Evolution of our mammalian ancestor’s ear bone

Related Articles

Related Articles

It has long been believed that the hearing bone called stapes, one of the smallest bones in ancestor of mammals, shows no differences between species.

Now, Dr Leandro Gaetano and Professor Fernando Abdala from the University of the Witwatersrand’s Evolutionary Studies Institute (ESI) have completed the first detailed and comprehensive analysis on the ear bone of Triassic cynodonts, and have found some noticeable variations in the morphology of this bone – even among animals of the same species.

“No one has really paid attention to this small bone before. In studying in this ear bone of Triassic cynodonts – the forerunners of mammals, including humans – the past two years we now start to see these differences,” says Gaetano.

 

Results from this study, which is only the first part of a more inclusive research project, will appear in a paper, titled: The stapes of gomphodont cynodonts: insights into the middle ear structure of non-mammaliaform cynodonts, in the journal, PLOS ONE, on Wednesday, 15 July 2015, at 20:00 (SATS).

The only ear bone in mammalian ancestors, the stapes – or stirrup in Latin, to which this bone is most similar in humans – has been recorded in many Triassic cynodonts (220 – 250 million years ago).

This image shows morphological variation in the stapes of Triassic gomphodont cynodonts. A, Diademodon; B, Trirachodon; C and D, Massetognathus. Below is the ventral view of the skull of a cynodont showing the position of the stapes. - WITS University
This image shows morphological variation in the stapes of Triassic gomphodont cynodonts. A, Diademodon; B, Trirachodon; C and D, Massetognathus. Below is the ventral view of the skull of a cynodont showing the position of the stapes. – WITS University

The stapes is a rectangular bone with a hole in the middle surrounded by anterior and posterior bone columns. It is the only bone of the middle ear and allowed for the transmission of the sound waves from the eardrum to the inner ear.

“Few contributions studied the stapes in cynodonts and it has been historically regarded as a conservative element, showing no differences among species. Surprisingly, we discovered that there are noticeable variations in the morphology of this bone, even within representatives of the same species,” says Gaetano.

One of the major unsolved issues regarding the ear of cynodonts has to do with the eardrum position and characteristics, for which three competing main theories have been proposed. “The cynodont stapes suggests that the sound waves in these animals were transmitted to the inner ear from an eardrum at the posterior part of the lower jaw through the stapes and the quadrate bones,” says Abdala.

He adds that their research are ongoing as they do not know yet whether the differences also imply different hearing capabilities as well and their more in-depth research will focus on how this bone changes from the youngest to the oldest animal in one species.

Gaetano and Abdala’s contribution results in a better understanding of the auditory system in basal cynodonts and its evolution, highlighting the variability of the middle ear bone anatomy. They are currently studying the change in this bone during growth in a South African Triassic cynodont.

UNIVERSITY OF THE WITWATERSRAND

 

Download the HeritageDaily mobile application on iOS and Android

More on this topic

LATEST NEWS

NASA Data Helps Uncover Our Solar System’s Shape

Scientists have developed a new prediction of the shape of the bubble surrounding our solar system using a model developed with data from NASA missions.

Ammonia Sparks Unexpected, Exotic Lightning on Jupiter

NASA's Juno spacecraft - orbiting and closely observing the planet Jupiter - has unexpectedly discovered lightning in the planet's upper atmosphere, according to a multi-institutional study led by the NASA/Jet Propulsion Laboratory (JPL), which includes two Cornell University researchers.

Plate Tectonics Goes Global

Today, the entire globe is broken up into tectonic plates that are shifting past each other, causing the continents to drift slowly but steadily. But this has not always been the case.

Lava Tubes on Mars and Moon Wide Enough to Host Planetary Bases

The international journal Earth-Science Reviews published a paper offering an overview of the lava tubes (pyroducts) on Earth, eventually providing an estimate of the (greater) size of their lunar and Martian counterparts.

Researchers Have Sequenced the Genome of the Tuatara, Revealing its Unique Evolutionary History

A global team of researchers has partnered up with the Māori tribe Ngātiwai to sequence the genome of the tuatara, a rare reptile endemic to New Zealand.

Optical Seismometer Survives “Hellish” Summit of Caribbean Volcano

The heights of La Soufrière de Guadeloupe volcano can be hellish, sweltering at more than 48 degrees Celsius (120 degrees Fahrenheit) and swathed in billows of acidic gas.

Herbivores, Not Predators, Most at Risk of Extinction

One million years ago, the extinction of large-bodied plant-eaters changed the trajectory of life on Earth.

Native American Stone Tool Technology Found in Arabia

A new study led by archaeologists from the CNRS, the Inrap, the Ohio State University and the Max Planck Institute for the Science of Human History, reports on fluted points from the archaeological sites of Manayzah in Yemen and Ad-Dahariz in Oman.

Popular stories

Port Royal – The Sodom of the New World

Port Royal, originally named Cagway was an English harbour town and base of operations for buccaneers and privateers (pirates) until the great earthquake of 1692.

Matthew Hopkins – The Real Witch-Hunter

Matthew Hopkins was an infamous witch-hunter during the 17th century, who published “The Discovery of Witches” in 1647, and whose witch-hunting methods were applied during the notorious Salem Witch Trials in colonial Massachusetts.

Did Corn Fuel Cahokia’s Rise?

A new study suggests that corn was the staple subsistence crop that allowed the pre-Columbian city of Cahokia to rise to prominence and flourish for nearly 300 years.

The Real Dracula?

“Dracula”, published in 1897 by the Irish Author Bram Stoker, introduced audiences to the infamous Count and his dark world of sired vampiric minions.