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J. Valiukevičius. Silurian acanthodians from Lūžņi-4
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The first microvertebrate report of the Lužni-4 core was provided by Gailite and
Ulst (1974) based mainly on thelodont identifications by V.Karatajute-Talimaa. In the
Pagegiai Formation (of the old nomenclature, embracing modern Mituva and Ventspils
formations), Thelodus laevis Thelodont Zone (TZ) was distinguished; Th. sculptilis TZ
in the lower part of the Minija Fm.; and Th. parvidens TZ in the upper Minija and the
principal part of the Targale Formation (until the depth of 195 m). Two following facts
obtained from this core are of great interest in discussing the completeness of the Silurian
profile in the basin, and in tracing the Silurian/Devonian boundary. These are the
discovery of the Katoporodus lithuanicus TZ (195-176.6 m), a short-ranging topmost
unit of the Silurian Vertebrate Standard Scheme (Karatajute-Talimaa 2000; Märss 2000),
and the earlier entry into the sequence of Turinia pagei, which first occurs here about
4.6 m below the traditional Silurian/Devonian boundary drawn at the base of the red
dolomitic marls. Both facts demonstrate the developmental peculiarities of this part of
the basin, which became more isolated and lagoonal, but with the complete occurrence
of index fossils which mark the Silurian/Devonian boundary beds with no stratigraphic
gap.
Acanthodians of the Lužni-4 collection were reported in the publications of 1974,
with only short biostratigraphical comments (Karatajute-Talimaa 1978). Only the widest
spread, commonly known taxa were recognized - Nostolepis striata Pander, N. gracilis
Gross, Gomphonchus sandelensis (Pander), G. hoppei (Gross) and representatives of
Poracanthodes. The present study extends the list to about 50 taxa or skeletal elements
of an animal (teeth, spines) which attribution to distinct taxa is uncertain (Table). The
collection is housed at the museum of the Institute of Geology and Geography
(abbreviated LIGG) in Vilnius and is numbered 25-A.
Systematic palaeontology
Class ACANTHODII Berg, 1922
Order CLIMATIIFORMES Berg, 1940
Family CLIMATIIDAE Berg, 1940
Genus Nostolepis Pander, 1856
Type species. Nostolepis striata Pander, 1856; Upper Silurian, Pridoli, Ohesaare
Regional Stage. Ohesaare Cliff, Saaremaa, Estonia.
Nostolepis alifera sp. nov.
Fig. 1A-L, 2 A-D
Etymology. Alifer (Latin) - winged, referring to the lateral crown slopes on scale
crowns.
Holotype. LIGG 25-A-2550, flank scale (Fig. 1 F).
Type horizon. Garzde Beds of the Targale Formation, Pridoli, Upper Silurian.
Range. Type horizon only.
Material. About 2500 scales.