Davies, W. L., Carvalho, L. S., Cowing, J. A., Beazley, L. D., Hunt, D. M., & Arrese, C. A. (2007).
Visual pigments of the platypus: a novel route to mammalian colour vision.
Current biology, 17(5), R161-R163.
Deeb, S. S. (2010).
Visual pigments and colour vision in marsupials and monotremes.
In Marsupial genetics and genomics (pp. 403-414). Springer Netherlands.
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