The earliest known bird, magpie-sized Archaeopteryx lithographica could hear just the same as a modern emu (Dromaius novaehollandiae), demonstrating that Archaeopteryx was more bird-like rather than reptilian, according to new research published today.
Using innovative modern technology, palaeontologists at the Natural History Museum in London have shown for the first time how the length of the inner ear of birds and reptiles can be used to accurately predict their hearing ability.
Dr Paul Barrett, Natural History Museum palaeontologist, explained ‘In modern living reptiles and birds, we found that the length of the bony canal containing the sensory tissue of the inner ear is strongly related to their hearing ability. We were then able to use these results to predict how extinct birds and reptiles may have heard, and found that Archaeopteryx had an average hearing range of approximately 2,000 Hz. This means it had similar hearing to modern emus, which have some of the most limited hearing ranges of modern birds.’
Previously, researchers have only been able to estimate how prehistoric animals heard sounds by examining the skulls of damaged fossils and relating brain region size to hearing ability, based on comparison with the fossil’s modern counterpart. However, modern computed tomography or CT imaging allowed Dr Barrett and his colleagues to accurately reconstruct the inner ear anatomy of various intact bird and reptile specimens.
‘Hearing ability in living species is relatively easy to measure, but such direct evidence cannot be gained from extinct animals for obvious reasons – we can’t just play sounds to a dinosaur and see how it responds to the noise. This has meant that we have not been able to fully understand how different animals developed hearing during their early evolution, until now that is,’ continued Dr Barrett.
Natural History Museum palaeontologist, Dr Stig Walsh explained ‘By examining the three dimensional CT scans, we were able to see for the first time the real relationship between hearing ability and behaviour in extinct reptiles and birds. The size of the cochlea duct (the bony part of the inner ear, housing the hearing organ) in living birds and reptiles accurately predicts the hearing ranges of these animals. This simple measurement can therefore provide a direct means for determining hearing capabilities and possibly behaviour in their extinct relatives, including Archaeopteryx.’
Natural History Museum palaeontologist, Dr Angela Milner explained ‘This adds yet more information about how bird-like Archaeopteryx was. Our previous research has shown that the part of the ear that controls balance was just like that of modern birds. Now we know that Archaeopteryx had bird-like hearing, too.’
Animals with a long cochlear duct tended to have the best hearing and vocal ability. Modern living bird species are known to possess relatively longer cochlear ducts than living reptiles. A long cochlear duct is also an indicator of an individual’s complex vocal communication, living in groups and even habitat choice. This is true for both mammals and birds.
“Species living in large social groups have more complicated vocal communication which is understandably influenced by an individual’s ability to hear. Species living in a closed environment, such as forests, where visual communication is ineffective often posses more complex vocal abilities, so now we can more accurately predict the habitat types that extinct animals lived in by examining their ability to hear and communicate,” concluded Dr Barrett.
The research received funding from the Natural Environment Research Council (NERC) and the findings are published in the latest issue of the Proceedings of the Royal Society B.
Claire Gilby | alfa
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