DSpace at VNU: The skull of Hagiangella goujeti Janvier, 2005, a high-crested acanthothoracid (Vertebrata, Placodermi) from the Lower Devonian of northern Vietnam

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This article was downloaded by: [Aston University] On: 18 January 2014, At: 11:58 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Journal of Vertebrate Paleontology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ujvp20 The skull of Hagiangella goujeti Janvier, 2005, a highcrested acanthothoracid (Vertebrata, Placodermi) from the Lower Devonian of northern Vietnam Vincent Dupret Janvier d e a f b b c , Ta Hoa Phuong , Tong-Dzuy Thanh , Nguyen Duc Phong , Philippe & Gaël Clément d a Université Lille 1—Sciences et Technologies , FRE 3298 Géosystèmes du CNRS, 59655, Villeneuve d’Ascq cedex, France b Department of Geology , Vietnam National University , 334 Nguyen Trai street, Thanh Xuan District, Ha Noi City, Viet Nam c Vietnam Institute of Geosciences and Mineral Resources (VIGMR) , Km9+300, Nguyen Trai Street, Thanh Xuan District, Ha Noi City, Viet Nam d Muséum National d’Histoire Naturelle , UMR 7207 du CNRS, CP38, 47 rue Cuvier 75231 Paris cedex 05, France e Palaeontology Department , The Natural History Museum , Cromwell Road, London, SW7 5BD, United Kingdom f Department of Evolutionary Organismal Biology , University of Uppsala , Norbyvägen 18A, 742 36, Uppsala, Sweden Published online: 09 May 2011 To cite this article: Vincent Dupret , Ta Hoa Phuong , Tong-Dzuy Thanh , Nguyen Duc Phong , Philippe Janvier & Gaël Clément (2011) The skull of Hagiangella goujeti Janvier, 2005, a high-crested acanthothoracid (Vertebrata, Placodermi) from the Lower Devonian of northern Vietnam, Journal of Vertebrate Paleontology, 31:3, 531-538, DOI: 10.1080/02724634.2011.558148 To link to this article: http://dx.doi.org/10.1080/02724634.2011.558148 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content This article may be used for research, teaching, and private study purposes Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions Journal of Vertebrate Paleontology 31(3):531–538, May 2011 © 2011 by the Society of Vertebrate Paleontology ARTICLE THE SKULL OF HAGIANGELLA GOUJETI JANVIER, 2005, A HIGH-CRESTED ACANTHOTHORACID (VERTEBRATA, PLACODERMI) FROM THE LOWER DEVONIAN OF NORTHERN VIETNAM ∗ ,1, VINCENT DUPRET, † TA HOA PHUONG,2 TONG-DZUY THANH,2 NGUYEN DUC PHONG,3 PHILIPPE JANVIER,4,5 ă CLEMENT and GAEL ´ ` Universite´ Lille 1—Sciences et Technologies, FRE 3298 Geosyst emes du CNRS, 59655 Villeneuve d’Ascq cedex, France; Department of Geology, Vietnam National University, 334 Nguyen Trai street, Thanh Xuan District, Ha Noi City, Viet Nam, tahoaphuong@gmail.com; tongdzuythanh@gmail.com; Vietnam Institute of Geosciences and Mineral Resources (VIGMR), Km9+300, Nguyen Trai Street, Thanh Xuan District, Ha Noi City, Viet Nam, phongcs@gmail.com; ´ Museum National d’Histoire Naturelle, UMR 7207 du CNRS, CP38, 47 rue Cuvier 75231 Paris cedex 05, France, janvier@mnhn.fr; gclement@mnhn.fr; Palaeontology Department, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom Downloaded by [Aston University] at 11:58 18 January 2014 ABSTRACT—The acanthothoracid Hagiangella goujeti Janvier, 2005, has been described exclusively on the basis of isolated thoracic plates from the Lochkovian (Lower Devonian) Khao Loc Formation of Tung Vai, Ha Giang Province, northern Vietnam It is characterized by a very high, triangular median crest on the median dorsal plate, and has been referred to the Acanthothoraci on the basis of the morphology of its fused anterolateral, spinal and anterior ventrolateral plates, and the characteristic stellate ornamentation of the group Isolated plates of H goujeti are relatively abundant at Tung Vai and no other placoderm taxon from this locality seems to share the same type of ornamentation However, the skull of this species remained elusive Here we report two well-preserved skull roofs from Tung Vai, which we refer to H goujeti They display the same stellate ornamentation and small size as the previously described plates of the thoracic armor of this species This new material shows that the head of H goujeti is surprisingly short (i.e., possibly lacking dermal rostral and pineal elements), in contrast to the elongate and narrow skull of all other acanthothoracids The combination of unique characters (e.g., presence of two pairs of posterior pit lines, two pairs of central and paranuchal plates, etc.) suggests a possible