这种变化表现在树木的年轮中。

This variation shows up in the trees growth rings.

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爬行动物的骨骼生长在本质上是周期性的，在骨头上产生一系列的同心圆，就像树木的年轮一样。

Bone growth in reptiles is periodic in nature, producing a series of concentric rings in the bone, not unlike the growth rings of a tree.

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替换可能是一个令人惊叹的精确过程，因此贝壳纹饰的细节，树木的年轮和骨的微妙结构都被准确地保存。

Replacement can be a marvelously precise process, so that details of shell ornamentation, tree rings in wood, and delicate structures in bone are accurately preserved.

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