下面一段出自 2013 年高考英语江苏阅C:
Other air-breathing animals also suffer this decompression (减压) sickness if they surface too fast: whales, for example. And so, long ago, did ichthyosaurs. That these ancient sea animals got the bends can be seen from their bones. If bubbles of nitrogen form inside the bone they can cut off its blood supply. This kills the cells in the bone, and consequently weakens it, sometimes to the point of collapse. Fossil (化石) bones that have caved in on themselves are thus a sign that the animal once had the bends.
请专家老师翻译一下最后一句:
Fossil (化石) bones that have caved in on themselves are thus a sign that the animal once had the bends.
自告奋勇,说一下我的理解。 (不当之处,还请其他老师们多多指正。)
Fossil bones that have caved in on themselves are thus a sign that the animal once had the bends.
句子主干: Fossil bones (主) are (谓) a sign (表). 化石骨是一种迹象。
Fossil bones that have caved in on themselves (后置定语修饰 Fossil bones)
a sign that the animal once had the bends(和 a sign 为同位语关系).
Fossil bones that have caved in on themselves are thus a sign that the animal once had the bends.
骨质疏松的化石骨骼即表明此动物曾患有减压病。
or
疏松的化石骨骼就是一种迹象,即此动物曾患有减压病。