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Gastornis facts: a bird with a skull the size of a horse’s head

As is known, dinosaurs ruled the earth in some prehistoric period. But then they became extinct. Scientists say different reasons for this extinction, but the most common version is considered to be the fall to Earth of a large celestial body, like a giant asteroid. Approximate calculations show that all the inhabitants of the planet, whose weight exceeded 10 kilograms, died then. 

And that’s when mammals began to occupy empty ecological niches. Before, this life form was something of a biological “underground” living in the shadow of the dinosaurs, but the death of the latter was their ticket to life.

This chance was used, of course, not only by mammals, which now make up the bulk of all existing animals, but also by birds, which, due to one evolutionary factor or another, had giant-sized species in their class, such as Gastornis.

The Gastornis is a genus of giant flightless birds belonging to the order Anseriformes that lived on Earth for about 15 million years (61.6-48.6 million years ago). Check out the facts about Gastornis birds below.

When the fossils of Gastornis were first discovered  

Diatryma and Gastorins are essentially the same bird. In 1855, Gaston Planté discovered the fossils of Gastornis near the Parisian suburb of Meudon and described them scientifically for the first time. The discovered species (Gastornis parisiensis) was named after its discoverer. In 1874, American paleontologist Edward Drinker Cope discovered one fragmentary set of fossils in the Wasatch Formation of New Mexico. He considered them to belong to a separate genus of giant flightless bird, which he named Diatryma gigantea in 1876. Based on various analyses, comparisons of body structure and reconstruction of external appearance, scientists have included these two species in one genus, which is known as Gastornis. But how did these two species end up in different parts of the planet?

The earliest fossil remains of Gastornis are attributed to the Paleocene sediments of Europe, so most scientists assume that this is where the genus originated. But fossil remains of these birds have been found in Europe (G. sarasini, G. geiselensis, G. russeli, G. laurenti), Asia (Gastornis xichuanensis), and North America (Gastornis gigantea). Interestingly, the latter species has even been found on Canada’s northernmost island, Ellesmere.

Earth’s climate in the Eocene was warmer, and on Ellesmere Island, where now there is only arctic desert and tundra, there grew underwater cypress forests that were home to turtles, alligators, primates and even large mammals resembling hippos and rhinoceroses.

However, it remains unclear how Gastornis adapted to the polar night or the polar day. They may have migrated to other places at one time or another, but this has yet to be established by scientists.

Scientists also believe that from Europe, their supposed cradle, these birds probably then migrated to Asia and North America in search of better climatic conditions. Interestingly, in South America (which was a separate continent during the Eocene), there existed terror birds, which looked like Gastornis.

What the Gastornis bird looked like: skull, legs, skeleton, feet, feathers and size

Gastornis birds or giant geese were very similar to modern ostriches and casuars. For example, they also had underdeveloped wings, which made them unable to fly. The inability of birds to fly is primarily due to the evolutionary activity: the extinction of their natural enemies, their ancestors (the dinosaurs) led these birds to develop the land for the needlessness of flight.

To move comfortably on the surface, it requires strong legs and large paws, tight to the surface of the ground. Gastornis paws could grow up to 40 cm in length and did not have large claws, footprints show.

But Gastornis ran relatively slowly, they could reach a maximum short-term speed of up to 40 km/h, which is 30 km less than the speed of ostriches.

The skull of Gastornis was huge, compared to the body, and strongly built. The beak was extremely tall and compressed (flattened from side to side). The “lip” of the beak was straight, without the predatory hook characteristic of terror birds or modern eagles. The nostrils were small and located close to the front edge of the eyes, about the middle of the skull. The skull, together with the beak, was the size of a modern horse’s head and served as the main tool for extracting food.   

The vertebrae were short and massive, even in the neck area. The neck was relatively short, consisting of at least 13 massive vertebrae. The torso was relatively short. It was a strongly built animal.

The wings were rudimentary, similar in size to the wings of a casuar. However, these wings may have served to attract females. They may have plumage of a different type or coloration.

However, these wings may have served to attract females. They may have plumage of a different type or coloration, than the body. The giant bird might have made attractive movements with them being in front of a female during the mating season. The small wings could also make it easier for the bird to get off the ground.  

