The terror bird, Gastornis (from Wikipedia)
The terror bird, Gastornis (from Wikipedia)

By Evan

I actually wanted to start making a post about terror birds last week, but I am glad I didn’t. According to ABC Science, one of the presentations at last week’s Goldschmidt conference (tea time in our department has been somewhat depleted by the amount of people who have gone to it), the mighty terror bird Gastornis was probably a vegetarian. Gastornis lived in the early Paleogene  (about 55-40 million years ago), and is thought to have been a plant eater based on its lack of claws, its large size, and calcium isotopes – which matched closer to herbivores than carnivores.No, the previous story, though very interesting, was not the reason I wanted to talk about terror birds. This is the reason:

Titanis

This is a Titanis walleri, one of the largest of the terror birds. Unlike Gastornis, Titanis was actually a large predator. And by large, this thing was 2.5 m tall! When you look at this fossil, you can really see the relation between dinosaurs like Tyrannosaurus and birds.

Titanis lived during the Pliocene, betwen 5 and 2 million years ago in North and South America. Early studies made claimed they had found fossils that were as young as 20,000 years old, but refined dating techniques proved that this was not the case. Apparently the fossils were found in late Pleistocene (<20,000 years old) deposits, which led them to think they survived until then. The follies of redeposition! That means that these bird could never have lived alongside humans. I guess we can only simulate it by being chased by emus.

A rendition of what a Titanis might have looked like.
A rendition of what a Titanis might have looked like. From Macfadden et al (2005).

The reason I came upon terror birds was my interest in the migration of mammals into the Americas. Humans came to the Americas across a land bridge known as Beringia (the “g” is hard), between Alaska and Siberia. This exchange lasted while sea level remained low enough to allow animals to cross. After the major continental ice sheets began to retreat, Beringia submerged, and the exchange ended.

Beringia was not the first time there was a massive exchange of animals between continents. The Great American Interchange was a dramatic event in the natural history of North and South America. It happened during the Pliocene about 3 million years ago, when, after millions of years of convergence between a bunch of tectonic plates, the Panama isthmus formed.

Central America in the early Pliocene.
Central and South America in the early Pliocene.

The formation of the Panama isthmus had a dramatic effect on the Earth’s climate. It marked the end of the interchange of water between the Pacific and Atlantic Oceans, and changed the current patterns to something that resembled modern conditions. One interesting note is that Darwin surmised in The Origin of Species that the formation of the isthmus must have been geologically recent, as the species on either side were similar.

The formation of Panama allowed animals that lived in South America to cross into North America, and vice-versa. It seems that the North American animals, such as camels, horses, bears and cats, were far better suited for invasion, and eventually out-competed South American species. Of the best surviving South American species to reach North America were porcupines and opossums. Titanis was one of the only South American predators to successfully invade North America (fossils have been found in Florida and Texas), though it was short lived. Titanis became extinct by the end of the Pliocene.

Opossum - more succesful than the terror birds at invasion.
Opossum – more successful at invasion than terror birds. Don’t let the cute face fool you!