When I considered how I might become a fossil, I mostly thought about the environment I’d have to be entombed in. Desert. Seafloor. Lakebed. These are all pretty typical burial spots that rely on sand, mud, or silt. But I hadn’t yet heard of an even better option when I wrote that piece. As it turns out, entombment in penguin guano is a great way to preserve bodies for thousands of years.
Not just any penguins will do. It has to be Adélie penguins. These amphibious Antarctic birds breed on solid ground – not ice – and carefully select pebbles to create their nests. That’s what traps their guano. As the penguins create a crap cap on their breeding ground, they preserve the remains of their meals and their deceased neighbors within a mix of sand, pebbles, and guano. And while they start off as relatively dark at first, the deep layers of penguin leavings eventually turn pink from the krill in the Adélie diet. In some places, these easily-identifiable layers are over three feet thick.
The Russian biologist E.E. Syroechkovsky named these bird-created deposits “ornithogenic soils” in 1959, and, as University of North Carolina ecologist Steven Emslie and coauthors review in a new paper, the bird dirt has become a treasure trove of information about life since the Ice Age.
While chinstrap and gentoo penguins also create ornithogenic soils, their records pale in comparison to that of their cousin. Adélie penguins have created expansive deposits that go back over 40,000 years in some places, allowing researchers to see how the birds coped with the world’s last great expansion of ice. While Adélie penguins thrived in the Antarctic’s Ross Sea prior to 20,000 years ago, for example, they disappeared as ice overtook their breeding grounds. They only returned when warmer temperatures released their breeding grounds from ice after 18,000 years ago.
And the penguin-made fossil record preserves even finer details. In addition to squid beaks and fish “earstones” that made their way through the avian digestive system, Emslie and colleagues point out, the soils also contain the bodies and bones of the penguins themselves. Some researchers have even uncovered complete penguin “mummies” within ornithogenic soils. The cold, dry conditions at the breeding grounds kept the bird remains in excellent condition, allowing paleogeneticists to extract and study DNA from penguin populations through time. That’s not to mention the additional geochemical insights drawn from some of the fossil and subfossil remains, such as that Adélie and gentoo penguins started eating more krill about 200 years ago – right when whalers and fur trappers slaughtered many of the whales and seals in the southern seas.
Will I ever request that my earthly remains be laid bare on an Adélie penguin colony? Despite the preservation potential, probably not. I’d rather my bones wind up in a museum. But as long as I’m alive, I’ll look forward to the Ice Age details ecologists extract from penguin plop.
[Hat-tip to Jacquelyn Gill for pointing out the Emslie et al. paper to me.]
Emslie, S., Polito, M., Brasso, R., Patterson, W., Sun, L. 2014. Ornithogenic soils and the paleoecology of pygoscelid penguins in Antarctica. Quaternary International. 352: 4-15. doi: 10.1016/j.quaint.2014.07.031