Connectivity and climate control fish distribution today
as well as in the geological past. We present here the Aquitanian (early
Miocene) marine fish of the Mesohellenic Basin, a restricted basin at the
border between the proto-Mediterranean and Paratethyan seas. Based on fish
otoliths, we were able to identify 19 species from 17 genera, including two
new species: Ariosoma mesohellenica and Gnathophis elongatus. This fish assemblage, in conjunction with the
accompanying molluscan assemblage, indicates a variable shelf
paleoenvironment with easy access to the open ocean. Although available data
on the Indo-Pacific fishes of the early Miocene are very limited, the fish
fauna of the Mesohellenic Basin has many elements in common with the North
Sea, the NE Atlantic, and the Paratethys.
Introduction
Connectivity between marine realms largely controls the fate of fish
populations and biodiversity (Worm and Tittensor, 2018). Early Miocene
proto-Mediterranean biodiversity is particularly interesting because, at
that time, the basin's connection with the Indo-Pacific realm ceased to
exist (Rögl, 1998; Bialik et al., 2019; Torfstein and Steinberg, 2020;
Sun et al., 2021), while the marine biodiversity hotspot was shifting toward
the southeast (Renema et al., 2008) and the climate was cooling (Cornacchia
et al., 2018), marking the onset of a subtropical gradually oligotrophic
regime in the proto-Mediterranean Sea. However, the early Miocene fossil
fish record from the Mediterranean area is particularly sparse. Moreover,
very few studies have focused on the fish otolith record (Steurbaut, 1979,
1982, 1984; Reichenbacher and Cappetta, 1999; Reichenbacher, 2004;
Hoedemakers and Batllori, 2005), despite its importance for revealing the
evolution of fish faunas and fish biogeography (Agiadi et al., 2011, 2017,
2018). At the crossroads between the proto-Mediterranean Sea, the Atlantic
Ocean, the North Sea, the Paratethys, and the Indo-Pacific realm, the
Mesohellenic Basin (MHB) during the early Miocene, a molassic basin at the
northern part of the proto-Mediterranean, directly at the intersection with
the Paratethys epicontinental sea, offers a unique opportunity to explore
the effects of interbasinal connectivity on fish faunas.
In this study, we identify the fossil fish otoliths found in the Aquitanian
(lower Miocene) sediments of the Felli section (Grevena Prefecture, NW Greece)
that were deposited in the MHB. The reconstructed assemblage is the first
record of fishes from the eastern part of the Aquitanian (∼ 23–20 Ma) proto-Mediterranean region. Furthermore, we discuss the
paleobiogeographic range of the identified fish species in order to draw a
conclusion regarding the factors that may have determined the subsequent
evolution of the Mediterranean marine fish fauna.
Geological setting
The study area is located in Grevena Prefecture, NW Greece, where the
molassic sedimentary sequence of the MHB is exposed (Fig. 1; Zelilidis et
al., 2002; Ferrière et al., 2004). The MHB was a synorogenic
molasse-type basin (Kilias et al., 2015), a separate paleogeographic area
from the late Eocene until the middle Miocene, between the internal and
external Hellenides, ENE and WSW, respectively. It was a narrow, 300 km long
trench, filled with up to 4.5 km of sediments, which have been separated
into the Krania, Eptachori, Pentalofos, Tsotyli, and Ondria formations
(Brunn, 1956; Wielandt-Schuster et al., 2004; Ferrière et al., 2013;
Kilias et al., 2015), deposited parallel to each other (except for the
Krania Formation) along the eastern margin of the trough (Kilias et al.,
2015). The studied sediments belong to the Pentalofos Formation, consisting
in general of upper Chattian–lower Miocene sandstones to silty marlstones
(Mavridis et al., 1985; Ferrière et al., 2004; Wielandt-Schuster et al.,
2004; Kilias et al., 2015). The Felli section, which is our study section,
includes only the uppermost part of the Pentalofos Formation corresponding
to the Aquitanian according to Mavridis et al. (1985). The Pentalofos Formation
overlies the Eptachori Formation and is overlain, conformably in the Grevena
area, by the Tsotyli Formation (Fermeli and Ioakim, 1992).
