A new deep-water Decapod Crustacean faunule from the Early Miocene of the Styrian Basin, Slovenia

Abstract

Previously, decapods from the Miocene strata in the Slovenian part of the Styrian Basin were reported by Glaessner (1928) and Mikuž (2003). In this contribution we present a report on a new decapod crustacean faunule from the respective area.

Full text

21. posvetovanje slovenskih geologov – Gašparič & Hyžný, Abstract
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A NEW DEEP-WATER DECAPOD CRUSTACEAN FAUNULE FROM THE EARLY
MIOCENE OF THE STYRIAN BASIN, SLOVENIA
Rok Gašparič 1 & Matúš Hyžný 2
1 Ljubljanska cesta 4j, 1241 Kamnik, Slovenija < rok.gasparic@gmail.com>
2 Department of Geology and Palaeontology, Faculty of Natural Sciences, Comenius University,
Mlynská dolina G1, Bratislava 842 15, Slovakia < hyzny.matus@gmail.com>
Previously, decapods from the Miocene strata in the Slovenian part of the Styrian
Basin were reported by Glaessner (1928) and Mikuž (2003). In this contribution we present a
report on a new decapod crustacean faunule from the respective area.
The studied locality is situated approximately 15 kilometers west of Maribor, along
the steep valley of the Drava River. The decapod bearing layers were exposed during road
renovation works on a local road connecting the towns of Ruše and Lovrenc na Pohorju and
are part of a Miocene sedimentary basin running from Maribor on the northern slopes of
Pohorje plutonic massif towards Radlje.
Fossil bearing micaceous laminated siltstones are part of the Ivnik beds (Mioč, 1972),
overlaying sequences of loosely bound chaotic conglomerates and sandstones. Conglomerates
are composed mainly of pebbles of metamorphic rock and Pohorje granodiorite (Pavšič &
Horvat, 2009). Results of nannoplankton sampling (Bartol et al., in print) indicate the
Karpatian age (nannoplankton zone NN4), based on coexistence of Sphenolithus
heteromorphus Deflandre, 1953 and Helicosphaera ampliaperta Bramlette and Wilcoxon,
1967.

21. posvetovanje slovenskih geologov – Gašparič & Hyžný, Abstract
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Fig. 1. – Geographical position of the fossil locality with simplified geological sketch.
The Karpatian signifies the beginning of the marine sedimentation regime in the
broader realm of the Central Paratethys and represents a short flooding event that resulted
from opening of a marine passage between the Paratethys and the Mediterranean Sea i.e.
Slovenian corridor (Rögl, 1998). Synrift tectonics with rapid subsidence of narrow elongated
sedimentation basins at the beginning of Karpatian (Jelen & Rifelj, 2003) and the described
foraminiferal assemblage indicate bathyal conditions with the basin depth exceeding 500
meters (Fodor, 2002). Our observation of decapod crustaceans and the associated assemblage
confirms the bathyal character of the investigated fauna.
The sample consists of 245 specimens of decapod crustaceans collected by one of the
authors (RG) and housed at the “Rok Gašparič paleontological collection”, part of
paleontological collections of Slovenian Museum of Natural History. Studied specimens are
compressed inside the siltstones and mainly retain the original cuticle. Many decapods are
still articulated which, considering their fragility, implies a very calm sedimentation
environment and excludes any greater post mortem transportation.

21. posvetovanje slovenskih geologov – Gašparič & Hyžný, Abstract
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Preliminary results allow us to assign the investigated specimens to the following taxa:
Order Decapoda
Infraorder Axiidea
Family Callianassidae
Callianassa cf. michelottii MILNE EDWARDS, 1860 (Fig. 2.A)
The material consists of three specimens. Only major cheliped propodus (in one case
associated with dactylus) is preserved. The material differs from Callianassa michelottii in the
nature of lateral propodal surface. In C. michelottii it typically has long keel extending onto
the fixed finger accompanied with two furrows. In our material the keel is faint and the
furrows do not seem to be present. More and better preserved material may resolve the
affinities of the studied material.
Callianassa sp. (Fig. 2.B)
The material consists of three specimens. One of the specimens exhibits a major chela
(propodus articulated with dactylus – its shape does not correspond to any other callianassid
specimen recovered at the locality).
Lepidophthalmus n. sp. (Fig. 2.C)
The material consists of 19 specimens. Usually major cheliped propodus is preserved;
sometimes articulated with dactylus. In one case major chela is associated with minor chela.
The assignment of the material to Lepidophthalmus is based on these characters: 1) typical
shape of minor chela, i.e. square propodus with long fixed finger, which is relatively high
proximally, no teeth or serration is present on occlusal margin of both fingers; 2) major chela
consisting usually of massive propodus with high dactylus, distal margin of propodus bears a
single blunt tooth below the articulation with dactylus; 3) ovoid merus in outline with tiny
meral hook positioned proximally; faint lobe positioned on the distal lower margin, which is
typical for the genus, is insufficiently preserved; 4) major cheliped carpus is distinctly shorter
than high. Occlusal margin of major cheliped fixed finger typically bears serration. No extant
of fossil congener has such armament.

