The most complete ancient terror bird

South America was isolated from North America during a long period of time and Central America did not exist. At that time, in the Southern cone, there were not carnivorous placental mammals such as pumas or bears, therefore the so called Terror Birds were the main carnivores in these ecosystems.

Federico Degrange – assistant researcher – and Claudia Tambussi – principal researcher – at the Centro de Investigaciones de Ciencias de la Tierra (CICTERRA, CONICET-UNC) [Centre for Research in Earth Sciences] study the most complete skeleton of this group of animals found so far. As a result, they described a new species: Llallawavis scagliai. This find led to a recent publication in the prestigious magazine Journal of Vertebrate Paleontology.

Phorusracids

These animals belong to a group that is completely extinct and has no similar species in the current days. The group is known as Terror birds, also called phorusracids. “This group was found in South America and it includes varieties of small and large species up to 3 meters long. They had very big skulls and carnivorous habits. The smallest ones could probably flap, but in general most of them did not”,Tambussi describes.

The majority of the phorusracids fossils were found in Argentina because the northeast and Patagonia are places likely to contain these types of finds, that is to say that the conditions were favourable for these remains to be preserved, fossilized and found.

Llallawavis scagliai’s identikit

In 2010, palaeontolists Matías Taglioretti, Alejandro Dondas and Fernando Scaglia found a skeleton of an unknown species of phorusracids in La Estafeta beach, near Chapadmalal. The fossil was in good conditions and it had 95% of its components.

“It is the most complete phorusracid skeleton ever found and is one of the most complete within the fossil birds in general”, Tambussi states. Besides, it is a holotype, that is to say, the piece that is used as a reference if researchers find other remains that seem to belong to the same species.

After analysing and confirming that they had found a new species, they named it Llallawavis scagliai. “Llallawa means marvellous in Quechua and avis is the scientific term –together with ornis – to name the birds. Scaglia is the grandfather of one of the authors who was a pioneer in palaeontology in Mar del Plata”, Degrange explains.

Llallawavis scagliai was one of the main predators in South America and lived in the northeast of what we currently know as Argentina, about 3.5 millions of years ago. This phorusracid was 1.20 metre (four feet) tall and weighed 18 kg. It lived in places associated to palm trees and bodies of water. Furthermore, it lived together with marsupial mammals – like the weasels-, glyptdont, great sloths, partridges, ducks, condors, rodents, mules and other phorusracids, apart from insects and plants.

Although there are some studies to be conducted, such as the reconstruction of the brain, the information obtained is really valuable. The trachea, for instance, is very well preserved and it can provide information regarding the song.

Regarding its hearing, the researchers managed to calculate the frequency range they could perceive. “We realized that the average frequency hearing of the Llallawavis was relatively low. Low frequencies tend to propagate without changes throughout great distances, which can be regarded as an advantage to catch preys. This hearing capability is similar to the hearing of running birds such as the rhea”, Degrange affirms.

Besides, the birds have a bone plate in the eyes called sclerotic ring and in this specimen it is very well preserved. In general, they do not have stereoscopic vision, that is to say, that they do not create only one image from the information they obtain from the two eyes, hence they do not have the same notion of distance humans have. However, depth perception is vital for hunting.

“The phorusracids might have had what is known as functional stereoscopic vision: when they lowered the beak and looked forwards, they could have created a single image, with depth of field. Besides, to avoid the formation of two separated images due to the great size of the beak, it would be necessary to have protruding eyes. So, we think that the sclerotic ring we found could have provided protection so as not to leave the eyes dangerously exposed”, Tambussi describes.

Furthermore, the team had also conducted a previous study on how the phorusracid skull worked. Through the analysis of finite element – an engineering technique to test materials’ resistance- the researchers determined how that long beak could work before the prey. “The bird had not only to kill the prey but also cut it because it did not have teeth. We hypothesize that the phorusracid followed the prey while running – hence we analysed the legs and noticed that they could run – and it used the beak as a guillotine or an axe, with an accurate blow”, Degrange explains.

With the study of the features of the skull of the Llallawavis it is possible to assume that it worked in the same way. Besides, more information supports this hypothesis. In general, birds move the beak separate from the skull and despite the fact that the ancestors of this species used to have that type of articulation, this new species lost it. “This reinforces the idea that they hunted their preys using their beak as guillotine, thus a rigid structure would be more useful than an articulated one”, Degrange comments.

Finally, “the study of the bone remains and the reconstruction of the muscles and joints of the neck indicate the range of movement was dorsoventral – from top to bottom and vice versa -, what coincides with the hypothesis of the hunting method we have worked with”, Tambussi states.