New Early Katian species of Leptestiidae and Hesperorthidae ( Brachiopoda ) from Lithuania Juozas Paškevi č iusa

A new leptestiid brachiopod species of the genus Sampo and a hesperorthid species of the genus Dolerorthis are described from the Early Katian Oandu Stage of southern Lithuania. The new species Sampo suduvensis and Dolerorthis nadruvensis are common brachiopods for the Howellites wesenbergensis–Hedstroemina subaequiclina–Reushella magna community of the Lithuanian shelf. In the East Baltic the brachiopods of the genus Sampo appear first in the deeper part of the Lithuanian shelf in siliciclastic lithologies. The genus Dolerorthis is identified for the first time in the East Baltic. The new species Dolerorthis nadruvensis differs from other related Hesperorthidae brachiopods in the region. An exception is the Late Katian species Boreadorthis recula from Estonia, which shows similarity with D. nadruvensis in shell size and ornamentation. Still, the generic relationship of these species requires further studies. The new species of brachiopods are a supplement to the brachiopod fauna of


INTRODUCTION
A rich and diverse brachiopod fauna occurs in the East Baltic in the lower Katian Oandu Stage (Rõõmusoks 1970;Hints & Rõõmusoks 1997;Paškevičius 1997;Hints & Harper 2003;Kaljo et al. 2011) (Fig. 1).Due to gaps, including the sedimentary gap on the lower boundary (Dronov & Rozhnov 2007), the Oandu Stage is stratigraphically less complete in the Estonian shallow shelf than in the sections in the deeper part of the Lithuanian Shelf (Fig. 2).The thick (up to 20 m), predominantly siliciclastic lithologies in southern Lithuania comprise the oldest strata, which could be included to the Oandu Stage (Hints et al. 2016).
The Ordovician brachiopod fauna of Lithuania comprises mostly species which are common or related with those in northern Estonia.The composition and stratigraphical distribution of Lithuanian brachiopods are presented in a summarized list of species according to formations and stages in Paškevičius (1997, table 5, pp. 330-336).The data on the distribution of brachiopod species in different Lithuanian drill core sections are available in Paškevičius (1973Paškevičius ( , 1997)), Laškovas et al. (1984), Laškovas & Paškevičius (1989) and Hints et al. (2016).The brachiopods, which are specific to or most characteristic of the Lithuanian sections, have been described in a few papers (Alikhova et al. 1954;Hints Fig. 1.Generalized correlation chart of the early Katian, formations and members (Mb.) of the East Baltic.Up.Ordovician, Upper Ordovician; Reg.Stage, Regional Stage; N, northern; S, southern part of the Estonian Shelf; the grey area marks the possible interval missing in the Keila-Oandu transitional interval of the shallow part of the Estonian Shelf.1973,1975) or are mentioned under open nomenclature (Paškevičius 1997).Two new species, Sampo suduvensis and Dolerorthis nadruvensis, are described in the present paper.Their detailed distribution in the Pajevonys-13 core section is presented in Hints et al. (2016).
subaequiclina-Reuschella magna community, which probably represents the Oandu age benthic association BA4 by Boucot (1975) (Paškevičius 2000).Several taxa of that community (Dolerorthis, Eoplectodonta, Platystrophia, Skenidioides, leptestiids Sampo or Leptestiina) are common with the Nicolella brachiopod community of the lowermost Woolstonian Substage (= uppermost Longvillian) of the Cheneyan Stage of North Wales of Avalonia (Pickerill & Brenchley 1979).The Cheneyan Stage is correlated with the Rakvere Stage (Ferretti et al. 2014) or with the Oandu Stage and part of the Rakvere Stage (Webby et al. 2004).This correlation suggests that the mentioned two brachiopod communities are almost contemporaneous in Baltica and Avalonia.Beside that, the Nicolella community is distributed in lithologies (fine silt) similar to those in the Oandu-Rakvere stratigraphical interval of the deeper part of the Lithuanian Shelf.This confirms the great affinity of the Early Katian brachiopod faunas on Baltica and Avalonia, identified by global studies on brachiopod distribution (Harper et al. 2013).
The new species Sampo suduvensis and Dolerorthis nadruvensis contribute to the data on early Katian brachiopod diversity.The latter species is the first identification of the genus Dolerorthis in the Ordovician of the East Baltic.Both species are found in the Oandu Stage, while occurrences in the younger strata of the Rakvere Stage are unclear.
The new species Sampo suduvensis and its comparison with the type species of the genus Sampo hiiuensis enabled us to specify the morphology of the cardinalia.Cocks & Rong (1989, p. 82) defined the terms socket plates or ridges for the plectambonitacean brachiopods 'as structures attached to the hinge line and arising from near the notothyrial platform'.Sampo suduvensis and S. hiiuensis have cardinalia with somewhat unusual socket plates, which have posterolaterally the plate-like callosity of shell material (Fig. 3).
