珍贵的小龙虾蜕皮化石

珍贵的小龙虾蜕皮化石 ))12 F. R. SCHRA M沈炎彬 ) 1Zoological Museum , U niversit y of Amsterdam , P O Bo x 94766 , 1090 GT Amsterdam , The Net herlands ) 2中国科学院南京地质古生物研究所 南京 210008 提要 淡水小龙虾化石在世界上十分少见 。龙虾蜕皮的化石还未曾有过记录 。文中讨论热河生物群上侏罗 统义县组发现的 、保存十分完好的蜕皮化石 。判断其蜕皮标本的 3 个理由是 :没有保存头胸甲 ;步足与体节之间的 关节膜很薄以及几乎看不到磷酸盐化的软组织 。 关键词 小龙虾 蜕皮 热河生物群 辽宁 辽宁凌源附近上侏罗统义县组富产淡水小龙虾 这块标本很明显没有保存头胸甲 。淡水小龙虾蜕皮 化 石 , 是 热 河 生 物 群 中 引 人 注 目 的 无 脊 椎 动 物 。 时 ,外骨骼都从背部中线位置滑落出来 ,使动物逐渐 () Taylo r 等 1999对部分化石进行了研究 。在继而获 脱离壳体 。头胸甲是通过鳃盖区和头的前部薄的关 得的众多化石中 ,其中有的具有特殊的生物学意义 , 节状膜附着于外骨骼上 ,它们很容易沿腹面与腹甲 ) 在此专门予以讨论报道 。 和外骨骼分离 。2胸肢节部分是非关节状的 ,蜕皮 (标本 126345 看来是一个个体蜕皮的外骨骼 图 时张开 ,部分胸节缝合线便是证据 。在蜕去的骨骼 ) ( ) 版 ?。以往颇多研究涉及甲壳类埋藏学 Hof and 上 ,步足与体节之间的关节膜很薄 ,很容易分离 。3 ) Briggs , 1997。在任何情况下 , 化石埋藏都要经历 当前标本几乎看不到有什么磷酸盐化的软组织 ,而 整个动物体的死亡和保存 。细菌起磷酸盐化的过程 热河生物群的小龙虾化石几乎都保存了软组织的残 几乎都是在动物死亡之后 ,这个过程可以分辨动物 留体 ,尽管对这些石化构造的解释很复杂 。本标本 体的外皮和软组织 。真正蜕皮标本的化石记录实 只是表皮有星点状磷酸盐化的迹象 。 蜕皮标本的属罕见 。一个节肢动物外骨骼的所有矿物质和大部 个体长度约有 11 . 5 cm , 在已知这 分有机质都在蜕皮前被重新吸收 。那些蜕下来的膜 一化石群中可谓是佼佼者 。在腹部第 4 、第 5 胸足 薄而软 ,很容易破裂 。此外 ,甲壳类经常吃脱落的外 之间显示了腹环沟构造 ,因此 ,可以推断这是一个老 骨骼 ,把不能消化的物质再循环返回到新骨骼层中 。 年期雌性个体蜕下来的外骨骼 。其腹足显示呈鞭节 ( 因此 ,蜕皮的骨骼如能被埋葬和石化 ,它不可能在环 状痕 迹 , 因 此 , 将 其 归 于 奇 异 环 足 虾 Cricoi dosce2 ) 境中保留很长时间 。 los us aet h us。对蜕皮标本的认识 ,使我们进而了解 ) 到热河生物群化石库中必然还会发现精美的标本 。 我们判断它是蜕皮标本根据以下 3 个理由 : 1 A N UNUS UAL SPECIM EN OF FOSSIL CRAY FIS H MOL T F. R. SCHRAM ( )Zoological M useu m , U ni versity of A mster da m , P O B ox 94766 , 1090 G T A mster da m , T he Net herl an ds SH EN Yan2Bin ( )N anji ng I nst it ute of Geology an d Paleontology , Chi nese A cadem y of S ciences , N anji ng 210008 收稿日期 :1999210230 3 ( ( ) 中国科学院资源与生态环境研究重大项目 KZ9512B12410202,荷兰科学研究组织 t he Net herlands Organizatio n fo r Scientific Research , ( ) ) 7502195212和荷兰皇家学会 t he Royal Net herlands Academy of Sciences资助课 。 ( ) Taylo r et al . 1999st udied t he fo ssil crayfish p ho sp hatized sof t tissue in t he specimen at hand. Crayfish of t he J ehol biota almo st always have re2 f ro m t he Upper J urassic Yixian Fo r matio n of J ehol Gro up , Liao ning Province , China . Very recently mains of t he sof t tissue p reserved , and indeed p re2 mo re specimens were fo und f ro m t hese sites. One of sence of t his material of ten co mplicates interp retatio n t hese is wo rt hy of special remar k and illust ratio n . of t he fo ssilized st ruct ures o n t hese animals. There is Specimen 126354 appears to be 2 so me indicatio n of spot p ho sp hatizatio n of t he cuticle a molted exo ( ) skeleto n Plate ?. Much research in t his specimen , akin to t hat documented by Hof and has been co n2 ( ducted o n t he tap ho no my of crustaceans e . g. , see ( ) Briggs 1997 , but we see no remnant s of p ho sp h2 ) Hof and Briggs , 1997 . In all cases , t hese experi2 tized muscles beneat h t he cuticle . ment s have involved t he deat h and p reservatio n of in2 This specimen p ro bably is a po st2adult individual tact animals. The p rocesses of bacterially mo dulated so me 11 . 