Anthrax dentoni Lewis, 1969

Greenwalt, Dale E., Wingerath, Jonathan G. & Evenhuis, Neal L., 2015, Two new and disparate fossil bee flies (Bombyliidae: Anthracinae) from the Americas and reassessment of Anthrax dentoni Lewis, 1969, Palaeontologia Electronica 24 (1), pp. 1-10 : 6

Anthrax dentoni Lewis, 1969 , reassigned

( Figure 4 )

Holotype. UCM # 28427 ; housed in the University of Colorado Paleontology Collection, Boulder , Colorado.

Type Horizon. Latah Formation, Miocene.

Type Locality. Deep Creek Canyon, Spokane, Washington

Remarks. Collected from the Early to Middle Miocene Latah Formation in northwestern Idaho, Anthrax dentoni was described by Lewis (1969) based on a single incomplete wing fragment. Although the Latah Formation was laid down over a period of approximately 9 million years (21.3– 12.1 mya), Lewis (1969) reported that this fossil was collected from the Deep Creek Canyon locality northwest of Spokane, Washington. K-Ar dating of basalt immediately above the fossiliferous sedimentary rocks at Deep Creek Canyon has provided a date of 13 +/- 0.5 mya ( Gray and Kittleman, 1967). Assignment of the fossil to the genus Anthrax was based on basal pigmentation, the origin of R 2+3 at right a right angle to Rs, the shape of the second posterior cell, the presence of adventitious veins, and the “stub of the vein above the r-m cross-vein.” Upon re-examination, this fossil consists of the partial venation of two wings, one superimposed on the other ( Figure 4 ). The venation pattern of the major wing fragment is presented in Figure 4 . Lewis’s “Vein R 1 incomplete, forming two separate adventitious veins rather than one continuous vein” evidently refers to vein R 2+3, not R 1; the two separate adventitious veins are actually veins from two different wings. The upturned end of the preserved portion of R 2+3 would be unique within Bombyliidae ; however, the specimen is very 3-dimensional, and redirection of the vein appears to be an artifact of the insect’s burial in relatively thick clastic sediments. The grain size of the tuffaceous matrix of this specimen is commonly several microns in diameter with crystals of mica as large as 65 P in length. The origin of R 2+3 is at a right angle to Rs and is in-line with r-m, identifying this specimen as a species in the subfamily Anthracinae . Given the essential absence of vein M 2, it is impossible to discern the shape of cell m 1. There is a very tiny portion of sclerotized vein basal to the origin of M 2 that may be a remnant of a spur vein, but its connection to m-cu is not preserved. Vein A 1 is also not preserved and the specific veins that make up what appears to be the apical venation of a second wing cannot be identified. The pigmentation of the anterobasal half of the wing, the particularly heavy areas of pigmentation at r-m ( Figure 4 ), the base of the 4th posterior cell, the origins of Rs and R 2+3 and, to a lesser degree, the terminus of m-cu, are found in a number of bombyliid subfamilies. It is impossible, however, to assign this specimen to a specific tribe, let alone genus, within Anthracinae . We, therefore, assign Anthrax dentoni to Anthracinae incertae sedis.

Figures

FIGURE 4. Anthrax dentoni Lewis, 1969, UCM # 28427. 1. Photograph of the fossil. 2. Line drawing of venation. Scale bar equals 1 mm.