Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

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