sister group relationship to the placoderm assemblage Petalichthyida + Ptyctodontida + Arthrodira INTRODUCTION The Placodermi McCoy, 1848, (‘armored fishes’) are the most diversified vertebrates of the entire Devonian period (Janvier, ă 1944, is con1996) Among them, the Acanthothoraci Stensio, sidered a paraphyletic ensemble of generalized placoderms, to which the different clades of placoderms are related (Goujet, 1984a; Janvier, 1996) So, in the paraphyletic family Palaeacană 1944, ‘Radotina’ prima is the sister group thaspididae Stensio, to the Arthrodira Woodward, 1891 (including the Phyllolepida ă 1934), on one hand, and to the Petalichthyida Jaekel, Stensio, 1911, plus the Ptyctodontida Gross, 1932, on the other (see Janvier, 1996:fig 4.57) A group including Brindabellaspis Young, 1980, Romundina Ørvig, 1975, and Palaeacanthaspis Brotzen, 1934, is the sister group to the Antiarchi Cope, 1885; a last ensemble comprising Radotina kosorensis Gross, 1950, Kosoraspis Gross, 1959, and Kimaspis Mark-Kurik, 1973a, is more closely related to the Rhenanida Broili, 1930 The supposedly monophyletic family Weejasperaspididae White, 1978, would be the sister group of a large clade that includes the Palaeacanthaspididae, Arthrodira, Petalichthyidae, and Ptyctodontida More recently, Goujet and Young (2004) have considered the Acanthothoraci monophyletic Given the present work, we follow a non-monophyletic hypothesis *Corresponding author Current address: Department of Evolutionă ary Organismal Biology, University of Uppsala, Norbyvagen 18A, 742 36 Uppsala, Sweden, vincent.dupret@ebc.uu.se The recently described Hagiangella goujeti Janvier, 2005, from the Lochkovian of northern Vietnam was not assigned to any particular acanthothoracid family, because the original material consisted only of some isolated thoracic armor fragments The new skull roof material described herein shows that this taxon is distinct from the Palaeacanthaspididae and represents the sister group to either the Ptyctodontida, or at least, the clade ((Ptyctodontida, Petalichthyida) Arthrodira) GEOLOGICAL SETTING, MATERIALS, AND METHODS The previously described postcranial material of Hagiangella gougeti, including the holotype, was collected at Tung Vai, Ha Giang Province, Vietnam, and comes from two outcrops that have been named “Tung Vai 1” (N23◦ 03.43, E104◦ 54.91, altitude 954 m) and “Tung Vai 2” (N23◦ 03.18, E104◦ 54.51, altitude 954 m), respectively (Racheboeuf et al., 2005) (Fig 1) The skull roofs described herein all come from Tung Vai 2, from which also comes the holotype of the species They are referred to H goujeti because no other placoderm taxon from the same locality bears the same, characteristic stellate ornamentation The specimens have been prepared by cleaning the natural mould of the skull roof with dilute hydrochloric acid An elastomer cast of the natural mould was made and whitened with magnesium oxide for photography Institutional Abbreviation—BT, Geological Museum, Hanoi, Vietnam 531 532 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL 31, NO 3, 2011 median pit line; N, nuchal plate; occ, occipital cross-commissure; p.PaN, posterior paranuchal plate; p.pop, posterior postorbital process; PaN, paranuchal plate; Pi, pineal plate; pmc, postmarginal sensory line canal or groove; PPi, postpineal plate; ppl, posterior pit line; ppl1, first (anterior) posterior pit line; ppl2, second (posterior) posterior pit line; Prm, premedian plate; PrO, preorbital plate; PtO, postorbital plate; R, rostral plate; SM, submarginal plate; soc, supraorbital sensory line canal or groove; s.p, pit for presumably cutaneous sensory organ; sov, supraorbital vault; tpl, transverse pit line (in Denison, 1978:fig.16A) SYSTEMATIC PALEONTOLOGY Class PLACODERMI McCoy, 1848 ă 1944 Order ACANTHOTHORACI Stensio, Family HAGIANGELLIDAE, fam nov Diagnosis—The same as for the type genus and type species, by monotypy Type Genus—Hagiangella Janvier, 2005 (see Racheboeuf et al., 2005:534 for taxonomic disclaimer) Downloaded by [Aston University] at 11:58 18 January 2014 Genus HAGIANGELLA Janvier, 2005 (see Racheboeuf et al., 2005:534 for taxonomic disclaimer) Diagnosis—The same as for the type species, by monotypy (Racheboeuf et al., 2005) HAGIANGELLA GOUJETI Janvier, 2005 Holotype—An isolated median dorsal plate (BT-186; Racheboeuf et al., 2005:fig 4A–D) New Materials—Two isolated skull roofs, BT231 (Fig 2A) and BT232 (Fig 2B–C), respectively Locality and Age—Tung Vai 2, Ha Giang