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The words
Researchers say they have [discovery / discovered] how humans got teeth. The researchers are from Uppsala University in Sweden. They say that human [tooth / teeth] "first evolved 400 million years ago". They [believe / belief] our teeth came from an [ancient / anchor] fish called an acanthothoracid. The researchers studied a fossil [off / of] the fish. It was difficult to study because the fish is encased [on / in] rock. The researchers had to use the strongest X-ray machine in the world to [analyse / realise] it. They used the X-ray machine to "digitally [dissect / insect] " the fish. The researchers discovered that the fish's teeth were [amazed / amazingly] similar to human teeth. The researchers also said humans and 60,000 [specials / species] of jawed vertebrates living on Earth today come from this fish.

The researchers say the acanthothoracid was one of [an / the] earliest jawed vertebrates with teeth ever to [lively / live] . They were very excited at seeing how similar its teeth were to [hours / ours] . A co-author of the study, Professor Per Ahlberg, said: "These findings [change / charge] our whole understanding of the [origin / original] of teeth." He commented on the similarity to the fish, saying: "Their jawbones [resemble / tumble] those of bony fish and seem to be directly ancestral to our [down / own] . When you grin at the bathroom mirror [in / on] the morning, the teeth that grin back at you can [brace / trace] their origins right back to the first jawed vertebrates." Another researcher said: "Nobody expected to find teeth so deep on the evolutionary [tree / shrub] ."

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