A nepticulid leaf-mine ichnofossil is described on the basis of a fossil leaf of Fagus from the early Miocene Geumgwangdong Formation (ca. 21–14 million years ago) in Pohang basin. This mine trace is characterized by a linear-blotch type with clear centric frass trail of closely and randomly dispersed pellets filling the mine width in early stage. We found traces of possible egg case and exit slit from the fossil. These features are most consistent with those produced by Nepticulidae. Our record represents the only reliably-identified nepticulid leaf-mine on Fagus in Miocene. Nepticulid leaf-mines in Miocene and the leaf-mine fossils from the Geumgwangdong Formation are briefly reviewed.

Lepidoptera, one of the major herbivore groups on terrestrial ecosystems, have evolved various feeding habits on theirhostplants. Diversification of feeding habits has led to their success in the extant fauna. However, there have been limitedstudies scrutinizing evolutionary patterns of such diversification (Kaila et al., 2011; Regier et al., 2015; Sohn et al., 2016).Leaf-mining is the major form of lepidopteran endophagy, occurring in at least 34 families (Hering, 1951). Leaf miningis considered a primitive trait in Lepidoptera because it characterizes the basal (non-ditrysian) lineages, while the derivedDitrysia and Macrolepidoptera trend strongly toward external feeding (Connor & Taverner, 1997). In contrast, internalfeeding is restricted to relatively derived lineages in other insect orders. This contrasting pattern may be a key for understandingthe evolutionary history of Lepidoptera. We discuss this issue based on two lepidopteran leaf-mine fossils discovered lately.

We describe an early angiosperm and a leaf mine ichnofossil from the Lower Cretaceous Potomac Group of Virginia, USA. The descriptions are based on a fossil leaf that was first reported in 1895 but identified as a fragment of a fossil fern. Leaf architectural features and sedimentological context indicate that this leaf was produced by an herbaceous eudicot angiosperm, possibly associated with Ranunculales. The leaf mine is a full depth linear-blotch mine with frass, a trace of puparium inside the blotch mine section, and feeding/oviposition-related puncture marks. The features of the mine are most consistent with those produced by agromyzid flies. This fossil extends the record of agromyzid flies by about 40 million years ago. This fossil provides evidence that agromyzid flies or their ancestors were feeding on herbaceous basal eudicots similar to modern herbaceous ranunculids during the Early Cretaceous, prior to the appearance and diversification of asterids. Our finding contradicts the previous hypotheses on the dipteran radiations associated with the past environmental changes. Insect feeding damages remained in fossilized leaves are currently considered as an important source for climate change studies. We review progresses in the study of the insect feeding trace fossils and their usefulness for monitoring environmental changes.