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

O.A. Lebedev. A new tetrapod from Russia
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Ketleri differs from the Greenland localities, on the one hand, and from Andreyevka, on
the other, by the almost complete absence of dipnoans (it provided only a few isolated
remains of Orlovichthys, see Lebedev and Lukševics 1996), which constitute one of
the most substantial elements in two other communities.
Despite all these facts, Remigolepis is recorded in the majority of known Devonian
tetrapod communities (at least five of 8), but the nature of this association is not yet
understood and requires further study.
Interestingly, the assemblage composition of the locality Rybnitsa (Lebedev 1995;
Lebedev and Lukševics 1996) is very close to that of Ketleri and differs in gross features
only by the dominance of several dipnoan species (Krupina 2000). However, during
almost 30 years of exhaustive exploration of this site, no traces of tetrapods have been
found at Rybnitsa; the same also applies to the absence of Remigolepis. These differences
cannot be explained by aspects of physical geography in this region, because as it was
demonstrated above, they were very similar to those at Andreyevka and Gornostayevka.
One more interesting feature characterising Upper Devonian tetrapod assemblages
is the absence of arthrodires. There are three exceptions; these are the Gornostayevka
locality, Red Hill and Scat Craig. In the first one, pachyosteomorph arthrodire plates
were found in the fossiliferous lens itself and in the overlaying clays and sands above it.
This suggests that wherever the tetrapod and accompanying fish materials were brought,
arthrodires dwelled both within this community and separately from it. The possibility
of transportation of the tetrapod and fish materials from upland basins cannot be
excluded.
The presence of the tristichopterid osteolepiform Eusthenodon, highly characteristic
of the west Laurussia localities, is however not recorded in the Ketleri community. This
genus is also missing from the Gondwanan, Chinese and Kazakhstan assemblages.
Daeschler (2000) noted that tetrapod morphological diversity in the Red Hill
community suggests numerous morphological lineages, which specialised in a variety
of ecological niches in Late Devonian ecosystems. This seems to be corroborated by
data from other localities and from Red Hill itself. A classic example of that is the
coexistence of Ichthyostega and Acanthostega in East Greenland (Bendix-Almgreen et
al. 1990); Ventastega coexisted with a “second tetrapod ?” in Ketleri (Ahlberg et al.
1994) and Tulerpeton and “undetermined tetrapod” in Andreyevka-2 (Lebedev and
Clack 1993), Hynerpeton and Densignathus in Red Hill Daeschler (2000). The presence
of more than one tetrapod within the same community might argue for their much more
diverse trophic specialisations than previously thought (for example, Lebedev 1992).
Acknowledgements. - Excavations in the Gornostayevka quarry became possible due to the
hospitable staff of the Livny town Natural history and Local Lore museum. Special thanks to its
member O.L. Jakubson, who enthusiastically supported excavations and other field work in the
Livny District in general.
References
Ahlberg P.E. 1995. Elginerpeton pancheni and the earliest tetrapod clade. Nature, 373 (6513):
420-424.
Ahlberg P.E. 1998. Postcranial stem tetrapod remains from the Devonian of Scat Craig,
Morayshire, Scotland. In: Norman, D.B., Milner, A.R., Milner, A.C. (eds.) A Study of Fossil
Vertebrates. Zoological Journal of the Linnean Society, 122: 99-141.