Tuesday, 14 April 2015

Voices Of The Terror Birds

The theropod resonating chamber from Jurassic Park III
In the third Jurassic Park film, Dr Alan Grant performed a laser scan on the skull of a theropod dinosaur. This 3D image was in-putted into a 3D lathe so that a precise anatomical model of the dinosaur's voice box could be constructed. Blowing air through this model, Grant resurrected the spine-chilling shriek of the theropod.

While this is science fiction it raises the interesting question as to what ancient creatures sounded like. A team of South American scientists has ascertained the vocal capabilities of a phorusrhacid, a species of terror bird which roamed the grasslands of South America until just a few million years ago.

The phorusrhacids were powerful predators, with some species growing up to three metres in height. Fast, and armed with a cleaver-like bill, they were the top predators in the South American grasslands until South America collided with North America, allowing sabre-toothed cats access to the south. This new study focused on the four foot, 3.5 million year old Llallawavis scagliai. The species was discovered only recently, but the type fossil is the most complete terror bird discovered. 90% of the skeleton was present including an exquisitely preserved skull.

The 90% complete skeleton of the 3.5 million
year old phorusrhacid Llallawavis scagliai
The new specimen contained anatomy details that are rarely preserved in the fossil record, including the auditory region of the skull, voice box, complete trachea, bones for focussing the eye, and the complete palate. This gives an unprecedented understanding of the sensory capabilities of these extinct predatory birds.

'The mean hearing estimated for this terror bird was below the average for living birds,' said Dr. Federico Degrange, lead author of the study from the Centro de Investigaciones en Ciencias de la Tierra, Argentina. 'This seems to indicate that Llallawavis may have had a narrow, low vocalization frequency range, presumably used for intraspecific acoustic communication or prey detection.'

This new understanding of the sensory capabilities shows why the phorusrhacids were successful for so many millions of years. Apart from a lack of other predators, their sensory capabilities were perfectly adapted to hunting and stalking prey. Llallawavis would not have preyed upon the same creatures as the larger species of terror bird, so different species may have had different vocal ranges dependent upon ecological conditions.