Icadyptes salasi – the giant spear-billed penguin

This post is dedicated to profiling one of the most impressive fossil penguins yet discovered: Icadyptes salasi – a giant, spear-beaked penguin from the Eocene.

Peruvian paleontologists discovered the first Icadyptes specimen in marine sediments from the Otuma Formation, deposited about 36 million years ago.  The name “Icadyptes” refers to the Department of Ica, the Peruvian state where the fossil was found and “salasi” honors Rodolfo Salas, a renowned Peruvian paleontologist.  Tiny shells from pelagic planktonic organisms and scales from fish related to anchovies and sardines show us that this penguin was buried in relatively deep waters off the ancient shoreline of Peru.  The penguin may have been foraging for prey when it died, or the carcass could have drifted out from shallower waters and then sank to the bottom. Because the bones are beautifully preserved and many still connected as in life, there was probably not a very long interval between death and burial.

For a long time, paleontologists have known at least some fossil penguins had long, strongly built beaks quite distinct from the generally stubby bill of most living species.  Bits and pieces of penguin skulls had been recovered from rocks in Antarctica, New Zealand and South America.  Icadyptes is important because it provides the first complete example of one of these spear-beaked penguin skulls.  Penguin bones are pretty resistant to destruction compared to typical birds bones, because they are extremely solid (unlike the hollow bones of “normal” birds like gulls or pigeons).  This has resulted in thousands of penguin bones making it into the fossil record.  But most of these bones are from the flipper or hindlimb – more delicate parts of the skeleton such as the skull and the sternum (breastbone) are frequently lost even in the best-preserved specimens.  So until Icadyptes was discovered, we had little idea what the skull of a giant penguin looked like.

Incredible might be the best word to describe it.  The beak is remarkably long, making up nearly two-thirds of the skull.  In terms of construction, it really is more like a spear than a modern penguin beak.

Many of the skull bones that remain separate in living penguins – such as parts of the premaxillae and palatines – are fused together into a solid structure.  Rather than having a hooked tip like the beak of modern penguins, the beak ended in a point.  Finally, the texture of the beak suggests the soft tissue overlying the bone was of a different form than modern penguins.  Today’s penguins have a very thick outer coating – the rhamphotheca, that covers their beaks.  This makes the beak thicker than would be obvious from the bony portion alone.  Icadyptes has unusual texturing on the bony beak, a network of shallow grooves for the blood vessels that nutrify the rhamphotheca.

This patterning is almost identical to the patterning in living frigatebirds, boobies and gannets – all birds with a very thin, layered, tightly fitted rhamphotheca.  Impressions on the bone thus suggest Icadyptes may have had a similar beak covering – a thin sheath rather than a thick horny covering.
Together, all of these features strongly indicate a unique feeding strategy for Icadyptes. Storrs Olson and Andrzeg Myrcha hypothesized that giant penguins probably fed by spearing prey, rather than capturing prey between the upper and lower jaws.  Icadyptes supports this idea – this penguin surely struck fear into Eocene fish and squid.

One final revelation from the Icadyptes holotype specimen is that although the beak was very long, the skull as a whole was disproportionately small compared to the total body size.  Because the hindlimbs and most of the vertebrae are missing, it is impossible to precisely reconstruct the total size of Icandyptes.  We do now, however, that it was far larger than even the Emperor Penguin, probably close to 5 feet standing higher and significantly heavier than a similar sized human.  Skull length is easily outstips that of even the largest living penguins, but the difference between the flipper bones is even greater.  With the small head atop the bulky body, Icadyptes probably looked like a linebacker penguin without its helmet.