Based on the results of molecular phylogenetics, this paper attempts to explain the migration of terrestrial animals between continents or between continents and islands by land bridges. The possibility of the existence of the land bridges are based on the sea-level rise curve since the end of the Jurassic period, which is inferred from deep-sea drilling and the deposition mechanism of stratigraphic formation, and is derived from the considerably low sea-level position in the past. Organisms inhabit and extend their ranges within those natural environments. The migration of terrestrial animals and segregation of their distribution should be based on this idea. Based on this idea, this paper estimates the past land bridges crossed by land animals that existed on the present-day ocean floor. These land bridges include the Scotian Arc from the South America to the Antarctica, the Pacific-Antarctic Ridge - the East Pacific Rise from the Australia to South America, the Davie Ridge between the Africa and Madagascar, the Carnegie Ridge from the South America to the Galápagos Islands, and the Mid-Atlantic Ridge from the Africa to the South America.

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 We report on the newly discovered Synechodontiform shark tooth from the Upper Cretaceous Kashima Formation (Santonian) in the Oyubari region, Hokkaido, Japan. This specimen is identified as Synechodus dubrisiensis (Paleospinacideae). This discovery is significant as the first record of S. dubrisiensis from the Santonian Series in Northwest Pacific region, not only in Japan, for this species has previously been recorded as from Hautelivian to Late Cenomanian deposits in the North Sea and Anglo-Paris Basin (Woodward 1889; Herman 1977; Underwood et al. 1999; Mellen and Hovestadt 2018). It is also extremely rare that multiple tooth classes (parasymphysial, anterior, lateral, and posterior teeth) in Synechodus occurred as free teeth from a single formation.

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