A Triassic Giant Amphipod from Nevada, USA
ABSTRACT The fossil giant amphipod Rosagammarus minichiellus n. gen., n. sp. occurs in Triassic limestone (Luning Formation, west-central Nevada) in association with giant ichthyosaurs (Shonisaurus sp.) and the deep-water trace fossil Protopaleodictyon ichnosp. Fossil pereion and pereiopod morphology suggest affinities with the Acanthogammaridae, a freshwater amphipod family largely endemic to Lake Baikal. The large size (17 cm) of the Triassic amphipod shows that supergiant, deep marine amphipods comparable to modern Alicella gigantea Chevreux, 1899 were extant during the early Mesozoic. By analogy with Alicella gigantea, Rosagammarus minichiellus n. gen., n. sp. was a necrophagous, benthopelagic scavenger that fed on ichthyosaur and other sea floor carcasses. Rosagammarus minichiellus n. gen., n. sp. appears to be the oldest known fossil amphipod. This discovery extends the known geological range of Amphipoda by at least 170 million years.
- SourceAvailable from: Enrique Lozano-Álvarez[Show abstract] [Hide abstract]
ABSTRACT: N-terminal amino acid sequences for the two hemocyanin subunits from the deep-sea crustacean Bathynomus giganteus have been determined by Edman degradation, providing the first sequence information for a hemocyanin from an isopod. In addition, purified hemocyanin from B. giganteus exhibited phenoloxidase activity in the presence of sodium dodecyl sulfate. Although a natural activator has not yet been identified, a preliminary study of the enzyme indicated a K(m) of 5mM for dopamine and an initial rate of 0.1 micromol per min per mg protein, values consistent with a significant role for this enzyme in the innate immune system of B. giganteus. Moreover, after separation of hemolymph by alkaline polyacrylamide gel electrophoresis, the only detectable phenoloxidase activity coincided with the two hemocyanin subunits. The hemocyanin of this primitive crustacean may fulfill dual functions, both as oxygen carrier and as the phenoloxidase crucial for host defense.Archives of Biochemistry and Biophysics 02/2003; 409(2):402-10. · 3.37 Impact Factor
Article: Bathymetry of trace fossils[Show abstract] [Hide abstract]
ABSTRACT: Trace fossil communities are mainly bathymetry-controlled. Their relative depth sequence has been established in sedimentary series of up to Cambrian age. Actual depth figures can now be added from counterparts in the present oceans. As exemplified by the spreite burrows, behavioural response to a bathymetric gradient in food suply is suggested as the main reason for the change of trace fossils with depth.Marine Geology - MAR GEOLOGY. 01/1967; 5:413-428.
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ABSTRACT: Here we provide the first record of the ‘supergiant’ amphipod Alicella gigantea Chevreux, 1899 (Alicellidae) from the Southern Hemisphere, and extend the known bathymetric range by over 1000 m to 7000 m. An estimated nine individuals were observed across 1500 photographs taken in situ by baited camera at 6979 m in the Kermadec Trench, SW Pacific Ocean. Nine specimens, ranging in length from 102 to 290 mm were recovered by baited trap at depths of 6265 m and 7000 m. Mitochondrial and nuclear DNA sequences obtained indicate a cosmopolitan distribution for the species. Data and observations from the study are used to discuss the reason for gigantism in this species, and its apparently disjunct geographical distribution.Deep Sea Research Part II Topical Studies in Oceanography 08/2013; 92:107–113. · 2.24 Impact Factor
JOURNAL OF CRUSTACEAN BIOLOGY, 33(6), 751-759, 2013
A TRIASSIC GIANT AMPHIPOD FROM NEVADA, USA
Mark A. S. McMenamin∗, Lesly P. Zapata, and Meghan C. Hussey
Department of Geology and Geography, Mount Holyoke College, South Hadley, MA 01075, USA
A B S T R A C T
A giant fossil amphipod Rosagammarus minichiellus n. gen., n. sp. occurs in a Triassic limestone (Luning Formation, west-central Nevada)
in association with ichthyosaurs (Shonisaurus sp.) and the deep-water trace fossil Protopaleodictyon ichnosp. Fossil pereion and pereiopod
morphology suggest affinities with Acanthogammaridae, a freshwater amphipod family largely endemic to Lake Baikal. The large size
(17 cm) of the Triassic amphipod shows that supergiant, deep marine amphipods comparable to modern Alicella gigantea Chevreux, 1899
were extant during the early Mesozoic. By analogy with A. gigantea, R. minichiellus was likely a necrophagous, benthopelagic scavenger
that fed on ichthyosaur and other sea floor carcasses. Rosagammarus minichiellus appears to be the oldest known fossil amphipod,
extending the known geological range of Amphipoda by at least 170 million years.
