Fossil vesicomyid bivalves from the North Pacific region

2007·16 MB·English

by  Kazutaka Amano

THE VELIGER
The Veliger49(4):270-293 (December 11, 2007) <: CMS, Inc., 2006
Fossil Vesicomyid Bivalves from the North Pacific Region
KAZUTAKA AMANO
Department ofGeosciences, Joetsu University of Education, Joetsu 943-8512, Japan
STEFFEN KIEL
School of Earth & Environment, University of Leeds, Leeds LS2 9JT, United Kingdom
Abstract. A review ofthe fossil record ofvesicomyid bivalves from the North Pacific region (Hokkaido, Japan;
Alaska and Washington, USA) allows the clarification of the status of several species based on new data and
observations, and four new species are recognized. Detailed examination of the hinge of Hubertschenckia ezoensis
shows that Hubertschenckia is a valid monotypic genus closely related to Archivesica and Calyptogena. Specimens of
'Calyptogenci chinookensis from its late Eocene type locality at Bear River have a hinge structure that clearly places
this species in Adulomya; silicified 'C chinookensis specimens described earlier from the late Oligocene have a very
different hinge structure and are assigned to the new species Archivesica knapptonensis. The hinge dentition of all
three Cretaceous vesicomyids proposed so far is unknown and their validity is doubtful. With Hubertschenckia
ezoensis, Adulomya chinookensis, and Archivesica cf. tschudi, three genera oflarge vesicomyids appear more or less
simultaneously at methane seeps in the late Eocene. OfOligocene age are the new species Archivesica georgemoorei
from Alaska, which is shorter and more oval than other known Archivesica species, and a possible Pliocardial sp.
from cold seeps in Washington. From the early Miocene ofWashington Isorropodon frankfortensis is described and
represents the first certain record ofthis genus from outside the Atlantic realm. The new middle Miocene Adulomya
hokkaidoensis is so far only known from a whale-fall community in Hokkaido and may have been endemic to this
type ofhabitat. The timing ofthe occurrences ofthese taxa shows no correlation to the evolution ofwhales in this
area, shedding further doubt on the 'whale stepping-stone' hypothesis for the origin ofvesicomyids.
INTRODUCTION & Baco, 2003). This hypothesiswasbased on the rough
correlation between the evolutionary age of vesico-
Fossil vesicomyid bivalves in the North Pacific region,
especially in Japan, have been described for more than myids estimated from molecular clocks and the first
aAmcaenntour&y (KYaonknooy,am2a00,5).189H0o;weMvaejri,maveseitcoamly.,id2s00r5e;- aSpmpietahr&ancBeacoof,w2h0a0l3)e.sSiqnutihreesEeotcealn.e(1(9B9a1c)oaentdalG.o,e1d9e9r9t;
ceived little scientificattention until thediscovery ofthe et al. (1995) however, had already pointed out that in
'Giant White Clam' Calyptogena nuignifica at hydro- the North Pacific, seep taxa such as vesicomyid
thermal vents on the Galapagos Ridge in the late 1970s bivalves were already very widely distributed before
(Boss &Turner. 1980). Sincethentheyhavebeen found theearliest knownappearance (latest Eocene) ofwhales
in many chemosynthesis-based ecosystems at hydro- in the region. The stepping-stone hypothesis was
thermal vents, hydrocarbon seeps, and whale carcasses challenged by Little & Vrijenhoek (2003) who called
throughout the world's oceans (Van Dover, 2000; Van attention to the discrepancy between the molecular age
Ma
Doveretal., 2002; Kojima, 2004). These discoveriesled estimates for vesicomyids [21.5^3.8 according to
paleontologists to take a new look at vesicomyid Peek et al. (1997)] and the oldest fossil vesicomyids
occurrences, and many of these sites have since been from the Early Cretaceous (upper Albian, 106 Ma) in
identified as fossil hydrocarbon-seep deposits. northern Japan (cf. Kanie et al., 1993; Kanie & Sakai,
The occurrence of vesicomyids at decaying whale 1997). It was also challenged by Kiel & Goedert (2006)
carcasses in the deep-sea (whale-falls) led to the who showed that vesicomyids and other taxa charac-
formulation of the 'stepping stone' hypothesis. This teristic ofmodern whale-falls were absent from Eocene
hypothesis suggested that whale-falls provide dispersal and Oligocene whale-falls and only appeared in
stepping stones for vent and seep taxa, and that Miocene examples.
therefore the rise of whales in the Eocene suddenly However, a thorough analysis ofthe fossil history of
(geologically speaking) extended the dispersal capabil- the Vesicomyidae and its potential correlation with the
ities of vent and seep taxa, resulting in a significant radiation of whales has so far been hampered by the
radiation amongtheseanimals(Bacoetal., 1999; Smith inconsistent use of generic names and concepts within
K. Amano & S. Kiel, 2006 Page 271
Figures 1^. Locality maps offossil specimens. Figure 1. Map showing the general location ofthe fossil sites described herein.
