Rudist bivalves and the Pacific in the late Jurassic and early Cretaceous

Although rudists of Late Jurassic to earliest Cretaceous age are known from Nova Scotia to Japan, the oldest specimens recovered from Pacific seamounts are Barremian (or possibly Hauterivian). The lack of evidence for disjunct endemism limited to either side of the ocean, then, precludes the inference that earlier rudists might have been present within it. Yet trans-Pacific range expansion of Caribbean-derived taxa, by means of larval 'island-hopping', was accomplished by the Early Aptian. Following a mid-Aptian mass extinction, the Pacific then became an important nursery of rudist re-diversification. Late Aptian rudists in Japan and derivative Late Aptian-Albian polyconitids in the Japanese Seamounts and Cebu show affinities with those from the eastern (Himalayan) sector of the northern Tethyan margin. By contrast, the caprinid Caprina mulleri in the Mid-Pacific Mountains is most closely allied with the C. choffati-C. adversa lineage known from the Atlantic-Mediterranean Tethyan region. However, the Pacific species could have been derived from an Early Aptian Caribbean Caprina that survived in some Pacific refuge, later reintroducing the genus to the Tethyan region in the Late Albian. Colonization of Pacific volcanic prominences ceased in the latest Albian, with the demise of carbonate platforms there, and was not resumed until the Campanian-Maastrichtian.