transitional fossil transitional fossil remains life form exhibits traits common ancestral group derived descendant group especially important descendant group sharply differentiated gross anatomy mode living ancestral group fossils serve reminder taxonomic divisions human imposed variation fossil record usually way know exactly close transitional fossil point divergence assumed transitional fossils direct ancestors recent groups frequently models ancestors published fossil record poorly known darwin described perceived lack transitional fossils obvious objection urged theory explained relating extreme geological record noted limited collections available time described available information showing patterns followed theory descent modification natural selection discovered years later represents classic transitional form birds transitional fossils discovered abundant evidence classes related form transitional fossils specific examples include humans fish birds term missing link extensively popular writings human evolution refer perceived gap evolutionary record commonly refer new transitional fossil finds scientists use term refers pre evolutionary view nature evolutionary phylogenetic taxonomy transitions phylogenetic nomenclature evolutionary taxonomy prevailing form taxonomy 20th century non specialist textbooks taxa based morphological similarity drawn bubbles branching forming evolutionary trees transitional forms seen falling groups terms anatomy having mixture characteristics inside outside newly branched clade establishment 1990s relationships commonly came expressed illustrate branching evolutionary stick like figures different called natural groups form units given phylogenetic names traditional classification fish seen different groups considered branch fish longer transition established groups term transitional fossils occurs groups represented branches context transitional organisms seen representing early examples branch traits typical previously known descendants branch evolved early representatives group usually termed basal taxa sister taxa depending fossil organism belongs daughter clade transitional versus ancestral source confusion notion transitional form different taxonomic groups direct ancestor groups difficulty exacerbated fact goals evolutionary taxonomy identify taxa ancestors taxa impossible sure form represented fossil record direct ancestor fact evolution branching process produces complex bush pattern related species linear process producing ladder like progression fossil record unlikely particular form represented fossil record direct ancestor concept taxonomic group ancestor instead emphasizes identification sister taxa share recent common ancestor groups exceptional cases marine fossil record complete suggest confidence certain fossils represent population actually ancestral later population different species general transitional fossils considered features illustrate transitional features actual common ancestors different taxa actual ancestors prominent examples genus dinosaur closely related birds late 19th century accepted celebrated lay reference works oldest known bird study cast doubt assessment suggesting instead non dinosaur closely related origin birds lived southern germany late period million years ago europe archipelago shallow warm tropical sea closer equator similar shape european largest individuals possibly attaining size raven grow metres length despite small size broad wings ability fly common small modern birds particular shares following features jaws sharp teeth fingers claws long bony tail second toes killing feathers suggest skeletal features features clear candidate transitional fossil birds making important study origin birds complete specimen announced fossils found known fossils include impressions feathers oldest direct evidence structures feathers advanced form flight feathers fossils evidence feathers began evolve late represents evolutionary transition modern humans ancestors number traits skeleton strongly reflect extent researchers suggested evolved long overall anatomy far human like like blades short wide wide positioned directly hip joint clear evidence strong attachment knee implying upright posture entirely like human markedly wide blades features point structure radically accommodate significant degree angles knee hip trait allows foot fall closer body strongly indicates present day humans spider possess feature feet feature big toes making difficult impossible grasp branches slightly larger brain modern closest living relative humans teeth human like marine descendants land mammals extinct family mammals earliest closest sister group family lived early million years ago fossils discovered river far shores hear water enhanced bone depending membranes like land mammals arrangement directional hearing water lived million years ago discovered pakistan probably amphibious looked like inhabited bays northern pakistan fossils found near shore shallow marine deposits associated abundant marine plant fossils found marine deposits oxygen values indicate consumed water range degrees specimens showing evidence sea water consumption fresh water consumption time teeth clear tolerated wide range salt concentrations diet probably included land animals approached water drinking freshwater aquatic organisms lived river represent transition phase ancestors freshwater marine habitat genus extinct lobe fish period features akin legged animals lines ancient develop adaptations oxygen poor shallow water habitats time adaptations led evolution preserved fossils found canada lived approximately million years ago suggest representative transition non known fossils million years old early known fossils million years old mixture primitive fish derived characteristics led characterize unlike previous fish like transitional fossils fins basic wrist bones simple rays reminiscent