Figure 2. Hokkaido, Japan, asterisks indicate the two fossil sites. Figure 3. Kodiak Island, Alaska, asterisk indicates the fossil
locality on nearby Sitkalidak Island. Figure 4. Localities in western Washington State, USA, A=Humptulips River sites,
B=Canyon River site, C=Satsop River site (LACMIP loc. 17747), D=Bear River site (LACMIP loc. 5802), E=Knappton
(LACMIP loc. 5843), F=Frankfort (USGS loc. M2790).
this family (see Krylova & Sahling, 2006 for a review), California State University, Northridge (CSUN) are
which partly results from incomplete knowledge of also used herein.
several of the type species. Important progress was
made recently by Cosel & Salas (2001) who revised the Japan, Hokkaido
genera Vesicomya, Waisiuconcha, Isorropodon, and
Callogonia, by Krylova & Sahling(2006) who redefined Poronai Formation: The Poronai Formation is
Calyptogena and revised its Recent species, and by Kiel a llOOm-thick sequence of deep-water mud- and
(2007) who clarified the status ofPleurophopsis. siltstone of late Eocene age, cropping out in central
The aim of this paper is to revise some ofthe fossil Hokkaido (Kaiho, 1983, 1984). Seventeen specimens of
vesicomyids from the North Pacific region (Figure 1) Hiibertschenckia ezoensis were collected from a cold-
based on newly collected material. We describe four seep deposit at a high cliff along the Ikushunbetsu
new species from Japan, Alaska, and Washington, and River, 200 m to the west of Yayoi Town in Mikasa
provide revised generic diagnoses for Adulomya Kur- City (Figure 2; see Amano & Jenkins, 2007 for more
oda, 1931, Archivesica Dall, 1908, and Hubertschenckia details). Here, a calcareous concretion approximately
Takeda, 1953. Finally, we discuss the evolutionary 2 m in diameter occurs in dark gray mudstone of the
implications ofour findings. Poronai Formation (B Zone of Teshima, 1955). The
Hubertschenckia specimens occur mostly within this
MATERIAL, STRATIGRAPHY, concretion but also directly adjacent to it. Almost all
AND OCCURRENCES specimens are articulated, but also a few disarticulated
valves were collected. The Yayoi fauna in the
All Japanese specimens described here are housed in surrounding mudstone consists of the protobranch
the Joetsu University of Education (JUE). Material bivalves Acila (Tniiicacila) pictwota (Yokoyama),
from Washington State will be housed in the Smithso- MaUetia poronaica (Yokoyama), Porlkmdia (Povtkin-
nian Natural History Museum (USNM) and the delki) watasei (Kanehara), the thyasirid bivalve Con-
Natural History Museum of Los Angeles County chocele bisecta (Conrad), the carditid bivalve Cyclo-
(LACMIP), the specimens from Alaska will be housed cavdia tokudai (Takeda) and the caenogastropod
in the Museum of Paleontology, University of Cali- Orectospira wadana (Yokoyama). The faunal compo-
fornia, Berkeley (UCMP). Locality numbers of the sition of the molluscan asseinblage is similar to the
United States Geological Survey (USGS) and the lower sublittoral to upper bathyal MaUetia poronaica-
Page 272 The Veliger, Vol. 49, No. 4
Cyclocardia tokudai assemblage of Suzuki (2000) from Isorropodon frankfortensis was recovered by acid
the lower part ofthe Poronai Fomiation. In addition, etching from two small blocks of cold-seep carbonate
Kaiho (1984) used benthic foraminifers to infer found as float on beach terraces near the abandoned
a maximum depth of 350 m for deposition of the settlement of Frankfort (Figure 4F). The type locality
Poronai Formation. of Isorropodon frankfortensis is equivalent to locality
M-25 of Wolfe & McKee (1972) and USGS loc.
ChikubetsuFormation: The ChikubetsuFormation is of M2790. Wolfe & McKee (1972) noted that the
middle Miocene age and subdivided into the lower
sediments in this area were deposited at a depth
sandstones (210 m) and the upper siltstones (230 m)
(Noda, 1992). When Amano & Little (2005) recorded between 16 and 650 m.
a Miocene whale-fall community from the uppermost HumptulipsFormation: This formationcrops out on the
part ofthe Chikubetsu Formation, they illustrated two southwestern slope of the Olympic Mountains (Fig-
specimens and the hinge ofa left valve of Calyptogena ure 4A), is approximately 1000 m thick (Rau, 1986),
sp. These were collected from a large roadside cliff and is oflate middle Eocene age (Prothero et al., 2001).
along the Setakinai River, 5.5 km upstream from It consists of siltstone and mudstone, and beds of
Shosanbetsu Village in northern Hokkaido (Figure 2; structureless sandy siltstone, deposited at depths
see Amano & Little, 2005 for more details). Sub- estimated to have been between 1500 and 2000 m
sequently, one right valve with adistinct pallial line and (Rau, 1986). Several seep carbonates have been
a specimen with the hinge ofthe right valve preserved reported from this formation, containing, among other
were collected from the same locality. All specimens fossils, Calyptogena chinookensis and Vesicomya sp.
