Fossil Asilidae 



A total of 39 species of fossil asilid flies are known 

 at the present time, excluding the species Leptogaster 

 erecta Meunier (1906) from Zanzibar copal. Several 

 curious results are apparent from a consideration of 

 these species and genera according to their separate 

 horizons and subfamilies. The final definition of the 

 genera in this family are to a very great extent based 

 on characters other than wing venation, which makes 

 many generic assignments problematical ; but it is upon 

 wing venation that an assignment of fossil flies must 

 be made to the family and to the subfamilies of the 

 Asilidae and this can be done with a high degree of 

 accuracy. Consequently, in the check list of known fos- 

 sil species here presented, I have used the names as- 

 signed by the original authors with comments only 

 where I myself have seen the type specimens. The 

 scope of this generic study does not permit a complete 

 review of the fossil asilid species. 



We know fossil asilids from a single Eocene de- 

 posit, the Green River shales, in which the family is 

 represented by 2 subfamilies, 3 genera and 3 species. 

 Among the 3 genera are 2 forms assigned to extinct 

 genera. One of these is Stenocinclis anomala Scudder 

 from the subfamily Dasypogoninae ; another, Asilopsh 

 fusculus Cockerel! is from the Asilinae. The third 

 species, Asilus palaeolestes Cockerell, was placed by 

 Cockerell in a Recent genus. The scarcity of Eocene 

 records in this family is much to be regretted. 



In the Oligocene, it is notable that six deposits show 

 asilids and that, while only one dasypogonine and one 

 leptogastrine fly are known, no less than seven species 

 of Asilinae in three genera have been described, besides 

 two other examples referred to Asilus Linne without 

 descriptions. 



In the Miocene the subfamily Leptogastrinae is 

 known by two species from two deposits. The Dasypo- 

 goninae are represented by 13 species in 10 genera ; of 

 these generic assignments 6 were made by Cockerell 

 and 3 by James. The Miocene Dasypogoninae all 

 come from deposits in the Miocene Florissant of Colo- 

 rado, with one exception from Radoboj and one from 

 the Ruby Basin of Montana. Also, no less than 12 

 species of Asilinae have been described from two Mio- 

 cene deposits, the Florissant of Colorado and Oeningen. 

 These 12 species of Asilinae, according to their authors, 

 fall into 3 genera. No fossil fly of the subfamily 

 Laphriinae is yet known from any formation. 



In connection with fossil Asilidae it should be noted 



that Bode (1953) has described and figured Eoasilidea 



fragmentosa Bode (1953) which he calls the type of a 



new family, the Eoasilidae. As I have not seen this 



22 



fossil fly I can not comment on it, except to point to the 

 apparently large number of crossveins in both this and 

 his other new genera and families. In many of these he 

 shows 30 or more crossveins. The material was reported 

 from the Upper Lias. 



From the fossil asilids what general conclusions, if 

 any, are we entitled to draw concerning the origin of the 

 family Asilidae? First, we must put the origin of the 

 family before the Eocene. Second, there is, perhaps, an 

 understandable dearth of fossils from the Eocene, but 

 in any case the two principal subfamilies make their 

 appearance in this horizon. There is a less understand- 

 able dearth of fossils of the subfamily Dasypogoninae 

 from the Oligocene, inasmuch as five deposits show 

 asilids with only one representative of the Dasypo- 

 goninae among the eight known species. The greater 

 number of these Oligocene species come from the Baltic 

 amber. This is a medium that could be expected to trap 

 both of these main subfamilies to about an equal extent. 

 Since I believe that we are obliged to accept the conclu- 

 sion that the Dasypogoninae and Leptogastrinae both 

 antedated the higher and more specialized Asilinae, it is 

 all the more peculiar that we have thus far not found 

 Dasypogoninae in abundance as fossils in pre-Miocene 

 formations. The explanation may well be that not until 

 Miocene times were the flies of this family differentiated 

 out into a multiplicity of types. On the other hand, fu- 

 ture collections of fossil flies may increase the number of 

 genera and species known from lower horizons. Thus 

 far, of the known species and genera, it is interesting 

 to note an approximate threefold increase in species 

 from the Oligocene over the Eocene, and a threefold in- 

 crease of species and genera as well, in the Miocene over 

 the Oligocene. 



• In the Dasypogoninae are to be noted three tribes, of 

 which one is the Dioctrini with two species; in this 

 study this tribe is assigned a key position as the most 

 generalized of all tribes within the subfamily. Of the 

 remainder, which fall into the Dasypogoninae, we note 

 that five species occur in the Stenopogonini or "simple 

 tibia" group, with the anterior tibia not spined at apex, 

 and five in the Dasypogonini. Recent genera with non- 

 rotate male terminalia are not represented. Of them 

 all, only the species of Dwctria Meigen represent 

 genera in which the female lacks acanthophorite spines. 



In a comparison of the fossil species assigned to 

 Recent genera and compared with present day forms, 

 we are frequently able to note small but interesting 

 changes in the wing venation suggesting subgeneric 

 status in some cases. I erected a subgenus Eosenopro- 

 sopis Hull (1957) for two of the fossil species of Seno- 



