A PALEOZOIC LEAF MINE FROM THE RHODE ISLAND FORMATION OF MASSACHUSETTS, USA; ITS EVOLUTIONARY IMPLICATIONS AND A REEXAMINATION OF THE ORIGIN OF ENDOPHYTIC HERBIVORY

Preserved tissue damage on fossil plants provides valuable insights into the evolutionary and ecological history of plant-insect interactions. Leaf mines, traces of insects whose larval stages feed and live primarily within the parenchymal and mesophyll layers of leaves, are well represented in the fossil record, with the oldest reliable examples dating to the Middle to Late Triassic (Ladinian-Carnian). Late Paleozoic leaf mines have been proposed but the specimens have lacked defining characters (e.g., stepwise increases in mine width, oviposition site, terminal chamber, etc.) required to be generally accepted. We describe a new fossil leaf mine, with clear defining characters, on a Neuropteris sp. pinnule from the Carboniferous Rhode Island Fm. (309.5-315.2 Ma) of Massachusetts. This leaf mine is coeval to the oldest known holometabolous insect, an exophytic larva, but extends the oldest occurrence of endophytic larvae by ~65 million years. Leaf mining is only found in the insect orders Coleoptera (8 families), Diptera (18 families), Hymenoptera (3 families), and Lepidoptera (34 families). Phylogenetic evidence and characters shared with modern leaf mines narrows the potential producers to early Lepidoptera or Coleoptera. This fossil supports earlier claims of Paleozoic leaf mining behavior and is an example of the hidden biodiversity that can be recovered through the study of continental trace fossils.