(A) Map of Greece where the Mesohellenic Basin is indicated. (B) Geological map of the study area: (1) Krania Formation (Eocene), (2) Eptachori
Formation (lower–upper Oligocene), (3) Pentalofos Formation (upper
Oligocene–lower Miocene), (4) Tsotyli Formation (middle Miocene), and (5) Quaternary. (C) Lithostratigraphic column of the Felli section with the sampled
levels (modified after Zelilidis et al., 2002, and Thivaiou et al., 2019).
Material and methods
We sampled a small section by the Aliakmon River banks, located east of
Felli village, SE of Grevena City (40∘01′4.55′′ N, 21∘33′34.37′′ E). The section is mainly composed of conglomerates and sands, and
the grain size decreases toward the top, where we find marls and then clays.
We obtained ∼ 20–25 kg of sediment from each of two
marl–clay beds, F11 and F12, following the numbering scheme of Thivaiou et
al. (2019). The samples were water-sieved using a 250 µm sieve, and the
residues were dried in an oven. The otoliths were handpicked from the
residues and identified under the microscope.
We adopted specific descriptive characters for the otoliths of Congridae
(Schwarzhans, 2019) and Pleuronectiformes (Schwarzhans, 1999). We followed
the fish classification scheme of Nelson et al. (2016). We made the
following measurements on the identified otoliths (reported in mm; Fig. 2):
OL, otolith length; OH, otolith height; AL, antirostrum length; RL, rostrum
length; CL, colliculum length; OCL, ostial colliculum length; CCL, caudal
colliculum length; OSL, ostium length; CaL, caudal length. In addition, in
Congridae, it proved significant to measure the sulcus angle (α), as
the angle formed between the sulcus direction and the otolith length
direction (Fig. 2). All data can be found in the Supplement.
In this section, we describe and explain the species identification of the
fossil otoliths from the Felli section. The measurements for all identified
otoliths are available in the Supplement. The studied material
has been deposited at the Athens Museum of Palaeontology and Geology –
Vertebrates Collection (AMPG(V)).
Infraclass Teleostei Müller, 1845 sensu Arratia, 1999
Order Anguilliformes Berg, 1943
Family Congridae Kaup, 1856
Genus Ariosoma Swainson, 1838
Ariosoma mesohellenica sp. nov.
urn:lsid:zoobank.org:act:4B603ED2-93BE-429E-B4EC-8D5F45A9C24C
registered on 21/7/2021
Two specimens, AMPG(V) 2362–3, same data as holotype; one
specimen, AMPG(V) 2364, Aquitanian, Felli section, level 12, Grevena
Prefecture, Greece.
Etymology
After the MHB, where the type section sediments were deposited.
Diagnosis
Elongated otoliths with OL/OH of 1.16–1.26. The sulcus extends
almost to the distal edge, with CL/OL of 0.58–0.74, and α between
2 and 6∘.
Description
Elongated, thick spindle-shaped otoliths with an elongated
central sulcus that opens toward the dorsal rim through an intricate ostial
channel. The ostial channel is placed almost at the proximal edge of the
sulcus and is perpendicular to it. The dorsal depression is well expressed.
The dorsal rim is curved in the distal part.
Distribution
Aquitanian of the western proto-Mediterranean and the MHB.
Remarks
These otoliths have a more elongated sulcus than Ariosoma balearicum otoliths, which
almost reaches the posterior edge (Fig. 3E–F; Agiadi and Albano, 2020).
Moreover, the dorsal extension is located more frontally, as it is in
Ariosoma moravica (Sulc 1932) (Nolf, 2013). The otoliths assigned to A. balearicum from the lower–middle Miocene of
Catalonia by Hoedemakers and Batllori (2005) also show a frontal positioning
of the dorsal extension. In contrast through to A. moravica, the sulcus is more
elongated, indicating that these specimens also should be placed in
Ariosoma mesohellenica sp. nov. Furthermore, the specimens assigned to Ariosoma aff. balearicum by Steurbaut (1984)
should not be placed within this species because their sulcus is much
shorter and does not extend close to the distal rim. Similarly, the otoliths
assigned by the same authors to Ariosoma globosum Steurbaut, 1984 are distinguished from
those of A. mesohellenica because their sulcus does not extend toward the distal rim and
their shape is pointed.
