New records of psammosteids from the Aruküla Regional Stage (Middle Devonian) of the Leningrad...

ISSN 0031�0301, Paleontological Journal, 2014, Vol. 48, No. 9, pp. 980–991. © Pleiades Publishing, Ltd., 2014.

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INTRODUCTION

During several decades after publication of mono�graphs by Halstead Tarlo (1964b, 1965) and Obruchevand Mark�Kurik (1965), which revised Arukülianpsammosteids, new material supplementing descrip�tions of some known taxa were collected.

The Aruküla Regional Stage of the Givetian Stageof the Middle Devonian was established by Mark�Kurik and named after outcrops near Aruküla caves inthe northern marginal area of the city of Tartu, Estonia(Mark, 1958; Mark and Tamme, 1964). Terrigenousdeposits of the Aruküla Regional Stage are widespreadin the western and central parts of the LeningradRegion. The most representative outcrops are on thebanks of the Luga River and its tributaries, the Lem�ovzha, Saba, and Oredezh rivers (Sammet, 1973;Ivanov and Lebedev, 2011).

Fossil remains of Pycnosteus palaeformis, Tartuos�teus giganteus, and Psammolepis proia are widespreadin the Aruküla beds of the eastern Main DevonianField. The material described in the present study wascollected in different years by Averianov (1990),Ivanov (1985, 2009, 2010), Kuleshov (2003–2011),and Skutschas (2001) and came from localities situ�ated near the villages of Siverskii, Belogorka, Novo�siverskaya, and Zaitsevo of the Gatchinskii District ofthe Leningrad Region (Fig. 1).

The Aruküla Regional Stage includes two zonesbased on the heterostracans Pycnosteus palaeformis

and Pycnosteus pauli. The material described belowcomes from localities corresponding in level to thePycnosteus palaeformis Zone.

The Siverskii locality is situated in the settlement ofSiverskii on the right bank of the Oredezh River, 120 mupstream from an old dam. Psammosteids occur in themiddle part of the outcrop, in red cross�bedded sand�stones and in interlayers and lenses of variegated con�glomerates (Ivanov et al., 2005). The Belogorka local�ity is in the village on the right bank of the OredezhRiver near the old dam. Psammosteids occur in thelower part of the outcrop in red cross�bedded sand�stones. The Novosiverskaya locality is situated in the vil�lage of Novosiverskaya, on the left bank of the OredezhRiver, 90 m downstream from the eastern bridge. Psam�mosteid specimens occur in red cross�bedded sand�stones in the lower and middle parts of the outcrop. TheZaitsevo locality is a sand quarry located 700 m east ofthe village of Zaitsevo. The material was collected in thebeds and lenses of red cross�bedded sandstones in themiddle and upper parts of the outcrop.

The specimens described below are stored in themuseum of the Paleontological Department ofSt. Petersburg State University (collection PM SPU,no. 69) and in the museum of the Department of Ver�tebrate Zoology of St. Petersburg State University(paleontological collection VZ PC, no. 1). The psam�mosteid systematics accepted here follows that devel�oped by Halstead Tarlo (1962; Halstead, 1993); the

New Records of Psammosteids (Heterostraci) from the Aruküla Regional Stage (Middle Devonian)

of the Leningrad Region, RussiaV. N. Glinskiy

Geological Faculty, St. Petersburg State University, Universitetskaya nab. 1, St. Petersburg, 199034 Russiae�mail: [email protected]

Received April 10, 2012

Abstract—Previously unknown exoskeletal plates of certain Middle Devonian psammosteids, i.e., Pycnos�teus palaeformis Preobrazhensky, Psammolepis proia Mark�Kurik, and Schizosteus (?) sp., from localities ofthe Aruküla Regional Stage of the eastern part of the Main Devonian Field (Leningrad Region, Russia) aredescribed. The psammosteid Schizosteus (?) sp. described in open nomenclature in connection with theabsence of well�preserved median plates has only been found in several localities (Zaitsevo, Siverskii, and Bel�ogorka). The shape of the branchial plate of Tartuosteus giganteus (Gross) and ventral plate of Psammolepisproia is specified. The psammosteid Psammolepis proia from the eastern part of the Main Devonian Field isdescribed for the first time.

Keywords: Agnatha, Heterostraci, Psammosteida, Middle Devonian, Givetian, Aruküla Regional Stage,Main Devonian Field, Leningrad Region

DOI: 10.1134/S0031030114090032

PALEONTOLOGICAL JOURNAL Vol. 48 No. 9 2014

NEW RECORDS OF PSAMMOSTEIDS (HETEROSTRACI) 981

scheme of measurements of particular plates followsthe same author (Halstead Tarlo, 1964b, text�fig. 9).

