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| Eogeometer vadens
Fischer, Michalski & Hausmann, 2019
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Abstract
Lepidoptera have little fossilization potential due to the presence of delicate structures and hence are exceptional findings, even in ambers that allow their preservation in sufficient detail for interpretation. From Eocene Baltic amber, the volumetrically largest known deposit of amber, there has been no reliable report of any member of the Macrolepidoptera (informal group of higher moths and all butterflies). Any such lepidopteran fossil would provide insight into evolutionary processes during the Eocene, long after flowering plants had completed their initial radiation. Here, we report on a first geometrid caterpillar from Baltic amber which is described as the oldest evidence for the subfamily Ennominae (tribe Boarmiini) and as one of the oldest records of the currently mega-diverse family. The new finding provides an important calibration point for molecular clock analyses within the family Geometridae and predates the basal divergence of Boarmiini from 32–38 to 44 Mya. It also predates the occurrence of this highly specialized form of caterpillar locomotion that allows for rapid movement.
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| Figure 1: Looping geometrid caterpillar from Baltic amber. It is situated in a dorsal to lateral aspect with the Geometridae-type prolegs clearly visible.
Scale bar equals 1 mm.
The software Helicon Focus Mac 7.0.1 was used (https://www.heliconsoft.com/helicon-focus-history-of-changes-mac/).
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Eogeometer vadens nov. gen., nov. spec
Systematics:
Order LEPIDOPTERA Linnaeus, 1758
Clade DITRYSIA Börner, 1925
Superfamily GEOMETROIDEA Leach, 1815
Family GEOMETRIDAE Leach, 1815
Genus Eogeometer nov. gen.
Etymology: The prefix ‘Eo’ refers to the Eocene, ‘geometer’ to the family name.
Eogeometer vadens nov. spec.
Holotypus: Specimen SNSB-ZSM-LEP amb002 (Fig. 1)
Locus typicus: Amber mine of Yantarni, Russia
Stratum typicum: “Blaue Erde” Horizon (Upper Eocene – Lower Oligocene)
Etymology: The species name ‘vadens’ - “walking” refers to the looping manner of locomotion.
Repository: Bavarian State Collection of Zoology, Munich, Germany; accession number SNSB-ZSM-LEP amb002.
Diagnosis of genus:
The genus Eogeometer is established for this Eocene geometrid caterpillar presumably belonging to the tribe Boarmiini. A differential diagnosis will be given when more Eocene geometrids will become known. Attribution to any extant geometrid genus would be highly speculative. The amber larva shares the character combination of supposed conifer-feeding (see below) and a conspicuous semicircular anal plate with only a few extant geometrid larvae (see discussion), which, however, do not show a longitudinal stripe pattern.
Description of species:
The looping caterpillar is 5 mm in length; the body is long and approximately cylindrical, smooth, but with transversal wrinkles. Along the uppermost ventral side of thorax and abdomen runs a longitudinal protruding and darkish stripe. The head diameter is about 1.5 times the diameter of the body, hypognathous and rounded; both parts of the head capsule show a symmetric spotty dark and light pattern. The legs are well developed (first right leg is missing); prolegs are well developed at abdominal segments A6 and A10 (one proleg of A10 is broken off and is preserved at some distance to the head of the caterpillar); only rudimentary prolegs are present at abdominal segment 5. There is a shield-like protrusion from the ventral side of A10. The setae D1, D2 are positioned at the edge of the longitudinal, dark protrusion. L1, L2 and SV1 are present in lateral positions. MD1, MSD1, MSD2, SD1, SD2 are seemingly absent (Setal map as Supplementary Information).
Taphonomy: The geometrid inclusion occurs within a flat piece of non-autoclaved Baltic amber with dimensions 30 mm by 20 mm, and a height of 4 mm. At one edge, about 5 mm were removed from the sample for IR analysis. The caterpillar is situated centrally within the amber, close to an internal boundary of two resin flows. The only syninclusions preserved adjacent the caterpillar are two different but poorly preserved mites. Some pyrite is present in cracks of the amber.
Thilo C. Fischer, Artur Michalski and Axel Hausmann. 2019. Geometrid Caterpillar in Eocene Baltic Amber (Lepidoptera, Geometridae). Scientific Reports. 9: 17201. DOI: 10.1038/s41598-019-53734-w
Erste Großschmetterlings-Raupe im Baltischen Bernstein entdeckt idw-online.de/-CxmEAA
