Levenson, D H, Ponganis, P J, Crognale, M A, Deegan, J F, Dizon, A, Jacobs, G H. (2006) Visual pigments of marine carnivores: pinnipeds, polar bear, and sea otter. Journal of Comparative Physiology A-Neuroethology Sensory Neural and Behavioral Physiology,
192(8) 833-843
Oppermann D., Schramme J., Neumeyer C. (2016) Rod-cone based color vision in seals under photopic conditions.
Vision Research 125:30-40
Griebel U., Schmid A. (1992) Color vision in the California sea lion (Zalophus californianus).
Vision Research 32(3): 477-482
Kirk, E. C., & Kay, R. F. (2004).
The evolution of high visual acuity in the Anthropoidea.
In Anthropoid Origins (pp. 539-602). Springer US.
Warrant E.J., Nilsson D.-E. (1998) Absorption of White Light in Photoreceptors. Vision Res., Vol. 38, No. 2, pp. 195-207. PII: S0042-6989(97)00151-X
Stavenga D., Smits R.P., Hoenders B.J. (1993) Simple Exponential Functions Describing the Absorbance Bands of Visual Pigment Spectra. Vision Res. 33(8) pp. 1011-1017. doi:10.1016/0042-6989(93)90237-Q