SYSTEMATIC PALEONTOLOGY

S U P E R C L A S S A G N A T H A C O P E , 1 8 8 9

SUBCLASS HETEROSTRACI LANKESTER, 1868

Order Psammosteiformes Berg, 1940

Family Pycnosteidae Tarlo, 1962

Genus Pycnosteus Preobrazhensky, 1911

Pycnosteus palaeformis Preobrazhensky, 1911

Plate 2, figs. 1–4; Plate 3, figs. 1–3

Trionyx spinosus: Kutorga, 1837, p. 12, pl. IV, fig. 11.Psammosteus arenatus: Woodward, 1895, p. 39; Goodrich,

1908, p. 774, pl. 43, fig. 4.Psammosteiden: Jaekel, 1902, p. 105.Psammosteus imperfectus: Preobrazhensky, 1911, p. 27, pl. 1.

fig. 6.Pycnosteus palaeformis: Preobrazhensky, 1911, p. 21, pl. I,

figs. 1–5; Gross, 1930, p. 5 (pars); Obruchev, 1931, p. 94; Gross,1933, p. 13 (pars), pl. II, figs. 22 and 23; 1935, p. 14 (pars), pl. II,fig. 1; Obruchev, 1940, p. 768, text�figs. 1d and 3; 1947, p. 196,pl. L, fig. 4; Mark, 1956, p. 76, pl. I, fig. 1, pl. II, fig. 1, text�figs. 1b, 2b, and 3a; Mark, 1961, p. 33, text�fig. 3a; Obruchev,1964, text�figs. 48 and 49; Hastead Tarlo, 1964b, pl. III, figs. 1 and3, text�fig. 7; Obruchev and Mark�Kurik, 1965, p. 135, pl. XXV,figs. 1–3, pl. XXVI, figs. 1 and 2, text�figs. 79–81; Halstead Tarlo,1965, p. 69, pl. XVIII, fig. 2, text�fig. 16; Novitskaya, 1965, p. 260,text�fig. 202; Obruchev and Mark�Kurik, 1968, text�figs. 1 and 2b;Moloshnikov, 2001, p. 73, text�figs. 1–6; Novitskaya, 2004, p. 178,text�fig. 104; Ivanov and Lebedev, 2011, text�figs. 10 B and 10C.

Pycnosteus?: Gross, 1930, p. 13.Psammolepis (Pycnosteus?) impertecta: Gross, 1933, p. 12.Schizosteus (?) imperfectus: Obruchev, 1940, p. 767.Pycnosteus? imperfectus: Gross, 1940, p. 74.Pycnosteus imperfectus: Mark, 1956, p. 74, text�figs. 1a and 2a.

H o l o t y p e. TUG (Museum of Geology, Univer�sity of Tartu, Estonia), no. 1552�6 (Pi 102), ventralplate, Preobrazhensky’s original (1911, pl. I, figs. 1–5);collection of Asmuss, 1842; Estonia, Aruküla caves inthe northern marginal area of Tartu; Middle Devo�nian, Givetian Stage, Aruküla Regional Stage.

D e s c r i p t i o n. The plates are covered with highrounded dentine tubercles varying from 0.2 to 1.3 mmin diameter, with sharp apices. The marginal cuspletsare short and massive, relatively widely spaced, passinto massive ridges, which do not reach the tubercleapices. The number of cusplets ranges from 4 to 15,usually 5–7. Tubercles are arranged relatively loosely.Fulcral and flank scales are characterized by roundand elongated tubercles, which are sometimes fused inshort ridges.

The orbital plate (Pl. 2, fig. 1) is oval, with a roundorbital foramen 4 mm in diameter; on the internalside, there is a depression 10 mm in diameter aroundthe foramen, which is displaced somewhat downwardsrelative to the plate center. The plate is curved longitu�dinally; the line of bending passes on the upper marginof the orbital foramen. At the broken medial margin,the plate is 3 mm thick. All margins display weartraces. The external surface is covered with 0.8�mm

tubercles with 5–7 cusplets. The plate is 3.3 cm longand 1.8 cm wide.

The postorbital plate (Pl. 2, figs. 2, 3) SpecimenPM SPU, no. 69�2 is slightly curved (the bend is 3 mmhigh). The sides of the lateral margin converge in thecenter of the plate at an angle of 142°. The anteriormargin is curved and the medial margin is concave.The medial and anterior margins of the dorsal side arebordered by an area without sculpture, which is up to7 mm wide. Plate PM SPU, no. 69�3 has distinctgrowth lines. The preserved part of curved lateral mar�gin has lifetime wear traces. The growth center of theplate is located at the bend of the lateral margin.Tubercles have from 5 to 8 cusplets and graduallydecrease in size from lateral to medial margin (from1 to 0.4 mm). On the visceral side, near the lateralmargin, a thickening is formed. A series of 1�mm�widetubercles comes onto the visceral side of the plate. Theplate (PM SPU, no. 69�2) is 7.5 cm long.