occurred in a bone-bearing concretion in siltstone. As (Squires & Goedert, 1991, 1996; Goedert & Kaler,
inferred by Amano & Little (2005), this community 1996). Thelatterspecies is here described asArchivesica
might have lived below the middle-bathyal zone, based cf. tschiidi (Olsson, 1931). The new material was found
on benthic foraminifers (cf. Maiya et al., 1982). in a small seep limestone block on a gravel bar in the
East Fork of the Humptulips River, approximately
USA, Alaska 400 m west and 600 m north ofthe southeast corner of
Sec. 6, T20N, R9W, Grays Harbor County, Washing-
Sitkalidak Formation: This formation is of Eocene to ton. The source of this material is likely the high cliff
Oligocene age and occurs in a series of patches at the just upstream and on the south side ofthe river at the
southeastern tips ofpoints on Kodiak, Sitkalidak, and sharp bend, either allochthonous cold-seep limestone,
Sitkinak Islands. It is a rather uniform, about 3000 m- or an in situ seep deposit. Additional specimens are
thick sequence ofgraded sandstone and siltstone beds, from seep carbonate at CSUN loc. 1583.
with a few conglomerate beds (Moore, 1969). The new
species Archivesica georgemoorei was found near the Lincoln Creek Formation: This formation is an
m
top ofthe Sitkalidak FoiTnation in the type area on the approximately 3000 thick sequence of deep-water
north shore near the east end of Sitkalidak Island mud- and siltstones of late Eocene to early Miocene
(Figure 3), where it co-occurred with the thalassinid age, that crops out in western Washington State,
shrimp Callianassa aff. porterensis (cf. Moore, 1969). between the southern slopes ofthe Olympic Mountains
Thedatingofthis siteis somewhat uncertain, becauseit and the Columbia River. Archivesica knapptonensis n.
is solely based on the lithological similarities between sp. is from two late Oligocene seep-carbonate outcrops
the Sitkalidak Formation, the Burls Creek member of of the Lincoln Creek Formation. Blocks of seep
the Katalla Formation (Alaska), and the Blakeley carbonate were collected on tidal terraces near Knapp-
Formation (Oregon) (F. S. MacNeil, written commu- ton on the north shore of the Columbia River at
nication to G. W. Moore, 13 Aug. 1963). The fossil site LACMIPloc. 5843 (Figure 4E). Theageofthis locality
is most likely a hydrocarbon-seep deposit (Goedert et was considered early Miocene by Moore (1984) and
al., 2003). late Oligocene by Goedert & Squires (1993). The
vertebrate assemblage ofthis locality indicates that late
USA. Washington State Oligocene is the more probable age ofthese sediments
(Barnes & Goedert, 2001; and J. L. Goedert, personal
Astoria Formation: This foiTnation crops out on the communication 2005). The mollusk fauna indicates
north shore (Washington) and south shore (Oregon) of a depositional depth of 100 to 350 m, whereas benthic
the Columbia River. In Washington, rocks referred to foraminifers indicate 300 to 1000 m depth (Moore,
as Astoria Formation in Pacific and Wahkiakum 1984). At another site (Figure 4B, referred to as
m
counties are 750 to 1000 in thickness, and consist 'Canyon River site" herein) occur carbonate "blebs'
of thick-bedded, coarse-grained grayish-brown marine with small mollusks and a very large bivalve (Crypto-
sandstone and soft, dark-gray siltstone (Moore, 1963; lucinal) on a low bench on the east side ofthe Canyon
Wolfe & McKee. 1972; Wells, 1989). The new species River, approximately40 m north and 260 m east ofthe
K. Amano & S. Kiel, 2006 Page 273
southwest corner of Sec. 25, R7W, T21N, Grays tions. Figure 5 shows the main hinge features that
Harbor County. This site is of Oligocene age. A characterize these genera. Table 1 gives an overview of
locahty on the Satsop River (Figure 4C; LACMIP loc. their synonymies. We provide a list ofthe fossil species
17747b; Oligocene) yielded a specimen of Pliocardidl that we consider to belong to each of the genera;
sp. with a drill hole. Seep-related mollusks were however, a full revision ofthe Recent species is beyond
described from two other carbonate blocks from that the scope ofthis study.
site by Kiel (2006), who also provided more details
Genus Hubertschenckia Takeda, 1953
about the locality.
Hubertschenckia Takeda, 1953:85.
Siltstone of Cliff Point: Deep-water siltstones crop out
on the north shore ofthe Columbia River, to the west
of the Lincoln Creek Formation. Wells (1989) stated Type species: Tapes ezoensis Yokoyama, 1890 (by
that this unit may be correlative with the 'Siltstone of monotypy); Poronai Formation, upper Eocene, Hok-
Unit B' of Wolfe & McKee (1972). The 'Siltstone of kaido, Japan.