The described new species occur in the Alvitas and Šakiai formations of the Oandu Stage (Fig. 1).Few finds come from the Jakšiai Formation (Fm.), whose position in the Rakvere Stage is unclear in some sections.The rock samples with fossils were collected from drill core sections in southern Lithuania (Fig. 2) in the 1960s.The brachiopods were studied later by J. Paškevičius and L. Hints.The specimens are housed at Vilnius University (VU, institutional abbreviation) and at the Institute of Geology at Tallinn University of Technology (GIT).
Description.Medium-sized concavo-convex shell with semi-circular to laterally elongate outline; shell length forms 50-70%, thickness 27-36% of shell width; maximum width and the strongest convexity in posterior half of ventral valve.Cardinal angles rounded to acute.Ornament parvicostellate with 5-10 costae at umbo of ventral valve, up to 8 additional accentuated ribs appear by intercalation on the middle of valve with up to 20 fine costellae between ribs.Ventral valve strongly convex, thickness about 50% of valve length and 27-36% of its width; middle sector of valve flattened, with weakly developed costae; interarea slightly concave orthocline to anacline, length about 4% of hinge line width.Ventral valve with small laterally inclined teeth; up to 20 tiny densely spaced denticles occur along the anterior margin of interarea (Fig. 4C4, H), which is separated from rest part of interarea by distinct growth line parallel to hinge line; denticulated margin turns anterolaterally to join with papillated lateral part of valve (Fig. 4H).Delthyrium triangular, up to 2 mm high and 0.8 mm wide; apical pseudodelthidium small (Fig. 4C1, F).Muscle field about 60% as wide as long (Fig. 4C4, F), anteriorly slightly bilobed, in dorsal view may be hidden in the strongly convex posterior part of valve.Interior surface covered by papillae, more strongly developed around the marginal area with mantle canals.
Dorsal valve strongly concave in umbonal area.Cardinal process robust, with strong grooves for diductor bases and higher median part (Fig. 3A).Hinge line with small fossettes.Sockets below the hinge line are separated from anterolaterally directed socket ridges by oblique plate-like thickenings; socket ridges merge with posterolateral edges of bema (Figs 3A, 4A).Bema about 40% as wide as valve width, reaches anteriorly about 60% of valve length; posterior part suboval, undercut up to the socket ridges, the anterior part developed as two weakly undercut short extensions.Low fold on bema has two weakly developed anterolaterally directed branches which separate the adductor scars (Fig. 4A1, A2).Vascula myaria are developed on anterolateral edges of bema (Fig. 4A).Platform subtriangular, rimmed with papillae.Mantle canals deeply expressed on valve floor before platform.
Comparison.The new species differs from the type species of the genus Sampo hiiuensis (Öpik 1933 6A) (Fig. 3B) from the uppermost Katian in smaller size and interior features of the dorsal valve (Fig. 4A1, 4B).Sampo hiiuensis has a two-stepped bema, high posteriorly directed cardinal process and laterally directed socket ridges instead of a bema with anteriorly directed lobes, a stout cardinal process and anterolaterally directed socket ridges on S. suduvensis.Vascula myaria on S. hiiuensis divide the bema into middle and lateral parts; on S. suduvensis they delimit the middle sector of the bema with its anteriorly extending parts.Sampo suduvensis has also less frequent 10-12 accentuated ribs against 14 on S. hiiuensis.
Sampo suduvensis is similar to Sampo transversa Cocks from the Late Katian of north (Hiller 1980) and southwestern Wales (Cocks 2014).It differs from S. transversa in smaller size (maximum widths 15.5 and 23.8 mm, respectively), higher average width/length ratio (0.59 and 0.54) and in the shape of the bema.In S. transversa the anterior sector of the bema (Cocks 2014) is about the same length as the posterior sector.The shells of S. suduvensis resemble in shell form and ornamentation another plectambonitacean species Sampo (Leptellina) indentata Spjeldnaes, 1957[= Bilobia indentata in Cocks & Rong 1989; Leangella (Leptestiina) indentata in Hansen 2008] from Norway (Harper & Owen 1984) and Sweden (Hansen 2008).However, the latter differs from species of Sampo in a simple bema and absence of denticles on the ventral interarea (Harper & Owen 1984).
