Fly palaeo-evo-devo: immature stages of bibionomorphan dipterans in Baltic and Bitterfeld amber

Abstract

Larvae of flies and gnats (Diptera) form a crucial component of many terrestrial and freshwater ecosystems in the extant biosphere. Larvae of Diptera play a central role in water purification, matter and energy transfer in riparian ecosystems in rivers, carbon cycling in lakes and forests as well as being major decomposers of dead organic matter. Despite all these important roles, dipteran larvae are most often ignored in palaeoecological studies, due to the difficulty of the taxonomic identification of fossil larvae, but also due to the perceived importance of adult dipterans in palaeoentomological and taxonomic studies. Despite that, much information on palaeoecosystems can be gained from studying fossil dipteran larvae, in particular for well preserved specimens from fossil resins (ambers and copals). Since ambers are selectively preserving fauna of trunks and leaf litter, it allows us to learn a lot about xylophages and saprophages of amber forests, such as Eocene Baltic amber forest. Here we present immature stages (larvae and pupae) of the dipteran ingroup Bibionomorpha, from Baltic and Bitterfeld amber forests. We have recorded at least four different larval morphotypes, one with four distinct instars, and at least three pupal morphotypes. One larva is recognised as a new species and can be interpreted either as a representative of a highly derived ingroup of Bibionidae or as a sister species to Bibionidae. Also represented by single larval specimens are the groups Pachyneura (Pachyneuridae) and Sylvicola (Anisopodidae). The majority of the recorded specimens are representatives of the group Mycetobia (Anisopodidae). Due to the abundance of immature stages of Mycetobia, we have been able to reconstruct the number of larval stages (4) and relative growth rate of these fossil dipterans. We discuss implications of these finds.

Staminate inflorescences with in situ pollen from Eocene Baltic amber reveal high diversity in Fagaceae (oak family)

“…Weitschat 1997;Weitschat & Wichard 1998, Weitschat 2008. This very coarse application of the uniformitarianism principle to the ecology of now extinct groups, however, has previously been critically assessed (Baranov & al. 2019).…”

Peer Review #2 of "Eco-morphological diversity of larvae of soldier flies and their closest relatives in deep time (v0.1)"

“…Each image detail was recorded by a stack of images of shifting focus to overcome the limitation of the depth of field (Haug, Haug, and Ehrlich 2008;Haug et al 2011;Haug, Müller, and Sombke 2013). Fusion into sharp images and panorama stitching was performed with the built-in software e.g., in Baranov, Schädel, and Haug (2019). We also employed the built-in HDR function of the digital microscope; therefore, every single frame is a composite from several images taken under different exposure times (cf.…”

“…An elongated metacephalic rod is in particular common in larvae of Mydidae, Xylophagidae, Thervidae and Scenopidae (Hennig 1968, James 1981Irwin and Leneborg 1981;Kelse 1981;Wilcox 1981). This makes the interpretation of morphotype 1 larvae relatively challenging, due to the "chimaera-like" combination of the traits, as a probable result of the "push of the past'' effect (Baranov, Schädel, and Haug 2019;Haug and Haug 2019). This effect seems quite common among fossil representatives of Holometabola, representing phenomena occurring when initial diversification events in extant hyper diverse groups lead to a number of "experimental" morphologies (Budd and Mann 2018; Haug and Haug 2019).…”

“…The fossil record of Stratiomyidae Given the important role of larval dipterans, their numerous ecosystem functions and their often very specific association with certain microhabitats (Baranov et al, 2019), their fossil records can provide a wealth of paleo-ecological information. Hence these new larval stratiomyomorphan specimens widen our understanding of the respective paleo-ecosystems from which they originated.…”

Peer Review #3 of "Eco-morphological diversity of larvae of soldier flies and their closest relatives in deep time (v0.1)"

“…it is impossible to see any tergite boundaries in the head capsule of the post-embryonic larvae. Nevertheless, it is well possible to reconstruct the sequence of the segments in the head capsule, using the arrangement of the appendages (Baranov et al, 2019).…”