RareFossilRecord
Thepreservationofembryosandjuvenilesisarareoccurrenceinthefossilrecord.Thetinydelicateskeletonsare
usuallyscatteredbyscavengers(食腐动物)weatheringbeforetheycanbefossilizedIchthyosaurs(鱼龙)hadahigherchanceofbeingpreservedthandidterrestr ialcreaturesbe-cause,asmarineanimals,theytendedtoliveinenvironmentsless
subjecttoerosion.Still,theirfossilizationrequiredasuiteoffactors:aslowrateofdecayofsofttissues,littlescavengingby
otheranimals,alackofswiftcurrentsandwavestojumbleandcarryawaysmallbones,andfairlyrapidburial.Giventhese
factors,someareashavebecomeatr easuryofwell-preservedichthyosaurfossils.
ThedepositsatHolzmaden,Germany,presentaninterestingcaseforanalysis.Theichthyosaurremainsarefoundin
black,bituminousmarineshales(页岩)depositedabout190millionyearsago.Overtheyears,thousandsofspecimensof
marinereptiles,fishandinvertebrateshavebeenrecoveredfromtheserocks.Thequalityofpreservationisoutstanding,butwhatisevenmoreimpressiveisthenumberofichthyosaurfossilscontainingpreservedembryos.
Ichthyosaurswithembryoshavebeenreportedfrom6differentlevelsoftheshaleinasmallareaaroundHolzmaden,
suggestingthataspecificsitewasusedbylargenumbersofichthyosaursrepeatedlyovertime.Theembryosarequite
advancedintheirphysicaldevelopment;theirpaddles,forexample,arealreadywellformed.Onespecimeniseven
preservedinthebirthcanal.Inaddition,theshalecontainstheremainsofmanynewbornsthatarebetween20and30
incheslong.
WhyaretheresomanypregnantfemalesandyoungatHolzmadenwhentheyaresorareelse-where?Thequalityof
preservationisalmostunmatchedandquarryoperationshavebeencarriedoutcarefullywithanawarenessofthevalueof
thefossils.Butthesefactorsdonotaccountfortheinterestingquestionofhowtherecametobesuchaconcentr ationof
pregnantichthyosaursinaparticularplaceveryclosetotheirtimeofgivingbirth.
11【单选】
Allofthefollowingarementionedasfactorsthatencouragefossilizationexceptthe _____
Aspeedofburying
Bconditionsofthewater
Crateatwhichsofttissuesdecay
Dcauseofdeathoftheanimal
答案及解析：第一段中间部分提到了theirfossilizationrequiredasuiteoffactors:软组织的腐烂速度缓慢;很少被其他动物残食;缺少混杂冲走小骨头的快速水流和波浪;以及相当快地被掩埋。因此只有D选项,也就是动物的死因没有被提及。