Province, Northern Vietnam; base of the Khao Loc Formation, Lochkovian (Early Devonian) Diagnosis (emended from Racheboeuf et al., 2005)—A small Acanthothoraci with a long spinal plate, and a very high, vertical, and triangular process of the median dorsal plate prolonged by a posterior blade The ventrolateral lamina of the shoulder girdle is expanded medially As in other acanthothoracids, the ornamentation of the armor consists of stellate tubercles The rostral and pineal plates are not fused to the postethmoid part of the skull roof, as is the case of the pineal plate in Radotina prima (see Denison, 1978:fig 22C) There is no evidence of a naso-capsular dermal entity involving the rostral, pineal and premedian plates The anterior surface of the preorbital plates is vertical and ornamented DESCRIPTION FIGURE Geographic location of Tung Vai and in northern Vietnam (modified after Tong-Dzuy et al., 1995:text-fig 1) Anatomical Abbreviations—a.PaN, anterior paranuchal plate; a.pop, anterior postorbital process; C, central plate; C1, first (anterior) central plate; C2, second (posterior) central plate; cc, central sensory line canal or groove; d.e, external foramen for the endolymphatic duct; ioc, infraorbital sensory line canal or groove; lc, cephalic main lateral sensory line canal or groove; lim.sov, limit of the supraorbital vault; M, marginal plate; mpl, Only the postethmoid ossification of the skull roof is preserved; no evidence of rostral, pineal, or premedian plates has been found in the material These dermal ethmoid and pre-ethmoid elements have maybe been detached after the death of the animal (as occurs in most acanthothoracids and other ‘loose-nose’ placoderms; e.g., Kujdanowiaspis, in which the postethmoid ossification is most often preserved), rather than having been simply absent Nevertheless, the ornamented anterior surface of the preorbital plates contradicts this latter hypothesis The plate boundaries are very difficult to identify, most sutures being unclear The radiation center of each plate (except that of the nuchal plate) seems to be slightly elevated This feature, along with the concentric pattern of the tubercles and the lack of tubercles along plate sutures (likely due to the differential growth of the plates), was used to identify the plate boundaries The sensory line system consists of deeply open grooves, except around the nuchal plate radiation center, where the grooves appear much shallower We have not identified the occipital cross-commissure, 533 Downloaded by [Aston University] at 11:58 18 January 2014 DUPRET ET AL.—SKULL OF HAGIANGELLA FROM DEVONIAN OF VIETNAM FIGURE Hagiangella goujeti, Janvier, 2005 Skull roof in dorsal view (left side) and schematic interpretation (right side) A, BT231 in external view B, BT232 part C, BT232 counterpart Scale bar equals mm Downloaded by [Aston University] at 11:58 18 January 2014 534 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL 31, NO 3, 2011 FIGURE Comparison of different placoderm skull roofs A, Hagiangella goujeti Janvier, 2005 (schematic reconstruction of the skull roof in external view after BT231-232; the right part of the reconstruction takes into account the possibility that the marginal plate extends mesially to the infraorbital and main lateral sensory line grooves; dotted line indicates the limit—in internal view—of the supraorbital vault.) B, Ctenurella gladbachensis Ørvig, 1960 (redrawn after Ørvig, 1962:fig 1A) C, “Radotina” prima (Barrande, 1872) (redrawn after Gross, 1958; Westoll, 1967; Denison, 1978:fig 22C) D, Romundina stellina (redrawn after Ørvig, 1975; Denison, 1978:fig 22G) E, Kimaspis tienshanica Mark-Kurik, 1973a (redrawn after Mark-Kurik, 1973a:text-fig 2, and Denison, 1978:fig 22D, who reconstructed the ethmoid and re-identified C2 and a.PaN—Elga Mark-Kurik, pers comm.) D, Sensory line system indicated in light grey Not to scale but two pairs of posterior pit lines are most probably present (see Discussion) One pair of sensory line grooves is puzzling (ppl1, Fig 1A–C; see below for discussion of homologies), because it does not cross any radiation center; on the contrary, it runs between the anterior and posterior central plate radiation centers towards the point of convergence between the supraorbital sensory line and the (second) posterior pit line on the nuchal plate These grooves may be suggestive of a plate boundary, but we consider that they could also be part of the sensory line system, because some grooves not necessarily cross