Muricidae (Mollusca: Gastropoda) of the Esmeraldas Beds, Northwestern Ecuador

Abstract

Inasmuch as the Bolivar Trough, or Atrato Strait, of Colombia and Ecuador is probably the largest and most long-lasting trans-American Tertiary seaway, a study of the muricid gastropods of the Pliocene Esmeraldas beds of Ecuador was undertaken to compare relationships with the contemporaneous Caribbean fauna. The results show much less correlation with the Caribbean fauna than anticipated; only seven of the 21 species studied occur in the Pliocene of the western Atlantic. The greatest number in common with any fauna proves to be 11 that are still living on the coast of western America. But, of these, six no longer occur in Ecuador (one is confined to the Galapagos, one to California, two are found only in the Gulf of California, and two do not extend south of Panama). Of the 21 species treated systematically, three are new: Murexsul pitti and Ceratostoma notiale, both confined to the Esmeraldas beds; and Murex (Haustellum) ruthae, from the Esmeraldas beds and the Recent fauna of the Gulf of California.

In terms of presumed ancestry. 12 of the species have unmistakable Caribbean ancestors, and an additional three are worldwide Tethyan genera that may have come from the Caribbean. However, three are northern California-Japanese in relationship, two probably came directly from West Africa, and one seems to be endemic to the tropical eastern Pacific.