KEY WORDS: Acanthogammaridae, Amphipoda, giant amphipods, Nevada, Triassic
Fossil amphipods are astonishingly rare considering their di-
versity and abundance in the modern biota. This may be the
case because amphipods decay rapidly after death in com-
parison to isopods and other better sclerotized and mineral-
ized crustaceans (Hurley, 1958). Also, amphipods typically
inhabit groundwater environments or marine habitats below
the Calcium Carbonate Compensation Depth (CCD), where
preservational conditions are not favorable (Holsinger and
Although amphipods are thought to have a Carbonifer-
ous origin (Bousfield, 1982a, b; Bousfield and Poinar, 1994),
until now their fossils are unknown before the late Eocene.
Woodward (1870) interpreted the Silurian fossil Necrogam-
marus as an amphipod, but Selden (1986) showed that this
fossil is an incomplete specimen of a pterygotid eurypterid.
Bate (1859) interpreted the Permian crustacean Palaeocran-
gon as an amphipod, but Glaessner (1957) showed that it is
in fact an isopod. Cretaceous amphipods were reported by
Alonso et al. (2000), but Vonk and Schram (2007) demon-
strated that these specimens are in fact fragmentary tanaids.
True amphipods Niphargus, Palaeogammarus, Synurella,
plus members of Cragonyctidae occur in Eocene-Oligocene
Baltic amber (Zaddach, 1864; Stebbing, 1888; Lucks, 1928;
Hurley, 1973; Just, 1974; Jazdzewski and Kulicka, 2000a, b,
2002; Coleman and Myers, 2001; Coleman and Ruffo, 2002;
Weitschat et al., 2002; Coleman, 2004, 2006; Jazdzewski
and Kupryjanowicz, 2010). Miocene amber has produced
Andrussovia, Gammarus, Hellenis, and Praegmelina and
other taxa (Hurley, 1973; Mukai and Takeda, 1987; Kara-
Coleman (2004: 122) notes that it is a mystery how these
∗Corresponding author; e-mail: email@example.com
appear to have been desiccated before preservation and
were windblown into the amber-forming resin (Coleman,
2004). Terrestrial amphipods (Talitridae) in amber have been
reported from Chiapas, Mexico (Bousfield and Poinar, 1994)
and the Dominican Republic (Bousfield and Poinar, 1995).
Modern talitrids frequently dry out and die when they are
washed up in the strandline.
Many extant families and genera of amphipods may
have lived during the Mesozoic (Myers and Lowry, 2003).
Karaman (1984) established new genera for several fossil
groups, and at present some 13 genera and 26 species of
fossil amphipods are known.
MATERIAL AND METHODS
A Mount Holyoke College expedition to the Shoshone Mountains, Nevada
during May 2013 produced a Triassic fossil specimen that appears to be
the oldest known amphipod, the largest fossil amphipod, and the first
amphipod confirmed from pre-Cenozoic strata. The new specimen was
collected in Union Canyon to the east of the eastern boundary of Berlin-
Ichthyosaur State Park (Fig. 1). The fossil is associated with specimens of
the graphoglyptid trace fossil Protopaleodictyon ichnosp. (Fig. 2). In turn,
Protopaleodictyon is associated with the Nereites ichnofacies (Seilacher,
1967; Frey and Pemberton, 1984), thus confirming the inference of Holger
(1992) of a deep-water environment for the Upper Shaly Limestone
Member of the Luning Formation.