5 cm in lengt h , and may be a female wit h an p ho sp hatizatio n co mmence almo st immediate af ter annulus vent ralis. It may belo ng to C ricoi doscel os us deat h , and distinctive stages in t he p rocess have been aet h us rat her t han Pal aeoca m ba r us l icen t i based o n recognized fo r bot h t he cuticles and sof t tissues t here2 it s flagellate pleopo ds. The recognitio n of t hese molt s in . Act ual molt s in t he fo ssil reco rd are rare . The en2 adds to t he unusual and distinctive p reservatio n now tire mineral and much of t he o rganic material of an beco ming recognized f ro m t he vario us localities and art hropo d exo skeleto n are reabso rbed p rio r to ecdysis. st rata of t he J ehol biota of no rt heaster n China . What is cast off t hen is very t hin and f riable , and t hese breakdow n very readily. Furt her mo re , crus2 REFERENCES taceans of ten eat t he shed exo skeleto n to recycle t he Hof C H J ,Briggs D E G , 1997 . Decay and mineralizatio n of mantis unabso rbed materials back into laying dow n t he layers ( ) shrimp s Sto matopo da : Crustacea —a key to t heir fo ssil reco rd. of t he new skeleto n . Co nsequently , molted skeleto ns Palaio s , 12 :420 - 438 . do not remain in t he enviro nment fo r lo ng in o rder to (Taylo r R S , Schram F R , Shen Y B , 1999 . A new family Decapo da : be buried and fo ssilized. ) Astacidaf ro m t he Upper J urassic of China , wit h a reinterp retatio n of ot her Chinese crayfish . Paleo ntological Research ,3 :121 - 136 . This specimen appears to us to be a molt fo r t hree reaso ns. First is it s apparent lack of a carapace . As crayfish molt , t he exo skeleto n typically split s 图版 ?( Plate ?) 说明 dow n t he do rsal midline to allow t he animal to step ( 标本保存在中国科学院南京地质古生物研究所 The specimens st udied here are kept in Nanjing Instit ute of Geology and Palaeo ntology , o ut of t he shell . The carapace is at tached to t he rest )Chinese Academy of Sciences of t he exo skeleto n by t hin art hro dial membranes in 1 . Cricoi doscelos us aet h us Taylo r , Schram and Shen 一个淡水小龙虾蜕t he branchio stegal regio n and at t he f ro nt of t he 皮标本的正模及外模 ,雌性 ;部分外骨骼 ,可见 第二触角及鞭节 、鳞cep halo n. These readily separate f ro m t he remains of 片 、一对第三颚足 、1 - 5 对步足 、第 4 和第 5 胸足之间的腹环沟 、 腹足 、腹肋叶 、尾节 、尾肢内 、外肢以及消化 道 。标本来源于辽宁t he ster nites and endo skeletal apo demes alo ng t he 凌源县大王杖子村附近 ,上侏罗统义县组 。 vent ral surf ace . ( ×1 . 14 ,登记号 : 126354 1a , 1b. Specimen 126354 part and co un2 Seco nd , t he t ho racic limbs are partially disarticu2 terpart of a molted crayfish exo skeleto n , female ; showing antennae , lated and splayed in a manner of a molt , and t he f rac2 flagellum , scap hocerite , a pair of 3rd maxillipeds , 1 - 5 pereipo ds , to ster nal sut ure rat her evident . The art hro dial mem2 p ro bably annulus vent ralis , pleura , pleopo ds , telso n , exopo d and en2 branes bet ween leg and bo dy segment s are very t hin dopo d of t he uropo d , and alimental canal . The specimen came f ro m in a molted skeleto n and can easily part . Upper J urassic Yixian Fo r matio n , Dawangzhangzi village , Lingyuan ) Co unt y , Liao ning Province ; nat ural size。 Third , t here is lit tle o r no evidence of inter nal