Fossil Collections

Icadyptes montage. A) Icadyptes and a Humboldt penguin (D. Ksepka);
B) Wings of (L-R) Short-tailed Shearwater, Waimanu, Icadyptes, Emperor Penguin
(Ksepka and  Ando 2011); C) Illustrator's interpretation of Icadyptes

The collected fossils of both Inkayacu and Icadyptes are fairly similar, as we would expect with contemporaneous and similarly sized penguins. What exists, however, to tell them apart from one another? The answer, as in any fossil animal, is in the bones. No one knows these fossil penguins better than Daniel Ksepka, now with the Bruce Museum in Greenwich, CT and it is thanks to his tireless study and description of both taxa that we know the key characters of each animal. He had help now and again and the description of Inkayacu was spearheaded by the University of Texas, overall, but much of what has been written about penguins in the past decade or so has been written by Ksepka and his collaborators. In the case of Inkayacu some of the evidence of difference from Icadyptes is actually found in the feathers of the animal. The precise imprints that were made in both the matrix material around the bones is so well preserved that the shapes and sizes of the pigment containing melanosomes has been preserved as well as the shape and size of the contour feathers that covered the body below the flight feathers. An important note of distinction ought to be mentioned here for the less avian-inclined. Despite not flying in the traditional sense, the feathers of the wing that are used in locomotion in penguins are considered flight feathers as they still perform the same role and the style of swimming of penguins is very much like a submarine flight. What is very interesting about the bones of Icadyptes shown here is their fairly obvious resemblance to those of other fossil penguins (Waimanu tuatahi) and extant penguins here represented by an Emperor Penguin (Aptenodytes forsteri). The flipper of Inkayacu is absent some elements, but it also very close in resemblance to extant and other fossil penguins. The skulls are morphologically similar as well, but the flippers are more important in showing that penguins were highly specialized as long ago as these 36 million year old animals. The skull shape had developed multiple times in other waterbirds, making their convergent shape less important for defining what makes a penguin.

From Clarke, et al. 2008

References:

• 1.- Clarke JA, et al. 2007. Paleogene equatorial penguins challenge the proposed relationship between biogeography, diversity, and Cenozoic climate change. PNAS 104 (28): 11545-11550.

• 2.- Clarke JA, et al. 2010. Fossil Evidence for Evolution of the Shape and Color of Penguin Feathers. Science 330 (6006): 954-957. 

• 3.- Ksepka DT and Ando T. 2011. Penguins Past, Present, and Future: Trends in the Evolution of the Sphenisciformes; del libro “Living Dinosaurs: The Evolutionary History of Modern Birds”, editorial John Wiley & Sons.