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.

Not so fossil penguin loose in the Georgia Aquarium

Happy Valentines Day from a non-fossil penguin.

Perudyptes – Fossil penguins at the equator!

When penguins at the equator are mentioned, half the time people think it is a joke.  What more ludicrous image than the tuxedoed denizens of the Antarctic ice sheets lounging about with tropical drinks on a sun-baked beach?  In fact, several living species of penguins inhabit equatorial waters today.  The Humbolt penguin (Spheniscus homboldti) occupies the coastlines of Peru, Ecuador and Chile reaching almost to the line, and Galapagos penguins (Spheniscus mendiculus) mock our preconceptions by happily swimming right across the equator daily. The latter are the only penguin species that naturally occurs in the Northern Hemisphere – by about a few hundred yards.

Still, penguins near the equator are remarkable, and still more amazing is the thought of these birds reaching the line during “Greenhouse Earth” conditions.  During the first half of the Cenozoic Era, the world was significantly hotter than today, with global temperatures averaging 5+ degrees  Celsius higher.  Penguins were long thought to have reached  low latitudes only after global cooling during the second half of the Cenozoic, when temperatures began approaching today’s averages.  One fossil changed these theories.

 

Perudyptes devriesi is an amazing fossil because it shows penguins were already thriving in equatorial waters by the middle of the Eocene Epoch, about 42 million years ago.   The penguin itself is quite a gem in terms of preservation quality.  Over 42 million years, a lot of bad things can happen to a fossil and often very little is left by the time paleontologists find it. Salt crystals embedded in bone and matrix, long dormant in the dry climate, begin to erupt from fossils from the deserts of Peru when they come into contact with the more humid air of Lima where the national museum is located.  Aside from the normal chipping away of rock and gluing fragile pieces, fossils have to be soaked in water to dissolve these crystals before they damage the bones.  Luckily, the Perudyptes fossil was rescued just in time. It was collected by Peruvian paleontologist extraordinaire Mario Urbina and studied by a large international team (Julia Clarke, Marcelo Stucchi, Mario Urbina, Norberto Giannini, Sara Bertelli, Yanina Narvaez and Clint Boyd) which I had the privilege to be a part of.

Reconstruction of Perudyptes devriesi diving. Bones are shown in life position (some are omitted due to technical limitiations.

Perudyptes still has its skull (rare in fossil penguins) as well as some major bones of the wing, pelvis and foot.  Such completeness gives us a much better idea of where the species fits in the penguin tree and how it swam and ate.  The genus name Perudyptes means “Peruvian diver”, and the species name devriesi honors Tom DeVries, an invertebrate paleontologist who has done decades of fine work mapping the fossil bearing strata of Peru and studying the mollusks that evolved in the region over the past 50 million years. Perudyptes devriesi would have been close to the size of a King Penguin – larger than most of the penguins alive today, but nowhere near the size of “giant” species like Icadyptes salasi.  I’ll provide more details on the osteology of this penguin a few posts down the road.

The discovery of Perudyptes means penguin spread very rapidly from their ancestral range (probably New Zealand based on the occurrence there of the oldest and most primitive penguin fossils).  In fact, by the end of the Eocene, penguins had reached Antarctica, Australia, and South America – all the major landmasses they now occupy except for South Africa.  This task may have been easier for early penguins than it would be today.  The continents of the Southern Hemisphere were much closer together – Australia and Antarctica were actually still connected.  Later in the Cenozoic, tectonic forces would rift these last remnants of the supercontinent Gondwana apart, with profound climactic consequences and major effects on ocean circulation.  By that time penguins where already well-established throughout the southern oceans.  We don’t know for sure whether they had reached all the minor islands they occupied (except in cases where the island in question had not yet been born out of the volcanic depths), but almost certainly they also had firm foothold on most of the habitable coasts – a fast rise to success.

You can read more about Perudyptes devriesi in the paper below.  More is on the way.  A much longer monograph on the morphology and phylogenetic significance of this species is coming in a few months from Julia Clarke and myself, and will be freely available from the American Museum of Natural History Bulletin.

References: Clarke, J.A., D.T. Ksepka, M. Stucchi, M. Urbina, N. Giannini, S. Bertelli, Y. Naraez and C. Boyd. 2007. Paleogene equatorial penguins challenge the proposed relationship between biogeography, diversity, and Cenozoic climate change. Proceedings of the National Academy of Sciences  104: 11545-11550.