As for feathers, Gastornis birds are usually recreated with feathers resembling hair, which would be good heat and water insulators. However, a possible Gastornis feather has been found in the Green River Formation, located in Colorado. It is the only feather among those previously discovered that resembles the body feathers of flying birds, it is wide and lobed. It was tentatively identified as a possible Gastornis feather based on its size; it was 240 mm (9.4 inches) long and would have belonged to a giant bird.

Depending on the species, Gastornis birds grew up to 2 meters (6 feet) tall and weighed up to 150-200 kg (200 pounds)! In fact, these birds surpassed the African ostriches and cassowaries, which are the largest birds on the planet today.

What the Gastornis diet consisted of

Some scientists believe that Gastornis used their giant beak to tear their prey apart, grabbing it by the neck and breaking its vertebrae, which is supported by biomechanical models and the supposed force of their bite.

Since Gastornis had a very powerful beak, which was estimated to be capable even of breaking bones, it was widely believed among scientists in the mid-20th century that these birds were either scavengers or predators.

As mentioned earlier, Gastornis birds lived at a time when dinosaurs were already extinct and mammals were still small and just beginning to evolve. Therefore, these birds were considered the supreme predators of that time on Earth.

This giant bird was often depicted hunting mammals, such as the distant ancestors of horses, Propaleoterium and Hyracotherium.

However, given the size of the Gastornis’ legs, the bird must have been much more agile to catch fast-moving prey than the fossils suggest.

However, some believe that Gastornis may have been an ambush hunter and/or used pack hunting to stalk prey. This point of view is supported by the fact that where the birds lived, there were dense forests with strong trees. The giants had places to hide.

However, a new study has shown that the opinion regarding the predatory lifestyle of Gastornis was erroneous and dictated more by the size and appearance of the bird.

Scientists found this out by “reading” the diet of Gastornis by the proportion of calcium isotopes in their bones. Typically, such studies are based on teeth that birds do not possess. Scientists were able to circumvent this problem by studying the concentration of these isotopes in layers of fossilized bones of giant birds related to the species Gastornis geiselensis, which inhabited the German territory 55-41 million years ago.

According to the researchers, the teeth and bones of carnivores in most cases contain relatively few heavy isotopes of calcium, and the more meat present in their diet, the fewer such isotopes it contains. Paleontologists took advantage of this correlation and compared the proportion of calcium in the remains of Gastornis, modern birds, Tyrannosaurus and some other animals.

It turned out that the concentration of “heavy” calcium in the bones of the giant bird was unexpectedly high, and corresponded to similar values for herbivorous mammals, dinosaurs and birds.

This fact suggests that Gastornis birds were most likely herbivorous birds and could not claim the role of “alpha-predators” of their time.

This leaves terror birds as the only giant carnivorous non-flying birds.

In addition, the beak of Gastornis birds was without the hook that modern eagles and hawks have. It was not very suitable for eating meat.

Scientists have found many similarities between the beaks of the giant prehistoric birds and the beaks of some parrots, which easily split nutshells with their “tool”.

Gastornis probably used its beak to dig up edible roots. The animal could use it to crack seeds, nuts, and tear fruits having thick rinds. 

Why Gastornis became extinct

It is currently unknown why Gastornis became extinct. Some scientists have suggested that increased competition with mammals may have led to the extinction of these birds. Other scientists suggest that their disappearance was probably due to climate change. 

Climatic changes remain one of the most likely causes: towards the end of the Eocene, a drastic global cooling began, causing tropical forests to disappear, giving way to vast grasslands.

During the Paleocene, Gastornis were the largest land animals in Europe, Asia, and North America. For most of the Paleocene, the fauna was represented by archaic mammals that mostly were omnivores. Presumably, these birds may have died out with the emergence of primitive large predatory mammals like hyenodons.  

Gastornis laid eggs in earthen nests, so they were easy prey for predatory mammals. If the eggs survived, the mammals preyed on the chicks that had barely been hatched. Presumably, it was this kind of guerrilla warfare on the part of the mammals that led to the Gastornis eventually going extinct, leaving no descendants.

By the way, terror birds in South America survived into the Pleistocene, probably thanks to the absence of large terrestrial placental predators present there.

Where Gastornis is found

Gastornis was featured in Episode 1 of a popular science series, Walking with Monsters. Despite belonging to the goose-like birds (Nidifugous and nidicolous organisms), in the film her chick is shown naked and helpless, as in chick birds (Precociality and altriciality). Kenneth Oppel’s book Darkwing also features Gastornis.

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