The
Satovcha Graben (depression formed by extension, as two geological
blocks draw apart causing the ground between to thin and slump) forms
a basin roughly 7 km in length and 1.5 km in width in the western
Rhodopes Mountains of southwest Bulgaria. During the
Miocene-Oligocene this depression was filled by a lake, and
surrounded by subtropical evergreen forests similar to those found in
Southeast Asia today. These deposits have produced a diverse range of
Plant fossils preserved in freshwater diatomites (sedimentary rocks
made up of the tests, or shells, of tiny planktonic Algae called
Diatoms). The site is also known to produce Insect fossils, including
Beetles, Coleoptera, Bugs, Hemiptera, Caddisflies, Trichoptera,
Earwigs, Dermaptera, Ants and Bees, Hymenoptera, Flies including
Mosquitoes, Gnats and Midges, Diptera, Cockroaches and Termites,
Dictyoptera, a Grasshopper and Crickets, Orthoptera, and Dragonflies
and Damselflies, Odonata; though to date these Insects have never
been formally described or studied in any organized way.
The first
Dragonfly species described is placed in the genus Oligaeschna,
which has previously been described from other locations of similar
age, and given the specific name bulgariensis,
meaning 'from Bulgaria'. The species is described from two specimens,
though both of these comprise the forewing only, one specimen
preserved as part and counterpart on s split block, the second as
part only. Insects in most groups can be identified to species level
using the venation on the their forewings, so it is not unusual to
describe new fossil species using isolated forewings.
Oligaeschna bulgariensis. (1) First specimen (part); (2)
Second specimen (counterpart); (3) Second specimen. Scale bars
represent 5 mm in all figures. Nel et al. (2016).
The second new Dragonfly species described is placed in the genus
Stenolestes, which has previously been described from the
Middle Oligocene to Early Miocene of Europe and Siberia, making this
potentially the youngest example of the genus, and given the specific
name rhodopensis, meaning 'from Rhodopes'; in reference both
to the Rhodopes Mountains and the mythical Thracian queen Rhodope.
The species is described from an isolated forewing preserved as part
and counterpart, plus a largely intact insect compressed in lateral
(side) view.
Stenolestes rhodopensis, whole Insect. Scale bar is 1 cm.
Nel et al. (2016).
The new Damselfly species is placed in the genus Primorilestes,
which has previously been used to describe species from the Early
Oligocene of Primorye Territory in Russia and Early Eocene of
Denmark, and is given the specific name magnificus, in
reference to the quality of preservation on the frst specimen. The
species is described from two specimens, a forewing preserved as part
and counterpart, and an isolated wing-tip.
Primorilestes magnificus, first specimen (part). Scale bar
is 5 mm. Nel et al. (2016).
See also...