The fossil preserves portions of two leg types that are characteristic for
Amphipoda. It consists of a partial dorsal pereion with portions of three
10). The taxonomically significant coxa 5 is preserved in its entirety, still in
its proper orientation with respect to the basis of pereiopod 5 (Fig. 7). Fine
details of cuticular structure are preserved on the fossil surface (Figs. 6, 9).
The anterior or posterior regions of the animal are not preserved, but the
specimen is nevertheless sufficiently complete to permit establishment of
the new taxon, Rosagammarus minichiellus n. gen., n. sp.
We estimate that R. minichiellus had a total length of 17 cm. Although
this is only one half the length of the largest specimens of Alicella
gigantea Chevreux, 1899, R. minichiellus is nevertheless a giant amphipod
comparable to modern supergiant deep-water amphipods.
© The Crustacean Society, 2013. Published by Brill NV, LeidenDOI:10.1163/1937240X-00002192
JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 33, NO. 6, 2013
(1959). The fossil site occurs in the Shaly Limestone Member of the Luning Formation in an eastward extension of its main outcrop area (Holger, 1992, her
Field locality map, West Union Canyon, Shoshone Range, showing the the fossil locality (asterisk) in Nye County, Nevada. Map from Silberling
Class Malacostraca Latreille, 1802
Superorder Peracarida Calman, 1904
Order Amphipoda Latreille, 1816
Gammaroidea Latreille, 1802
?Acanthogammaridae Garyaev, 1901
Rosagammarus n. gen.
Description.—The specimen consists of the anterior-central
portion of the pereion, including portions of pereionites,
coxal plates and pereiopods 3-5. The animal is preserved ly-
ing on its side (as would be expected for the laterally flat-
tened amphipod body) in a somewhat compressed lateral-
Nye County, Nevada. Field sample 1 of 5/16/13. Scale bar in centimeters.
Protopaleodictyon ichnosp. Shaly Limestone Member of the
dorsal view. The various parts of the pereion have been com-
pressed and displaced by sediment compaction. Pereiopod 4
has been rotated approximately 135° counterclockwise (as
viewed from a dorsal vantage) during compaction.
Coxal plates 3 and 4 are well developed and elongate,
not fused with pereionites. Coxal plate 3 with widely-
spaced setal spurs on its posterior margin (Fig. 5), with
broad ridge on its dorsolateral surface (Fig. 3). Coxa 5
short and wide, greatest dimension 8 mm (Fig. 7), with an
acutely narrowing anterior end and an oblique notch along
its distal edge that nests with a comparable notch on the
proximal end of the pereiopod 5 basis (Figs. 7-8). Pereiopod
3 with a slightly conical ischium, relatively short merus that
expands rapidly at its distal end, and a cylindrical to distally
gradually tapering carpus (Fig. 3). Pereiopod 4 with narrow,
cylindrical basis, a short, roughly cylindrical ischium and
a very elongate (15 mm), curved merus (Fig. 3). Only the
proximal part of the Pereiopod 4 carpus known (Fig. 3).
Pereiopod 5 known from the coxa and a robust, elongate
basis bearing a proximal notch as noted above (Figs. 7-8).
Gnathopod 2 known only from a short fragment that may
represent part of its basis (Fig. 3). A pereion dorsal plate
(from the mid-pereion) bears a broad spine on its lateral
edge (Fig. 8). A second pereion dorsal plate (from a more
anterior section of the pereion, inferred here to be pereion
dorsal plate2) apparentlylacksa spine (Fig.9). It has rotated
about 140° clockwise with respect to the other parts of the
animal as viewed from the amphipod’s left side. Recessed
setal pores are evenly distributed over the surface of the
heavily mineralized exoskeleton (Figs. 9-10). Setal pores on
the proximal part of coxal plate 3 are surrounded by smaller
satellite pores or pore-like structures (Fig. 6).
