2.7亿年历史的鲨鱼骨骼中发现绦虫卵化石

A cluster of tapeworm（绦虫） eggs discovered in 270-million-year-old fossilized shark feces suggests that intestinal¹（肠的） parasites² in vertebrates are much older than previously³ known, according to research published January 30 in the open access journal PLOS ONE by Paula Dentzien-Dias and colleagues from the Federal University of Rio Grande, Brazil. Remains⁴ of such parasites in vertebrates from this era are rare- of 500 samples examined, only one revealed the tapeworm eggs. This particular discovery helps establish a timeline for the evolution of present-day parasitic⁵ tapeworms that occur in foods like pork, fish and beef.   The fossilized eggs were found in a cluster very similar to those laid by modern tapeworms. Some of them are un-hatched and one contains what appears to be a developing larva（幼虫）. According to the study, "This discovery shows that the fossil record of vertebrate intestinal parasites is much older than was previously known and occurred at least 270-300 million years ago."   The fossil described in this study is from Middle-Late Permian times, a period followed by the largest mass extinction⁶ known, when nearly 90% of marine⁷ species and 70% of terrestrial（陆地的） species died out.