中国石蚕巢化石(昆虫纲,毛翅目)的发现与初步研究

毛翅目昆虫幼虫俗称石蚕,大部分石蚕就地取材,构筑不同形状,不同质地的巢,多数为管状.石蚕巢化石是一类较重要的遗迹化石,在国外中、新生代报道较多,但在我国未见发表.本文根据作者十多年来在华北及东北地区的大量野外工作,报道了石蚕巢化石在我国的发现.介绍了石蚕巢在中侏罗世道虎沟动物群,早白垩世热河动物群及卢尚坟昆虫群中的类型与特征.石蚕巢是我国遗迹化石研究中的薄弱环节,实际上它们在中生代中期以后的陆相地层分布很广.由于这类昆虫对水质变化的敏感性和适应的相对狭隘性,可用于恢复古环境.一些特殊类型的出现,对地层对比也将起到作用.

THE DISCOVER AND PRELIMINARY SYUDY OF FOSSIL CADDIS CASE IN CHINA

Most of caddis larvae constructed cases by using various materials such as sand grains,plant fragments,and small shells of different shapes.Caddis cases are important trace fossils that are common worldwide in the Mesozoic and Cenozoic.But hitherto they have not been reported from China,and this study is the first report of their occurrence in many localities.For example,hundreds of caddis cases from the Lower Cretaceous Lushangfen Formatio,collected since 1995.A few cases are examined from a collection from the Middle Jurassic Daohugou fauna.Caddis cases occur widely in the Lower Cretaceous Yixian Formation at Western Liaoning(e.g.Huangbanjigou,Jianshangou,and Sihetun of Beipiao City),Inner Mongolia(e.g.Liutiaogou of Ningcheng County),and Northern Hebei(e.g.Gaositai of Chengde City).Moreover,a few caddis cases have been collected from the Lower Cretaceous Laiyang Formation at Nanligezhuang of Laiyang City,Shandong Province and Jiufotang Formation at Pijiagou of Yixian County,Liaoning Province.Cenozoic cases are poorly known from China,and only a few Miocene specimens have been found in the Shanwang Formation at Changle County of Shandong Provinee.The earliest caddis case iS known from the Early Jurassic of Transbaikalia.However,specimens of pre-Cretaceous age are very rare.A few small caddis cases have recently been collected from the Middle J urassic Daohugou fauna.These relatively straight tubular cases are constructed basically by fine sand grains.Various caddisflies have been examined in the Daohugou fauna dominated by small forms.At least the Philopotamidae and Necrotauliidae can be identified from our material.However,recent philopotamids are net-spinners.The Necrotauliidae is a complex extinct family with unknown larval habit.Thus,the understanding of the constructers of the Middle Jurassic cases may provide some clues to the classification of the Necrotauliidae and early Trichoptera.The caddis cases in the Yixian Formation occur in numerous localities.Most of them are characterized by a slightly curved thick tube composed of sand grains or small shells(mainly ostracods and rarely bivalve fragments).The cases made up from plant fragments are rather rare.Some entirely secretion cases have also been found in the Yixian Formation.The Early Cretaceous Lushangfen entomofauna is a local ecosystem confined to western Beijing region,represented by Hemeroscopus baissicus and Xishania fusiformis.The abundant cases in the Lushangfen Formation exhibit an outline of curved tostraight tube that more or less tapering backwards,composed mostly of sand grains,with very rare plant fragments.The representative species H.baissicus indicates a comparable geological age of the Lushangfen Formation and the Zaza Formation in the Baissa locality of Siberia.This correlation is also supported by the resemblance of caddis case,especially the occurrence of a special bacilliform(of annelid affinity according to the original author)in both localities.The findings of caddis cases in this study may be used for the palaeoenvironmental analysis in further studies.Their biostratigraphical implications for Mesozoic terrestrial strata also deserve further study.