fingers weight bearing like modern rib bones mobile neck separate pectoral lungs gills scales fins fish found poland reported nature january dated million years older oldest known example implying animals like possessing features evolved million years ago late surviving relics direct transitional forms highlight little know earliest history land order ray fish obvious characteristic modern eyes head adult fish families eyes right body right eyed left left eyed primitive include equal numbers left eyed individuals generally families distinguishing features order presence eyes adaptation living extension dorsal fin head million year old fossil fish identified early relative transitional fossil transition typical head incomplete eye placed near center head concluded change happened gradually way consistent evolution natural selection suddenly researchers little choice believe fossil fish species known related similar fossil slightly earlier strata france middle precursor seed plants identified belgium earliest seed plants million years small symmetrical surrounded bears extension protruding suspected extension involved sheds new light sequence character acquisition leading seed having qualities seed plants solid seed coat system guide seed fossil record transitional form appears fossil record fossil record complete organisms rarely preserved fossils best circumstances fraction fossils discovered noted illustrated fact number species known fossil record number known living species suggesting number species known fossils far species lived specialized rare circumstances required biological structure logic known fossils represent small percentage life forms existed discovery represents evolution transition illustrated transitional fossils demonstrate exact half way point clearly forms fossil record uneven exceptions heavily organisms hard parts leaving groups soft bodied organisms little fossil record groups considered good fossil record including number transitional fossils traditional groups groups history transitional fossils idea animal plant species constant changed time suggested far 18th century darwin published gave firm scientific basis weakness darwin work lack evidence pointed darwin easy imagine natural selection producing variation seen genera families higher categories harder imagine dramatic find london specimen years publication darwin work offered time link class highly derived birds primitive reptiles letter darwin wrote commissioned august command turn strange executed behest transitional fossils like came seen darwin theory icons evolution right example swedish dictionary showed inaccurate reconstruction illustration fossil significant discoveries rise plants transitional fossils animals increasing mapping divisions plants beginning 20th century search began ancestor plants found remains extremely primitive plant scotland named plant small stick like simple branching stems leaves tipped simple form echoes shown generations corresponding form crowded stems millimetres height falls midway early plants like carpet moss like larger grew like simple spreading means horizontal growing stems growing anchored plant substrate unusual mix moss like traits extreme structural simplicity plant huge implications botanical understanding missing links term missing link refers originally static pre evolutionary concept great chain idea existence linked lowest dirt living kingdoms angels finally god idea living things linked sort process darwin theory evolution envisioned life generated form simplest creatures constantly complexity perfection humans series lower forms view lower animals simply newcomers evolutionary scene idea lower animals representing earlier stages evolution demonstrated figure human pedigree seen forming sort evolutionary sequence classes distinct intermediate forms called missing links term scientific context edition book elements geology relation missing parts geological column popularized present meaning appearance page book antiquity man time generally thought end glacial period marked appearance humanity drew new findings antiquity man origin human beings deep geological past wrote remained profound mystery huge gulf man beast vivid writing fired public imagination inspiring journey center earth second edition avant earth flood included dramatic illustrations savage men women wearing animal skins wielding stone axes place garden shown edition idea missing link humans called lower animals remains lodged public imagination search fossil showing transitional traits humans fruitless young dutch found banks java find combined low like skull roof brain estimated midway adult human single larger modern human tooth long straight knee angle showing java man walked upright given erect man long list human evolution fossils time hailed missing link helping set term primarily human fossils like dinosaur bird missing link popular term recognized public popular media avoided scientific press relates concept great chain notion simple organisms primitive versions complex ones discarded biology case term misleading known transitional fossil like longer missing find rise new gaps evolutionary story discovery transitional fossils continues add knowledge evolutionary transitions punctuated theory punctuated developed presented mistakenly drawn discussion transitional fossils theory documented transitions taxa closely related taxa short period time transitions usually geological small jumps morphology extended periods morphological stability explain jumps envisaged comparatively long periods genetic stability separated periods rapid evolution following observation concerning work deny existence transitional fossils proposed punctuated explain trends quoted design know admitting fossil record includes transitional forms occur level species directional trends staircase model higher level transitions major groups
Transitional fossil