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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 JediJeb on 4/19/2011 4:08:39 PM , Rating: 2
The Dark Matter question you talk about is one I have been pondering also. What gets me about it is that instead of questioning the theories on the behavior of gravity they just made up more mass to compensate. Maybe gravity behaves differently over large distances than we have been able to experimentally discern. If gravity is not constant, but actually varies more with distance could that explain the disparity in the rotational speeds of galaxies and thus all the way down to quantum level interactions? If gravity is a variable with a very very small delta over distance, instead of a constant maybe that would explain a lot of things. Problem is if that is actually true, then a lot of scientists have to admit they were wrong, and we have seen in the past just how hard that can be even with things like relation of planets to the sun, size and shape of the Earth, whether or not you can travel faster than the speed of sound( was once believe that if anyone tried they would disintegrate) and many other scientific "truths" we now take for granted.

Even with evolution, the evidence works for now, but if in the future some evidence points to a different conclusion will scientists be able to change their views? Scientists for all their logical thinking can also be some of the most stubborn people when their theories are challenged. Not saying scientists are better than religious people or vice versa, just pointing out that both sides can be guilty of being bull headed in their views so it isn't always warranted that scientists must bash the religious for their views or the other way around.


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