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.
Highlights
Fossil Lepidoptera are among the rarest findings among insect orders, and mainly occur in ambers
The specimen shows the characteristics of Geometridae caterpillars
The most important features of loopers are the presence of strongly developed prolegs only at abdominal segments A6 and A10, but “sometimes with small or rudimentary prolegs on abdominal prolegs 4 and 5”14–16
Summary
Fossil Lepidoptera are among the rarest findings among insect orders, and mainly occur in ambers. The family Geometridae presently is unknown from Baltic amber[1,2], the main deposit of amber. Their caterpillars are familiar as geometers, inchworms or loopers due to their peculiar way of moving, accompanied by a reduced number of prolegs. Geometridae is a family of macrolepidopterans within the superfamily Geometroidea[8]. The prolegs of their caterpillars are reduced as a functional adaptation to the specialized locomotion of the caterpillars, leaving only the anal prolegs at abdominal segment A10 and another pair at A69,10. Fossilized loopers in amber presently had only been known from Miocene amber of the Dominican Republic (16 mya)[13]
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