A fossil Gymnopternus Loew (Diptera: Dolichopodidae) from the Florissant Beds, Colorado.
Psyche 102(3-4):169-172, 1995.
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A FOSSIL GYMNOPTERNUS LOEW
FROM THE FLORISSANT BEDS, COLORADO.
Australian Museum, College & William Streets Sydney South, NSW 2000 AUSTRALIA
Gymnopternus lacustris n. sp. (Diptera: Dolichopodidae) is described from a compression fossil from the Eocene/Oligocene Florissant beds of Colorado, U.S.A. Gymnopternus has a rich recent fauna in North America, and its fossil presence in these deposits is evidence of the essentially "modern" generic composi- tion of the Tertiary dolichopodid fauna. Early Tertiary lacustrine beds from western North America often contain insects as compression fossils, and the quality of preservation is such that more than 200 insect families have been recorded (Wilson, 1978). Of these Tertiary deposits, the Florissant Beds of Colorado are among the most famous. Although early papers referred to them as Miocene in age, they are now regarded as Early Oligocene or along the Eocene-Oligocene boundary, some 34 million years B.P. (see references in Wilson, 1978). A new species of the family Dolichopodidae (Diptera) from the Florissant Beds is described below.
Genus Gymnopternus Loew
Gymnopternus lacustris n. sp.
Holotype, 0, compression fossil, lacustrine shales; collected by Marion Clare, July 1994, along Grape Creek, north of Florissant Manuscript received 10 October 1995.
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Fossil Beds National Monument, Colorado, U.S.A.; deposited in the United States National Museum, Washington, D.C. (USNM #486681).
Body length, head to apex of abdomen: 3.6 mm; wing length, thorax to apex: 2.5 mm (Figs 1 & 2).
The specimen is laterally compressed and is rendered only by a black film of carbon. The description is based on visible characters and text numbers in parentheses refer to numbers on Fig. 2. HEAD: strong vertical and ocellar setae present; palp (1) ovate with apical seta; antenna (2) with first flagellomere subtriangular, bearing a dorsal, distinctly pubescent arista. THORAX: specimen compressed and somewhat distorted; strong mesonotal (3) and scutellar (4) setae present. LEGS: covered with fine vestiture; femur I without strong setae; tibia I with a distinct row of short dorsal setae (5) along distal two- thirds; femur I1 without strong setae; tibia I1 with distinct mid-dor- sal seta (6); femur 111 with strong anterior subapical seta (7); tibia I11 with row of strong dorsal setae (8), at least along distal half. WING: veins R4+5 and M subparallel to apex; vein M straight, without flexion; crossvein m-cu straight; m-cu/ distal CuA ratio: 2.5.
ABDOMEN: terga with short vestiture; hypopygium (9) subrec- tangular and pedunculate.
Etymology: The specific epithet "lacustris" refers to the pres- ence of this species in fossil lacustrine or lake deposits. This fossil is regarded as a member of the genus Gymnopternus Loew. However, its assignment to a species is rather arbitrary. Most dolichopodid species are defined on diagnostic details of the male genitalic capsule and/or male secondary sexual characters. Compression fossils cannot be described in the detail possible and necessary for recent or amber fossil species. Nevertheless, such Figs. 1-2. Gymnopternus lacustris n. sp.: Fig. 1. Photograph of holotype. Fig. 2. Line drawing of holotype; numbers refer to the text description. Scale line = 1.0 mm.
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fossil species are useful in establishing the age and history of higher taxa.
Some 74 species are recognized in the recent North American Gymnopternus fauna (Robinson and Vockeroth, 198 1). G. lacustris extends the history of this genus back to Eocene/Oligocene time. A distinctive character evident on this compression fossil, the dorsal row of setae on tibia I, is shared with such recent Nearctic species as G. crassicauda Loew and G. opacus Loew. As shown by the Baltic Amber fauna (Larsson, 1978 and per- sonal examination of collections), many recent genera of Dolichopodidae had originated and radiated by the late Paleogene. The presence of Gymnopternus in the Eocene1 Oligocene deposits of western North America is further evidence for the essentially modern character of the Tertiary dolichopodid fauna. [Meunier (see references in Evenhuis, 1994) described Baltic amber fossils as Gymnopternus, but his descriptions are inadequate for generic placement.]
The specimen was given to me for description by M.E. Irwin, University of Illinois, and was originally obtained by J. Fisher of New Mexico State University from M. Clare, a dealer and owner of "Nature's Wealth," Florissant, Colorado. Evenhuis, N.L. 1994. Catalogue of the fossil flies of the world (Insecta: Diptera). Backhuys Publishers, Leiden, 600 p.
Larsson, S.G. 1978. Baltic Amber-a paleobiological study. Entomonograph 1. Scandinavian Science Press, Copenhagen. 192 p. Robinson, H. and J.R. Vockeroth. 1981. Dolichopodidae. p.625-639, In J.F. McAlpine, et al., Manual of Nearctic Diptera Vol 1, Research Branch Agricul- ture Canada Monograph 27, Ottawa, 674 p. Wilson, M.V.H. 1978. Paleogene insect faunas of western North America. Quaest. Ent. 14:13-34.
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