The branchial plate (Pl. 3, fig. 1) is long and narrowin a young individual; it is curved (the bend is 30 mmhigh). The anterolateral margin is convex and the pos�terior margin is concave; the angle between them is90°. The distal end of the plate is rounded. The medialmargin is curved. The plate margins are 2 mm thick.On the dorsal side, the sculptured area is narrowerthan the area without sculpturing. The border of thesculptured area is wavy; at the posterior margin, itcurves medially and is separated by a distinct gentle2�mm�deep depression. The sculptured area displaysseveral pathologies, that is, small thickenings and a

Ladoga

Gulf of

St. Petersburg

Luga 0 50 100 km

Rozhdestveno

Voznesenka

Bol'shevo

Druzhnosel'e

Stroganovo Zaycevo

Ostrov

Divenka riverKuznecovo

Orlinskoe lake

Druzhnaya Gorka

Orlino

Orl

inka

riv

er

SiverskiyBelogorka

Zelionaya Gora

Starosiverskaya

Oredezh river Novosiverskaya1

23

4

0 1 2 3 km

lake

Finland

Lampovo

L e n i n o g r a dr e g i o n

Fig. 1. Maps of (a) Leningrad Region. Hatching designatesthe territory of the Gatchinskii District; (b) psammosteidlocalities: (1) Siverskii, (2) Belogorka, (3) Novosiverskaya,and (4) Zaitsevo.

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Plate 2

1a

2d

3e

1a 1b 1c 1d

2a

2b

2c

3a 3b

3d 3c

4a 4b 4c 4d



E x p l a n a t i o n o f P l a t e 2

Figs. 1–4. Pycnosteus palaeformis Preobrazhensky, Aruküla Regional Stage, Zaitsevo locality: (1) PM SPU, no. 69�1, orbitalplate: (1a, 1b) dorsal and (1c, 1d) internal sides; (1e) sculptural details marked by framework in 1b; (2) PM SPU, no. 69�2, pos�torbital plate: (2a, 2b) external and (2c) internal sides; (2e) sculptural details marked by framework in 2b; (3) PM SPU, no. 69�3,postorbital plate: (3a, 3b) dorsal and (3c, 3d) internal sides; (3e) sculptural details marked by framework in 3b; (4) PM SPU,no. 69�7, flank scale: (4a, 4b) external and (4c, 4d) internal sides; (4e) sculptural details marked by framework in 4b. Area withsculpture is filled with dark gray; light gray is area without sculpturing, and hatching is abraded area. Scale bars: (1a, 1c, 3a, 3c)2 cm; (2a, 2c, 4a, 4c) 1 cm; and (1e, 2e, 3e, 4e) 1 mm.

5�mm�high ridge parallel to the posterior margin; inthis zone, tubercles grow at an angle and retainpointed apices, which have not been worn during theanimal’s life or postmortem. On the dorsal side, tuber�cles gradually decrease in diameter from the anterolat�eral and posterior margins to the border of the sculp�tured area (from 1 to 0.5 mm). On the ventral side,there is a 3�mm�wide border without sculpturing atthe medial margin. Tubercles decrease in diameterfrom the external margins towards the medial margin(from 1 to 0.2 mm). In general, the ventral side of theplate has smaller tubercles.

The cornual plate (Pl. 3, figs. 2, 3) is round andcurved (the bend is up to 10 mm high). The growthcenter is at the posterior margin of the plate and dis�placed proximally. At the posterior margin of the prox�imal plate part, the sculptured area curves inside,forming a thickening. On the dorsal side, there is anarea at the posterior margin which was worn during theanimal’s life; in specimen PM SPU, no. 69�6, it israther large. The area without sculpture, which is up to4 mm wide, has a wavy border with the lateral, medial,and probably anterior margins and partly with the dis�tal part of the posterior margin. Tubercles range from0.4 to 1 mm in diameter, have 4–6 cusplets. The plate(PM SPU, no. 69�5) is 6.5 cm long and 6.8 cm wide.

The flank scale (Pl. 2, fig. 4) is rhombic, flat, withpartly broken edges. The external region is coveredwith angular elliptical tubercles fused in ridges, whichresemble 0.5–2–mm�long petals with massive cus�plets, the number of which varies from 11 to 13. Roundtubercles with 5–7 cusplets are less frequent. Theridges become longer towards the distal margin of thescale. The flank scale is 1.8 cm wide.

C o m p a r i s o n. In the shape of tubercles Pycnos�teus palaeformis is most similar to P. pauli Mark�Kurikand differs from it in the shorter and more widelyspaced cusplets; Pycnosteus pauli usually has 6–12 cusplets, which are frequently divided into two orthree branches (Obruchev and Mark�Kurik, 1965,pl. XXVII, figs. 1–3). In contrast to P. palaeformis, thebranchial plates of P. pauli and P. tuberculatus Rohonhave a concave anterolateral margin. The cornualplates of P. palaeformis resemble that of P. tuberculatus(Mark�Kurik, 1968); however, in P. palaeformis, thegrowth center is displaced proximally and the borderof the zone without sculpture is only located in the dis�tal part of the posterior margin.

