First record of Acanthuridae ( surgeonfish ) from the Miocene deposits of the Medvednica Mt .

Middle Miocene deposits at the Dubravica locality in SW Medvednica Mt. (N Croatia) contain various marine fossils, including one tooth of the surgeonfish (Acanthuridae). This is the first such record in Croatia and the second in the wider region, besides the Vienna Basin. The appearance of surgeonfishes in the Paratethys coincides with the Miocene thermal maximum. Their distribution was probably controlled by available reef habitat and their palaeobiogeography and migration routes are yet to be studied.


INTRODUCTION
Northern and north-eastern Croatia during the Miocene epoch were covered by the Paratethys Sea (Fig. 1). Abundant and diverse marine fossils can be found in sedimentary rocks of this age. Med vednica Mt. acted as an island near the SW coast of the Paratethys, and Miocene shelf deposits are exposed today in the form of a belt around the mountain core.
Middle Miocene marine environments of Medvednica Mt. were divided into the ''Dolje'' development in the south-western part of Medvednica Mt., the ''Čučerje'' development in the central part of Medvednica Mt., and the ''Zelina'' development in the south-eastern part of Medvednica Mt., each characterized by different fossil assemblages (KOCHANSKY, 1944).
The Dubravica locality ( Fig. 1), records the first occurrence of fossil Acanthuridae in Croatia, and is situated on the south-western slopes of Medvednica Mt. The surgeonfish tooth was dis covered during recent field work (BOŠNJAK et al., 2014;TRI-PALO et al., 2015).

GEOLOGICAL SETTING
The investigated area is a part of the Miocene deposits belt surrounding Medvednica Mt., and is situated on its south-western slopes (Fig. 1). Geological and palaeontological features of this area were summarized in publications following the Basic Geological Mapping, by ŠIKIĆ et al. (1977ŠIKIĆ et al. ( , 1979, and later by ŠIKIĆ (Edit.) (1995).
During the Miocene, the whole area palaeogeographically belonged to the south-western margins of the Central Paratethys ( Fig. 1), and geotectonically to the Pannonian Basin System (PA-VELIĆ, 2002).
An approximately 16 metre high subvertical outcrop, with sedimentary rocks of ca. 11.5 m in thickness, is exposed at the Dubravica locality near the path leading to the Veternica Cave ( Fig. 2). Triassic dolomites in the base are transgressively overlain with dolomitic breccias, which gradually pass into brecciasconglomerates, and are later replaced with floatstones containing The Acanthuridae includes fishes whose common name (surgeonfishes) derives from the presence of a scalpel-like modified scale on the caudal peduncle (WINTERBOTTOM, 1993), which may be used in inter-and intra-specific aggressive behaviour (RAN-DALL, 2001).
Today, acanthurids all live in tropical and subtropical seas, and are one of the dominant groups of fish on the coral reefs (PUR-CELL & BELLWOOD, 1993 and references therein; SOREN-SON et al., 2013;LUDT et al., 2015). Their modern geographic distribution is similar to other reef fish families and largely reflects Neogene biogeographic influences (PELLISSIER et al., 2014).
Surgeonfishes are primarily herbivores, but consume a relatively wide variety of dietary resources, including planktonic animal matter, organic detritus and invertebrates (SORENSON et al., 2013). Dentition can vary dramatically within and across genera, and it is strongly related to diet (TYLER, 1970) (Fig. 3).
bivalve moulds and dispersed dolomitic cobbles. A horizon composed of dark grey marl, ca. 2.5 m thick, overlies this layer. It contains molluscs, solitary corals, bryozoans, echinoids and trace fossils. The upper part of the column is characterized by a lightgrey marl, ca. 3 m thick, with molluscs. An intercalation of yellowish sandstone with bivalves and gastropods, ca. 0.5 m thick, occurs within this horizon (Fig. 2).
In the vicinity of the sampled section, ca. 15 m towards the south, marls are laterally replaced with a coralgal reef buildup ("Lithothamnium limestone", sensu KOCHANSKY, 1944) of con temporary age. The visible part of this buildup is ca. 10 m wide and ca. 5 m high.