MCMENAMIN ET AL.: TRIASSIC AMPHIPOD
diagrammatic sketch of Fig. 3A identifying key parts of exoskeleton. Abbreviations are as follows: B, basis; c, carpus; cx, coxa; CP, coxal plate; G,
gnathopod; i, ischium; m, merus; Pp, pereiopod; Pt, pereionite; S, spine.
Rosagammarus minichiellus n. gen., n. sp. Luning Formation, Nevada, Triassic. A, Photograph of fossil specimen; scale bar in centimeters; B,
Rosagammarus minichiellus n. sp.
Material collected.—One specimen found in float derived
from the Shaly Limestone Member of the Luning Formation
(Late Triassic, Norian (Tropiteswelleri-Mojsisovicsites kerri
zones; Silberling, 1959)) in a dry stream bed north of the
Union Canyon jeep trail (National Forest District Road
024; Fig. 1). The fossil is probably derived from the
middle part of the Shaly Limestone Member of the Luning
Formation, where interbedded limestones are brownish-gray
with “irregular orange-brown, red, or lavender patches”
(Silberling, 1959, p. 16) as visible on the specimen. The site
is located outside of the boundary of the state park. Rangers
at Berlin-Ichthyosaur State Park routinely direct visitors to
this site for recreational fossil collecting.
Body Length.—Estimated total body length 17 cm.
amphipod, using a sketch of a generalized acanthogammarid as template.
Fossil material recovered is shown in gray. Head and tail regions are
conjectural. Estimated total length 17 cm.
Rosagammarus minichiellus n. gen., n. sp. Reconstruction of entire
Types.—Deposited in the North Carolina Museum of Nat-
ural Sciences. Holotype: adult, NCSM 11756. Collected 15
May, 2013 (field sample 2 of 5/15/13; Lat 38.884340; Long
Description.—As for the genus.
Etymology.—Named for Rose Minichiello, who discovered
Superfamily Gammaroidea includes a large number of fam-
ilies and subfamilies. Phylogenetic relationships among
the Gammaroidea remain controversial even after Bous-
field’s reorganization of Gammaridae (Bousfield, 1973,
1977; Holsinger, 1974, 1977; Karaman and Barnard, 1979;
Barnard and Karaman, 1980). Interfamilial taxonomic rela-
tionships are so uncertain that Ahyong et al. (2011) list 190
amphipod families in alphabetical order rather than recog-
Rosagammarus may belong to an extinct family that in-
cluded giant, deep-sea early Mesozoic amphipods with elon-
of the coxa deeper in coxa 5. Rosagammarus shows pro-
nounced morphological similarities to the Acanthogammari-
dae, a freshwater family largely endemic to Lake Baikal. We
suggest this could indicate a phylogenetic affinity between
Rosagammarus and Acanthogammaridae. Our rendition of
R. minichiellus (Fig. 4) maps the fossil material onto a gen-
eralized outline of an acanthogammarid.
Acanthogammarids are characterized by being mainly
“large, carinate and/or processiferous...[pereiopods] often
very elongate...coxal plates 1-4 deep, coxae 5-7, anterior
lobe usually deeper” (Bousfield, 1977: 294). Regarding
the latter feature (anterior lobe of the coxa deeper), most
acanthogammarids are unlike Rosagammarus.
There are some similarities in leg structure between
Rosagammarus and members of the Eusiridae; however,
overall pereionite and coxal plate structure in Rosagam-
marus would seem to be more similar to that of the acan-
JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 33, NO. 6, 2013
indicated, scale bar in centimeters; B, coxal plate 3, showing setal spurs, inset box shows position of Fig. 5C; C, posterior edge of coxal plate 3 with arrows
indicating setal spurs.
