The Call of the Terror Bird

When you think of a scary dinosaur, what comes to mind? The agile, sickle-clawed Utahraptor? A towering Tyrannosaurus? Something as alien as the croc-snouted, sail-backed Spinosaurus, perhaps? Books and museum halls are well-stocked with such Mesozoic nightmares, but scary dinosaurs have also stalked the land in the days after the end-Cretaceous mass extinction. There’s an entire group of fossil dinosaurs – technically known as phorusrhacids – that are imposing enough that paleontologists often call them by a more evocative name. These were the terror birds.

There aren’t any terror birds around today. The first evolved around 62 million years ago and the last perished about 2.5 million years ago, most of them playing the part of apex predator among the forests and plains of ancient South America. Their skeletons are evolutionary works of frightful beauty, and the latest to be described is the best-preserved terror bird ever seen.

Paleontologist Federico Degrange of Argentina’s Centro de Investigaciones en Ciences de la Tierra and colleagues named the old bird in the latest Journal of Vertebrate Paleontology. Drawing from Quechua and Latin, they’ve called it Llallawavis – the “magnificent bird”. It’s an apt title. Found in the 3.3 million year old rock of Argentina, Llallawavis is represented by a nearly-complete skeleton that includes the delicate bones of the middle ear, the bony ring of the eye, and ossified rings of the avian’s throat.

Aside from giving Degrange and coauthors a more detailed look the specific group of terror birds to which Llallawavis belonged – called mesembriornithines – the beautiful fossil adds some new details about how this 40 pound, 4-foot-tall carnivore interacted with the Pliocene world.

Thanks to the inner ear of Llallawavis, for example, the paleontologists were able to estimate that the terror bird had a relatively narrow range of hearing in the neighborhood of 3800 Hz. And since birds often vocalize in the lower ranges of what they can hear, Degrange and coauthors point out, this hints that Llallawavis may have communicated with low-frequency sounds that could travel long distances. Unfortunately, despite having part of the throat set in stone, the branches of the bird’s airway critical for sound-making were not fossilized to check what sounds they could have produced. What these impressive avians actually sounded like is still left to our imagination.

Reference:

Degrange, F., Tambussi, C., Taglioretti, M., Dondas, A., Scaglia, F. 2015. A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds. Journal of Vertebrate Paleontology. 35 (2). doi: 10.1080/02724634.2014.912656

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