Polskaakademianauk Instytutpaleobiologii

POLSKA AKADEMIA NAUK INSTYTUT PALEOBIOLOGII im. Romana Kozłowskiego

SILURIAN AND DEVONIAN HETEROSTRACI FROM POLAND

AND HYDRODYNAMIC PERFORMANCE OF PSAMMOSTEIDS

Sylurskie i dewońskie Heterostraci z Polski

oraz efektywność hydrodynamiczna psammosteidów

Marek Dec

Dissertation for degree of doctor of Earth and related environmental sciences, presented at the Institute of Paleobiology of Polish Academy of Sciences

Rozprawa doktorska wykonana w Instytucie Paleobiologii Polskiej Akademii Nauk pod kierunkiem prof. dr hab. Magdaleny Borsuk-Białynickiej w celu uzyskania stopnia doktora w dyscyplinie Nauki o Ziemi oraz środowisku

Warszawa 2020 CONTENTS

ACKNOWLEDGMENTS…………………………………………………………….….... 3

STRESZCZENIE………………………………………………………………….....….. 4

SUMMARY……………………………………………………………………….…….. 8

CHAPTER I…………………………………………………………………………….. 13

TRAQUAIRASPIDIDAE AND CYATHASPIDIDAE (HETEROSTRACI) FROM LOWER

DEVONIAN OF POLAND

CHAPTER II……………………………………………………………………….…… 24

A NEW TOLYPELEPIDID (AGNATHA, HETEROSTRACI) FROM THE LATE SILURIAN OF

POLAND

CHAPTER III…………………………………………………………………………... 41

REVISION OF THE EARLY DEVONIAN PSAMMOSTEIDS FROM THE “PLACODERM

SANDSTONE” - IMPLICATIONS FOR THEIR BODY SHAPE RECONSTRUCTION

CHAPTER IV……………………………………………………………………….….. 82

NEW MIDDLE DEVONIAN (GIVETIAN) PSAMMOSTEID FROM HOLY CROSS

MOUNTAINS (POLAND)

CHAPTER V……………………………………………………………………………109

HYDRODYNAMIC PERFORMANCE OF PSAMMOSTEIDS: NEW INSIGHTS FROM

COMPUTATIONAL FLUID DYNAMICS SIMULATIONS

ACKNOWLEDGMENTS

First and foremost I would like to say thank you to my supervisor Magdalena Borsuk-Białynicka who supported me throughout my time as a PhD student and served with good advice.

I would like to thank Piotr Szrek and Grzegorz Niedźwiedzki for cooperation and all support. My time during field trips would not have been half as enjoyable or fun without them.

I thank employees of Institute of Paleobiology PAS, especially Marian Dziewiński for photographic work, Jolanta Kobylińska and Piotr Gryz for their help during studying collections in their care.

I thank to Przemysław Gorzelak and Sebastian Tasakowski for support with linguistic correction of the manuscript. To all my wonderful family and friends who have supported me, encouraged me, and believed in me.

SYLURSKIE I DEWOŃSKIE HETEROSTRACI Z POLSKI ORAZ EFEKTYWNOŚĆ HYDRODYNAMICZNA PSAMMOSTEIDÓW

STRESZCZENIE Heterostraci były dużą i zróżnicowaną grupą ryb bezszczękowych, która występowała od wczesnego syluru do dewonu (Janvier 1996). Główną cechą wyróżniającą tę grupę była para pojedynczych otworów skrzelowych (Janvier 1996). Ich podłużne i wrzecionowate ciało było pokryte łuskami. Przednia część ciała pokryta była dwiema dużymi tarczami (grzbietową i brzuszną), pomiędzy którymi znajdowały się jedna lub kilka tarcz skrzelowych (Janvier 1996). Pancerz skórny heterostraków zbudowany był z trzech warstw: laminowanej warstwy bazalnej, środkowej, przypominającej plaster miodu, warstwy kości beleczkowej oraz warstwy powierzchniowej, w której znajdowały się kanały linii bocznej. Powierzchniową warstwę pokrywały dentynowe grzbiety lub guzki pokryte enameloidem (Janvier 1996, Keating et al. 2015, Keating and Donoghue 2016). Najstarszym znanym przedstawicielem Heterostraci jest Athenaegis chattertoni opisany z dolnosylurskich (wenlok) utworów Gór Mackenzie w Kanadzie (Soehn and Wilson 1990) Athenaegis ma wiele cech (m.in. pojedyncza tarcza grzbietowa i brzuszna czy ornamentacja składająca się z jednostek przypominających łuski) łączących go z jedną z dwóch głównych grup heterostaków, a mianowicie z cyathaspidiformami. Dlatego pierwotnie Athenaegis włączony był do najbardziej przypominających je tolypelepidów. Jednak, jak stwierdził Janvier (1996), u Atheanegis nie stwierdzono obecności pojedynczego otworu skrzelowego, wyróżniającego Heterostaci i prawdopodobnie rodzaj ten powinien zostać z tej grupy wykluczony. Natomiast do momentu lepszego rozpoznania systemu skrzelowego u Athenaegis uważany jest za takson siostrzany do tzw. wyższych Heterostraci (senesu Janvier 1996), z którymi łączy go pojedyncza tarcza grzbietowa oraz łuski w kształcie rombu (Janvier 1996).

Przedstawiciele Heterostraci są słabo rozpoznaną grupą na obszarze Polski. Jedyne opisy ich przedstawicieli przedstawił Tarlo (1957, 1961, 1964, 1965) w latach sześćdziesiątych. Bogaty materiał z emskich piaskowców występujących w Górach Świętokrzyskich na Górze Podłazie niedaleko Daleszyc zawierał szczątki pteraspidiformów, Rhinopteraspis sanctacrucensis (Tarlo 1961) i psammosteidów

4 z rodzaju Guerichosteus i Hariosteus (Tarlo 1964, 1965). Od tamtego czasu z Polski nie opisano nowych przedstawicieli heterostraków. Jednym z nowo opisanych przedstawicieli tej grupy z terenu Polski jest Toombsaspis (Rozdział 1), którego tarcza brzuszna została znaleziona w utworach wczesnego dewonu wiercenia Białopole-IG1. Przedstawiciele rodziny Traquairaspididae (sensu Randle 2017), do której należy Toombsaspis, mają pojedynczy otwór skrzelowy, podobnie jak u heterostraków. Otwór ten znajduje się w tarczy skrzelowej, a nie pomiędzy tarczą grzbietową i skrzelową, jak to ma miejsce u heterostraków. Dlatego relacje tej grupy w obrębie Hetrostaci są niejasne (Obruchev 1967, Janvier 1996, Randle and Sansom 2017a), natomiast obecnie Traquairaspididae są umiejscowione poza tzw. wyższymi heterostakami.

Wyższe Heterostraci (sensu Janvier 1996) reprezentowane są przez dwie monofiletyczne grupy, Cyathaspidiformes i Pteraspidiformes (Janvier 1996, Randle 2017). Cyathaspidiformy, występują od środkowego syluru do dolnego dewonu. Ich pancerz złożony jest z pojedynczej tarczy grzbietowej i tarczy brzusznej rozdzielonej przez pojedynczą tarczę skrzelową. Układ kanałów linii bocznej składa się z dwóch par podłużnych kanałów i co najmniej trzech poprzecznych, a kanały nadoczodołowe nie łączą się ze sobą. Zębinowe grzbiety pokrywające tarczę grzbietową są rozmieszczone wzdłużnie, a ich krawędź ma płytkie zaokrąglone wcięcia. Powyższe cechy zidentyfikowano w okazach pochodzących z wykonanego w Mielniku otworze Mielnik IG-1, który przewiercił późnosylurską (pridol) sukcesję reprezentującą platformę węglanową strefy nerytycznej. Okazy te reprezentują nowy gatunek bezszczękowca z rodziny Tolypelepididae, Tolypelepis mielnikensis (Rozdział 2). Tarcza grzbietowa tego gatunku dzieli się na epitega, podobnie jak u innych przedstawicieli rodziny Tolypelepididae. Ornamentacja tarcz tolypelepididów składa się z dentynowych grzbietów ułożonych w jednostki przypominające łuski, gdzie centralny grzbiet jest szerszy i wyższy od okalających go węższych i niższych grzbietów, co znacząco odróżnia je od cyataspidiformów, których tarcze pokryte są podłużnymi dentynowymi grzbietami, ułożonymi mniej lub bardziej równolegle względem siebie. Występujący u tolypelepidów typ ornamentacji jest obecnie uważany za prymitywny, dlatego umiejscowiono tę grupę jako bazalną w obrębie cyathaspidiformów (Janvier, 1996).

Kolejny przedstawiciel cyathaspidiformów został znaleziony w utworach wczesnego dewonu wiercenia Ciepielów-IG1. Materiał ten zawierał fragment tarczy grzbietowej z widocznymi odciskami struktur wewnętrznych i został zaliczony do rodzaju

Paraliliaspis (Rozdział 1). Rodzaj ten należy do rodziny Cyathaspididae i jest blisko spokrewniony z Liliaspis. Opisany materiał uzupełnia informacje dotyczącą szerszego paleogeograficznego rozprzestrzenienia Paraliliaspis, które odpowiada zasięgowi Anglaspis (Denison, 1964; Ilyes et al., 1995), uważanego za przodka Paraliliaspis i Liliaspis.

Pteraspidiformes, druga główna grupa heterstraków, na terenie Polski reprezentowana jest głównie przez psammosteidy. Przynależność rodziny Psammosteidae do pteraspidiformów jest powszechnie uznana (Blieck et al. 1991, Janvier 1996, Pernegre 2002, Pernegre and Elliott 2008, Randle and Sansom 2017, Glinsky 2017), natomiast najwięcej wątpliwości dotyczy ich stosunków filogenetcznych w obrębie pteraspidiformów.

Przedstawiciele psammosteidów (Guerichosteus i Hariosteus) z Gór Świętokrzyskich zostali opisani przez Tarlo (1964, 1965). Bogaty materiał pochodził z tzw. piaskowców plakodermowych, które występują na Górze Podłazie koło Daleszyc. Ponowna analiza wcześniej opisanych okazów oraz nowy materiał dostarczyły dodatkowych danych anatomicznych na temat psammosteidów (Rozdział 3). Morfologia i ornamentacja tarcz potwierdzają ustanowione wcześniej rodzaje Guerichosteus i Hariosteus. Natomiast G. kotanskii, G. kulczyckii i G. lefeldi uznane zostały (Dec 2019) jako młodsze synonimy Guerichosteus kozlowskii. Ustanowiony przez Tarlo (1964) Hariosteus lobanowskii, uważa się za wątpliwy (nomen dubium), a H. kotanskii został włączony do Hariosteus kielanae. Trójwymiarowe skanowanie tarcz Guerichosteus pozwoliło się uzyskać dokładniejsze opisy oraz wykonać rekonstrukcję ciała. Głęboka tarcza brzuszna w przekroju poprzecznym jest bardziej V-kształtna, a nie U-kszałtna, jak wcześniej przedstawiano. Wczesnodewoński psammosteid Drepanaspis gemuendenensis miał zapewne podobnie wykształconą tarczę brzuszną.

Nowe dane dotyczące psammosteidów z obszaru Gór Świętokrzyskich przyniosły materiały pozyskane z utworów środkowego dewonu (żywetu) z odsłonięcia położonego niedaleko miejscowości Śniadka. Analiza materiału, w szczególności obserwacje dotyczące morfologii tarcz (zwężona przednia część tarczy grzbietowej oraz długa i wąska tarcza zaoczodołowa) oraz ich ornamentacji pozwoliły na ustanowienie nowego rodzaju i gatunku Psarkosteus mediocris (Rozdział 4).

Kształt pancerza chroniącego ciało paleozoicznych bezszczękowców, takich jak

Heterostraci, odgrywa ważną rolę hydrodynamiczną w generowaniu siły nośnej lub siły oporu. Z pomocą obliczeniowej mechaniki płynów (ang. Computational Fluid Dynamics, CFD) obliczono hydrodydynamiczną siłę wznoszenia/oporu oraz współczynik wznoszenia/oporu dla dwóch psammosteidów Guerichosteus i Tartuosteus oraz jednego pteraspida Errivaspis (Rozdział 5). Wyniki symulacji pokazują znacznie wyższe wartości współczynnika siły nośnej i doskonałości aerodynamicznej (ang. lift-to-drag ratio) dla psammosteidów Guerichosteus i Tartuosteus niż dla Errivaspis. Wyniki tych badań wskazują, że w trakcie ewolucji pancerza psammosteidów gdzie tarcze skrzelowe uległy poszerzaniu, zwiększała się wytwarzana siła zapewniając im bardziej efektywne pływanie.

Literatura (patrz str. 11–12)

SILURIAN AND DEVONIAN HETEROSTRACI (AGNATHA) FROM POLAND AND HYDRODYNAMIC PERFORMANCE OF PSAMMOSTEIDS

SUMMARY

The Heterostraci are a large and diverse group of so-called ostracoderms (Keating et al. 2015, Randle and Sansom 2017) occurring from the Early Silurian to the Devonian (Janvier 1996). Their fusiform body was covered with scales, two large shields around the head (dorsal and ventral), between which different numbers of branchial plates occured (Janvier 1996). Heterostacans exoskeleton is composed of a basal laminar layer, a middle cancellar layer with honeycomb-shaped cavities, and an superficial layer of dentine ridges or tubercles covered with enameloid (Janvier 1996, Keating et al. 2015, Keating and Donoghue, 2016). The most recognizable character of the Heterostraci is a pair of single branchial openings (Janvier 1996). The earliest known representative is Athenaegis chattertoni described from the Lower Silurian (Wenlock) sediments of Canada (Mackenzie Mountains) (Soehn and Wilson 1990). Athenaegis resembles the cyathaspidiforms in having the dorsal and ventral plates made up of a single unit each and ornamentation consists of scales-like units, and originally was included in the most similar tolypelepids. However, as Janvier (1996) stated Atheanegis, with three rows of branchial plates, shows no evidence of a common branchial opening (Soehn and Wilson 1991, suggest that the branchial opening was placed posterior to most or all of the branchial scales and platelets), and should be exlcluded from the Heterostaci.

However, until the unique branchial system of Athenaegis is better understood, which supports its exclusion from the “higher Heterostraci”. Athenaegis is currently considered a possible sister taxon of the “higher Heterostraci”, because it shares their single dorsal shield and the diamond-shaped flank scales of higher Heterostraci (Janvier 1996). Heterostraci fauna is poorly known from Poland. Since last Tarlo’s (1964 1965) description of agnathans from the Lower Devonian deposits in the Holly Cross Mountains, containing the remains of pteraspidiforms, Rhinopteraspis sanctacrucensis (Tarlo 1961) and psammosteids Guerichosteus and Hariosteus (Tarlo 1964, 1965), no new one has been described.

The drill cores from Poland have yielded new agnathan material. In the Białopole-IG1 drilling core passing through early Devonian deposits one ventral disc of Toombsaspis (Chapter 1) was found belonging to the Traquairaspididae sensu Randle (2017). This family is considered to represent Heterostraci, by having a single pair of branchial openings, but the relations within heterostracans are unclear (Obruchev 1967, Janvier 1996, Randle and Sansom 2017). In Traquairaspididae the common branchial opening pierces the branchial plate (Tarrant 1991), so they are placed outside the ‘higher heterostraci’ in which the branchial opening is delimited by various plates (Janvier 1996). Higher Heterostraci sensu Janvier (1996) are represented by two monophyletic groups, Cyathaspidiformes and Pteraspidiformes (Janvier 1996, Randle 2017). Their armor is composed of single dorsal and ventral median plate, separated by one branchial plate on each side. The sensory canal system of the dorsal shield consists of two pairs of longitudinal canals and at least three transverse commissures, perpendicular to the longitudinal ones. The supraorbital canals do not join each other. The dentine ridges of the superficial layer of the dorsal shield are mainly longitudinally arranged, each ridge having an unornamented central part and finely crenulated edges. Such features were identified in specimens found in Mielnik IG-1 drill core, which contained the Late Silurian (Přidoli) succession representing periplatform setting on a neritic carbonate platform. Two specimens are included into Tolypelepididae (new species of Tolypelepis, Tolypelepis meilnikensis)(Chapter 2) virtue of the dorsal shield divided into epitega, and ornamentation of short dentine ridges grouped into scale-like units with a coarser, higher median ridge encircled by narrower and lower ridges. The latter feature significantly differentiate the family from the cyathaspidiforms, in which shields are covered with longitudinal and more or less parallel ridges. The type of Tolypelepididae ornamentation, suggestive of many separate growth centers, is currently considered primitive, the group is located as a basal group within Cyathaspidiformes.

Another representative of the cyathaspidiforms was found in the bore core of the Ciepielów-IG1 drilling. The material contained fragment of dorsal disc with the impressions of internal structures and belong to the genus Paraliliaspis (Chapter 1). This genus represents the Cyathaspididae family, and it is closely related to Liliaspis. The material from the bore core extends the information regarding the wider paleogeographic range of the genus, and corresponds to the distribution of Anglaspis

(Denison 1964, Ilyes et al. 1995), which is considered as the ancestor of Paraliliaspis and Liliaspis.

Pteraspidiformes is the second major group of the heterostracans in Poland it is mostly represented by psammosteids. Psammostidae are generally regarded as monophyletic and their pteraspidiformes affinity is well accepted (Blieck et al. 1991, Janvier 1996, Pernegre 2002, Pernegre and Elliott 2008, Randle and Sansom 2017, Glinsky 2018). Most questions concern their position within a Pteraspidiformes.

Tarlo (1964, 1965) described two new psammosteid genera; Guerichosteus (four species included) and Hariosteus (three species included). The fossils were collected at Podłazie Hill located about 2 km to the north of the Daleszyce, in the southern part of the Holy Cross Mountains. The material from quartzitic sandstone bone-beds (called “Placoderm sandstone”) consists of natural molds of dissolved fish remains. New material obtained allows for a revision of the psammosteids formerly described by Tarlo (Chapter 3). The analysis of ornamentation and plate morphology supports the establishment of Guerichosteus (one species G. kozlowskii) and Hariosteus (one species Hariosteus kielanae). The three-dimensional scanning of plates of Guerichosteus allows for a more detailed description and reconstruction of Guerichosteus. In cross section the deep ventral part of the trunk is V-shaped in contrast to previous U-shaped restorations. Probably, the Early Devonian psammosteids, Drepanaspis gemuendenensis in particular, shared this body shape.

New information regarding psammosteids provide material obtained from Middle Devonian (Givetian) limestone, marly and clayey shales representing the upper part of Skały Formation of Świętomarz-Śniadka section near Śniadka. A set of features present in psammosteid plates, in particular the shape of the plates (dorsal plate with constricted anterior part and very long and narrow postorbital plate) and the variability of ornamentation, has been considered sufficient for the erection of a new genus and species Psarkosteus mediocris (Chapter 4). The lateral line system in Psarkosteus is developed similar to that of Drepanaspis gemuendenensis and corresponds to earlier reconstructions proposed by Gross (1963).

The shape of dermal armor protecting the body in the Paleozoic agnathans including Heterostaci has an important hydrodynamic role in providing lift or drag force generation. By using computational fluid dynamics simulations (CFD) the hydrodynamic lift or drag

10 force and coefficient were calculated for two psammosteids Guerichosteus and Tartuosteus with reference to the pteraspid Errivaspis (Chapter 5). The measurements from simulation show substantially higher values of the lift coefficient and lif-to-drag ratio for the psammosteids Guerichosteus and Tartuosteus compared with Errivaspis. The widening of branchial plates during the evolution of dermal exoskeleton of psammosteids, was directed towards the increase of the lift force generation to provide efficient cruising, and suggest advantages in more effective acquisition of widely distributed food or for predator escape.

REFERENCES

BLIECK, A., D.K. ELLIOTT, AND P.Y. GAGNIER. 1991. Some questions concerning the phylogenetic relationships of heterostracans, Ordovician to Devonian jawless vertebrates; pp. 1–17 in M.M. Chang, Y.H. Liu, and G.R. Zhang (eds.), Early Vertebrates and Related Problems of Evolutionary Biology. Science Press, Beijing, China.

DENISON, R.H. 1964. The Cyathaspididae, a family of Silurian and Devonian jawless vertebrates. Fieldiana Geology 13: 311-473.

ILYES, R.R., OHTA, Y. AND GUDDINGSMO, J. 1995. The Downtonian and Devonian Vertebrates of Spitsbergen. XV. New Heterostracans from the Lower Devonian Red Bay Group, Northern Spitsbergen”. Polar Research 14, nr 1 (czerwiec 1995): 33–42. https://doi.org/10.1111/j.1751-8369.1995.tb00708.x.

GLINSKIY, V. 2018. Phylogenetic relationships of psammosteid heterostracans (Pteraspidiformes), Devonian jawless vertebrates. Biological Communications, 62:219–243. https://doi:10.21638/11701/spbu03.2017.402.

GROSS, W. 1963. Drepanaspis gemuendenensis Schlüter, Neuuntersuchung. Palaeonogreaphica, 121A:133-155, Stuttgart.

JANVIER, P. 1996. Early Vertebrates. Oxford, Oxford Science Publications, Clarendon Press.

KEATING, J.N., MARQUART, C.L. & DONOGHUE, P.C.J. 2015. Histology of the heterostracan dermal skeleton: Insight into the origin of the vertebrate mineralised

skeleton. Journal of Morphology, 276: 657-680.

KEATING, J.N. AND DONOGHUE, P.C.J 2016. Histology and affinity of anaspids, and the early evolution of the vertebrate dermal skeleton. Proceedings of the Royal Society B: Biological Sciences, 283: 1–10.

OBRUCHEV, D. 1967. On the evolution of the Heterostraci. Problemes actuels de Paleontologie, 163: 37–43.

PERNÈGRE, V.N. AND ELLIOTT, D.K. 2008. Phylogeny of the Pteraspidiformes (Heterostraci), Silurian-Devonian jawless vertebrates. Zoologica Scripta, 37:391- 403. https://doi.org/10.1111/j.1463-6409.2008.00333.x

PERNÈGRE, V.N. (2002) The genus Doryaspis White (Heterostraci) from the Lower Devonian of Vestspitsbergen, Svalbard. Journal of Vertebrate Paleontology, 22: 735–746.

RANDLE 2017, PhD thesis. Heterostraci systematics, phylogenetics and macroevolution: investigating evolutionary patterns of extinct jawless vertebrates.

RANDLE, E. AND SANSOM, R.S. 2017. Phylogenetic Relationships of the ‘Higher Heterostracans’ (Heterostraci: Pteraspidiformes and Cyathaspididae), Extinct Jawless Vertebrates”. Zoological Journal of the Linnean Society, 181(4): 910–26. https://doi.org/10.1093/zoolinnean/zlx025.

SOEHN, K.L., AND M.H.V. WILSON. 1990. A complete, articulated heterostracan from Wenlockian (Silurian) beds of the Delorme Group, Mackenzie Mountains, Northwest Territories, Canada. Journal of Vertebrate Paleontology 10: 405–419.

TARLO, L.B. 1957. A preliminary note on new ostracoderms from the Lower Devonian (Emsian) of central Poland. Acta Palaeontologica Polonica, 2: 225-233.

TARLO, L.B. 1961. Psammosteids from the Middle and Upper Devonian of Scotland. The Quarterly Journal of the Geological Society of London, 117:367-402.

TARLO, L.B. 1964.Psammosteiformes (Agnatha) – a review with descriptions of new material from the Lower Devonian of Poland. I - general part. Palaeontologia Polonica, 13:1-135.

TARLO, L.B. 1965. Psammosteiformes (Agnatha) – a review with descriptions of new material from the Lower Devonian of Poland. II - systematic part. Palaeontologia Polonica, 15:1-168.

CHAPTER I

TRAQUARIASPIDIDAE AND CYATHASPIDIDAE (HETEROSTRACI) FROM 1 LOWER DEVONIAN OF POLAND

MAREK DEC

Institute of Palaeobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland.

ABSTRACT Lower Devonian strata from the drill cores from Poland have yielded new Heterostraci material. One ventral shield of Toombsaspis (Traquairaspididae, Phialaspidinae) discovered in the Białopole IG-1 drill core, and a fragment of dorsal shield of cf. Paraliliaspis (Cyathaspididae, Anglaspidinae) with the impressions of internal structures from Ciepielów IG-1 are described and provide new information on paleogeographic disparity of these groups

INTRODUCTION The Heterostraci fossil record is poor in Poland, athough fossils are known from drill core samples and from the Holly Cross Mountains Devonian deposits. The Late Silurian (Přidoli) succession from a core sample of Mielnik (Eastern Poland) has yielded Tolypelepis mielnikensis (Dec 2015), recently considered as a subjective junior synonym of Tolypelepis undulata (Märss 2019). A rich vertebrate assemblage from Emsian sandstone deposits in the Holy Cross Mountains (Podłazie Hill and Bukowa Hill) comprises pteraspidiforms with Rhinopteraspis sanctacrucensis (Blieck 1980, Tarlo 1961) and psammosteids with Guerichosteus kozlowski and Hariosteus kielanae (Tarlo 1964, 1965, Dec 2019). Herein, a find of a traquairaspidid (Toombsaspis sp.) and that of a cyathaspidid (cf. Paraliliaspis sp.) are described from drill cores from eastern Poland containing Lower Devonian sediments.