Genus Gnathophis Kaup, 1860
Gnathophis elongatus sp. nov.
urn:lsid:zoobank.org:act:EF4B2DCC-4246-45AB-840E-1BC29C675410
registered on 21/7/2021
Nine specimens, AMPG(V) 2366–74, same data as holotype.
Etymology
Due to the distinct elongated shape of its otoliths.
Diagnosis
Elongated otoliths with OL/OH of 1.60–2.06. The angle of the
sulcus relative to the otolith length plane is 10–20∘.
Description
These otoliths are elongated with a long sulcus that forms an
angle to the otolith length direction, which opens posterodorsally through a
wavy ostial channel. The posterior edge is slightly protruding dorsally. The
ventral rim forms an angle.
Distribution
Aquitanian of the proto-Mediterranean Basin.
Remarks
The otoliths of Gnathophis elongatus are elongated and more similar to Conger, unlike
Pliocene–Holocene specimens of Gnathophis mystax that are more quadrate (Tuset et al., 2008;
Agiadi et al., 2020, 2019, 2018). However, the orientation of the sulcus
forms an angle with the otolith length direction, as in Gnathophis species. The
otolith figured as Gnathophis catalinensis (Wade) by Steurbaut (1984), now accepted as a
synonym of Gnathophis cinctus (Garman) (Grove and Lavenberg, 1997), also displays the
same elongate shape, distinct sulcus-to-otolith length angle as those
described here. However, the sulcus is much narrower in G. elongatus, making it
distinguishable from G. cinctus. Compared to G. saubriguensis (Steurbaut), G. elongatus has a much more
elongated shape, the posterodorsal edge is protruding, and the distal–ventral
angle is not pointed.
2004 Gnathophis saubriguensis (Steurbaut, 1979) – Nolf and Brzobohaty, pl. 1, fig. 3–5
Material
Fifteen specimens from level 11 and three specimens from level 12.
Distribution
Aquitanian of the Aquitaine Basin (SW France; Steurbaut, 1979,
1984) and the MHB, and Burdigalian of northern Italy (Nolf and Brzobohaty,
2004).
Remarks
The orientation of the sulcus relative to the posterior–anterior
axis is angular, with an 11–24∘ angle. The anterior edge shows
the same opening feature as the specimens from the late Burdigalian of
Piedmont, Italy (Nolf and Brzobohaty, 2004). The distal–ventral angle is
pointed, as in the specimens figured from the late Oligocene–lower Miocene
of France (Steurbaut, 1984).
Order Stomiiformes Regan, 1909
Family Phosichthyidae Weitzman, 1974
Genus Vinciguerria Jordan & Evermann, 1896
Vinciguerria sp.
Material
Two otoliths from level 11 and one otolith from level 12.
Remarks
These otoliths resemble Vinciguerria lucetia (Garman) in the shape and angle of
the ventral rim. However, they are too eroded for confident specific
identification.
Order Myctophiformes Regan, 1911
Family Myctophidae Gill, 1893
Genus Diaphus Eigenmann & Eigenmann, 1890
Diaphus sp.
Material
Five otoliths from level 11.
Remarks
The state of preservation of these otoliths does not permit their
identification to species level.
Genus Lobianchia Gatti, 1904
Lobianchia sp.
Fig. 4A
Photographs of the identified otoliths from the Felli section. (A)Lobianchia sp., Felli 11; (B–C)Myripristis verus Steurbaut, (B) Felli 11, (C) Felli 12; (D)Echiodon heinzelini Huyghebaert and Nolf, Felli 11; (E)Apogon moyesi Steurbaut, Felli 11; (F) “Batrachoidida” vigneauxi (Steurbaut), Felli 11; (G)Blennius sp., Felli 11; (H)Arnoglossus holleri Weinfurter,
Felli 11; (I)Microchirus latior (Schubert), Felli 11; (J–K)Mullus elongatus Steurbaut, (J) Felli
11, (K) Felli 12; (L)Cepola yrieuensis Steurbaut, Felli 11; (M–N)Pomadasys sp., Felli 11; (O)Pagrus sp., Felli 11. (F), (H), (J), and (K) have been mirrored to facilitate comparison.
Material
One otolith from level 11.
Remarks
Compared to Lobianchia dofleinoides Steurbaut, the otolith found here shows neither
an anterodorsal curvature of the rim nor a strong dorsal depression.
