81 



Sexual dmiorpliism: 



- Within the genus PhyUostomiis which was examined as an outgroup, ahnost all skull 

 measures of male P. hastatus - a very large species - range above the female ones. 

 Swanepoel & Genoways (1979) recorded the forearm lengths and seven skull measures of 

 eight individuals collected at different locations showing that the relations between the 

 sexes appeared similar in forearm length. In biological terms, this difference in size may 

 be explained by the social system of these bats; in PhyUostomiis hastatus, the males 

 establish harem groups within territories (Koepcke 1987). 



- In all species of Choeroniscus examined so far, the female length values of the skull 

 exceed those of the males in a statisticaUy significant way. Probably, this difference in 

 size allows these bats to utilize their resources in a more efficient way, as they live in 

 very small family groups (Koepcke 1987). Though the rain forest teems with chiroptero- 

 phile flowering plant species, they occur in quite low density. Probably it is only due to 

 slightly diverging niches that both sexes may survive sharing the same habitat. Appro- 

 priate evidence is, however, still to come. It is quite as probable that body size is deter- 

 mined by social factors rather involving the females. 



- The only measured male of Lonchophylla robusta is definitely larger than all the female 

 individuals - unhke smaller species of the genus where the females are larger, hi L. 

 handleyi which grows even a bit larger, the data of the males exceed those of the females 

 in 12 of 17 parameters on the average, but based on the available sample this could not be 

 secured statistically. 



Females larger than males are not unconmion among bats. This may be a response to the 

 increased energetic demands of flight in pregnant females (Myers 1978; Williams & 

 Findley 1978). Williams & Findley (1978) however suggested other factors like thermore- 

 gulation and fat storage might be more important determinants of body size of females 

 than adaptations to flight (Sahley et al. 1995). 



Skull proportions 



An account of both, the absolute size relations and adaptive degree of the species 

 examined, gives the sunmiary of measurement relations of tlie 'Results': this refers to 

 rostrum length and gives evidence of decreasing functional significance of the masticatory 

 apparatus. 



1) Proportions of total skull length to length of the palatea: Although palate length is a 

 part of total skull length, it remams a useful measure for recording the size of the visceral 

 skuU. 



Both phyllonycterine genera (Phyllonycteris and Erophylla) perform an even higher 

 quotient (= shorter bony palate) m tab. 5 than the outgroup (Carollia). Here, there must be 

 considered that both genera have a V-shaped edge of the palate riuming at a very acute 

 angle and thus affecting the value in this parameter (but not total rostnmi length). 

 Furthermore, this ranking essentially represents the degree of specialization witliin the 

 nectar feeders: Lionycteris and Glossophaga / Monophyllus proved to be basal forms in 

 this respect, Choeroniscus and Choeronycteris the most speciahzed ones. 



2) Total skull length to length of upper tooth row: Some aspects in dentition which cannot 

 be explained exclusively by rostnmi prolongation prove inconvenient: the nmiiber of teeth 

 varies considerably among the genera (cf. dental formulas). In the course of rostnmi 

 prolongation only the distance between the postcanine teeth is enlarged in all long-headed 

 species, but the measured length may consist of just four to six teeth. 