The agnathan fossil record from the Late Silurian to the Lower Devonian deposits of Poland, provides new information on paleogeographic distribution and possible migrations of agnathans at this time.

1 In press in Annales de Paléontologie (available online 19 December 2019)

PHYLOGENETIC BACKGROUND The Traquairaspididae sensu Randle (2017) is considered to represent Heterostraci, by having a single pair of branchial openings (Janvier 1996). However, their exact relationship remain ambiguous (Obruchev 1967, Janvier 1996, Randle and Sansom 2017a). The common branchial opening pierces the branchial plate (Tarrant 1991), so the group is placed outside the ‘higher heterostraci’ in which the branchial opening is bordered by various plates, instead of piercing one (Janvier 1996). One specimen described herein (ZPAL Ag. IV/1) has been assigned to Toombsaspis sp. within the Traquairaspididae.

The second specimen (ZPAL Ag. IV/2), assigned to cf. Paraliliaspis sp. belongs to Cyathaspidiformes, which together with Pteraspidiformes are grouped in ‘higher hetrostraci’ (Janvier 1996). Cyathaspidiformes are represented by large variety of forms found from the Middle Silurian to Lower Devonian and characterized by an ornamentation of longitudinal dentine ridges with finely crenulated margins (Janvier 1996). The interrelationships within the Cyathaspidiformes have been studied by many authors (Tarlo 1962, Denison 1964, Novitskaya 1973, Janvier 1996, Lundgren and Blom 2013, Randle and Sansom 2017a, b). Currently, Paraliliaspis is placed in Cyathaspididae and is considered (Randle and Sansom 2017b) to be closely related to Liliaspis and regarded as descendant of Anglaspis. Their close relationship was also pointed out in work by Novitskaya (2004) in which she included Liliaspis, Paraliliaspis and Anglaspis in the same family Anglaspisdidae.

MATERIAL AND GEOLOGICAL SETTING The Ciepielów IG-1 borehole pierces Lower Devonian deposits. They consist of dark gray calystone containing interbeds of sandstone and limestone intercalations. The agnathan specimen ZPAL Ag.IV/1 was found at a depth of 2229 m. From this drill core tentaculites were described by Hajłasz (1976).

Białopole IG-1 reached a depth of 3017.6 m in Ediacaran rocks. The Devonian succession in the borehole (depth 1031.84–1592.5 m) is represented only by its lower series. The agnathan specimen ZPAL Ag.IV/2 was collected from the Lower Devonian (Lower Lochkovian) sample at a depth of 1333.9–1340.5 m. The Devonian succession is represented by the Sycyna Formation and consists of dark gray claystones, locally marly or dolomitic, containing interbeds of organodetrital limestones, in places rich in the remains of bivalves (Grammysia sp., Nuculites sp., Pterinea sp., Ctenodonta sp.),

14 scolecodonts, bryozoans, tentaculitids, trilobites (Paracryphaeus sp.), ostracods and brachiopods: Isorthis cf. szajnochai, Protathyris praecursor, Spiriferida indet., Lingula sp. (Studencka 2012). The terrigenous clay sediments represent the deep sea with bottom below the wave base (Miłaczewski 2012).

FIGURE 1. Map showing the location of boreholes Białopole IG-1 (1) and Ciepielów IG-1(2).

SYSTEMATIC PALEONTOLOGY Subclass HETEROSTRACI Lankaster, 1868

Family TRAQUAIRASPIDIDAE Tarlo, 1962

Subfamily PHIALASPIDINAE White, 1945

Genus TOOMBSASPIS Tarrant, 1991

Diagnosis. Small phialaspidines with lateral keels. Low dorsal vane. Ventral, longitudinal cyclomoriform units bordering the ventral, smooth central area. Ornament of stellated equilateral and elongated tubercles divided by fine ridges. Ventral shield tubercles elongated on sides, in stacked V-shapes at back (after Tarrant 1991).

Toombsaspis sp.

Referred material. Ventral shield ZPAL Ag. IV/1 Occurrence. Ciepielów; Ciepielów IG–1 drill core, depth 2229 m, (Fig. 1), Lower Devonian.

Description. The ventral shield (ZPAL Ag. IV/1) shows a fragment of external surface of bone, recognized as the left posterior corner. The rest of the specimen shows the imprint of the visceral surface (Fig. 2). The shield generally oblong, 60 mm in length. It is widest (37 mm) about one-third of the way from anterior margin, along the length of the plate. The width to length ratio is 0.66. It is wider in the anterior part, while tapering smoothly posteriad to 30 mm, and then narrows rapidly posteriorly. The anterior margin is slightly concave,then turns posteriorly and forms a gently curved lateral edge. The flat and smooth central area is elevated by 1 mm. The ornamented margin has a width of 6 mm and consists of long and serrated ridges protruding parallel to the edge.

FIGURE 2. Toombsaspis sp. Specimen ZPAL Ag. IV/1, ventral plate preserved as natural mold with fragmentary preserved bone with ornamentation consists serrated long ridges (1) and drawing of the specimen (2) showing also elevated central area (dashed line).

Remarks. The coffin shaped ventral shield corresponds to that of traquairaspidids (Dineley 1964, Tarrant 1991) in having a smooth and raised central region, surrounded by an ornamented brim. The length (60 mm) of the plate is shorter than in Phialaspis (68– 100 mm) but is longer than in Toombsaspis (32–39 mm). But the overall proportion, expressed by ratio of width to length (0.66), is comparable to both Phialaspis (0.54–0.75) and Toombsaspis (0.53–0.69). The relatively narrow ornamented brim of the specimen ZPAL Ag.IV/1 seems not to differ from that in Toombsaspis while being narrower than in Phialaspis. Also the ornamentation is more comparable to the former genus where

16 the ridges tend to become elongated posteriorly. However, in specimen ZPAL Ag.IV/1 the ridges seem to be longer than in other representatives of the group. Described morphological features, except the length of the plate, place the specimen ZPAL Ag.IV/1 in Toombsaspis. They do not allow to determine species, so it is left in open taxonomy as Toombsaspis sp.

Ordo CYATHASPIDIFORMES Kiaer and Heintz, 1935

Family CYATHASPIDIDAE Kiaer, 1932

Subfamily ANGLASPIDINAE Kiaer, 1932

Genus PARALILIASPIS Novitskaya et al., 1994

Paraliliaspis sp.

Diagnosis. Dorsal shield wide, elliptical, truncated rear. Its length is 45 mm, the ratio of width to length is 0.73. Front edge forms a very short corner. The rear edge of the dorsal shield has a short median projection and small lateral projections. In the lateral edge of the dorsal shield branchial openings are not visible. Ornament formed of dentine ridges. Along the front edge of the dorsal shield dentine ridges considerably narrower than the rest of its surface. The boundaries of the central and lateral epitegum hardly visible or absent. On the ventral shield distinguishable central and lateral hypotega. Sensory canal system consist of pores and fissures (pit lines). Lateral line furrows developed on the ventral plate. On the dorsal shield, they are confined to the peripheral areas of it. Supraorbital sensory commissure developed but central posterodorsal sensory canal lacking. Pineal macula weakly developed or not discernible (after Novitskaya et al., 1994).

cf. Paraliliaspis sp.

Description. The specimen ZPAL Ag. II/2 consists of a fragmentary dorsal shield (Fig. 3.2, 3.4) and a more complete natural cast of internal surface of the same specimen (Fig. 3.1, 3.3). The exposed internal surface of the shield shows imprints of anatomical structures, also visible on the cast. Its length is 50 mm and the estimated maximum width is about 54 mm in its posterior part. The distance between the center of the shield, set by the impression of the medulla oblongata, to its edge is 27 mm. The shield is convex, except for its central part, which is flat. It bents downward only near to lateral border. In dorsal view, the lateral margin is curved and widens posteriad. In halfway along the lateral edge, the dorsal shield starts to form a narrow and flattened lateral shelf.

The orbital notch is deep with a diameter, measured along the edge, reaching is 4.5 mm. A superficial ornament (Figs. 3.2, 3.4, 4) impressed on the posterior part of the specimen consists of parallel and longitudinal ridges with smooth edges of moderate width (2–2.5 mm). The pores of sensory system trace one dorsal transverse commissure (Fig. 4). The sensory canal is marked by a slight elevation of the plate surface.

FIGURE 3. Paralilaspis sp., specimen ZPAL. Ag.IV/2, fragment of dorsal shield. Impression of the visceral surface (1) and the counterpart with bone preserved (2). Drawing

of the principal part of the shield (3, 4)

The internal surface ofthe shield bears impressions of two semicircular canals on each side, the brain (medulla oblongata), and a fragment of pineal macula (Fig. 3.3). The impressions of at least 6 (7?) gill pouches may be traced at right angle to the lateral edge. Lateral to them, closer to the lateral boarder, are longitudinally arranged scars.

FIGURE 4. Drawing of impressed dentine ridge pattern on the fragment of the Paralilaspis dorsal shield ZPAL Ag.IV/2.

Referred material. Fragment of dorsal shield and its mould ZPAL Ag. IV/2

Occurrence. Białopole; Białopole IG–1 drill core, depth 1333.9-1340.5 m, (Fig. 1), Lower Devonian (Lower Lokchovian).

Remarks. The described specimen displays a pattern of ornamentation (longitudinally arranged) similar to that of the other known representatives of the Anglaspididae sensu Novitskaya (2004).Although, the ridges are parallel and longitudinal and undulate slightly or bend near transverse commissures in Paraliliaspis (Novitskaya et al. 1994), the ridges in Liliaspis are almost straight on the entire surface of the dorsal shield. Moreover, the present specimen is similar to Paraliliaspis in that it lacks the elevation of the central part of the shield. Specimen described herein is out of size range of the only species of Paraliliaspis, P. ergegia (length of 42–47 mm). It also differs in comparatively narrower ridges on central part of the shield, and probably merits specific distinction. However, both a small number and incompleteness of the specimen make determination impossible, and so the material from Ciepielów IG-1 is left in open taxonomy as cf.

Paraliliaspis sp.

DISCUSSION AND CONCLUSION The Traquairaspidids and cyathaspidids underwent much evolutionary diversification during Silurian time (Dineley and Loeffler 1976). They were mostly widespread around the margins ofthe Old Red Sandstone (ORS) Continent (Blieck and Elliott 2017) and can be used in biostratigraphy of the Lower to Upper Devonian of the entire ORS Continent. Therefore, traquairaspidids have also been used as biozonal (cenozone) markers (Blieck and Janvier 1989). The finding from Ciepielów IG-1 bore core corresponds to the stratigraphic and paleogeographic range of the group (Fig. 5), which is Upper Silurian to Lower Devonian. The geological range of cyathaspidids is from Lower or Middle Silurian to Lower Devonian (Denison 1964, Novitskaya 2004, Märss 2019). The fossil record of closely related Paraliliaspis and Liliaspis is Lower Devonian, while their possible ancestor Anglaspis appeared in the Přidoli (Upper Silurian) with the last occurrence in the Lower Devonian. The material from Białopole IG-1 falls within the stratigraphic range of the group. The paleogeographic distribution of Paraliliaspis seems not to be restricted to the northern part of ORS (Novitskaya et al. 1994, Novitskaya 2004) but also spreads over the southern part of this continent (Fig. 5).

This distribution corresponds to that of Anglaspis (Denison 1964, Ilyes et al. 1995).

REFERENCES

BLIECK, A. 1980. Le genre Rhinopteraspis Jaekel (Vertébrés, Hétérostracés) du Dévonien inférieur : systématique, morphologie, répartition. Bulletin du Muséum national

d’Histoire naturelle, 4e série, 2, section C, pp. 25-47.

BLIECK, A., AND ELLIOTT, D.K. 2017. Pteraspidomorphs (Vertebrata), the Old Red Sandstone, and the Special Case of the Brecon Beacons National Park, Wales, U.K. Proceedings of the Geologists’ Association 128(3). 438–46. https://doi.org/10.1016/j.pgeola.2016.07.003.

BLIECK, A. AND JANVIER, P. 1989. Vertébrés Agnathes du Dévonien inférieur de l’Artois (Pas-de-Calais, France): implications biostratigraphiques. In: Annales de Paléontologie. pp. 125-167.

DEC, M. 2015. A New Tolypelepidid (Agnatha, Heterostraci) from the Late Silurian of Poland”. Journal of Paleontology, 89: 637–644.

DEC, M. 2019. Revision of the Early Devonian Psammosteids from the “Placoderm Sandstone”: Implications for Their Body Shape Reconstruction. Palaeontologia Electronica, 22.2.36A 1-26.

DENISON, R.H. 1964. The Cyathaspididae, a family of Silurian and Devonian jawless vertebrates. Fieldiana Geology, 13: 311-473.

DINELEY, D.L. 1964. New specimens of Traquariaspis from Canada. Palaeontology, 7 (2): 38-39

DINELEY, D.L., and LOEFFLER, E.J. 1976. Ostracoderm faunas of the Delorme and associated Siluro-Devonian formations, North West Territories, Canada. Special Papers in Palaeontology, 18:1–214.

HAJŁASZ, B. 1976. Tentakulity i ich znaczenie dla stratygrafii (dolny dewon). Geological Quarterly, 20 (2): 273–288. [In Polish, English summary]

ILYES, R.R., OHTA, Y. and GUDDINGSMO, J. 1995. The Downtonian and Devonian Vertebrates of Spitsbergen. XV. New Heterostracans from the Lower Devonian Red Bay Group, Northern Spitsbergen”. Polar Research 14, nr 1 (czerwiec 1995): 33–42. https://doi.org/10.1111/j.1751-8369.1995.tb00708.x.

JANVIER, P., 1996. Early Vertebrates. Oxford monographs on Geology and Geophysics.

Clarendon Press, Oxford. 393 pp.

KIAER, J. 1932. The Downtonian and Devonian vertebrates of Spitsbergen. IV. Suborder

Cyathaspida. Skrifter Svalbard Ishavet 5,:7–26.

LANKESTER E. 1868. A monograph of the fishes of the Old Red Sandstone of Britain. Part

1. The Cephalaspidae. Palaeontological Society, London, pp. 1–33.

LUNDGREN, M. AND BLOM, H. 2013. Phylogenetic Relationships of the Cyathaspidids (Heterostraci). GFF 135(1): 74–84. https://doi.org/10.1080/11035897.2013.770792.

MIŁACZEWSKI, L. 2012. Dewon, Chronostratygrafia. W: Białopole IG 1. Profile Głębokich Otworów Wiertniczych Państwowego Instytutu Geologicznego, 134: 80–81. [In Polish, English summary]

NOVITSKAYA, L. 1973. Liliaspis - ein Poraspide aus dem Unterdevon des Urals und einige

Bemerkungen über die Phylogenie der Poraspiden (Agnatha). Palaeontographica

Abteilung A, 25-34.

NOVITSKAYA, L.I. 2004. Agnathans and early fishes. Fossil vertebrates of Russia and adjacent countries. Moscow: GEOS, 540 pp.

NOVITSKAYA, L., KARATAJUTE-TALIMAA, V., AND JURJEVA, Z. 1994. Paraliliaspis - A new genus of cyathaspids (Cyathaspidiformes, Agnatha) from the Lower Devonian of the Timano-Pechorian Province. Paleontologicheskii Zhurnal, 3: 94- 102.

OBRUCHEV, D. 1967. On the evolution of the Heterostraci. Problemes actuels de Paleontologie, 163: 37-43.

RANDLE 2017, PhD thesis. Heterostraci systematics, phylogenetics and macroevolution: investigating evolutionary patterns of extinct jawless vertebrates.

RANDLE, E. and SANSOM, R.S. 2017a. Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters, Journal of Systematic Palaeontology, 15(7) 583-599, doi: 10.1080/14772019.2016.1208293

RANDLE, E. and SANSOM, R.S. 2017b. Phylogenetic Relationships of the ‘Higher Heterostracans’ (Heterostraci: Pteraspidiformes and Cyathaspididae), Extinct Jawless Vertebrates”. Zoological Journal of the Linnean Society, 181(4): 910–26. https://doi.org/10.1093/zoolinnean/zlx025.

STUDENCKA, B. 2012. Ramienionogi w utworach dewonu. W: Białopole IG 1. Profile Głębokich Otworów Wiertniczych Państwowego Instytutu Geologicznego 134: 80–

81. [In Polish, English summary]

TARLO, L.B. 1961. Psammosteids from the Middle and Upper Devonian of Scotland. The

Quarterly Journal of the Geological Society of London 117, 367-402.

TARLO, L.B. 1962. The classification and evolution of the heterostraci. Acta Paleontologica Polonica, 7(1-2): 249- 289.

TARLO, L.B. 1964.Psammosteiformes (Agnatha) – a review with descriptions of new material from the Lower Devonian of Poland. I - general part. Palaeontologia Polonica, 13:1-135.

TARLO, L.B. 1965. Psammosteiformes (Agnatha) – a review with descriptions of new material from the Lower Devonian of Poland. II - systematic part. Palaeontologia Polonica, 15:1-168.

TARRANT, P. R. 1991. The ostracoderm Phialaspis from the Lower Devonian of the Welsh Borderland and South Welsh. Palaeontology 34 (2): 399-428.

WHITE, E. I. 1945. The Genus Phialaspis and the “Psammosteus Limestones”. Quarterly Journal of the Geological Society, 101: 207–42.

CHAPTER II

A NEW TOLYPELEPIDID (AGNATHA, HETEROSTRACI) FROM THE LATE 2 SILURIAN OF POLAND

MAREK DEC

Institute of Palaeobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland.

ABSTRACT Tolypelepis mielnikensis n. sp. from a bore-core sample of the Late Silurian (Přidoli) succession in Mielnik, Poland shares such tolypelepidid features as a subdivision of the dorsal shield into epitega, and ornamentation of short dentine ridges grouped into scale-like units with a coarser, higher median ridge encircled by narrower and lower ridges. A constriction of the dorsal shield anterior to the orbit level with the orbital notches significantly deeper than in other tolypelepidids discriminates it from other Tolypelepis species.

INTRODUCTION The genus Tolypelepis was monotypic over for 120 years, the only species included being T. undulata. The original description by Pander (1856) was based on a small shield fragment from the Ohesaare Cliff (Estonia), which was Přidoli in age. Schmidt (1891) introduced the new name Tolypaspis for a well preserved dorsal shield of the same species. A more detailed description of Tolypaspis undulata, published by Rohon (1893) was based on the material from the same locality (Saarema Island, Ohesaare Cliff). All the above mentioned material belongs to the same genus Tolypelepis, now considered valid due to clarification by many subsequent authors ( Rohon 1893, Hoppe 1931, Kiaer 1932). Other materials assigned to Tolypelepis undulata by these authors have mainly been obtained from the same locality and strata (Ohesaare Cliff, Přidoli Series, Upper Silurian, Mark-Kurik 1969, Mark-Kurik and Noppel 1970). Märss (1977) described all the material of Tolypelepis undulata. The new material, that she described and figured

2 First published in Journal of Paleontology 89: 637–44. https://doi.org/10.1017/jpa.2015.28.

24 came from the same strata of Ohesaare Cliff and Ruhnu drill core in Estonia. Dineley and Loeffler (1976) reported a new species of Tolypelepis, T. lenzi, from the Upper Silurian of northern Canada (Mackenzie Mountains). They also established a new genus, Asketaspis, related to Tolypelepis (Dineley and Loeffler 1976), from the same Upper Silurian strata. This decision supports the monophyletic suprageneric taxon, Tolypelepidinae, first used by Denison (1964), nested in Heterostraci. Tolypelepis material was also described by Loeffler and Jones (1977) from Arctic Canada (Somerset Island), and assigned to a new species Tolypelepis leopoldensis and to T. cf. leopoldensis. Recently, a complete, articulated specimen of a putative tolypelepidid, Athenaegis chattertoni, has been described from Wenlock, Lower Silurian beds, Mackenzie Mountains (Soehn and Wilson 1990).

Two associated specimens (ZPAL Ag–II/1–2), described herein, were collected by Henryk Tomczyk (Institute of Geology, Warsaw) from one bore-core sample of the Late Silurian (Přidoli) succession and to the Institute of Paleobiology, Polish Academy of Sciences, for further studies.

MATERIAL AND GEOLOGICAL SETTINGS The specimens described in this paper were collected from a drill core at Mielnik (Fig. 1), eastern Poland. The deep-boring was designed by the Polish Geological Institute and drilled in 1959. Drilling reached a depth of 1813.10 m in Precambrian rocks (Urbanek 1997). The Precambrian basement is overlain by Ordovician and Silurian deposits which are uncomformably covered by Permian clastics. There is no precise analysis to ascertain how deep the Permian erosion was or how big was the stratigraphical gap that comprises the Devonian and Carboniferous, but also potentially includes the uppermost part of the Silurian strata.

The Mielnik IG-1 drill core was almost complete, with a core diameter of 10–12 cm (Urbanek 1997). The specimens ZPAL Ag–II/1–2 were collected from one bore-core sample from the Late Silurian (Přidoli) succession at a depth of 602.3–606.8 m (Fig. 1). According to Kozłowski and Sobień (2012), the succession of the borehole “represents periplatform setting on a neritic carbonate platform located on the palaeocontinent of Baltica”. The considerable thickness, along with the low-energy sedimentary environment and completeness of graptolite succession, suggest a continuous and nearly constant rate of sedimentation. The sample is accurately dated on the basis of graptolites (Urbanek 1997). The graptolites are numerous and well preserved, varying from flattened

FIGURE 1. Map showing the location of Mielnik with simplified lithological section and graptolite zone subdivision in the Upper Silurian of the Mielnik IG-1 bore-hole (Urbanek, 1997).

specimens to 3-D preservation. The degree of graptolite compression is correlated with the clay content in the matrix, as flattening most probably depends on the compaction of the initially loose silty sediments (Urbanek 1997). A combination of three- dimensional and flattened specimens are present within one sample. The agnathan remains were found about 30 m above the last occurrence of the graptolite Neocolonograptus lochkovensis lochkovensis, at a depth of 634.15 m (Urbanek 1997), which defines the lochkovensis graptolite Zone.

The measurements of the shield of T. mielnikensis n. sp. from Mielnik follow those used by Denison (1964).

SYSTEMATIC PALEONTOLOGY Class PTERASPIDOMORPHI Goodrich, 1909

Subclass HETEROSTRACI Lankester, 1868

Order CYATHASPIDIFORMES Berg, 1937

Family TOLYPELEPIDIDAE Denison, 1964

Occurrence. Both Tolypelepis undulata and T. mielnikensis come from the youngest, upper Silurian (Přidoli) sediments of the Paleobaltic shelf (Fig. 2). Older or equal in age

(Ludlow or Přidoli; Loeffler and Jones 1977) are rocks from Somerset Island, Arctic Canada, where Tolypelepis leopoldensis was collected. Other Silurian tolypelepidids, such as Asketaspis interstincta or Tolypelepis lenzi are known from Laurentian epicontinental sediments (Mackenzie Mountains), but their exact dating is uncertain (Dinley and Loeffler 1976). Only some Tolypelepis sp. remains from the same area of Laurentia are well dated and referred to the Early Silurian (Wenlock; Soehn and Wilson 1991). The Early Silurian (early Wenlock) agnathan fish, Athenaegis, currently considered as a possible sister taxon of the “higher Heterostraci” (Janvier 1996), comes also from this part of Laurentia. Its suggested basal position, stratigraphic age and geographic province are suggestive of a Laurentian origin of the whole heterostracan clade, but this is very uncertain at this time.

FIGURE 2. Paleogeographical (Silurian map modified from Scotese, 2001) distribution of tolypelepidids in the stratigrapic context with location of described material.

Remarks. Two genera included in Tolypelepididae, Tolypelepis Pander, 1856, Asketaspis Dineley and Loeffler, 1976. Given the range of taxonomic characters applied herein, Asketaspis should be included within the genus Tolypelepis, which would result in monotypy of Tolypelepididae and reduction of its diagnosis to that of the genus. However, Asketaspis, a monotypic genus with a species A. interstincta represented by an only specimen, has not been available for study by the present author, and thus is left as valid. The present ranking of the “tolypelepidids” is here considered tentative until new material will clarify the situation.

Genus TOLYPELEPIS Pander, 1856 Diagnosis. Dorsal shield broad and the preorbital length rather short (orbital ratio 0.14). Dorsal shield subdivided into epitega. On the central epitegum and postrostral field the dentine ridges short and in most grouped into scale-like areas, with narrower, lower ridges arranged around a coarser, higher central ridge (after Denison 1964).

Tolypelepis mielnikensis new species

Figure 3.1, 3.2

1977 Tolypelepis undulata (Pander); Märss, pl. 1, fig. 3; fig. 2D.

Etymology. Named in reference to the type locality, Mielnik village.

Material. Dorsal shield, ZPAL Ag–II/1 (holotype); incomplete dorsal shield, ZPAL Ag– II/2.

Occurrence. Mielnik; Mielnik IG–1 drill core, depth 602.3–606.8 m, (Fig. 1), upper Silurian (Přidoli).

Diagnosis. Rostral region constricted at orbital level with orbital notches deep. Dorsal shield of moderate dimensions (width ratio 0.62), with uniform width. Postbranchial lobes of dorsal shield not evident. Pineal macula distinct. Ornamentation of central epitegum of short dentine ridges of low relief. Ridges in anterior part of epitegum generally uniform in height, but difference between median and adjacent ridges increasing posteriad, the units becoming scale-like.

