Because they lack a bony skeleton , cartilaginous Fish like shark are often thought of as primitive . And as such , when imagining the show of an root of all jawed vertebrates — from reptiles and amphibians to birds , mammals , and people — we frequently envisage something resemble a shark . Now , researchers re - examining a 415 - million - yr - old fish head from Siberia bring out how the last common ancestor of jawed vertebrates was amazingly not shark - like : Instead , it resembled bony fishes , like tunny or codfish . That means sharks had ancestors that were once bony too . Thefindingswere published inNaturethis week .
Currently domiciliate in Estonia , the skull was discovered near Sida River in Siberia in 1972 . free-base on its external feature of speech , researchers previously think it belong to to an former bony Pisces the Fishes ( orosteichthyan ) , a chemical group that not only have skeletons made of off-white , but also armor on their faces , like tuna , salmon , and even coelacanths . But now , Martin Brazeau of Imperial College London , together withOxford ’s Matt FriedmanandSam Giles , used X - ray CT scan to make a 3D virtual model of the fossil — revealing never - before - see anatomical inside information inside the skull , such as the traces left by networks of blood vessel and nerves .
Underneath its bony skull roof was a brainpan interchangeable to that of gristly fish ( orchondrichthyans ) , like today ’s sharks and rays . The team placed it in a new spot at the stem of all jawed vertebrate , before bony fish and sharks spilt .
Chondrichthyans are often treat as proxies for what the ancestral jawed craniate would have looked like because of their want of a bony underframe . “ The results from our depth psychology help to turn this view on its head : The early jawed vertebrates would have looked somewhat more like bony fishes , at least outwardly , with large cutaneal plates covering their skulls , ” Giles explain in auniversity statement . “ In fact , they would have had a intermixture of what are now view as cartilaginous- and bony Pisces - like features , supporting the theme that both radical became independently specialized afterwards in their separate evolutionary history . ”
That means that sharks lost their bony armor betimes in their evolution . " Losing your bony skeleton vocalize like a pretty extreme adaptation,“Friedman says , but fresh discovery like these indicate that " the ancient ancestors of modern shark and their kin group started out just as ' bony ' as our own ancestor . ”
Because of its newfound dual - sided nature , the ancient Pisces the Fishes was renamedJanusiscus schultzeiafter Janus , the double - faced Roman god .
" It ’s deceptive to think of evolution as a ladder which we restore with ' miss links ' , " Brazeau aver in anews release . " It ’s more precise to call back of it as a menage tree , and research into evolution is like work a mystifier . Each Modern opus you ascertain throws the surrounding spell into linguistic context and helps you to understand them better . Janusiscushas helped us to take care at sharks differently and will insure they are no longer dismissed as being ' frozen ' at a primitive level of phylogenesis . "
Images : S. Giles et al . , Nature 2015