Acanthuridae gen. et sp. indet.
Material: one partially preserved tooth with accreted sediment ( Fig. 4) As shown on Fig. 4, the exposed part of the small incisiform tooth is almost black in color. Dimension of the tooth (in mm) are: 1.95 height, 1.13 width.
The tooth has a multidenticulate structure typical of the majority of acanthurids. One apical denticulation, two denticulations on the right and three on the left side of the tooth are visible. Denticulations on both sides increase in size towards the base of the teeth. The investigated tooth is slightly curved inward. Its surface is almost smooth on both the labial and lingual side (Fig. 4). Considering the partial tooth preservation, and range of genera with this configuration, determination at the generic level was not possible.

DISCUSSION
Fossil Acanthuridae or surgeonfishes are among the best studied fossil percomorph fishes.
The rich fossil record indicates that acanthurids reached a significant diversity by the Middle Eocene (SORENSON et al., 2013). Abundant and diverse surgeonfishes from the Monte Bolca locality, at least 14 extinct genera and 16 species, were studied by several authors (BLOT & TYLER, 1990;SORBINI & TYLER, 1998a, b;TYLER, 1999TYLER, , 2005aTYLER & BANNIKOV, 2000). The Monte Bolca fish assemblage represents the oldest known fauna that may be defined as a coral reef fish assemblage (BELL-WOOD, 1996) and is a key fossil deposit at the birth of modern coral reefs . Several genera share the multidenticulate tooth form at this time  suggesting that they may have been feeding on short algal turf (PURCELL & BELLWOOD, 1993).
Previously Miocene surgeonfishes have only been reported from Sulawesi (TYLER, 1997) and from the Miocene of the Vienna Basin (MEYER, 1842;SCHULTZ, 2003). Austrian acanthurid fish teeth were described as Acanthurus haueri (MEYER, 1842). They are of similar size as the specimen from Dubravica, but differ from it in shape. As we are lacking other parts of the skeleton, we can only speculate whether this is a different species, but it is also possible that the tooth belongs to the same species, but had a different position within the jaws (SCHULTZ & BELLWOOD, 2004).
Miocene reefs and reef-like structures in Paratethys which were suitable habitats for acanthurids were predominantly com-posed of coralline algae: Lithothamnion valens, Phymatoliton calcareum and Mesophyllum roveretoi (BASSO et al., 2008), sometimes in association with bryozoans and, sporadically, corals (VRSALJKO et al., 2006). Interestingly only one other herbivorous reef fish has been recorded from this region, the parrotfish Calotomus from the Badenian of Austria (BELLWOOD & SCHULTZ, 1991).
Findings of acanthurid teeth in the Paratethys realm coincide with the Miocene thermal maximum. We can discuss why are these finds so scarce; the small size of acanthurid teeth and their rather bizarre shape may be the reason that palaeontologists do not register or recognize them in the sieved material.
The Croatian surgeonfish record opens discussion of the possible ancestral populations and fish migration routes, but such study requires reexamination of other contemporary rocks along the Paratethys reef formations and the possible discovery of more surgeonfish remains.

CONCLUSIONS
A small fish tooth from the Dubravica locality in the south-western part of Medvednica Mt. represents the first record of surgeonfishes (Acanthuridae) in Croatia. In the nearby area, similar teeth from Miocene deposits of the Vienna Basin have been referred to the type Acanthurus haueri (MEYER, 1842;SCHULTZ, 2003).
The tooth from the Dubravica locality differs from the Austrian samples in shape, but is of similar size. It may belong to another species, or to the same species, but from a different position within the jaw.
The appearance of acanthurids in the Paratethys corresponds with the Miocene thermal maximum, and it opens discussion about the ancestral populations and possible biogeographic extent of the Acanthuridae across Paratethys.
Palaeoecologically it was controlled by distribution of suitable benthic habitats, in this case coralgal or coralgal-bryozoan reef buildups.