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Liaoconodon hui  (Source: Jin Meng)
A new fossil, Liaoconodon hui, was found in China and has all three middle ear bones

Researchers have discovered a complete mammalian fossil that includes a transitional middle ear, which consists of three bones that paleontologists have been searching for over 150 years.  

Jin Meng, study leader and curator in the Division of Paleontology at the American Museum of Natural History, along with Wang Yuanqing and Li Chuankui, both from the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences in Beijing, have found the first complete mammalian fossil that includes the transitional middle ear.

Mammals are defined as a class of air-breathing vertebrate animals that share characteristics like hair and mammary glands in mothers with young. They also share three middle ear bones called the malleus, incus and ectotympanic. Two of these bones are found in the joint of the lower jaw in reptiles, and researchers believe that an evolutionary shift from lizards to mammals separated the quadrate and articular plus prearticular bones from the posterior lower jaw, and they became associated with hearing as the malleus and the incus.

Previous fossils show early mammals with reptilian jaw joints and reductions in these bones for both chewing and hearing while other early mammalian fossils have ossified cartilage still connected to the groove on their lower jaws. But none of these fossils had the middle ear bones, and more evidence was needed to confirm this early transition and the mysteries of the mammalian middle ear. 

"People have been looking for this specimen for over 150 years since noticing a puzzling groove on the lower jaw of some early mammals," said Meng. "Now we have cartilage with ear bones attached, the first clear paleontological evidence showing relationships between the lower jaw and middle ear." 

The new fossil, which is called Liaoconodon hui, is a medium-sized mammal measuring 35.7 cm long. It dates from the Mesozoic (about 125 to 122 million years) and was named after the fossil beds in Liaoning, China, which is where it was discovered. It was also named after Yaoming Hu, who was a graduate of the American Museum of Natural History's doctoral program and passed away recently.  

Liaoconodon hui is complete, and shows researchers that the incus and malleus are detached from the lower jaw in order to create part of the middle ear. According to the study, the incus and the malleus "remain linked to the jaw by the ossified Meckel's cartilage that rests in the groove on the lower jaw," and the eardrum was stabilized with this cartilage as support. 

"Before we did not know the detailed morphology of how the bones of the middle ear detached, or the purpose of the ossified cartilage," said Meng. "Liaoconodon hui changes previous interpretations because we now know the detailed morphology of the transitional mammals and can propose that the ossified cartilage is a stabilizer."

This study also found that the middle ear "probably" evolved twice in monotremes, marsupials and placentals. This was determined by features associated with the groove on the lower jaw and other bones, including the presence of ossified Meckel's cartilage.  

This study was published in Nature.



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By Fritzr on 4/19/2011 8:15:31 PM , Rating: 2
Half assed theories are the very basis of good science. When someone says "that's strange...I wonder why that happened", you are seeing the beginning of a new theory. Sure the first stabs at answering the question may be dead wrong, but they are things that can be tested and modified until the results of extrapolating from the theory match what happens in nature.

This happens repeatedly in Theoretical Physics where scientists spout off with half assed theories and then spend years discovering what the reality is.

A very good example is phlogiston. Researchers noted that a fire in an enclosed container would go out. Animals placed in the container with the fire died as the fire went out. These observations along with others formed the basis of a theory that stated that an unidentified component of air dubbed phlogiston was required by living creatures and was destroyed by fire. This theory was updated when oxygen was discovered and is now known as the Oxidation Theory where oxygen combines with other chemicals in the presence of high temperatures creating the phenomonon called "fire" and is acquired by living beings in a process known as "respiration" for the purpose of providing energy in the living cells through "oxidation". Today Phlogiston Theory is considered half assed, but virtually all the observations and predictions of that outmoded theory remain correct.

Another half assed theory that remains in common use because it is accurate enough is Newton's Law of Gravity.

Just because Phlogiston has been replaced and Newton's Law of Gravity has been shown to be incorrect is no reason to state that they should have never been used due to inaccuracy. Instead both theories formed the basis for the research that eventually disproved them.

"I don't know therefore it cannot be" is not something that advances science.
"I think this might be, let's check it out" is something that advances science.


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