On which of these animals would you find a plastron?

在这些动物中，哪种动物身上有腹甲？

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

海龟底部有龟甲。

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腹甲时候，腹甲最终变成了一个完护壳。

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

形状很像乌龟，但只有壳底部——腹甲。

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， 随着海龟发育，基本上起一组下肋骨作用骨骼变宽并融合，形成了腹甲。

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

这么老龟爷爷似乎标志着一种过渡阶段，介于具有更宽肋骨真诺龙和具有完腹甲齿甲龟之间。

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

有一个没有甲壳腹甲这一事实有力地证明了发育生物学家假设，即腹甲首先进化。

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.

下半部分龟壳是胸甲，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.

我意思是，有一个壳，底部有一个扁平腹甲，与顶部甲壳融为一体——所以具备制造官方海龟所有要求。