A plastron is the underside of a tortoise or turtle's shell.

海龟的底部有龟甲。

On which of these animals would you find a plastron?

在这些动物中，哪种动物身上有甲？

And that's when the ribs started to fuse into a plastron, which eventually became a full, protective shell.

那就是肋骨开始融合成甲的时候，甲最终变成了一个完整的保护壳。

It was shaped a lot like a turtle, but it only had the bottom part of the shell — the plastron.

它的形状很像乌龟，但只有壳的底部——甲。

The fact that it had a plastron without a carapace was pretty strong evidence for the developmental biologists' hypothesis, that the plastron evolved first.

它有一个没有甲壳的甲这一事实有力地证明了发育物学家的假，甲首先进化。

They found that, as turtles develop, bones that basically function as a set of lower ribs widen and fuse, forming the plastron.

他们发现， 随着海龟的发育，基本上起一组下肋骨作用的骨骼变宽并融合，形成了甲。

So old grandpa turtle seemed to mark a kind of transitional stage between Eunotosaurus, with its wider ribs, and Odontochelys, with its full plastron.

这么老的龟爷爷似乎标志着一种过渡阶段，介于具有更宽肋骨的真诺龙和具有完整甲的齿甲龟之间。

The development of the bottom half of the shell, the plastron, is driven by neural crest cells, which can produce a variety of different cell types including neurons, cartilage and bone.

下半部分的龟壳是胸甲，它由神经嵴细胞主导形成，神经嵴细胞可以发育出多种细胞，像神经元、软骨和骨细胞。

I mean, it had a shell, with a flat plastron on the bottom that was fused to a carapace on top — so it had all the requirements for what makes an official turtle.

我的意思是，它有一个壳，底部有一个扁平的甲，与顶部的甲壳融为一体——所以它具备制造官方海龟的所有要求。