Description. The dorsal shield is complete, but the middle right side of the specimen is slightly collapsed. Nevertheless the left part of the dorsal shield and rostral region are perfectly preserved except a small scratch of the left side of the specimen which does not affect the general shape of this part. Therefore the natural shape of the shield can be restored. The shield length is 37 mm and width 23 mm. It is oval in shape and of rather uniform width, and slightly arched dorsally. The anterior border is smoothly rounded and lacks the median rostral process. The width of the dorsal shield is reduced in front of the deep orbital notches (both sides of this part are symmetrical); the preorbital process is well developed. The lateral edges are almost straight exept anteriorly and posteriorly where they are lightly curved. In lateral view the edge is also straight. The branchial notch and post-branchial lobes are not developed. The posterior margin is zigzag in shape and concave. The epitega are distinct; the post-rostral field can be distinguished from

FIGURE 3. Tolypelepis mielnikensis, n. sp. 1. holotype Ag–II/1, dorsal shield; 2. fragment of dorsal shield Ag–II/2; 3. drawing of left lateral view of holotype Ag–II/1; 4—5. drawing of the dentine ridge pattern of the dorsal shield.

29 the central epitegum. Boundaries between epitega are clearly designated by sutures and by the pattern of dentine ridges.

The ornamentation of the dorsal shield comprises non-uniform dentine ridges of low relief, with scalloped edges. Ridges (5 per mm) on the rostral epitegum are uniform in height, broad and arranged mostly transversely in the anterior part of the epitegum. Posteriorly on the epitegum, they are shorter and form small denticles. The most posterior ridges are shorter. They are orientated diagonally, some of them grouped into units. The ridges (5 per mm) on the lateral epitega are almost uniform in height. They are narrow and long, generally arranged parallel to the margin of the epitegum. In the middle of the lateral epitegum there are several singular ridges with higher relief and oriented diagonally. In the orbital region, ridges (4 per mm) are curved around the orbital notch.

On the central epitegum the ridges are variable in height, and the average density is 4 per mm. On the anterior half of the shield the median ridge of each unit has the same height or is subtly higher than adjacent ones, the difference increasing posteriad. In the posterior half of the epitegum the ornamentation looks like imbricated, fused scales. The typical size of each unit is 1.8 mm long (+/- 0.3 mm) and 1 mm (+/- 0.2 mm) wide. Such scale- like units are absent from the postrostral field of the epitegum. Only one ridge group resembles such a unit. The ridges have uniform height and largely diagonal arrangement. The pineal macula is clearly visible on both specimens. Its central region is elevated and surrounded by encircling ridges.

The lateral line system is conspicuous over the entire specimen. It consists of pores in the superficial layer arranged in two pairs of longitudinal canals and four transverse commissures, perpendicular to the longitudinal ones (Fig. 4.1).

Remarks. The following character states of the dorsal shield are to be considered in a comparative analysis of the armor: the pattern of superficial ornamentation, dimensions and proportions of the dorsal shield, outline of the shield (uniform or variable width associated with lateral margin straight or slightly convex, posterior edge convex or concave), and pore canal system.

Eight tolypelepidid specimens of six species are considered here (Table 1). The length of the dorsal shield ranges from 27 to 38mm. The Mielnik specimen matches this variability range, and so does Asketapis interstincta.

As regards the overall proportions of the shield, expressed by width ratio, T. mielnikensis (width ratio 0.62), the longest among the tolypelepidids, is the slimmest of all, whereas the range for species of Tolypelepis is 0.67-0.77. If not ontogenetic (which is unclear as yet), this difference may be a taxonomically useful feature at a generic or specific level. Morphometric characters, other than the width ratio, do not significantly differ from those of T. undulata (Table 1).

More readily discriminated from other tolypelepidids is Tolypelepis leopoldensis. With the length (35mm) comparable with the Mielnik specimen (37mm), it is slightly broader (width ratio 0.77) than other Tolypelepis representatives (0.67–0.74), thus displaying a different combination of morphometric characters. It also differs in orbital width ratio (0.31), which is lower than in other tolypelepids (0.44–0.52), and in a very high pineal length ratio (0.57) which is dramatically different from that of all other tolypelepidids(0.22–0.28). In other words, the pineal macula is placed much more posteriorly in T. leopoldensis. These data show the amount of variability within the genus Tolypelepis, and, combined with other characters, these differences are here considered specific (see below).

Table 1. Measurements and ratios of well–preserved specimens of the Tolypelepididae. Tolypelepis undulata (after Märss 1977), Tolypelepis undulata (Kiaer 1932), Tolypelepis leopoldensis (Loeffler and Jones 1977), Tolypelepis lenzi (Dineley and Loeffler 1976), Asketaspis interstincta (Dineley and Loeffler 1976).

Species Tolypelepis Tolypelepis Tolypelepis Tolypelepis Asketaspis Tolypelepis Dimensions undulata undulata leopoldensis lenzi interstincta mielnikensis Median length (mm) 32-38 32 35 27 >30 37 Maximum width (mm) 23 23 27 20 21 23.5 Pineal length (mm) - 8 20 6 - 8.5 Orbital length (mm) - 5 5 4.5 - 5 Orbital width (mm) - 14.5 11 14 - 15.5 Width ratio 0.67–0.70 0.69 0.77 0.74 <0.7 0.62 Pineal length ratio 0.24-0.25 0.25 0.57 0.22 - 0.23 Orbital length ratio 0.14-0.18 0.16 0.14 0.13 - 0.13 Orbital width ratio - 0.44 0.31 0.52 - 0,42 Ridges on central 3-5 4 6-7 5 6.5 5 epitegum (per mm) Ridges on lateral 8 8 - - 6.5 7 epitegum (per mm)

Another alleged tolypelepidid, Asketaspis, seems not to differ in morphometric terms from Tolypelepis at the generic level (Table 1), but some other characters (e.g,. presence

31 of inter-epitegal tubercles) may suggest the opposite (see below).

Apart from overall proportions, the shape of the shield depends on the degree of tapering, which is expressed by having either straighter or more convex sides. Tolypelepis mielnikensis is uniform in width. In this regard it recalls both Asketaspis interstincta (Fig. 4.5; Dineley and Loeffler 1976:fig. 22, pl. 6, fig. 1), and one specimen of Tolypelepis undulata figured by Märss (1977:fig. 2 D, pl. fig. 3), the lateral margins of these specimens being straight in dorsal view. All three specimens contrast with other representatives of Tolypelepis, where the lateral margin is convex (Rohon 1893:pl. I, fig. 45, Kiaer 1932:l. X, Stensio 1958:fig. 169B, Loeffler and Jones 1977:fig. 3, pl. 80, figs. 3, 5). This unique character may suggest that all three specimens are congeneric (or conspecific if belonging to Tolypelepis), and belong to Asketaspis, but other characters (e.g., presence of interepitegal tubercles, do not support this view (see below)).

The Mielnik specimen is unique in that the rostral region is constricted anterior to the orbits. The specimen Pi 5003/GIT 168-4 figured by Märss (1977: fig. 2D) shows a similar rostral shape. In contrast, Asketaspis and other representatives of Tolypelepis (Fig. 4.3–4.7) lack such narrowing, the tapering of the anterior part of the shield being gradual and smooth beginning from the orbital region to the anterior tip of the rostral margin (Märss 1977:fig. 3, fig. 11 A–B; Denison and Loeffler 1976:fig. 21–22, pl. 6, figs. 1, 3; Loeffler and Jones 1977:fig. 3, pl. 80, figs. 3, 5). Rostral region narrowing in front of orbits is known in Poraspis (Denison 1964, Loeffler and Jones 1977, Elliott and Petriello 2011) so this feature concerns the generic rather than specific level, which precludes the inclusion of the Mielnik specimen in Asketaspis. Moreover, the Mielnik specimen differs from Asketaspis in the degree of delimitation of the orbital epitegum, which is not distinct in the former (similar to Tolypelepis), while being distinct in the latter (Dineley and Loeffler 1976:fig. 22, pl. 6, fig. 1).

Complete articulated skeletons, of tolypelepidid-like agnathan fish, are only known for one species, Athenaegis chattertoni, recorded from the Early Wenlock (Early Silurian) of the Mackenzie Mountains, and originally considered to be a tolypelepidid (Soehn and Wilson 1990). More than 14 specimens were assigned to A. chattertoni. In terms of dorsal shield proportions and outline, Athenaegis differs from tolypelepidids at a generic level, but it is excluded from the Tolypelepididae on the basis of branchial structure (Janvier 1996). If so, its strikingly tolypelepidid ornamentation (i.e., grouping of dentine ridges into scale-like units, each with narrow and low ridges arranged around

32 a wider central ridge) is to be considered plesiomorphic. In taxonomic terms the width of the ridges is important, defined as the number of ridges per millimeter (Denison 1964), their length, orientation and variation in height and thickness. Tolypelepis shares with Asketaspis transversely aligned ridges, but differs in having diagonally oriented, short ridges, sometimes grouped into units (T. undulata, T. lenzi or T. mielnikensis).

On the lateral epitegum of T. mielnikensis, ridges are arranged longitudinally and are parallel to the lateral margin (Fig. 3.1, 3.4), which is the pattern shared by all tolypelepidids and by Athenaegis as well, associated with the long and narrow shape of the lateral epitegum. The width of ridges in the lateral epitegum of Tolypelepis undulata is 8 per mm on average (Table 1). Tolypelepis mielnikensis has slightly coarser ridges (7 per mm). The information about Asketaspis (6.5 ridges per mm), given by Dineley and Loeffler (1976) is not precise as regards the topography of the dorsal shield. There is no information about T. leopoldensis and T. lenzi.

The ornamentation of the central epitegum in T. mielnikensis consists of short dentine ridges of low relief and is similar to that of Asketaspis interstincta, and particularly so in the changing relations of the ridge heights. In the anterior part of the epitegum of both these taxa, the ridges are generally uniform in height, but the difference between the median ridge and adjacent ones increases posteriad. This changing pattern ofornamentation is shared also by the specimen Pi 5003/GIT 168-4 of Tolypelepis undulata (Märss 1977:pl. fig. 3), which stresses the similarity of these three specimens, as suggested by the shield outline. In other Tolypelepis species the median ridge is higher than the adjacent ones on the whole central epitegum. However, a significant difference does exist between both the Mielnik specimen and Märss’s specimen (1977:fig. 2D) onone hand and Asketaspis on the other. The former lacks an inter-epitegal band of tubercles, characteristic of Asketaspis, and so a generic difference between those taxa is supported. However, the character may be subject to infrageneric variability as demonstrated by the presence of the tubercles in Tolypelepis leopoldensis.

Most posterior units of the Mielnik specimen look like imbricated scales (Fig. 3.1, 3.4) as they do in some other Tolypelepis species, T. lenzi (Dineley and Loeffler 1976:fig. 22, pl. 6, fig. 1) and specimens of T. undulata described by Rohon (1893:pl. I, fig. 45) and Kiaer (1932:pl. X). The main difference between the taxa is in the relative size of units, which in T. mielnikensis are proportionally smaller than those in other Tolypelepis species, but larger than those in Asketaspis. In this regard, the Mielnik

33 specimen is morphologically intermediate between Tolypelepis and Asketaspis, but themosaic pattern of similarities within the Tolypelepis group suggests undetermined variability at the generic or specific level.

Comparisons of other characters are inconclusive. The posterior edge of the shield is concave in the specimen from Mielnik (if this is not an artifact of preservation), while convex in Tolypelepis. In Asketaspis the posterior part of the dorsal margin is not preserved.

In Tolypelepis, the construction of the branchial region is unclear, as it is in Tolypelepis mielnikensis. However, a fragment of Tolypelepis branchial plate (Märss 1977:fig. 6B) reveals a branchial notch, and, posterior to it, an expanded dorsal lobe of the branchial plate. Asketaspis displays also a branchial notch and moderately well developed postbranchial lobe (Dineley and Loeffler 1976). This structure is probably more or less typical for the early cyathaspidiforms, tolypelepidids included, which thus recalls the morphology of the cyathaspidid genus Nahanniaspis (Dineley and Loeffler 1976:figs. 33–34). Presumably, the overall branchial structure was similar (branchial notch mostly created by the incised branchial plate). The situation is different in Asketaspis which displays a branchial notch and postbranchial lobe, both moderately well developed. The dorsal shield of T. mielnikensis apears straight in lateral view (Fig. 3.3), as it does in Athenaegis, thus suggesting that the postbranchial lobe is absent. Whether these minor differences are properly understood and taxonomically valid for low level taxonomy cannot currently be estimated. The sensory line canal system of the Mielnik specimen is typical for cyathaspidiforms, with two pairs of longitudinal canals and at least three transverse commissures on the dorsal shield (Fig. 4.1). The pineal branches of the supraorbital canals do not join each other, similar to the other Cyathaspidiformes, and in contrast to Pteraspidiformes where the canals join and make a V-shaped pineal canal.

PHYLOGENY Heterostracan ingroup relationships are still debated, but two major groups, regarded as monophyletic, the Cyathaspidiformes and Pteraspidiformes (Fig. 5), have been proposed (Blieck et al. 1991, Janvier 1996, Elliott and Blieck 2010, Elliott and Swift 2010). The most significant character of Heterostraci is a common branchial opening (Janvier 1996) that does not pierce but incises the single branchial or branchiocornual plate. According to Janvier (1996), a putative early Silurian (Wenlock) tolypelepid,

FIGURE 4. Diversity of dorsal shield outlines in the Tolypelepididae. 1-2. Tolypelepis mielnikensis, n. sp.; 3-4. Tolypelepis undulata; 5. Asketaspis interstincta; 6. Tolypelepis lenzi; 7. Tolypelepis leopoldensis. 2. after Märss 1977; 3. after Rohon, 1893 and Märss 1977; 4. after Kiaer 1932 and Märss 1977; 5-6. after Dineley and Loeffler 1976; 7. after Loeffler and Jones 1977. Abbreviations: cd1-cd4, dorsal transverse commissures; cep, central epitegum; ifc, pores of infraorbital canal; ldl, pores of lateral dorsal canal; lep, lateral epitegum; mdl, pores of medial dorsal canal; rep, rostral epitegum; soc, pores of supraorbital canal.

Athenaegis (Soehn and Wilson 1990), should be excluded from Cyathaspidiformes, or even from the Heterostraci (Fig. 5), because it lacks this feature. The presence of three rows of small branchial plates (Fig. 5.1) on each side further discriminates Athenaegis from the “higher heterostracans” (sensu Janvier 1996). Soehn and Wilson (1990) suggested that a single pair of branchial openings may have opened posterior to most or all of the branchial scales and platelets in Athenaegis, but none has been documented. The branchial system of Athenaegis appears unique, until it is better understood, which supports its exclusion from the “higher Heterostraci”. Athenaegis is currently considered a possible sister taxon of the “higher Heterostraci”, because it shares their single dorsal shield and the diamond-shaped flank scales of higher Heterostraci (Janvier 1996). Tolypelepidids (Fig. 5, node F, taxon 2) share the following cyathaspidiform

(synonymous with the cyathaspids and amphiaspids in Blieck et al. 1991) features: 1) the armor consists of one dorsal and one ventral median plate, separated by one branchial plate on each side; 2) the sensory canal system of the dorsal shield consists of two pairs of longitudinal canals and at least three transverse commissures, perpendicular to the longitudinal ones; 3) supraorbital canals do not join each other to make a V-shaped pineal canal; 4) the dentine ridges of the superficial layer of the dorsal shield are mainly longitudinally arranged, each ridge having an unornamented central part and finely crenulated edges. Which of these characters are synapomorphies is still unknown, but their whole complex is characteristic for Cyathaspidiformes. However, tolypelepidids (Fig. 5, node F) do not share the longitudinal and more or less parallel ridges of other

Cyathaspidiformes, but, instead, display an ornamentation of many scale-like units, with short ridges surrounding the central one. This type of ornamentation, suggestive of many separate growth centers, is currently considered primitive. Therefore, tolypelepidids are located as a basal group within Cyathaspidiformes. Greeniaus and Wilson (2003) showed that plate growth reconstruction based on the ornamentation can lead to erroneous conclusions. Their description of juvenile cyathaspidids (Greeniaus and Wilson 2003) included ontogenetic observation. It showed rapid cyclomorial development of the dermal skeleton, despite previous interpretation (Denison 1964, Dineley and Loeffler 1976) of simultaneous plate growth. Therefore these features should be treated with caution.

Comparison of the dorsal shield within the Tolypelepididae revealed a mosaic structure in certain taxa. Different aspects of shield outline might due to be individual variation unless associated with differences in degree of distinctness of the epitega (orbital epitegum, postbranchial lobes, pineal macula), details of ornamentation, presence versuss absence of rostral constriction and presence versuss absence of inter-epitegal tubercles. These mosaic character complexes are considered as representing true taxonomic variability of infrafamilial rank. The present author tentatively considers them as specific while accepting generic difference between Tolypelepis and Asketaspis (Dineley and Loeffler 1976, Soehn and Wilson 1990) until the revision of the last genus is possible.

FIGURE 5. Outline of interrelationships within Heterostraci based on Janvier (1996) A. Heterostraci, a single external branchial opening; B. A less inclusive heterostracan group (“higher heterostracans” plus Athenaegis), single dorsal shield, loss of oak leaf-shaped tubercles. C. “higher heterostracans”, branchial or branchio-cornual plate not pierced by branchial opening. D. Cyathaspidiformes, ornamentation of longitudinaly arranged dentine ridges with finely crenulated margins. E. Pteraspidiformes, ornamentation of concentric dentine ridges with serrated margins, dorsal spinal plate. F. Tolypelepididae, dorsal shield composed in part of scale-like units, especially posteriorly, dentine ridges mostly short; G. Cyathaspidiformes without Tolypelepididae, ornamentation of longitudinal dentine ridges, more or less parallel; H. Amphiaspidida, derived pattern of armor. Terminal taxa: 1. Athenaegis, three series of branchial plates, no trace of branchial opening(s); 2. Tolypelepis mielnikensis, branchial opening placed dorsally, incising branchial plate (after Märss 1977); 3. Nahanniaspis, branchial opening placed dorsally, incising branchial plate; 4. Anglaspis, typically cyathaspidiform branchial opening placed postero- dorsally, incising branchial plate; 5. Amphiaspidida, Kureykiaspis, branchial opening placed dorsally in fused head armor plate; 6. Errivaspis, typically pteraspidiform branchial opening between branchial and cornular plates. 37

CONCLUSIONS A set of character states present in a tolypelepidid dorsal shield from a bore-core sample of the Late Silurian (Přidoli) succession in Mielnik, Poland, has been considered sufficient for the erection of a new species Tolypelepis mielnikensis. The unique character of the new species is a constriction of the rostral region in front of the orbit level with orbital notches significantly deeper than in other Tolypelepis species or in Asketaspis. This character is shared by the specimen Pi 5003/GIT 168-4 (Märss 1977; fig. 2D) from Ohesaare Cliff which is thus considered conspecific with Tolypelepis mielnikensis and included in this species. Ohesaare Cliff and the Mielnik beds both represent upper Přidoli (Mark-Kurik 1969, Märss 1997, Kaljo and Nestor 1990, Urbanek 1997) carbonate facies of the Paleobaltic shelf.

The paleogeographic distribution of the tolypelepidids demonstrates that at the beginning of the Early Silurian the representatives of the family were distributed in epicratonic seas of Baltica and north-west Laurentia terranes (Fig. 2). It demonstrates that the clade was subjected to adaptative radiation on the whole territory of Baltica and Laurentia, but the scarcity of records and gaps in stratigraphic dating preclude any conclusions as to interrelationships of particular tolypelepidid genera and species.

ACKNOWLEDGMENTS I am grateful to M. Borsuk-Białynicka (Institute of Paleobiology, Polish Academy of Sciences,) for comments and suggestions on several drafts of this manuscript that greatly helped to improve the final version of the paper. I thank Tiuu Märss for helpful comments on the manuscript. I would especially like to thank David Kenneth Elliott and Mark V. H. Wilson for their constructive reviews of the manuscript.

REFERENCES

BERG, L.S. 1937. A classification of fish-like vertebrates. Bulletin of the Academy of Sciences of URSS, Biology Series 4:1277–1280.

DENISON, R.H. 1964. The Cyathaspididae: a family of Silurian and Devonian jawless vertebrates. Fieldiana Geology 13:30–473.

DINELEY, D.L., AND E.J. LOEFFLER. 1976. Ostracoderm faunas of the Delorme and associated Siluro-Devonian formations, North West Territories, Canada. Special Papers in Palaeontology 18:1–214.

ELLIOTT, D.K., AND A. BLIECK. 2010. A new Ctenaspis (Agnatha, Heterostraci) from the Early Devonian of Nevada, with comments on paleobiology and biogeographic significance; pp. 25–38 in D.K. Elliott, J. G. Maisey, X. Yu, and D. Miao (eds.), Morphology, Phylogeny, and Paleobiology of Fossil Fishes. Verlag Dr. F. Pfeil, Munchen.

ELLIOTT, D.K., AND S. SWIFT. 2010. A New species of Ariaspis (Agnatha, Heterostraci) from the Late Silurian of the Canadian Arctic. Journal of Vertebrate Paleontology 30:1874–1878.

GOODRICH, E. S. 1909. Vertebrata Craniata. First Fascicle: cyclostomes and fisches. In A treatese on zoology, London, Vol. 9.

GREENIAUS, J.W., AND M.V.H. WILSON. 2003. Fossil juvenile Cyathaspididae (Heterostraci) reveal rapid cyclomorial development of the dermal skeleton. Journal of Vertebrate Paleontology 23:483–487.

HOPPE, K.H. 1931. Die Coelolepiden und Acanthodier des Obersilurs der Indel Ösel. Palaeontographia 76:35–94.

JANVIER, P. 1996. Early Vertebrates. Oxford Science Publications, Clarendon Press, Oxford, 393 pp.

KIAER, J. 1932. The Downtonian and Devonian vertebrates of Spitsbergen. IV. Suborder Cyathaspida. Skrifter Svalbard Ishavet 52:7–26.

KOZŁOWSKI, W., AND K. SOBIEŃ. 2012. Mid-Ludfordian coeval carbon isotope, natural gamma ray and magnetic susceptibility excursions in the Mielnik IG-1 borehole (Eastern Poland)—Dustiness as a possible link between global climate and the Silurian carbon isotope record. Palaeogeography, Palaeoclimatology, Palaeoecology 339–341:74–97.

LANKESTER, E. R. 1868. A monograph of the fishes of the Old Red Sandsone o Britain. Part I. The Cephalaspidiae. Monograph of the Palaeontographical Society, London, 1–62 pp.

LOEFFLER, E.J., AND B. JONES. 1977. Additional Late Silurian Ostracoderms from the Leopold Formation of Somerset Island North West Territories, Canada. Palaeontology 20:661–674

MARK-KURIK, E. 1969. Distribution of vertebrates in the Silurian of Etonia. Lethaia 2:145–152

MARK-KURIK E. AND NOPPEL T. 1970. Additional notes on the distribution of vertebrates in the Silurian of Estonia. ENSV TA Toimetised. Keemia. Geoloogia 19:171–173.

MÄRSS, T. 1977. Structure of Tolypelepis from the Baltic Upper Silurian. Eesti NSV Teaduste Akadeemia Toimetised, Keemia: Geoloogia 26:57–69.

MÄRSS, T. 1997. Vertebrates of the Přidoli and Silurian-Devonian boundary beds in Europe. Modern Geology 21:17-42.

NESTOR, H. 1990. Locality 7:4 Ohesaare cliff; pp. 175–178 in D. Kaljo, and H. Nestor (eds.), Field meeting, Estonia 1990. An Excursion Guidebook. Institute of Geology, Estonian Academy of Sciences, Tallinn.

PANDER, C.H. 1856. Monographie der fossilen Fische des silurischen Systems der russisch-baltischen Gouvernements. St. Petersburg, 91 pp.

ROHON, J.V. 1893. Die obesilurischen Fische von Oesel. II Theil. Selachii, Dipnoi, Ganoidei, Pteraspidae und Cephalaspidae. Mémoires de l'Académie Impériale des Sciences de St.-Petersbourg 41:1–124.

SCOTESE, C.R., 2001. Atlas of Earth History, Volume 1, Paleogeography, Paleomap Project, Arlington, Texas, 52 pp. Availble at www.scotese.com.

SCHMIDT. 1893. Ueber neue silurische Fischfunde auf Oesel. Neues Jahrbuch für Mienralogie, Geologie und Paläontologie 1:99–101.

STENSIÖ, E.A. 1958. Les cyclostomes fossiles ou ostracodermes; pp. 173–425 in P. Grassé, Traite de Zoologie. Masson, Paris.

URBANEK, A. 1997. Late Ludfordian and early Přidolí monograptids from the Polish Lowland. Palaeontologica Polonica 56:87–232.

CHAPTER III

REVISION of the Early Devonian psammosteids from the “Placoderm Sandstone” - implications for their body shape reconstruction3

MAREK DEC

Institute of Palaeobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland.

