And heterostracans, osteostracans and placoderms have been found in both salty AND fresh water environments.

在咸水和淡水环境中都发现了 heterostracans、osteostracans 和 placoderms。

And scientists have seen signs of those changes in the armor of heterostracans, osteostracans and placoderms.

科学家们已经看到了异类动物、骨类动物和盾皮动物的盔甲发生这些变化的迹象。

They didn't have much of one -- their backbones, like those of heterostracans and earlier fish, was made of cartilage.

它们的脊椎骨并不多——它们的脊椎骨，就像杂鱼和早期鱼类的脊椎骨一样，是由软骨构成的。