Reading the Mind of the Oldest Penguin

The fossil skull (left) and a virtual endocast (right). Figure from Proffitt et al. (2016).

Today is World Penguin Day, which makes a good excuse to catch up on fossil penguin blogging. Recently, James Proffitt and colleagues published a study on fossil penguin neuroanatomy. As we’ve discussed previously, the brain morphology of extinct animals can be reconstructed by computed tomography (CT) scanning, which allows researchers to map out the volume and shape of the brain based on the cavity it once occupied in the skull. This paper provides the first look at the neuroanatomy of the early penguin Waimanu.

Waimanu is the oldest reported penguin taxon. It is known from Paleocene rocks in New Zealand, where two species have been discovered (Waimanu manneringi and Waimanu tuatahi). The skull that was scanned for this study belongs to the genus Waimanu, but whether it represents one of the two known species or a third new species has not yet been untangled.  Even though Waimanu is a very early penguin, probably representing a point in the evolutionary history of penguins just a few million years after the loss of aerial flight, it already shows many of the features that are typical for penguin brains. These include the widening of the cerebellum, and the lack of any impressions of cerebellar folds on the endocast (interestingly, modern penguin brains do have cerebellar folds like other bird brains, and it has been suggested that the lack of folds on the endocast is due to the “cushioning” of the brain by meningeal tissue).  On the other hand, Waimanu is primitive in showing weak development of the “Wulst”, a structure associated with complex visual processing and other functions. The Wulst becomes expanded later in penguin evolution, as seen in some of the endocasts I have studied from Eocene and Miocene penguins.

An evolutionary tree mapping endocast shape in aquatic birds.  Figure from Proffitt et al. (2016)

These new data let us push deeper into the history of penguin brain evolution. As we get closer and closer to the loss of aerial flight by probing deeper down the trunk of the tree, it will be interesting to see when some of the “penguiny” brain features that are already present in Waimanu first arose.  As a whole, endocast studies of penguins are a great example of how new research becomes possible with new technology. Five years ago, there were no fossil penguin endocasts at all, and today we have five and there are plenty of additional fossils that have already been scanned or are waiting patiently for their turn in the CT lab. Perhaps by the next World Penguin Day we will have ten endocasts?

Reference:

Proffitt, J. V., J. A. Clarke, and R. P. Scofield. “Novel insights into early neuroanatomical evolution in penguins from the oldest described penguin brain endocast.” Journal of Anatomy (2016).