Introducing Inkayacu, the First Fossil Penguin with Feathers

Today, an important  fossil penguin discovery was announced in the journal Science.  A new Peruvian penguin has been added to the panthenon of extinct species.  This fossil species was larger than the living Emperor Penguin and lived near the Equator, but that is only a small part of the story.  This fossil is goundbreaking because it is the only fossil penguin ever discovered with preserved feathers. I was fortunate to be involved in this study myself, so it seems like a good opportunity to provide some behind-the-scenes details of how a fossil goes from the desert to the museum to (hopefully) the popular imagination. Over the next two weeks, I’ll be posting some more details of the new fossil and what it means for our understanding of penguin evolution.  Today, we can start with the basics.

Soft tissue structures like skin and feathers are rarely preserved in the fossil record.  Feathers are even more rarely preserved in marine settings – most of the famous feathered fossils like the Liaoning dinosaurs and the Green River birds are from freshwater lakes. Nevertheless, the feathers of Inkayacu are preserved in remarkably good condition.  In the image below, a pair of Inkayacu feathers are compared to a feather from a living Emperor Penguin.   The rachis, or shaft, of the feather is clearly visible and shows the characteristic flattened shape of a modern penguin feather. Even the fine barbs branching off the rachis are visible.  And it doesn’t end there – under a scanning electron microscope, even microscopic melanosomes, intracellular structures that impart color to feathers, are visible.  This reveals a lot about Inkayacu, and we’ll delve into that a few posts down the road.  Note that even though we are dealing with a giant, roughly 5 foot long (swimming length) penguin the fossil feathers shown below are small, like those of living penguins, reaching about 3cm each.

Fossil feathers of Inkayacu compared to a modern Emperor Penguin feather. Note the flattened shape of the feather shaft, the fine preservation of the barbs and the similar darkened tips in two specimens.

The new species is named Inkayacu paracasensis. “Inkayacu” means “Water King” in the Quechua language, while “paracasensis” refers to the Reserva Nacional de Paracas, the national park where the fossil was found.  The nickname of the new fossil has long been Pedro, after a TV character popular in Peru.  The skeleton itself is exquisitely well preserved after lying buried in silt and sandstone in the desert for 36 million years.  In fact, it would be quite a big deal if only the bones were found – giant penguin skulls and skeletons are still very rare, and the skeleton of Inkayacu is remarkably complete.  These bones will be given their due in a follow-up post.

Reconstruction of Inkayacu paracasensis diving. Artwork by Katie Browne.

This is a good opportunity to thank the institutions that supported this research.  Our team is very grateful to the National Science Foundation and the National Geographic Society Expeditions Council for funding the fossil fieldwork in Peru and back in the lab that helped make the Inkayacu project a reality.

To read the full story, follow this link to the original paper: http://www.sciencemag.org/cgi/content/abstract/science.1193604

Reference:

Julia A. Clarke, Daniel T. Ksepka, Rodolfo Salas-Gismondi, Ali J. Altamirano, Matthew D. Shawkey,, & Liliana D’Alba, Jakob Vinther, Thomas J. DeVries, Patrice Baby (2010). Fossil Evidence for Evolution of the Shape and Color of Penguin Feathers Science : 10.1126/science.1193604 (Pre-print PDF at Science Express)

Big Penguin News Coming Soon!

I have an exciting topic to blog about next Thursday.  Make sure to check in then.

Tour of the Penguin Skeleton I: Scapula

Remarkable is a fair way to describe the penguin skeleton.  Each bone seems perfectly molded to the complex mission of the penguin – to swim, dive, scramble across rocks, or catch prey as the situation calls.   One obvious difference between penguin bones and those of other birds is their density.  Pick up box of penguin bones (most species skeletons will pack neatly into the average tennis shoe box) and a box of chicken bones and you’ll instantly notice the weight difference.  Increased density and reduction of air space helps penguins maintain negative buoyancy while diving.  While almost every bone in the penguin skeleton has undergone increased osteosclerosis for density, the shape of each bone also tells its own story.  Some are identical to the comparable element in a “normal” bird, while others would barely be recognized as avian by most non-specialists.

I’d like to review the entire penguin skeleton bone by bone.  This will take a long time – there are over one hundred free elements in the adult penguin skeleton (some are formed by multiple bones that fuse together as the penguin grows).  Let’s start with the scapula, one of the most unusual.

The scapula is commonly known as the shoulder blade in humans.  In fact it is even more blade-shaped in birds.  Most living birds have a scapula that looks somewhat like a curved sword.  The “blade” extends over the front part of the birds back.  The “handle” contacts two other bones, the furcula (wishbone) and coracoid, forming the an opening in between called the triosseal canal.  This canal is very important because the tendon that helps birds lift their wings travels through it.  Lifting the wing is of course part of the wingbeat cycle – up, down, up ,down and there goes the bird through the air.

In volant (flying) birds, the upstroke is really used only to re-position the wing for the next downstroke, which does all of the actual thrust generation to push the bird through the air.  In penguins though, the upstroke is much more important.  Because water is so much denser than air, a penguin can push against the water as it lifts its flipper up.  Therefore, it can generate thrust on both the upstroke and the downstroke.

This high density of water also creates a problem though – it requires a lot more force to flap a flipper in water than a wing in air.  So penguins have maxed out the muscles that lift the wing.  One of these, the scapulohumeralis caudalis, attaches to the scapular blade.  In most birds, this muscle does not have to be very large, so the thin blade provides more than enough room for it to attach.  In penguins, the muscle needs more room and the blade is greatly expanded to accommodate this. A penguin scapula looks almost like a tennis racket, with a normal thin “handle” and a flattened, paddle-like blade region.  Interestingly, the blade is only slightly widened in the earliest fossil species, suggesting that penguins gradually improved their wing upstroke strength over time.

Comparison of the scapula in a petrel ( a close relative of penguins) and a penguin.