Well, I just asked you to try to guess where penguins entered the geological scene in the last page. If you guessed that they came after dinosaurs, sometime in the Paleogene era, then you were correct. Here's a basic look at the continuum:

    You can see the brontosaurus, a dinosaur, lingering around in the Jurassic age. Not being a dinosaur expert, I don't really know if brontosaurus existed in the Jurassic era, but the point is that dinosaurs were the ruling species until the Cretaceous period ended. There have been numerous theories posited as to why the dinosaurs ceased to flourish after this period -- everything from elevated temperatures to elevated CO₂ to volcanic eruptions to catastrophic extraterrestrial collisions with the planet. In my opinion, who cares? The issue of what killed off the dinosaurs doesn't interest me as much as the question of why the dinosaurs existed so long does. Regardless, dinosaurs ceased to exist and gave rise to the age of mammals and birds.

    Before the end of the Cretaceous period, there occurred an evolutionary turning point in which a group of dinosaurs began to appear and function differently from the others. Over time, these dinosaurs evolved into birds. They began to develop features that present-day birds possess: feathers, "hollower" bones, reverse pubis (bone connecting hips together anteriorly), keratinization of the oral cavity, and of course, wings. For a number of years, it was believed that Archaeopteryx was the first proof of this divergence. (Recently, a fossil of an earlier bird, Protopteryx was discovered.) Both these birds had characteristics of modern birds, but were relatively heavier and were often found to have dentition or teeth, unlike modern birds. Were it not for the faintly obvious patterns in the fossil created by feathers, this fossil would have been misclassified as one of the advanced dinosaurs.

    So, what changed that made dinosaurs fly? Good question (if you asked it). The development of a wing-to-body weight ratio that favored flight is the reason. To be a reductionist, precursors to birds slowly evolved wings, or coverings of their upper limbs, that enabled them to elevate their bodies off the ground. When this was originally postulated, two theories were offered to explain how birds gained the ability to fly. They were the ground up theory and the tree down theory. The prior stated that dinosaurs began as runners that were successful in leaping large distances and gliding/coasting to a safe landing. This enabled them to evade predators/find food faster, etc. and the trait propagated. The latter theory posits that tree climbing dinosaurs evolved mechanisms to glide from trees or other elevations to some distance away from that spot, landing on the ground. While the latter is more attractive than the prior on the surface level, the prior theory is most likely the correct theory. I don't know if it is codified, however, and it may still be subject to intense debate.

    Over the eons, regardless of how they gained the ability to fly, birds evolved to become fairly diverse. And with that increasing diversity came the ancestors of modern penguins. Birds diverged early too. Some of them continued to evolve their flying ability, and others like Hesperonis lost it completely. Check out a picture of Hesperonis. This bird is not closely related to penguins despite its tempting similarities. Penguins are modern birds, or Neornithes.

    Look at the classification tree on the left. You can see the evolution of modern birds. Neornithes developed into Paelognathes (old jaw) and into Neognathes (new jaw). From this group of birds developed some other specifics, but the two of interest to us are the Chardriiformes and the Ciconiiformes. Notice that from the Ciconiiformes stem the Pelecaniformes (obviously containing pelicans), and from the Pelecaniformes stem the Procellariformes, which gave rise to Graviidae (loons, etc.) and Spheniscidae. There's Spheniscidae, our old friend the penguin. So, you can see that the auks, which are often mistaken as being closely related to the penguin due to their similar size, shape and ecological niche, aren't closely related to penguins at all. However, you can see what are closely related to penguins: the Procellariformes from which penguins descend directly, and the Graviidae, which is a daughter clade of the Procellariformes with the Spheniscidae.

    What would be interesting to me is to be able to observe and trace the divergence in the Spheniscidae and the Graviidae. How did they evolve to be so separate? Interesting discussion.

    So, you can see how different, based on the phylogeny chart, penguins are from modern birds. Despite the fact that they don't fly either, ratites (ostriches, emus, rheas) aren't closely related to penguins. The closest relatives of penguins are albatrosses, petrels, and shearwaters. They are all Neornithes. It seems ironic that even though they look like penguins, puffins, razorbills and murres aren't related to penguins either.

Darwin, Charles. On Evolution. Glick & Kohn, eds. 1996. Hackett Publishing Company, Inc.: Indianapolis.

Krebs, J.R. & Davies, N.B. 1993. An Introduction to Behavioural Ecology. London: Blackwell Scientific Publications.

Krebs, J.R. & Davies, N.B. 1991. Behavioural Ecology: An Evolutionary Approach. London: Blackwell Scientific Publications.

Young, David. 1992. The Discovery of Evolution. Cambridge University Press: Cambridge.

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