Unit B' was deposited at depths between 300 and
c1a,0r0b0onmate(Wionlftheis&forMmcaKtieoen, at197L2A).CMAIPlalrogce. 5s8e0e2p cTtieaaoxlluoysn"odmedseipccorsihibitessdtorb=yy:EoHYcuoebnkeerotyPsaocrhmoeanncaki(i1F8a9o0re)zmoaeftnrisooinsm)w"aaCrsroeuitnnaid--
(chFiingouorkeen4sDi)s iSsquitrhees t&ypeGoleodcearlitt,y 1o9f91."CaTlhyeptohgienngae PToarpoensaiMiiohnlfHeolkd,k(a1i8d1o1,. aMnidnaptloac&edUinoztuhemive(n1e9r5i1d)gweenrues
dentition of two specimens from this site is described the first who illustrated the hinge dentition of a left
to clarify its systematic position. valve and noticed that this hinge resembles that of
Akebiconcha Kuroda, 1943. Following the advice given
SYSTEMATIC DESCRIPTIONS
to them by Dr. Tokubei Kuroda, they placed the
Family Vesicomyidae Dall & Simpson, 1901 species in the Veneridae and suggested that it may
belong to a new genus.
When Takeda (1953) eventually proposed Hu-
Remarks: The Vesicomyidae are used here in the bertschenckia based on Tapes ezoensis, he placed it in
traditional sense. Based on anatomical and concholo- theVeneridae and indicated a lateOligocene age forthe
gical observations on Recent North Atlantic species of Poronai Formation. He re-illustrated the figure of the
Kelliella Sars, 1870 and Vesicomya Dall, 1886, Allen left valve hinge provided by Minato & Uozumi (1951)
(2001) suggested that the Vesicomyidae should be and described the hinge structure as follows: 1)
synonymized with Kelliellidae. However, Cosel & Salas presence oflaterals, 2) diminishing ofanteriorcardinal,
(2001) noted that Allen (2001) had misidentified some 3) bifid middle cardinal in the right valve, 4) fusion of
of his Kelliella species and pointed out distinctive anterior lateral with cardinal tooth in the left valve.
differences between Kelliella and Vesicomya; hence, However, his description of the hinge dentition of the
retaining the name Vesicomyidae. right valve was taken mainly from notes provided to
Thevarious genera related to Calyptogena Dall, 1891 him by Dr. Takumi Nagao, and he erroneously
are currently used very differently in the literature. On described the anteriorcardinal teeth (2a, 3a) as anterior
one end of the spectrum, Coan et al. (2000) treated lateral teeth. Moreover, the bifid tooth in the right
Calyptogena as a subgenus of Vesicomya; Akebiconclia, valve is the posterior cardinal one (3b), not the middle
Kuroda, 1943, Archivesica Dall, 1908, Ectenagena one. Oyama et al. (1960) also placed Hubertschenckia
Woodring, 1938, and Phreagena Woodring, 1938 were in the Veneridae. Keen (1969) illustrated the same
considered synonyms ofCalyptogena. On the otherend specimen as Minato & Uozumi (1951) and Takeda
of the spectrum. Keen (1969) considered all hitherto (1953), followed Takeda's description, and placed
proposed names valid, except for Adulomya Kuroda, Hubertschenckia in the Vesicomyidae. Subsequent
1931, which was erroneously placed in the Solemyidae. workers have followed this placement (Kanno, 1971;
Based on a combination of conchological and molec- Habe, 1977; Boss & Turner, 1980; Krylova & Sahling,
ular data, Okutani et al. (2000) and Sasaki et al. (2005) 2006). Also Keen (1969) gave the stratigraphic age as
recognized three subgenera of Calyptogena: Calypto- Oligocene, following Takeda (1953). Then, Kaiho
gena S.S., Archivesica, and Ectenagena. This classifica- (1983, 1984) assigned the age of Poronai FoiTnation
tion scheme is largely followed here, with the modifica- to the late Eocene. Kanno & Teshima (1994) described
tions that Ectenagena is shown here to be a junior Hubertschenckia ezoensis again and mentioned the
synonym of Adulomya. The latter and Archivesica are followingcharacteristics: 1)thin anteriorcardinal tooth
considered herein to be independent genera. of left valve along dorsal margin, connecting with the
We provide translated and emended generic di- middle tooth under the umbo, 2) existence of a sub-
agnoses for these genera, based on our own observa- umbonal pit injuvenile specimens, butnotdeveloped in
Page 274 The Veliger, Vol. 49, No. 4
Hubertschenckia
Calyptogena
Figure 5. Terminology of tlie main hinge characters used in the text; not to scale. Sources: Hubertschenckia drawn from the
specimens figured herein on Figures 6-7; Acluloiuya from Boss & Turner (1980:fig. lOE, ofthe holotype ofAchi/omya elongara);
Archivesica from Okutani et al. (2000:fig. 12, which is based on specimen L99264A1-54 of Archivesica gigas provided by the
Monterrey Bay Aquarium Research Institute); Calyptogena from Krylova & Sahling (2006:fig. 2, sourcenot specified); Vesiconiya
from Cosel& Salas (2001:figs. 16-11, based on a specimen of Vesiconiyaaclainsicollected offNamibia); Isorropodon redrawn from
specimensofIsorropodonperplexumfiguredbyCosel& Salas(2001:figs. 44and47); PliocardiaredrawnfromWoodring's(1925, pi.