ABSTRACT The Early Devonian psammosteid agnathans (Guerichosteus and Hariosteus) originally described by Tarlo (1964, 1965) from the so-called “Placoderm Sandstone” are revised. The newly collected material from the Holy Cross Mountains allows detailed reexamination and provides new anatomical information. The morphology and ornamentation of the plates supports the establishment of the genera Guerichosteus and Hariosteus. However, G. kotanskii, G. kulczyckii and G. lefeldi should be considered as junior synonyms of Guerichosteus kozlowskii. Hariosteus lobanowskii, erected by Tarlo (1964), is considered here as invalid (nomen dubium) and H. kotanskii is included with Hariosteus kielanae. The three-dimensional scanning of plates belonging to Guerichosteus allows for a more detailed description and reconstruction. In cross section the deep ventral part of the trunk is V-shaped in contrast to previous U-shaped restorations. Probably, the Early Devonian psammosteid, Drepanaspis gemuendenensis in particular, shared this body shape.

INTRODUCTION Psammosteids are an extinct group of armored agnathans occurring exclusively in the Devonian. Among these fishes, the Early Devonian Drepanaspis is best recognized. It is the only psammosteid with a nearly completely preserved exoskeleton composed of the entire armored body surface, trunk and tail (Janvier 1996). First reconstructions of Drepanaspis (Traquair 1899, 1903) showed the dorsal and ventral surface incorrectly, as noted by Dean (1904). This was later confirmed by Kiaer (1915) and most subsequent authors (Stensiö 1927, Kiaer 1928, Stetson 1931, Obruchev 1943, Gross 1963). The most

3First published in Palaeontologia Electronica 22(2): https://doi.org/10.26879/948.

41 detailed description together with reconstructions of Drepanaspis gemuendenensis were made by Gross (1963), although many other authors also provided some reconstructions (Stenson 1931, Obruchev 1943, Tarlo 1961, Tarlo 1964, Obruchev and Mark-Kurik 1965) (Fig. 1).

FIGURE 1. Drepanaspis reconstruction: by Gross (1963) in front (1), lateral (2), dorsal (3) and ventral (4) view; cross section (5) by Tarlo (1961); by Obruchev and Mark-Kurik (1965) in dorsal (6) and ventral (7) view; by Patten (1932) in dorsal (8) view.

The large collection of psammosteids from the Lower Devonian of “Placoderm Sandstone” was described by Tarlo (1964, 1965). This author described two new genera, Guerichosteus containing four new species and Hariosteus containing two species. The material, represented by numerous fragments of plates, is preserved as natural molds in fine-grained sandstone. Many elements of the armor are perfectly preserved and show the most delicate ornamentation which can be examined by using latex or silicone casts. Despite the abundance of Guerichosteus kozlowskii, no restoration of the species has been made until now. New material obtained during field work with Piotr Szrek and Grzegorz Niedźwiedzki at Podłazie Hill outcrop, conducted in 2011-2013 (Szrek et al. 2014), allows for a revision of the psammosteids formerly described by Tarlo (1957, 1961, 1964, 1965).

The described material is stored at the Institute of the Paleobiology of the Polish Academy of Sciences (abbreviation: ZPAL Ag. III/4), the Museum of the Earth of the Polish Academy of Sciences in Warsaw (abbreviation: MZ-VIII/Vp-430) and the Polish Geological Institute – National Research Institute (abbreviation: MUZ.PIG.1733.II.353). All current specimen numbers with reference to the numbers from the Tarlo (1964, 1965) are presented in Table 1.

MATERIAL AND GEOLOGICAL SETTING The outcrop of Podłazie Hill is located about 2 km to the north of the Daleszyce, in the southern part of the Holy Cross Mountains (Fig. 2.1). The quarry is located on the southern slope of the hill (Fig. 2.2). The succession dominated by thick-bedded, quartzitic sandstone is considered to be of Emsian age (Tarnowska 1976, 1981, Szulczewski and Porębski 2008), based on miospores and tephrocorrelation (Fijałkowska- Mader and Malec 2011).

The siliciclastic, storm-originated, bone-bearing beds yield a rich vertebrate accumulation deposited in a marginal-marine (e.g., lagoon) environment. The skeletons of fish were broken and sorted, likely as a result of their redeposition in shallow water. Ichnofossils show the presence of the Cruziana ichnofacies in the section (Szrek et al. 2014).

The material from the quartzitic sandstone bone-beds consists of natural molds of since dissolved fish remains, mostly secondarily filled with clay. Therefore, bony tissues are not preserved, although the imprints reveal minute structural details, such as those of histological aspects (e.g., the boundary between parts previously occupied by cartilage

FIGURE 2. Map showing the location Podłazie Hill (1) in the Holy Cross Mountains (HCM), and map of Daleszyce (2) with the position (magnified part) of abandoned quarry at Podłazie Hill. and membranous bones; Tarlo, 1964). In some cases, bone tissue is preserved, but the apatite has been replaced by plumbogummite-group minerals (Kruszewski and Dec 2018) without alteration of bone histological structures.

The specimens preserved in quartzitic sandstone filled with silt had to be mechanically cleaned and brushed in hot water with detergent. After removing silt from cavities with bone imprints, the latex casts (colored in grey) were made with Gumosill WW.

Most material is composed of broken plates, whereas any smaller plates or scales are preserved completely (Szrek et al. 2014). Most specimens lack deformation and the latex casts reflect the shape of actual bone or plate.

METHOD OF PSAMMOSTEIDS MORPHOLOGY RECONSTRUCTION Computer methods in paleontology have developed substantially in the last decade, especially three-dimensional (3D) digitization of specimens and models achieved

44 by different processes. Photogrammetry was a basic method used herein to produce the 3D models of specimens presented. To achieve a good resolution and models with a good accuracy (Falkingham, 2012), specific steps were followed (Mallison and Wings 2014):

1. Photography;

2. Model calculation;

3. Polygon and texture mesh generation;

4. Data export.

The photography is the important part of the process and has significant influence on the final effect. Therefore, the high resolution Digital Single Lens Reflex Camera (DSLR), Canon 70D (20.2-megapixels), was used. To visualize most specimens, theSigma DC 17-50 mm 1:2.8 EX HSM lens was used (usually a 50 mm focal length and an f/10 aperture were used). For small (about 1-3 cm) specimens, a Canon EF-S 55- 250 mm 1:4-5.6 IS with macro lens +4D was used (usually a 105 mm focal length and an f/10 aperture were used).

The photographs were taken with the camera mounted on a tripod and specimen placed on rotating stage at the desired angle. To generate a mesh, photographs were taken from at least two levels, one at a low angle 10-20 degree) and the second at a high level (40-60 degree). Model creation involved a point cloud calculation in VirtualSFM, polygon and texture mesh generation in MeshLab 2016.12, and exporting object mesh to Blender 2.79 (3D modeling software) to put together the plates.

SYSTEMATIC PALEONTOLOGY Subclass HETEROSTRACI Lankester, 1868

Order PTERASPIDIFORMES Berg, 1940

Family PSAMMOSTEIDAE Traquair, 1896

Remarks. Psammosteids are considered to be closely related to Pteraspidiformes. Different phylogenetic reconstructions recognized them either as a derived (Janvier, 1996), basal or sister (Halstead 1973, Blieck 1984, Pernègre and Elliott 2008) group of Pteraspidiformes. While the precise clade position is still ambiguous, the pteraspidiform affinity seems to be uncontested (Randle and Sansom 2017a). Therefore, at present psammosteids are considered to be the family Psammosteidae

(Janvier 1996, Pernègre and Elliott 2008, Randle and Sansom 2017a, 2017b), which is a position adopted herein, although currently some authors nest them in suborder Psammosteida within the order Pteraspidiformes (Elliott, Mark-Kurik, and Daeschler 2004, Glinskiy and Mark-Kurik 2016, Glinskiy and Nilov 2017).

Genus GUERICHOSTEUS Tarlo, 1964

Type species. Guerichosteus kozlowskii Tarlo, 1964, by original designation.

Guerichosteus kozlowskii Figures 3-11, 16, Appendices 1-21, 30 v. 1957. Psammosteid type A; Tarlo 1957, p. 230, pl. 1, fig. 1.

. 1965 Guerichosteus kozlowskii; Tarlo 1965: pp. 40-50, text-figs. 5B-C, pl. X, figs. 2, 5, 7; pl. XI, figs. 6, 8-9; pl. XII, fig. 2. v. 1965 Guerichosteus kozlowskii; Tarlo 1965: pp. 40-50, text-fig. 4, 5A, 6-8, pl. IX figs. 1A-B, 4, 5, 6; pl. X, figs. 1, 3-4, 6, 8-9; pl. XI, figs. 2-4, 7, 10-13; pl. XII figs. 1, 3-4.

. 1965 Guerichosteus kotanskii; Tarlo 1965: pp. 50, pl. XII, figs. 5-6. v. 1965 Guerichosteus kotanskii; Tarlo 1965: pp. 50, pl. XII, fig. 7.

. 1965 Guerichosteus kulczyckii; Tarlo 1965: pp. 50-51, pl. VII, figs. 3-4, XI, fig. 15. v. 1965 Guerichosteus lefeldi; Tarlo 1965: pp. 51-52, pl. XII, fig. 9.

. 1965 Guerichosteus lefeldi; Tarlo 1965: pp. 51-52, pl. XII, fig. 8.

Ocurrence. Lower Devonian (Emsian), Placoderm Sandstone, Podłazie Hill near Daleszyce, Holy Cross Mountains, Poland.

Diagnosis. Ventral median plate deep, rectangular in outline with posterior notch developed as narrow and shallow longitudinal depression reaching the center of plate instead of slit. Dorsal median plate roughly circular in outline with anterior re-entrant angle present. Branchial plate long and fairly narrow. Cornual plate rectangular. Ornamentation consists of closely-packed, rounded crenulated tubercles varying in size from 7 to 16 per mm (emended after Tarlo 1965).

Description

Dorsal plate. The specimen ZPAL Ag. III/4 (Fig. 3.1-3; Appendix 1) described by Tarlo (1965, fig. 5A; pl. XII, fig. 3-4) as a ventral median plate is the right part of the dorsal plate. The internal side (10 cm long and 7.7 cm wide) shows an anterior margin with

46 re-entrant angle, lateral and half of posterior margins. Along the edge an area of 2-7 mm extends without a basal layer. The anterior portion of the plate is flat while bending posteriad to the growth center creating a slight convexity (Appendix 1 in supplementary material). The anterior half of the external surface shows the ornamentation with a distinct growth line. The plate is subcircular in outline and gets slightly constricted anteriad at the re-entrant angle level.

The large posterior part (9 cm long, 13.8 cm width) of median plate ZPAL Ag. III/1 (Fig. 3.4-7; Appendix 2; Tarlo 1965, pl. X, fig. 9) shows both sides, external (Fig. 3.5, 3.7) and internal (Fig. 3.4, 3.6; note that Tarlo (1965) showed only the external ornamented side of the specimen), with a natural posterior and lateral margin preserved. Posterior edge, fairly straight, undulates and curves around to the lateral margin. Well-marked growth lines extend parallel to the margin. In specimens ZPAL Ag. III/4 and ZPAL Ag. III/1 there is lack of the basal layer near the edge, but in the latter specimen this area is much wider (10-18 mm).

Several fragments of flat plates such as ZPAL Ag. III/2 (Fig. 3.8-9; Appendix 3; Tarlo 1965, pl. X, fig. 1), MUZ.PIG.1733.II.13 (Fig. 3.10-11; Appendix 4) and MZ-VIII/Vp- 438 (Fig. 3.12-13; Appendix 5), appear to be parts of a dorsal plate. ZPAL Ag. III/2 shows growth line patterns similar to ZPAL Ag. III/4. If so, it may indicate ZPAL Ag. III/2 is a fragment of the right side of the plate. In the latter specimen the tubercles are well preserved, and short radial grooves are visible on the surface (Fig. 3.8). They were probably a part of the sensory canal system (Tarlo 1965).

Ventral plate. The specimen MUZ.PIG.1733.II.353 (Fig. 4.3-8; Appendix 6) is the largest and most complete plate. However, only the internal side (Fig. 4.5-6) displays the whole surface of the plate. The external, ornamented surface is exposed only in the anterior part of the plate (Fig. 4.3-4). The plate is rectangular in shape with a length of 118 mm and a width of 103 mm (length-to-width ratio is 1.15). The plate is 20 mm deep and trapezoidal in transverse section along the posterior notch (here developed as a depression instead of a slit), while anteriorly it is more rounded (Fig. 4.6-7). The anterior margin is straight with a very shallow concavity in the middle. The posterior margin is smoothly rounded and arched to the medially located posterior notch. The margins of the slit are irregular, which suggests a crack more than a natural edge. On the internal side along the slit there is a slight thickening visible, so the posterior notch is developed as a low depression rather than a slit like in Tartuosteus or Schizosteus.

FIGURE 3. Guerichosteus kozlowskii, 1-3. dorsal plate ZPAL Ag. III/4, internal (1) and external (2) view, shape reconstruction (3); 4-5. dorsal plate ZPAL Ag. III/1, internal (4) and external (5) view, drawing of internal (6) and external (7) view with growth line marked 8-9. dorsal plate ZPAL Ag. III/2, external (8) view and drawing (9); 10-11. specimen MUZ.PIG.1733.II.13, external (10) view and drawing (11); 12-13. dorsal plate MZ-VIII/Vp- 438, external (12) view and drawing (13).

FIGURE 4. Guerichosteus kozlowskii, 1-2. ventral plate ZPAL Ag. III/45, external view, (1), shape reconstruction (2); 3-8. ventral plate MUZ.PIG.1733.II.353, external (3) and internal (5) view, drawing of external (4) view with growth line marked (hached line), drawing of internal (6) view with cross section (7), left lateral view (8).

ZPAL Ag. III/45 is fragment of a ventral plate of a juvenile specimen (Fig. 4.1-2; Appendix 7; Tarlo 1965, pl. XII, fig 9). The plate is deeply arched and resembles the anterior portion of large specimen MUZ.PIG.1733.II.353 in shape. Near the posterior broken edge a low depression marks the posterior notch (Fig. 4.2).

Branchial plate. Most specimens of branchial plates are broken or incomplete. The most complete is a small, triangular, left branchial plate, ZPAL Ag. III/1089 (Fig. 5.1-2; Appendix 8), of a juvenile individual. The plate shows only a dorsal view of the anterior

49 half of the external, ornamented, dorsal surface and the internal side of the ventral surface. The plate is 40 mm long (measured along the median margin of dorsal ornamented surface) and its maximum width is 28 mm (measured perpendicularly to the length). The dorsal ornamented surface is narrow with a straight medial margin except for the tapering of the proximal tip. The medial margin of the ventral surface is concave. The angle between the dorsal and ventral parts is about 65 degrees. The angle and shape of the last specimen resemble those of small fragments of MUZ.PIG.1733.II.185 (Fig. 5.7-10) and MZ-VIII/Vp-533 (Fig. 5.13-14) as well as the posterior half of the larger ZPAL Ag. III/16 (Fig. 5.3-4; Appendix 9), which is 62 mm long. Although in ZPAL Ag. III/16 the anterior half is elongated and narrow, the ventral surface’s maximal width is 18 mm and the dorsal surface’s maximal width is 12 mm. Therefore, the lateral margin and the median margin of the ventral and dorsal surface run parallel. Also the proximal part of the specimen is less angled (40 degrees). Various fragments of larger specimens showed on Figures 5 and 6 (ZPAL Ag. III/7, ZPAL Ag. III/8. ZPAL Ag. III/9, ZPAL Ag. III/15, MZ-VIII/Vp-423, MUZ.PIG.1733.II.185) are incomplete. Nevertheless, all features of the plate possibly show the mid-part of the plate. Their shape (i.e., narrow anterior part and considerably expanded posterior part) is in general similar to ZPAL Ag. III/16. However, the larger ZPAL Ag. III/15 specimen (Fig. 5.5-6; Appendix 10) of the right branchial plate displays a dorsal view of a distal tip, where the medial margin of the dorsal surface is slightly curved. The margin tapers with its posterior corner creating the edge of a branchial opening. In ZPAL Ag. III/9 (Fig. 6.5-8; Appendix 13), probably representing the biggest individual, and in ZPAL Ag. III/7 (holotype) (Fig. 6.1- 4; Appendix 12) the ventral surface is concave. Although the holotype is slightly crushed, the damage occurred probably post-mortem. The angle between the dorsal and ventral surface is about 35-40 degrees in ZPAL Ag. III/9 and ZPAL Ag. III/7. More than half of the space between those surfaces is filled with bone (about 15 mm in ZPAL Ag. III/7), so the plate is quite thick. The proximal tip of the left branchial plate ZPAL Ag. III/14 (Fig. 6.9-10; Appendix 14) shows an undulating medial margin in ventral view. The lateral margin is arcuate near the anterior tip and almost straight posteriorly. The plate is 98 mm long and expands to the rear up to 40 mm.

Cornual plate. The almost complete cornual plate ZPAL Ag. III/19 (Figure 7.1-2; Appendix 15) is rectangular and slightly convex. The specimen is 55 mm long and 53 mm

FIGURE 5. Guerichosteus kozlowskii, A. left branchial plate ZPAL Ag. III/1089, dorsal view(A),drawing of dorsal view (B); C. fragment of right branchial plate ZPAL Ag. III/16, dorsal view (C), drawing of dorsal view (D); E. right branchial plate ZPAL Ag. III/15, dorsal view (E); drawing of dorsal view (F); G. posterior tip of left branchial plate

FIGURE 6. Guerichosteus kozlowskii, 1. fragment of right branchial plate ZPAL Ag. III/7, dorsal (1) ventral (2) view, drawing of dorsal (3) and ventral (4) view; 5. fragment of right branchial plate ZPAL Ag. III/9, ventral (5) and dorsal (6) view, reconstruction of ventral (7) and dorsal (8) view; I. anterior tip of left branchial plate ZPAL Ag. III/14, ventral view(9), drawing of ventral view (10).

52 wide (length to width ratio is 1.04). The postero-lateral corner of the plate is rounded posteriorly (also the area bent inside) and forms a thickening. The growth center is at the posterior margin of the plate and is displaced laterally (Fig. 7.1).

Orbital plate. The trapezoidal right orbital plate is 13 mm long and 25 mm width (length-to-width ratio is 0.52). A round opening for the eye with a diameter of 3.5 mm is in the middle of the inclined lateral margin (Fig. 7.3-4; Appendix 16).

FIGURE 7. Guerichosteus kozlowskii, A. cornual plate ZPAL Ag. III/19, dorsal view (1) with drawing (2); 3. orbital plate MUZ.PIG.1733.II.154, ventral view (3), internal view on orbital opening (4); 5. median oral plate ZPAL Ag. III/23; 6. lateral oral plate MUZ.PIG.1733.II.355, ventral view (6) and drawing of ventral view (7); 8. complex plate MUZ.PIG.1733.II.357, ventral view, cross-section (9); 10. Close up on median oral plate and lateral oral plate of Drepanaspis gemuendenensis specimen stored in Muséum national d'Histoire naturelle in Paris.

Complex plate. One, almost pentagonal, left complex plate MUZ.PIG.1733.II.357 (Fig. 7.8-9; Appendix 17) is 42 mm wide and 30 mm long. In transverse (sagittal) section the S-shaped curvature of the plate is visible (Fig. 7.9). The anterior margin is sinusoid with the medial part convex forming a space for oral plates. The tubercles on the most prominent part of the plate are weathered.

Oral plate. An almost complete and triangular median oral plate is 30 mm long and 26 mm wide (specimen, Fig. 7.5; Appendix 18). In transverse section the plate has a slightly S-shaped curvature similar to a complex plate. Beside the median oral plate described by Tarlo (1965; fig. 7A-C), a newly found plate appears to be a lateral oral plate (Figure 7.6-7; Appendix 19). This nearly complete and triangular specimen is 30 mm long and 26 mm wide (Fig. 7.6; Appendix 19). In transverse section the plate has a slightly S-shaped curvature similar to a complex plate. The internal side of the plate shows a narrow area with tubercles along a straight anterior margin. The internal margin of the ornamented area is sinusoidal. The anterior edge smoothly turns rearward at an almost right angle forming a concave edge. The third medial edge is not preserved, although on the basis of the overlapping area (Fig. 7.7, light gray) the boundary of the plate can be stated. The external side, visible only near the edges of the plate, shows closely packed and small dome shaped tubercles. Those two oral plates, medial and lateral, look similar to those of Drepanaspis gemuendenensis presented by Tarlo in 1965 (pl VI, figure 1) andtoa specimen stored in National Museum of Natural History in Paris (Fig. 7.10) showed by Lehman (1967; planche 1).

Ridge scales. A few incomplete ridge scales (Fig. 8) vary in length from 15 mm (MUZ.PIG.1733.II.13, Fig. 7.10-11) to 69 mm (ZPAL Ag. III/27A, Fig. 7.1-2; Appendix 20). The maximal width is from 8 mm (MUZ.PIG.1733.II.13) to 24 mm (ZPAL Ag. III/27A and MZ-VIII/Vp-463). Most specimens are long and slender apart from MZ-VIII- Vp-463 (Fig. 7.14-15) which is relatively wider and shorter. Ridge scales are roundly curved dorsally in the small specimens (ZPAL Ag. III/26, Fig. 7.7-9) and became more triangular in the larger specimens (MZ-VIII/Vp-335, Figure 7.12-13 and ZPAL Ag. III/27A, Fig. 7.3). The maximal high of the ridge scale is 9 mm and the maximal thickness is 4 mm (MZ-VIII/Vp-335). The tubercles cover the entire external side and thevisceral surface, without its proximal unornamented part (light gray in Fig. 7.2, 7.5, 7.15) that was in contact with body tissues.

FIGURE 8. Guerichosteus kozlowskii, A. ridge scale ZPAL Ag. III/27A, internal view (1) and drawing of internal view with photo of close-up on tubercles (2), cross-section (3); 4. ridge scale MZ-VIII/Vp-488, internal (4) and external (5) view with drawing of internal view and shape reconstruction (5); 6. ridge scale ZPAL Ag. III/26, external view (7), cross-section (8), drawing with shape reconstruction (9); 10. small ridge scale MUZ.PIG.1733.II.13, external view (11), drawing with shape reconstruction (12); 13. ridge scale MZ-VIII/Vp-335, external (13) and internal (14) view; O. ridge scale ZPAL Ag. III/30, internal view (15), 16. drawing of internal view and shape reconstruction; 17. specimen ZPAL Ag. III/27B, external view (16), drawing of internal view with photo of close-up on tubercles (17); 18. body scale ZPAL Ag. III/33; 19. body scale ZPAL Ag. III/22 with close-up on tubercles; 20. body scale MZ-VIII/Vp-536.

Trunk scales. In the studied material several trunk scales are recognized. The largest scale ZPAL Ag. III/27B is 28 mm long and 17 mm wide and shows a narrow (3 mm) overlapping area in the proximal margin (Fig. 8.16-17). ZPAL Ag. III/33 resembles the latter specimen, but is poorly preserved. Its length is 23 mm and width is 10 mm (Fig. 8.18). This specimen also has a row of longitudinal tubercles arranged perpendicularly to the margin of the scale. ZPAL Ag. III/28 and ZPAL Ag. III/33 represent more proximal trunk scales. A more distal scale is ZPAL Ag. III/22, which is 25 mm long 17 mm wide (Fig. 8.19; Appendix 21).

FIGURE 9. Guerichostus kozlowskii, 1. right branchial plate ZPAL Ag. III/9, ventral surface with fragments showing the detail of ornamentation (2-3); 4. left branchial plate ZPAL Ag. III/8 with fragments showing the detail of ornamentation (5).

The central part of the scale is elevated (about 1 mm). The last scale was probably placed in the tail area. A small and rhomboidal scale MZ-VIII/Vp-536 is 17 mm long and 13 mm wide (Fig. 8.20). In CONTRAST to ZPAL Ag. III/27B and ZPAL Ag. III/33, which are flat and thin, this scale is convex and thick.

Ornamentation. The ornamentation consists of closely packed, rounded, irregular topentagonal tubercles (Fig. 9, 10). All tubercles have well-marked crenulation at the base. On branchial plates the largest tubercles (7-8 per mm) are located along the lateral margin (Fig. 9.3, 9.5), most of them are low and pentagonal in shape. Toward the medial part of the plate, the size of tubercles decreases from 10-12 per mm (Fig. 9.3) to 15-16 per mm (Fig. 9.2). The tubercles are mostly low, almost flat and irregular to pentagonal in shape. Nevertheless, in some parts the tubercles may be higher and more dome-shaped (Fig. 9.5). Lower, more closely packed and less varied are tubercles on the dorsal (Fig. 10) and ventral plates whose shape is pentagonal or irregular. The difference is in size of tubercles; on the dorsal plate tubercles are larger (12-14 per cm; Fig. 10.2, 10.4) than

FIGURE 10. Guerichosteus kozlowskii, 1. dorsal plate ZPAL Ag. III/1 with fragment showing the detail of ornamentation (2); 3. dorsal plate ZPAL Ag. III/2 with fragment showing the detail of ornamentation (4); 5. cornual plate ZPAL Ag. III/19 with fragment showing the detail of ornamentation (6).

57 those on the ventral plate (18-20 per cm). The cornual plate possesses dome-shaped tubercles (9-13 per cm) with a well-visible base crenulation (Fig. 10.6).

