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Devonian Scolecodonts from the Tyrnaueralm, Graz Palaeozoic, Austria

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Devonian Scolecodonts from the Tyrnaueralm, Graz Palaeozoic, Austria Devonian scolecodonts from the Tyrnaueralm, Graz Palaeozoic, Austria THOMAS J. SUTTNER & OLLE HINTS SUTTNER, T.J. & HINTS, O. 2010:10:29. Devonian scolecodonts from the Tyrnaueralm, Graz Palaeozoic, Austria. Memoirs of the Association of Australasian Palaeontologists 39, 139-145. ISSN 0810-8889. A small assemblage of about 70 disarticulated polychaete jaws (scolecodonts) from Devonian limestones (Plabutsch Formation) at the Tyrnaueralm, Austria, represents the first discovery of these fossils within the Graz Palaeozoic. Due to tectonic development of the area and burial temperatures over 300°C the scolecodonts are diagenetically altered and fragmented, which impedes full taxonomic study. However, maxillae of paulinitids and probable polychaetaspids and kielanoprionids can be identified, indicating that the polychaete assemblages in the Graz area include representatives of families occurring in Devonian faunas in other parts of Europe and in North America. Based on local facies the polychaete jaws were deposited in back-reef or lagoonal settings. Thomas J. Suttner ([email protected]), Commission for the Palaeontological and Stratigraphical Research of Austria, c/o University of Graz, Institute of Earth Sciences (Geology and Palaeontology), Heinrichstrasse 26, A-8010 Graz, Austria. Olle Hints ([email protected]), Institute of Geology at Tallinn University of Technology, Ehitajate 5, 19086 Tallinn, Estonia. Received 18 May 2010. Keywords: scolecodonts, polychaete jaws, Devonian, Plabutsch Formation, Graz Palaeozoic, Austria. THE OLDEST FOSSIL polychaete jaws recently been incorporated also in the study of (scolecodonts) are known from the uppermost extant eunicids (Paxton 2009). Cambrian (Williams in Hints & Nõlvak 2006), Polychaetes of the Order Eunicida are regarded and from the Middle Ordovician onwards they as important members of Palaeozoic marine are among the most common organic-walled benthic communities. This is inferred from the microfossils. The initial reports of scolecodonts, abundance of scolecodonts in the fossil record, dating back to the 1850s (Eichwald 1854), were and from the wide distribution and role of extant based on single-element taxonomy, which generally eunicidans in various types of environments and disregarded the fact that isolated scolecodonts ecological niches ranging from tidal flats and reefs were derived from complex jaw apparatuses. A to black smokers and abyssal plains (e.g., Rouse new era in scolecodont research began particularly & Pleijel 2001). in the 1960s, when large numbers of articulated The biogeographic and stratigraphic distribution jaw apparatuses were extracted from lower of fossil scolecodont-bearing polychaetes is Palaeozoic limestones, and a well founded genus- nevertheless relatively poorly known, and most and family-level classification was introduced (cf. data hitherto available relate to the Ordovician Kielan-Jaworowska 1966). It has been shown and Silurian of Baltica and Laurentia (Eriksson et subsequently that jaw apparatuses can also be al. 2004; Hints & Eriksson 2007a, b). Likewise, reconstructed from isolated scolecodonts and a palaeoecological studies of fossil eunicidans multi-element-based classification can be used for have been restricted both geographically and fossil polychaete jaws (Szaniawski & Gazdzicki stratigraphically, with only a few reports from 1978; Bergman 1989; Hints 1998; Eriksson et al. outside the aforementioned regions and periods. 2004; and many others). Following the Ordovician and Silurian in terms Models for phylogenetic relationships between of the number of scolecodont publications is the extinct eunicidan families have been proposed by Devonian, with reports from, e.g., the United Kielan-Jaworowska (1966), Kozur (1970), Edgar States, Canada, Brazil, France, Poland, North (1984), Szaniawski (1996) and Szaniawski & Africa, Siberia and Vietnam. However, in only Imajima (1996). Data on jaws of fossil taxa have a few of these papers is the apparatus-based 140 AAP Memoir 39 (2010) Figure 1. A, map of Austria showing location of the Graz Palaeozoic in the state of Styria. B, more detailed map showing location of studied section at the Tyrnaueralm near Mixnitz. C-D, outcrops at Tyrnaueralm section showing basal part of the Plabutsch Formation and underlying Flösserkogel Formation (C) and upper boundary of the Plabutsch Formation with the Tyrnaueralm Formation (D); scolecodonts were found in samples Ty/01, Ty/02 and Ty/03. classification used and the faunas described ascending order into the Flösserkogel, Plabutsch, in sufficient detail (notably Lange 1947 and Tyrnaueralm, Zachenspitz and Hochlantsch Szaniawski & Wrona 1973). formations. The