Evolution and Distribution of the Genus My a, and Tertiary Migrations of Mollusca GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G Evolution and Distribution of the Genus My a, and Tertiary Migrations of Mollusca By F. STEARNS MACNEIL CONTRIBUTIONS TO PALEONTOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-G Known first in the early Tertiary of Japan, the genus Mya migrated to western North America, the Arctic Ocean, and to both the European and the American sides of the North Atlantic UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library has cataloged this publication as follows : MacNeil, Francis Stearns, 1909- Evolution and distribution of the genus Mya and Tertiary migrations of Mollusca. Washington, U.S. Govt. Print. Off., 1964. iv. 51 p. illus., map, diagrs. 30 cm. (U.S. Geological Survey. Professional Paper 483-G) Contributions to paleontology. Bibliography: p. 45-47. 1. Mollusks. 2. Paleontology Tertiary. I. Title. (Series) For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C , 20402 - Price 65 cents (paper cover) CONTENTS Page Page Abstract. __________________________________________ Gl Phylogeny and distribution of species Continued Introduction _______________________________________ 1 Morphologic characters Continued Migrations of Pacific and Atlantic Ocean mollusks______ 2 Ligament.________-___________---___---____ G21 Biological and temporal aspects of migration.______ 2 Spoon.________-____-_-___-_-_----_ ____ 21 Migration and dispersaL-____________________ 2 Ligamental callus___________________ ___- 22 Migration and ecology.._____________________ 2 Subumbonal solution._______________ ____ 24 Migration and specific variability.____________ 4 Systematic paleontology.__-________--_----__ ____ 25 Migration and evolution.____________________ 5 Genus Mya Linne", 1758________________ ____ 25 Migration and correlation.___________________ 5 Subgenus Arenomya Winckworth, 1930____ ____ 26 Tertiary paleogeography of the Arctic and the boreal Mya (?Arenomya) producta Conrad__ ____ 26 regions._____________________________________ 6 M. (1A.) ezoensis Nagao and Inoue..__ ____ 26 Arctic climate and its effect on organisms__________ 7 M. (?A) kusiroensis Nagao and Inoue. ____ 27 Periods and routes of migration __________________ 8 M. (1A.) grewingki Makiyama________ ____ 27 Phylogeny and distribution of species________________ 10 M. (?A) grewingki haboroensis Fujie__ ____ 28 Identity of Mya japonica Jay-.___________________ 10 M. (?A) dickersoni Clark___________- __._ 28 Mya crassa Grewingk, Mya elegans (Eichwald), and M. (?A) elegans (Eichwald)________ --__ 29 Mya intermedia Dall__________________________ 12 M. (Arenomya) fujiei MacNeil, n. sp__ __._ 30 Ancestry of Mya______________________________ 13 M. (A.) arrosis MacNeil, n. sp________ ____ 31 Indigenous Atlantic species Mya producta Conrad _ 13 M. (A.) japonica Jay________________ _.__ 31 Early Pacific species---__________________________ 13 M. (A.) arenaria Linne.____-----____ ___. 33 Mya arenaria group_____________________________ 14 Subgenus Mya Linne".-_________-----____ ____ 35 Mya elegans group______________________________ 17 Mya (Mya) salmonensis Clark._______ ____ 35 Mya truncata group_____________________________ 18 M. (M.) cuneiformis (Bohm)_________ ____ 35 Morphologic characters._________________________ 20 M. (M.) pseudoarenaria Schlesch_.____ .___ 37 Shell thickness.___________________________ 20 M. (M.) truncata Linne-------------- __._ 38 Shell shape_______________________________ 20 M. (M.) priapus Tilesius-__________ ____ 40 Variability of form._________________________ 20 M. (M.) pullus Sowerby_____________ ____ 42 Sculpture._________________________________ 20 Localities. _______________-__-_-_-_-------_- .___ 43 Pallial line and pallial sinus__________________ 21 Bibliography.______________________________ .___ 45 Muscle scars.______________________________ 21 Index.__________________________________ __._ 49 ILLUSTRATIONS [Plates follow Index] PLATES 1-11. Mya from the 1. Choptank Formation (Maryland), the Poul Creek Formation (Alaska), and the Acila shumardi zone, Popof Island (Alaska). 2. Briones and Neroly Formations (California), Pliocene beds, Chignik Bay (Alaska), Pleistocene beds, St. Paul Island (Alaska), Recent (Alaska). 3. Briones, Cierbo, and Neroly Formations (California), Pleistocene beds, Cape Kruzenstern (Alaska), and Recent (Alaska). 4. Pleistocene beds, Nome (Alaska), and Recent (Japan and Alaska). 5. Briones, Cierbo, Etchegoin, and San Joaquin Formations (California), and the Yorktown Formation (Virginia). 6. Red Crag and Icenian Crag (England), Pleistocene beds, Nome (Alaska), and Recent (Denmark and British Co­ lumbia. 