![]() This is not so when toucans sense danger, they come out of the cavity entrance in a hurry, threatening the enemy only out in the open, if at all. Originally, observers suggested that the bill was a weapon used to defend the nest cavity. Naturalists have long puzzled over the significance of the toucan's large bill. The toe arrangement is zygodactylous, with two toes projecting towards the front and two to the back. In almost all species, male and female look alike only the black toucanets ( Selenidera) and green aracari ( Pteroglossus viridis) are sexually dimorphic. Toucans range in length from 13–24 in (33–60 cm). Another trait characteristic of toucans is a tongue with a bristly or brushy tip. With a downcurved tip and serrated edges. Toucans are characterized by brightly colored plumage and an unusually long and bulky, but very lightweight, bill The mimic benefits because it avoids being attacked by the larger model, while its appearance deters smaller species from trying to share feeding sites. Among toucans, it is apparent in the yellow-ridged toucan ( Ramphastos vitellinus culminatus), which mimics the color and appearance of the larger white-throated toucan ( Ramphastos tucanus cuvieri). Social mimicry is the situation in which two or more distantly related species are more similar to one another than they are to other, more closely related species. Social mimicry, a relatively rare evolutionary event in nature, is seen in this group. The green toucanets ( Aulacorhynchus) are represented by seven species the aracaris ( Pteroglossus) by 12 species the black toucanets ( Selenidera) by six species the saffron toucanet ( Baillonius) is monotypic and in Peters is lumped into genus Andigena the mountain toucans ( Andigena) are represented by four species and the true toucans ( Ramphastos) by 11 species. Species derived from drier biomes later became sympatric (inhabiting the same range but not interbreeding) when tropical forest expanded in Amazonia, forcing the dry forest specialists to adapt to tropical forest or perish. The rapid formation and disappearance of new Pleistocene biomes enhanced speciation rates in this region. Toucan speciation apparently occurred during Pleistocene glaciations (characterized by dry forest expansions) and interglaciations (characterized by tropical forest expansions). Haffer proposed the most widely accepted theory of speciation in toucans, and his model has since been applied to other Amazonian bird groups. The toucans' closest relatives are barbets (Capitonidae), and the two groups are thought to have evolved from a common ancestor in their landmark 1993 study, Sibley and Ahlquist describe toucans as "New World barbets with big bills." Woodpeckers (Picidae) are closely allied to the toucans, which are also similar to hornbills (Bucerotidae), albeit more distantly related. No fossilized remains of this family are known recent remains of a toco toucan ( Ramphastos toco), from the Pleistocene (20,000 years old) have been found, in Minas Gerais, Brazil. The toucans (Ramphastidae) are a very striking group. South America south to northern Argentina Evolution and systematics Predominately tropical and montane rainforest Medium-sized to large birds, instantly recognizable by their strikingly large and colorful bills often associate in small flocks when foraging
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