R e m a r k s. The orbital plates of Pycnosteus lackcanals of the lateral line, which are present in Schizos�teus heterolepis and the genus Psammolepis (Obruchevand Mark�Kurik, 1965; Elliott and Mark�Kurik,2005). Drepanaspis gemuendenensis Schlüter also dis�plays distinct grooves (Gross, 1963, pl. 8, fig. 4; Lehman,1967, pl. 1), which diverge from the posterior marginof the orbital foramen. The postorbital plates ofP. palaeformis are similar in general shape to the platesof D. gemuendenensis, S. heterolepis, and S. striatus(Gross, 1963; Obruchev and Mark�Kurik, 1965).Judging from the growth lines, the anterior margin ofthis plate was probably straight or curved (Pl. 2,figs. 2b, 3b). The shape of branchial plates is close tothat of Pycnolepis splendens and Schizosteus striatus(Obruchev and Mark�Kurik, 1965, text�figs. 25, 33).The area of the sculptured zone on the dorsal side ofthe branchial plate was regarded as a diagnostic char�acter (Obruchev and Mark�Kurik, 1965; Moloshni�kov, 2001). A smaller area of the sculptured zone onthe dorsal side of branchial plates of some individuals(Pl. 3, figs. 1a, 1b; Obruchev, 1940, text�fig. 3) pre�vents the use of this character for comparison anddiagnostics.

M a t e r i a l. Right orbital plate (PM SPU, no. 69�1),Zaitsevo locality; anterior fragment of a right postor�bital plate (PM SPU, no. 69�2), Zaitsevo locality; frag�ment of a right postorbital plate (PM SPU, no. 69�3),Zaitsevo locality; left branchial plate of a juvenile (PMSPU, no. 69�4), Siverskii locality; left cornual plate(PM SPU, no. 69�5), Zaitsevo locality; posterior frag�ment of left cornual plate (PM SPU, no. 69�6), Bel�ogorka locality; and flank scale (PM SPU, no. 69�7),Zaitsevo locality.

O c c u r r e n c e. Middle Devonian, GivetianStage, Aruküla Regional Stage, Pycnosteus palaeformisZone of Latvia, Estonia (Mark�Kurik, 2000), andRussia (Leningrad Region). According to Mark�Kurik, the finds of this species in the Pycnosteus pauliZone of Latvia (Lyarskaya and Lukševi s, 1992)require confirmation based on new material.

Genus Tartuosteus Obruchev, 1961

Tartuosteus giganteus (Gross, 1933)

Plate 5, fig. 2

Psammolepis gigantea: Gross, 1933, p. 11, pl. I, fig. 8, text�figs. 1D, 2C, 2D, and 3; 1935, pl. 2, fig. 4.

Tartuosteus giganteus: Obruchev, 1961, p. 108, text�figs. 1b and2; 1964, pl. VII, fig. 6; Obruchev and Mark�Kurik, 1965, p. 111,

c

^

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1e

Plate 3

1f

2e

3e

1a 1b

1c 1d

2a 2b

2c 2d

3a

3b

3c

3d



pl. XX, figs. 2 and 3, pl. XXI, fig. 1, text�figs. 48–55; HalsteadTarlo, 1965, p. 85, text�figs. 24 and 25; Obruchev and Mark�Kurik, 1968, text�figs. 1, 2A; Novitskaya, 2004, p. 175, 176, text�figs. 98 and 99.

H o l o t y p e. MB.f.2, Museum für Naturkunde,Berlin, Germany; left branchial plate, original ofGross (1933, pl. I, fig. 8), Estonia, outcrop Haaslavaon the Mõra Creek (tributary of the Emajõgi River);Middle Devonian, Aruküla Regional Stage.

D e s c r i p t i o n. The species is characterized byvery small tubercles ranging from 0.07 to 1 mm, mostly0.3 mm. They are low, round, angular or somewhatextended, densely spaced, with simple, relativelyshort, rarely bifurcating marginal cusplets identical inlength, from 6 to 12 in number. The cusplets form ribs,which do not reach the rounded apex. Tubercles formregular diagonal rows. The cusplets of neighboringtubercles pass in between each other.

The branchial plate is long and wide. The antero�lateral margin is convex, with traces of lifetime wear.The external angle is 80°; the distal end is rounded andcurved posteriorly. The posterior margin is wavy, has adistinct proximal projection. The medial margin iscurved. The plate decreases in thickness towards themedial margin (from 10 to 1 mm). The plate is curved(the bend is 30 mm high). On the dorsal side, thesculptured area is approximately equal to the areawithout sculpture. The boundary between the surfacesis wavy, with a gentle depression, up to 5 mm deep. Atthe posterior margin, this boundary curves mediallyand passes to the proximal projection on the posteriormargin at a sharp angle. On the ventral side, the medialmargin is bordered by an area without tubercles, whichis up to 23 mm wide. Tubercles of the plate are round,rhomboid, or hexagonal, with small cusplets. Theydecrease in diameter from the anterolateral to posteriorand medial margins on the dorsal side from 0.5 to 0.1 mmand, on the ventral side, from 1 to 0.2 mm. The dorsalside of the branchial plate is characterized by on averagesmaller tubercles (0.1–0.3 mm). The plate is 35 cmlong.