20, figs. 3 and 5) figures ofPliocardia bowdeniana.
K. Amano & S. Kiel, 2006 Page 275
Table
1
Type species and synonymies oftiie genera used herein.
Genus Type species Synonyms
Aduloma KuToda, 1931:27. Aduloniya uchiiiniracnsis Kuroda, 1931 EctenagenaV^oodv'mg, 1938:51.
IPIeurophopsis Van Winkle, 1919:23.
Arc/nvesica rtall 1908:418. Callocardiagigas Dall, 1896 Akehiconcha Kuroda, 1943:17.
Phreagena Woodring, 1938:50.
Hiibertschenckia Takeda, 1953:85. Tapes ezoensis Yokoyama, 1890
Isorropodon Sturany, 1896:17. Isorropodonperplexiini Sturany, 1896
PUocardia Woodring, 1925:147. Anomcdocardia bowdeniami Woodring, 1903
adults, 3) existence of a pallial sinus throughout the indications as to their repository. At the time ofwriting
entire ontogeny, suggesting an infaunal mode of life. his report, Matajiro Yokoyama was based in Munich,
This characterization agrees with our observations, Germany, and the specimens may have been deposited
except that the subumbonal pit can in fact also be in the Bavarian State Collection. However, they could
observed in adult specimens. not be located there (A. Niitzel, personal communica-
tion 2007), and may either have never been deposited
Remarks: Archivesica is most closely related to there, or were destroyed during World War II. Takeda
Hiibertschenckia in having a bifid posterior cardinal
(1953, p. 86) indicated that the holotype is 'preservedin
atosohtahll(o3wb)pailnliatlhesirniusg.htHovawlevvee,ra, tshuebuhimnbgoenadelntpiitti,onanodf Tokyo University,' where it could not be located (T.
Sasaki, personal communication 2007), and that
Hubertschenckia is more primitive than in Archivesica a syntype from the collection of Dr. Satoru Uozumi
from the viewpoint of evolutionary change of the is deposited as UH. Reg. No. 11181 at Hokkaido
heterodont hinge (Cox et al., 1969). Hubertschenckia University in Sapporo. Because the holotype could
has a long anterior cardinal tooth (3a), a long central neither be located in Munich nor in Tokyo, it is
tooth (1) along basal margin of hinge, and a stout considered lost and we designate the specimen UH.
vertical posterior one (3b) in the right valve. Hu- Reg. No. 11181 as neotype.
bertschenckia shares with Calyptogena the posterior
nymphal ridge and the posterior cardinal (3b) that Originaldescription(translatedfromtheGermanbySK):
points in an anteroventral direction. "We have several specimens, but with only partly
Hubertschenckia ezoensis (Yokoyama, 1890) preserved shell. Shell thick, moderately convex, elon-
gate elliptical, strongly inequivalved; posterior side
(Figures 6^12) approximately 2 Vi times as long as anterior side.
Anterior and posterior margins rounded; ventral
Tapes ezoensis Yokoyama, 1890:197, pi. 25, figs. 6-8. margin only slightly convex, almost parallel to hinge.
Tapes (new gen.?) ezoensis Yokoyama. Minato & Beaks small, pointed, cvn-ved, almost touching each
Uozumi, 1951:150, pi. 13, figs. 108a-c. other. The surface shows only irregular, concentric
Hubertsclienckia ezoensis (Yokoyama). Takeda, growth lines. The anterior muscle attachment scar is
1953:85, pl.l3, fig. 5; Oyama et al., 1960:188-189, pear-shaped, the posterior one rounded. Sinus finger-
pi. 58, figs. 2a-d.
non Meretrix (Macrocallista) ezoensis (Yokoyama).
Yokoyama, 1928:77, pi. 8, fig. 1. Table 2
non Hubertschenckia ezoensis (Yokoyama). Honda, Measurements ofHubertsclienckia ezoensis specimens.
1989:79, figs. 13, 14.
No. of Length Height Thickness
specimens (mm) (mm) (mm)
Material: Seventeen specimens from the Poronai
Formation at Yayoi, Mikasa City, Hokkaido. For JJUUEE nnoo.. 1155883377--12 7743..60 4413..17 2289..34
measurements ofshell length, height and thickness see JUE no. 15837-3 72.8 40.0 32.6
Table 2. JUE no. 15837-4 65.3 39.0 29.0
JUE no. 15837-5 56.7 29.1 24.1
Type locality: Poronai, Mikasa City, Hokkaido. JUE no. 15837-6 50.9 32.1 22.4
Type material: Yokoyama (1890) did not designate JUE no. 15837-7 35.4 24.5 17.1
a holotype. He mentioned that 'several' specimens were JJUUEE nnoo.. 1155883377--89 2177..26 1170..40 108..12
available, figured three of them, and made no
Page 276 The Veliger, Vol. 49, No. 4
Figures6-12. Huhertsclienckkiezoensis(Yokoyama). Figure6. Left-valvehinge,hingelength 14.8 mm,JUEno. 15837-11. Figure
7. Right-valvehinge, hingelength29.7 mm,JUEno. 15837-12. Figures8,9. Pallial sinusofbothvalves; Figure8, length43.6 mm+,
JUE no. 15837-10; Figure 9, length 17.6 mm, JUE no. 15837-9. Figures 10-12. Outline ofshells; Figure 10a, dorsal view showing
longexternal ligament. Figure 10b, lateralview, length 35.4, JUEno. 15837-7; Figure 11, length50.9 mm,JUEno. 15837-6; Figure
12, length 74.6 mm, JUE no. 15837-1.
