The Largest Penguin Ever?

What was the biggest penguin ever?  It’s a popular question.  Today, as every schoolchild knows, the largest penguin is the Emperor Penguin.  That species measures about 3 feet tall, when standing with its feet flat and it head at resting posture. We already know that some extinct penguins got much bigger.  But, paleontologists are not certain which was the largest ever. Two contenders are Anthropornis nordenskjoeldi and Pachydyptes ponderosus.  The scientific names of these penguins reference their mighty stature.  Anthropornis translates to “man bird” and Pachydyptes to “stout diver”.   Sadly, only isolated bones have been found from the two species.  Yet there is no denying they were tremendous birds – compare the major wing bone of Pachydyptes to a typical penguin below.

Humerus (wing bone) of the giant penguin Pachydyptes ponderosus compared to the humerus of a typical living penguin.

Extrapolating the total size of an extinct animal from a few bones is a  real challenge. Despite the impressive size of the bones we have found so far, it is not even clear whether either of them was the biggest penguin of all time.  Part of this issue depends on what we mean by “biggest”.   The tallest and heaviest species within any given clade of animals is not necessarily the same – just think of the tallest and heaviest land mammals alive today – the giraffe and an elephant.  If we go by the length of the humerus (the major bone of the flipper), there are actually penguins out there that would come out a few millimeters ahead of Pachydyptes.  But if we go by the length of the coracoid (a bone of the shoulder girdle), Pachydyptes wins hands down against all other penguins.

The proportional differences between a fossil penguin and the average living species are not as extreme as those between an elephant and a giraffe, but there is a lot of uncertainty. For example, if we compare the wing bones of Pachydyptes to an Emperor penguin, they are about 35% longer but almost twice as thick.  It gets even more complicated when we see that the shoulder girdle bones are only slightly longer but also a different shape.  So we can’t just scale directly – we need to find a complete skeleton to truly understand what is going on. Even amongst living penguin species the relative proportions of the beak, legs, flippers and trunk vary fairly widely and fossil penguins do not always fall even within that range.  Was Anthropornis taller because it was perched on long, slender limbs?  Was Pachydyptes ridiculously short-necked with thick, short legs?  Dimensions from the bones we have give us some clues as to standing height of the largest penguins, but without the hindlimb, pelvis and vertebral column there is always going to be a wide range of error.

Still, we can get to a ballpark total. George Simpson did some back-of-the-envelope equations back in 1946 and put the tallest penguins at around 5 feet tall.

Simpson's (1946) line-up of penguins showing the rough size of the largest fossil species (B), some more modest fossil species (C,E) and the living Emperor Penguin (D) and Galapagos Penguin (F). As noted by Simpson (1946), these are not meant to be exact reconstructions of particular fossil species, but rather to give an idea of scale.

Weight is a separate issue from height.  Personally, I have little doubt that Pachydyptes was the heaviest fossil penguin (at least the heaviest discovered so far).  The wing bones are just so wide compared to other similarly sized species that the animal, from little we know of it, appears to have been extremely stocky.  Imagine the Chicago Bears defensive lineman William “The Refridgerator” Perry with flippers.  Piotr Jadwiszczak used regression equations relating the limb bone proportions of living penguins to mass, and estimated the largest species would tip the scales at over 170 pounds.  Another rough estimate for the present, but nonetheless evocative. Pack this mass into a 5 foot frame and you have penguin that could bowl over pretty much anything in its way.

So the answer to the opening question is – we don’t know what the biggest penguin species is, or exactly how big it got.  This is no reason to become frustrated.  It’s one more question about extinct birds we can seek an answer to by continuing to search for new fossils and better methods of reconstructing total mass from the dimensions of individual bones.