C o m p a r i s o n. Tubercles of Tartuosteus gigan�teus are similar to that of T. maximus Mark�Kurik, but,in the first, they are less diverse, their cusplets are morewidely spaced, whereas T. maximus has from 17 to25 cusplets and they are continued in the shape of dis�tinct low ribs (Obruchev and Mark�Kurik, 1965).Branchial plates of T. giganteus resemble in shape thatof T. maximus, the distal end of which is also curvedposteriorly and the proximal part of the posterior mar�

gin has a rounded projection. In proportions, thebranchial plates of T. giganteus are narrower than inT. maximus. T. giganteus differs from T. (?) luhaiMark�Kurik in the less concave posterior margin ofbranchial plates, the narrower area without tubercleson the ventral side of plates, and in the symmetricaltubercles forming dense regular rows. It differs fromT. (?) ornatus (Rohon) and Rohonosteus (? = Tartuos�teus) complicatus (Kiaer) in the smaller size andgreater diversity of denticle shapes and also in thelarger branchial plates. In addition, it differs fromT. (?) ornatus in the less concave posterior margin ofbranchial plates. It differs from T. (?) zheleznogorsken�sis Moloshnikov in the shape of the external margins ofbranchial plates, the greater sculptured area on thedorsal side, and in the less diverse shape of tubercles.

R e m a r k s. Three previously described branchialplates of this species (Gross, 1933, p. 11, pl. I, fig. 8;Obruchev and Mark�Kurik, 1965, p. 113, text�fig. 50)found in Estonia have incomplete or strongly abradedmargins. The specimen described here, with preservedmargins, is similar in some characters to branchialplates of T. maximus. Tubercles of T. giganteus are sim�ilar in size and, sometimes, shape to tubercles ofPsammolepis proia; however, in the first, they arelower, regularly arranged, and are not fused even inrare ridges.

M a t e r i a l. Left branchial plate (PM SPU,no. 69�9) from the Siverskii locality.

O c c u r r e n c e. Middle Devonian, GivetianStage, Aruküla Regional Stage, Pycnosteus palaeformisand Pycnosteus pauli zones in Latvia, Estonia (Mark�Kurik, 2000), and the Leningrad Region of Russia.

Family Psammolepididae Tarlo, 1962

Genus Psammolepis Agassiz, 1845Psammolepis proia Mark�Kurik, 1965

Plate 4 figs. 1 and 2.

Psammolepis paradoxa: Bystrow, 1955, text�figs. 26–29, 31–35.Tartuosteus giganteus: Obruchev, 1961, p. 108, text�figs. 1a and

3 (pars).Psammolepis sp.: Obruchev, 1964, text�figs. 11 and 53.Psammolepis proia (nomen nudum): Halstead Tarlo, 1964a,

p. 12, text�fig. 5; 1964b, p. 104, pl. 5.Psammolepis proia: Obruchev and Mark�Kurik, 1965, p. 164,

pl. XXXVI, figs. 1 and 2, pl. XXXVII, figs. 1–3, text�figs. 121–127;Halstead Tarlo, 1965, p. 106, text�fig. 33; Obruchev and Mark�Kurik, 1968, text�figs. 1, 3, and 4; Novitskaya, 2004, p. 183, text�figs. 112 and 113; Elliott and Mark�Kurik, 2005, pp. 101–103,text�fig. 4.


Figs. 1–3. Pycnosteus palaeformis Preobrazhensky, Aruküla Regional Stage: (1) PM SPU, no. 69�4, left branchial plate, Siverskiilocality: (1a, 1b) dorsal and (1c, 1d) ventral sides; (1e) sculptural details marked by framework in 1b; (1f) sculptural details markedby framework in 1d; (2) PM SPU, no. 69�5, left cornual plate, Zaitsevo locality: (2a, 2b) dorsal and (2c, 2d) internal sides;(2e) sculptural details marked by framework in 2b; (3) PM SPU, no. 69�6, left cornual plate, Belogorka locality: (3a, 3b) dorsaland (3c, 3d) internal sides; (3e) sculptural details marked by framework in 3b. Area with sculpture is filled with dark gray; lightgray is area without sculpturing, and hatching is abraded area. Scale bars: (1a, 1c) 2 cm; (2a, 2c, 3a, 3c) 1 cm; and (1e, 1f, 2e, 3e)1 mm.

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Figs. 1 and 2. Psammolepis proia Mark�Kurik, Aruküla Regional Stage: (1) PM SPU, no. 69�8, left orbital plate, Zaitsevo locality:(1a, 1b) dorsal and (1c, 1d) lateral sides; (1e) sculptural details marked by framework in 1b; (2) VZ PC 1–3, ventral plate, Novo�siverskaya locality: (2a, 2b) ventral and (2c, 2d) internal sides; (2e) sculptural details marked by framework in 2b.Fig. 3. Schizosteus (?) sp., Aruküla Regional Stage, Zaitsevo: (3) PM SPU, no. 69�11, right cornual plate: (3a, 3b) dorsal and(3c, 3d) internal sides; (3e) sculptural details marked by framework in 3b. Area with sculpture is filled with dark gray; light gray isarea without sculpturing, and hatching is abraded area. Scale bars: (1a, 1c) 1 cm; (2a, 2c; 3a, 3c) 2 cm; and (1e, 2e, 3e) 1 mm.