Moreover, the ostium is separated from the cauda with a clearly angular
boundary, not one that is perpendicular to the posterodistal direction, as
is the case for L. dofleinoides. Nevertheless, the sulcus, especially the ostium part, is
quite wide, resembling more L. dofleinoides than L. dofleini (Zugmayer). Thus, it was not
possible to assign this specimen to either species, despite similarities,
and we therefore left it in open nomenclature.
Order Beryciformes Regan, 1909
Family Holocentridae Richardson, 1846
Genus Myripristis Cuvier, 1829
Myripristis verus Steurbaut, 1979
Fig. 4B–C
1979 Myripristis verus – Steurbaut, pl. 7, figs. 3–4
One otolith from level 11 and one otolith from level 12.
Distribution
Aquitanian–Burdigalian of SW France (Steurbaut, 1979, 1984)
and Aquitanian of the MHB.
Remarks
Myripristis verus otoliths are not as high as those of Myripristis planodorsalis Schwarzhans, 1994. Compared
to the “genus Myripristinarum” banaticus Weiler (Steurbaut, 1979) and the
“genus Myripristinarum” sp. figured by Steurbaut (1984), the inner face of
M. verus is more triangular, and its sulcus is more strongly bending ventrally.
Order Ophidiiformes Berg, 1937
Family Carapidae Poey, 1867
Genus Echiodon Thompson, 1837
Echiodon heinzelini Huyghebaert and Nolf, 1979
Fig. 4D
1979 Echiodon heinzelini – Huyghebaert and Nolf, p. 74, fig. 5
1984 Echiodon heinzelini Huyghebaert and Nolf, 1979 – Steurbaut, pl. 13, figs. 1–6
2004 Echiodon heinzelini Huyghebaert and Nolf, 1979 – Nolf and Brzobohaty, pl. 8, fig. 6
Material
One otolith from level 11.
Distribution
Lower Miocene of Belgium (Huyghebaert and Nolf, 1979), SW
France (Steurbaut, 1984), northern Italy (Nolf and Brzobohaty, 2004), and
the MHB.
Remarks
The sulcus reaches both the proximal and almost the distal tip,
similar to E. heinzelini from the lower Miocene of Belgium (Huyghebaert and Nolf, 1979),
the Oligocene–lower Miocene of SW France (Steurbaut, 1984), and the
Aquitanian of Piedmont, Italy (Nolf and Brzobohaty, 2004), and unlike “genus
Neobythitinorum” boulangeri Nolf (Steurbaut, 1984) and the modern species
Echiodon dentatus (Nolf, 1980).
Order Batrachoidiformes
Family Batrachoididae
“Batrachoidida” vigneauxi (Steurbaut, 1984)
Fig. 4F
1984 “genus Apogoninarum” vigneauxi – Steurbaut, pl. 20, figs. 14–19
2013 “Batrachoidida” vigneauxi (Steurbaut, 1984) – Nolf, pl. 144.
Material
Two otoliths from level 11.
Distribution
Aquitanian of SW France (Steurbaut, 1984) and the MHB.
Remarks
These otoliths are elongate with a higher anterior than posterior
part and a prominent anterodorsal high. The sulcus is divided into a large,
oval ostium that almost reaches the anterior rim, and a smaller, also
oval-shaped cauda that is situated slightly dorsally. The specimens examined
here resemble very much those figured by Steurbaut (1984) from the
Oligocene–lower Miocene of France and reassigned by Nolf (2013) to
Batrachoididae.
Order Kurtiformes Jordan, 1923
Family Apogonidae Günther, 1859
Genus Apogon Lacepède, 1801
Apogon moyesi Steurbaut, 1982
Fig. 4E
1982 Apogon moyesi – Steurbaut, pl. 2, figs. 14–18
Aquitanian of SW France (Steurbaut, 1982) and the MHB.
Remarks
This specimen is significantly shorter than those assigned to
Apogon vigneauxi (Steurbaut, 1984), and it shows the same dorsal depression and relative
size of the ostium to the cauda (OSL : CaL = 1.128) as A. moyesi from the
Oligocene–Miocene of Aquitaine Basin (Steurbaut, 1982, 1984). Compared to
the modern species Apogon imberbis from the Pliocene–Holocene of the eastern Mediterranean
Sea (Agiadi et al., 2019, 2020; Agiadi and Albano, 2020), this specimen is
shorter (OL : OH = 1.33 compared to a mean of 1.42 in A. imberbis).
