A New Middle Devonian (Givetian) Psammosteid (Vertebrata: Heterostraci) from Poland
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Annales Societatis Geologorum Poloniae (2020), vol. 90: 75 – 93 doi: https://doi.org/10.14241/asgp.2020.04 A NEW MIDDLE DEVONIAN (GIVETIAN) PSAMMOSTEID (VERTEBRATA: HETEROSTRACI) FROM POLAND Marek DEC Institute of Palaeobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland; e-mail: [email protected] Dec, M., 2020. A new Middle Devonian (Givetian) psammosteid (Vertebrata: Heterostraci) from Poland. Annales Societatis Geologorum Poloniae, 90: 75 – 93. Abstract: A new genus and species of psammosteid heterostracan, Psarkosteus mediocris gen. et sp. nov., is de- scribed from the Middle Devonian (Givetian) of the Skały Formation, the Holy Cross Mountains, Poland. The dor- sal plate of Psarkosteus is constricted in its anterior part and the postorbital plate is long and narrow. Both features, along with the morphology and variety of tubercles, distinguish it from other representatives of the group. Most distinctive are big, teardrop-shaped tubercles, each with a flat or slightly concave surface and with its tip directed posteriorly, and a crenulated base, located along the branchial plates. The lateral line system in Psarkosteus is similar to that of Drepanaspis gemuendenensis and confirms earlier reconstructions. Key words: Pteraspidomorphi, Heterostraci, Psammosteidae, Middle Devonian, Holy Cross Mountains. Manuscript received 19 February, 2020 accepted 1 June 2020 INTRODUCTION The fossil record of the Heterostraci is poor in Poland, 2017; Glinskiy, 2018). The main problem is concerned although fossils are known from Upper Silurian, Lower with their relationships within the Pteraspidiformes. The and Middle Devonian deposits. From a core sample of the Psammosteidae were supposed to be (1) a sister group to the Upper Silurian (Přidoli) succession in Mielnik a represen- pteraspids s.l., that is Protopteraspididae + Pteraspididae s.l. tative of the Tolypelepididae was described (Dec, 2015). (in Blieck, 1984), or (2) a sister group to solely the Some basal heterostracan groups (Traquairaspididae and Protaspididae (sensu Blieck, 1984; Janvier, 1996a), or Cyathaspididae) have been described from Lower Devonian (3) a derived clade within the Pteraspidiformes, with drill cores in Poland. A rich vertebrate assemblage from Pteraspididae (‘pteraspidids’) as a sister group (Blieck et al., Emsian sandstones in the Holy Cross Mountains (Podłazie 1991; Janvier, 1996b). Hill and Bukowa Hill) includes fish remains belonging to The phylogenetic relationships within psammosteids were the sarcopterygians, osteichthyans, acanthodians, placo- studied by several authors (Tarlo, 1964; Obruchev and Mark- derms and ostracoderms (sensu Janvier, 1996a). The latter Kurik, 1965, 1968). Tarlo (1965) considered that the ‘main comprise two pteraspidiform groups, the Pteraspididae with lineage’ of psammosteids diverged from Guerichosteus Rhinopteraspis sanctacrucensis (Tarlo) and Psammosteidae kozlowskii. Glinskiy (2018) compiled the findings of ear- with Guerichosteus kozlowskii Tarlo and Hariosteus kiela- lier authors about in-group relationships and proposed the nae Tarlo (for details, see Dec, 2019). The specimens are phylogenetic analysis of the group, in which Drepanaspis curated in the Institute of Palaeobiology of Polish Academy and Guerichosteus are basal to all other psammosteids. The of Sciences with specimen numbers cited in the text. most recent study (Dec, 2019) of Guerichosteus shows its close affinity to Drepanaspis, while features of Hariosteus PHYLOGENETIC BACKGROUND indicate its affinity to younger genera, such asPycnosteus. In the present account, psammosteids are considered to MATERIAL AND GEOLOGICAL SETTING represent the family Psammosteidae (sensu Janvier, 1996b; Pernègre and Elliott, 2008; Randle and Sansom, 2017a, The material described here was obtained from an out- b) which generally is regarded as monophyletic and allied crop located to the east of Śniadka village, on the left bank to the Pteraspidiformes (Blieck, 1984; Blieck and Elliott, of Psarka River and south of the entrance of the ravine 76 M. DEC called Sitka (Fig. 1). It comprises limestone and marly waves, as being responsible for the rapid burial of the or- and clayey shales, representing the upper part of the Skały ganisms (Orłowski and Radwański, 1986). Formation (Sobolev, 1909; Kłossowski, 1985; Woroncowa- Most of the collection was obtained by Magdalena Marcinowska, 2012). The sedimentary structures on the Borsuk-Białynicka in 1978–1979, but during fieldwork in layer surfaces show that the strata in the exposed section 2012–2013 new material was collected by the present au- are overturned (Kłossowski, 1985). This lithostratigraphic thor. The psammosteid remains at Śniadka occur in marly unit is a part of the Świętomarz-Śniadka section, located and clayey shales. All specimens are flattened; moreover, in the NE of the Holy Cross Mountains, in the Łysogóry some are deformed (stretched, foliated). Most of the fos- Mountains (Fig. 1A, B). The interpretation of the geological siliferous material was found in one horizon, below the cross-section of the central part of the Bodzentyn Syncline, part with the cephalopod fauna, and preserved as isolated located between Świętomarz and Śniadka and exposed plates. In some cases, plates were associated with accumu- along the Psarka River, has been investigated by many au- lations of scales (Fig. 2). thors: Sobolev (1909), Mizerski (1981), Kłossowski (1985), The rock matrix with specimens was impregnated with Turnau and Racki (1999), Malec (1993), Halamski (2005), dilute cyanoacrylic in order to prevent fracture due to the Halamski and Segit (2006), and Woroncowa-Marcinowska drying of the slab. The specimens were cleaned mechan- (2012). Most of the discussion concerned the tectonic and ically and brushed with detergent. The procedure was re- stratigraphic interpretation of this site (Turnau and Racki, peated until the desired result was obtained. 1999; Woroncowa-Marcinowska, 2012). The clastic influx For photographic purposes, the specimens were coated represented by these sediments shows a terrigenous influ- with ammonium chloride. ence from the north (Kłossowski, 1985; Racki, 1997). The layer with psammosteids is located (Fig. 2) just below SYSTEMATIC PALAEONTOLOGY the goniatite horizon and corresponds with the rhenanus/ varcus Conodont Zone (Woroncowa-Marcinowska, 2012) that in standard conodonts zonation is correlated with the Class Pteraspidomorphi Goodrich, 1909 Lower varcus Zone (Narkiewicz and Bultynck, 2007). Subclass Heterostraci Lankester, 1868 A sedimentological analysis made by Kłossowski (1985) Order Pteraspidiformes Berg, 1937 shows relatively shallow-water conditions, which have Family Psammosteidae Traquair, 1896 been confirmed by the assemblage analysis of the fauna in- Genus Psarkosteus gen. nov. cluding conodonts, bivalves, gastropods and brachiopods (Dzik, 2002). Type and only species: Psarkosteus mediocris gen. et sp. The ichnofossil Alpetria sanctacrucensis Orłowski and nov. Radwański, 1986, interpreted as a sea-anemone burrow, also Etymology: In reference to the type locality near the Psarka indicates a shallow, sublittoral environment. Furthermore, River. they indicate hydrodynamic agents, such as currents or Diagnosis: As for the type species. The genus is monotypic. Fig. 1. Map showing the location of: A. Holy Cross Mountains (HCM). B. Śniadka in HCM. C. Collection site on the left bank of the Psarka River. A NEW MIDDLE DEVONIAN PSAMMOSTEID 77 Psarkosteus mediocris gen. et sp. nov. ZPAL Ag. I/4 (Figs 4B, 10B), ZPAL Ag. I/5 (Fig. 5B), ZPAL Ag. I/6 (Figs 6E, 7E), ZPAL Ag. I/7 (Figs 6B, 7B, Etymology: From Latin mediocris, in reference to its mod- 12B), ZPAL Ag. I/8 (Figs 4C, 10A), ZPAL Ag. I/9 (Fig. 5C), erate size. ZPAL Ag. I/10 (Fig. 3D), ZPAL Ag. I/11 (Fig. 6A), ZPAL Holotype: Dorsal plate ZPAL Ag–I/32 (Figs 3A, 9A) Ag. I/12 (Figs 6C, 7C), ZPAL Ag. I/15.1 (Fig. 8E), ZPAL Reference material: ZPAL Ag. I/1.1 (Figs 5A, 11), ZPAL Ag. Ag. I/15.2 (Fig. 8F), ZPAL Ag. I/15.3 (Fig. 8D), ZPAL Ag. I/1.2 (Fig. 3E), ZPAL Ag. I/2 (Fig. 4E), ZPAL Ag. I/3 (Fig. 4A), I/16 (Fig. 8G), ZPAL Ag. I/17.1 (Figs 6G, 7G), ZPAL Ag. Fig. 2. Stratigraphical location of the psammosteids-bearing level with the geological column in part of the Skały Formation at the locality shown in Figure 1C. 78 M. DEC I/17.2 (Figs 6F, 7F, 12A), ZPAL Ag. I/18 (Figs 6H–J, 7H–J), in length) and 11.6 cm in width (Fig. 4A). Most edges are ZPAL Ag. I/19 (Fig. 3C), ZPAL Ag. I/20 (Fig. 4D), ZPAL broken-off; only the margin of the posterior notch is pre- Ag. I/22 (Fig. 8A), ZPAL Ag. I/23 (Fig. 8B), ZPAL Ag. I/26 served, but the growth lines are clearly visible around the (Fig. 8C), ZPAL Ag. I/31 (Figs 3B, 9B, 14D), ZPAL Ag. centrally located growth centre. Anterior part of the plate I/32 (Figs 3A, 9A, 14C), is trapezoidal (Fig. 4A); the plate widens to the middle of Type locality: Śniadka, outcrop located on the left bank of the plate and smoothly turns to the posterior notch. Right the Psarka River, south of the entrance of the Sitka Ravine fragment of ventral plate of small specimen ZPAL Ag. I/8, (GPS coordinates 50°57’32.4”N 21°00’51.6”E). The vil- 4.7 cm in length and 2.1 cm in width (Fig. 4C). It allows es- lage is in the administrative district of Gmina Bodzentyn, timation of its total width as 4.2 cm. Lateral, posterior mar- within Kielce County, Świętokrzyskie Voivodeship, in gin as well as posterior notch margins are well preserved. south-central Poland (Fig. 1). Posterior notch extends well into the central area, but it does Stratigraphical occurrence: Middle Devonian (Givetian) not reach the growth centre. Skały Formation, Lower varcus conodont Zone. Branchial plate. Eight specimens of plates are preserved Occurrence: Middle Devonian (Givetian) Skały Formation, (Figs 5–7), including two large and near-complete ones the conodot Lower varcus Zone. Locality: Śniadka, the out- (Fig. 7). The first one (ZPAL Ag. I/5) has its postero-lateral crop located on the left bank of the Psarka River, south of corner broken off (Fig.