Researchers say they have discovered how humans got teeth. The researchers are from Uppsala University in Sweden. They say that human teeth "first evolved 400 million years ago". They believe our teeth came from an ancient fish called an acanthothoracid. The researchers studied a fossil of the fish. It was difficult to study because the fish is encased in rock. The researchers had to use the strongest X-ray machine in the world to analyse it. They used the X-ray machine to "digitally dissect" the fish. The researchers discovered that the fish's teeth were amazingly similar to human teeth. The researchers also said humans and 60,000 species of jawed vertebrates living on Earth today come from this fish.
The researchers say the acanthothoracid was one of the earliest jawed vertebrates with teeth ever to live. They were very excited at seeing how similar its teeth were to ours. A co-author of the study, Professor Per Ahlberg, said: "These findings change our whole understanding of the origin of teeth." He commented on the similarity to the fish, saying: "Their jawbones resemble those of bony fish and seem to be directly ancestral to our own. When you grin at the bathroom mirror in the morning, the teeth that grin back at you can trace their origins right back to the first jawed vertebrates." Another researcher said: "Nobody expected to find teeth so deep on the evolutionary tree."
1.It was difficult to study because the fish is encased in rock.
When nuclear fuel is manufactured it is encased in metal cans.
2.They used the X-ray machine to "digitally dissect" the fish.
Her latest novel was dissected by the critics.
研究人员表示，acanthothoracid是有史以来最早的有牙齿的颚脊椎动物之一。看到它的牙齿和我们的牙齿如此相似，他们非常兴奋 。该研究的联合作者Per Ahlberg教授表示：“这些发现改变了我们对牙齿起源的全面理解 。”他对和鱼的这种相似性进行评论，并表示：“它们的颚骨与多骨鱼的颚骨相似，似乎是我们人类牙齿的祖先 。当你早上对着浴室的镜子笑时，对着你笑的牙齿，它们的起源可以追溯到最早的有颚的脊椎动物 。”另一名研究人员表示：“没人想到会在进化树这么底层的地方发现牙齿 。”