MOUTHPARTS, NECTARIVORY AND POLLINIVORY BY ADULT BRACHYCEROUS DIPTERA DURING THE MID-MESOZOIC

The Brachycera, a clade of flies defined by short antennae, diversified during the Middle Jurassic to Early Cretaceous. They are fossilized as soft-bodied compressions in Eurasian lacustrine deposits where, in particular, they occur as the plesiomorphic subclades Nemestrinidae, Apioceridae, Tabanidae and Therevidae. Features such as body vestiture, eyes, antennae, and mouthparts (labella) often are preserved, the latter as elongate and tubular structures that siphoned streams of fluid or possibly particulate pollen, or alternatively as more squat, fleshy and pseudotracheate labella that sponged surface fluids. These two proboscis types have lacked the attention of paleoentomologists, which is attributable to the absence of supportive plant-associational evidence such as gut contents.

New occurrences from four deposits: Karatau of eastern Kazakhstan (latest Callovian–early Oxfordian), Baissa in transbaikalean Russia (early Neocomian); Yixian in northeastern China (Barremian); and Las Hoyas in Spain (Barremian) indicate that both long-proboscate and fleshy-labellate mouthpart types imbibed hidden to exposed plant fluids in floras overwhelmingly or entirely dominated by pteridiphytes and gymnosperms. Although Yixian has basal angiosperms, these flowers lacked structures consistent with nectar feeding by probing brachycerous flies. However, the presence of Classopollis pollen clumps on head regions adjacent to the proboscides of Apioceridae and especially a new genus of basal therevids, indicates that cheirolepidaceous conifers—a clade with an atypical pollination system—provided pollination drops as fluid food. Features of Classopollis pollen ultrastructure and female cone structure of related Frenelopsis suggest insect pollination. Extant analogs include pollination drop feeding by flies on all three gnetalean clades. Collectively these data provide evidence that seed-plant nectarivory and pollinivory were established on gymnosperms prior to the earliest angiosperms.