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 ...
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144<br />
ADVANCES IN PALAEOICHTHYOLOGY<br />
for biozonal purposes. N. alta is the topmost Pridolian vertebrate zonal fossil in the<br />
SVSS. However, a recent study, which includes the Lužni <strong>and</strong> Lithuanian boreholes,<br />
pro<strong>vides</strong> material (in preparation) for the revision of acanthodian zonality in this part.<br />
In the Lužni-4, Gomphonchus mediocostatus <strong>and</strong> Cheiracanthoides planus intervals<br />
are defined with the bo<strong>un</strong>dary between them at the depth of 176.3 m. In west Lithuania,<br />
all taxa of these two intervals (listed in Fig. 9) are recognized also, but the Pridolian<br />
zonal chart is captioned by the two other, presumedly yo<strong>un</strong>ger associations of<br />
acanthodians, Vesperalia perplexa <strong>and</strong> Endemolepis inconstans characterizing the<br />
topmost profile part that appears absent? in Lužni-4.<br />
Conclusions<br />
1. Detailed results obtained from the well sampled Lužni-4 core are very useful for a<br />
further regional acanthodian study of the Baltic Silurian from taxonomical, biozonal,<br />
correlational, palaeogeographical, <strong>and</strong> palaeobiogeographical aspects.<br />
2. Eleven biostratigraphic intervals of acanthodians proposed may form the basis for<br />
the forthcoming zonal scheme of Latvia following the reappraisal of the available<br />
sampled acanthodian collections (Ventspils-3 D, Kolka-54, etc. boreholes).<br />
3. Lužni-4 core contributes to the correction of previous records of the regional<br />
occurrence of stratigraphically significant taxa, e.g., zonal Nostolepis gracilis, for which<br />
the range must be extended down to the Ludlow.<br />
4. Most acanthodians are represented here by shortened stratigraphic ranges that are<br />
mainly caused by their later entry into the sequence as compared with Lithuania.<br />
5. Nevertheless, some taxa, such as Rohonilepis breviornatus, Nostolepis (cf.) linleyensis,<br />
Fec<strong>un</strong>dosquama basiglobosa <strong>and</strong> many others of the late Pridoli, are of great interest<br />
as the potential indices for more detailed regional biozonality; some are applicable for<br />
wider interregional correlations.<br />
6. Lužni-4 core contributes to the <strong>un</strong>derst<strong>and</strong>ing of regional taxonomic diversity <strong>and</strong><br />
the facies dependence of Silurian acanthodians, e.g., the newly described species<br />
Gomphonchus? minutus, Nostolepis latvica, N. alifera, Poracanthodes sulcatus, P.<br />
marssae are not fo<strong>un</strong>d in Lithuania.<br />
Acknowledgements. - My special thanks to Habil. Dr V. Karatajute-Talimaa (Vilnius) for donation<br />
of acanthodian collection <strong>and</strong> helpful discussions on stratigraphic distribution of acanthodians<br />
<strong>and</strong> other groups of vertebrates. Dr T. Märss (Tallinn) is acknowledged for the help in the taxa<br />
determination <strong>and</strong> a possibility of acanthodian study of some Latvian <strong>and</strong> Estonian cores.<br />
Reviewers of the manuscript, Dr C. Burrow (Queensl<strong>and</strong>) <strong>and</strong> Dr E. Lukševics (Riga) are<br />
acknowledged for comments <strong>and</strong> corrections. Dr V. Mikli (Tallinn) is thanked for the micrographs<br />
of acanthodian scales.<br />
This is a contribution to IGCP 491 Project: Middle Palaeozoic Vertebrate Biogeography,<br />
Palaeogeography <strong>and</strong> Climate.