Gastornis

Gastornis is an extinct genus of large birds that could not fly. They lived from the middle Paleocene to the middle Eocene, during the Paleogene period. Most of their fossils come from Europe, though some species that are usually placed in this genus have also turned up in North America and Asia. For a long time, people thought these birds hunted small mammals, like ancient tiny horses. But now, based on several clues—such as the lack of hooked claws in known footprints, studies of their beak shape, and chemical signatures in their bones—many scientists believe Gastornis was actually a plant-eater, crunching tough seeds and vegetation. It is widely accepted that Gastornis belongs to the group Galloanserae, which includes modern waterfowl and gamebirds.

The genus was first described in 1855 from a partial skeleton. It was named after Gaston Planté, a "studious young man full of zeal" who found the first fossils in clay deposits at Meudon, near Paris. This discovery was notable because the bird was so large and, at the time, was one of the oldest known birds. More bones of the first named species, G. parisiensis, were dug up in the mid-1860s. In the 1870s, somewhat more complete specimens—then called G. edwardsii (now considered the same as G. parisiensis)—were found. These formed the basis for a widely circulated skeletal reconstruction by Lemoine. However, the skulls from these original fossils were mostly unknown, except for a few fragments and some bones Lemoine used in his drawing that actually came from other animals. As a result, the European bird was long pictured as a giant, crane-like creature.

In 1874, American paleontologist Edward Drinker Cope found another set of fragmentary fossils in New Mexico’s Wasatch Formation. He thought they belonged to a different genus and species of giant ground bird, and in 1876 he named it Diatryma gigantea—from the Greek for "through a hole," referring to large perforations in some foot bones. In 1894, Cope’s rival Othniel Charles Marsh described a single toe bone from New Jersey as a new genus and species, Barornis regens. By 1911, it was recognized that this could also be considered a junior synonym of Diatryma (and later, Gastornis). More fragments from Wyoming were found in 1911 and named Diatryma ajax in 1913 (now also considered a synonym of G. giganteus). In 1916, an expedition from the American Museum of Natural History to Wyoming’s Bighorn Basin uncovered the first nearly complete skull and skeleton, described in 1917, which gave scientists their first clear picture of the bird. Matthew, Granger, and Stein (1917) classified it as another new species, Diatryma steini.

After Diatryma was described, most new European finds were assigned to that genus instead of Gastornis. But researchers had already noticed similarities between the two as early as 1884, when Elliott Coues placed Diatryma gigantea under Gastornis as G. giganteus—a synonymy the American Ornithologists' Union agreed to in 1886. Meaningful comparisons were made harder by Lemoine’s incorrect skeletal illustration, whose composite nature wasn’t discovered until the early 1980s. After that, several authors saw greater similarity between the European and North American birds, often putting them in the same order (Gastornithiformes) or family (Gastornithidae). This led many scientists to tentatively accept the synonymy, with Gastornis having priority, pending a full review of both genera’s anatomy. Some later studies kept using Diatryma or argued against the synonymy, noting that a detailed comparison of type specimens hasn’t been done yet and that clear differences exist between the species originally assigned to Diatryma and the type species of Gastornis.

A lot of fossil remains of Gastornis exist, but the clearest picture comes from a few nearly complete specimens of G. giganteus. These were very large birds with huge beaks and massive skulls that look superficially like those of the carnivorous South American "terror birds" (phorusrhacids). The largest known species, G. giganteus, would have stood about 2.15 meters (7 feet 1 inch) tall at most and weighed between 175 and 225 kilograms (386 to 496 pounds). Its skull was enormous compared to its body and powerfully built. The beak was extremely tall and flattened from side to side. Unlike other Gastornis species, G. giganteus lacked the grooves and pits on the underlying bone. The beak’s "lip" was straight, with no raptorial hook like those of predatory phorusrhacids. The nostrils were small and placed near the front of the eyes, about midway up the skull. The vertebrae, even in the neck, were short and massive. The neck itself was relatively short, made up of at least 13 heavy vertebrae. The torso was short. The wings were vestigial, with the upper wing bones small and greatly reduced, similar in proportion to those of a certain other group.