Rosagammarus minichiellus n. gen., n. sp. Setal spurs on the posterior margin of coxal plate 3. A, entire specimen with position of coxal plate 3
thogammarids. Furthermore, large spines in eusirid am-
phipods occur on the pereion in a saggital position, not in
a lateral position as seen in both Rosagammarus and the
acanthogammarids. In eusirids, coxa 5 tends to taper more
sharply in a posterior direction instead of tapering more
sharply in an anterior direction, as is the case for Rosagam-
await either more complete fossil material, clarification of
family-level relationships among Gammaroidea, or both.
Incidentally, the supergiant modern deep sea amphipod
A. gigantea Chevreux (Lysianassoidea: Alicellidae) lacks
spines, has subquadrate coxal plates that become deeper in
an anterior direction, relatively short pereiopods, and is quite
distinct from R. minichiellus at the superfamily level.
The large, elongate basis of pereiopod 5 is comparable
to the elongate, robust basis of Propachygammarus maxi-
mus (Garyaev, 1901) from Lake Baikal, a freshwater acan-
thogammarid that reaches 7 cm in length. The juxtaposition
of a robust basis in pereiopod 5 and elongate merus and car-
pus in pereiopod 4 with an oblique distal end of its merus
are also features shared with Propachygammarus maximus
(Garyaev, 1901). A broad spine occurs on one of the pereion
dorsal plates in R. minichiellus.
Takhteev (2000) identified three different ecomorphs
among nectobenthic amphipods. Both Rosagammarus and
Propachygammarus belong to Takhteev’s type 2 ecomorph,
whose main morphological characteristics are “large body
size, strong cuticle and widely outstretched extremities”
(Takhteev, 2000: 204). Takhteev (2000) emphasized the
large number of morphological convergences known be-
tween marine and freshwater amphipod genera.
The setal pore arrangement on the exoskeleton in Rosa-
gammarus is very similar to that seen on Brandtia sp.,
3, with inset box showing position of Fig. 6B; B, satellite pore structures surrounding larger setal pores, scale bar = 0.5 mm; C, sketch from photograph
showing relationship between satellite pore structures and setal pores, scale bar = 0.25 mm.
Rosagammarus minichiellus n. gen., n. sp. Satellite pore structures surrounding setal pores on the proximal part of coxal plate 3. A, coxal plate
MCMENAMIN ET AL.: TRIASSIC AMPHIPOD
centimeters; B, coxa 5 and pereiopod 5 basis, with box showing position of Fig. 7C, negative image; C, coxa 5 showing acutely narrowing anterior end and
an oblique notch along its distal edge that nests with a comparable notch on the proximal end of the pereiopod 5 basis.
Rosagammarus minichiellus n. gen., n. sp. Coxa 5 and pereiopod 5 basis. A, entire specimen with coxa 5 and pereiopod 5 basis in box, scale bar in
photograph showing relative positions of: B, basis; cx5, coxa 5; CP, coxal plate; i, ischium; m, merus; Pt, pereionite; S, pereionite spine.
Rosagammarus minichiellus n. gen., n. sp. Pereiopod 5 region. A, enlargement of the pereiopod 5 region, scale bar = 7 mm; B, sketch from
bar = 2 mm; B, negative image of same view; scale bar = 2 mm.
Rosagammarus minichiellus n. gen., n. sp. Anterior pereionite, probably pereion dorsal plate 2 (indicated as Pt2 in Fig. 3B). A, reflected light, scale
JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 33, NO. 6, 2013
image to show setal pore details, scale bar = 1.5 mm; B, cuticle ornamentation of Brandtia sp., an acanthogammarid amphipod from Lake Baikal. Scanning
electron micrograph showing plate arrangement and setal pore pattern, width of view approximately 2.0 mm, courtesy Petr Jan Juraˇ cka; C, low vacuum
scanning electron micrograph showing setal pores on pereiopod 5 basis, scale bar 2 mm; D, low vacuum scanning electron micrograph showing setal pores
on pereiopod 5 basis, scale bar 500 μm.