the radiation centers in Radotina (see Mark-Kurik, 1973a) Nevertheless, the skull roof of some species of Radotina consists of plates but also of many tesserae, as in Kimaspis but contrary to Hagiangella The skull roof of H goujeti is shorter than in any other Acanthothoraci, especially in the postorbital area Its median anterior edge is straight and vertical, and covered with stellate tubercles Therefore, we assume that the rostral, pineal, and premedian plates were lacking, or that a gap separated them from the preor- bital plates, as in the Antiarchi-related Romundina stellina (see Ørvig, 1975) The orbits are very large (almost half of the skull roof length); the supraorbital vault is visible in ventral view in specimen BT232 (sov, Fig 2B) The posterior part of the skull roof is deeply embayed medially, and somewhat elevated, most probably to fit the very high median dorsal plate (see Racheboeuf et al., 2005:figs 4A–D, 5) Nevertheless, the posterolateral corner of the skull roof (i.e., the posterior edge of the paranuchal plates) does not extend as posteriorly as in others species of Acanthothoraci (Fig 3) The boundary between the two adjacent preorbital plates (PrO, Fig 2) is very difficult to discern They form the anterior half of the orbital edge and are crossed by the straight supraorbital sensory line grooves (soc, Fig 2) that extend until the level of the radiation center of the nuchal plate (N, Fig 2) They contact the postpineal plate posteriorly (Ppi, Fig 2) in the midline The postorbital plates (PtO, Fig 2) constitute the posterior part of the orbital edge In Radotina they are crossed by the infraorbital sensory line grooves, but this is harder to assess in Downloaded by [Aston University] at 11:58 18 January 2014 DUPRET ET AL.—SKULL OF HAGIANGELLA FROM DEVONIAN OF VIETNAM Hagiangella because the boundary between the postorbital and marginal plates is not discernible In other words, there is a possibility that the infraorbital groove could be borne by the marginal plate, as in the Ptyctodontida; nevertheless, this is doubtful because the angle of the infraorbital groove is well marked (about 90◦ ) in Hagiangella, compared to the slight bow observable in the Ptyctodontida (see Fig 3B) No central sensory groove or canal is visible The postpineal plate is of uncertain shape, but its approximate location can be identified owing to a different tuberculation (i.e., more dense) in this area, especially in specimen BT231 (Ppi, Fig 2A) The lateral margin of the marginal plate (M, Figs 2A, C, 3A) is unknown, and its boundary is indistinct medially It seems that on specimen BT232 (Fig 2C), the plate extends into a lateral blade, circling the orbit posteriorly, and following the infraorbital sensory line groove These features are comparable to those observed in the Ptyctodontida The marginal plate is crossed by the postmarginal sensory line groove (pmc, Figs 2A–B, 3A) The internal view of specimen BT232 exposes two neurocranial processes, respectively identified as the anterior and the posterior postorbital process (a.pop, p.pop, Fig 2B) The paired central plates (C1, C2, Fig 2) surround the nuchal plate laterally The anterior central plates contact the preorbital, postorbital, posterior central, anterior paranuchal, nuchal, and most probably the postpineal plates The anterior central plate is not crossed by any sensory line groove The posterior central plate constitutes the posterior edge of the skull roof, together with the nuchal and the posterior paranuchal plates The boundary between the anterior and posterior central plates and the nuchal plate is not discernible The shape of the nuchal plate (N, Fig 2) cannot be determined, because the boundary with the central plates is not clear It contacts anteriorly the postpineal plate anteriorly (which, as noted, shows a denser tubercle distribution; Ppi, Fig 2A) The radiation center of the nuchal plate, situated in the middle of the plate, is slightly depressed; the supraorbital sensory groove and the two pairs of posterior pit lines become shallower and most probably converged at this point Because the course of these sensory grooves where they converge is not as obvious as in other grooves, we believe that this confluence was more superficial The anterior and posterior paranuchal plates (a.PaN, p.PaN, Fig 2) are crossed by the two pairs of posterior pit lines Only their mutual boundaries, as well as those with the postorbital and central plates, are discernible The boundary with the