76 



or possibly just stabilizing the closed jaws against distortion when the canines interlock. 

 Freeman (1995) states a considerable tootli-on-tooth wear (thegosis) on the anterior surface 

 of upper canines in nectarivoroiis microchiropterans. This is interpreted as indicator for 

 tight embracement of lower canines by the upper ones to support the jaw during the rapid 

 movement of the tongue during feeding. 



Premolars 



Within the Lonchophyllinae, Lionycteris still bears very strong premolars resembling 

 canine teeth. In Brachyphylla, the posterior upper premolars also are of similar relative 

 size to the canme tootli, tlie anterior one, however, remaining very small as specific for 

 this genus. In the comse of further specialization the premolars become tricuspid, moving 

 apart widely as the jaw bone prolongates. Only in Anoiira - unique among phyllostomids - 

 there are three premolars on each side of the upper jaw. Hiis situation represents a 

 virtually reverse evolutionary trend and possibly originated from a secondary doubhng of 

 the anterior premolars (Pliillips cited by Koopman, pers. conmi. 1991). Tliis secondary 

 replenislmient of tlie gap between the upper canine tooth and the upper P-^ having 

 developed in tlie course of rostrum prolongation may derive its ecological significance 

 from the high percentage of insect food which has been reported for tliis genus. 



Molar teeth 



Considerable changes occurred in the molar teeth: whereas Glossophaga and Lionycteris 

 still show the dilambdodont profile of the masticatory surface typical of insectivorous bats, 

 Choeronisciis, Hylonycteris and Choeronycteris hardly have any crown cusps nor W- 

 shaped ectolophs. 



With increasing jaw length, the molar teeth increasingly moved apart, too. Thus, in the 

 very long-muzzled forms there is apparently no masticory function any more. Furthermore, 

 the crowns are not only narrow in top view, but also hardly project beyond the gums. The 

 masticatory surfaces are largely reduced; leaving only few pointed cusps (premolarifomi) 

 with a physiological value on wliich we only can speculate. Tliey appear of very little use 

 in food preparation and do not seem to be essential for a nectarivorous way of hfe. 



Rostrum 



Within the PhyUostomatidae, tlie specialized nectar feeding bats of the New World are 

 characterized by a prolongation of the visceral cranium mvolving the maxillaria, nasalia, 

 palatina, the vomer and the mandibulae. 



Tlie degree of tliis prolongation varies considerably between single species and may thus 

 be considered an evidence of the degree of feeding specialization. Species preferring 

 varied diet like Glossophaga or Lionycteris have shorter rostra tlian highly specialized 

 nectar feeders like Choeronycteris. 



Within a genus these proportions are also influenced by body size of the species. Smaller 

 species showing comparatively larger braincases and shorter jaw lengtlis, respectively. In 

 this case, the constmction prmciples are just the same despite their differring proportions. 

 Differences in proportion are fomid in closely related taxa (subspecies, species) whereas 

 different construction prmciples occur beyond the species level. 



In contrast to the short viscerocraniimi of the predominantly frugivorous genus 

 Brachyphylla, the Pliyllonycterinae {Erophylla and Phy lionycteris) were subject to a 

 moderate muzzle prolongation as they specialized in nectarivory. Tlie situation is the same 



