Early Pliocene tracer of North Atlantic and South Pacific sea surface currents: Janthina typica (Bronn, 1860) (Mollusca: Gastropoda)

Abstract

Janthina typica is an extinct, rare, floating species of gastropod
from the early Pliocene whose fossils have an unusual geographic
distribution, appearing in the eastern North Atlantic archipelagos
(Canary, Azores, Madeira and Selvagen Islands), Morocco, and Pacific
(New Zealand, Australia and Japan). This study examines the origin
of this biogeography and how the species may have dispersed via sea
surface currents. We have considered the published ecological aspects
of the genus Janthina, the Janthina typica fossil localities, and ocean
palaeocurrents. Abundant specimens of J. typica are found in marine
deposits on Gran Canaria island (northeast Atlantic), 40Ar/39Ar dated
at 4.2 Ma. These deposits therefore accumulated just before the end
of the early Pliocene warm climate and closely predate the start of
global changes that gave rise to the world’s present climate. In the early
Pliocene, the cold Canary Current did not yet exist. The subtropical
northeastern Atlantic Ocean was warmer than today and its waters
would have met the Circumtropical Current that crossed the Central
American Seaway from the Caribbean to the Pacific. From there, the
South Equatorial Current flowed towards the eastern coast of Indonesia
before splitting north towards Japan and south as the East Australian
Current. The latter must also have extended along the southern
coast of Australia, crossing the Bass Strait before reaching the area
of modern-day Perth in southwestern Australia. The reverse journey
(from Australia to the eastern Atlantic Ocean) would have posed far
more obstacles, and is considered improbable. J. typica therefore likely
originated in the East Atlantic. The main causes for its extraordinary
geographic distribution are its ecology as a floating animal in warm
water, tectonic plate movements that permitted an open Central
American Seaway and a restricted Indonesian Seaway, and Earth’s
rotation and its influence on marine currents.

Full text

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Meco, J., Lomoschitz A, Betancort, J.-F., 2016, Early Pliocene tracer of North Atlantic and South Pacific sea surface currents: Janthina typica (Bronn, 1860) (Mollusca:
Gastropoda): Revista Mexicana de Ciencias Geológicas, v. 33, núm. 2, p. 192-197.
ABSTRACT
Janthina typica is an extinct, rare, floating species of gastropod
from the early Pliocene whose fossils have an unusual geographic
distribution, appearing in the eastern North Atlantic archipelagos
(Canary, Azores, Madeira and Selvagen Islands), Morocco, and Pacific
(New Zealand, Australia and Japan). This study examines the origin
of this biogeography and how the species may have dispersed via sea
surface currents. We have considered the published ecological aspects
of the genus Janthina, the Janthina typica fossil localities, and ocean
palaeocurrents. Abundant specimens of J. typica are found in marine
deposits on Gran Canaria island (northeast Atlantic), 40Ar/39Ar dated
at 4.2 Ma. These deposits therefore accumulated just before the end
of the early Pliocene warm climate and closely predate the start of
global changes that gave rise to the world’s present climate. In the early
Pliocene, the cold Canary Current did not yet exist. The subtropical
northeastern Atlantic Ocean was warmer than today and its waters
would have met the Circumtropical Current that crossed the Central
American Seaway from the Caribbean to the Pacific. From there, the
South Equatorial Current flowed towards the eastern coast of Indonesia
before splitting north towards Japan and south as the East Australian
Current. The latter must also have extended along the southern
coast of Australia, crossing the Bass Strait before reaching the area
of modern-day Perth in southwestern Australia. The reverse journey
(from Australia to the eastern Atlantic Ocean) would have posed far
more obstacles, and is considered improbable. J. typica therefore likely
originated in the East Atlantic. The main causes for its extraordinary
geographic distribution are its ecology as a floating animal in warm
water, tectonic plate movements that permitted an open Central
American Seaway and a restricted Indonesian Seaway, and Earth’s
rotation and its influence on marine currents.
Key words: pelagic mollusk; warm water species; Pliocene climate;
plate tectonics; Coriolis effect; early Pliocene currents.
