extinct stem group found british_columbia canada fewer good specimens described specimens known greater bed comprise community soft bodied animal modest size body sides fan shaped tail head shows unusual features eyes mouth head facing backwards probably passed food mouth probably lived seek small soft food thorough examination revealed unusual features thought unrelated known possibly related hypothetical ancestor worms finds notably suggested belonged group animals closely related ancestors living animals members 1970s ongoing debate multi animals appeared suddenly early event called explosion arisen earlier leaving fossils regarded strong evidence explosive hypothesis later discovery series similar animals closer development idea stem groups suggested early time relatively fast evolution understood assuming unique evolutionary processes history discovery found complete fossils classified media published description generic derived pass mount southeast lake british_columbia canada found good specimen published detailed description based thorough specimens photographs specimens lit variety angles analysis cover media specimens species identified collection russian described specimens found region siberia labelled fossils poorly preserved feel provided information classified members genus occurrence recognized specimens found far come bed canadian british_columbia reported south_australia new specimen better preserved previous specimens leading conclude close relative interpretation later questioned instead concluded worm description looked strange audience presentation analysis laughed length head tail ranged centimetres centimetres animal hollow total length body projected head curved forwards upwards like vacuum cleaner probably flexible ended like structure inner edges bore spines projected forwards head bore eyes near fairly close middle head pointing upwards forwards larger eyes near rear outer edges head pointing upwards sideways single eye shorter stalk larger pair eyes pointing upwards assumed eyes compound like lateral eyes reconstruction backed evidence somewhat mouth head pointed backwards digestive tract formed bend way rear animal appeared sufficiently long flexible reach mouth main body typically millimetres wide segments pair flaps pointing downwards overlapped covered rear edge ahead body ended looked like single conical segment bearing pairs overlapping pointed forming tail like shaped double fan interpretations features fossils differ animals armor tough organic like insects bodies flattened buried smaller internal features appear markings outlines fossils interpreted gills markings upper surfaces thought gills flat underneath overlapping layers attached bases thought consisted separate blades attached edges found marks inside edges interpreted internal channels connecting gills interior body interpreted mark internal channel hand interpreted gills covering upper surface body found evidence near triangular features body concluded internal structures likely sideways extensions gut interpreted contained sides thought wide fit slender body cross section views showed attached separately lower extended body later found specimens appeared preserve legs exterior cuticle interpreted short conical legs found small patches tips interpreted claws analyzed chemical composition concluded composition gut agreed digestive system instead regarded lobe gill arrangement early form limbs seen crustaceans original form similar chemical composition associated digestive tract suggest represents forming fluid filled body consistent hollow legs lifestyle way animals buried sediment laden current acted suggests lived surface probably search sediment food particles pass mouth sign function jaws food presumably small soft believing legs thought slowly especially timed movements create mexican waves hand thought body flexible allow fish like body classification considering differ surprising animal classification debated original considered following earlier work thought belonged called thorough analysis concluded found evidence limbs like flexible probably fluid filled known left classification family level open articulated body unusual lateral gills persuaded representative ancestral stock arose published description swedish suggested animals related shared lateral flaps gills eyes features classified primitive considered single found considered evidence short legs examination million years ago years older convinced similar legs considered legs genera similar modern regarded closely related ancestors examining sets features shared similar drew broad scale reconstruction stem group words considered evolutionary cousins striking feature family tree modern closest living evolutionary relatives disagreed diagnosis legs resemblance saw lobe gill arrangement limbs led conclude closely related fact presented family tree similar theirs mention theoretical significance clear little known soft bodied animals usually leave fossils described mid-1970s vigorous debate early evolution animals argued process explosive early 1970s developed theory punctuated views evolution long intervals near punctuated short periods rapid change hand time argued animal kingdom long history hidden lack fossils concluded taxa accommodated modern groups primary reasons book considered early life diverse experimental later set animals explosion truly dramatic event possibly driven unusual evolutionary mechanisms regarded important understanding phenomenon wanted book homage discoveries analyses soon followed revealing similar looking animals animal considered similar modern regarded close relatives defined group called include animals thought close relatives lack limbs debate include descendants single common ancestor sub group sister group discussion specific fossils going concept stem groups introduced cover evolutionary cousins crown group group closely related living animals plus common ancestor plus descendants stem group contains members lineage earlier common ancestor crown group relative concept example living animals form crown group right regarded stem group relative viewing strange looking organisms like way makes possible explosion unusual understood terms normal evolutionary processes
Opabinia