科研之友
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摘要
A key fact in the history of Neogene Caribbean marine molluscs is the disappearance of the "paciphile" taxa that occurred throughout Tropical America during the Miocene and the Pliocene, but subsequently suffered a range contraction, and became largely or entirely restricted to the eastern Pacific portion of their original distribution. What forces led to the disappearance of these paciphile taxa in the Atlantic portion of their original distribution is at present unclear, as there seem to be no obvious common environmental factor or ecological requirements uniting this paciphilic assemblage of taxa. It is suggested that for paciphile species the emergence of the isthmus during the Late Pliocene cut off the source populations of the planktonically-dispersing molluscs dependent on Pacific source populations. The sink populations thus became stranded on the Atlantic coast of South America and elsewhere in the Caribbean, where they became unsustainable and eventually disappeared. A reappraisal of all known paciphile species indicates an inferred planktotrophic larval development, which supports this hypothesis. Paciphiles did not disappear simultaneously, but seem to have suffered a steep decline during the Late Pliocene. A revision of all known gastropod paciphile generic, subgeneric and specific taxa allowed us to recognise three Gatunian Neogene Paciphile Molluscan Units (GNPMU). GNPMU I is characterized by the highest number of paciphile taxa. This unit is already in place in the Early Miocene and ends at the beginning of the Late Pliocene. GNPMU 2 is characterized by an impoverished number of paciphilic elements, devoid of the two largest paciphilic groups; the cancellarids and the muricids. This unit straddled the Pliocene-Pleistocene boundary and ends during the Early Pleistocene. GNPMU 3 is characterized by the absence of any paciphilic elements in their assemblages, and runs into Recent times. Based on these paciphile generic, subgeneric and specific taxa, for the Gatunian Province, two pulses of local disappearance from the Atlantic portion of their original distribution can be identified. The first marked by the overall decrease in Atlantic paciphile diversity and the total disappearance of all the paciphilic cancellarids and muricids, roughly corresponding with the timing given for the closure of the CAS. The second marked by the complete disappearance of all paciphiles from the Atlantic roughly coincides with the total closure of all connections between the Atlantic and Pacific.
- 出版日期2009
