New Study Indicates that Archaeopteryx had Hearing Ability similar to an Emu’s

A new study conducted by scientists at the Natural History Museum in London, has provided further insight and improved understanding of the hearing ability of the world’s oldest known bird – Archaeopteryx.  This ancient, crow-sized creature with teeth in its jaws (modern birds don’t have teeth in their beaks) and claws on its wings, but covered in feathers and capable of flight is the oldest known bird.  The ten or so specimens found (all of which have been recovered from deposits in Bavaria, Germany), are regarded as some of the most important fossil discoveries ever made.

When Charles Darwin published his book “The Origin of Species”, one of the criticisms of his theory of natural selection put forward at the time, was that the fossil record showed few signs of intermediary forms as one species evolved into another over time.  The realisation that a fossil “dino-bird” had been discovered occurred in 1861 when an almost complete fossil of Archaeopteryx was unearthed at Solnhofen in Germany.  The very fine-grained lithographic limestone had preserved the specimen in exquisite detail and permitted scientists to study closely the mix of reptilian and bird features.  This was the proof the evolutionists had wanted – Archaeopteryx was an intermediate form between the reptiles and true birds.

To read more about the discovery of Archaeopteryx and its impact on the theory of evolution: The Link Between Dinosaurs and Birds

Now a new study using the fossils of Archaeopteryx has concluded that this ancient creature’s hearing may have been more like a primitive bird’s than that of a reptile.  Using the more complete fossils such as the “London specimen” purchased by Sir Richard Owen for what was to become the London Natural History Museum; for the princely sum of £600, the team have been able to construct models of the inner ear.  From this research, they have concluded that the structure of the inner ear resembles that of an emu and it is possible to deduce that the hearing ability of an emu may reflect the hearing capability of its long dead ancestor.

The research team examined whether the length of the cochlear duct, which lies in the inner ear and is part of the cochlea, could be used to calculate the hearing ability in a group of modern birds and reptiles such as the primitive emu, an owl, turtles and alligators.  Modern bird species such as owls and emus are known to have longer cochlear ducts than living reptiles.

A Fossil of an Archaeopteryx “Ancient Wing”

Picture Credit: Stanford University

Indeed, the study’s results confirmed that animals with a long cochlear duct were more likely to have better hearing and vocal ability.  And for both mammals and birds, a long cochlear duct is also an indicator of vocal communication, living in groups and even habitat choice.  The research which has been published in the journal of the Proceedings of the Royal Society, could lead to further analysis into the social and herding behaviour of dinosaurs and other extinct animals.  There is a correlation between the ability of higher animal’s to communicate and their ability live in social groups or herd structures.

Commenting on the published research, Dr Paul Barret of the Natural History Museum stated:

“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”.

By examining and comparing the length of the cochlear duct, the team were then able to make predictions on the capabilities of extinct organisms such as Archaeopteryx lithographica (the full scientific name for Archaeopteryx).

Palaeontologist Dr. Barrett added:

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”.

Ears are an amazing sensory organ that enables organisms to hear what is going on around them.  The bones in the ear were originally believed to have been in the upper part of the pectoral fins of fish.  As these animals ventured onto land, they had to evolve a whole range of new senses to help them to adapt to their new environment.  Over millions of years, a sense of hearing evolved.  These sense organs help organisms to pick up sound waves and vibrations.  Sound vibrations can travel through air, water and the ground.  The number of vibrations that are produced per second by a sound is called the frequency, and this varies for each sound produced.  Low pitched sounds have a low frequency, whilst high pitched sounds have more vibrations per second and thus a higher frequency.

The unit used to measure sound vibrations is the hertz, one hertz is equal to one vibration per second.  The range of human hearing varies depending on the person and their age.  The older we get the less sensitive we are to sounds.  As a rough estimate, human hearing range can be up to 20,000 hertz so our hearing range would have been 10x bigger than the hearing range of Archaeopteryx as stated in the new British research.

According to this study, the hearing range of Archaeopteryx would have been very limited, comparable to the range of hearing seen in extant animals (animals that are around today), like the Australian emu.

Using powerful computed tomography (CT) imaging, Dr Barrett and his team were able to accurately reconstruct the inner ear anatomy of a variety of intact bird and reptile specimens.  Such scanning technology can be used to “look” deep inside a fossil, helping the researchers to create models of the internal structure of the skull of Archaeopteryx.

A number of research teams have been working on the fossils of Archaeopteryx recently, trying to unravel the secrets of bird evolution.  For example, a team of American researchers have been using other scanning and imaging technology to try to understand more about the anatomy of this relic from the Jurassic.

To read another article on Archaeopteryx research: Archaeopteryx goes for an X-ray

The development of CT, otherwise known as computed axial tomography CAT scans, has enabled scientists to gain more information from the relatively few articulated fossils of this ancient bird.  Dr Angela Milner, also of the Natural History Museum in London produced a related paper recently that analysed the ability of Archaeopteryx to balance and manoeuvre in flight.  Her team’s work concluded that Archaeopteryx would have been quite an accomplished flier.  Certainly, Archaeopteryx could fly and although it may have lacked the grace, speed and manoeuvrability of a modern bird such as swallow, flight did give it an evolutionary advantage and birds rapidly diversified and many new forms quickly evolved.  The development of the bird lineage is reflected in the amazing fossils found in the Liaoning province of northern China.  These deposits, some 30 million years younger than the strata in Germany in which Archaeopteryx is found, have a wide variety of bird and feathered dinosaur fossils.

It seems that although Archaeopteryx may not have had great hearing, the ability to fly was going to be a real evolutionary winner.  Perhaps the work of the British scientists could be extended and some analysis could be undertaken on a few of the  fossils from mid Cretaceous China.  In this way, researchers might be able to plot the development of the hearing sense in birds, or at least get a partial understanding of how this sense developed over time in our feathered friends.

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