Remarks. Revision of psammosteid collection described by Tarlo (1964, 1965) shows that some plates were incorrectly identified. The studied collection lacks several specimens of Guerichosteus described by Tarlo (1964, 1965): D.5.U.W., D.6.U.W., D.10.U.W., D.11.U.W., D.12.U.W., D.18.U.W, D.20.U.W., D.21.U.W., D.31.U.W., D.32.U.W., D.34.U.W., D.37.U.W., D.40.U.W., D.41.U.W, D.42.U.W., D.43.U.W., D.44.U.W., D.82.U.W., D.84.U.W.

ZPAL Ag. III/4, originally described by Tarlo (1965; pl. XII, figs. 3-4) as the right half of the posterior end of a ventral plate, is in fact the right half of the dorsal plate (Fig. 3.1- 3). The edge considered by Tarlo (1965) as the margin of the posterior notch is irregular in outline which has been likely formed by breaking the plate fragment.

The part of the ZPAL Ag. III/1 dorsal plate illustrated in Fig. 3.4-7 is recognized as the lateral edge rather than a posterior one as described by Tarlo (1965). Well visible growth lines with an almost straight posterior edge and roundly curved lateral margin resemble ZPAL Ag. III/4.

During the investigation of the collection an additional tip of the ZPAL Ag. III/14 branchial plate was found (presented in Tarlo 1965: pl. X, fig. 6). It shows larger, anterior portion of the ventral and external ornamented surface (Fig. 6.9-10).

The ZPAL Ag. III/22 pineal plate (Fig. 8.19), recognized by Tarlo (1965), is more likely a scale as it resembles scales illustrated by Mark-Kurik (1965).

Neither the Gurichosteus kotanskii holotype D.37.U.W nor two other specimens (D.39.U.W and D.40.U.W) were found in the studied collection. Only ZPAL Ag. III/38 (in Tarlo (1965) D.38.U.W) shows the ornamentation similar to G. kozlowskii. According to Tarlo (1965), the tubercles of G. kotanskii are extremely large, but ZPAL Ag. III/38 has 8-10 tubercles per cm (diameter 1-1.25 mm), such as those observed in the G. kozlowskii branchial plate. The measurements of specimens not currently in the collection, but presented in Tarlo (1965), were taken from figures. So the holotype had approximately 7-10 tubercles per cm and specimen D.40.U.W had 5-9 tubercles per cm. The last specimen shows slightly larger tubercles than G. kozlowskii. However, this is insufficient to support the creation of the new species Guerichosteus kotanskii.

The ZPAL Ag. III/45 holotype of Guerichosteus lefeldii (Tarlo 1965: pl. XII, fig. 9)

58 is the antero-median part of the ventral plate with a visible posterior notch (Fig. 4.1-2). Tarlo (1965) distinguished this genus based on ornamentation of minute, closely packed, rounded tubercles, approximately 0.3 mm in diameter. This study shows (similar to G. kozlowskii) ornamentation of small tubercles, approximately 0.5 mm (18-20 per cm). The tubercles of MUZ.PIG.1733.II.252 and ZPAL Ag. III/1080 G. kozlowskii specimens are slightly bigger than those of ZPAL Ag. III/45, albeit it may be due to the closer position of the tubercles to the growth center instead of marginal within former specimens. It should be classified as G. kozlowskii, such as a body scale of ZPAL Ag. III/47 (Tarlo 1965: pl. XII, fig. 8). Therefore, Guerichosteus lefeldii is considered here as a junior synonym of Guerichosteus kozlowskii.

No Guerichosteus kulczycki specimens (D.42.U.W., D.43.U.W, D.44.U.W.) were found in Tarlo’s collection, even the holotype (D.41.U.W.). The investigation of descriptions and figures suggests the affinity of G. kozlowskii. Tarlo decided to distinguish the species G. kulczyski from other species of Guerichosteus by its fairly small (diameter – 0.5 mm) and clearly separated tubercles. However, it resembles the ornamentation observed on the ventral plate, especially the small and pointed tubercles, of ZPAL Ag.III/45 (Fig. 4.1).

The species erected by Tarlo (1965, 1966), G. kulczyckii, G. lefeldi and G. kotanskii, are in the range of variability of Guerichosteus kozlowskii and are here included in this species. Several specimens (ZPAL Ag. III/17, ZPAL Ag. III/24, ZPAL Ag. III/25, ZPAL Ag. III/26) included by Tarlo in Guerichosteus are moved to Hariosteus (see description below).

The ventral plate of Guerichosteus displays the intermediate stage of development between Drepanaspis and all other members of the group (except Psammosteus, in which the posterior notch was reduced). The plate has a shallow and narrow depression rather than a notch. Whereas Drepanaspis lacks a posterior notch, it is well developed among other psammosteids. The improvement of this structure might be the result of the increase in body size and can be related to ecological adaptation.

Apart from growth lines visible on the external surface, one branchial plate (ZPAL Ag. III/7) reveals a layered pattern of internal growth of the plate. The broken surface of the dorsal part exposes layers of the bone (Fig. 11, hatched line). In median view, the middle vascular layer shows thin bone layers obliquely arranged to the dorsal surface

59 of the plate and proximally thinned-out (Fig. 11.1). At the posterior broken margin of the plate, the layers correspond to the shape of the branchial plate surface (Fig. 11.2). The bone layers show forward and inward ossification which also caused increase of the plate thickness. Therefore, it is consistent with the medial direction of ossification, expressed by presence of growth lines on ornamented external surface of the branchial plate.

FIGURE 11. Guerichosteus kozlowskii, 1. right branchial plate ZPAL Ag. III/7, dorsomedial (1) and posterior (2) view (white hatched line mark bone layer in vascular middle layer).

Genus HARIOSTEUS Tarlo, 1964 Type species. Hariosteus kielanae Tarlo, 1964, by original designation.

Hariosteus kielanae Figures 12-15; Appendix 22-29

. 1957. Psammosteid type B; Tarlo 1957, p. 230, pl. 1, fig. 2.

. 1965. Hariosteus kielanae; Tarlo 1965: pp. 52-55, pl. XI, fig. 14, pl. XIII, figs. 3, 6-10. v. 1965. Hariosteus kielanae; Tarlo 1965: pp. 52-55, text-figs. 9, 10, pl. XIII, figs. 1-2, 4, 11. v. 1965. Guerichosteus kozlowskii; Tarlo 1965: pp. 47, Figure 7D-E, pl. IX, fig. 2A-B, pl. XI, figs. 1, 5.

Occurrence. Lower Devonian (Emsian), Placoderm Sandstone, Daleszyce, near Kielce, the Holy Cross Mountains, Poland.

Diagnosis. Branchial plate wide and short, ornamentation composed of well separated,crenulated tubercles with smaller accessory tubercles between them. Presence of alternate bands of larger and smaller ornamentation, giving distinguishing growth zones, especially on the dorsal median plate (modified from Tarlo 1965).

Description Dorsal plate. Apparent left posterior fragment (ZPAL Ag. III/48) of a dorsal plate (Fig. 12.1-12.3, Appendix 22) preserves both sides, external surface with tubercles and visceral.

The fragment is flat, 44 mm long, 63 mm wide and 4 mm thick. Well-recognizable growth lines reflect the posterior margin. The visceral surface is smooth with several grooves and ribs, mostly concentrated near the plate margin (Fig. 12.2). They both mirror the growth zones marked in external, superficial ornamentation. Two other thin and flat specimens, MZ-VIII/Vp-549 (Figure 12.4) and ZPAL Ag. III/50 (Fig. 12.5, 12.6), are possibly fragments of the dorsal median (Figure 12.4-5). The latter one is the largest specimen and shows very well-preserved tubercles characteristic for Hariosteus.

Branchial plate. There are branchial plates of two specimens present in the material, ZPAL Ag. III/17 (Fig. 13.1-3; Appendix 23) and MUZ.PIG.1733.II.185 (Fig. 13.4-5; Appendix 24); specimens are in order, right and left branchial plate. ZPAL Ag. III/17 preserves both sides of the plate (dorsal and ventral). The plate is 49 mm wide and 57 mm long. The plate is dorsally convex. Its lateral margin is strongly arched and the posterior margin creates a slight sinus. The posterior part of the lateral margin and the posterior margin form a right angle. The ventral side of the plate is weathered and only the most anterior and posterior parts of the lateral edge have preserved tubercles (Fig. 13.2). The dorsal surface with tubercles is triangular with a concave posterior margin and a waving medial edge. The Branchial plate of MUZ.PIG.1733.II.185 is similar to the one of ZPAL Ag. III/17 where only the dorsal side is preserved. The overall shape of the plates is comparable. However, the lateral margin is more arched than in ZPAL Ag. III/17 and the posterior edge of the dorsal ornamented surface is deeper (Fig. 13.4). The plate is 55 mm wide and 45 mm long. Its thickness, measured anteriorly along the broken antero-lateral edge, is 7 mm and gradually increases to 10 mm. ZPAL Ag. III/56 shows a distal tip of the ventral side of the branchial plate. The plate preserves a fragment of the posterior and lateral margin (Fig. 13.6). The smaller ZPAL Ag. III/24 specimen, described as an oral plate by Tarlo (1965, fig. 7D-E),

FIGURE 12. Hariosteus kielanae 1. fragment of dorsal plate ZPAL Ag. III/48, external (1) and internal (2), 3. drawing of dorsal view with growth line (hatched line); 4. external view of dorsal plate fragment MZ-VIII/Vp-549; 5. external view of dorsal plate fragment ZPAL Ag. III/50; 6. drawing of dorsal view with growth line (hatched line); 7. branchial plate ZPAL Ag. III/83, 8. drawing with growth line (hatched line).

FIGURE 13. Hariosteus kielanae; A. right branchial plate ZPAL Ag. III/17, dorsal (1) and ventral (2) view, 3 drawing of dorsal view with grow line (fine hatched line) ; 2. left branchial plate MUZ.PIG.1733.II.185, dorsal (4) view and drawing of dorsal view (5); 6. left branchial plate MZ-VIII/Vp-452, ventral view; 7. left branchial plate ZPAL Ag. III/24, dorsal view.

63 seems to be in fact a distal tip of the branchial plate. The dorsal side of the plate is visible (Fig. 13.7; Appendix 25). The lateral margin is arched similarly to two larger specimens, ZPAL Ag. III/17 and MUZ.PIG.1733.II.185. Also the thickness (8 mm) is comparable. However, whether the specimen represents a small individual or if it is just a broken fragment of a plate is inconclusive, albeit the former interpretation is likely more probable. The tubercles along the medial margin of the plate seem to be natural, at least in the anterior half, which supports the assumption that the specimen is a small individual branchial plate.

Ridge scales. Three specimens (ZPAL Ag. III/25, ZPAL Ag. III/28, MZ-VIII/Vp-67) include ridge scales. An incomplete ridge scale is ZPAL Ag III/28 (Fig. 14.1-3; Appendix 27). The external surface covered with tubercles is visible, although the most prominent part lacks tubercles (probably due to post-mortem abrasion). The specimen is 60 mm long, the maximum width is 15 mm and its height is 10 mm. The scales are relatively high and U-shaped in transverse section. The more complete ZPAL Ag. III/28 shows the internal, posterior and right lateral part of the external surface of the scale (Fig. 14.4- 6; Appendix 26). Its length is 65 mm and maximum width is 20 mm. More than a half of specimen (35 mm) has an unornamented proximal part which was connected with soft tissue. In the smaller MZ-VIII/Vp-67 (ZPAL Ag. III/29) the proximal smooth part reaches more than a half of the specimen (it is 21 mm of about 38 mm of the estimated length of this specimen; Figure 14.7). The ridge scales show high and slightly elongated tubercles on the external surface (ZPAL Ag. III/25; Fig. 14.1), while near the lateral edges tubercles are more elongated (ZPAL Ag. III/28; Fig. 14.2). The internal surface shows radially propagating, loosely dense tubercles. Tubercles change from being round in front and long and thin in back parts. The same pattern is visible on MZ-VIII/Vp-67 (Fig. 14.7; Appendix 28), which is 25 mm long and 14 mm of its maximum width.

Trunk scales. In the studied material several trunk scales are recognized. Scale MUZ.PIG.1733.II.309 is 21 mm long,15 mm high and shows a wide (about 7 mm) overlapping area (Fig. 14.8-9; Appendix 29). Near the center of the scale extends a groove of lateral line which ends with a minute pore. A larger body scale MZ-VIII/Vp- 410 (Fig. 14.10-11) is rather high (24 mm) and short (17 mm). The last one (MUZ.PIG.1733.II.184) is more pentagonal in shape, 17 mm wide, 21 mm long and 3 mm thick (Fig. 14.12-13). The proximal margin is convex with narrow unornamented area.

FIGURE 14. Hariosteus kielanae, 1. ridge scale ZPAL Ag. III/25, external view with close- up on tubercles, 2. drawing of the scale with shape reconstruction (hached line) and cross section (3); 4. ridge scale ZPAL Ag. III/28, visceral view with close-up on tubercles, 5. drawing of the scale with shape reconstruction (hatched line) and cross sections (6); 7. ridge scale MZ-VIII/Vp-67, internal view; 8. body scale with lateral line canal MUZ.PIG.1733.II.309, external view, 9. drawing with growth line and photo with close-up on tubercles; 10. body scale MZ-VIII/Vp-410, external view, 11. drawing with growth line and photo with close-up on tubercles; 12 trunk scale MUZ.PIG.1733.II.184, external view with drawing (13) presenting overlapping area (light grey).

Ornamentation. Tubercles vary from 0.1 to 1.2 mm diameter. The larger ones (on branchial plates) are placed near the edge and decrease in size medially. Between larger, dome-shaped tubercles there are low and cone-shaped accessory tubercles (Fig. 15.4) which may be absent on branchial plates (Fig. 15.5). Narrow, marginal cusplets reach the cupola-shaped apex of both tubercles and accessory tubercles (Fig. 15.6). The characteristic growth zones of alternate bands of larger and smaller tubercles are

FIGURE 15. Hariosteus kielanae, 1. dorsal plate ZPAL Ag. III/2 with fragment showing the detail of ornamentation (4); 1. left branchial plate MUZ.PIG.1733.II.185, dorsal surface with fragment showing the detail of ornamentation (5, 6); 3. dorsal plate ZPAL Ag. III/50 with fragment showing the detail of ornamentation (7).

66 visible best on the median dorsal plate (Fig. 15.7), while near the branchials margin there is a lack of them or they are barely visible (Fig. 15.5). The accessory tubercles, variously arranged, may fill the space between larger tubercles in disarray or they can encircle larger tubercles.

Remarks. The studied collection lacks several specimens of Hariosteus described by Tarlo (1964, 1965): D.52.U.W, D.54.U.W, D.55.U.W, D.58.U.W, D.59.U.W, D.61.U.W, D.62.U.W.

Tarlo (1964, 1965) described two species of the genus Hariosteus kielanae and Hariosteus lobanowskii. The holotype of Hariosteus lobanowskii (ZPAL Ag. III/60) is poorly preserved, especially tubercles. The ornamentation may vary depending on a specific plate or part of the plate where the tubercles are located. Therefore, a small number of the available specimens may not reveal full variability among members of the Hariosteus genus. For example, in Guerichosteus, one specimen reveals slightly different ornamentation. Also ZPAL Ag. III/61 and ZPAL Ag. III/62 are missing andare not illustrated in the Tarlo monograph (1965). Therefore, the species H. lobanowskii erected by Tarlo is considered here as invalid.

Tarlo (1965) interpretation of ZPAL Ag. III/51 as a postorbital seems to be doubtful. The plate is incomplete and the most characteristic feature (except the ornamentation) are almost straight growth lines extended perpendicular to the bent edge (Fig. 12.7-8). Such bending is not restricted to postorbital plates. In Psammolepis venyukovi and Ganosteus stelatus, the proximal ventral surface of the branchial plate looks similar (Obruchev and Mark-Kurik 1965). Moreover, the branchial plate of Hariosteus is thick. This is why this fragment is probably more a proximal part of a larger individual in which the edge is not as rounded as in ZPAL Ag. III/17 or MUZ.PIG.1733.II.353.

ZPAL Ag. III/83, considered as Gurichosteus kozlowskii by Tarlo (1965), is a fragment of a branchial plate of Hariosteus kielanae. The edge of the plate is rounded with nearly parallel dorsal and ventral surfaces similar to the one of Hariosteus, in contrast to the more triangular and angled edge of Guerichosteus. Also the ornamentation shows several accessory tubercles like in Hariosteus.

The studied material of Hariosteus is insufficient to make an overall restoration of the shields and body. The most complete branchial plate with overall proportions resembles those of Pycnosteidae (sensu Obruchev and Mark Kurik 1965). Both width

67 and length of the plate is nearly the same and resembles the young stage of Schizosteus spendens and Tartuosteus giganteus. This is what distinguishes it from Guerichosteus kozlowskii, having the branchial plate long and narrow as in Drepanaspis.

In recent papers, Hariosteus is considered as a junior synonym of Guerichosteus (Glinsky 2018, Glinskiy and Pinakhina 2018). However, apart from differences in branchial plates, the ornamentation is also clearly different in these two genera. Moreover, Hariosteus features may suggest its affinity to younger genera such as Pycnosteus or Schizosteus. Thus, if we consider the taxonomic division by Tarlo (1964, 1965) or Glinsky (2018), this genus should be excluded from the Guerichosteidae and placed in Pycnosteidae. The ornamentation is also suggestive for the latter group of psammosteids.

RECONSTRUCTION The knowledge of an animal’s appearance is the key to any considerations regarding not only its taxonomic status, but also its biomechanical and ecological aspects. The reconstruction of the psammosteids can mostly be based on Drepanaspis gemuendenensis as it is the best known representative of the group. But specimens that consist of complete armor are flattened, while those preserved with no deformation are mostly isolated plates. Also, preservation of naturally connected plates is rare (as in the case of the specimens from Holy Cross Mountains). The new findings of the complete ventral plate, along with the posterior tip of the branchial plate, orbital plate and complex plate together (and fragments of plates), as well as the application of computer methods, reveal not only a more accurate view of Guerichosteus kozlowskii, but they also provide new insights into Drepanaspis and other psammosteid morphology. In this study only Guerichosteus kozlowskii may be reconstructed, as the Hariosteus material is insufficient.

The first step of Guerichosteus kozlowskii reconstruction was a single plate restoration. Most plates (orbital plate, postorbital plate, ventral median plate, cornual plate and complex plate) are represented by at least one slightly damaged or complete plate; the median dorsal plate and branchial plate (beside one small/juvenile specimen) are broken fragments. Next all 3D reconstructed plate models were imported to the Blender software. Because the Guerichosteus remains came from specimens of all sizes, they had to be scaled (reduced or enlarged). The reference size was the (MUZ.PIG.1733.II.353) ventral plate. The size relation of individual plates was based on the reconstructions of Drepanaspis gemuendenensis by Gross (1963). Then,

68 the individual plates were fitted together in the proper configuration (Fig. 16). In ventral and lateral views, the curvature of the lateral margin of the ventral plate reflects the inner margin of the ventral part of the branchial plates. Furthermore, the transition between the plates (looking at the transverse section) is smooth and the inclination of the ventral plate corresponds to the concave ventral side of the branchial plate (Fig. 16.3-4). In dorsal view, the external surface of the branchial plate changes from flat (in the posterior part of small specimens), to slightly concave (in the anterior part of larger specimens). The ventral surface of the plate is concave. It widens in the anterior tip and extends parallel to the lateral margin. At the midpoint of the plate length it expands strongly and forms a broad postero-medial projection. In the smallest specimen, ZPAL Ag.III/1089, the ventral surface is triangular.

FIGURE 16. Guerichosteus kozlowskii three-dimensional reconstruction; dorsal (1), ventral (2), front (3) back (4) and left lateral (5) view.

There were some problems with setting and reconstructing the dorsal plate properly, as several pieces represent distinct parts of the plate, although the dorsal plates show clear growth lines reflecting the subsequent ontogenetic stages. As it is shown in Figure 16 (Appendix 30), the lateral curvature of the plate is not smoothly arched as it was shown in the previous reconstruction of the psammosteid Drepanaspis, but it is slightly S-shaped and resembles more pteraspidids, such as Pteraspis or Errivaspis. Therefore, similar to these specimens the anterior margin of the plate is set slightly back in relation to the ventral plate, while the posterior edge of plates reaches the same point (Fig. 16.1-2, 16.5).

The cornual plate is placed similar to Drepanaspis (Gross 1963). The most anterior part of the body is limited by a complex plate. The dorsal margin of the plate is located at the point of the lateral margin of branchial plates, similarly to the Gross (1963) restoration of Drepanaspis. It is unknown how far the plate reached forward; here (in lateral view) it is placed in the extension of the antero-ventral surface of the ventral plate (Fig. 16.5).

CONCLUSIONS Investigation of the morphology, with consideration of ornamentation features, of psammosteid remains from “Placoderm Sandstone” supports the establishment of the genera Guerichosteus and Hariosteus by Tarlo (1964, 1965). The reexamination of the studied material reveals a new interpretation of some specimens such as ZPAL Ag. III/4. Tarlo (1965) described it as a ventral plate; however, it seems to be the dorsal plate. Detailed examination of the Guerichosteus species G. kotanskii, G. kulczyckii and G. lefeldi revealed that they were junior synonyms of the revised species Guerichosteus kozlowskii Tarlo, 1965. The analysis of ornamentation and plate morphology of Hariosteus kotanskii indicates their resemblance to Hariosteus kielanae. Thus H. kotanskii should be included in the species Hariosteus kielanae Tarlo, 1965. Hariosteus lobanowskii is considered here as invalid (nomen dubium).

Guerichosteus kozlowskii lacks the typically developed posterior notch. Instead of having a slit, it has a low depression. Also the Early Devonian Drepanaspis gemuendenensis seems to have a similarly developed posterior notch as Guerichosteus, although in the former species the analysis and revision is problematic due to taphonomic issues.

The development of the posterior notch from a depression might have resulted from enlargement of the psammosteids body during evolution. The ventral plate of Drepanaspis gemuendenensis resembles the one of Guerichosteus kozlowskii. Therefore, it is probably deeper and not so roundly arched as shown by Gross (1963). The three-dimensional restoration of Guerichosteus kozlowskii demonstrates its more streamlined body shape in comparison to the previous Drepanaspis gemuendenensis reconstruction.

ACKNOWLEDGMENTS The material obtained during fieldwork in 2011-2013 was financed by the Ministry of Science and Higher Education (grant No. IP2010 041470 awarded to Piotr Szrek). Piotr Szrek and Grzegorz Niedźwiedzki for cooperation and all support. I thank to Barbara Studencka, Cezary Krawczyński and Dariusz Nast, the Museum of the Earth of the Polish Academy of Sciences in Warsaw employees, for their support during collection studying. Studencka, Ce for their help during examine specimens. I thank to Przemysław Gorzelak (Institute of Paleobiology, Polish Academy of Sciences) and Sebastian Tasakowski for the linguistic correction of the manuscript. Furthermore, I thank three anonymous reviewers for their helpful comments and linguistic improvement.

REFERENCES

BERG, L.S. 1940. Classification of fishes, both recent and fossil. Trudy Zoologicheskogo Institua Akademii Nauk SSSR, 5:85-517.

BLIECK, A. 1984. Les Hétérostracés Ptéraspidiformes, Agnathes du Silurien-Dévonien du Continent nord-atlantique et des blocs avoisinants: révision systématique, phylogénie, biostratigraphie, biogéographie.

DEAN, 1904. Fishes of Gemunden. Science, 19:64–65.

ELLIOTT D.K., E. MARK-KURIK, and E.B. DAESCHLER. 2004. A revision of Obruchevia (Psammosteida: Heterostraci) and a description of a new obrucheviid from the Late Devonian of the Canadian Arctic. Acta Universitatis Latviensis, 679:22–45.

FALKINGHAM, P. L. 2012. Acquisition of high resolution 3D models using free, open- source, photogrammetric software. Palaeontologia Electronica Vol. 15, Issue 1; 1T:15p; https://doi.org/10.26879/264

FIJAŁKOWSKA-MADER, A. AND MALEC, J. 2011. Biostratigraphy of the Emsian to Eifelian in the Holy Cross Mountains (Poland). Geological Quarterly, 55:109-138.

GLINSKIY, V.N. AND PINAKHINA, D.V. 2018. New data on psammosteid heterostracans (Pteraspidomorpha) and acanthodians (Acanthodii) from the Pärnu Regional Stage (Lower Eifelian, Middle Devonian) of Estonia. Estonian Journal of Earth Sciences, 67:76. https://doi:10.3176/earth.2018.05.

GROSS, W. 1963. Drepanaspis gemuendenensis Schlüter, Neuuntersuchung. Palaeonogreaphica, 121A:133-155, Stuttgart.

HALSTEAD, L.B. 1973. August. The heterostracan fishes. Biological Reviews, 48:279– 332. https://doi:10.1111/j.1469-185X.1973.tb01005.x.

JANVIER, P. 1996. Early Vertebrates. Oxford, Oxford Science Publications, Clarendon Press.

KIAER, J. 1915. Upper Devonian Fish remains from Ellesmere Land, with remarks on Drepanaspis. Report of the Second Norwegian Arctic expedition in the "Fram" 1898-1902, 33:1-72. Kristania.

KIAER, J. 1928. The structure of the mouth if the oldest know vertebrates, pteraspis and cephalaspis. Palaeobiologica, 1:117-134, Vienna.

