MYRICK ET AL.: DENTAL LAYERS IN HAWAIIAN SPINNER DOLPHINS 





FIGURE 11.— Cementum of dolphin carcass WFP 670 tooth in de- 

 calcified and stained thin section. The number of dark layers is eight, 

 about double the age in years of this captive-born specimen (150X, 

 plain transmitted light). 



presented in Table 2. Although distinct labels were 

 not always successfully introduced, dentinal and 

 cemental GLGs continued to be accumulated at a 

 uniform rate of one per year. A comparison of 

 accumulated dentine and labels in the first two 

 extracted teeth of specimen ACM 106 (Fig. 12) 

 showed two experimental treatments and one 

 (unscheduled) clinical treatment accounted for in the 

 second tooth (Fig. 2A-C). Specimen ACM 103, in 

 which premonitor labels were indistinct, showed no 

 experimental labels but clearly showed continued 

 accumulation of dentine, the third extracted tooth 

 having added about one GLG over the 1-yr period. 

 No experimentally introduced labels were observed 

 in the (less sensitive) cementum in any teeth of the 

 three animals, but cemental deposition of about one 

 complete GLG occurred in each animal for the period. 



Seasons of birth. — By determining the dates of key 

 dentinal labels introduced at or near the thin, light 

 component layers of GLGs and by noting the approx- 

 imate time of formulation of component layers in the 

 teeth extracted during the monitor period, it was 

 found that GLG-boundary and mid-GLG layers were 

 formed at about 6 mo intervals. In five specimens, 

 GLG-boundary layers were deposited in or about 

 August and the mid-GLG layers were deposited in or 

 about March. In the two other specimens the timing 

 was reversed, i.e., GLG-boundary layers formed in 

 March, mid-GLG layers in or near August, Proceed- 

 ing on the assumption that the timing of layer forma- 

 tion (determined from the labeled or monitored 



Table 2.— Results of examinations of teeth extracted from three live Hawaiian spinner dolphins, 

 Stenella longirostris , over a 1-yr period monitoring accumulation of layers and labels. GLGs = 

 growth layer groups. 



Unscheduled medical treatment 1 8 d in duration. 

 Not examined because of poor preparation of section. 

 3 Cementum showed a number of GLGs equal to that of the dentine as well as half that of the dentine. 



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