Normally, atoms react with each other to get a full outer shell of electrons, because that's when they're the most stable.

一般情况下，原子之间相互反应是为了使其最外层电子达到饱和，因为那样它们才会最稳定。

Our first fossil evidence of the full shell characteristic of modern turtles is about 210 million years old, and belongs to a species called Proganochelys quenstedti, whose ribs had fused.

我们的第一个化石证据表明，现代海龟具有完整外壳特征大约有 2.1 亿年的历史，化石是一种原颚龟物种，其肋骨已融合在一起。

It's stacked with a diverse array of reptilian characters, some of which have no shells, others of which have partial shells, and others still who sport the full, beautiful shells and famously slow gaits that we know today.

它堆放着各种各样的爬行动物角色，其中一些没有壳，另一些有部分壳，还有一些仍然拥有我们今天所知的完整、美丽的壳和著名的缓慢步态。