Leaf-miners are insects that dwell inside of leaves during their larval stage, where they feed on the leaf mesophyll and leave a conspicuous trail in their wake. Several different groups of insects have independently evolved the leaf-mining behavior including Lepidoptera (butterflys and moths), Diptera (flies), Hymenoptera (sawflies) and Coleoptera (beetles) and the mines of the different groups can be distingiushed by the morphology of the mines. When fossil leaves are well-preserved, leaf mines are often well-preserved too, providing and opportunity to study intertrophic interactions in the fossils record.
In my hunt for the fossils of early flowering plants, particularly early eudicots, I have been scouring old collections for plants misidentified as ferns. Some of the features I look for are reticulate venation, glandular teeth along the leaf margin, and the shape of lobes and sinuses along the leaf margin. This is the search image that I developed while working on Potomacapnos apeleutheron (Jud and Hickey, 2013).
One day while a graduate student I was looking through the collections of Lester Ward at the Smithsonian I came across a small eudicot leaf from the Albian of Virginia that was misidentified as a fern. This one got me particularly excited because it was not only an angiosperm leaf, but it has a leaf mine that Ward had apparently not noticed (Ward 1895, Plate II, Figure 5). I took the leaf to my colleague Dr. Jay Sohn, also a graduate student at the University of Maryland at the time, and he began the work of identifying the miner while I set about describing and identifying the leaf.
The results of our analysis were published in Cretaceous Research earlier this year. The leaf contributes to the growing number of herbaceous eudicots known from the Lower Cretaceous Potomac Group deposits and highlights the value of museum collections as sources of new discoveries. The mine has features that are characteristic of leaf-mining flies and suggests that they started out associated with basal eudicots and later expanded their hosts to include other groups, such as asterids, rather than the other way around as previously thought.
We had some nice coverage of the story from the University of Florida, where I was a postdoc when the paper came out. Check it out here:
ttp://news.ufl.edu/articles/2016/04/george-washingtons-little-buttercup.php