first three formations are exposed In this paper we report the first discovery of in the studied section but only the Plabutsch Devonian scolecodonts from the Graz region, and Tyrnaueralm formations were sampled for Austria. Although the collection is very small, scolecodonts. and the material is poorly preserved due to The Plabutsch Formation is about 45 m thick the thermal history of the area, it adds another at the Tyrnaueralm (80-100 m in the Rannach record to the global distribution of scolecodont- Nappe). Based on conodont biostratigraphy bearing polychaetes and helps to achieve a it is probably late Emsian to Eifelian in age. stepwise refinement in understanding of their From bioclastic limestones near the base of the palaeoecology and palaeobiogeography during formation we extracted mainly icriodontids, the Palaeozoic Era. some simple cone taxa and a few Pa elements of Pandorinellina sp. and Polygnathus serotinus STUDY AREA from several localities (e.g., Forstweg Attems, The studied section is exposed in a small road- Ölberg, Tyrnaueralm section). Gollner & Zier cut located within the Hochlantsch area, some (1985) mentioned Icriodus corniger ssp. and hundred metres WSW of the refuge at the Latericriodus sp. from coeval deposits of Tyrnaueralm (47°20’2’’N, 15°25’40’’E; Fig. 1A- the Tiefenbachgraben, and recorded Eifelian B). This area is in the northern part of the Graz icriodontids like Icriodus struvei from the middle Palaeozoic (Styria, Austria). At Mt Hochlantsch, part of the formation at the southern slope of the the Devonian sequence, part of the Hochlantsch Hochlantsch. Group (sensu Gollner & Zier 1985), consists of up The succeeding Tyrnaueralm Formation to 2000 m of sandstones, dolostones, limestones, consists of dolostones and sandstones, volcanics tuffs and volcanics, ranging in age from Emsian and limestones with a maximum thickness of to Famennian. The sequence is divided in about 500 m. The conodonts Icriodus brevis, AAP Memoir 39 (2010) 141 Figure 2. Reconstructions of the eulabidognath (Family Paulinitidae) and labidognath (Family Polychaetaspidae) jaw apparatuses (modified from Kielan-Jaworowska 1966). Only jaws belonging to these families (indicated by ovals in the range chart) were obtained from the Plabutsch Formation, the stratigraphic range of which is indicated by the horizontal bar. I. difficilis, I. latericrescens latericrescens, residues were dried in a laboratory-type drying Polygnathus linguiformis ssp. obtained from cabinet at 50°C the fraction of 125-500 µm was the sequence indicate a Givetian age (Gollner & treated with heavy liquid (sodium polytungstate, Zier 1985). density: 2.79 g/mL). Finally, the residues were The conodont alteration index (CAI) in the picked for microfossils under a stereomicroscope. study area has been estimated as 5-5.5 (data by Both heavy and light fractions were examined, TS), indicating burial temperatures over 300°C. but most scolecodonts were recovered from Similar CAI values have been reported previously the heavy fraction due to their replacement by from the Tyrnaueralm Formation by Hasenhüttl pyrite. Scolecodont material figured was sputter- & Russegger (1992, p. 292). coated with a fine gold-palladium alloy for 420 sec. and scanned in a JEOL JSM-6400 scanning MATERIAL AND METHODS microscope at 10 kV. Thirty-three samples of limestone weighing The scolecodont collection is stored at the between 0.6 kg and 6.5 kg were obtained from Universalmuseum Joanneum in Graz (illustrated the Tyrnaueralm section. Three of the samples and additional material: UJ209171-209209); (Ty/01, Ty/02 and Ty/03; Fig. 1C-D) yielded abbreviation of sampling campaign numbers: e.g.: polychaete jaws, most of which were fragmented Ty/03 = Tyrnaueralm/sample 3. and diagenetically altered (the original material commonly replaced by pyrite). Out of 72 SCOLECODONT ASSEMBLAGE specimens, 9 MI, 5 MII and 13 broken maxillae All identifiable scolecodonts were obtained from from sample Ty/03 (Plabutsch Formation) could dark, bituminous, biomicritic mud- to wackestones be identified at some taxonomic level, the rest at the base and top of the Plabutsch Formation being unidentifiable fragments. (late Emsian to Eifelian). The scolecodonts are The specimens were obtained from the associated with crinoidal debris (e.g., stem- limestone using methods common for extracting plates of Cupressocrinites), coral fragments conodonts. Each rock sample was crushed into (e.g., Thamnopora), ostracods, gastropods, pieces of about 2 cm and put in sieves hung in calcareous algae, remains of placoderms as well buckets filled with water. For dissolution ca. 15% as icriodontid and simple-cone conodonts. The formic acid was used. The insoluble residues fossil assemblage apparently indicates back- were separated into three fractions by wet sieving reef and/or lagoonal depositional environments (meshes
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