1978] 
Burnham — Social Insects in Fossil Record 
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preservation as fossils and this may explain their absence in pre- 
Cretaceous deposits. 
The first Hymenoptera appear in the Triassic and belong to the 
primitive family Xyelidae (Symphyta). Social Hymenoptera are not, 
however, found in the fossil record until the Upper Cretaceous. The 
ant species discovered in deposits of this age are more primitive than 
any now existing and have been of paramount importance in our 
understanding of ant phylogeny. By the mid-Tertiary, the ant fauna 
was extremely diverse; by the Miocene, the genera were essentially 
modern, and geographic distribution of the ants was apparently 
similar to that of today. 
The Vespoidea although not very numerous in fossil deposits, 
have been found as far back as the Late Cretaceous, represented by 
one specimen assignable to the Masaridae. The presence of several 
vespoids in Eocene deposits strongly supports the possibility that 
social wasps evolved during the Late Cretaceous or Early Paleocene. 
Apoidea extend into the fossil record only as far as the Oligocene, 
although it is speculated that they may have evolved much earlier. 
This is suggested by the fact that the bee fauna was essentially 
modern by the end of the Oligocene and also because the inter- 
dependence of angiosperms and bees suggests a co-evolutionary 
relationship beginning sometime in the Cretaceous. 
Any discussion of sociality in the geological past must necessarily 
involve a certain amount of speculation. Morphological characters 
play an essential role in the analysis of an insect’s social status, an 
example of this being the presence of the humeral suture in 
Cretatermes. In those social insect groups possessing very little 
morphological variation between castes, recognition of such social 
distinctions in the fossils is virtually impossible. It is generally 
assumed that extinct species belonging to extant genera possessed a 
similar type of social behavior in the past as is exhibited by the 
group today. To speculate further about the social habits of fossil 
insects is simply not possible. The mechanisms behind the evolution 
of eusociality in the insects remain unknown, yet the success of this 
form of social behavior is unquestioned. Only the recovery of 
additional material will provide evidence to further elucidate our 
understanding of the paleontological record of these insects. 
As the record now stands, it is possible to state with a fair degree 
of certainty that insect sociality had evolved by the middle of the 
Cretaceous and perhaps much earlier. 