Order Blenniiformes Bleeker, 1860
Family Blenniidae Rafinesque, 1810
Genus Blennius Linnaeus, 1758
Blennius sp.
Fig. 4G
Material
One otolith from level 11.
Remarks
This otolith is triangular in shape with a sulcus divided into an
oval-shaped ostium and a thinner but approximately equal in length oval
cauda that slightly turns towards the dorsal side. These characteristics
make this specimen similar to “Blennida” bicipitis Steurbaut from the Rupelian of the
Aquitaine Basin (Nolf, 2013). However, the specimen examined here has a
square posterior rim.
2004 Arnoglossus holleri Weinfurter, 1952 – Nolf and Brzobohaty, pl. 11, fig. 15
Material
One otolith from level 11.
Distribution
Miocene of the Styrian Basin (Weinfurter, 1952), middle
Miocene of NW Germany (Weiler, 1962), lower–middle Miocene of the
Aquitanian Basin (Steurbaut, 1979, 1984), Miocene of Portugal (Steurbaut and
Jonet, 1981), middle Miocene (Badenian) of Poland (Radwanska, 1992), lower
Miocene of northern Italy (Nolf and Brzobohaty, 2004) and southern France (Nolf
and Cappetta, 1980), and Aquitanian of the MHB.
Remarks
This small otolith is rectangular in shape, with rounded angles.
The sulcus is sloping posteroventrally and approximately straight, divided
into a long ostium and a rectangular, short cauda. In contrast to the
specimen figured by Nolf and Brzobohaty (2004), the otolith found in Felli
shows a more regular rectangular shape. Our specimen is quite similar to the
modern species Arnoglossus rueppellii (Cocco), but its inner and outer face have the same
convexity, whereas A. rueppellii has a flatter inner face (Agiadi and Albano, 2020).
Two otoliths from level 11 and one otolith from level 12.
Distribution
Lower Miocene of Italy (Nolf and Brzobohaty, 2004), the
Aquitanian Basin (Steurbaut, 1984), and the MHB. Middle Miocene (Badenian)
of Poland (Radwanska, 1992).
Remarks
The otoliths of Microchirus latior are rounded, unlike those of Microchirus variegatus (Donovan, 1808) that
have edges on the posterior side (Schwarzhans, 1999; Agiadi et al., 2020).
Order Perciformes Bleeker, 1859
Family Serranidae Swainson, 1839
Genus Mullus Linnaeus, 1758
Mullus elongatus Steurbaut, 1984
Fig. 4J–K
1984 Mullus elongatus – Steurbaut, pl. 29, figs. 8–12
2013 Mullus elongatus Steurbaut, 1984 – Nolf, pl. 285
Material
Two otoliths from level 11 and two otoliths from level 12.
Distribution
Lower Miocene of the Aquitanian Basin (Steurbaut, 1984) and
the MHB.
Remarks
These otoliths have a long sulcus, comprised of a small circular
ostium and a long cauda, which turns toward the ventral area and opens in the
posterior end. The dorsal rim is straight. Compared to the modern species
Mullus surmuletus Linnaeus and Mullus barbatus Linnaeus (Hoedemakers and Batllori, 2005; Tuset
et al., 2008; Agiadi et al., 2019), the otoliths of M. elognatus are not as high, but
more elongated (OL : OH = 1.76–1.82 in M. elongatus but 1.23 in M. barbatus and 1.52 in M. surmulatus, both
values from the Pleistocene of the eastern Mediterranean; Agiadi et al.,
2019), more so than Mullus bifurcatus Strashimirov reported from the lower–middle
Miocene of the Paratethys (Bratishko et al., 2015).
Family Cepolidae Rafinesque, 1810
Genus Cepola Linnaeus, 1764
Cepola yrieuensis Steurbaut, 1984
Fig. 4L
1984 Cepola yrieuensis –Steurbaut, pl. 29, figs. 13–17
2013 Cepola yrieuensis – Nolf, pl. 294
Material
Two otoliths from level 11.
Distribution
Lower Miocene of the Aquitanian Basin (Steurbaut, 1984) and
the MHB. Priabonian–lower Oligocene of SE France (Nolf and Girone, 2008;
Girone and Nolf, 2009).
