Record Breaking Penguins: The Tallest Penguin Ever?

Which species is the largest penguin ever to have lived?  Well, there may be multiple answers to that question.  Kairuku grebneffi breaks the record for the longest humerus (the main flipper bone).  Measuring 176.6 mm, the humerus of this species narrowly beats the record of  175.8 mm held by Pachydyptes ponderosus since 1930.  On the other hand, the humerus of Pachydyptes ponderosus is almost 50% wider than that of Kairuku grebneffi.  This is really interesting, because it suggest that the enigmatic Pachydyptes ponderosus was a really stout penguin at the the opposite end of the spectrum from the slender Kairuku grebneffi.  In terms of which species is largest, it is quite possible that Kairuku grebneffi was the tallest penguin species ever to have lived and Pachydyptes ponderosus was the heaviest.  It’s note really possible to tell for sure at this point, because Pachydyptes ponderossus is known only from three bones.  Maybe it had wide wings and long legs, maybe it had a stubby bill and a long tail.  We won’t know how the rest of the penguin looked until we find more fossils.  It’s also important to keep in mind that only a fraction of the species that have evolved over the billions of years of Earth history have made it into the fossil record, and only a fraction of these have been discovered.  There may be an even bigger penguin lurking out just under the surface  in the rocks of New Zealand, lying exposed in the remote deserts of Peru, or buried in a layer of ice in Antarctica.

The humerus of Pachydyptes ponderosus compared to that of Kairuku grebneffi (mirrored to aid comparison).