MYRICK ET AL.: DENTAL LAYERS IN HAWAIIAN SPINNER DOLPHINS 



sections, cemental GLGs were defined indirectly 

 by comparing them with the pattern and number 

 of cemental GLGs determined in untreated 

 sections. 



Direct Monitoring 



Calculation of depositional rates and calibration 

 and definition of GLGs in dentine and cementum 

 were achieved by comparing tooth specimens con- 

 taining successively introduced labels and/or 

 additional tissue accumulated over the 1-yr period of 

 monitoring. To make determinations, for cases in 

 which labels were not distinct or not successfully pro- 

 duced, the additional tissue was measured from 

 structural landmarks or labels in the extracted series 

 of thin sections. 



RESULTS 



Dentinal labels. — The untreated thin sections for 

 all seven specimens contained multiple labels. Most 

 attempts to match labels with treatments were suc- 

 cessful (Figs. 2-6). However, in four specimens more 

 labels occurred than could be accounted for from 

 clinical records. In the only captive-born specimen, 

 WFP 670, numerous TCL labels were observed (Fig. 

 7A, B), but only three were found to have been caused 

 by intentional therapeutic treatments (Fig. 7D, 

 labels C, F, and G). Labels A and B apparently were a 

 result of TCL impaired to the then-calf through the 

 milk of its mother, who was treated with the drug for 

 two periods while the calf nursed. The other labels 

 appear to have resulted from frequent ingestion of 

 stolen TCL-dosed smelt intended for other dolphins 

 being treated at various times while sharing a com- 

 mon tank with this animal. 



No treatment was recorded for label A found in the 

 dentine of dolphin carcass WFP 669 (Fig. 4A, C) and 

 live dolphin ACM 104 (Fig. 6A, C). Judging from the 

 relative positions of the "A" labels to the other labels 

 for which matches were found with recorded treat- 

 ments, "A" labels were introduced into both 

 specimens at or about their respective dates of cap- 

 ture. It is a fairly common practice in commercial 

 aquaria to give medication (often tetracycline) to 

 newly captured dolphins recovering from stress of 

 capture and adjusting to the captive environment 8 . 



Labels B and G in the dentine of dolphin carcass 

 WFP 671 could not be identified from clinical 

 records (Fig. 5A, C), although the numerous other 



"William A. Walker, Los Angeles County Museum of Natural His- 

 tory, Los Angeles, Calif., pers. commun. 1982. 



labels match well in relative thickness and spacing 

 with the treatment dates for this specimen. 



In teeth of live dolphin ACM 103 the labels were 

 indistinct. The presence of TCL, introduced 

 clinically during three periods of treatment over 2 yr 

 and experimentally at 3-mo intervals in 1980, was 

 indicated only by several areas of hazy fluorescence 

 in the dentine near the pulp cavity. 



Dentinal GLG pattern. — The use of plastic overlays 

 of key labels enclosing 6-mo or 1 -yr segments of den- 

 tine on plain-light photographs of the dentine for 

 each specimen permitted repeated calibrations of 

 the annual dentinal layering pattern for six of the 

 seven specimens (the seventh specimen, ACM 103, 

 had no discrete labels). In untreated thin sections, a 

 dentinal GLG contained four major components 

 deposited in the following sequence: 1) A thin, light 

 (GLG-boundary) layer, 2) a thicker dark layer, 3) 

 another thin, light (mid-GLG) layer, and 4) a second 

 thick, dark layer (Figs. 3A, 4B, 5B, 6B). 



In addition to the four components, many of the 

 earliest deposited GLGs had an infrastructure com- 

 posed of finer alternating dark and light layers. 

 Counts made at 150X under low transmitted light 

 showed that each of these annual GLGs contained 13 

 pairs of fine layers (Figs. 3A, 4B, 6D, 7C). Where 

 layers were sufficiently distinct to be counted be- 

 tween labels (e.g., between label B and M, Fig. 4A, B), 

 counts indicated that each pair |"LML," (lunar 

 monthly layer) Myrick 1980b] represented about 1 

 lunar month. The full complement of LMLs was vis- 

 ible throughout the dentine in the captive-born 

 specimen, WFP 670, i.e., 13 LMLs in each of the first 

 three complete GLGs and 9 in the incomplete fourth 

 GLG (Fig. 7C). In specimen ACM 103, 13 LMLs were 

 observed in the first 12 of the 14.5 GLGs present (Fig. 

 8). But in other specimens, LMLs were clear enough 

 to be counted only in the first five or six GLGs. 



In D/S thin sections, the annual GLG pattern con- 

 sisted of two lightly stained and two darkly stained 

 layers. The thin, light, GLG-boundary layers and 

 mid-GLG layers in untreated thin sections corres- 

 ponded to the lightly stained layers in D/S thin- 

 sections (Fig. 9A, B). LMLs were indistinct in almost 

 all GLGs in D/S preparations. 



Age-specific GLG thickness.— Table 1, showing 

 dentinal GLG thickness measurements made from 

 the most symmetrical side of the tooth of each of the 

 seven dolphins, indicates that for each animal a GLG 

 of a specific thickness was produced that appears 

 to be related to the year of life in which the GLG 

 was formed, i.e., an age-specific GLG thickness. 



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