Battle of the Birds: Ostrich vs. Penguin

Why do flightless birds exist? Are they the proof of avian descent from dinosaurs? The answer to this question may surprise you, because it’s actually no!

Most birds belong to an infraclass known as Neognathae, meaning “new jaws,” as their jaws deviate anatomically from their reptilian predecessors. However, some of the oldest birds are in a separate infraclass, Paleognathae, for their much more reptilian jaw structure. Many birds species in Paleognathae can actually fly, but certain ones can’t; these flightless birds are known as “ratites,” and you may recognize certain ratite species like the ostrich, cassowary, emu, or kiwi. Given an ostrich’s resemblance to dinosaur species like Gallimimus, it’s probably tempting to imagine ostriches as living fossils whose dinosaur ancestors also couldn’t fly.

However, as far as paleontologists can determine, all modern birds descend from flying ancestors, even in the case of ratites. The real mystery is why ratites themselves stopped flying. There are competing theories, but they generally come down to matters of energy conservation or the absence (or presence) of certain competing non-bird species. Just like how cetaceans (whales, dolphins, and porpoises) evolved from land-dwelling mammals, this goes to show that while we often imagine evolution as working in a perfect straight line of life forms getting “better and better,” the reality is that natural selection allows for the best traits to persist in a species’ environment at that time. Very useful traits can still become unnecessary in the right context!

Of course, you’d still be correct to say that ostriches and their ratite relatives look a lot like dinosaurs. Contrast this with a generally smaller, chubbier group of flightless birds: penguins! Though the penguin family is rather old in its own right, its lineage stretches back through thousands of other modern birds. Penguins are actually more closely related to other water birds like albatrosses, loons, and storks — with many other less-distant cousins before you ever get to ostriches.

In the course of evolution, penguins have lost many more visibly dinosaur-like traits, but they also lost their ability to fly because they became more advanced underwater divers in extremely cold water. Flight-capable wings are not compatible with the fat reserves, musculature, and dense feathers that enable the penguin lifestyle!

So of the flightless birds, which one is more your style? There’s the ostrich, representative of the ratites and also the biggest bird on Earth, or there’s the penguin, superstar of Antarctic fishing. The competition starts at 11:00 AM EST on 2/19 and goes for 48 hours! Bonus information is detailed in your notifications.

Images by Dharmit Shah and Hubert Neufeld