Rosagammarus minichiellus n. gen., n. sp. and acanthogammarid Brandtia sp. Comparisons of cuticular structure. A, pereiopod 5 basis, negative
an acanthogammarid amphipod (Fig. 10). Coxa 5 has an
oblique notch along its posterior edge that nests with a com-
parable notch on the pereiopod 5 basis, a feature that occurs
in the same region in Brandtia (Fig. 10). This coxal notch is
comparable to the notch visible on the ventral edge of coxa
5 in Valettiopsis ruffoi Serejo and Wakabara, 2003 as shown
in Fig. 2A of Serejo and Wakabara (2003). The shape of
coxa 5 in R. minichiellus with its acutely narrowing anterior
end is quite comparable to that of Eulimnogammarus (Eu-
limnogmmarus) czerskii (Dybowsky, 1874). This is in con-
trast to Acanthogammarus (Brachyuropus) nassonowi Doro-
gostaiskii, 1922 and Garjajewia dogieli Bazikalova, 1945
where coxa 5 becomes conspicuously wider at its anterior
edge. Coxal plates 3 and 4 in R. minichiellus are of compa-
rable relative size to those of Hyalellopsis (Dorogammarus)
castanea (Dorogostaiskii, 1930), where the coxal plates 1-4
are broad and shield-like.
Setal spurs similar to those on the posterior edge of coxal
plate 3 in Rosagammarus minichiellus n. gen., n. sp. are seen
in Micruropus galasii Bazikalova, 1962, Acanthogammarus
(Acanthogammarus) subbrevispinus Bazikalova, 1945 and
other Baikalian species.
Capture of supergiant amphipods in deep marine traps has
focused interest on these colossal crustaceans, whose max-
imum length may exceed 34 cm (Lowry and De Broyer,
2008; Jamieson et al., 2013). Abyssal gigantism in isopods
has been linked to increased oxygen availability in cold bot-
tom waters (Chapelle and Peck, 1999, 2004). Giant isopods
belonging to the genus Bathynomus, however, inhabit deep,
low oxygen waters in the Gulf of Mexico (Pless et al., 2003).
Rosagammarus minichiellus was probably a deep marine,
necrophagous, benthopelagic scavenger ecologically com-
parable to members of Alicellidae and other deep marine
amphipods (Lowry and De Broyer, 2008; Duffy et al., 2012).
If Rosagammarus was as patchily or sparsely distributed on
the deep-sea floor as is Alicella, then this fossil represents
an exceptionally rare and fortunate discovery. This may in
fact represent a case of exceptional fossil preservation. It ap-
pears that a Stow Sequence fine-grained turbidite, consisting
of carbonate mud emplaced in deep water (Stow, 2006), led
to a local cessation of carbonate dissolution (as would ordi-
narily occur below the CCD), and hence preservation of the
MCMENAMIN ET AL.: TRIASSIC AMPHIPOD
calcareous amphipod fossil in a micritic (lithified lime mud)
Timofeev (2001) interpreted deep-water gigantism in ma-
rine crustaceans as a temperature-dependent phenomenon
al. (2013: 111) note that this concept “does not adequately
explain deep sea gigantism where little or no variation has
been recorded in temperature vertically through the water
column.” Jamieson et al. (2013) instead favor the hypothesis
that gigantism in A. gigantea renders the animal somewhat
immune to predation from abyssal predators due to its size.
Another factor that may influence abyssal gigantism in
necrophagous, benthopelagic scavengers is the quantity of
large detritus that falls to the sea floor. The ichthyosaur
Shonisaurus is comparable in size (Holger, 1992) to a
modern sperm whale (Physeter). The appearance of very
large sea floor carcasses (Dahl, 1979; Thurston et al., 2002)
on the Triassic sea floor could have provided the trophic
resources needed for the appearance of giant deep marine
amphipods such as Rosagammarus.
