鰭脚類における系統進化, 食性の多様化, 古環境変遷の連鎖(<特集>生物イベントとしての哺乳類の海生適応)

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The pinnipeds (otariids, odobenids, phocids and their fossil allies) are fin-footed carnivores having been adapted to life in water since the late Late Oligocene, ca 28 million years ago (Ma) or much earlier. Recent investigations on the phylogenetic relationship of the pinnipeds reveal that the Oligo-Miocene enigmatic mustelidan, Potamotherium species, are recognized to have special affinities with the pinnipeds. The oldest known record (OKR) of Potamotherium species are late Late Oligocene in age, ca 26-25 Ma. Therefore, their speciation events are thought to lie near the time of the pinnipeds' OKR. When we recognize such speciations as biotic events of the pinnipeds and their allies, then we can recognize two additional biotic events in the pinnipeds. The second event may be the family level diversification at the boundary of the Early/Middle Miocene, approximately 17-16 Ma. Intriguingly, the depositional environments of early otariids are regarded roughly as bathyal, in contrast to the inshore preference of the contemporaneous odobenids. It suggests that the initial habitat preference of the early otariids had been mainly the pelagic ocean except for the pupping and breeding season. The third biotic event may be the ecological shift of the otariids from pelagic to inshore which may coincide with the change of the dietary preference of odobenids from inshore piscivory to molluskivory during Early Pliocene (ca. 5-3Ma). These three events must have been introduced by the global climatic changes, especially by the seismic transgression-regression cycles.
日本古生物学会の論文
2005-03-25

鰭脚類における系統進化, 食性の多様化, 古環境変遷の連鎖(<特集>生物イベントとしての哺乳類の海生適応)

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