Saturday, 4 September 2021

A fossil Jewel Beetle from the Middle Miocene of the Satovcha Basin, Bulgaria.

The Satovcha Basin, located in the southwestern Rhodope Mountains of Bulgaria, records a sequence of sedimentary and volcanic deposits laid down in a deep freshwater palaeolake that formed in an extensive graben (a structure formed when extensional activity draws rock structures apart, causing them to thin and sag, thereby creating a depression in the middle). The deep waters of the lake were eutrophic (lacking in oxygen), leading to excellent preservational conditions. The rocks of the basin are divided into two units, the Satovcha Formation, which comprises Oligocene volcanic and sedimentary deposits, and the Middle Miocene Sivik Formation, which overlies the Satovcha Formation unconformably includes a range of lake sediments, including a diatomite clay layer which has produced numerous Insect fossils, including a number of Dragonflies and March Flies which have previously been described.

In a paper published in the journal Historia naturalis bulgarica on 17 March 2021, Nikolay Simov and Mario Langourov of the Bulgarian National Museum of Natural History, and Vladimir Sakalian and Vladimir Bozukov of the Institute of Biodiversity and Ecosystem Research of the Bulgarian Academy of Sciences, describe a Jewel Beetle from the Middle Miocene Sivik Formation.

The specimen is placed in the Family Dicercini, but nor assigned to genus or species level as in is incomplete, lacking a head, and preserved as a compression fossil in dorsal view with its elytra (wing cases) covering much of its body. The specimen is about 22 mm in length and 10.5 mm in width, and brownish in colour with some darker markings. The pronotum (section of the body behind the head and in front of the elytra is 8.6 mm in length and 10.5 mm in width. The elytra are about 15.5 mm long and 5.5 mm wide, with roughly parallel sides for most of their length, but narrowing at both the front and rear. The wing tips, tip of the abdomen and some legs are also visible.

Jewel Beetle from the Middle Miocene Sivik Formation of Bulgaria. Simov et al. (2021).

The Middle Eocene deposits of the Satovcha Basin record a warm broadleafed or mixed evergreen forest in an environment that probably had temperatures permanently above 15°C and no winter frosts, similar to the forests of Southeast Asia today, an environment where Jewel Beetles are particularly successful and diverse.

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