Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ... Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
80 ADVANCES IN PALAEOICHTHYOLOGY Town in Oryol Region (Central Russia) (Fig. 1) were made by crews of the Palaeontological Institute of the Russian Academy of Sciences, headed by V.V. Dobrokhotova in 1976 and N.I. Krupina in 1977 (Obrucheva and Obrucheva 1977; Moloshnikov 2001). Subsequently between 1997 and 2000 collecting was carried out by a field crew headed by the author in collaboration with a member of the Livny Town Natural History and Local Lore museum, O.L. Jakubson. During the 1999 season the first tetrapod remains were found in this locality. Previously the only Devonian tetrapod from Russia was Tulerpeton curtum Lebedev, 1984, known from the Andreyevka-2 locality (Fig. 1) situated in the Tula Region (Khovanshchinian Regional Stage, uppermost Famennian, praesulcata conodont zone) (Lebedev 1984; Lebedev and Clack 1993; Lebedev and Coates 1996). Postcranial remains of Devonian tetrapods and more specifically limb bones play an important role in the solution of the question whether tetrapod digited limbs were formed in an aquatic environment as a special kind of paddles used for swimming, or in terrestrial environments as specialised lever-type props used for walking (for example, Romer 1958). Clack and Coates (1995) argued that the earliest tetrapods acquired digited limbs while still dwelling in water and were primarily aquatic, based upon Acanthostega material. Newly described material provides further arguments in favour of the latter point of view. Geological setting, sedimentology and taphonomy The Gornostayevka industrial quarry exposes deposits of the Evlanovian, Livnian (Upper Frasnian) and Zadonskian Regional Stage (lower Famennian). Specimens of Jakubsonia livnensis gen. and sp. nov. were collected from the Gornostayevka locality situated within the limits of the upper part of the section within the Zadonskian Regional Stage (Moloshnikov 2001). This stage is correlated to the ?triangularis-crepida Zone of the Standard conodont scale (Alekseev et al. 1996). The lower part of the Zadonskian sandstones inconformably overlie the Livnian (Upper Frasnian) limestones. In the west the part of the Zadonskian deposits exposed at the surface is dominated by terrigenous, sometimes coarse-grained rocks. To the east carbonates become dominant (Rodionova 1995), suggesting their outlying position from a denudation area (Voronezh Uplift). The locality under discussion is situated in the western part of the Zadonskian basin in which a terrigenous type of sedimentation prevailed. Fossiliferous coarse-grained sands and sandstones intercalated with fine-grained clays and thin limestone layers occur in the middle of the Zadonskian Regional Stage section of the quarry. These deposits imply sedimentation in hydrodynamically active conditions (Moloshnikov 2001). However, preserved shells of rhynchonellid brachiopods in the layers immediately above and below the vertebrate fossiliferous layer suggest deposition in a marine environment. The bone-bearing coarse-grained sands and gravels form a lens and a pocket about 15-30 cm thick and extending for several square meters. Bones demonstrate insignificant sorting by size or by weight and no orientation. A special feature of sorting is the complete absence of the smallest skeletal elements, like acanthodian scales, despite abundant presence of their fin spines. Probably, this reflects easy transport of scales by
O.A. Lebedev. A new tetrapod from Russia 81 Fig. 1. Map showing location of the Gornostayevka quarry, marked by an asterisk. Location of previously known tetrapod site Andreyevka-2 marked by a black diamond. currents to burial in different environments. The fossiliferous lens and pocket are overlain with a thin layer of plastic reddish-brown clay and fine-grained quartz, white and brownish sands containing rare and poorly preserved vertebrate fragments. Moloshnikov (2001) suggested that the site was formed as a result of temporary stream activity within the shallow-water near-shore zone of an epicontinental basin. Most of the bones are to some extent eroded, however some of them are intact, implying different conditions of transport. Bone colour varies from white to brown and black depending on the rate of their impregnation with iron and manganese oxides and salts. The hardness of the bone is also influenced by mineral impregnation, making white and yellowish bone very fragile and dark-brown and black ones extremely solid. The amount of iron and manganese oxides and salts may suggest former proximity to denudation areas (Tolstikhina 1952). Thus, it is not clear how much of the bone was brought from uplands by streams and how much was deposited in situ.
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O.A. Lebedev. A new tetrapod from Russia<br />
81<br />
Fig. 1. Map showing location of the Gornostayevka quarry, marked by an asterisk. Location of<br />
previously known tetrapod site Andreyevka-2 marked by a black diamond.<br />
currents to burial in different environments. The fossiliferous lens <strong>and</strong> pocket are overlain<br />
with a thin layer of plastic reddish-brown clay <strong>and</strong> fine-grained quartz, white <strong>and</strong> brownish<br />
s<strong>and</strong>s containing rare <strong>and</strong> poorly preserved vertebrate fragments. Moloshnikov (2001)<br />
suggested that the site was formed as a result of temporary stream activity within the<br />
shallow-water near-shore zone of an epicontinental basin.<br />
Most of the bones are to some extent eroded, however some of them are intact,<br />
implying different conditions of transport. Bone colour varies from white to brown <strong>and</strong><br />
black depending on the rate of their impregnation with iron <strong>and</strong> manganese oxides <strong>and</strong><br />
salts. The hardness of the bone is also influenced by mineral impregnation, making<br />
white <strong>and</strong> yellowish bone very fragile <strong>and</strong> dark-brown <strong>and</strong> black ones extremely solid.<br />
The amo<strong>un</strong>t of iron <strong>and</strong> manganese oxides <strong>and</strong> salts may suggest former proximity to<br />
denudation areas (Tolstikhina 1952). Thus, it is not clear how much of the bone was<br />
brought from upl<strong>and</strong>s by streams <strong>and</strong> how much was deposited in situ.
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