21. posvetovanje slovenskih geologov – Gašparič & Hyžný, Abstract
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Infraorder Gebiidea
Family Laomediidae
Jaxea kuemeli BACHMAYER, 1954 (Fig. 2.D)
A single specimen consisting of two equal chelipeds, with fragmented remains of associated
carpus. The fossil specimen represents the first report of Jaxea from Slovenia. Jaxea kuemeli
Bachmayer, 1954 was first described from the Miocene of Austria (Bachmayer, 1954) and
from lower to middle Miocene strata of Slovakia and Hungary (Hyžný, 2011).
Infraorder Brachyura
Family Retroplumidae
Retropluma n. sp. (Fig. 2.E)
Material consists of 97 mostly articulated specimens, making it the most abundant species in
the studied assemblage. Several retroplumids are described from Europe. The oldest species
are Retropluma gallica Artal, 2006 and Retropluma eocenica Via Boada, 1959 from the
Eocene layers of Spain and Italy (Beschin et al., 1996). Retropluma cf. eocenica is also
described from the Oligocene of Italy (Marangon & De Angeli, 2007). Miocene species
Retropluma borealis Fraaije, 2005 is described from Gram in Denmark as the northernmost
locality of the genus Retropluma. The youngest fossil species Reropluma craverii De Angeli,
2011 is described from the Pliocene of Italy. The Činžat material differs from the known
Retropluma species by well marked regions, strong carinas forming lateral projections, strong
outwards facing postorbital teeth, a presence of infraorbital teeth, and long distally widening
rostrum. It resembles a recent Retropluma serenei Saint Laurent, 1989, but has more
pronounced regions and carinas as well as stronger supraorbital and postorbital teeth then the
extant species.
Family Pilumnidae
Styrioplax exiguus GLAESSNER, 1928 (Fig. 2.F)
Altogether 72 specimens could be observed in various modes of preservation, some are dorso-
ventrally compressed, but some also in three-dimensional preservation. Almost all specimens
are articulated. After Glaessner’s (1928) description the material from Šentilj and Lenart was
cited as Austrian (Karasawa & Kato, 2003). The redescription (Hyžný & Schlögl, 2011)
recognizes the Slovenian origin of this material and adds additional lower Miocene localities
from the Austrian quarry Retznei and from Slovakia.

21. posvetovanje slovenskih geologov – Gašparič & Hyžný, Abstract
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Family Mathildellidae
Neopilumnoplax n. sp. (Fig. 2.G)
The material consists of three specimens, including an isolated cheliped. The described
material represents the first species of the genus Neopilumnoplax in the fossil record. Several
Paleocene to Oligocene members of the Mathildellidae have been described from North
America (Karasawa et al., 2008), but no Neogene representatives of the family have been
known so far. A new species from Činžat resembles the recent Neopilumnoplax lipkeholthuisi
Tavares, 2010, but differs in front and orientation of anterolateral teeth.
Family Goneplacidae
Goneplax cf. sacci CREMA, 1859 (Fig. 2.H)
Three specimens of partially preserved carapace are assigned to the Goneplacidae and closely
resemble Goneplax sacci Crema, 1895. The specimens differ from Goneplax rhomboides
Linnaeus, 1758 (Garassino, 2012) in having more convex anterolateral margins with shorter
anterolateral teeth and wider front, similar to Goneplax sacci (Bachmayer, 1953).
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Fig. 2. – A) Callianassa cf. michelottii, B) Callianassa sp., C) Lepidophthalmus n. sp., D)
Jaxea kuemeli, E) Retropluma n. sp., F) Styrioplax exiguus, G) Neopilumnoplax n. sp., H)
Goneplax cf. sacci. Scale bar in all is 10 mm.