Gastornis: An Eocene Bird

Gastornis was a large, flightless bird of the late Paleocene and early Eocene Period that inhabited the lush forests that covered the world during that time. Fossils of gastornis have been found primarily in Germany and the United States. Gastornis proper has only been found in Europe, but a very close relative called diatryma was native to North America during the Eocene. The latter was a slightly taller and less stocky version of its European counterpart.

This giant bird could reach heights of 1.75 meter (5.75 feet) and had a stocky build, weighing in at nearly 600 pounds. Due to its weight and tiny wings, there is no way gastornis could ever have gotten off the ground for longer than a split second. It is likely that once its ancestors began to become increasingly successful in the Paleocene and Eocene forests, its wings began to shrink to allow for increased mobility on the ground. More powerful hind legs replaced powerful forelimbs in order to support its body weight and also propel it forward in quick bursts of speed.

It is unclear what gastornis ate in the Eocene forests in which it thrived. Given its powerful build, many scientists have suggested that this large bird helped fill the niche of large predatory dinosaurs left open after the Cretaceous-Tertiary extinction. Further evidence for this is in gastornis' giant beak, which proponents of the predator theory believe was a powerful means of biting animals and delivering bone-shattering blows. However, others argue that the beak was more suited for cracking hard seeds and nuts. This is possible, though it seems unlikely that the bird would need such a large beak in order to deal with seeds in the Eocene forests. The beak itself has been a great area of contention, and some scientists have suggested that it was primarily used for mating displays where larger beaks would have a better chance of attracting a female. The beak itself does not resemble the curved, sickle-like beak of eagles, hawks, or other carnivorous, present-day buteos.

If it was indeed a hunter, gastornis would have needed a lot of food in order to maintain its large body weight and was most likely a solitary hunter. Also, given its bipedal gait and heavy constitution, it doesn't seem likely that it could run for long distances very fast. Generally, large predators like this rely on ambush tactics in which stealth and quiet leads up to an explosive burst of speed that either catches the prey or doesn't, with minimal pursuit. Also, since the gastornis would need to feed its young, it is likely that it wouldn't have laid a great number of eggs. Also, many eggs would attract attention of omnivores since they would need to be laid on the ground.

As the vast forests of the Eocene began to thin out and the large birds were losing their food chain positions to large mammals, gastornis did not survive past the Eocene. Whether or not it was a hunter or a herbivore, it still remains a very impressive piece of evolution following the demise of the dinosaurs.