marginal plate is unknown The posterior paranuchal plate does not extend posteriorly contrary to its homologue in other Acanthothoraci DISCUSSION Sensory Line Groove Homology in Hagiangella goujeti Although the homology between the supraorbital, infraorbital, cephalic main lateral, and postmarginal sensory grooves of Hagiangella and those of other placoderms is clear, this is not the case for the posterior pit line and the occipital crosscommissure, which cross the posterior central, anterior, and posterior paranuchal and nuchal plates Moreover, determining homologies is made more difficult by the fact that a real central groove and a median pit line are not observed on the material, so that the posterior pit line and the occipital cross-commissure cannot be identified by a process of elimination However, first, because the median pit line runs parallel to the central sensory groove in most placoderms that display these two sensory lines, and second, because no similar structure is observed in the material of Hagiangella goujeti, we consider that the latter lacks the central sensory groove and the median pit line 535 In most placoderms, the occipital cross-commissure runs either through a gap behind the nuchal plate or in the posterior part of the nuchal plate, but rarely at the level of the nuchal plate radiation center On the contrary, when an element of the sensory line system crosses the radiation center of the nuchal plate, it may be the supraorbital grooves, the central grooves, or the median and posterior pit lines (as in the Phyllolepididae and Wuttagoonaspididae) The occipital cross-commissure is documented in acanthothoracids (e.g., Mark-Kurik, 1973a, 1994), as in all other placoderm groups Usually, this groove runs from the posterior paranuchal (or single paranuchal) plate radiation center and crosses either the posterior-most part of the nuchal plate or through the nuchal gap or extrascapular plates The origin of this occipital crosscommissure in Acanthothoraci is situated posteriorly in the posterior extension of the posterior paranuchal plate, and is directed toward the nuchal gap The posterior pit line, when single, runs between the paranuchal and the central or nuchal plate radiation centers When two pairs of posterior pit lines occur, the first (anterior) one runs between the central and the marginal radiation centers (as is the case in Yiminaspis shenme, see Dupret, 2008:fig 2A–B), or its course is visible (if not restricted) on the central plate only (see ppl.a of Romundina stellina in Ørvig, 1975:fig.1A; or Lunaspis broilii, Gross, 1961; or pp1 in Eurycaraspis incilis Liu, 1991:fig 1) but still oriented onto the marginal plate (see also Dupret, 2008, for discussion) Additionally, when two pairs of paranuchal plates are present, the second (posterior) posterior pit line always runs between the nuchal and the anterior paranuchal plates Nevertheless, in the basal arthrodire Yiminaspis shenme, in which only one pair of paranuchal plates occurs, the second posterior pit line is anchored in the posterior part of the paranuchal plate, in the immediate vicinity of the occipital cross-commissure (the latter running further posteriorly from the nuchal plate radiation center) Consequently, as far as Hagiangella is concerned, and because the supraorbital groove has been identified and the central groove is absent, the posterior-most sensory line component (ppl2, Figs 2, 3A), running between the posterior paranuchal and the nuchal plate radiation centers, can be homologized with the second posterior pit line rather than with the occipital crosscommissure As for the more anterior sensory line component (ppl1, Figs 2, 3A), it should not be homologized with a median pit line, because in most cases it parallels the course of the central groove Hence, this component is considered homologous with the first posterior pit line of the Petalichthyida (though incomplete in this taxon) and of Yiminaspis shenme (see Dupret, 2008:fig 2), thereby entailing the presence of two pairs of posterior pit lines on the skull roof of Hagiangella goujeti The presence of two pairs of posterior pit lines is not unique among placoderms The Petalichthyida also possess two pairs of posterior pit lines, although the anterior one is never complete Recently, two pairs of posterior pit lines have been identified in the basal arthrodire Yiminaspis shenme Dupret, 2008 (Fig 2A–B); it is nevertheless noteworthy that these are associated with one pair of central and