The original news story can be found here. The discovery of the fossil in Hyogo prefecture was announced last Thursday. The fossil was of a mammal and was found in a geological area that dates from 139 to 136 million years ago. The archaeologists were only able to find the lower right portion of the animals jaw, but that was enough to tell scientists what the animal might have been. It is assumed that the animal looks like a mouse that was 10 to 20 centimetres in body length. You can see the fossil in the picture below.
This fossil is the oldest mammal fossil found in Japan and it may be a good clue about the evolution of mammals. The teeth in the jaw that they found had molars that are similar to the ones find in mammals of today, so it is thought that this animal is a distant cousin of the mammals that we see walking the earth today.
The fossil contains a part of the jaw which is 2.5 centimeters in length and contains the lower portion of the jaw and 8 teeth including a cuspid, premolars and molars. The roots of these teeth are actually bifurcated, a characteristic that is found only in mammals. From the teeth, scientists hypothesize that the animal would have eaten plants and small bugs.
This fossil resembles a fossil that was found in China 6 years ago. The Chinese fossil was placed in the taxon of eutheria, which means that is a placental mammal. It got the name of Eomaia scansoria and was thought to live about 125 million years ago. This means that the Japanese fossil is actually older than the Chinese fossil. Scientist think that the Japanese fossil gives a picture of what mammals may have been like before their offspring evolved into eutheria mammals.
There are only 11 other places in the world that have produced fossils from the same era as the one found in Japan. That means this fossil is something that is extremely important and can give everyone a good idea of the way this animals have evolved over generations. This find is very excited and I hope they can find more fossils like it in the same fossil bed.
Any way, it is now time for the word of the day. Today's word is 哺乳類(ほにゅうるい). It is pronounced honyuurui and means mammal. Mammal (or Mammalia) is a class. Eutheria is actually an infraclass. I guess "King Phillip Came Over From Great Spain " has gone out the window now that there are so many different subclasses for taxons now.
That's it for today. See you next time at JJNN.
Cool!
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