RESUMEN
Janthina typica es un molusco gasterópodo flotante, extinguido
y raro del Plioceno. Sus fósiles presentan una distribución geográfica
inusual apareciendo en los archipiélagos del este del Atlántico norte
(Islas Canarias, Azores, Madeira y Salvajes), en Marruecos y en el
oeste del Pacífico (Nueva Zelanda, Australia y Japón). En el presente
trabajo se estudia la causa de esta biogeografía y de su dispersión
mediante corrientes marinas de superficie. Para ello se han considerado
los aspectos ecológicos del género Janthina, las localidades fósiles de J.
typica y las paleocorrientes oceánicas. Abundantes ejemplares de J. typica
se han encontrado en depósitos marinos de la Isla de Gran Canaria
que han sido datados en 4.2 Ma. Esta época es justamente anterior a
la terminación del clima cálido del Plioceno inferior y se aproxima al
comienzo de los cambios globales que van a dar lugar al modelo climático
actual. En el Plioceno inferior la corriente fría de Canarias no existía.
El Atlántico norte subtropical era más cálido que en la actualidad y sus
aguas se encontrarían con la Corriente Circumtropical que cruzaba
el Paso de América Central desde el Mar Caribe al Océano Pacífico.
Desde ahí, la Corriente Ecuatorial del Sur fluye hacia las costas de
Indonesia en donde se divide, al norte hacia Japón y al sur hacia las
costas de Australia llegando a alcanzar una posición frente a la actual
ciudad de Perth tras atravesar el Estrecho de Bass. El trayecto inverso
(de Australia al este del océano Atlántico) encontraría más obstáculos
y puede considerarse altamente improbable. De ello se deduce que J.
typica se originó en el Atlántico europeo. Las principales causas de su
extraordinaria distribución geográfica son su ecología, por ser un animal
flotante en aguas cálidas, los movimientos de las placas tectónicas, que
permitieron el paso de América Central y un estrechamiento del paso
de Indonesia, y el movimiento de rotación de la Tierra y su influencia
sobre las corrientes marinas.
Palabras clave: moluscos pelágicos; fauna de aguas cálidas; clima del Plio-
ceno; placas tectónicas; efecto Coriolis; corrientes del Plioceno temprano.
INTRODUCTION
On Gran Canaria (Canary Islands, Spain; Figure 1) marine de-
posits at La Esfinge site (Figure 2) host a considerable accumulation
of Janthina typica (Figure 3). These deposits have been recently dated
(Meco et al., 2015) using 40Ar/39Ar to 4.2 Ma from samples of pillow
lava that entered into contact with it. The aim of the present paper is to
show the geographic distribution of J. typica in the Atlantic and Pacific
oceans during the early Pliocene. The paper presents hypotheses that
could explain its notable dispersal as a floating animal in warm water.
REVISTA MEXICANA DE CIENCIAS GEOLÓGICAS
v. 33, núm. 2, 2016, p. 192-197
Early Pliocene tracer of North Atlantic and South Pacic sea surface currents:
Janthina typica (Bronn, 1860) (Mollusca: Gastropoda)
Joaquín Meco1,*, Alejandro Lomoschitz2 and Juan-Francisco Betancort1
1 Departamento de Biología, Universidad de Las Palmas de Gran Canaria (ULPGC),
35017, Las Palmas de Gran Canaria, Canary Islands, Spain.
2 Instituto de Oceanografía y Cambio Global, Universidad de Las Palmas de Gran Canaria (ULPGC),
35017 Las Palmas de Gran Canaria, Canary Islands, Spain.
* joaquinfrancisco.meco@ulpgc.es

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18º 17º 16º 15º 14º W
CANARY ISLANDS
El Hierro
La Palma
Gomera
Tenerife
Gran Canaria
Fuerteventura
Lanzarote
28º
27º
29º
N
AFRICA
02 3 4
15 km
La Esfinge
Northeastern
Gran Canaria
Las Palmas de
Gran Canaria
Janthina typica: ecology and palaeodistribution
The geographic distribution of fossil specimens of the tropical
gastropod Janthina typica (Bronn, 1860) (= Hartungia typica Bronn
= Janthina Hartungi Mayer = Hartungia chuberti Chavan) is strik-
ing for the great distances between the sites where this taxon has
been found: from the Canary Islands (Meco et al., 2015), the Azores
(Bronn, 1860; Mayer, 1864), Madeira (Mayer, 1864), S elvagem Grande
(Joksimowitsch, 1911) and Atlantic Morocco (Chavan, 1951) to the
antipodean locations of New Zealand, Australia and Japan (Tomida
and Kitao, 2002; Beu and Raine, 2009).
