Functional cranial analysis of large animalivorous bats (Microchiroptera)

Abstract

Large animalivorous bats include carnivorous, piscivorous and insectivorous microchiropterans. Skull proportions and tooth morphology are examined and interpreted functionally. Four widefaced bats from four families are convergent in having wide skulls, large masseter muscle volumes and stout jaws, indicating a powerful bite. Three of the four also have long canine teeth relative to their maxillary toothrows. Carnivorous bats have more elongate skulls, larger brain volumes and larger pinnae. The wide-faced bats are all dral emitters and have heads positively tilted relative to the basicranial axis. The carnivorous species are nasal-emitting bats and have negatively tilted heads. The orientation of the head relative to the basicranial axis affects several characters of the skull and jaws and is not correlated with size. The speculation that the type of echolocation may be more of a determinant of evolutionary change than the feeding mechanism is addressed. Wide-faced bats are thought to be capable of eating hard prey items (durophagus) and are probably nondiscriminating, aurally less sophisticated insect generalists while the carnivorous and nondurophagus insectivorous bats may be more discriminating and aurally more sophisticated in what they eat.

Call Parameters and Facial Features in Bats: A Surprising Failure of form Following Function

“…As in Freeman (1984Freeman ( , 1988 we used the sum of the natural logs of length, width, and height of head to cslinlatc head volume and thus, size of bat. Natural logs of all but one (angle of pinna) facial measurements were regressed against this cotnposite size character (SIZE) to determine whether facial measurements were correlated.…”

“…(1993) found no significant correlations between pinnal measurements and echolocation paraineters across families. Obligatory carnivorous bats, all nasal emitters, were found to have larger ear areas than oral emitting animalivorous bats (Freeman, 1984). Henson (1970), after reviewing several studies on the role of the pinnae in bats, concluded that the pinnae's main f~lnction was to increase the directionality of the sound reception system.…”

“…The need for directionality of sound reception increases with increasing frequency (Obrist et al, 1993). Ears set more caudally on the head and partially facing laterally (outward) aide in the collection of faint high or low frequency echoes (Fenton, 1984;Freeman, 1984;Bruns et al, 1989;Obrist et a/., 1993). The ridges on the inner sul-face of the pinna are thought to reflect sound that then enters the e x canal after the original echo and could help the bat dete~mine the vertical direction of the sound source (Lawrence and Simmons, 1982).…”

“…The noseleaf in nasal emitting bats and the mouth <and lips in oral emitting bats has been demonstrated to have different patterns of sound emission (Griffin, 1958;Simmons, 1969;Hartley and Sutllers, 1987). Freeman (1984) reported that heads of oral elllitters are positively tilted relative to the basicrslnial axis while heads of nasal emitters are ~legatively lilted. This tilting is tlloughl to cause the nasal region of nasal emitters to point directly forwzu-d during flight and affects several chwacters of the skull uncl jaws independently of the bat's size.…”

Morphology of the axial skeleton of seven bat genera (Chiroptera: Phyllostomidae)

“…This scarcity of studies on postcranial elements is surprising because bats are considered as a model for the study of the anatomy for the great diversification in their trophic niches, which has led to the development of many investigations about variations in the shape of the skull, mandible and teeth, particularly with regard to the type of food they consume (e.g. Freeman 1981Freeman , 1984Freeman , 1988Freeman , 1995Freeman , 1998.…”