Xylomyidae

Grimaldi, David A., Arillo, Antonio, Cumming, Jeffrey M. & Hauser, Martin, 2011, Brachyceran Diptera (Insecta) in Cretaceous ambers, Part IV, Significant New Orthorrhaphous Taxa, ZooKeys 148, pp. 293-332 : 298

Xylomyidae (?) genus indet. Fig. 3

Description.

Head: Lost. Thorax: Partially preserved, relatively broad (width of mesonotum equal to length, 1.40 mm), mesoscutellum of moderate size. Notum foveolate and scutellum covered only with numerous fine setulae, no macrosetae. Left wing 3.57 mm long, it and halter entirely preserved; right wing partially preserved. Vein C ends either at apex of R4 or R5; Sc long, meets C beyond midpoint of wing length, approximately at same level as crossvein r-m. R1 parallel and very close to Sc, with slightly sclerotized, pterostigmatic membrane where they diverge slightly at apex. Base of Rs (before fork of R2+3 and R4+5) short, Rs connected to R1 quite distad, at 0.42 complete length of wing. Veins R4 and R5 forked, branches of fork relatively straight (not curved), with R5 distinctively ending at apex of wing rather than below it. Cell d small, distinctively short (length 2.5x greatest width); closed cells m3 and cup present, cell m3 triangular, short branches of M3+CuA1 and A1+CuA2 present. Alula relatively small. Halter relatively short and stout. LEG: [Presumably] hind leg without macrosetae on it; presence of an empodium difficult to discern, but pulvilli well developed. Abdomen: Relatively broad, ending short of wing apex.

Specimen.

MCNA 8833, Spain: Álava: Peñacerrada I, Escucha Formation, Lower Cretaceous (Albian). Specimen lacks a head, and the thorax and abdomen are only partially preserved.

Discussion.

Because of the incomplete preservation, a precise diagnosis and family placement of the specimen is not possible, so we did not provide a name and formal description. There are genera of lower Brachycera in several families that have a venation similar to this fossil, including the closed cell m3. A distinctive feature of the fossil is vein R5 ending at the apex of the wing. This is rarely seen in the lower Brachycera, occuring, for example, in Xylomyiidae and Apsilocephala Kröber, 1914 ( Apsilocephalidae ). Unlike Apsilocephala , which has the branches of R4 and R5 curved, these branches in the fossil are straight. Also, Apsilocephala and most therevids usually have a longer, more slender abdomen (although see Kumaromyia , vide infra), and usually have bristle-like setae on the mesonotum. These features, plus the short branch of Rs and its distal connection to R1 indicate that the fossil is in the Stratiomyomorpha , not the Asiloidea .