africa. Scientifc Reports, 11:11859
Torsvik, T. H. & Cocks, R. M. (2004). Earth geography from 400 to 250 Ma: a palaeomagnetic, faunal and facies review. Journal of the Geological Society, London. 161, 555–572