KRUSZEWSKI, Ł. AND DEC, M. 2018. Plumbogummite group minerals in Lower Devonian placoderm sandstones from Podłazie Hill, Holy Cross Mountains, Poland. Geological Quarterly, 62. https://doi:10.7306/gq.1410.

MALLISON, H. AND WINGS, O. 2014. Photogrammetry in paleontology – a practical guide. Journal of Paleontological Techniques, 12:1-31.

LANKESTER, 1868. Part 9, Vertebrata Craniata, London, 1-518.

OBRUCHEV, D. 1943. A new restoration of Drepanaspis. The Proceedings of the USSR Academy of Sciences, 41:268-271.

OBRUCHEV, D. AND MARK-KURIK, E. 1965. Psammosteids of the Devonian of the USSR. Akademiya Nauk Estonskoy SSR, Institut Geologii, Trudy. Tallinn, Estonia.

RANDLE, E. AND SANSOM, R.S. 2017a. Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters, Journal of Systematic Palaeontology, 15:583-599, https://doi: 10.1080/14772019.2016.1208293

RANDLE, E. AND SANSOM, R.S 2017b. Phylogenetic relationships of the ‘higher heterostracans’ (Heterostraci: Pteraspidiformes and Cyathaspididae), extinct jawless vertebrates, Zoological Journal of the Linnean Society, 181:910–926. https://doi.org/10.1093/zoolinnean/zlx025

STENSIÖ, E.A. 1927. The Downtonian and Devonian Vertebrates of Spitsbergen. I. Family Cephalaspidae. Skrifter om Svalbard og Nordishavet, 12:1-391.

STETSON, H.C. 1931. Studies on the Morphology of the Heterostraci. The Journal of Geology, 39:141–154. https://doi:10.1086/623803

SZREK, P., NIEDŹWIEDZKI, G. AND DEC, M. 2014. Storm origin of bone-bearing beds in the Lower Devonian placoderm sand stone from Podłazie Hill (Holy Cross Mountains, central Poland). Geological Quarterly, 58:795–806. https://doi.org/10.7306/gq.1191

SZULCZEWSKI, M. AND PORĘBSKI, S. 2008. Stop 1 – Bukowa Góra, Lower Devonian, p. 18-37. In Pieńkowski, G. and Uchman, A (ed.). Ichnological Sites of Poland. The Holy Cross Mountains and the Carpathian Flysch. The Second International Congress on Ichnology. Cracow, Poland, August 2-September 8. The Pre- Congress and Post-Congress Field Trip Guidebook, Warszawa

TARNOWSKA, M. 1976. Lithological correlation of the Lower Devonian in the eastern part of the Holy Cross Mountains (in Polish with English summary). Biuletyn Instytutu Geologicznego, 296: 75–115.

TARNOWSKA, M. 1981. Lower Devonian in the central part of the Holy Cross Mountains. Przewodnik 53 Zjazdu Polskiego Towarzystwa Geologicznego, Kielce. 57–67, Instytut Geologiczny.

TARLO, L.B. 1957. A preliminary note on new ostracoderms from the Lower Devonian (Emsian) of central Poland. Acta Palaeontologica Polonica, 2: 225-233.

TARLO, L.B. 1961. Psammosteids from the Middle and Upper Devonian of Scotland. The Quarterly Journal of the Geological Society of London, 117:367-402.

TARLO, L.B. 1964. Psammosteiformes (Agnatha) – a review with descriptions of new material from the Lower Devonian of Poland. I - general part. Palaeontologia Polonica, 13:1-135.

TARLO, L.B. 1965. Psammosteiformes (Agnatha) – a review with descriptions of new material from the Lower Devonian of Poland. II - systematic part. Palaeontologia Polonica, 15:1-168.

TRAQUAIR, R.H. 1896. The extinct Vertebrata of the Moray Firth Area, p. 235-285 in Harvie-Brown, J.H. and Buckley, T. E. (ed.). Vertebrate Fauna of the Moray Basin, Edinburgh.

TRAQUAIR, R.H. 1899. Report on Fossil Fishes collected by the Geological Survey of Scotland in the Silurian Rocks of the South of Scotland. Transitions of the Royal Society of the Edinburgh, 39:827-864.

TRAQUAIR, R.H. 1903. The Lower Devonian Fishes of Gemünden. Transitions of the Royal Society of the Edinburgh, 40:723-739.

SUPPLEMENTARY MATERIAL

APPENDIX 1. 3D model of Guerichostus kozlowskii dorsal plate ZPAL Ag. III/4.

APPENDIX 2. 3D model of Guerichostus kozlowskii dorsal plate ZPAL Ag. III/1.

APPENDIX 3. 3D model of Guerichostus kozlowskii dorsal plate ZPAL Ag. III/2.

APPENDIX 4. 3D model of Guerichostus kozlowskii dorsal plate MUZ.PIG.1733.II.13.

APPENDIX 5. 3D model of Guerichostus kozlowskii dorsal plate MZ-VIII/Vp-438.

APPENDIX 6. 3D model of Guerichostus kozlowskii ventral plate

MUZ.PIG.1733.II.353.

APPENDIX 7. 3D model of Guerichostus kozlowskii ventral plate ZPAL Ag. III/45.

APPENDIX 8. 3D model of Guerichostus kozlowskii branchial plate ZPAL Ag. III/1089.

APPENDIX 9. 3D model of Guerichostus kozlowskii branchial plate ZPAL Ag. III/16.

APPENDIX 10. 3D model of Guerichostus kozlowskii branchial plate ZPAL Ag. III/15.

APPENDIX 11. 3D model of Guerichostus kozlowskii branchial plate ZPAL Ag. III/8.

APPENDIX 12. 3D model of Guerichostus kozlowskii branchial plate ZPAL Ag. III/7.

APPENDIX 13. 3D model of Guerichostus kozlowskii branchial plate ZPAL Ag. III/9.

APPENDIX 14. 3D model of Guerichostus kozlowskii branchial plate ZPAL Ag. III/14.

APPENDIX 15. 3D model of Guerichostus kozlowskii cornual plate ZPAL Ag. III/19.

APPENDIX 16. 3D model of Guerichostus kozlowskii orbital plate

MUZ.PIG.1733.II.154.

APPENDIX 17. 3D model of Guerichostus kozlowskii complex plate

MUZ.PIG.1733.II.357.

APPENDIX 18. 3D model of Guerichostus kozlowskii median oral plate ZPAL Ag.

III/23.

APPENDIX 19. 3D model of Guerichostus kozlowskii lateral oral plate

MUZ.PIG.1733.II.357.

APPENDIX 20. 3D model of Guerichostus kozlowskii ridge scale ZPAL Ag. III/27A.

APPENDIX 21. 3D model of Guerichostus kozlowskii trunk scale ZPAL Ag. III/22.

APPENDIX 22. 3D model of Hariosteus kielanae dorsal plate ZPAL Ag. III/48.

APPENDIX 23. 3D model of Hariosteus kielanae branchial plate ZPAL Ag. III/17.

APPENDIX 24. 3D model of Hariosteus kielanae branchial plate MUZ.PIG.1733.II.185.

APPENDIX 25. 3D model of Hariosteus kielanae branchial plate ZPAL Ag. III/24.

APPENDIX 26. 3D model of Hariosteus kielanae ridge scale ZPAL Ag. III/25.

APPENDIX 27. 3D model of Hariosteus kielanae ridge scale ZPAL Ag. III/28.

APPENDIX 28. 3D model of Hariosteus kielanae ridge scale MZ-VIII/Vp-67.

APPENDIX 29. 3D model of Hariosteus kielanae trunk scale MUZ.PIG.1733.II.309.

APPENDIX 30. 3D model of Guerichostus kozlowskii reconstruction.

TABLE 1. List of current specimen numbers with reference to the specimen numbers from Tarlo (1964, 1965).

TABLE 1. List of current specimen numbers with reference to the specimen numbers

from Tarlo (1964, 1965).

Current Current Old specimen collection specimen Locality Group Name Part/element Belongs to number number number Institute of Guerichosteus D.1.U.W. ZPAL Ag. III/ 1 Podłazie Hill Psammosteidae dorsal plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.2.U.W. ZPAL Ag. III/ 2 Podłazie Hill Psammosteidae dorsal plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.3.U.W. ZPAL Ag. III/ 3 Podłazie Hill Psammosteidae ventral plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.4.U.W. ZPAL Ag. III/ 4 Podłazie Hill Psammosteidae dorsal plate Paleobiology, Polish kozlowskii Academy of Science Institute of lack in Guerichosteus D.5.U.W. Podłazie Hill Psammosteidae dorsal plate Paleobiology, Polish collection kozlowskii Academy of Science Institute of lack in Guerichosteus D.6.U.W. Podłazie Hill Psammosteidae ventral plate Paleobiology, Polish collection kozlowskii Academy of Science Institute of Guerichosteus D.7.U.W. ZPAL Ag. III/ 7 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.8.U.W. ZPAL Ag. III/ 8 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.9.U.W. ZPAL Ag. III/ 9 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kozlowskii Academy of Science Institute of lack in Guerichosteus D.10.U.W. Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish collection kozlowskii Academy of Science Institute of lack in Guerichosteus D.11.U.W. Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish collection kozlowskii Academy of Science Institute of lack in Guerichosteus D.12.U.W. Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish collection kozlowskii Academy of Science Institute of Guerichosteus D.13.U.W. ZPAL Ag. III/ 13 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.14.U.W. ZPAL Ag. III/ 14 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.15.U.W. MZ-VIII/Vp- 85 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.15.U.W. ZPAL Ag. III/ 15 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.16.U.W. ZPAL Ag. III/ 16 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kozlowskii Academy of Science Institute of lack in Guerichosteus D.18.U.W. Podłazie Hill Psammosteidae postorbital plate Paleobiology, Polish collection kozlowskii Academy of Science Institute of Guerichosteus D.19.U.W. ZPAL Ag. III/ 19 Podłazie Hill Psammosteidae cornular plate Paleobiology, Polish kozlowskii Academy of Science

Current Current Old specimen collection specimen Locality Group Name Part/element Belongs to number number number Institute of lack in Guerichosteus D.20.U.W. Podłazie Hill Psammosteidae cornular plate Paleobiology, Polish collection kozlowskii Academy of Science Institute of lack in Guerichosteus D.21.U.W. Podłazie Hill Psammosteidae rostral plate Paleobiology, Polish collection kozlowskii Academy of Science Institute of Guerichosteus D.22.U.W. ZPAL Ag. III/ 22 Podłazie Hill Psammosteidae body scale Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.23.U.W. ZPAL Ag. III/ 23 Podłazie Hill Psammosteidae oral plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.26.U.W. ZPAL Ag. III/ 26 Podłazie Hill Psammosteidae ridge scale Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.27.U.W. ZPAL Ag. III/ 27 Podłazie Hill Psammosteidae ridge scale Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.29.U.W. MZ-VIII/Vp- 67 Podłazie Hill Psammosteidae ridge scale Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.30.U.W. ZPAL Ag. III/ 30 Podłazie Hill Psammosteidae ridge scale Paleobiology, Polish kozlowskii Academy of Science Institute of lack in Guerichosteus D.31.U.W. Podłazie Hill Psammosteidae body scale Paleobiology, Polish collection kozlowskii Academy of Science Institute of lack in Guerichosteus D.32.U.W. Podłazie Hill Psammosteidae body scale Paleobiology, Polish collection kozlowskii Academy of Science Institute of Guerichosteus D.33.U.W. ZPAL Ag. III/ 33 Podłazie Hill Psammosteidae body scale Paleobiology, Polish kozlowskii Academy of Science Institute of lack in Guerichosteus D.34.U.W. Podłazie Hill Psammosteidae body scale Paleobiology, Polish collection kozlowskii Academy of Science Institute of Guerichosteus D.35.U.W. ZPAL Ag. III/ 35 Podłazie Hill Psammosteidae ornamentation Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.36.U.W. ZPAL Ag. III/ 36 Podłazie Hill Psammosteidae ornamentation Paleobiology, Polish kozlowskii Academy of Science Institute of lack in Guerichosteus D.44.U.W. Podłazie Hill Psammosteidae body scale Paleobiology, Polish collection kozlowskii Academy of Science Institute of Guerichosteus D.45.U.W. ZPAL Ag. III/ 45 Podłazie Hill Psammosteidae ventral plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.57.U.W ZPAL Ag. III/ 57 Podłazie Hill Psammosteidae fargment of plate Paleobiology, Polish kozlowskii Academy of Science Institute of Guerichosteus D.76.U.W. ZPAL Ag. III/ 76 Podłazie Hill Psammosteidae Paleobiology, Polish kozlowskii Academy of Science Institute of lack in Guerichosteus D.82.U.W. Podłazie Hill Psammosteidae fragment Paleobiology, Polish collection kozlowskii Academy of Science Institute of lack in Guerichosteus D.84.U.W. Podłazie Hill Psammosteidae fragment Paleobiology, Polish collection kozlowskii Academy of Science Institute of Guerichosteus ZPAL 1089 ZPAL Ag. III/ 1089 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kozlowskii Academy of Science

Current Current Old specimen collection specimen Locality Group Name Part/element Belongs to number number number

Geological Museum, Guerichosteus Institute of 1733.II. Podłazie Hill Psammosteidae postorbital plate kozlowskii Paleobiology, Polish Academy of Science

Geological Museum, Guerichosteus Institute of 1733.II. Podłazie Hill Psammosteidae dorsal plate kozlowskii Paleobiology, Polish Academy of Science

Geological Museum, Guerichosteus Institute of 1733.II. 353 Bukowa Hill Psammosteidae ventral plate kozlowskii Paleobiology, Polish Academy of Science

Geological Museum, Guerichosteus Institute of 1733.II. 355 Podłazie Hill Psammosteidae lateral oral plate kozlowskii Paleobiology, Polish Academy of Science

Geological Museum, Guerichosteus Institute of 1733.II. 357 Podłazie Hill Psammosteidae complex plate kozlowskii Paleobiology, Polish Academy of Science

Geological Museum, Guerichosteus Institute of 1733.II. 154 Podłazie Hill Psammosteidae orbital plate kozlowskii Paleobiology, Polish Academy of Science

Geological Museum, Guerichosteus Institute of 1733.II. 185 Podłazie Hill Psammosteidae branchial plate kozlowskii Paleobiology, Polish Academy of Science

Polish Academy of Guerichosteus MZ-VIII/Vp- 438 Podłazie Hill Psammosteidae dorasal plate Sciences Museum of kozlowskii the Earth in Warsaw

Polish Academy of Guerichosteus MZ-VIII/Vp- 463 Podłazie Hill Psammosteidae ridge scale Sciences Museum of kozlowskii the Earth in Warsaw

Polish Academy of Guerichosteus MZ-VIII/Vp- 335 Podłazie Hill Psammosteidae ridge scale Sciences Museum of kozlowskii the Earth in Warsaw

Polish Academy of Guerichosteus MZ-VIII/Vp- 423 Podłazie Hill Psammosteidae branchial plate Sciences Museum of kozlowskii the Earth in Warsaw

Polish Academy of Guerichosteus MZ-VIII/Vp- 488 Podłazie Hill Psammosteidae ridge scale Sciences Museum of kozlowskii the Earth in Warsaw

Polish Academy of Guerichosteus MZ-VIII/Vp- 533 Podłazie Hill Psammosteidae branchial plate Sciences Museum of kozlowskii the Earth in Warsaw

Polish Academy of Guerichosteus MZ-VIII/Vp- 536 Podłazie Hill Psammosteidae body scale Sciences Museum of kozlowskii the Earth in Warsaw

Institute of Hariosteus D.17.U.W. ZPAL Ag. III/ 17 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kielanae Academy of Science

Current Current Old specimen collection specimen Locality Group Name Part/element Belongs to number number number Institute of Hariosteus D.24.U.W. ZPAL Ag. III/ 24 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kielanae Academy of Science Institute of Hariosteus D.25.U.W. ZPAL Ag. III/ 25 Podłazie Hill Psammosteidae ridge scale Paleobiology, Polish kielanae Academy of Science Institute of Hariosteus D.28.U.W. ZPAL Ag. III/ 28 Podłazie Hill Psammosteidae ridge scale Paleobiology, Polish kielanae Academy of Science Institute of Hariosteus D.48.U.W. ZPAL Ag. III/ 48 Podłazie Hill Psammosteidae dorsal plate Paleobiology, Polish kielanae Academy of Science Institute of Hariosteus D.49.U.W. ZPAL Ag. III/ 49 Podłazie Hill Psammosteidae dorsal plate Paleobiology, Polish kielanae Academy of Science Institute of Hariosteus D.50.U.W. ZPAL Ag. III/ 50 Podłazie Hill Psammosteidae dorsal plate Paleobiology, Polish kielanae Academy of Science Institute of Hariosteus D.51.U.W. ZPAL Ag. III/ 51 Podłazie Hill Psammosteidae fragment Paleobiology, Polish kielanae Academy of Science Institute of lack in Hariosteus D.52.U.W Podłazie Hill Psammosteidae fragment Paleobiology, Polish collection kielanae Academy of Science Institute of Hariosteus D.53.U.W ZPAL Ag. III/ 53 Podłazie Hill Psammosteidae fragment Paleobiology, Polish kielanae Academy of Science Institute of lack in Hariosteus D.54.U.W Podłazie Hill Psammosteidae fragment Paleobiology, Polish collection kielanae Academy of Science Institute of lack in Hariosteus D.55.U.W. Podłazie Hill Psammosteidae fragment Paleobiology, Polish collection kielanae Academy of Institute of Hariosteus D.56.U.W. ZPAL Ag. III/ 56 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kielanae Academy of Science Institute of lack in Hariosteus D.58.U.W. Podłazie Hill Psammosteidae body scale Paleobiology, Polish collection kielanae Academy of Science Institute of lack in Hariosteus D.59.U.W. Podłazie Hill Psammosteidae body scale Paleobiology, Polish collection kielanae Academy of Science Institute of Hariosteus D.60.U.W. ZPAL Ag. III/ 60 Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish kielanae Academy of Science Geological Museum, Hariosteus Institute of 1733.II. Podłazie Hill Psammosteidae dorsal plate kielanae Paleobiology, Polish Academy of Science

Geological Museum, Hariosteus Institute of 1733.II. 70 Podłazie Hill Psammosteidae branchial plate kielanae Paleobiology, Polish Academy of Science

Geological Museum, Hariosteus Institute of 1733.II. 309 Podłazie Hill Psammosteidae body scale kielanae Paleobiology, Polish Academy of Science

Geological Museum, Hariosteus Institute of 1733.II. Podłazie Hill Psammosteidae body sclale kielanae Paleobiology, Polish Academy of Science

Polish Academy of Hariosteus MZ-VIII/Vp- 410 Podłazie Hill Psammosteidae body sclale Sciences Museum of kielanae the Earth in Warsaw

Current Current Old specimen collection specimen Locality Group Name Part/element Belongs to number number number Hariosteus Institute of lack in kielanae D.61.U.W. Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish collection (H. Academy of Science Lobanowskii) Hariosteus Institute of lack in kielanae D.62.U.W. Podłazie Hill Psammosteidae branchial plate Paleobiology, Polish collection (H. Academy of Science Lobanowskii) D.38.U.W. ZPAL Ag. III/ 38 Psammosteidae

CHAPTER IV

A NEW MIDDLE DEVONIAN (GIVETIAN) PSAMMOSTEID (VERTEBRATA: 4 HETEROSTRACI) FROM POLAND MAREK DEC

Institute of Palaeobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland.

ABSTRACT A new genus and species of psammosteid heterostracan, Psarkosteus mediocris gen. et sp. nov., is described from the Middle Devonian (Givetian) of the Skały Formation, the Holy Cross Mountains, Poland. The dorsal 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 representarives of the group. Most distinctive are big teardrop-shaped tubercles with a flat or slightly concave surface with its tip directed posteriorly, and a crenulated base placed along the branchial plates. The lateral line system in Psarkosteus is similar to that in Drepanaspis gemuendenensis and confirms earlier reconstructions.

INTRODUCTION The fossil record of Heterostraci is poor in Poland, yet the fossils are known from the Upper Silurian, Lower and Middle Devonian deposits. From a core sample of the Upper Silurian (Přidoli) succession in Mielnik a representative of the Tolypelepididae was described (Dec 2015). Some basal heterostracan groups (Traquairaspididae and Cyathaspididae) have been described from the Lower Devonian core drillings of Poland. A rich vertebrate assemblage from Emsian sandstones in the Holy Cross Mountains (Podłazie Hill and Bukowa Hill) include fish remains belonging to sarcopterygians, osteichthyans, acanthodians, placoderms and ostracoderms (sensu Janvier 1996a). The latter comprise two pteraspidiform groups, the Pteraspididae with Rhinopteraspis sanctacrucensis (Tarlo) and Psammosteidae with Guerichosteus kozlowskii Tarlo and Hariosteus kielanae Tarlo (for details see Dec 2019). Described below psammosteids fossil record from the Givetian of the Holy Cross Mountains (Łysogóry region, Śniadka), with Psarkosteus mediocris gen. et sp. nov. provides new

4 In press in Annales Societatis Geologorum Poloniae

82 information on evolution, morphology and paleogeographic of psammosteids. Specimens are curated in the Institute of Paleobiology of Polish Academy of Sciences under references.

PHYLOGENETIC BACKGROUND Herein psammosteids are considered to represent the family Psammosteidae (sensu Janvier 1996b, Pernègre and Elliott 2008 Randle and Sansom 2017a, b) which is generally regarded as monophyletic and allied to Pteraspidiformes (Blieck 1984, Blieck and Elliott 2017, Glinskiy 2018). The main problem is concerned with their relationships within Pteraspidiformes Psammosteidae were supposed to be (1) either a sister group to pteraspids s.l., that is Protopteraspididae + Pteraspididae s.l. (in Blieck 1984), or (2) a sister group to solely Protaspididae (sensu Blieck 1984, Janvier 1996a), or (3) a derived clade within Pteraspidiformes, with Pteraspididae ('pteraspidids') as a sister group (Blieck et al. 1991, Janvier 1996b).

The phylogenetic relationships within psammosteids were studied by several authors (Tarlo 1964, Obruchev and Mark-Kurik 1965, 1968). Tarlo (1965) considered that the 'main lineage' of psammosteids diverged from Guerichosteus kozlowskii. Glinskiy (2018) compiled the knowledge of earlier authors about ingroup relationships and proposed the most complete phylogenetic analysis of the group, where Drepanaspis and Guerichosteus are basal to all other psammosteids. The most recent study (Dec 2019) of Guerichosteus shows its close affinity with Drepanaspis, while features of Hariosteus suggest its affinity to younger genera such as Pycnosteus.

MATERIAL AND GEOLOGICAL SETTING The material described here was obtained from an outcrop placed on the east of Śniadka village, on the left bank of Psarka river, and south from the entrance of a ravine called Sitka (Fig. 1.3). It comprises limestone, marly and clayey shales representing the upper part of the Skały Formation (Sobolew 1909, Kłossowski 1985, Woroncowa-Marcinowska 2012). The sedimentary structures on the layer surface show that the strata in the exposed section are overturned (Kłossowski 1985). This lithostratigraphic unit is part of the Świętomarz-Śniadka section located in NE of the Holy Cross Mountains, in the Łysogóry Mountains (Fig. 1.1-2). The interpretation of the geological of cross-section of the central part of the Bodzentyn Syncline placed between Świętomarz and Śniadka, and exposed along the Psarka River, has been investigated by many authors: Sobolew (1909), Mizerski (1981), Kłossowski (1985),

Turnau and Racki (1999), Malec (1990, 1993), Halamski (2005), Halamski and Segit (2005), Woroncowa-Marcinowska (2012). Most discussion concerned tectonic and stratigraphic interpretation of this site (Turnau and Racki 1999, Woroncowa- Marcinowska 2012). Clastic influx represented by those sediments shows terrigenous influence from the north (Kłossowski 1985, Racki 1997).

The layer with psammosteids is located (Fig. 2) just below the the goniatite horizon and corresponds with the rhenanus/varcus Conodont Zone (Woroncowa- Marcinowska 2012), that is correlated in standard conodonts zonation correlated with the Lower varcus Zone (Narkiewicz and Bultynck 2007). A sedimentological analysis made by Kłossowski (1985) shows relatively shallow water conditions, which have been confirmed by the assemblage analysis of the fauna including conodonts, bivalves, gastropods and brachiopods (Dzik 2002).

The ichnofossil Alpetria sanctacrucensis Orłowski & Radwański, 1986 interpreted as a sea-anemone burrow also suggest a shallow sublittoral environment. Further they indicate hydrodynamic agents such as currents or waves are responsible for rapid burial of the organisms (Orłowski and Radwański 1986).

FIGURE 1. Map showing the location of: 1. Holy Cross Mountains (HCM), 2. Śniadka in HCM, 3. collection site placed on the left bank of the Psarka river.

Most of the part of collection was obtained by Magdalena Borsuk-Białynicka in 1978-79, but during the fieldwork in 2012-2013 new material was collected by the present author. The psammosteid remains at Śniadka occur in marly and clayey shales. All specimens are flattened, moreover some are deformed (stretched, foliated).

Most fossiliferous material was found in one horizon, below the part with the cephalopod fauna, and preserved as isolated plates. Sometimes plates were associated with accumulations of scales (Fig. 2).

