DOLICHODERUS TASCHENBERGI MAYR 
(HYMENOPTERA: FORMICIDAE) FROM AN EARLY 
HOLOCENE FOSSIL INSECT ASSEMBLAGE IN THE 
COLORADO FRONT RANGE 
By ANDRfe Francoeur* and Scott A. ELiAst 
A paleoenvironmental study of Holocene (Post-glacial) age sites 
in the Front Range of the Colorado Rocky Mountains was begun in 
1981, with the excavation of organic detrital sediments from a del- 
taic deposit at the point where South St. Vrain Creek enters Lake 
Isabelle (Fig. 1). The study site lies in the ecotone between the 
subalpine forest and alpine tundra, and the insect faunal assemb- 
lages from the site consistently reflect past environments that fall 
within the same zone. Sediments ranging in age from 9000 to 7900 
years before present (yr. BP) were analyzed for insect fossils, and 
yielded a total of 138 taxa, dominated by Coleoptera (Elias, 1985). 
A head capsule of a gynomorph of the ant Dolichoderus taschen- 
bergi Mayr was recovered from an interval correlated with a radio- 
carbon age of 7900 yr. BP (Fig. 2). Other ant taxa from this time 
interval include Camponotus cf. herculeanus L., Formica neorufi- 
barbis Emery and Myrmica sp., all of which may be found in the 
forest-tundra ecotonal regions of the Front Range today. In general, 
fossil insect assemblages from this and other high altitude sites in 
the Colorado Rockies suggest that the time interval associated with 
these ant fossils falls approximately in the middle of a two thousand 
year climatic optimum, in which altitudinal tree limit was at least as 
high as it is today (Elias, 1983, 1985). 
The recovered fossil head capsule of Dolichoderus agrees 
obviously with recent specimens of taschenbergi Mayr (Fig. 3.). 
Such characters as the habitus of the capsule, the position, size and 
shape of the eyes, the diverging and widely separated frontal cari- 
nae, the flanges overhanging in part the antennal sockets, the sinu- 
ous anterior margin of clypeus, the absence of sculpture on the 
♦Pure Sciences Department, University of Quebec at Chicoutimi, 555, boulevard de 
l’Universitfc, Chicoutimi, Quebec, Canada, G7H 2B1 
■flnstitute of Arctic and Alpine Research, Campus Box 450, University of Colorado, 
Boulder, Colorado, 80309, USA 
Manuscript received by the editor October 10, 1984 
303 
