Stephen Dallon; NHPA 



A roosting little brown bat, below, exposes its daggerlike teeth, 

 evolved for crunching the exoskeletons of insects. Right: A mouse 

 fieesfrom a dive-bombing false vampire bat, a Southeast Asian 

 species. Bats that feed on small mammals have stronger wings tlian 

 do insect-eating bats but are less versatile aerial acrobats. 



Wayne Lankinen; Bruce Coleman. Inc. 



about thirty-five days after fertilization. At 

 this stage, the cartilaginous model for the 

 entire skeletal system had already formed. 

 In fact, some calcification had begun in the 

 lower jaw (dentary) and collar bone (clav- 

 icle), as indicated by their absorption of 

 red stain. The embryo's eyes, which had 

 long been apparent as small black dots, 

 now appeared as larger, hollow spheres. Its 

 mitten- shaped, cartilaginous hands with 

 incipient models of each finger were also 

 visible. The hand was about one-third the 

 size of the head, which is about average 

 for many mammaUan species at this stage. 

 No features indicated that this embryo was 

 to become a flying mammal. 



Only near the beginning of the third 

 trimester, about forty days into gestation, 

 did the fetus begin to appear distinctly 

 "batlike." As development continued, the 

 fingers grew at an accelerated rate that 

 outpaced that of the body — the first indi- 

 cation of the formation of wings. We could 

 now see bone at the centers of the hmbs; it 

 would continue to be deposited outward 

 toward both ends, which is typical for 

 mammals. At this stage, we also saw cal- 

 cification of the cartilaginous ribs, scapula, 

 and the spine. 



Dramatic changes now took place in the 



fingers, which continued their accelerated 

 growth until, just before birth, they ex- 

 ceeded the length of the forearm. At the 

 end of the third trimester, the feet were al- 

 most fully developed; the toes and thumbs 

 had grown claws. These little hooks will 

 allow the juvenile bat to cling to its 

 mother's fur immediately after birth. In a 

 few more days, a newborn can hang from 

 its feet in the roost while its mother leaves 

 the colony to feed. 



Although the most striking feature of 

 bats is certainly their wings, other anatom- 

 ical features show a unique pattern of 

 growth. The timing of their dental devel- 

 opment, for instance, is different from that 

 of most other mammals. Their highly re- 

 curved milk teeth, which are apparent pre- 

 natally, are probably adapted for grasping 

 the mother's nipple while suckling. 

 Whereas most mammals retain their milk 

 teeth for months, some bat species lose 

 these teeth soon after birth and have adult 

 denfition even before they are weaned. In 

 other species, the process begins before 

 birth. The molars that really grind the 

 food, and do not have milk teeth precur- 

 sors, typically begin erupting in utero. 

 This early start may mean the difference 

 between life and death for young bats by 



52 Natural History 1/94 



