A glimpse of a fish face — An exceptional fish feeding trace fossil from the Lower Devonian of the Holy Cross Mountains, Poland
Introduction
Trace fossils not only express behaviour of their tracemakers, but in some cases, especially if very well preserved, they may record important information about the morphology of the trace maker's body. This information, called the “bioprint” (see Rindsberg and Kopaska-Merkel, 2005, Seilacher, 2007), is especially valuable if the soft body of the tracemaker is unknown.
During fieldwork conducted in the Holy Cross Mountains (southern Poland) in 2011–2014, an exceptionally well-preserved assemblage of numerous invertebrate and vertebrate trace fossils was discovered and investigated in a series of small outcrops of the Lower Devonian near Ujazd village. Among them are unusual depressions that occur at top of some beds in one of the outcrops. They are interpreted herein as fish feeding traces that reveal imprints of some anatomical details of the fish snout, in a manner comparable to recent fish traces. The aim of this paper is to present this peculiar trace fossil as a new ichnospecies of Osculichnus Demírcan and Uchman (2010). The trace fossils provide information about the snout anatomy and feeding behaviour of Early Devonian fishes. Associated invertebrate trace fossils that help to interpret the Osculichnus behaviour and palaeoenvironment, are briefly characterized as well.
The Lower Devonian of the Holy Cross Mountains is composed of siltstone and sandstone beds intercalated by mudstones. In contrast to the Middle or Upper Devonian rocks of this region, which are dominated by carbonate sediments, trace fossils are abundant in some Lower Devonian formations, where sandstone–mudstone interfaces provide favourable conditions for their preservation. Nevertheless, they have so far received very little attention (but see Tarnowska, 1976, Tarnowska, 1997). An exception is the description of a very rich and exceptionally well preserved ichnoassemblage in the Bukowa Góra quarry (Szulczewski and Porębski, 2008). More than 20 invertebrate ichnogenera identified at this locality point to palaeoenvironments ranging from the shoreface-offshore shelf transition to lagoonal and marine depositional environments. The age of the section is well constrained as middle to upper Emsian (Malec, 1990, Fijałkowska-Mader and Malec, 2011), and generally corresponds with the age of the section from the locality presented herein.
Section snippets
Geological setting
The outcrop studied is located in the small village Ujazd near Iwaniska, near the NW–SE road from Iwaniska to Staszów, in the central part of the Holy Cross Mountains, about 190 km south of Warsaw (50°42′34.1″N; 21°19′26.1″E; Fig. 1). It is the small abandoned quarry mentioned by Szrek et al., 2012, Szrek et al., 2015, where sandstone was exploited for local needs.
Preliminary data on the Lower Devonian of the Holy Cross Mountains were published by Gürich (1896); Czarnocki, 1919, Czarnocki, 1936
The Ujazd section
The Lower Devonian at Ujazd can be observed in a series of small exposures of white quartzite sandstones. These sandstones were last exploited by local residents more than 30 years ago. Recently, the exposures have become almost completely overgrown by plants, partly in a forest (Fig. 1B). One of those outcrops was re-investigated by the authors between 2011 and 2014.
The section studied in detail is about 4 m thick (Fig. 1A, B). It is composed of 1–2 m-thick sandstone beds interbedded with
Methodology
The trace fossils occur in an old abandoned sandstone quarry, so at first some partially exposed surfaces of sandstone with numerous traces were excavated from a debris cover and washed. Most of the well-preserved fossils were photographed in the field, protected and prepared for further investigation. The morphology of the best preserved traces was investigated using silicone casts. These reveal the general shape of the snout and details such as wrinkles on the skin that covered lips and
Trace fossils
Ichnogenus Osculichnus Demírcan and Uchman (2010).
Type ichnospecies: Osculichnus labialis Demírcan and Uchman (2010).
Osculichnus tarnowskae isp. nov. (Fig. 4).
Associated invertebrate trace fossils
In addition to O. tarnowskae isp. nov., three other trace fossils have been recognized: Protovirgularia isp., cf. Cruziana isp. and ?Planolites isp.
Protovirgularia isp. (Fig. 8A, B) is preserved as a straight or curved, V-shaped epichnial furrow that is up to 11.5 mm wide, up to 12 mm deep, and up to 70 mm long. The furrow is narrower and shallower towards both ends up to total disappearance, gradually, or more abruptly at the distance of 15 mm. Slopes of the furrow show very low corrugations or
Discussion
Comparisons of Osculichnus with other trace fossils were exhaustively discussed by Demírcan and Uchman (2010). Arguments presented in their paper are equally applicable to the Devonian O. tarnowskae isp. nov. A similar but unnamed trace fossil, asymmetric in vertical–longitudinal cross-section, has been described by Pieńkowski (1985: Fig. 2G) from Lower Jurassic brackish-marine deposits of the Holy Cross Mountains. They, however, differ from Osculichnus isp. by non-bilobate morphology and
Conclusions
Traces described above are the oldest evidence of the ichnogenus Osculichnus Demírcan and Uchman (2010), which has been known mostly from hypichnia so far. O. tarnowskae isp. nov. is interpreted as a hunting trace of a fish intruding its mouth into the sediment. The trace makers probably belong to one genus. The basic morphological details, including the U-shaped and/or trapezoidal shape of the mouth, the probable presence of tuberculate tooth-plates, and the imprints of folding skin, point to
Acknowledgements
We thank Andrew K. Rindsberg (University of West Alabama) and to the editor David Bottjer for their very useful revision and helpful comments. The trace-bearing deposits were examined during the fieldwork in 2012–2014 financed by the Ministry of Science and Higher Education (grant no IP2010 041470 awarded to P.S.). G.N. was funded by a Wallenberg Scholarship from the Knut and Alice Wallenberg Foundation, awarded to P.E.A. We are grateful to the outcrop's owners Monika and Jarosław Górczyńscy
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