Remarks
These otoliths are boat-shaped and have open, divided sulcus. The
ostium is oval–rectangular and has an oval colliculum, whereas the cauda is
oval-shaped, with an oval colliculum, and placed more dorsally than the
ostium. There is a pronounced ventral fissure. These specimens have distinct
posterior and posterodorsal angles that only appear on the otoliths of C. yrieuensis
previously reported from the Rupelian of France (Steurbaut, 1984). Compared
to C. macrophthalma, these otoliths have an oval, rather than circular cauda, which is
placed dorsally. Cepola aff. macrophthalma (Linnaeus) from the middle Miocene of Austria
(Nolf, 2013) also has an oval-shaped cauda but lacks a posterodorsal angle.
On the contrary, this angle is present in C. robusta Nolf from the Ypresian of
France (Nolf, 2013), but only in the young specimens.
Order Spariformes Bleeker, 1876
Family Sparidae Rafinesque, 1810
Genus Pomadasys Rafinesque, 1810
Pomadasys sp.
Fig. 4M–N
Material
Six otoliths from level 11.
Remarks
These otoliths are oval-shaped, with a small circular–oval ostium
and a long straight cauda. The ventral area is distinctly larger than the
dorsal area, and its rim is rounded.
Genus Pagellus Valenciennes, 1830
Pagellus sp.
Material
One otolith from level 11 and one otolith from level 12.
Remarks
These otoliths are fusiform in shape with a well-curved ventral rim
and a sulcus divided into a triangular ostium and a long straight cauda,
which is curved at the posterior end.
Genus Pagrus Cuvier, 1816
Pagrus sp.
Fig. 4O
Material
One otolith from level 11.
Remarks
This otolith is characterized by a pronounced ventral angle. The
sulcus is divided into a triangular ostium and a long cauda, which curves at
its posterior end. The dorsal area forms a clear angle in the anterior part.
There is some resemblance to Pagrus sp. 1 figured by Steurbaut (1984).
Genus Spicara Rafinesque, 1810
Spicara cf. gossei Steurbaut, 1984
Fig. 3M–O
Material
Nine otoliths from level 11 and seven otoliths from level 12.
Remarks
The general shape of the otoliths is fusiform. They have a straight
sulcus and a triangular ostium, which is characteristic of all Spicara spp., but
these specimens are particularly angular in shape and have a strongly
delineated sulcus. The rostrum is more robust in these specimens than in the
modern species Spicara flexuosa, S. smaris, and S. maena (Agiadi and Albano, 2020), and S. gossei from the
Oligocene–lower Miocene of France (Steurbaut, 1984). In addition, the
posterior end of the cauda is very pointed in the examined specimens.
Paleogeographic map of the proto-Mediterranean, showing its
connections to the Paratethys, Atlantic, and Indo-Pacific realms, and the
location of the Mesohellenic Basin (MHB) and the Felli section (modified after
early Burdigalian scheme of Popov et al., 2004), and list of the species
identified at Felli color-coded to indicate their paleobiogeographic
distribution.
Results and discussionAquitanian fish biogeography
The fish fauna of the Aquitanian MHB is quite diverse. We identified 19
species from 17 genera, including 2 new species: Ariosoma mesohellenica and Gnathophis elongatus. Overall, the
identified fish fauna comprises several species of congrid eels, flatfishes,
and sparids, along with lanternfishes, reflecting a shelf environment with
easy access to the open ocean. The great diversification of congrids
especially reflects a variety of microhabitats along this shelf.
The geological events that led to the formation of the proto-Mediterranean
have shaped the distribution of marine taxa (Hou and Li, 2018; Worm and
Tittensor, 2018). In the area of the Western Tethys, the late Eocene–middle
Miocene MHB (Fig. 5) constituted a marine corridor at the border between the
proto-Mediterranean and the Paratethys (Rögl, 1998); the
proto-Mediterranean Sea developed due to the closure of the western part of
the Tethys Ocean (Bialik et al., 2019; Torfstein and Steinberg, 2020). At
this time, the proto-Mediterranean Sea, including the MHB, transited from a
global biodiversity hotspot to a subtropical marine sea (Renema et al.,
2008). Therefore, any faunal exchanges between the proto-Mediterranean, the
Paratethys, the North Sea, the Atlantic, and the Indo-Pacific realms would
be expressed in this study area.