The current Janthinidae comprise a family of pelagic gastro-
pods that live in colonies in warm and temperate seas, floating on a
bubble-like raft of their own making, bound by mucus secreted from
the organisms´ feet, and they feed on hydrozoans such as Velella and
Physalia (Nicklès, 1950; Laursen, 1953; Powell, 1979; Janssen, 2007;
Churchill et al., 2011). This unusual adaptation enables them to travel
enormous distances by drifting along with the currents, and s ometimes
they are cast onto beaches in significant numbers by on-shore winds
(Beu and Raine, 2009).
J. typica is a fossil species from the early Pliocene (5.3 Ma to
3.6 Ma; Gradstein et al., 2004). The other localities where J. typica
is found span much of the Pliocene. On Santa María Island in the
Azores, specimens have been found in Feteirinhas and Pinheiro on
the southeastern tip of the island (Reiss and Bronn, 1863). In a nearby
locality, Pedra que Pica, the marine deposits have been attributed to
the Messinian based on an 87Sr/86Sr age of 5.51 Ma (Kirby et al., 2007).
The oldest shield of Madeira Island has yielded a 40Ar/39Ar age >4.6 Ma
(Geldmacher et al., 2000) to 5.3 Ma (Klügel, 2009); therefore, the marine
deposits at the Sao Vicente locality are also probably early Pliocene.
In Selvagem Grande the marine deposits accumulated before the
Pliocene volcanic cycle occurring at 3.4 Ma (Geldmacher et al., 2001).
The marine deposits at Aïn Sebaa near Casablanca in Morocco are
referred to the Piacenzian stage (Chavan, 1951). In New Zealand, J.
typica has been found in deposits assigned to the Kapitean to Waipipian
stages (Beu and Raine, 2009), which are roughly contemporaneous with
the uppermost Messinian-Lower Zanclian to Lower Piacenzian stages
(ca. 6 Ma to ca. 3 Ma). In southeastern Australia (Victoria) and western
Australia (Perth) the deposits that yielded J. ty pica were included in the
Kalimnan stage (Tate, 1893; Beu and Raine, 2009), which corresponds
roughly to the Upper Zanclian and Lower Piacenzian (ca. 4.4 to ca.
3 Ma). The J. typica specimens found in Kyushu, South Japan, were
included in the earliest Pliocene (Tsuma Formation ca. 5 Ma) and in the
latest Pliocene (Takanabe Formation, 2.6–2.5 Ma; Tomida et al., 2013).
In the early Pliocene (5 Ma to 4 Ma), Earth's climate was warm
in many regions and temperate in others. The gradual cooling that
followed the early Pliocene led to the establishment of modern tem-
perature patterns (Fedorov et al., 2013). Thus, the age of the Gran
Canaria marine deposits with J. typica (4.2 Ma) falls within the early
Pliocene warm period, but is close to the transition into the cooling
period that followed.
The geological characteristics and sedimentary interpretation of
the Gran Canaria marine deposits that contain a significant acc umula-
tion of J. typica shells, along with their isotopic age (4.2 Ma; Figure 2),
were reported in a previous paper (Meco et al., 2015). Other marine
deposits of Las Palmas de Gran Canaria are also early Pliocene but these
sediments provided a 40Ar/39Ar age of 4.8 Ma (Meco et al., 2015) and
no fossil specimens of J. typica have been found in them. The fossils
contained indicate a coastal and littoral habitat (e.g., Patella ambrog-
gii Lecointre) with a warm intertropical climate (e.g., Persististrombus
coronatus Defrance), Nerita emiliana Mayer).
In the present paper the ecology of Janthina is discussed and the
oceanic currents of ca. 4 Ma are summarized, mainly from the findings
Figure 1. Location of La Esfinge site in northeastern Gran Canaria, where Janthina typica has been found.

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1
1
a)
b)
c)
3
22a
2a
2b
2b
a)
b)
c)
d)
e)
f)
1 cm
of the Ocean Drilling Program (ODP), which allow sites where fossil
specimens of J. typica have been found to be connected. The dispersal
of this species from the eastern Atlantic to the western Pacific (or
vice-versa), must have been determined by the sea surface currents
at that time, which were in turn controlled by tectonic plate move-
ments, and pressure gradients and the effect of the Earth’s rotation
(the Coriolis effect).
