Thursday, February 21, 2013

The stork that is a pelican


In the mixed papyrus swamps of central-eastern Africa, there lives a large bird by the name of Balaeniceps rex: the king whale-head. No one really calls it that, though, as it had a more comical common name: the shoebill, for its beak’s likeness to a large piece of footwear.
The majestic shoebill Balaeniceps rex. Not to be confused with Big Bird. Photograph by Bill Gracey.
The shoebill is a bizarre bird, and while I was originally going to write about just how odd they are, I came across something even more puzzling:  how they are classified and their mysterious evolutionary history.


In 1852, Gould described the shoebill as an “aberrant pelican,” and his claim wasn’t far off from recent studies. Anatomical characteristics led to the placement of the shoebill in an outlying position, sharing a common ancestor with frigatebirds, pelicans, gannets, anhingas, and cormorants. (Mayr, 2003)


The most recent genetic analysis declares that pelicans are, in fact, the closest living relatives of the shoebill. Also included in this monophyly are herons and ibises, and even more distantly, cormorants and storks, though the latter is far removed from the shoebill. (Hacket et. al., 2008) However, the shoebill has only recently become settled, if it is truly settled, in its position in the great ornithological cladogram. Over the years, it has been regarded as closely related to storks, ibises, and New World vultures; monophyletic with herons (which is not far off, according to recent evidence); or offshoots of birds such as gannets, cormorants, and frigatebirds.
Another shoebill. Not much else to say 'bout this one. Photograph by _yasa, from Flickr.

Origins of the stork-pelican
It’s funny; I grew up referring to the bird as a shoebill stork, which is one of the species’ common names, and all these years later I learn that it’s just a big, Muppet-looking pelican. Okay, not exactly. But if shoebills and pelicans share a common ancestor, when did the two groups diverge? Clearly, the body shapes of these two families of birds are extremely different. The disappointing truth is that we don’t know much about the evolution of the shoebills.

Only two relatives of the shoebill are known from the fossil record, both hailing from Egypt: the Oligocene species Goliathia andrewsii, and the Miocene Paludavis. G. andrewsii probably very similar to the modern shoebill; in fact, it may be classifiable as the same genus. It lived in an environment very similar to preferred shoebill habitat today, and shared its wetland home with catfish and lungfish, both preferred prey items. At about the same size as the extant shoebill, and possibly belonging to the same genus, it appears that modern-looking shoebills had already evolved very early in the Cenozoic. (Rasmussen et. al., 1987)

Regardless of its relationships to other birds, one thing is certain: the shoebill is just plain weird. In the next post, we'll examine the behavior and biology of this oddity.

References
Hackett, S.J.; Kimball, R.T.; Reddy, S.; Bowie, R.C.K.; Braun, E.L.; Braun, M.J.; Chojnowski, J.L.; Cox, W.A.; Han, K.-L.; Harshman, J.; Huddleston, C.J.; Marks, B.D.; Miglia, K.J.; Moore, W.S.; Sheldon, F.H.; Steadman, D.W.; Wiit, C.C.; and Yuri, T. 2008. A phylogenomic study of birds reveals their evolutionary history. Science 300, doi:10.1126/science.1157704

Mayr, G. 2003. The phylogenetic affinities of the shoebill (Balaeniceps rex). Journal für Ornithologie 144, 157-175.

Olson, S.L.; Rasmussen, D.T.; and Simons, E.L. 1987. Fossil birds from the Oligocene Jebel Qatrani Formation, Fayum Province, Egypt. Smithsonian Contributions to Paleobiology 62.

No comments:

Post a Comment