Deeb, S. S. (2010).
Visual pigments and colour vision in marsupials and monotremes.
In Marsupial genetics and genomics (pp. 403-414). Springer Netherlands.
Bickelmann, C., Morrow, J. M., Mueller, J., & Chang, B. S. (2012).
Functional characterization of the rod visual pigment of the echidna (Tachyglossus aculeatus), a basal mammal.
Visual neuroscience, 29(4-5), 211-217.
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