H o l o t y p e. GIT, no. 116�165 (Pi 148), Instituteof Geology, Tallinn University of Technology, Tallinn,Estonia; incomplete ventral plate, original of Mark(Obruchev and Mark�Kurik, 1965, text�fig. 121,pl. XXXVI, figs. 1a, 1b); Paul’s collection, 1936; Esto�nia, Tamme on the shore of Lake Võrtsjärv; MiddleDevonian, Aruküla Regional Stage.

D e s c r i p t i o n. The species is characterized byround, asymmetrical, angular, extended tuberclesvarying from 0.1 to 1 mm in diameter. They have from4 to 18 (usually about 10) relatively narrow marginalcusplets. Tubercles are sometimes fused in short or,less frequently, long ridges. The cusplets of tuberclesfrequently vary in length and are continued by ribsreaching its cupola�shaped apex. Because of variationin shape, tubercles are arranged irregularly, but fre�quently densely spaced. The cusplets of neighboringtubercles frequently pass in between each other. Thebranchial and ventral plates are characterized bytubercles varying in size, with the prevalence of verysmall tubercles.

The orbital plate (Pl. 4, fig. 1) is curved, with anoval orbital foramen (5 mm long and 3 mm wide); onthe internal side, there is a depression around the rim,which repeats its shape and is surrounded by a ridgel�ike thickening (7 mm long and 4 mm wide). Theexternal side is covered with tubercles of the averagesize of 0.5 mm, each with 9–14 cusplets. The platecenter has longitudinal canals of the lateral line. At theorbital foramen, the plate is 3 mm thick; closer to theedges, it decreases to 1 mm of thickness.

The ventral plate (Pl. 4, fig. 2) is oval, convex (thebend is 30 mm high). The ventral plate side in the mostprojecting regions shows traces of lifetime wear. Thecentral and distal parts of the plate are covered withtetra–heptagonal tesserae. Among large tesserae(up to 10 mm), there are smaller ones (5 mm). Themargins of tesserae form an angular border of thesculptured area. The area without sculpture is up to10 mm wide, borders the plate. Tubercles are small(from 0.3 to 0.5 mm), round, asymmetrical orextended; there are usually about 10–14 short andnarrow marginal cusplets. The cusplets of neighboringtubercles frequently pass in between each other.Tubercles are sometimes fused into long ridges. On thevisceral surface, some aspidin tubercles have openingsof vascular canals; they are particularly abundant in

the region of an early growth stage of the plate. Theplate is 7 mm thick and 15 cm wide.

C o m p a r i s o n. In the shape and size of dentinetubercles, Psammolepis proia is somewhat similar toP. abavica Mark�Kurik and differs from it in the cha�otically arranged tubercles; in P. abavica, tuberclesform a regular herringbone pattern. P. abavica differsfrom P. paradoxa Agassiz, P. alata Mark�Kurik, andP. undulata (Agassiz) in the more diverse irregularshape of tubercles and their size. In P. proia, tuberclesare less frequently fused in extended ridges or rowsthan in P. heteraster Gross. In the round tubercles,P. proia sharply differs from P. venyukovi Obruchev,P. arctica (Kiaer), and P. granulata (McCoy), inwhich they are pyramidal. It differ from P. groenlan�dica Tarlo in the smaller tubercles and the ribs almostreaching its apex. The orbital plates of P. proia haverare longitudinal canals of the lateral line, which arecharacteristic of all known orbital plates of the genusPsammolepis (Obruchev and Mark�Kurik, 1965;Elliott and Mark�Kurik, 2005). The shape of ventralplates resembles P. abavica and P. paradoxa. However,in P. proia, the entire anterior part of the plate shaperepeats the outline of the juvenile growth stage of thesame plate; it has a deep notch, while in P. abavica andP. paradoxa, the same outlines are relatively smaller,with a shorter notch, and covered on sides withtesserae. The tesserae of the ventral plate of Psammo�lepis proia are transversely extended, as in P. abavicaand P. alata. The species in question differs from ven�tral plates of P. alata and P. undulata in the smallerarea with tesserae (Obruchev and Mark�Kurik, 1965;Lyarskaya, 1971).