paranuchal plates In Yiminaspis shenme, the first (anterior-most) posterior pit line runs from the radiation center of the marginal plate to the sensory groove confluence at the level of the radiation center of the nuchal plate This pattern is very similar to that of the first posterior pit line of Hagiangella goujeti It is also noteworthy that the lateral end of the first posterior pit line lies close to the postmarginal groove in both Hagiangella and Yiminaspis The second (posterior-most) posterior pit line of Hagiangella runs between the radiation center of the paranuchal plate and the confluence of the sensory grooves at the level of the radiation center of the nuchal plate, as in its homologue in Yiminaspis shenme Therefore, the two 536 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL 31, NO 3, 2011 medial transverse sensory grooves in Hagiangella goujeti can be homologized with the first and second posterior pit lines of Yiminaspis shenme Affinities of Hagiangella with the Ptyctodontida Downloaded by [Aston University] at 11:58 18 January 2014 Although the skull roof of Hagiangella goujeti is far from displaying a typical ptyctodontid-like pattern, some of its features compare to either this group or closely related ones: The orbits are very large, as in the Ptyctodontida, and represent about one half of the skull roof length Large orbits, though possibly related to lifestyle, occur mostly in the Ptyctodontida and some Acanthothoraci (e.g., Romundina stellina), and is probably an apomorphic character state (yet possibly homoplastic, i.e., acquired by convergence) Nevertheless, large orbits may represent a juvenile feature The latter interpretation may be supported by the presence of only one tubercle generation in Hagiangella goujeti (D Goujet, pers homologized) Although the number of specimens is not large enough to assess any of these hypotheses, because the skull roof specimens are about half the size they should be to fit the thoracic armor material (see Racheboeuf et al., 2005), we favor the juvenile specimen hypothesis For this reason, we not include the large orbits in the diagnosis The skull roof of the Ptyctodontida is laterally composed by slender blades (i.e., the marginal plates) that surround the orbits posteroventrally Such a feature is unknown in the Acanthothoraci A possible exception may be Romundina stellina, in which a slight and tiny process surrounds the orbit posteroventrally, but it is unclear whether the plate in question is the postorbital or the marginal plate (see Denison, 1978:fig 22G; Fig 2D; however, the marginal plate in Romundina stellina does not appear to extend onto the orbital edge) Moreover, this area of the skull roof is not well preserved in Hagiangella goujeti Nevertheless, one specimen (BT232, Fig 2B–C) suggests the presence of large infraorbital processes for the marginal plate at least, thus displaying a condition similar to that observed in the Ptyctodontida The central sensory line is lacking in Hagiangella goujeti, as well as in the Ptyctodontida and in the Petalichthyida, the latter two forming a clade according to Goujet and Young (1995) For these authors, the absence of this central sensory line represents a derived condition The sensory line system of the skull roof of Hagiangella goujeti seems to consist of grooves, rather than enclosed canals that open to the exterior via pores, though it is possible that a thin bone layer roofed those canals; the superficial dermal bone layer has been partly destroyed during fossilization (Fig 2) The possession of canals plus pores is present in the Petalichthyida and the Ptyctodontida (it is one of the synapomorphies considered by Goujet and Young, 1995, for this clade), as well as in the palaeacanthaspid Kimaspis tienshanica Mark-Kurik, 1973a (which Mark-Kurik considered as close to “the hypothethical ancestor of placoderms”; MarkKurik, 1973a:329) It is uncertain whether a closed sensory line canal condition is derived relative to the presence of grooves (as in the Arthrodira), but it is possible that this combination of canals and pores is inherited from a single common ancestor, shared the Ptyctodontida, the Petalichthyida, and possibly Kimaspis and Hagiangella (if the presence of sunken canals vs grooves can be determined in new, better-preserved material) The supraorbital sensory groove and the two pairs of posterior pit lines meet at the radiation center of the nuchal plate in all Ptyctodontida, except in Rhamphodopsis threipandli