The biogeographic distribution of Cancer s. l., and by implication, the Cancridae, has been addressed on numerous occasions (Ekman, 1953; Nations, 1975; 1979; Carvacho, 1989; Newman, 1991). Ekman (1953), Nations (1975; 1979), and Carvacho (1989) suggested that the genus had a primarily North Pacific Ocean origin and subsequently dispersed throughout the Pacific Ocean by following the continental shelves; to New Zealand via Antarctica; and to the Atlantic Ocean by crossing the Arctic polar ocean. Newman (1991) suggested that Cancer s. l . displayed a relict amphitropical distribution in the temperate North Pacific and South Pacific Oceans. This conclusion was based on the belief that Cancer s. l. was the sole extant genus of the family. The extinction of several tropical to subtropical genera in the Eocene to Miocene was cited as evidence that the genus, and by implication, the family, arose and subsequently became extinct in the tropics, resulting in a formerly Tethyan distribution for Cancer s. l. and the family. However, this hypothesis is no longer tenable for several reasons. The genus Cancer sensu Newman has been redefined; for example, Newman (1991) considered species of all four of the former subgenera of Cancer as well as members of the genus Platepistoma in his discussion of the genus. The redefinition of these genera results in a very different distributional pattern for Cancer s. s. as well as the four additional genera Newman (1991) considered as members of Cancer s. l. Furthermore, Newman (1991) cited the appearance and extinction of Parapirimela in the Miocene of Angola as evidence of a formerly tropical distribution of the Cancridae. However, that genus is probably not a member of the family, and in any case, its familial placement cannot be verified. The revision of each of the genera within the Cancridae makes it possible in this report to recast the biogeographic history of the family, the two included subfamilies, and each genus (generic discussions above).
The earliest known confirmed occurrences of the family are Lobocarcinus of the Lobocarcininae from the middle Eocene of Egypt and Notocarcinus of the Cancrinae from the middle Eocene of South America. Anisospinos is known from late Eocene rocks of Washington, and Metacarcinus makes its first appearance in Oligocene (?) rocks of Alaska. Several genera make their first appearance in the Miocene, including Cancer s. s . from Japan, Anatolikos from Japan, Platepistoma from Japan, Romaleon from Japan and California, Miocyclus from Bulgaria, and Tasadia from Romania and Belgium; the latter two genera are members of the Lobocarcininae and the rest are members of the Cancrinae. It is difficult to determine when and where the family first appeared because the earliest known occurrences from Eocene rocks are known from each of the two subfamilies. This suggests that the family arose sometime before the middle Eocene. However, further speculation upon exactly when and where this occurred is unwarranted until more fossil material is recovered.
Several patterns emerge from these occurrences. Clearly, the two subfamilies have had very different evolutionary and dispersal histories. The Lobocarcininae has a primarily Tethyan distribution, as has already been discussed above, since all but one species of one genus are known from the Tethys region. The Cancrinae appear to have evolved in the southern hemisphere, based upon the occurrence of Notocarcinus in the middle Eocene of Argentina, and subsequently dispersed northward along the coast into the North Pacific Ocean. All other genera referred to the Cancrinae have their earliest recorded occurrence in the North Pacific region. Several genera within the Cancrinae are endemic to the North Pacific Ocean, including Anatolikos, Anisospinos, and Glebocarcinus. Platepistoma is known only from the Indo-Pacific region. Cancer s. s. and Metacarcinus range throughout the North Pacific Ocean, into the southeastern Pacific, and into the North Atlantic Ocean. One species of Metacarcinus is known from New Zealand. Romaleon is known from the circum-North Pacific Ocean, with one species ranging into the southeastern Pacific region. These distributions suggest that the North Pacific Ocean is the area of origin and subsequent dispersal for almost all of the cancrine genera.