Possibly due to the warm Aquitanian climate (Zachos et al., 2001; Westerhold
et al., 2020), the distribution ranges of North Sea and NE Atlantic fish
species included the MHB in the south. Indeed, this is supported by the
distribution of the identified fish species (Fig. 5). Most fish species in
the MHB were also present in the NE Atlantic, and, in fact, Echiodon heinzelini was also
present in the North Sea. Moreover, the flatfishes Arnoglossus holleri and Microchirus latior were also reported
in the Paratethyan realm, which is understandable considering the close
proximity between these areas. We do not find any exclusively Indo-Pacific
taxa in our fossil assemblage. However, we must note that data on the
Miocene fishes of the Indo-Pacific realm are scarce; data outside the
Mediterranean and the Atlantic exist mostly from New Zealand (Grenfell,
1984; Schwarzhans et al., 2017). This knowledge gap hampers any further
evaluation of the paleobiogeographic distribution of the identified species.
Comparison with the paleobiogeography of the accompanying molluscan fauna
In the early Neogene, the Mediterranean–Iranian biogeographical province of
mollusks (Harzhauser et al., 2002) covered part of the Western Tethys
region. The molluscan fauna in this province had a similar taxonomic
composition with those of the North Atlantic of France and the Paratethys
(Harzhauser et al., 2002; Lozouet, 2014), as in the case of fishes. Shallow
marine faunas from the Indo-West Pacific show high degrees of endemism in
the early Miocene (Harzhauser et al., 2007, 2017), whereas a turnover in the
composition of nearshore mollusks is evident in the Oligocene to early
Miocene in the Indian Ocean (Harzhauser et al., 2009).
The molluscan fauna of the Felli section is most similar to shallow marine and
coastal assemblages from the NE Atlantic and the Paratethys (Thivaiou et
al., 2019). However, in contrast to fishes (for which we do not have an
Indo-Pacific fossil record to compare with), the molluscan fauna of the Felli
section also includes genera that are characteristic of subtropical to
tropical environments (Houbrick, 1991; Janssen et al., 2011), such as the
widespread coastal mudflat Terebralia (Thivaiou et al., 2021), currently
inhabiting only the Indo-West Pacific, and Finella, which has recently re-entered
the Mediterranean Sea from the Red Sea after the opening of the Suez Canal
(Albano et al., 2021). This observation might suggest that mollusk and fish
distribution ranges may not be similarly affected by paleoenvironmental
change, although such a conclusion is in both cases heavily affected by
sampling and study bias.
Conclusions
The fish fauna of the early Miocene MHB was in general influenced by the
connectivity of the proto-Mediterranean to its surrounding marine basins.
The early Miocene fish fauna of the proto-Mediterranean, as revealed by the
otolith assemblage of the Felli section, was a mixture of Atlantic,
Paratethyan, North Sea, and Mediterranean endemic elements. Unfortunately,
the fossil record so far for this interval has been scarce. Nevertheless,
the present findings offer some insight into the early Miocene evolution of
the Mediterranean marine fish fauna. Future research should aim to fill in
the considerable gaps in the record for the early–middle Miocene,
especially in the Indo-Pacific realm.
Data availability
The supplementary data are available open-access with this article.
The supplement related to this article is available online at: https://doi.org/10.5194/fr-24-233-2021-supplement.
Author contributions
KA was responsible for data curation, formal analysis, investigation, methodology, resources,
and writing; DT for conceptualization, funding acquisition, investigation,
methodology, resources, and writing; and EK for investigation, resources, and
writing.
Competing interests
The authors declare that they have no conflict of interest.
Disclaimer
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Acknowledgements
This research has been co-financed by Greece and the European Union
(European Social Fund-ESF) through the operational program “Human
Resources Development, Education and Lifelong Learning 2014–2020” in the
context of the project “Mollusc and fish migrations in the dynamic
environments of the early to middle Miocene in the Mediterranean” (MIS
5047960). The authors would like to thank Gary Stringer and the
anonymous reviewer for their constructive comments.
Financial support
This research has been supported by the Ministry of National Education and Religious Affairs (grant no. MIS 5047960).
Review statement
This paper was edited by Florian Witzmann and reviewed by Gary Stringer and one anonymous referee.
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