shaped, approximately as deep as wide. Pallial line The interior ofthe shell shows radial striations, which
entire. Thehinge dentition could not be examinedfully. are well-visible in worn specimens" (Yokoyama, 1890).
One specimen shows that the central ofthe three teeth
ofthe right valve is bifurcated. A rather well-preserved Redescription: Shell of moderate size, attaining
specimen is 65 longand40 mm high. Another, which is 74.6 mm length; shell outline elliptical, moderately
damagedat bothends, is 32 mm thick and45 mm high. inflated, equivalve and inequilateral, sculptured by
K. Amano & S. Kiel, 2006 Page 277
irregular growth lines. Beak prosogyrate, situated at the left valve, and the nymph is shorter in Archivesica
anterior fifth of shell. Anterodorsal margin broadly georgemoorei.
arched, graduating into rather straight and oblique
Remarks: Yokoyama (1928) described Meretrix
anterior margin; ventral margin broadly arcuate;
postero-dorsal margin nearly straight, forming obtuse (MacrocaUista) ezoensis (Yokoyama) from the Plio-
Pleistocene "upper Byoritsu Bed" in Taiwan. However,
angle with rounded posterior margin. Escutcheon
as noted by Takeda (1953), the hinge and shell mor-
demarcated by blunt ridge running from beak to
phology is distinctly different from Hubertschenckia
posterior end; lunule absent. External ligament strong
ezoensis. Honda (1989) described two articulated
and occupying two-fifths ofposterior length.
specimens from an Ostrea-hcAvrng sandstone of the
Hinge plate rather wide, with three cardinal teeth in Eocene Shitakara Formation in eastern Hokkaido as
each valve. Right valve hinge: anterior cardinal tooth
Hubertschenckia ezoensis, but did not illustrate their
(3a) long, parallel to dorsal margin; posterior cardinal hinge structures. From their mode of occurrence, we
tooth (3b) vertical, stout, bifid, connected to anterior infer that these specimens were shallow water-dwelling
tooth above central tooth; area behind posterior
venerids rather than vesicomyids.
cardinal tooth deeply excavated; posterior nymphal
ridge low but distinct; central tooth (1) thin and long, Distribution: Upper Eocene Poronai Formation in the
nearly parallel to the anterior one, inserting its top Yubari coal-field, central Hokkaido; upper Eocene?
under dorsal teeth (3a, b); subumbonal pit long and Tappu Formation in the Uryu coal-field, northwestern
shallow just below umbo. Left valve hinge: anterior Hokkaido (Ohara& Kanno, 1969, 1973); upper Eocene
tooth (2a) long, parallel to antero-dorsal margin, Omagari Formation and lower Oligocene Nuibetsu
connected to short central tooth (2b); posterior tooth Formation (Takeda, 1953) in the Kushiro coal-field,
(4b) thin, oblique posteriorly, separated from central eastern Hokkaido.
tooth by deep groove; subumbonal pit deeply excavat- Genus Adulomya Kuroda, 1931
ed, situated above posterior tooth.
Anteriormuscle scar subcircular; posterior one pear- IPleurophopsis Van Winkle, 1919:23.
shaped; pallial sinus shallow, as wide as deep; strong Adulomya Kuroda. 1931:27.
ridge running from beak to deepest point of pallial Ectenagena Woodring, 1938:51.
sinus; radial interior striae rather weak.
Type species: Adulomya uchimuraensis Kuroda, 1931
Comparison: Hubertschenckia is currently only known (by monotypy); Miocene Bessho Formation, central
from its type species H. ezoensis. The most closely Honshu, Japan.
related species are found in the genus Archivesica: A.
kawamurai (Kuroda, 1943) and A. georgeinoorei n. sp. Redefinition: Shell thin, large, elongate or cylindrical,
describedherein. Hubertschenckiaezoensisresembles A. ventral margin concave or almost straight; both ends
kawamurai in having a bifid posterior cardinal tooth rounded; beaks prosogyrate, situated anteriorly; sur-
and a thin anterior cardinal tooth along the dorsal face with coarse, concentric growth increments. Inner
margin in the right valve, and in the existence of surface with deep anterior muscle scar bounded by
subumbonal pit and a shallow pallial sinus. However, a deep groove; posteriormuscle scar indistinct. Interior
A. kawamuraidiffers from H. ezoensisin having a more of ventral margin thick, with numerous fine radial
verticalcentraltooth (1) and a shorteranteriorcardinal riblets. Ligament external and long. Left valve with
tooth (3a) in the right valve, a longer and anteriorly strong posterior cardinal (4b) parallel or oblique to
inclinedcentraltooth (2b) and a shorterposteriortooth posterior shell margin; anterior cardinal strong, 2b
(4b) in the left valve; a smaller and deeper subumbonal points ventrally, 2a parallel or subparallel to the
pit, and strongly impressed radiating interior striae. antero-dorsal margin; nymph short. Right valve with
The extant species Archivesica solidissima (Okutani, two cardinals, anterior tooth (1) weaker than posterior
Hashimoto & Fujikura, 1992) was recently synony- one, pointing in an antero-ventral direction, posterior
tooth (3b) pointing in a postero-ventral direction.
