Table 2. Infrared peak assignments for Sepia officinalis melanin, extant Marabou stork and White-naped Crane feathers and fossil Gansus yumenensis feathers MGSF317 and MGSF318.

Functional group	Bond	Wavenumber range (cm-1)	Intensity	Mode of vibration	MGSF318	MGSF317	Marabou stork feather (black)	White-naped Crane feather	Sepia melanin standard
Silicon compounds (Si-O)	Si-O	1100–1000	Strong	Stretching	—	—	X	X	—
	Si-O	990–945	Strong	Stretching	—	—	X	X	—
Ketone (C-(C = O)-C-OH)	C = O	1640–1540	Strong	Stretching	X	X	?	?	X
Carboxylic acid (COOH)	C = O	1600–1560	Strong	Asymmetric Stretching	X	X	?	?	X
	C = O	1420–1400	Strong	Symmetric Stretching	X	X	?	?	X
Hydroxyl (R-OH)	OH	3300–3280	Strong	Stretching	X	X	X	X	X
	OH	1450–1330	Medium	Deformation	X	X	X	X	X
	C-O	1100–1000	Strong	Stretching	X	X	X	X	X
Secondary amine (CH-NH-CH2)	N-H	3500–3300	Weak	Stretching	?	?	?	?	?
	N-H	1650–1550	Variable-weak	Deformation	?	?	?	?	?
	C-N	1191–1171	Weak	Stretching	?	?	?	?	?
	N-H	750–700	Strong	Wagging	?	?	?	?	?
Alkenes (C = C)	CH	3080–3000	Medium	Stretching	—	—	X	X	?
	CC	1690–1640	Medium	Stretching	—	—	X	X	?
Alkanes (R-CH3)	CH	2972–2952	Strong	Asymmetric stretching	—	—	X	X	—
	CH	2882–2862	Strong	Symmetric stretching	—	—	X	X	—
	CH	1475–1435	Medium	Asymmetric deformation	—	?	X	X	—
	CH	1380–1375	Medium	Asymmetric deformation	?	?	X	X	—
Alkanes (R′-CH2-R″)	CH	2936–2916	Strong	Asymmetric stretching	—	—	X	X	—
	CH	2863–2843	Strong	Symmetric stretching	—	—	X	X	—
	CH	1485–1445	Medium	Deformation	—	?	X	X	—
Amides (-CO-NH-C)	NH	3320–3270	Medium	Stretching	—	—	X	X	—
	C = O	1680–1630	Strong	Stretching	—	—	X	X	—
	CNH	1570–1515	Strong	Combination	—	—	X	X	—
	CNH	1305–1200	Medium-weak	Combination	—	?	X	X	—