R e m a r k s. The sculpture of the ventral plate isclose to that of the central part of the same plate ofTartuosteus giganteus (Gross). Psammolepis proia dif�fers in the chaotic arrangement of tubercles with betterdeveloped cusplets and ridges. The morphology of theventral plate suggests the following growth model: atthe juvenile stage, the plate was round, with a wide anddeep posterior incisure, which is overgrown in thecourse of maturation, becomes oval in shape and cov�ered with tesserae (Obruchev and Mark�Kurik, 1965).It seems correct that, as Obruchev and Mark�Kurik(1965) proposed, the incisure is absent in adultP. proia, since the growth center is located in the ante�rior part of the plate and the entire worn area corre�sponding to the juvenile growth stage of the plate isseparated from the posterior margin by a large field



Plate 4

1e

1a 1b

1c 1d

2e

2a2b

2c 2d

3a 3c

3b 3d3e

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1e

Plate 5

1f

2e

2d

1a 1b

1c 1d

2a

2b

2c

2d



with tesserae. The presence of a large field of tesseraein the posterior part of the ventral plate distinguishesP. proia from T. giganteus, in adults of which this platehas a few tesserae and a relatively deep incisure.

M a t e r i a l. A left orbital plate fragment(PM SPU, no. 69�8), Zaitsevo locality; ventral plate(VZ PC 1�3), Novosiverskaya locality.

O c c u r r e n c e. Middle Devonian, GivetianStage, Aruküla Regional Stage, Pycnosteus palaeformisand Pycnosteus pauli zones in Latvia, Estonia (Mark�Kurik, 2000), and the Leningrad and Pskov regions,Russia.

Family Guerichosteidae Tarlo, 1964

Genus Schizosteus Obruchev, 1940Schizosteus (?) sp.

Plate 4, fig. 3; Plate 5, fig. 1

D e s c r i p t i o n. Schizosteus (?) sp. has round, lessfrequently, rhombic or extended dentine tubercles,ranging from 0.1 to 1 mm (usually 0.3–0.5 mm),which have from 4 to 13 (often 6–9) well�pronouncedpointed marginal cusplets varying in length, rarelybifurcating at the end, and passing into ridges. Tuber�cles have a pointed apex, which is usually worn duringthe animal’s life by the bottom sediments and onlyrarely preserved. Tubercles are usually densely spacedand regularly arranged due to the rounded stellarshape. The cusplets of neighboring tubercles fre�quently pass in between each other.

The branchial plate (Pl. 5, fig. 1) is long and narrow.The anterolateral margin is curved. The posterior mar�gin is straight; a gentle projection is formed in its prox�imal part. The external angle is 90°; the distal end ofthe plate is worn and rounded. The medial margin isbent. At the anterolateral margin, the plate is 2 mmthick, increasing to 4 mm of thickness towards thecenter. The plate is convex (the bend is 18 mm high).The sculptured area on the dorsal side is smaller thanthe area without sculpturing. The boundary betweenthe areas is curved, turns medially near the posteriormargin. The boundary comes to the proximal part ofthe posterior margin at an angle of 40°. Two types ofgrowth lines are observed on both sides of the plate;some pass in parallel to the boundary of the sculpturedareas, while others extend at an angle from the antero�lateral plate margin. The boundary of sculptured areasis separated by a low 3�mm�deep depression. On theventral side, the area without ornament borders the

medial margin of the plate, its maximum width is28 mm. Tubercles of the branchial plate are rounded,varying in shape, densely spaced, with distinct mar�ginal cusplets varying in length and large ridges; in rel�atively small tubercles, the cusplets rarely bifurcate atthe end. The tubercles are small; on the dorsal side,they range from 0.1 to 0.5 mm. Tubercles are some�times chaotically arranged; some are extended andrhomboid; very rarely, short incompletely fused ridgesare formed. On the ventral side, tubercles decrease indiameter from the anterolateral to medial margin(from 1 to 0.08 mm); they are arranged regularly,round tubercles prevail. The apices of tubercles areusually worn. The plate is 28.5 cm long and presum�ably 22 cm wide.

The cornual plate (Pl. 4, fig. 3) is probably isomet�ric, longitudinally convex (the bend is 2 mm high).The posterior margin is partially curved, forming aparallel ridgelike thickening in the internal region.The lateral, medial, and anterior margins are not pre�served. The growth center is located at the posteriorplate margin, displaced somewhat towards the lateralmargin. Radial and concentric growth lines divergefrom it. Tubercles are round, dome�shaped, rarely,somewhat polygonal and extended. They vary in sizefrom 0.1 to 1 mm, reaching the greatest size at the pos�terior plate margin. Tubercles usually have 6–9 dis�tinct marginal cusplets and are densely and rather reg�ularly arranged. The internal region of the plate has aconcavity in the medial part. At the posterior margin,the plate is 3 mm thick, decreasing to 2 mm towardsthe anterior margin. The plate is presumably 9 cm longand 9 cm wide.

