Sand and mud do not build up over animal carcasses which is required for the fossilisation process.

沙子和泥土不会堆积在化石过程所需的动物尸体上。

And the entire tail was preserved, including the very tip, so we know that it hadn't just lost its knob, say, during the process of fossilisation.

并且整个尾巴都被保存下来，包括最尖端，所以我们知道它并没有在化石化过程中失去它的旋钮。