INFLUENCE OF TECTONIC PLATE MOVEMENTS
Around 4.2 Ma ago, the geographic distribution of land masses
(and so of the seas) differed significantly from today. Two important
changes took place around this time that were caused by the movement
of tectonic plates, and resulted in the closure of inter-ocean connec-
tions. One change caused the closure of the Central American Seaway,
as the South American, Caribbean and North American plates moved
closer together, and the Atlantic Ocean became isolated from the Pacific
Ocean (Schmidt, 2007). In the other major change, the Indonesian
Seaway closed as the Australian and Eurasian plates moved closer
together, bringing about a partial isolation of the Pacific Ocean from
the Indian Ocean (Gallagher et al., 2009).
Closure of Central American seaway
The closure of the Central American Seaway (also called the
Panamanian Seaway) can be deduced from the progressive differen-
tiation in salinity between the Caribbean Sea and the Pacific Ocean
which was taking place about 4 Ma ago (Keigwin, 1982). This change is
documented in isotopic analyses of foraminifera extracted from ODP
oceanic drilling samples, including ODP Site 1241 (Groeneveld et al.,
2006) in the eastern equatorial Pacific Ocean, and ODP Site 999 (Steph
et al., 2006) in the Caribbean Sea. Salinity was virtually the same on
both sides of present day Panama 4.2 Ma ago (Sarnthein et al., 2009),
but shortly thereafter began the first phase of an increase in Caribbean
salinity that concluded some 3.7 Ma ago. This time interval is consid-
ered to reflect the initial stage in the closure of the Central American
Seaway (Chaisson and Ravelo, 2000). Thus, 4.2 Ma ago, the seaway still
existed, and the Circumtropical Current that flowed east-to-west from
the Caribbean to the Pacific, was still operative (Iturralde-Vinent and
MacPhee, 1999; Mestas-Nuñez, 2014).
The Pacific Ocean warm pool
A comparison of foraminifera from ODP Site 806, near the
Solomon Islands, and ODP Site 847, near the Galapagos Islands,
reveals important changes 4.2 Ma ago that establish the timing of
salinity differentiation at the latitude of Ecuador between the eastern
and western sides of the Pacific Ocean. From this point onwards an
enlargement of the West Pacific Warm Pool began and an eastwards
lengthening of the cold tongue was initiated. The evolution of plank-
Figure 2. Geological context at La Esfinge (Gran Canaria). (a) Section showing
the fossiliferous marine deposit (2) between pillow lavas with a 4.2 Ma 40Ar/39Ar
age (1) (from Meco et al., 2015) and Pleistocene volcanics (3); (b) detail of layer
2: 2a marine sands with fossils inside and 2b aeolian sands; (c) accumulation
of Janthina typica at the top of layer (2).
Figure 3. Janthina typica (Bronn, 1861) showing a) apertural view b) apical view
c) lateral view (LE2051) from the early Pliocene (4.2 Ma) at La Esfinge (Gran
Canaria, Spain). Note that it has faint but visible folds; d) drawing of apertural
view from early Pliocene (Opoitian) at southwest Aukland, New Zealand (Beu
and Maxwell, 1990); e) apertural view (MGF3472) from the Pliocene of Japan
(Tomida et al. 2013); f) apertural view (MFM112203) from Upper Pliocene of
Japan (Tomida and Kitao, 2002) as Hartungia japonica (Tomida and Itoigawa,
1984).

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tonic foraminifera and their ecology suggest that surface water cooling
was taking place between 4.5 Ma and 4.0 Ma (Chaisson and Ravelo,
2000, Li et al., 2006), which is interpreted to be a consequence of the
Panamanian Seaway closure.
Indonesian Seaway closure
Foraminiferal analyses of Miocene to Holocene strata of the
northwestern continental shelf off Australia have been used to chart
the influence of the West Pacific Warm Pool (Gallagher et al., 2009).