The rock matrix with specimens was impregnated with dilute cyanoacrylic in order to prevent fracture due to the drying of the slab. The specimens were cleaned mechanically and brushed with detergent. The procedure was repeated up to the desired result.

For taking photographs, specimens were coated with ammonium chloride.

FIGURE 2. Stratigraphical position of the psammosteids-bearing complex with geological column with part of the Skały Formation in the locality shown in Fig. 1.3.

SYSTEMATIC PALEONTOLOGY

Class PTERASPIDOMORPHI Goodrich, 1909

Subclass HETEROSTRACI Lankester, 1868

Order PTERASPIDIFORMES Berg, 1937

Family PSAMMOSTEIDAE Traquair, 1896

Genus PSARKOSTEUS gen. nov.

Type and only species. Psarkosteus mediocris gen. et sp. nov.

Etymology. In reference to the type locality near Psarka river.

Diagnosis. As for the type species. The genus is monotypic.

Psarkosteus mediocris gen. et sp. nov.

Etymology: From Latin mediocris, in reference to its moderate size.

Holotype: Dorsal plate ZPAL Ag–I/32 (Figs 3.1, 9.1)

Referred material: ZPAL Ag. I/1.1 (Figs 5.1, 11), ZPAL Ag. I/1.2 (Fig. 3.5), ZPAL Ag. I/2 (Fig. 4.5), ZPAL Ag. I/3 (Fig. 4.1), ZPAL Ag. I/4 (Figs 4.2, 10.2), ZPAL Ag. I/5 (Fig. 5.2), ZPAL Ag. I/6 (Figs 6.5, 7.5), ZPAL Ag. I/7 (Figs 6.2, 7.2, 12.2), ZPAL Ag. I/8 (Figs 4.3, 10.1,10.3-4), ZPAL Ag. I/9 (Fig. 5.3), ZPAL Ag. I/10 (Fig. 3.4 ), ZPAL Ag. I/11 (Fig. 6.1), ZPAL Ag. I/12 (Figs 6.3, 7.3), ZPAL Ag. I/15.1 (Fig. 8.5), ZPAL Ag. I/15.2 (Fig. 8.6), ZPAL Ag. I/15.3 (Fig. 8.4), ZPAL Ag. I/16 (Fig. 8.7), ZPAL Ag. I/17.1 (Figs 6.7, 7.7), ZPAL Ag. I/17.2 (Figs 6.6, 7.6, 12.1), ZPAL Ag. I/18 (Figs 6.810, 7.8- 10), ZPAL Ag. I/19 (Fig. 3.3), ZPAL Ag. I/20 (Fig. 4.4), ZPAL Ag. I/22 (Fig. 8.1), ZPAL Ag. I/23 (Fig. 8.2), ZPAL Ag. I/26 (Fig. 8.3), ZPAL Ag. I/31 (Figs 3.2, 9.2, 14.4), ZPAL Ag. I/32 (Figs 3.1, 9.1, 14.3).

Type locality: Śniadka, outcrop placed on the left bank of the Psarka river, south to the entrance of Sitka ravine (GPS coordinates 50°57'32.4"N 21°00'51.6"E). A village is in the administrative district of Gmina Bodzentyn, within Kielce County, Świętokrzyskie Voivodeship, in south-central Poland (Fig. 1).

Occurrence: Middle Devonian (Givetian) Skały Frmation, Lower varcus conodot zone. Locality: Śniadka, the outcrop placed on the left bank of the Psarka river, south to the entrance of Sitka ravine (Fig. 1).

Diagnosis. Relatively medium sized species (up to 16 cm in dorsal plate length). Dorsal plate is elongated, with an elliptical shape (width ratio 1.5–1.8). It differs from that in other psammosteids by constriction of its anterior part. Ventral plate oval in shape with deep posterior notch that almost reaches the growth center placed posterior to mid-length of the plate. Postorbital plates triangular and slender. Branchial plates narrow, triangular in shape with convex lateral edge; rnamented part of the dorsal surface relatively narrow. The distinctive big teardrop-shaped tubercles with flat or slightly concave surface and well developed basal crenulation extend along the lateral margin of branchial plates.

Description

Dorsal plate. Two complete specimens ZPAL Ag. I/31–32 and three partially preserved specimens ZPAL Ag. I/1.2, 10, 19, were recognized (Fig. 3). The large plate (ZPAL Ag. I/32) is elongated, with an elliptical shape (l:w=1.48). Its length is 15.8 cm, measured along the central axis of the plate, the maximum width 10,7 cm, at the level of growth center. The specimen has its anterior margin broadly rounded with front part of the plate (2.3 cm in length) narrowed to 7.8 cm in width. The lateral margin turn posteriorly over right angle, diverge strongly to maximum width, and extend parallel by a certain length (about 5 cm). From about 2/3 of its length the plate tapers, its lateral margins turning posteriorly at an angle of 75°. The distal end is pointed. The plate bears well marked growth lines that surround the growth center situated little in front, 7 cm from the anterior margin.

Two dorsal plates of small individuals ZPAL Ag. I/31 (Fig. 3.2) and ZPAL Ag. I/10 (Fig. 3.4) are considered as juvenile. The former one is complete, 6.4 cm in length and 3.6 cm in width (l:w=1.8), with the same overall shape as in the largest specimen, but much more slender. The second one is incomplete and looks wider than the former, but the margins of the plate are damaged. The length of the preserved part is just 5.3 cm and its width is 5.3 cm, but the shape of the plate can be restored (Fig. 3.4) on the basis of the growth lines visible around the center of growth. The estimated length to width ratio of the plate is 1.2.

Ventral plate. Five incomplete specimens ZPAL Ag. I/2–4, 8, 20 are known (Fig. 4). The largest specimen ZPAL Ag. I/3 represents a central and right part of a plate and measures 13.3 cm in length (on more complete natural mold 16.3 cm in length) and 11.6 cm in width (Fig. 4.1). Most edges are broken-off, only the margin

87 of the posterior notch is preserved, but the growth lines are clearly visible around centrally located growth center. Anterior part of the plate is trapezoidal (Fig. 4.1), then the plate widens to the middle of the plate and smoothly turns to the posterior notch. Right fragment of ventral plate of small specimen ZPAL Ag. I/8, 4.7 cm in length and 2.1 cm in width (Fig. 4.3). It allows to estimate of its total width to 4.2 cm. Lateral, posterior margin as well as posterior notch margins are well preserved. Posterior notch extends well into the central area, but it does not reach the growth center.

Branchial plate. Eigth specimens of plates are preserved (Figs 5–7), including two large and near-complete ones (Fig. 7). The first one (ZPAL Ag. I/5) has its postero- lateral corner broken off (Fig. 7.2), while the second one (ZPAL Ag. I/9) is almost complete (Fig. 7.3). As far as the natural mold of the first specimen is preserved, the shape of the plate can be restored. The plate is triangular, its length varies from 58 mm to 150 mm (the largest was probably 190 mm). The lateral margin is convex, the posterior almost straight margin smoothly turns (about 110°) to the straight medial margin. Anterior tip of the plate is best preserved on the specimen ZPAL Ag. I/9 and ZPAL Ag. I/17 (Figs 5.5, 7.3), where the angle between lateral and medial margin is 50° (measured in the most anterior part which is undisturbed). The ZPAL Ag. I/17 specimen has very narrow dorsal surface covered with tubercles, while it is wider and extends posteriorly in the larger specimen ZPAL Ag. I/15 (Figs 5.6, 6.6). The posterior part of the free surface is visible only on imprints of ZPAL Ag. I/12 (Figs 5.3, 6.3) and ZPAL Ag. I/6–7 (in parts where bone is broken-off), it turns along the lateral margin and tapers to the postero-median corner, so the branchial opening was probably located more medially.

Postorbital plate. Only one, near-complete specimen ZPAL Ag. I/1.1 of a left postorbital plate has been collected (Fig. 7.1). The plate is slender, the maximum length is 13.3 cm. Anterior half of the plate is the widest part, its width is 3.1 cm. Then, from the mid-length the plate tapers posteriorly. The rounded front edge of the plate smoothly turns round into the medial margin. The most anterior lateral part of the plate gradually increases in thickness (from 3 mm to 6 mm) anteriorly, but does not bend to internal side. The lateral margin is arched only near the growth center, about 5.5 cm from the front part of the plate. Anterior and posterior to the growth center the laterl margin extend almost straight and the angle between them is 163°. The growth lines run parallel to the medial and front margins of the plate (Fig. 7.1).

Scales. Different scales are preserved, varying from small body scales to larger ridges scales (Fig. 8). The small scales are diamond-shaped with anteriorly placed narrow area (specimen ZPAL Ag. I/22–23; Fig. 8.1-2) to be overlapped by the more anterior scales. The specimen ZPAL Ag. I/26 is triangular (8 mm long and 6 mm high) with an undulate anterior margin of tuberculated area and a narrow anterior area to be overlapped (Fig. 8.3). Four incomplete ridge scales (Fig. 8.4-7) are preserved, and only two are near-complete and vary in length from 38 cm (ZPAL Ag. I/16, Figure 8.7) to 70 mm (estimated on the basis of ZPAL Ag. I/15.1, Fig. 8.5). The maximum width is up to 26 mm (ZPAL Ag. I/15.1, Fig. 8.5). Most specimens are long and slender and the anterior margin, preserved only on the specimen ZPAL Ag. I/15.3, is sinusoidal which is also marked by a visibile growth line (Fig. 8.4). Ornamentation. It consists of tubercles that vary in size according to the region of the body, and even within particular plates. The ornamentation also depends on the growth stage of the plate. At the growth centers of dorsal and ventral plates the tubercles are variable in size, generally small (0.60 mm; 17 per cm) and conical, with their tip pointed upwards (Figs 9.5, 10.6). A little away from center, they are still conical, although the tip is directed posteriorly and they are crenulated at the base (Figs 9.6-7, 10.3, 10.6). Distant from the middle, the tubercles decrease in height (Figs 9.1, 10.5) and vary in shape; anteriorly the tubercles are symmetrical and teardrop-shaped with a flat or slightly concave surface, with the tip directed posteriorly. Sides of the plate are covered with asymmetrical tubercles where the tip is directed to the mid-line (Fig. 9.3-4). Therefore, the tubercles situated posteriorly to the growth center, at mid-line axis, converge inward (Fig. 9.7). The smallest (0.40–0.45 mm; 22–25 per cm) and lowest tubercles are located near the edge of the dorsal and ventral plates, as well as near the medial border of branchial (Fig. 12.5) and postorbital plates (Fig. 11.4). In contrast at the lateral (outer) margins of the branchial and postorbital plates, that create the margins of the animal body, the tubercles are the biggest (Figs 11.2, 12.6-7). Also anterior to the growth center, on the postorbital plate, the tubercles are almost fused and show the signs of abrasion of the ornamentation (Fig. 11.3). Toward the anterior part of the plate, the tubercles are more separate and the tips become slightly less flattened (Fig. 11.2). On branchial plates along the lateral edge the tubercles range from 0.70 to 0.90 mm (11–14 per cm), while decreasing in size toward the anterior tip.

Remarks: Psarkosteus mediocris is a middle-sized psammosteid, its size estimation being based on the length of the dorsal plate. It is 15 cm in the largest, whereas it usually reaches 20 cm in other psammosteids. In the Śniadka material the smallest dorsal plate is 6 cm long, and is considered a young individual. The elongated, with an elliptical shape dorsal plate of Psarkosteus has a distinctive anterior constriction (Figs 3, 13.1). This shape stands out among psammosteids. With the value 1.5–1.8, the length to width ratio of Psarkosteus is quite high. In most psammosteids the value covers a range from 0.7 to 1.3 and only Psammosteus undulata (1.4–1.6 length to width ratio) falls outside of the range. The overall shape of dorsal plate of Psarkosteus resembles those of Schizosteus striatus (Obruchev and Mark-Kurik 1965, fig. 37), except that growth lines undulate in the latter.

The variability of plates may be related to ontogenetic growth or to individual variation, but other factors, such as diagenetic and tectonic stretching, may also be involved, and probably had a greater impact for the biometric differences. Taking into account the above factors the reconstruction of Psarokosteus mediocris is shown on Fig. 13. To receive the deep ventral plate, the flat plate reconstruction was printed in natural size and bent so that the way that the inner margins of the posterior notch were parallel to each other as they are in psammosteids like Schizosteus and Tartuosteus.

The very long and narrow postorbital plate is distincitve among Psammosteidae even more than in derived Psammolepis.

The general morphology and variety of tubercles presented in Psarkosteus mediocris distinguish it from Schizosteus striatus and other psammosteids. Most characteristic are tubercles placed along the branchial plate margin. The big teardrop-shaped tubercles have flat or slightly concave surface with well visible crenulation of the base. The tips of tubercles are pointed posteriorly.

FIGURE. 3. Psarkosteus mediocris, dorsal plate, external view of specimen. 1. ZPAL Ag. I/32, 2. ZPAL Ag. I/31. 3. ZPAL Ag. I/19. 4. ZPAL Ag. I/10, 5. ZPAL Ag. I/1.2. 6-10, specimens drawing with growth line marked (densely dashed line) and lateral line (doted line). Plate shape restoration marked with loosely dashed line.

FIGURE. 4. Psarkosteus mediocris, ventral plate, external view of specimen: 1. ZPAL Ag. I/3, 2. ZPAL Ag. I/4, 3. ZPAL Ag. I/8, 4. ZPAL Ag. I/20, 5. ZPAL Ag. I/2; 6-10, specimens drawing with growth line marked (densely dashed line) and lateral line (doted line). Plate shape restoration marked with loosely dashed line.

FIGURE. 5. Psarkosteus mediocris, branchial plate, specimen. 1. ZPAL Ag. I/ 11, ventral view of left branchial plate. 2. ZPAL Ag. I/7, ventral view of right branchial plate. 3. ZPAL Ag. I/12, ventral view of right branchial plate. 4. Imprint of ZPAL Ag. I/12 with small broken fragment of plate where dorsal side with ornamentation is preserved. 5. ZPAL Ag. I/6, ventral view of left branchial plate. 6-7. ZPAL Ag.I/17, right branchial plate: ventral (6) and dorsal (7) views. 8-10. ZPAL Ag. I/18, left branchial plate: dorsal (8), ventral (9) and imprint of dorsal (10) views.

FIGURE. 6. Psarkosteus mediocris, branchial plate, drawings of specimens showed on Fig. 5.

FIGURE. 7. Psarkosteus mediocris gen. et sp. nov. 1. ZPAL Ag. I/1.1 left postorbital plate, external view. 2. ZPAL Ag. I/5, ventral view of right branchial plate. 3. ZPAL Ag. I/9, ventral view of right branchial plate. 4-6, specimens drawing with growth line marked (densely dashed line) and plate shape restoration marked with loosely dahed line.

FIGURE. 8. Psarkosteus mediocris. 1. body scale ZPAL Ag. I/22. 2. body scale ZPAL Ag. I/23 with close-up on tubercles. 3. body scale ZPAL Ag. I/26. 4. ridge scale ZPAL Ag. I/15.3, external view of anterior tip fragment (4) and drawing with growth line marked (hached line). 5. ridge scale ZPAL Ag. I/15.1, external view with close-up on tubercles. 6. ridge scale ZPAL Ag. I/15.2 external view. 7. ridge scale ZPAL Ag. I/16, external view.

FIGURE. 9. Psarkosteus mediocris. 1. dorsal plate ZPAL Ag. I/32 with fragment showing the detail of ornamentation (3-4). 2. dorsal plate ZPAL Ag. I/31 with fragment showing the detail of ornamentation (5-7).

FIGURE. 10. Psarkosteus mediocris. 1. ventral plate ZPAL Ag. I/8 with fragment showing the detail of ornamentation (3-4). 2. ventral plate ZPAL Ag. I/4 with fragment showing the detail of ornamentation (5-7).

FIGURE. 11. Psarkosteus mediocris. 1. postorbital plate ZPAL Ag. I/1.1 with fragment showing the detail of ornamentation (2-4).

FIGURE. 12. Psarkosteus mediocris. 1. branchial plate ZPAL Ag. I/17.2 with fragment showing the detail of ornamentation (3-5). 2. branchial plate ZPAL Ag. I/7 with fragment showing the detail of ornamentation (6-7).

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FIGURE. 13. Psarkosteus mediocris reconstruction; 1. dorsal view. 2. ventral view, restoration of flattened ventaral plate (3) to deep ventral plate in ventral view (4) and lateral view (5).

LATERAL LINE

The heterostracan lateral line system consists of a network of canals closed in cancellous layer of dermal bone and connected to the surface by pores. The psammosteid sensory line system was identified by Gross (1963, fig. 3; Fig. 14.1) in Drepanaspis gemuendenensis dorsal and ventral plates. According to latter author, the ridges radiating from the center of plate represent sensory line canals. Tarlo (1964) disagreed with this interpretation and considered those ridges as associated with the pattern of the plate growth. Also Obruchev and Mark-Kurik (1965) did not support Gross identification at the time. However, the Drepanaspis gemuendenensis material from Rhineland, Germany stored in Tallinn, allowed the confirmation of the identification by Gross (Elliott and Mark-Kurik 2005). Psarkosteus gen. nov. (Figs 3, 14.3-4) has radial ridges on the dorsal plates similar to those observed in Drepanaspis gemuendenensis, which look like traces of more pronounced distoriotn. Occasionally they bear collapsed superficial tubercles that trace the radial lines. Apparently as a result of the plate compaction the largest deformation occurred in weaker parts of plates

101 previously occupied by canals of the sensory line system. The distortion is probably due to tectonic flattening, which is only visible on flattened specimens of Drepanaspis or Psarokosteus gen. nov. Less deformed paltes as those seen in Guerichosteus kozlowskii, Tartuosteus maximus or Psammolepis venyukovi have actually natural curves and lack of compaction-related deformation. The deformation is also observed on a specimen of the geological collection at Tallinn University of Technology (GIT 116– 51) that contains dorsal plate of Schizosteus striatus (personal observation). Three genera Drepanaspis, Schizosteus and Psarkosteus show the same pattern of four pairs of canals radiating from the growth center (Fig. 14). The original description by Gross (1963) presented four pair of the sensory canals. The first (dc1) and second (dc2) pair placed in the anterior region, dc1 near the front recces and dc2 placed laterally of the front corner. The two other (dc3 and dc4) are placed in posterior region, dc3 near the side edges of the plate and the fourth pair dc4 on the side of the rear corners. In Psarkosteus the divergence of the canals is similar to that in Drepanaspis (Fig. 14.1) and Schizosteus (Fig. 14.5). However, the dc3 canal is placed more anteriorly than in Drepanaspis

FIGURE. 14. Dorsal plate sensory lateral line system in Drepanaspis gemuendenensis (1. after Gross, 1963; 2. after Glinsky 2017) Psarkosteus mediocris adult (3) and juvenile (4), Schizosteus striatus (5. modified from Obruchev and Mark-Kurik 1965) and Psammolepis proia (6. after Elliot and Mark-Kurik 2005) dorsal plate. Median comissure (mc), transverse commisure (tc).

102 or Schizosteus. On the basis Elliott and Mark-Kurik’s (2005) review of the lateral line sensory system in psammosteids, it can be concluded that dc2 and dc3 canals shown by Gross (1963) correspond to transverse commissure of Psammolepis proia (Fig. 14.6). The dc1 and dc4 canals of Drepanaspis apparently represent the median dorsal canal of Psammolepis proia (Fig. 14.6). However Glinski (2018) on fig. 2 showed the dc4 canal of Drepanaspis as a third transverse commissure (Fig. 14.2). He added a medial canal, despite that there is no evidence of one more pair of canal in known Drepanaspis remains. Therefore more probable is the occurrence of one pair of median canal and two oblique commissures that radiate from the growth center in Drepanaspis, Schizosteus and Psarkosteus dorsal plate. In that state the dc1, dc4 in the latter genera correspond to Psammolepis proia median canal (mc), and dc2, dc3 to transverse commissure (tc) shown in Elliott and Mark-Kurik (2005).

DISPERSAL OF PSAMMOSTEIDS

Psammosteids have an exclusively Devonian distribution and are restricted to the coastlines of Laurussia (Fig. 15) with one exception of Lower/Middle Devonian Schizosteus perneri Růžička, known from Prague Basin on the peri-Gondwanan shelf (Vaškaninová and Kraft, 2016). The earliest species of psammosteids is the Early Devonian Drepanaspis, known from the Pragian-Emsian of England (Cornwall), western Germany (Rhenish Slate Massif), Belgium and Luxembourg (Ardenne Massif). Apearently from this region psammosteids may have spread northward along continent, where Guerichosteus and Hariosteus are known in the Emsian sandstone deposits of the Holy Cross Mountains (Tarlo 1964, 1965, Szrek et al. 2014, Dec 2019). During the Emsian/Eifelian Schizosteus perneri is noted from peri-Gondwanan (Prague Basin) shelf while the main radiation has taken place to the north in the Middle Devonian. The Eiffelian dispersal of psammosteids (Schizosteus and Pycnolepis) to north (Estonia and Latvia) was the beginning of the Givetian diversification. Six genera (21 species): Psammosteus, Psammolepis, Ganosteus, Tartuosteus, Schizosteus and Pycnosteus are known from Estonia, Latvia and Russia in that time. Although the geographical distribution is not only restricted to this part of Laurussia, Psrakosteus mediocris gen. et sp. nov., described herein from the Holy Cross Mountains shows a more southern of Psammosteus meandrinus from Estonia, Obruchevia heckeri and Persheia pulla from the Canadian Arctic. Both latter genera are the most northerly and western recognized representatives of the group.

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FIGURE. 15. Paleogeographical (modified from Scotese, 2001) distribution of psammosteids in the Lower (400 Ma) and Middle (385 Ma) Devonian.

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CONCLUSION

Herein, Psarkosteus mediocris gen. et sp. nov. from the Middle Devonian of the Holy Cross Mountains is described. The study of the morphology and ornamentation of plates present in the material has shown differences in size (9 to 15 cm), proportion (width ratio 1.5–1.8), shape of the dorsal plate (oblong with an anterior constriction) and ornamentation (big teardrop-shaped tubercles with flat or slightly concave surface, and crenulated base extend along the lateral margin of branchial plates) with respect to other psammosteids, which are considered sufficient for the erection of a new genus and species. Psarkosteus mediocris is the first Middle Devonian psammosteid genus and species described from Poland. The new genus marks the southernmost occurrence of the Psammosteidae in the Middle Devonian. The new genus is considered most similar, probably most closely related to Schizosteus striatus (Fig. 16) on the basis of their lateral line system and shape of growth lines of the dorsal plate. This relationships with Schizosteus striatus suggest a possibility of migration from north to south of the Laurussia.

ACKNOWLEDGEMENTS

I thank to Magdalena Borsuk-Białynicka (Institute of Paleobiology, Polish Academy of Sciences) for access to collections, comments and suggestions on drafts of this manuscript that helped to improve the final version of the paper. I thank to Marian Dziewiński (Institute of Paleobiology PAS, Poland) for technical support during preparation of photographs. I would especially like to thank David Kenneth Elliott and Alain Blieck for their constructive reviews of the manuscriptfor their helpful comments and linguistic improvement.

REFERENCE

BLIECK, A., ELLIOTT, D.K., AND GAGNIER, P.Y. 1991. Some questions concerning the phylogenetic relationships of heterostracans, Ordovician to Devonian jawless vertebrates. Early vertebrates and related problems of evolutionary biology. Science Press, Beijing, 1-17.

BLIECK, A., 1984. Les Hétérostracés Pteraspidiformes, Agnathes du Silurien-Dévonien du Continent Nord-Atlantique et des blocs avoisinants - Révision systématique, phylogénie, biostratigraphie, biogéographie. Cahiers de paléontologie (Section Vertébrés), C.N.R.S. édit., Paris, 199 pp. [In French, with English abstract.]

105

BLIECK, A., ELLIOTT, D.K. & GAGNIER, P.Y., 1991. Some questions concerning the phylogenetic relationships of heterostracans, Ordovician to Devonian jawless vertebrates. In Early vertebrates and related problems of evolutionary biology. Science Press (ed. Chang M.-M, Liu, Y.-H. and Zhang, G.-R.), Beijing, 1–17.

BLIECK, A. & ELLIOTT, D.K. 2017. Pteraspidomorphs (Vertebrata), the Old Red Sandstone, and the special case of the Brecon Beacons National Park, Wales, UK. Proceedings of the Geologists' Association, 128, 438–446.

ELLIOTT, D.K., MARK-KURIK, E. AND DAESCHLER, E.B., 2004. A revision of Obruchevia (Psammosteida: Heterostraci) and a description of a new obrucheviid from the Late Devonian of the Canadian Arctic. Acta Universitatis Latviensis, 679, 22– 45.

DEC, M., 2015. A New Tolypelepidid (Agnatha, Heterostraci) from the Late Silurian of Poland. Journal of Paleontology, 89, 637–44.

DEC, M., 2019. Revision of the Early Devonian Psammosteids from the “Placoderm Sandstone”: Implications for Their Body Shape Reconstruction. Palaeontologia Electronica, 22.2.36A, 1–26.

DZIK, J., 2002. Emergence and collapse of the Frasnian conodont and ammonoid communities in the Holy Cross Mountains, Poland. Acta Palaeontologica Polonica, 47: 565–650.

