Several groups of modern Birds are known to feed by visiting flowers to collect nectar, and in the process serve as pollinators for the plants. Most notable are the Hummingbirds of the Americas, but Sunbirds, Flowerpeckers, Honeycreepers, Honeyeaters, Lorikeets and Hanging Parrots all feed partially or completely from flowers. Identifying such behavior in the fossil record is difficult. Many insect groups known to be exclusively flower feeders appear in the Cretaceous as the Flowering Plants radiated and came to dominate floral communities, and are presumed to have began flower feeding at the same time. This is supported by several cases of Insects preserved in amber with pollen on their bodies. With Birds amber does not help, as no known Birds have ever been found preserved in amber, and all are probably to large to be trapped in this way. The oldest fossil birds that can be confidently identified as flower feeders are Hummingbirds from the Early Oligocene of Europe, which resemble modern forms closely enough that we presume they had similar behavior.
In a paper published in the journal Biology Letters on 28 May 2014, Gerald Mayr and Volker Wilde of the Senckenberg Research Institute and Natural History Museum describe a fossil Bird from the Middle Eocene Messel Shale of Germany, preserved with stomach contents intact, which appears to have been consuming a diet of pollen and (by inference) nectar.
The Bird belongs to the species Pumiliornis tessellatus, which has been described previously from two other specimens, also from the Messel Shale. The affinities of Pumiliornis tessellatus are uncertain. It has been suggested that it is related to either Parrots or Cuckoos, and it probably has no living descendants. Flower feeding is not a total surprise for this species, as it has a long probing beak similar to that of a Sunbird or Hummingbird (although such beaks can also be an adaptation to insectivory).
Skeleton of Pumiliornis tessellatus from the Middle Eocene of Messel with preserved stomach contents. (a) Overview of specimen, framed area indicates position of detail shown in (b). Mayr & Wild (2014).
(b) Stomach contents of Pumiliornis tessellatus. Mayr & Wild (2014).
The nature of the pollen within the stomach of the Bird was not identifiable. This is not altogether surprising, as while pollen has a long and well studied fossil record, this is almost entirely of wind-blown pollen, which relies on high levels of production by the plant, and by its very nature tends to be scattered widely in its environment, while plants using animal pollinators can produce much less pollen, and do not typically scatter it at all.
Details of pollen preserved in the stomach contents of Pumiliornis tessellatus. (a) UV-induced fluorescence stereomicrographs of main area with pollen and (b,c) selected pollen grains; framed areas in (a) indicate the position of the details in (b,c); the arrows in (b) point to the three colpi. SEM pictures of individual pollen grains; panel (d ) is from a sample taken before preparation, and panels (e,f ) are unsputtered details of the fossil slab. Except for the small pollen in (f ), all pollen is of the large type. Mayr & Wild (2014).
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