Between 10 Ma and 4.4 Ma ago, the collision of Australia and Asia nar-
rowed the Indonesian Throughflow. This “S” shaped current connects
the West Pacific Warm Pool and the Indian Ocean, passing from sout h
of the Philippines through the Makassar Strait (between Borneo and
Sulawesi), turning southwards through the Flores Sea and the Timor
Sea, ultimately heading southwest to the Indian Ocean (Figure 4).
Warmer waters became trapped in the Pacific, creating a central West
Pacific Warm Pool marine biogeographic province spanning a zone
from the equator to 26°N (Gallagher et al., 2009).
Between 4.4 Ma and 4 Ma, Indo-Pacific marine taxa migrated
to waters off of northwestern Australia possibly because of a limited
Indonesian Throughflow, and the absence of these taxa after 4 Ma
indicates the possible restriction of this current. The L eeuwin Current,
which flows from south of Java to the south of Australia along its west
coast, did not begin until much later, in the Early Pleistocene (Gallagher
et al., 2009), and so offered no viable route for faunal migration
4.2 Ma ago. At the same time, beginning with the northward displacement
of New Guinea and the emergence of the islands of Indonesia 5 Ma
ago, exchange between the Pacific and Indian Oceans through the
Indonesian Seaway was interrupted between 4 Ma and 3 Ma (Cane and
Molnar, 2001). This had the effect of redirecting oceanic circulation
from the southern Pacific warm waters northward to Japan surrounded
by relatively cold waters of the northern Pacific. The presence of J.
typica at ca. 5 Ma in southern Japan shows that the warm Kuroshio
Currents flowed strongly in the earliest Pliocene (Tomida et al., 2013).
Southern Australia
The Pliocene climatic and environmental evolution of southeastern
Australia (Bass Strait) indicates that relatively stable and warmer marine
conditions than the present day prevailed throughout most of the early
Pliocene (Gallagher et al., 2003). This corresponds to a period of low
marine δ18O values (corresponding to warmer waters and/or lower
ice volume) from 4.2 Ma to 4.0 Ma (Shackleton et al., 1995). This was
also a time of relatively low ice volume in the Antarctic (Bart 2001;
Gallagher et al., 2003).
POSSIBLE HYPHOTHESES
There are no significant age differences among the sites where
J. typica has been collected in the Pacific and Atlantic. This suggests
that two opposing hypotheses may explain the path of its biogeo-
graphic dispersal: (a) migration from the eastern Atlantic Islands to
the Australian coasts; or (b) migration from the western Australian
coast to the eastern Atlantic islands.
Hypothesis 1: dispersal of J. typica from the eastern Atlantic Islands
to the western Australian coast
At present, the Azores, Madeira, Salvagen and Canary Islands
are situated within the North Atlantic subtropical gyre. Around 4.2
Ma, the waters were warmer and this gyre would have been weaker
(Meco et al., 2015). Nevertheless, the trade winds and associated
currents likely existed, and would have allowed J. typica to disperse
into the Caribbean Sea, and cross the Central American Seaway to
the equatorial Pacific. Once it reached the equatorial Pacific Ocean,
the trade winds of the intertropical zone could have carried J. typica
westward into the southern hemisphere toward Indonesia. Because
the Indonesian Troughflow was closed at the time, once the Equatorial
Current reached the western Pacific, separate currents may have
formed, one moving northward in the direction of Japan, and another
southward to Australia and New Zealand (Figure 4).
Hypothesis 2: dispersal of J. typica from the western Australian coast
to the eastern Atlantic islands
The reverse route, from the western Pacific to the eastern Atlantic,
would have posed significant difficulties. Two possible paths could be
invoked: (1) following the oceanic gyres through the Indian Ocean
into the South Atlantic, and from there into the North Atlantic. This
would have endangered the survival of J. typica, a warm water species,
as it would have required passage through long sections of cold waters
in both the northern and southern hemispheres; or (2) following the
Equatorial Counter Currents eastward across the Pacific, though this
would have meant overcoming the obstacle of the "doldrums", the
area of low pressure around the equator where prevailing winds are
calm. It should be noted that the Pacific Equatorial Countercurrent
originated in the west and advanced eastward as modern climate
conditions began to set in (Li et al., 2006). Some 4.2 Ma ago, however,
the countercurrent was shorter and the oceanic gyres were only in the
formative stage of their modern configurations (Li et al., 2006). The
Pacific currents were no doubt different from those of today and in
some areas may not have even existed. It would have been difficult for
J. typica to migrate from the western Australian coast to the eastern
Atlantic Ocean ca. 4.2 Ma ago.
