io W. A. SANDS 



PHYLOGENY 



The subdivision of the Nasutitermitinae into two branches at an early stage in the 

 evolution of the subfamily was postulated by Ahmad (1950). His phylogeny was 

 based mainly on the " imago-worker " mandible dentition. A detailed study of the 

 soldier mandibles (Sands, 1957) supported Ahmad's fundamental conclusions, but 

 indicated more frequent occurrence of parallel evolutionary trends. Each of the 

 two branches was referred to by the name of its most primitive genus, these being 

 Procornitermes and Paracornitermes. The genera of the Ethiopian Region are 

 divided between the branches as follows: 



" Procornitermes branch " " Paracornitermes branch " 



Nasutitermes Dudley Eutermellus Silvestri 



Leptomyxotermes gen. n. Afrosubulitermes Emerson 



Grallatotermes Holmgren Postsubulitermes Emerson 



Fulleritermes Coaton V errucositermes Emerson 



Rhadinotermes gen. n. Mimeutermes Silvestri 



Mycterotermes gen. n. Tarditermes Emerson 



Trinervitermes Holmgren 

 Baucaliotermes gen. n. 

 The two branches are, according to Ahmad, characterized by the long straight 

 cutting edge between first and third marginal teeth of the left " imago-worker " 

 mandible, and the narrower angle between apical and first marginal in the " Procorn- 

 itermes branch ", as contrasted with the shorter sinuate cutting edge, and the 

 wider angle between apical and first marginals in the " Paracornitermes branch ". 

 While these distinctions are correct for the species actually chosen by Ahmad to 

 represent the genera, there are many other species belonging to the same genera 

 which do not fit this classification so exactly. 



The two branches appear to have arisen because one of them became adapted early 

 to feeding on soil-humus, and has remained so, whilst the other was less specialised, 

 and its members have diverged to fit many " ecological niches ". It has been stated 

 by several authors including Ahmad that the " imago- worker " mandibles do not 

 exhibit clearly identifiable adaptive characteristics related to the food supply. The 

 grounds for disagreement with this statement will be discussed elsewhere; for the 

 present purpose it is sufficient to note that the most characteristic adaptation of 

 soil-humus feeding termites is the loss of transverse grinding ridges on the molar 

 plates, particularly the right one, and their transformation to crushing cups by the 

 development of rounded flanges on both sides. This occurs convergently in the sub- 

 families Termitinae, Amitermitinae, and Nasutitermitinae, and in the latter is the 

 distinguishing feature of the " Paracornitermes " branch. In some genera the ridges 

 are not entirely lost, remaining as differences in sclerotisation of an otherwise smooth 

 surface (Text-figs. 431-450). 



The " Procornitermes branch " possesses variously modified mandibles, but these 

 always have prominently ridged molar plates (Text-figs. 157-196). 



The detailed aspects of phylogeny can only be discussed tentatively in a study 

 based on species from only one zoogeographical region. The genus Nasutitermes 