R e m a r k s. In the round cupola�shaped tuber�cles, which are sometimes regularly arranged, Schizos�teus (?) sp. is similar to S. asatkini Obruchev. However,tubercles of Sch. asatkini have a greater number ofmarginal cusplets, from 9 to 15 (usually 10–13). InS. asatkini, tubercles range from 0.1 to 0.7 mm indiameter; in Schizosteus (?) sp., they reach 1 mm.Tubercles of S. asatkini in general retain their shapeand size, while in Schizosteus (?) sp., tubercles arenonuniform in size; in particular, on the branchialplates, they decrease in size medially (from 0.2 to0.08 mm in diameter) and have widely spaced cusplets(usually 4 or 5). The shape of branchial plates ofSchizosteus (?) sp. resembles that of S. striatus (Gross)(Obruchev and Mark�Kurik, 1965, text�fig. 33).S. asatkini was described based on the material


Fig. 1. Schizosteus (?) sp., Aruküla Regional Stage, Zaitsevo locality: (1) PM SPU, no. 69�10, right branchial plate: (1a, 1b) dorsaland (1c, 1d) ventral sides; (1e) sculptural details marked by framework in 1b; (1f) sculptural details marked by framework in 1d.Fig. 2. Tartuosteus giganteus (Gross), Aruküla Regional Stage, Siverskii locality: (2) PM SPU, no. 69�9, left branchial plate:(2a, 2b) dorsal and (2c, 2d) ventral sides; (2e) sculptural details marked by framework in 2b; (2f) sculptural details marked byframework in 2d. Area with sculpture is filled with dark gray; light gray is area without sculpturing, and hatching is abraded area.Scale bars: (1a, 1c, 2a, 2c) 2 cm and (1e, 1f, 2e, 2f) 1 mm.

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belonging to a small psammosteid form, possibly ajuvenile (Obruchev and Mark�Kurik, 1965); Schizos�teus (?) sp. shows large dimensions of exoskeletalplates.

Schizosteus (?) sp. resembles in the shape of bran�chial plates S. striatus (Gross) (Obruchev and Mark�Kurik, 1965, text�fig. 33) and differs from it in theshape of tubercles, which are not fused into longridges, in the absence of papillary and hat�shapedforms, and in the relatively larger cusplets and ridges.Schizosteus (?) sp. differs from S. heterolepis (Preo�brazhensky) in the more densely spaced tubercles,their size, the longer pointed cusplets of tubercles, thefewer cusplets, and in the relatively more massiveridges. It differs from S. perneri (Rü i ka) in the widerbranchial plates and the less regular arrangement oftubercles on the dorsal side of the branchial plate. Itdiffers from S. wellsi Tarlo in the presence of distinctcusplets on tubercles.

Schizosteus (?) sp. differs from Psammolepis proiaMark�Kurik in the more widely spaced cusplets ontubercles, the rounded stellar tubercles which aremore regularly arranged; on the dorsal side of thebranchial plate of Schizosteus (?) sp., pairs of tuberclesare very rarely fused to form something like ridges,which are distinguished from tubercles fused intoridges in P. proia.

Future finds of Schizosteus (?) sp., particularly itscentral plates, will add to the characteristics of thetaxon and better understanding of its taxonomic posi�tion among psammosteids.

M a t e r i a l. Right branchial plate (PM SPU,no. 69�10), Zaitsevo locality; fragment of right cor�nual plate (PM SPU, no. 69�11), Zaitsevo locality.

O c c u r r e n c e. Middle Devonian, GivetianStage, Aruküla Regional Stage, Pycnosteus palaeformisZone in Russia (Leningrad Region).

CONCLUSIONS

New finds in the Leningrad Region essentiallyexpand the previous descriptions and specify the shapeof some plates based on better preserved specimens.The psammosteid Schizosteus (?) sp. described in opennomenclature because of the absence of well�pre�served central plates has only been found in a fewlocalities (Zaitsevo, Siverskii, and Belogorka).

Pycnosteus palaeformis is represented by an almost complete set of the main exoskeletal plates. The shape of postorbital plates makes P. palaeformis similar to the ancient genera Drepanaspis and Schizosteus and distinguishes it from Tartuosteus and Psammolepis. From the eastern Main Devonian Field, the psam� mosteid Psammolepis proia is described for the first time. Although fragments are rather frequent, only a few plates of this species have been found. Tartuosteus giganteus is only represented by worn and fragmentary

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branchial plates; the new material shows the uniqueshape of branchial plates of this species.

In the diagnosis of the species Schizosteus (?) sp.,Tartuosteus giganteus, and Psammolepis proia and, to alesser extent, Pycnosteus palaeformis, the topographi�cal variation of tubercles is used, enabling the determi�nation of species based on small exoskeletal fragmentsof psammosteids.

ACKNOWLEDGMENTS

I am grateful to A.O. Averianov (Zoological Insti�tute, Russian Academy of Sciences), A.O. Ivanov,P.P. Skutschas, G.O. Cherepanov (St. Petersburg StateUniversity), and private collector M.Yu. Kuleshov forthe material transferred to me for studying. I am alsothankful to A.O. Ivanov and E.J. Mark�Kurik (Insti�tute of Geology, Tallinn University of Technology) forvaluable discussions and help with the literature.

REFERENCES

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Translated by G. Rautian

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New records of psammosteids from the Aruküla Regional Stage (Middle Devonian) of the Leningrad...

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Transcript of New records of psammosteids from the Aruküla Regional Stage (Middle Devonian) of the Leningrad...