78 



have any bony zygomatic arches, these structures remain detectable at least by X-ray prior 

 to preparation (Choeroniscus). Only in the extremely long-nosed species of the genus 

 Choeronycteris no zygomatic arches could be found. 



Braiiicase (fig. 56) 



Although cranial modifications with reference to nectarivory predominantly manifest 

 themselves in tlie viscerocranium, m some respects also the braincase of nectar feeding 

 bats is clearly distinguishable from that of other phyllostomids. This is principally due to 

 recedmg significance of the masticatory muscles; as tlie origin of the M. temporalis does 

 not express itself at the vertex of the bone surface any more. 



hi the predominantly frugivorous genus Brachyphylla, a Crista sagittalis is just present to 

 some extent. In all genera of the remaining nectarivorous subfamilies this characteristic 

 lacks in both sexes. 



Tlie Pars petrosa is merely developed (i.e. = in specialized nectar feeders Hke 

 Choeroniscus, the width of the braincase exceeds mastoid width). 



Skull base (fig. 57) 



In most species, the base of the neurocranium and the palate are arranged in an almost 

 parallel way, i.e. there are no angles between both areas. On tlie other hand, the outgroup 

 genera of Phyllostominae and Carollimae, but also Brachyphyllmae and Phyllonycterinae 

 show an inclination of the palate plane towards the skull base. In Choeroniscus and 

 Hylonycteris, there is a striking elevation of the brain capsule against the palate plane 

 (fig.57). Tliis affects measurements of skull height m so far as the slide caliper rests on 

 the hamuli rather than the Bullae tynipanicae. Wliether tliis arrangement is possibly 

 significant for some special form of nectarivory camiot be assessed at the moment. In 

 terms of functional morphology, there is a reference to the position of the mandibular 

 joint. In comparison, the even longer skull of Choeronycteris tends to the opposite angular 

 mclination. Tins might be due to mechanical constraints which require the elongate 

 rostmni bent down in ventral direction to gain stability. 



Tlie convexities of the basisplienoid vary considerably between the species of a genus, too 

 the "basisphenoid pits" represent an essential detemimation feature within the genus 

 Glossophaga (Webster & Jones 1980). 



One of the strangest features witliin the family is the extreme prolongation of the 

 pterygoid processes (hamuli), hi Choeroniscus and Choeronycteris they are extending to 

 the Bullae tynipanicae with lateral widenings. Functional significance may not have been 

 interpreted properly on tlie basis of tlie preserved material. Tlie soft palate is, however, 

 probably prolonged in occipital direction: the hamuh fimction as an abutment (roller 

 bearing) against the tendons of the M. levator velum palatini. Functionally, this might 

 improve efficiency of the swallowing motor apparatus during liigh- frequency tongue 

 movements. 