mized with A. kawamurai based mainly on molecular
Subumbonal pit in both valves present or in some
datTahe(Khoijnigemao^etAracl.h,iv2e0s0i6c)a.georgemooreiresembles that cases absent (modified from Kanno et al., 1998).
ofH. ezoensisin having a bifid posteriorcardinal tooth Remarks: Because he had only a few articulated
in the right valve (3b) and a thick anterior cardinal (1) specimens at hand, Kuroda (1931) erroneously de-
parallel to the dorsal shell margin. It differs signifi- scribed Adulomya uchimuraensis as edentulous and
cantly, however; in having a more posteriorly directed consequently placed the genus in the protobranch
posterior cardinal (3) in the right valve, and a thinner family Solemyidae Adams & Adams, 1857. When
posterior cardinal (4), a smaller anterior cardinal (2) in Kanno & Ogawa (1964) allocated Adulomya chitcmii
Page 278 The Veliger, Vol. 49, No. 4
Kanehara, 1937 to Akebiconcha (=Archivesica), they age in the Makah Formation in Washington State
emphasized the edentulous hinge of A. iichimuraensis. (Goedert & Squires, 1993).
AKdaimdaondiaya(1w96a2s),sCuobsxeqeuteanlt.l(y19t6r9)e,ataedndasBosssol&emyTiudrnbeyr Adulomya hokkaidoensis Amano & Kiel, sp. nov.
(1980), among others. (Figures 13-18)
However, Habe (1977) had already described the
strong cardinal teeth and the absence ofa pallial sinus Calyptogena sp. Amano & Little, 2005:figs. 5 A, E, F.
in A. iichiinuvaeusis and placed Adidoniya in the
Vesicomyidae. Kanno et a). (1998) used many newly Diagnosis: A medium-sized Adulomya with elongate
collected specimens of Adidoniya iichiniiiraensis from
shell, sculptured by rough concentric ridges; subumbo-
one of the localities described by Kuroda (1931) to
nal pit very elongate; ligament exterior and short, two
redefine Adidoniya. They pointed out that Adidoniya
radiating cardinal teeth in right valve; left valve with
shares almost all its characters with Ectenagena, but three radiating teeth, middle one strongest.
differs by its subumbonal pit which is present
throughout the entire ontogeny of the shell, whereas Holotype: Length 46.2 mm, height 16.7 mm, JUE
in Ectenagenathe subumbonal pit is supposedlypresent no. 15848.
only injuveniles. This distinction, however, is doubtful.
The holotype of Calyptogena elongata Dall, 1916, type Paratype: Length 59.4 mm, height 16.7 mm-H, JUE
species of Ectenagena has a subumbonal pit judging no. 5849; Length 66.2 mm-H, height 22.6 mm, JUE
1
from the figures provided by Boss (1%8). Kanno et al. no. 15850.
(1998) noted that the holotype with a shell length of
mm
43 isa young specimen, but Coanet al. (2000)gave Type locality: Large road side cliffalong the Setakinai
its maximum length as 50 mm. Thus, Ectenagena is River, 5.5 km upstream from Shosanbetsu Village,
here regarded as a synonym ofAdidoniya. Hokkaido; lower middle Miocene Chikubutsu Forma-
Pleurophopsis Van Winkle, 1919, from the middle tion.
Miocene ofTrinidad (Caribbean) resembles Adidoniya
in all known characters, but its type species P. imioides Description: Shell ofmoderate size, more than 66.2 mm
Van Winkle, 1919, is only known from incomplete long, thin-walled, elongate, equivalve and inequilateral,
specimens that lack crucial characters including cardi- weakly inflated, sculptured by few rough concentric
nal tooth 3b, escutcheon, and nymph. Therefore the ridges on posterior part, growth lines cover the entire
name Plewopliopsi.s should not be used (Kiel, 2007). surface. Beak prosogyrate, situated at anterior fifth
Other species assigned or referred to Pleurophopsismay of shell. Antero-dorsal margin broadly arched, gradu-
be vesicomyids, but do not belong to Adidoniya(Kiel & ating into rounded anterior margin; ventral margin
Peckmann, in press). straight and slightly excavated at middle portion;
Archivesica resembles Adidoniya in having three postero-dorsalmarginnearlystraight,parallel toventral
radiating cardinal teeth in the left valve and a sub- margin, graduating into rounded posterior margin.
