Aspartic acid racemization rate in narwhal (Monodon monoceros) eye lens nuclei estimated by counting of growth layers in tusks

Figures & data

Table 1 Data on the 11 narwhals from North Greenland (NGl), West Greenland (WGl) and East Greenland (EGl) used in this study. Note that tusks nos. 4080, 4084 and 953 were received with ca. 5, 6 and 7 cm, respectively, cut off the bases. These missing centimetres are added to the total length of the tusks in the table. Also, it was uncertain whether the neonatal line was present in tusk no. 956 Growth layer group is abbreviated to GLG.

ID no.	Location	Year	Sex	Body length (cm)	Tusk length (cm)	External tusk length (cm)	Length of pulp cavity (cm)	Diameter of pulp cavity (mm)^a	Diameter of tusk (mm)^a	Tusk weight (kg)	Neonatal line present	Tip of tusk present	Base of tusk present	No. of GLGs	Average GLG width (mm)	d/l ^b
4080	Qaanaaq, NGl	2008	Na^c	Na	91.5	62	66	5.5	26	0.47	x	x	–	17	1.84	Na
4084	Qaanaaq, NGl	2008	Na	Na	130	97	107	11	36	1.16	x	x	–	19	1.71	Na
4075	Qaanaaq, NGl	2008	F	430	164	138	155	26	49	1.95	x	x	x	25	1.57	0.05973
4076	Qaanaaq, NGl	2008	M	491	255	Na	255	Na	Na	7.45	–	–	x	60	Na	0.10805
841	Fisher Isl. WGl	2006	M	456	179	145	165	26	58	3.58	x	x	x	31	2.08	0.06914
950	Niaqornat, WGl	2008	M	306	34	13	19	0	12	0.06	x	x	x	5	1.04	0.03561
951	Niaqornat, WGl	2008	M	358	109	81	92	6.84	28	0.79	x	x	x	18	1.67	0.04592
953	Niaqornat, WGl	2008	M	471	201	160	171	18.84	51	2.77	x	x	–	26	2	0.05763
888	Niaqornat, WGl	2009	M	435	181	Na	Na	Na	Na	2.33	x	x	–	24	Na	0.05850
974	Sc. Sound, EGl	2010	M	430	173	137	156	19	46	1.92	x	x	x	19	2.85	0.05287
956	Niaqornat, WGl	2010	M	440	247.5	208.5	245	12	63	6.9	(x)	x	x	70	Na	0.1005

^aMeasured at the melon front.

^b D/L ratios corrected according to regression equations.

^cData not available.

Fig. 1  (a) Root of proximal part of tusk no. 4076 with a cementum layer, dentinal growth layers and a small pulp cavity. (b) Apical tip (distal part) of tusk no. 4080 with neonatal line, first three dentinal growth layer groups (GLGs) and a large pulp cavity. (c) Detail of narwhal tusk no. 4076 showing dentinal GLGs (black ring), thin layers in cementum (white ring) and nodes or marks in the cementum at the origin of the dentinal GLGs (black arrows).

Fig. 2  Narwhal tusk length (cm) versus number of growth layer groups (GLGs). One GLG is assumed to constitute one year of tusk growth.

Fig. 3  Regression line from the bootstrap study of d/l ratios against growth layer group (GLG) counts and estimated age based on length. The slope of the regression line corresponds to twice the racemization rate (2k _Asp) and the intercept corresponds to twice the (d/l)₀ value.