ELLIOTT, D. K., MARK-KURIK, E. & DAESCHLER, E. B., 2004. A revision of Obruchevia (Psammosteida: Heterostraci) and a description of a new obrucheviid from the Late Devonian of the Canadian Arctic. Acta Universitatis Latviensis, 679, 22–45.

ELLIOTT, D. & MARK-KURIK, E., 2005. A Review of the Lateral Line Sensory System in Psammosteid Heterostracans. Revista Brasileira de Paleontologia, 8, 99–108.

GLINSKIY, V., 2018. Phylogenetic relationships of psammosteid heterostracans (Pteraspidiformes), Devonian jawless vertebrates. Biological Communications, 62, 219–243.

GROSS, W., 1963. Drepanaspis gemuendenensis Schlüter, Neuuntersuchung. Palaeonogreaphica, 121A, 133–155.

HALAMSKI, A.T., 2005. Annotations to the Devonian Correlation, Poland; Holy Cross Mts; Łysogóry Region. Senckenbergiana lethaea, 85, 185–187.

HALAMSKI, A.T. & SEGIT, T., 2006. A transitional stringocephalid from the Holy Cross Mountains, Poland, and its evolutionary and stratigraphic significance. Acta Geologica Polonica, 56, 171–176.

106

JANVIER, P., 1996a. The dawn of the vertebrates: characters vs. common ascent in the rise of current vertebrate phylogenies. Palaeontology, 39, 259–287.

JANVIER P., 1996b. Early Vertebrates. Oxford Science Publications, Clarendon Press, Oxford, 393 pp.

KŁOSSOWSKI, J., 1985. Sedimentation of the Middle Devonian In the Łysogóry Region (Świętomarz – Śniadka profile). Przegląd Geologiczny, 33, 264–267. [In Polish, with English summary.]

MALEC, J., 1990. Profil górnego syluru i dolnego dewonu z północncj części Kielc w aspekcie regionalnym. Geological Quarterly, 34, 778–780.

MALEC, J., 1993. Upper Silurian and Lower Devonian in the western Holy Cross Mts. Geological Quarterly, 37, 501–536.

MARK-KURIK E., BLIECK A., LOBOZIAK S. & CANDILIER A.M., 1999. Miospore assemblage from the Lode Member (Gauja Formation) in Estonia, and the Middle–Upper Devonian boundary problem. Proceedings of the Estonian Academy of Sciences, 48, 86–98.

MIZERSKI, W., 1981. Structural analysis of Devonian exposures within the middle part of the Bodzentyn Syncline in the Holy Cross Mts. Acta Geologica Polonica, 31: 251–263.

NARKIEWICZ, K. & BULTYNCK, P., 2007. Conodont biostratigraphy of shallow marine Givetian deposits from the Radom-Lublin area, SE Poland. Geological Quarterly, 51, 419–442.

OBRUCHEV, D. & MARK-KURIK, E., 1965. Psammosteids of the Devonian of the USSR. Akademiya Nauk Estonskoy SSR, Institut Geologii, Trudy, Tallinn, 304 pp. [In Russian, with English abstract.]

OBRUCHEV, D. & MARK-KURIK, E., 1968. On the evolution of the psammosteids (Heterostraci). Eesti NSV Teaduste Akadeemia Toimetised, Keemia, Geoloogia, 17, 279–284. [In Russian, with English abstract.]

ORŁOWSKI, S. & RADWAŃSKI, A., 1986. Middle Devonian sea-anemone burrows, Alpertia sanctacrucensis ichnogen. et ichnosp. n., from the Holy Cross Mountains. Acta Geologica Polonica, 36, 233–250.

PERNÈGRE, V.N., 2002. The genus Doryaspis White (Heterostraci) from the Lower Devonian of Vestspitsbergen, Svalbard. Journal of Vertebrate Paleontology, 22, 735–746.

PERNÈGRE, V.N. & ELLIOTT, D.K., 2008. Phylogeny of the Pteraspidiformes

107

(Heterostraci), Silurian–Devonian jawless vertebrates. Zoologica Scripta, 37, 391– 403.

RACKI, 1997. Devonian eustatic fluctuations in Poland. Courier Forschungsinstitut Senckenberg, 199, 1–12.

RANDLE, E. & SANSOM, R.S., 2017a. Exploring phylogenetic relationships of Pteraspidiformes heterostracans (stem-gnathostomes) using continuous and discrete characters. Journal of Systematic Palaeontology, 15, 583–599.

RANDLE, E. & SANSOM, R.S., 2017b. Phylogenetic relationships of the ‘higher heterostracans’ (Heterostraci: Pteraspidiformes and Cyathaspididae), extinct jawless vertebrates, Zoological Journal of the Linnean Society, 181, 910–926.

SCOTESE, C.R., 2001. Atlas of Earth History. Volume 1, Paleogeography, Paleomap Project. Texas, Arlington, 52 pp.

SOBOLEW, D., 1909. Srednij devon Kelecko-Sandomirskogo Krjazha. Materialy dla geologii Rossii, 24, 41–536. [In Russian.]

SZREK, P., NIEDŹWIEDZKI, G. & DEC, M., 2014. Storm origin of bone-bearing beds in the Lower Devonian placoderm sandstone from Podłazie Hill (Holy Cross Mountains, central Poland). Geological Quarterly, 58, 795–806.

TARLO, L.B., 1964. Psammosteiformes (Agnatha) - a review with descriptions of new material from the Lower Devonian of Poland. I - general part. Palaeontologia Polonica, 13, 1–135.

TARLO, L.B. 1965. Psammosteiformes (Agnatha) - a review with descriptions of new material from the Lower Devonian of Poland. II - systematic part. Palaeontologia Polonica, 15, 1–168.

TURNAU, E. & RACKI, G., 1999. Givetian palynostratigraphy and palynofacies: new data from the Bodzentyn Syncline (Holy Cross Mountains, central Poland). Review of Palaeobotany and Palynology, 106, 237–271.

WORONCOWA-MARCINOWSKA, T., 2012. Middle Devonian conodonts and structural implications for Świętomarz-Śniadka section (Holy Cross Moun tains). Annales Societatis Geologorum Poloniae, 82, 349–360.

VAŠKANINOVÁ, V. & KRAFT, P., 2016. A unique occurrence of a psammosteid heterostracan on the peri-Gondwanan shelf in the Lower/Middle Devonian boundary marine deposits. Fossil Imprint, 72, 155–160.

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CHAPTER V

HYDRODYNAMIC PERFORMANCE OF PSAMMOSTEIDS: NEW INSIGHTS FROM 55 COMPUTATIONAL FLUID DYNAMICS SIMULATIONS

MAREK DEC

Institute of Palaeobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland.

ABSTRACT The shape of dermal armor protecting the body in the Paleozoic agnathans such as the Heterostaci has an important hydrodynamic role in providing lift or drag force generation. Here, by performing computational fluid dynamics simulations (CFD), the measurements of hydrodynamic lift/ drag force and lift or drag coefficients were taken for two psammosteids Guerichosteus and Tartuosteus with reference to the pteraspid Errivaspis. This study shows the substantially higher values of the lift coefficient and lift- to-drag ratio for the psammosteids Guerichosteus and Tartuosteus compared with Errivaspis. The tendencies in the evolution of dermal exoskeleton, especially the widening of the branchial plates of psammosteids was directed towards the increased generation of lift force to provide efficient cruising.

INTRODUCTION The Heterostraci are a Silurian–Devonian clade of jawless vertebrates characterized by a pair of common external branchial openings. The two major groups are Cyathaspidiformes and Pteraspidiformes and are represented by a large variety of forms (e.g., Blieck 1984, Denison 1964, Janvier 1996). Cyathaspids posses a head shield that is oval to almost circular in cross section, an adaptation belived to be related to producing lift force for a rapid rise from the bottom (Novitskaya 2007). Pteraspis, in turn, also have oval cross-sections of a head shield but are wider laterally. Conversely, the head shield of psammosteids are dorso-ventral asymmetric with wide branchial plates (Obruchev and Mark-Kurik 1965, Tarlo 1964, 1965), which are purportedly more

5 First published in Acta Palaeontologica Polonica 64 (4), 2019: 679-684 doi:https://doi.org/10.4202/app.00623.2019

109 efficient at creating lift. The fish body shape is significantly connected to functional aspects of hydrodynamic, locomotion, and their swimming mode (Aleyev 1977, Webb 1984). Therefore the study of these aspects on Recent fishes offers the tools for the partial reconstruction of the mode of life and habits of fossil fishes. Recently, the hydrodynamics of the cephalic shield of Errivaspis was studied in a wind tunnel to show the detailed flow pattern around the head shield which was shown to be comparable with a delta wing aircraft (Botella and Farina 2008). The purpose of this article is to investigate the hydrodynamic effects of the psammosteid body plan, a poorly understood feature of psammosteid morphology. Psammosteids are considered to be bottom-dwellers (Tarlo 1957). Some authors suggested that they fed on starfish which they picked up from the sea floor (Patten 1932), but they have also been interpreted as mud grubbers living in shallow seas (Tarlo 1965). The wide and downwardly curved branchial plates of large psammosteids were considered to be a support while resting on soft bottom substrates (Janvier 1996). In addition to the supporting nature of the head shield, the tail fin of the psammosteid Drepanaspis gemuendenensis, which comprises the 1/4 of the total length of the body, is responsible for generating considerable propulsive force (Mark- Kurik 1992). These fishes, regardless of their possible substrate-dwelling habits, were also capable of active swimming. A new reconstruction of Guerichosteus kozlowskii recently shed light on the body shape of this psammosteids (Dec 2019). The development of computer methods that use numerical analysis and data structures to solve and analyze problems that involve fluid flows (computational fluid mechanics) gives the possibility of a better understanding of the hydrodynamic properties (Rahman 2017) of the psammosteid body form. Assessing the drag and lift forces, generated on hydrofoils is an important step in identifying the performance characteristic of the hydrofoil during swimming. This study focusses on the psammosteid gliding locomotion, especially the influence of the geometrical shape of the psammosteid body form on hydrodynamic performance. In this instance, gliding involves the motionless movement of the body through a current and represents the steady state condition of flow over the body surface.

Abbreviations. 3D, three dimensional; α, angle of attack; ρ, density of fluid; A, surface 2 wetted area [m ]; CFD, computational fluid dynamics; CD , drag coefficient; CL, lift -1 coefficient; CL/CD, lift-to-drag ratio; D, drag forces [N]; L, lift forces [N]; ms , meters per second; N, Newtons; p, pressure [Pa]; Re, Reynolds number; U, velocity [ms-1]; v, kinematic viscosity [m2s-1].

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METHODS The computer used for the simulation is a Linux Ubuntu 18.10 machine running on a Intel® Core™ i7-2630QM CPU 2.00GHz × 8 with 16GB RAM.

Mesh generation. A 3D model of Errivaspis and Guerichosteus (Fig. 1) was created using the free and open-source 3D computer graphics software Blender. The model of Errivaspis was created based on Botella and Farina (2008). Only the tail was modified where the extended lower lobe was shortened (Mark-Kurik and Botella 2009). The Guerichosteus mesh was created in reference to work by Dec (2019) concerning the revision and 3D reconstruction of the genus. To compare the geometry characteristics of the 3D models, all models were scaled to the same length (0.5 m). The triangulated surface geometries were exported from Blender as .stl files to the snappyHexMesh tool (OpenFoam). A computational box-shaped flow domain with width and height of 2 m and a length of 3 m was generated (Fig. 1.1) (Moukalled et al. 2016). To increase mesh fineness around the fish models a refinement volume region (1.18 m in length, 0.38 m in width and height) was set. The cells (with additional cells layer near surface) are mostly located in the region around the model which allows for a good resolution of the wake region (Moukalled et al. 2016). The mesh statistics are shown in Table 1 and details of the grid generated around the model are shown in Fig. 1.2 .

FIGURE 1. Box-shaped flow domain, mesh and coordinate system used for computational fluid dynamics (1); 2, an enlargement view on the mesh.

Boundary and initial condition. The range of Reynolds numbers conducted in

111 simulation varies from 238000 to 1190000, using the equation Re=Ul/v, where U is the flow speed (ms -1), l is the length of the object in the direction of flow, in this case the chord length (0.5 m), v refers to the kinematic viscosity (sea water =1.05e-6·m2s-1). The simulation consists of flow around a fish model at various angles of attack (α) and velocity. The angle of attack converging a range from -10 to +20 degrees in twodegree increments.

The boundary face was defined as the velocity inlet with various speed (0.5 ms-1, 1.5 ms- 1, 2.5 ms-1) in different cases. In analogy to the previous analysis of Errivaspis the swimming speed was estimated for three body length per second (Botella and Farina 2008). Here for the model of 0.5 m long, the swimming speed of three body length persecond gives the value of velocity 1.5 ms-1. The top speed of five body length per second (here 2.5 ms-1) is applied in reference to the boxfish (Van Wassenbergh et al. 2014). This fish has a carapace protecting the body so undulation to power swimming is limited to rare. Therefore, like psammosetids are believed to have swum, the acceleration is a result of the single beats of the caudal fin.

The front, back, upper and lower walls were set to slip boundary condition to provide a slip constraint. For the simulation of turbulent flows the Reynolds-Averaged Simulation (RAS) model was applied with komegaSST turbulent modeling. The simpleFoam steady- state solver for incompressible, turbulent flow was used in the open-source package OpenFoam. This solver uses the SIMPLE algorithm which is an iterative process that is repeated until convergence. In most cases iterative convergence was reached after 500 iterations. The simulation result is the sum of the forces acting in each direction on the model, or any part of it. The lift and drag force were calculated in Paraview software by summing up the pressure distribution around the whole model surface.

Lift force is defined as the component of the net force (due to viscous and pressure forces) that is perpendicular (along Y axis) to the flow direction (along X axis). Drag force is the component of the net force along the flow direction (along X axis), that is opposed to the motion. So the lift and drag force of the model is the vector sum of the pressure times the area around the entire solid body.

The lift or drag coefficient has been applied to eliminate the size effect as a universally comparable measure of lift/drag force. The lift and drag coefficient is a number used to model all of the complex dependencies of shape (size and body shape), inclination,

112 and some flow conditions (velocity, viscosity).

The lift coefficient CL:

The drag coefficient CD:

RESULTS Pressure. The surface pressure distribution on the fish models at 1.5 ms-1 velocity is presented on Figure 2. Defined gauge pressure is the pressure relative to 0 Pa set in simulation boundary condition. Gauge pressure is positive for pressures above boundary condition pressure, and negative for pressures below it.

In each models, the highest pressures are registered in the anterior part of the head and at the leading edges of the branchial plates in the case of Tartuosteus. The lowest pressures are observed in the middle and thickest part of the head shield. The area of low pressure extends around the mid part of the body, including branchial plates, of Tartusteus. While in Guerichosteus and Errivaspis it is mainly observed in the ventral plate.

FIGURE. 2. Distribution of pressure on the fish bodies at flow velocity 1,5 ms-1, in anterior (1) and lateral (2) views.

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FIGURE 3. Comparison lift, drag, CL, CD versus the angle of attack and various velocity.

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Lift. The variation of lift coefficient with angle of attack and various flow speeds are shown in Fig. 3.1-2. The lift coefficient increases near linearly with the angle of attack

α for each tested flow velocity for all three models. Only for Tartuosteus CL reaches a maximum at about a 8°, and then starts to decrease. This decrease of lift is called stall and it is generated by flow separation. It is not observed for two other models due to a limited range of analysis and it will occur at high angles of attack.

Drag. The most efficient model for generating lift, indicated by body orientation, also exhibits the lowest drag (Fig. 3.3-3.4). The lowest drag observed in all three genera is between -4° and 0° α for 0.5 ms-1 and 1.5 ms-1 velocity and rapidly increased with -1 increasing angle of attack. At a velocity of 2.5 ms the drag coefficient CD shows a similar pattern to the drag force for Errivaspis, whereas for Guerichosteus (α -6° to -4° ) and Tartuosteus (α -4° to -2°) a narrower range of degree of the lowest CD was found than in Errivaspis.

The minimum drag coefficient at 0.5 ms-1 flow velocity for the three genera can be ordered as: Errivaspis (CD =0.0037) < Guerichosteus (CD =0.0065) < Tartuosteus

(CD =0.0101). In all models the drag coefficient decreased with increasing velocity. -1 So when flow velocities increased to 2.5 ms , the minimum CD for Errivaspis decreased as well (CD =0.0025). This value is smaller than for the other two genera Guerichosteus and Tartuosteus, where drag coefficient values are almost the same (CD =0.0033) -1 at 2.5 ms .

The tip vortex associated with induced drag is generated by the branchial plate tip, similar to an airplane wing (see Çengel and Cimbala 2006, fig.10-49, 10-50). The produced vortices reduce the pressure along the rear edge of the branchial plate, increasing drag. The vorticity shown in Fig. 4 is presented with the iso-vorticity surface at U=1.5 ms-1 and α = 0° and identified by Q-criterion (Kolář 2007). The most abundant vortex is observed in Tartuosteus and Guerichosteus, and is considerably less in Errivaspis. However, through analogy from modern aircraft, the further a trailing vortex is from the body of the branchial plates, the less influence on the plate (Çengel and Cimbala 2006). Therefore Tartuosteus long branchial plates produce less drag produced by vortex drag than Guerichosteus, but reduce maneuverability because of their larger moment of inertia.

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FIGURE 4. Vorticity patterns using Q-criterion for 0 angles of attack and flow velocity 1,5 ms-1 in Errivaspis (1) Guerichosteus (3) and Tartuosteus (5). Each displayed lateral (left)(1,3,5) and top views (2, 4, 6) on the models. Iso-vorticity surface is colored by the

magnitude of velocity.

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Lift-to-drag ratio. The ratio is a measure of hydrodynamic performance for the fish model, which is equivalent to the ratio of the lift-to-drag coefficients CL/CD.

This is shown in Fig. 3E in a plot of CL/CD versus the angle of attack with various speed (0.5 ms-1, 1.5 ms-1, 2.5 ms-1).

The lift-to-drag ratio of three genera increases with the angle of attack α. At a velocity of 0.5 ms-1 it reaches a maximum at α = 4° for Tartuosteus, α = 6° for Errivaspis -1 and Guerichosteus. For the three genera, the maximum CL/ CD of 0.5 ms flow velocity is ordered: Errivaspis (CL/CD=4.13) < Guerichosteus (CL/ CD=6.56 ) < Tartuosteus (CL/ -1 CD=8.29). In a higher flow velocity of 2.5 ms the lift-to-drag ratio differs from the lower velocities and the maximum CL/ CD is at α = 2° for Tartuosteus and Guerichosteus and α = 6° for Errivaspis. In Tartuosteus the lift-to-drag ratio at 2.5 ms-1 flow velocity increased twice to 16.99 compared to 0.5 ms-1, while for Errivaspis it raised only to 4.98 and for Guerichosteus to 8.46.

DISCUSSION AND CONCLUSION CFD simulation was performed to investigate the hydrodynamic properties (qualitative and quantitative) of gliding psammosteids, Guerichosteus (Early Devonian) and Tartuosteus (Middle Devonian). The properties of their body armor differ mostly in the proportions of the branchial plates, which are broader in Tartuosteus (Obruchev and Mark-Kurik 1965) than in Guerichosteus (Dec 2019), and is critical for hydrodynamic efficiency, where the main propulsive power is generated by the tail. CFD simulation of the three agnathan genera has been performed to verify the hypothesis that the broadening of the branchial plate increased the lift force generation to provide efficient cruising. Changing the angle of attack has been shown to result in a change of lift and drag. The more streamlined body produces a lower drag coefficient, and for the three genera studied, Errivaspis has the lowest drag coefficients at varying current velocities followed Guerichosteus then Tartuosteus. The drag coefficient is comparable to living animals, for example dolphins, in which the drag coefficient on the wetted skin area is about 0.0035 (Çengel and Cimbala 2006). Producing the least drag and generating the most lift are desirable characteristics of swimming organisms that need to maintain a depth in the water column. The change of the lift and drag characteristics of models is related to the changes of the angles of attack. The most favorable lift-to drag ratio (positive values) at higher velocities of 2.5 ms-1 was experienced by Tartuosteus. Guerichosteus and Errivaspis exhibited similar lift-to

117 drag ratios at the same velocity. To produce more lift, the angle of attack has to be higher, however, the maximum CL/CD is noted in lower angles of attack for Tartuostaus and Guerichosteus than for Errivaspis. The highest lift-to-drag ratio is noted for Tartuosteus (CL/CD = 16.99) which is comparable to jet airplane (Airbus A320-200 CL/CD = 16.3; Martinez-Val et al. 2005). This study demonstrates the adaptive reason behind the relative widening of branchial plates in psammosteids. The widening of branchial plates increases the lift force, which apparently provide efficient cruising. Additionally, the wider branchial plates of Tartuosteus might have reduced its maneuverability, comparing to Guerichosteus and Errivaspis. Higher hydrodynamic quality suggests advantages of Tartuosteus in more effective acquisition of widely distributed food or for predator escape. However, the ecomorphologic classification is still ambiguous, there is not enough information of the ecological connection of psammosteids with the bottom (benthonekton) or with the water column (planktonekton, eunekton).

ACKNOWLEDGMENTS I thank to Przemysław Gorzelak for a fruitful discussions on hydrodynamic and correction on drafts of this manuscript. I would especially like to thank Héctor Botella and Tom Challands for their constructive reviews of the manuscript.

REFERENCES

ALEYEV, Y. G. 1977. Nekton. Springer Science & Business Media.

BOTELLA, H. AND FARIÑA, R.A. 2008. Flow pattern around the rigid cephalic shield of the devonian agnathan Errivaspis waynensis (Pteraspidiformes: Heterostraci). Palaeontology 51:1141–1150. https://doi:10.1111/j.1475-4983.2008.00801.x.

ÇENGEL, Y.A. AND CIMBALA, J.M. 2006. Fluid Mechanics: Fundamentals and Applications. 992 pp. McGraw-Hill Higher Education, Boston

DEC, M. 2019. Revision of the Early Devonian psammosteids from the “Placoderm Sandstone” implications for their body shape reconstruction. Palaeontologia Electronica. 22.2.36A [published online https:// doi.org/10.26879/948]

118

DENISON, R.H. 1964. The Cyathaspididae: a family of Silurian and Devonian jawless vertebrates. Fieldiana Geology 13:30–473.

JANVIER, P. 1996. Early Vertebrates: Oxford, Oxford Science Publications, Clarendon Press, 393 pp.

KOLÁŘ, V. 2007. Vortex identification: New requirements and limitations. International Journal of Heat and Fluid Flow, 28:638–652. doi:10.1016/j.ijheatfluidflow.2007.03.004.

MARK-KURIK, E. 1992. Functional aspects of the armour in the early vertebrates. Mark- Kurik, E. (Ed.), Fossil fishes as living animals, Academia, pp. 107-116.

MARK-KURIK E. BOTELLA H. 2009. On the tail of Errivaspis and the condition of the caudal fin in heterostracans. Acta Zoologica 90: 44-51.

MARTINEZ-VAL, R., PEREZ, E., and PALACIN, J.F. 2005. Historical evolution of air transport productivity and efficiency. In 43rd AIAA Aerospace Sciences Meeting and Exhibit (p. 2005). https://doi:10.2514/6.2005-12.

MOUKALLED, F., MANGANI, L. and DARWISH, M. 2016. The Finite Volume Method in Computational Fluid Dynamics: An Advanced Introduction with OpenFOAM® and Matlab. T. 113. Fluid Mechanics and Its Applications. Cham: Springer International Publishing. https://doi.org/10.1007/978-3-319-16874-6.

NOVITSKAYA, L.I. 2007. Evolution of Generic and Species Diversity in Agnathans (Heterostraci: Orders Cyathaspidiformes, Pteraspidiformes). Paleontological Journal 41(3): 268–80. https://doi.org/10.1134/s0031030107030069.

OBRUCHEV, D. and MARK-KURIK, E. 1965. Psammosteids of the Devonian of the USSR.

PATTEN, W. 1932. Foundation of the face. Scientific Monthly 35:v 511-521.

RAHMAN, I.A. 2017. Computational Fluid Dynamics as a Tool for Testing Functional and Ecological Hypotheses in Fossil Taxa. Palaeontology 60(4): 451–59. https://doi.org/10.1111/pala.12295.

TARLO, L.B. 1957. A preliminary note on new ostracoderms from the Lower Devonian (Emsian) of central Poland. Acta Palaeontologica Polonica 2: 225-233.

TARLO, L.B. 1964. Psammosteiformes (Agnatha) – a review with descriptions of new material from the Lower Devonian of Poland. I - general part. Palaeontologia Polonica 13: 1-135.

TARLO, L.B. 1965. Psammosteiformes (Agnatha) – a review with descriptions of new material from the Lower Devonian of Poland. II - systematic part. Palaeontologia Polonica 15: 1-168.

119

WEBB, P.W. 1984. Body Form, Locomotion and Foraging in Aquatic Vertebrates. American Zoologist 24(1): 107–20.

VAN WASSENBERGH, S., VAN MANEN, K., MARCROFT, T.A., ALFARO, M.E., AND

STAMHUIS, E.J. 2014. Boxfish swimming paradox resolved: forces by the flow of water around the body promote manoeuvrability. Journal of The Royal Society Interface 12.103: 20141146.

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