|Budget Amount *help
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1999: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1998: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1997: ¥2,300,000 (Direct Cost: ¥2,300,000)
Adaptation to reworking, rapid burial and other physical disturbances is found to be a major control on the ecology and evolution of soft-bottom, suspension-feeding bivalves. These modes of adaptations are linked to specific position in transgressive-regressive sedimentary cycles. Thus, we can predict the mode of adaptation of fossil benthos in the sedimentary cycles by sequence-stratigraphic and paleoecological observations. By using these methods, habitats of fossil bivalves were reconstructed for more than 50 fossiliferous shoreface sediments spanning from the Triassic to Holocene and Recent in Japan, based on my own observations along with examinations of published information. The results well outlined the long history of bivalve habitat expansion to shoreface environments and evolutionary replacement within this environment.
Trigoniids were the chief inhabitants of shoreface in the Mesozoic. For example, lower shoreface environments were inhabited by a trigoniid, Vaugonia in the earliest Jurassic. Nipponitrigonia was probably the first bivalve, which appeared in abundance from upper shoreface sediments, and this occurred in the Late Jurassic or early Cretaceous. In addition, venerids and glycymeridids occurred in the lower shoreface, but they but did not expand into the upper shoreface at that time.
Members of the Veneridae and Mactridae successfully established their habitats in the upper shoreface sometime between the Late Cretaceous and Miocene. Particularly mactrids became abundant in the Miocene of north Japan, along with other bivalves with various modes of life, such as members of the Cardiidae, Tellinidae, Solenidae and Hiatellidae.