Alicella gigantea, the largest known amphipod (Chevreux,
1899; De Broyer and Thurston, 1987; Lowry and De Broyer,
2008; Jamieson et al., 2013), inhabits deep abyssal and
hadal plains (Barnard and Ingram, 1986, 1990). Alicella
occurs at great depth in both the Atlantic and the Pacific. Its
rarity in spite of wide biogeographic distribution is puzzling
(Barnard and Ingram, 1986; De Boyer and Thurston, 1987).
Jamieson et al. (2013: 112) attribute the “extremely disjunct
geographical distribution...of this most enigmatic species”
to A. gigantea being either very patchily distributed, or very
Large (but not supergiant) deep-sea amphipods belonging
to the genus Eurythenes have extremely wide geographic
distribution in the modern seas. For example, Eurythenes
gryllus (Lichtenstein in Mandt, 1822) has been reported
from all major marine bodies of water with the interesting
exception of the Mediterranean (Stoddart and Lowry, 2004).
Due to limitations of the fossil record, amphipod paleo-
history is largely inferred from modern geographic distribu-
tions (Myers, 1991; Conlan, 1995). Vonk and Schram (2003)
utilized cladistics to reveal some of these biogeographic pat-
terns for ingolfiellidean amphipods. Biogeographic analysis
indicates that amphipods had to be widespread in Pangea,
Gondwana, and Laurentia (Vonk and Schram, 2003; Myers
and Lowry, 2009; Väinöla et al., 2008). For example, the
global distribution of Bactrurus has been linked to the for-
mation and breakup of Pangea (Holsinger, 1986).
Considerable uncertainty has been expressed regarding
whether or not the highly diverse, endemic Lake Baikal
amphipod fauna (72 genera and 363 species) represents an
in situ freshwater diversification (Danileya et al., 2011),
or whether the diversity was inherited from an earlier
freshwater forms are not entirely restricted to Lake Baikal.
For example, a “Baikaloid” deep-water amphipod occurs in
Fuxian Hu, a karst lake in Yunnan, China (Sket, 2000).
Hou et al. (2011) used phylogenetic analysis to show that
the modern amphipod Gammarus originated in salt water of
the Tethyan region and subsequently (by the Middle Eocene)
colonized freshwater habitats. The gammaridean stygobiont
amphipods of Metacragonyctidae, formerly thought to be an
exclusively New World taxon, were recently found in the
this biogeographic pattern to a wide Tethyan distribution for
the ancestors of Metacrangonyx.
If pereion, pereiopod, setal spur, and cuticular surface tex-
ture similarities between R. minichiellus and acanthogam-
marids indicate shared descent, the result has important im-
plications for our understanding of the paleobiogeography
of the ancient Pacific Ocean and the dispersal patterns of
organisms of the Tethyan region (Newton, 1988; Smith et
al., 1990) during the Norian Stage (Late Triassic). Norian
species of the plicate, thin-shelled clam Monotis occur abun-
dantly both in Nevada-California (M. subcircularis) and in
eastern Siberia (M. zabaikalica). The biogeographic range
of Monotis is thought to have expanded dramatically during
the Late Norian (Westermann, 1973).
The occurrence of a fossil amphipod with acanthogam-
marid affinities in Cordilleran North America suggests that
acanthogammarids were once widespread in Tethyan marine
environments. Marine acanthogammarids appear to be ex-
tinct, but we should not exclude the possibility that some
still occur in an unsurveyed deep marine habitat.
We wish to express our sincere thanks to D. B. Cadien, C. O. Coleman, R.
Kamaltynov, L. Orr, D. Orr, N. Orr, J. M. McMenamin, G. J. Maarchand,
D. L. Schulte McMenamin, D. Fleury, R. Minichiello, F. R. Schram, A. J.
Jamieson, and R. Riggs for assistance with various aspects of this research.
This work was supported by a Mount Holyoke College Faculty Grant to M.
A. S. McMenamin and Mount Holyoke Summer Research Fellowships to
both M. C. Hussey and L. P. Zapata.
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