First thing: TERROR BIRDS must be written in all caps and whenever you say it, you must squawk and raise your arms as if they were useless, tiny wings.

So what are TERROR BIRDS?

Imagine an ostrich. Only on steroids so it’s 10 feet tall, weighs 300 pounds, has a giant razor beak, and uh-oh it’s looking pretty hungry and then it’s dismembering you.

These are some very large and very hungry chickens.

These things lived in (South) America and were the apex predator in the Cenozoic era (65 to a mere 2 million years ago).

In essence, TERROR BIRDS were some of the most vicious and simultaneously mostly-terrifying-but-also-hilarious-looking predators to ever stalk terra firma…or is that TERROR FIRMA? No, it’s just terra firma according to Websters.

Except, at least not in one case. See the yellow bird on the far right? Gastornis?

It lived between 55 and 40 million years ago, and certainly looked the part of a TERROR BIRD, being 6 feet tall and having a giant beak that looks just fantastic for crushing spines and severing limbs.

Except Gastornis probably didn’t do those things.

But recent research has found that Gastornis wasn’t so terrifying, after all. While a 1991 paper concluded that the bird’s beak could have made short work of many small mammals, other publications pointed out that such a beak would have been just as well-suited to cracking seeds and crunching tough fruit. More recently, tracks of Gastornis found in Washington show that the bird had blunted toes rather than vicious talons, and a preliminary study of dietary clues preserved in the bones of a German specimen of the bird suggested a menu of plants rather than flesh.

These things were known, but a recent study by Delphine Angst and colleagues has looked at the diet of these (fossilized) birds and found more evidence indicating that Gastornis was probably not the terror of the North American landscape.

Sounds weird, right? How can paleontologists tell what a bird that lived 50 million years ago ate?

Through SCIENCE!, that’s how. TL;DR below big block of quote if you’re feeling lazy.

Chemical signatures in the extinct bird’s bones are at the center of the Naturwissenschaften study. Angst and coauthors studied carbon isotope (δ13C) traces in the bones of Gastornis, small herbivorous mammals the bird lived alongside, and modern hawks and ostriches. This isotope acts as a proxy for diet. Generated inside plants, the carbon isotope becomes preserved in the tissues of herbivores that eat those greens and, further down the line, in the tissues of the carnivores that consume those herbivores. Locked in bones and teeth, this carbon isotope allows paleontologists to outline what individual animals were consuming and how they may have split up resources in the same habitat.

By themselves, these chemical traces don’t automatically label an individual as an herbivore, carnivore, or omnivore. What the carbon isotope values mean rely on comparison and analysis. In the case of Gastornis, Angst and colleagues used the data to investigate the opposing views of the bird as carnivore or herbivore.

Part of what makes carbon isotopes useful in paleontology is that they can be tied back to different types of plants that photosynthesize in different ways. This detail is  what led  Angst and coauthors to throw out the idea that Gastornis sliced small mammals. If the big bird was a carnivore, the researchers found, then the carbon isotope signatures inside it’s bones would indicate that it ripped open prey that, in turn, relied upon C4 plants – grasses and other plants that rely on a distinct form of carbon fixation. The snag is that plants didn’t evolve that C4 method of photosynthesis until about 14 million years after Gastornis lived. The chemical trace didn’t match up with the ecology of the time.

TL;DR: Scientists analyzed levels of radioactive carbon isotope that is generated in certain kinds of plants to determine that Gastornis likely did not eat substantial quantities of meat.

Well, that evidence might be a bit shaky, so Angst and her colleagues used a different route to lend more credence to the “Gastornis didn’t primarily slaughter hapless mammals and feast on their bones” hypothesis. TL;DR below block’o’quote if you’re feeling lazy.

Through dissections of modern birds ranging from Darwin’s finches to Eurasian sparrowhawks, Angst and colleagues studied the anatomy and connection points of the external adductor muscle in modern herbivorous and carnivorous birds. This is a major muscle that powers bird bites, and the herbivorous, seed-cracking birds typically had wider muscles with increased space for attachment on the lower jaw. That fits they way they feed. Much more power is needed to bust open hard fruits than to tear soft flesh.

The actual muscles of Gastornis rotted away over 40 million years ago, but the bird’s lower jaw shows a wide space for the external adductor muscle to attach. Taken together, the bird’s beak, feet, reconstructed musculature, and chemical signature best fit a large herbivore that snacked on plants rather than the mammals that lived underfoot.

TL;DR: By comparing the jaw structure of Gastornis to modern birds, we see that the jaw structure is much more similar to herbivorous, seed-cracking birds (which interestingly enough need a hell of a lot more power, as hard nuts>>>soft, tender flesh).

So, it seems like Gastornis, kinda like Oviraptor, has been maligned as a TERROR BIRD, when in reality, it probably just wandered around North America looking for nuts to eat. Our mammalian ancestors can retroactively be at slightly more peace.

Oh, one last thing.

While Gastornis was similar in size to other TERROR BIRDS, and looked the part, the other TERROR BIRDS almost certainly ate meat (whether or not they were primarily scavengers or predators or some blend is unclear, but we do know they ate lots of meat and probably killed things dead to do so).

Also, we’re pretty sure TERROR BIRDS ate everything that wasn’t much bigger than them, so yea, sucks to be…well, probably anything if you were where these overgrown death chickens lived.

I cannot get over how creepy those arms look in that pose.


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