In the first species, the denticulate scale topography acts as diffraction grating generating an iridescent effect 24. The role of microornamentation for generating specific optical properties has been assumed since its discovery 38 and is documented for the indigo snake ( Drymarchon couperi) and fossorial uropeltid snakes. Frictional modulation by ventral microornamentation has been previously shown 52, 53, 54, 55. Its taxonomic relevance 40, 50 and correlations between microornamentation type, phylogeny and animal's habitat 51 have been previously discussed.
West african black rhinoceros skin#
Skin microornamentation has a great variability in the micro- and nanometre range in different snake species 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49. Snake scales feature specific structures at their surface, so called microornamentation 36. Thus, the body contour of the large snake is nearly invisible at the richly-patterned ground of the forest ( Fig. This results in high-contrast to the pale-coloured rest. Intense colouration of black spots is reminiscent of black velvet and purports spatial depth. The West African Gaboon viper′s skin is divided in sharp contoured hourglass-shaped spots in shades of white, brown and black ( Fig. The West African Gaboon viper, Bitis rhinoceros (SCHLEGEL, 1855), is by far the largest of the African vipers 35 and the unique colouration makes this species a master of camouflage among snakes.
Obvious markings, such as geometrical spots, are used to create false edges or boundaries to veil the animal′s true outline and shape (disruptive colouration) or to distract the attention of the spectator to parts of the body (distractive markings) 34. Colour, lightness and colouration pattern can be either adapted to the surrounding (background matching) or arranged to markings that blur during motion in order to match the animal′s surface in locomotion to the surrounding (flicker-fusion camouflage). While colouration in these examples provides conspicuity, colouration is also applied to prevent detection (crypsis) which is a benefit for animals of prey as well as for predators (aggressive mimicry) 7.Ĭountershading cancels out shadows originating from directional light (self-shadow concealment) or obliterates the spatial body form of an animal (obliterative shading). This effect has been convergently evolved in insects, snakes and the feathers of birds 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33. Iridescence, the phenomenon of viewing angle depending colour shifting, is another structural effect based on coherent scattering. In poikilothermic vertebrates iridophores yield hues of white, blue and khaki by the absorption, reflection, refraction and scattering of light 14, 15, 21. In skin and feathers of birds the wide range of colouration can be ascribed to coherent scattering by integumental arrays like spongy keratin matrix 18, 19, 20. The limited range of these pigmental colours is extended with optical effects based on the surface or/and material structure (structural colours) 17. Besides the omnipresent dark melanin also yellowish and reddish pigments are known in many vertebrates, such as reptiles and birds 12, 13, 14, 15, 16. Thus, pigments are widely spread in the animal kingdom. Moreover, colouration enables body temperature control 8, 9, 10, 11. poisonous or venomous prey and is imitated in mimicry 7. Conspicuous aposematic colouration warns predators of inedibility, i.e. Intense colours are a tool in mate choice 1, 2, 3, 4, 5 and communication 6. A view-angle independent black structural colour in snakes is reported here for the first time.Ĭolour plays an important role in animal signalling. The combination of surface structures impeding reflectance and absorbing dark pigments, deposited in the skin material, provides reflecting less than 11% of the light reflected by a polytetrafluoroethylene diffuse reflectance standard in any direction. Velvet black sites demonstrate four times lower reflectance and higher absorbance than other scales in the UV – near IR spectral range.
We revealed a unique hierarchical pattern of leaf-like microstructures striated with nanoridges on the snake scales that coincides with the distribution of black colouration. Our study shades light on micromorphology, optical characteristics and principles behind such a velvet black appearance. Its skin is geometrically patterned and features black spots that purport an exceptional spatial depth due to their velvety surface texture. The West African Gaboon viper ( Bitis rhinoceros) is a master of camouflage due to its colouration pattern.
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