7. Poul Creek and Yakataga Formations (Alaska), middle Miocene beds (Sakhalin and Kodiak Island), Pleistocene beds, Yenisey River (Russia), and Recent (Alaska). 8. Yakataga Formation (Alaska), the Icenian Crag (England), the Clyde Beds (Scotland), Pleistocene beds, Nome (Alaska), and Recent (Alaska). 9. Icenian Crag (England), Pliocene beds, Tugidak Island (Alaska), postglacial beds, Juneau (Alaska), and Recent (Greenland and Alaska). 10. Recent (Kamchatka and Alaska). 11. Red Crag (England), Pleistocene beds, Wingham Island (Alaska), postglacial beds, Kachemak Bay (Alaska), and Recent (Alaska). in IV CONTENTS Page FIGURE 1. Most probable late Tertiary and Quaternary migration routes between eastern Asia and western North America and between the North Pacific Ocean and the North Atlantic Ocean.___________________________________ Gil 2. Diagram showing terminology of parts of spoon. Upper, Mya (Arenomya); lower, Mya (Mya). From Fujie (1957)_.___._-__-_-_-_____________-._____. ___._____._____--.....__._--_--____-_---.----..-_--- 22 3. Phylogeny of myarian subgenera and species, showing distribution of the two types of ligamental callus.______ 23 CONTRIBUTIONS TO PALEONTOLOGY EVOLUTION AND DISTRIBUTION OF THE GENUS MYA, AND TERTIARY MIGRATIONS OF MOLLUSCA By F. STEARNS ABSTRACT Two new species are described: Mya fujiei MacNeil, based on M. japonica oonogai Fujie (1957, pi. 2. figs, la-b) from the Two genera, Mya, a pelecypod, and Neptunea, a gastropod, Takinoue Formation (early middle Miocene) of Hokkaido, were selected as vehicles for a study of late Tertiary to Recent and M. arrosis MacNeil, based on specimens in the collections faunal migrations from the Pacific to the Atlantic Ocean by way of the University of California from the Cierbo Sandstone of the Arctic Ocean because they are mollusks of large size, and (middle late Miocene) of the San Pablo Group, Contra Costa because they have unlike larval stages; Mya has small current- County, Calif. borne pelagic larvae, and Neptunea has large bottom-crawling INTRODUCTION benthonic larvae. This report considers chiefly the genus Mya but also includes a general discussion of Arctic faunal migrations The genus Mya,, by virtue of both its morphological and its bearing on Tertiary paleogeography of the Arctic. Avail­ peculiarities and its heavy commercial harvest, should able evidence suggests that during early Tertiary time the be one of the best understood mollusks. Instead, its Arctic regions either had greatly reduced marine embayments, or they were entirely land. The earliest known marine comparatively few species, comparatively simple evolu­ Tertiary deposits in the high Arctic, found in northern Alaska tion, and comparatively restricted geographical occur­ and Spitzbergen, are of middle or late Miocene age. The rence involve subtleties that evade and confuse pale­ first boreal species of Pacific origin to be found in Atlantic ontologists and malacologists alike. Besides, there are Ocean deposits is in the Yorktown Formation of Virginia. still sizable gaps in our knowledge of phylogenetic The Yorktown Formation is currently assigned to the Pontian (late Miocene) Stage. lines. All known species of the genus Mya are defined and delimited, Numerous attempts have been made to resolve the and an attempt is made to resolve the synonymy of Japanese systematics of Mya,. Until recently the most careful and American and Pacific and Atlantic species. American, studies were by European and American workers Arctic, and European species are illustrated; Japanese species whose main interest was in Atlantic and Arctic have been illustrated elsewhere. The geographical distribution of Mya is treated from an species, and who were dealing literally with the outer­ evolutionary and migrational standpoint. The genus is re­ most fringes of the problem. In the last three decades, stricted to the Northern Hemisphere. Its ancestry is unknown, however, several important studies have been made by but it may stem from temperate or subtropical early Eocene Japanese paleontologists. These studies show con­ forms currently assigned to the genus Sphenia. The earliest clusively that the greater part of the genus evolved in known species of Mya occurs in late Eocene or early Oligocene beds of Japan. One indigenous Atlantic species is known. The East Asia, although its place of origin remains un­ remaining 16 recognizable taxa are indigenous to the North known. It remained for knowledge of the Japanese Pacific. Three, and possibly four, of the Pacific species Tertiary species to be reasonably complete before any migrated subsequently by way of the Arctic Ocean to northern clear picture of the evolution of the genus