Dorsal valve with simple wedge-like cardinal process, which rises on the narrow notothyrial platform up to the level of interarea.Brachiophores long, with dorsally inclined anterior part (Fig. 5H), posteriorly merge with anterior part of notothyrial platform.Sockets as oblique depressions between fulcral plates and posterior edge of interarea, raised from valve surface.Small accessory sockets occur laterally to brachiophores.Notothyrial platform continues anteriorly as wide median ridge extending for 60% of valve length.Short anterior subtriangular adductor scars are separated from larger posterior scars by anterolaterally inclined septa.Mantle canal system unclear.Exterior ribbing strongly expressed around interior margin.
The new species differs from other species of the genus Dolerorthis occurring in Baltica (Norway, Sweden), Avalonia (Wales, England) and eastern Laurentia (Girvan, Scotland) mainly in shell outline and size, the density of ribbing and size of brachiophores.The species Dolerorthis cf.virgata (J.de C. Sowerby) from the upper Furuberget Fm. and the Nakkholmen Fm. in Norway (Harper & Owen 1984;Harper et al. 1984), the Avalonian species D. virgata from the Woolstonian to Onnian substages of Wales (Hurst 1979)

Table 1 .
Measurements of shells.D.v., dorsal valve; V.v., ventral  valve; S., shellKaliningrad region (Russian Federation) in the Alvitas and Šakiai formations of the Oandu Stage and in the basal beds of the Jakšiai Fm. of the Rakvere?Stage.Derivation of name.From Nadruva, a historical 13thcentury name for the Aisčiai area of southwestern Lithuania where the drill cores with the described new species are located.

ja Hesperorthidae (Brachiopoda) Vara-Kati uued liigid Leedust Juozas
and the Laurentian species D.Williams 19Harper 1984;1977)diffWright 1964)Baltic species in more rounded outline, different arrangement of ornamentation and short or stout brachiophores.Some other Laurentian species, D. rankini (Davidson)(Lower Ardwell Fm. in Girvan;Williams 1962) and D. inaequicostataWright (the  Drummuck Group in Scotland;Harper 1984; the Killey  Bridge Fm. in Ireland; Mitchell 1977)differ in having a strong sulcus on the convex dorsal valve.In addition to these differences, the species D. inaequicostataWright  (Portrane Limestone and Killey Bridge Fm. of Ireland;Wright 1964)and D.? wattersorum (Whitehouse Group, Scotland; Harper 1984) differentiate in finer ornamentation of numerous costellae.Distribution.The new species occurs in the lowermost Katian Oandu Stage in Lithuania, southern East Baltic (Hints et al. 2016).Few fragments are found in strata whose age, Oandu or Rakvere, is not very clear.The new species Sampo suduvensis and Dolerorthis nadruvensis contribute to the data on early Katian brachiopod diversity in the southern East Baltic.2. Sampo suduvensis and also the type species of the genus Sampo hiiuensis have unusual socket ridges, which are posteriorly supported by plate-like callosities.3. The described species Sampo suduvensis and Dolerorthis nadruvensis belong to the Howellites wesenbergensis-Hedstroemina subaequiclina-Reuschella magna brachiopod community of the Oandu Stage in the southern East Baltic.The appearance of brachiopods of that community in the lowermost part of the Oandu Stage marks the faunal renovation event on the Sandbian-Katian transitional interval.4. The brachiopod community of Baltica with the new species has affinity with the more or less contemporaneous Nicolella community in Avalonia.5.The age of the last occurrences of the described species is not clear.Some finds belong to the strata which are included to the Rakvere Stage.However, at least in some drill cores (Hints et al. 2016) the Rakvere age needs more detailed palaeontological improvement.Paškevičius ja Linda Hints On kirjeldatud kaht uut brahhiopoodiliiki Sampo suduvensis (Leptestiidae) ja Dolerorthis nadruvensis (Hesperorthidae), mis esinevad Ülem-Ordoviitsiumi Vara-Kati Oandu lademes Lõuna-Leedus.Need liigid täiendavad Howellites wesenbergensis -Hedstroemina subaequiclina -Reuschella magna brahhiopoodikooslust. Sampo suduvensis'e dorsaalse poolme lukustuselemendid sisaldavad täiendavat plaatjat paksendit, mida teistel perekonna esindajatel ei ole täheldatud.Erandiks on perekonna tüüpliik Sampo hiiuensis Öpik.Dolerorthis nadruvensis on perekonna Dolerorthis liigi esmane nimetamine ja kirjeldamine Baltikumis.Uus liik eristub sugukonna Hesperorthidae teistest esindajatest suuruse ja radiaalse skulptuuri poolest ning sellel on siiski suurim sarnasus liigiga Boreadorthis recula Öpik.Viimase liigi perekondlik kuuluvus vajab edaspidist täpsustamist uute leidude põhjal.