Other older species of Janthina are very similar morphologically to
the Canary I. J. typica (4.2 Ma), but designated Hartungia instead in the
literature (for a taxonomic study, see Beu and Raine, 2009). Hartungia
elegans occurred along the Pacific coast of southern and central Japan
during the Late Miocene (planktonic foraminiferal Zone N. 17, at ca.
6.8 Ma; see Tomida and Nakamura, 2001) and Hartungia pehuensis
occurs at Taranaki in northwestern New Zealand also during the Late
Miocene (Marwick, 1926). The Late Miocene oceanic circulation pat-
tern (Iturralde-Vinent and MacPhee, 1999, fig. 10; Li et al., 2006, fig.
8) may have set the precedent for the early Pliocene dispersal route of
J. typica from the Atlantic Ocean to the Pacific Ocean.
CONCLUSIONS
The principal explanation for the extraordinary geographic disper-
sal of J. typica are a combination of factors of different scale: ecological,
geological and astronomical. Its ecology as a floating animal in warm
waters and capable of long-distance transport in a short period of time
(for a modern analog, see Bryan et al., 2004) and the tectonic plate
configuration that permitted an open Central American Seaway and
also brought about a restricted Indonesian Seaway. The ancestor of J.
typica is unknown. The great similarity between the Pacific and Atlantic
forms (Figure 3) suggests a rapid dispersal rather than a geographic
speciation. Accordingly, this species must have originated in the west-
ern Atlantic during the Late Miocene or earliest Pliocene and experi-
enced a remarkable dispersal, crossing into the Pacific during the early
Pliocene before reaching the vicinity of present-day Perth in Western
Australia, as well as southern Japan. The presence of J. typica in these
diverse localities indicates that warm waters existed throughout the
dispersal route, and that the Canary Current was at that time warmer.
The Circumtropical Current must have extended to the western Pacific,

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4,000 km
0º
15º
15º
45º
45º
30º
30º
0º
~ 4.2 Ma
T
T
T
T
T
T
6
5
4
23
1
7
8
9
T806
999
847
1,241
PKC
WPWP
EAWP
WCC
Atlantic Ocean
Pacific Ocean
CC
CAS
SEC
WEAC
ITF
while the cold Humboldt Current in the area of the Galapagos Islands
must have been weak or absent. On reaching Panama, the Equatorial
Countercurrent must have been deflected southward. This would al-
low connection with the Pacific South Equatorial Current, and end in
a bifurcation in Indonesia with one branch heading north (Kuroshio
Current) and the other south (East Australian Current). This latter
current would extend through the Bass Strait and along the southern
coast of Australia as far as modern-day Pert h, which would also require
some distancing of the West Wind Drift.
ACKNOWLEDGEMENTS
We are grateful to Daniel R. Muhs (U.S. Geological Survey), Alan
G. Beu (GNS Science, New Zealand) and to Francisco García-Novo
(Universidad de Sevilla, Spain) for comments on a draft of this manu-
script. We also thank the comments from editor Thomas M. Lehman
(Texas Tech University) and the suggestions of Sandra Gordillo and
two anonymous reviewers.
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Figure 4. Biogeography of Janthina typica and reconstruction of the oceanographic dispersal route around 4.2 Ma in accordance with the most likely hypothesis.
Important localities (pink squares) are shown with numbered circles: (1) Santa Maria I. (Azores Islands), (2) Madeira I., (3) Selvagem Grande I., (4) Casablanca
(Morocco), (5) Gran Canaria I. (Canary Islands), (6) Auckland (New Zealand), (7) Victoria (Australia), (8) Perth (Australia) and (9) Kyushu (Japan). ODP Sites
(black circles). Dispersal route of Janthina typica (black arrows) from the East Atlantic Warm Pool (EAWP), through the Warm Canary Current (WCC), the
Circumtropical Current (CC), the Central America Seaway (CAS), and the South Equatorial Current (SEC), and to the Warm East Australian Current (WEAC); or
trough the Western Pacific Warm Pool (WPWP) to the Proto Kuroshio Current (PKC). Indonesian Through Flow (ITF). T: Trade winds (red arrows).

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