Яндекс.Метрика

Scientists from the Trofimuk Institute of Petroleum Geology and Geophysics SB RAS study graptolites – extinct marine colonial animals that lived in prehistoric oceans and reached their greatest diversity during the Ordovician– of which dendroidea are the most primitive graptolites appearing in the Lower Ordovician. Dendroidea were benthic forms, which attached their colonies to the ocean floor by a root-like base (like mosses and corals) and are arranged in branches (stipes) to make up the whole colony - rhabdosome (for which currently the term “tubarium” is employed, instead). The living representatives of such graptolites are considered to be pterobranchia, which live in modern seas.

Dendroid graptolites are commonly encountered in Paleozoic sedimentary strata of many regions of the world, however, their finds in good 3D preservation are quite rare. Scientists from IPGG SB RAS can boast of a fascinating discovery of a unique fossil site of dendroid graptolites of exceptional 3D preservation - buried in their erected lifetime position in the northwestern Gorny Altai (Altai Mountains) – in the Vtorye Utyosy Formation (Tekhten cross-section). These deposits range from 438 to 443 million years in age corresponding to the Silurian period, a time when this area of the Altai Mountains was covered by water.



About 440 million years ago this part of the Gorny Altai was a sea


This fossil site ranks as unique, because in the vast majority of cases, dendroid graptolites are found in layers not related to the places of their benthic habitat. Colonies were relatively fragile even in calm conditions, so under the action of near-bottom water movements, they detached from the bottom of the substrate and broke into separate parts before burial and their fragments might be carried away from the tubarium’s attachment point, to places other than their habitat. As a result, dendroidea is typically encountered in locations, in the form of discrete fragments of colonies consisting of several, rarely numerous branches.

Among the taxa of Silurian benthic dendroid graptolites found in the Gorny Altai are representatives of the four genera Dictyonema Hall, Callograptus Hall, Desmograptus Hopkinson, Koremagraptus Bulman from the family Callograptidae Hopkinson, the order Dendroidea Nicholson. The Altai representatives of these genera have the appearance of fairly full, voluminous, bushy and tree-branched, cone-shaped or funnel-shaped goblets, preserved in situ.



Fragment of rock containing graptolites


As a result of fieldworks, IPGG specialists have prepared a unique Altai collection comprising more than 35 specimens of attached tubaria, with their long axis oriented across the bedding. Colony growth direction from bottom to the top can be discerned. Some of the colonies are partially deformed, but most of the tubaria have fairly complete life-time configurations

“ The in situ positions of the Altai tubaria indicate a calm environment - either with no or inconspicuous near-bottom currents”, –specialists pointed out.

Complete (intact) colonies of dendroid graptolites are characterized by successive development stages: juvenile, neanic, ephebic (adults), while the general configuration of the tubarium changed from the proximal to distal. In a number of cases, later stage of colony development — the gerontic stage (senilis) is found.



Morphological analysis of dendroid graptolite tubaria of various development stages, showing eight morphotypes of the colonies: cylinder, disc, disc on a stem, hemisphere, cone, goblet, blooming flower, and funnel type. The examples of some shapes are shown in the pictures above.


A group of researchers from the laboratory of Paleozoic Paleontology and Stratigraphy that collected the materials for the geological collection and their processing consisted of Nikolay Sennikov (discoverer of this fossil site and participant in subsequent fieldworks), Dr Sc (geol.-mineral.) principal researcher, Elena Lykova, PhD (geol.-mineral.), senior researcher, Igor Korovnikov, Dr Sc (geol.-mineral.), lead researcher, Dmitry Tokarev, PhD (geol.-mineral.), senior researcher, and Olga Obut , PhD (geol.-mineral.), Head of the laboratory. In the future, the research team will continue in-depth studies of dendroid graptolites in the Gorny Altai.


IPGG SB RAS researchers engaged in the fieldworks


Reference

This study was carried out within the frames of the state assignment of the Russian Academy of Sciences FWZZ-2022-0003 and works under contracts

The studied material is stored in the Collective Use Center ‘‘GEOCHRON” (Collections of unique geological (paleontological, micropaleontological and palynological) materials from Siberia and Arctic regions), at the Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk.

For more details see the article by Sennikov N.V., Lykova E.V. Unique 3D preservation of Rhuddanian (Silurian) Callograptidae (Gorny Altai, Russia) // Palaeoworld, https://doi.org/10.1016/j.palwor.2023.12.003

Photos courtesy of E.V. Lekova, N.V. Sennikov


Published by IPGG Press Service