Watson, 1934 (attributed to a nuchal plate instead of a postpineal plate by Long, 1997) This feature also occurs in basal Arthrodira (i.e., the Wuttagoonaspididae Wutta- goonaspis fletcheri Ritchie, 1973, and Yiminaspis shenme), and in some more derived Arthrodira (i.e., the Phyllolepididae) In phyllolepidids, however, this confluence occurs on the ‘centronuchal’ plate, recently considered as consisting of the fused central plates only, the nuchal plate being absent (see Dupret and Zhu, 2008, for details) It is nevertheless noteworthy that Young (2005) considers this sensory line confluence on a medial dermal element as a primitive condition for placoderms No endolymphatic foramen or duct has been identified in the skull material of Hagiangella This structure is absent (presumably lost) in the Ptyctodontida The trunk armor is known from median dorsal plates, possible posterior dorsolateral plates, and a single dermal element formed from the fusion of the anterior ventrolateral, anterolateral, and spinal plates (Racheboeuf et al., 2005) Racheboeuf et al pointed out the resemblance between the median dorsal plate of Hagiangella and that of the ptyctodontid Rhamphodopsis and some high crested groenlandaspidid arthrodires Recent phylogenetic analyses show the Groenlandaspididae and Phlyctaenididae as basal taxa among the Phlyctaenii (e.g., see Dupret, 2004; Dupret et al., 2007, 2009; Dupret and Zhu, 2008) Some groenlandaspidid taxa (i.e., Mulgaspis Ritchie, 2004) also retain the presence of anteroventral plates that were once considered typical for the actinolepidoid arthrodires (Miles, 1973) until their discovery in some Chinese quasipetalichthyids (Liu, 1991) Also, the internal side of the median dorsal plate shows a pair of strong ridges, that Racheboeuf et al (2005) compare to the Petalichthyida and the posterior median dorsal plate of the Antiarchi; this structure is also comparable to that in some Actinolepidoidei (e.g., Actinolepis magna, Mark-Kurik, 1973b:text-fig 3B; Erikaspis zychi, Dupret et al., 2007) and Phlyctaenii (e.g., see Dicksonosteus arcticus, Goujet, 1984b:fig 56, bcp.d), and may be related to the attachment of the axial muscles of the trunk (Goujet, 1984b) The trunk armor of the earliest ptyctodonts (i.e., Tollodus brevispinus Mark-Kurik, 1977, from the Lochkovian of Kotelny Island, New Siberian Archipelago; N.B., first mentioned and illustrated as ‘ptyctodont’ in Mark-Kurik, 1974; see below) shows interesting comparisons with that of Hagiangella A comparison between the trunk armor of Hagiangella and other Acanthothoraci is given in Racheboeuf et al., 2005 The median dorsal plate of both Hagiangella and Tollodus shows a broad and flat basis from which extends a flattened triangular blade in Hagiangella (Racheboeuf et al., 2005:figs 4A–F, 5), and a ‘spiny’ process in Tollodus (Mark-Kurik, 1974:text-fig 1(11), pl.1 fig 3; Mark-Kurik, 1977:figs 1–3) In later ptyctodonts, the median dorsal blade is short based and presents a high sub-vertical spiny process The anterior dorsolateral plate of Tollodus already shows the features of the later ptyctodonts (short, deep unornamented overlap blades for the median dorsal and anterolateral plates; Mark-Kurik, 1974:pl.1 fig.2, text-fig 1(3); Mark-Kurik, 1977:fig 4) Nevertheless, the shape of the articular condyle (for the craniothoracic dermal articulation) seems to be much simpler than the hollow one of the later ptyctodonts The anterolateral plate of Hagiangella is as long as high, whereas that of Tollodus is much higher than long (MarkKurik, 1977:fig 5), as in later ptyctodonts Lastly, the ventral armor in Tollodus is composed of the possibly fused interolateral and anterior ventrolateral plates (Mark-Kurik, 1977:fig 1), whereas it is considered that the later ptyctodonts only possess a pair of interolateral plates (e.g., Long, 1997) The ventral armor of Hagiangella shows a pair of well-developed anterior ventrolateral plates (of which a medial expansion of is reminiscent of the Phlyctaenididae), but no interolateral (the latter being also absent in all Acanthothoraci; Racheboeuf et al., 2005:figs 6, 7) It is hence possible, though speculative, DUPRET ET AL.