生物イベントとしてのヒゲクジラ類の出現(<特集>生物イベントとしての哺乳類の海生適応)

概要

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The concept of toothed mysticets has been accepted during these decades. Toothed mysticetes do not constitute a single taxon but included in several families. There is wide variation in their morphology, such as size, progress of telescoping and tooth arrangement. But the similarity of auditory bullae of toothed mysticetes strongly suggests their close origin in phylogeny. The specimen from Oligocene Ashiya Group, Japan has many characters of the family Cetotheriidae, but has remnants of teeth. The animal had teeth at least its certain stage of ontogeny. It shows process of losing teeth in toothed mysticetes to true cetotheres. Toothed mysticetes lived in the Late Oligocene with a few exception. Appearance of mystecetes is an interesting bioevent as an example of mammalian adaptation to water, relation to paleoecology, paleogeography, paleoclimatology, and many other viewpoints.
2005-03-25