Freitag, 13. Februar 2009

Permotriassic entomofaunal change + the Madygen

Dmitry E. Shcherbakov from Moscow is one of the paleobiologists studying the very group of beings for which Madygen really is a lagerstätte: insects.

Some of his 2008 papers in the Moscovian Paleontological Journal and Alavesia, a relatively new journal for fossil insects, can be found as .pdfs on the library page of the International Palaeoentomological Society (IPS).

Shcherbakov, D.E. 2008. Insect recovery after the Permian/Triassic crisis. Alavesia 2: 125-131. [pdf]

Shcherbakov, D.E. 2008. On Permian and Triassic insect faunas in relation to biogeography and the Permian–Triassic crisis. Paleontological Journal 42 (1): 15-31. [pdf]

The Alavesia paper outlines a three phase development of Triassic entomofaunas, beginning with
(I) a low-diversity episod of P/T recovery dominated by Paleozoic insect groups, followed by
(II) a summit phase with typical Triassic taxa in the Anisian-Carnian, and, with a decline in diversity, ending in
(III) a phase dominated by Late Mesozoic elements, especially featuring new aquatic insect groups.
Shcherbakov suggests, that each of the transitions began in the humid low latitudes and occurred later in the higher latitudes, i.e. the boundaries between those three stages are diachronous.

In the Paleontological Journal paper Dmitry Shcherbakov looks at the insect diversity of Late Carboniferous to Triassic localities, counting the proven occurrences of insect families per stage ('stage' as a chronostratigraphic unit). He illustrates the change in aquatic/ terrestrial, phytophages/ predators, modern/ ancient groups and explains the ecological, evolutionary, and biogeographic background of diversity fluctuations.

Shcherbakov, D.E. 2008. Madygen, Triassic Lagerstätte number one, before and after Sharov. Alavesia 2: 113-124.[pdf]

This review paper begins with a recount of the research history of the Madygen Formation as a Triassic fossil locality, beginning with the geological fieldwork in the 1930s (by Kochnev) which led to the first finds of a fossil flora, classified as Triassic, and to the introduction of the Madygen strata as a separate stratigraphic unit.

In detail the role of paleoentomologist Alexander G. Sharov is recognized, who lead five field expeditions between 1962 and 1966 to a fossiliferous point in the northern Madygen outcrop area (Dzhailoucho). These campaigns turned out as the most successful with regard to the number of recovered insect specimens and other fossils. The historical part is followed by a short overview of the flora and non-insect fauna.

The main part is a synopsis of the particular insect fauna of Madygen. Besides the exquisite state of preservation, several figures illustrate why Madygen really is a lagerstätte: Members of twenty insect orders and 96 out of 106 insect families known from the Ladinian/Carnian have been reported from the Madygen Formation.

In this order beetles, cockcroaches, and homopterans represent the most abundant groups. Among rarer groups are certain specialities, such as the most diverse assemblage of titanopterans. Modern insect orders are represented by several groups of early dipterans and the earliest hymenopterans (belonging to the group of sawflies).

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