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.

A reconstruction of Llallawavis. The white elements are those that have been discovered. From Degrange et al., 2015.
A reconstruction of Llallawavis. The white elements are those that have been discovered. From Degrange et al., 2015.

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.


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

4 thoughts on “The Call of the Terror Bird

  1. I always forget that phorusrhacids were not elephant-sized monsters, but most were emu-sized or smaller, like this new guy. The low-frequency sounds makes me think of an emu, as well–they make a very interesting “drumming” sound that I’ve been lucky enough to hear up close. It’s quite loud, and seems to be made independently of the mouth!

  2. I always have founded it interesting on all of the prehistoric life that has been on the Earth.I always found a passion for learning about dinosaurs from a very young age. It is always worth learning more about the past to understand what might happen in the future.

  3. I found it very interesting about all of the new breakthroughs on prehistoric life. I love learning more about the prehistoric life.

  4. The artwork attached is extremely missleading.
    Lets put this into perspective: this “terror bird” weighs 40 Lbs. That’s 18.2 kilos. My ridgeback (domestic dog) weighs 55 Kilos, that’s 121 Lbs! It would frighten the eggs out of a terror bird. Fortunately he loves people….

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