In the lig 1920s, Dr. Erik Stensiö, ntawm Swedish Tsev khaws puav pheej ntawm Natural History hauv Stockholm, tsim cov ntsiab lus ntawm placoderm anatomy thiab txheeb xyuas lawv tias muaj tseeb lub puab tsaig ntses ntsig txog sharks. Nws coj cov pob txha pob txha nrog pob txha taub hau zoo thiab muab pov tseg, ib feem kaum ntawm ib millimeter ib zaug.
thawj placoderm yog dab tsi?
Fossil cov ntaub ntawv
Cov pob txha placoderm ntxov tshaj plaws yog los ntawm Tuam Tshoj thiab hnub mus rau lub Silurian thaum ntxov. Thaum lub sij hawm ntawd, lawv twb sib txawv rau hauv cov antiarchs thiab arthrodires, nrog rau lwm yam, ntau primitive, pawg. Yav dhau los fossils ntawm basal Placodermi tseem tsis tau pom.
Placoderm thawj zaug tshwm sim thaum twg?
Placoderms muaj nyob thoob plaws Lub Sijhawm Devonian (kwv yees li 416 lab rau 359 lab xyoo dhau los), tab sis tsuas yog ob hom txuas ntxiv mus rau lub sijhawm ua tiav Carboniferous. Thaum lub sij hawm Devonian lawv yog ib pawg tseem ceeb, tshwm sim nyob rau hauv txhua lub teb chaws tshwj tsis yog South America nyob rau hauv ntau yam marine thiab dej tshiab sediments.
Placoderm fossils pom nyob qhov twg?
Placoderm tseem suav nrog cov ntaub thaiv taub hau ntawm Macropetalithys, muaj nyob hauv Middle Devonian pob zeb hauv Ohio. Txawm li cas los xij, qhov kev nplua nuj tshaj plaws thiab ntau haiv neeg ntawm placoderm tseem yog paub los ntawm Upper Devonian Ohio Shale thiab tshwj xeeb yog Cleveland Shale Cov Tswv Cuab ntawm chav tsev no hauv cheeb tsam Cleveland.
Thaum twg cov ntses armored nrhiav tau?
Dunkleosteus tau ploj mus nrog rau tag nrho lwm cov Placoderms thaum lub sijhawm Devonian loj ploj mus. Dunkleosteus cov seem tau pom thawj zaug los ntawm cov kws paub txog kev ua neej ua haujlwm paleontologist Jay Terrell thiab nws tus tub hauv 1867raws ntug dej hiav txwv Lake Erie ntawm lub nroog Sheffield Lake. Nws hu tias tus tsiaj no phem heev.
