Pollination by a Lesser long-nosed bat  
(Leptonycteris curasoae)
Pollination by animals

Several plants, mostly angiosperms, rely on some animal vector to transport the pollen from the anther of one flower to the stigma of another. These plants are said to be zoophilous. Animal vectors can be insects, like bees, birds, such as hummingbirds and certain bats. Usually, pollen from these species is poorly represented in the fossil record. The reason for this is the specialization of the plants to certain vectors. Zoophilous blossoms are sensitive to particular stimuli from specific animal vectors.
    Pollination by a bee
Only then, when the right visitor behaves properly, will the pollen grains be released and firmly attached to the vector. The grains are later removed by the stigma only. So a problem for the dispersion of such pollen arise; unless the pollen-carrier animal perishes in a water body, or bog, or the whole flower itself accidentally drops in the water, pollen from these species is rarely found in normal deposits. “The more specialized and the more effective the zoophilous pollination, the smaller the production of pollen dispersal units and the fewer units are liberated into the air” (Faegri, 1989).
    Pollination by a hummingbird
However, there are some cases, where the production of pollen is greater, in which there is a lost of a fair amount of grains. These are usually liberated into the air or will fall on the ground. With these conditions, pollen of zoogamous species might commonly be found in sediments.

Wind Pollination