Understanding the origin and chronicle of on-key dolphin has been complicated by the fact that scientists were presented with an uncomplete and unreliable fossil platter . But a late re - verbal description of the oldest delphinid fossil , nowEodelphis kabatensis , may finally shed light on the cloudy evolution of early dolphin .
Delphinidaeis the most various kin of marine mammals , embrace 36 extant species such as spinner dolphin and killer whales . A huge act of delphinid dodo have been described , however , many are thought to have been wrongly impute to this family , resulting in an unreliable fossil phonograph record . It ’s thought that the oldest specimen were from the tardy Miocene , but the majority of these fossils were fragmentary and thus difficult to confidently designate .
Back in 1977the partial skull of a delphinid was found in the Mashike Formation in Hokkaido , Japan . The specimen was the oldest do it delphinid dodo , date back to the later Miocene ( 8.5 - 13.0 million years ago ) , making it an important piece of music of the evolutionary puzzle of family Delphinidae . It was primitively assigned to the genusStenella ; however , many scientists were dubious about this decision because of the limited accessibility of species for comparability . Consequently , a 2005 revaluation of Japanese cetaceous fossils play up the need for re - scrutiny of this metal money .
In this late study , put out in theJournal of Vertebrate Paleontology , the scientists refresh the fossil propose that the specimen in fact go to theEodelphisgenus . “ The early evolution of reliable mahimahi is still compensate in mystery . Eodelphis kabatensisinforms us about the geomorphology of early dolphin , ” said star author of the subject area Mizuki Murakami in apress - release .
Before this particular study , molecular - based studiescontradictedthe fogy disk of dolphins . The former suggested that dolphin develop and diversified around 9 - 12 million years ago , whereas the dodo record implied that the quondam true dolphins appear slightly later , around 6 million year ago . “ Eodelphiskabatensis , being attain from sediment that were deposited 8 - 13 million years ago , has largely resolved this discrepancy and provide the good glimpse yet of what the skull of the first dolphins may have looked like , ” said marine mammal palaeontologist Jonathan Geisler in apress - release .
moreover , this new analysissuggeststhe extraction and former variegation of Delphinidae may have happen in the middle Miocene Pacific Ocean , although more samples would be required to confirm this supposition .