umbonal pit. It differs from Adidoniya by having Escutcheon and lunule absent; ligament exterior, weak
a narrow hinge plate, three cardinal teeth in the right and short.
valve, and a shallowpallial sinus. Calyptogena(s.s.)can Hinge plate narrow, with two cardinals in right valve
easily be separated from Adulomya by its threecardinal and three cardinals in left valve. Right valve hinge:
teeth including a very stout right posterior one, and by anterior cardinal tooth (3a) reduced; posterior cardinal
the lack ofa subumbonal pit. tooth (3b) slightly bifid, oblique posteriorly; central
tooth (1) thin, anteriorly slightly oblique; subumbonal
Included fossil species: Adulomya ucliiniuraensis Kur- pit longand shallowjust below umbo. Left valve hinge:
oda, 1931, Adulomya chitanii Kanehara, 1937, Calyp- anterior tooth (2a) thin, slightly oblique anteriorly,
togena (C) chinookensis Squires & Goedert, 1991, and connected to stout middle tooth (2b); posterior tooth
Adulomya hokkaidoensis Amano & Kiel, sp. nov. (4b) very thin, oblique posteriorly; subumbonal pit
shallow, situated above posterior tooth.
Distribution: Recent species are known from vents and Anterior muscle scar subcircular; posterior one
seeps in the northeastern Pacific (Coan et al., 2000; ovate; pallial sinus absent; deep groove running just
Desbruyes et al., 2006) and from seeps in the under posterior muscle scar; radial interior striae
northwestern Pacific (Sasaki et al., 2005); fossil species distinct.
are known from late Eocene seeps in Washington State
(this study), from early to middle Miocene whale-falls Comparison: The extant species Adulomya elongata
in Japan (Amano & Little, 2005; Amano et al., 2007), (Dall, 1916) resemblesA. hokkaidoensisinhavinga thin
and from a turbidity current deposit ofearly Oligocene and compressed shell with two cardinal teeth in the
K. Amano & S. Kiel, 2006 Page 279
Figures 13-18. Adulomya hokkaidoensis sp. nov. Figure 13. Holotype, length 46.2 mm, JUE no. 15848. Figure 14. Paratype,
length 59.4 mm,withslightlybrokenventralpart, showingdistinct radiatinginteriorstriae,JUEno. 15849. Figure 15. Rubbercast
ofleftvalvehingeofparatype (JUEno, 15849), hinge length 25.7 mm. Figure 16. Rubbercast ofleft valvehingeofparatype(JUE
no. 15851), hingelength 16.5 mm. Figure 17. Paratype, dorsalviewshowingtheshortligament, lengthofspecimen40.8 mm+,JUE
no. 15852. Figure 18. Pai'atype showing entire pallial line and posterior adductor scar, length 66.2 mm+, JUE no. 15850.
right valve, a subumbonal pit and lacking a pallial Supplementary description: Left-valve hinge with strong
sinus. However, its more elongate shape and the posterior cardinal (4b) pointing in postero-ventral
presence of concentric undulations on the posterior direction, slightly tapering at its dorsal side; cardinal
surface distinguish A. hokkaidoensis from A. elongata. 2b solid, same length as cardinal4b, pointingin ventral
The fossil A. uchimuraensis and the extant A. phaseo- direction, anterior cardinal 2a detached from 2b,
liformis (Metivier, Okutani & Ohta, 1986) have larger thinnerthan the othercardinals, elongate, andpointing
and more elongate shells. in anterior direction. Right valve hinge with two
Distribution: Known only from the whale-fall commu- cardinals, middle cardinal 1 elongate-lenticular, point-
ing in anterior direction, posterior cardinal 3b strong,
nity at the type locality.
bifid, peg-like, pointing in ventral direction. Pallial line
Etymology: For its occurrence on Hokkaido. entire, starting at postero-ventral end of anterior
Adulomya chinookensis (Squires & Goedert, 1991) oafddsuhceltlorhesicgahrt, bdeisltoawntumfbroo,m 4ve4n%traalt mpoasrtgeirnior(cat.ur2ni2n%g
(Figures 19-23) point), no pallial sinus but pallial line merges with the
elongate posterior adductor scar.
Calyptogenan. sp. Goedert & Squires, 1990:figs. 2 o-p.
Calyptogena (Calyptogena) chinookensis Squires & Remarks: Specimens previously assigned to Calypto-
Goedert, 1991:413--415, figs. 2.7-2.11; Goedert & gena (Calyptogena) chinookensis from various forma-
Squires, 1993:74-76, fig. 3. tions apparently belong to more than one species.
Vesicomya {Calyptogena) sp. Goedert et al., 2003:228, Figures 19, 20, 22, and 23 show a silicone rubber cast
PI. 42, figs. 6, 7. ofan internal mold ofa specimen from the type locality
non Calyptogena (Calyptogena) chinookensis Squires & at Bear River (LACMIP loc. 5802), which we consider
Goedert. Goedert & Squires, 1993:fig. 4. to represent the 'true' chinookensis. Its right valve hinge