—SKULL OF HAGIANGELLA FROM DEVONIAN OF VIETNAM to suggest that the anterior ventrolateral plate of Hagiangella and the possibly fused interolateral and anterior ventrolateral plates of Tollodus are homologous The ventral armor of Tollodus and other ptyctodonts is very short, compared to that of Hagiangella Also, in lateral view the trunk armor of Tollodus (Mark-Kurik, 1977:fig 1B) is at least twice as short as that of Hagiangella, and hence is more ‘ptyctodont’ than that of Hagiangella The spinal plate of Hagiangella is strong and long, extends beyond the posterior edge of the anterior ventrolateral plate, and belongs to a unit composed of this plate with the anterolateral and the anterior ventrolateral plates (similar to that in the acanthothoracids Romundina stellina, Palaeacanthaspis vasta, and Kosoraspis peckai; Racheboeuf et al., 2005) The spinal plates of Tollodus and later ptyctodonts are very reduced Downloaded by [Aston University] at 11:58 18 January 2014 Phylogenetic Position and Systematics of Hagiangella goujeti Despite many common features shared by Hagiangella and the Ptyctodontida, we cannot consider Hagiangella goujeti as a Pyctodontida s.s because it lacks the diagnostic characters of this group Alternative hypotheses would consider Hagiangella as the sister group of the Ptyctodontida (Fig 4, hypothesis 1) Alternatively, because Hagiangella possesses two pairs of central and paranuchal plates, it could also be considered as closely related to the group Ptyctodontida + Petalichthyida (Fig 4, hypothesis 2) Moreover, because two pairs of paranuchal plates occur in the Petalichthyida, and occasionally in the most primitive members of the Arthrodira (e.g., Yujiangolepis liujingensis Wang et al., 1998; see revision in Dupret et al., 2009), Hagiangella could also be considered as the sister taxon to the group Ptyctodontida + Petalichthida + Arthrodira (Fig 4, hypothesis 3) The presence of two pairs of central plates was previously regarded as typical for the Acanthothoraci, although some possess one pair, as is the case for ‘Radotina’ prima, which is considered as most closely related to the group Arthrodira + Petalichthyida + Petalichthyida (Goujet, 1984a; Janvier, 1996) Hence, Hagiangella may equally be considered as the sister group of this latter group (including ‘Radotina’ prima) (Fig 4, hypothesis 4) However, a close relationship between ‘Radotina’ prima and Hagiangella seems unlikely (different skull roof, trunk armor, and sensory line patterns; compare Fig 3A and C) 537 Lastly, with regards to the stellate tubercle ornamentation, although considered for some time as exclusive to the acanthothoracids, it appears that many groups of placoderms show this ornamentation on the scale cover—but not the dermal armor—though not necessarily the most primitive taxa (e.g., the scales of arthrodires of the ‘buchanosteid-type’ of Turner and Murphy, 1988, or of the rhenanid Ohioaspis tumulosa, in Burrow and Turner, 1999:figs 3D–F, 4C) Considering the numerous problems of homology and character coding for the Placodermi in general (notably the large number of non-applicable data), an extensive phylogenetic analysis will be the subject of a subsequent article The phylogeny proposed in Figure has to be considered as showing provisional phylogenetic hypotheses described above Regarding the familial attribution of Hagiangella, and considering that we have pointed out some features it shares with the Petalichthyida, the Ptyctodontida, and the basal Arthrodira, we have for some time considered the possibility that it could be referred provisionally to the family “Palaeacanthaspididae.” However, as already stressed in Introduction, this family is considered as paraphyletic, relative to the Arthrodira and the group Petalichthyida + Ptyctodontida Therefore, we propose here the erection of a new family, for the only genus Hagiangella CONCLUSIONS The skull roof of Hagiangella goujeti Janvier, 2005, displays a typical acanthothoracid set of characters (e.g., stellate ornamentation, two pairs of central and paranuchal plates), but also features that recall conditions observed in the Petalichthyida and the most primitive Arthrodira (e.g., two pairs of posterior pit lines, two pairs of paranuchal plates) and the Ptyctodontida (e.g., wide postorbital blade most probably contributed by the marginal plate) This leads us to consider four possible phylogenetic relationships for Hagiangella, including one in which Hagiangella is the sister taxon to the ensemble Arthrodira + Petalichthyida + Ptyctodontida ACKNOWLEDGMENTS V.D contributed to this article during a temporary position at the USTL (Villeneuve d’Ascq, France; credits to the ECLIPSE Project—Terrestrialization of the INSU/CNRS [Marco Vecoli], of which this publication is a contribution); the article has been finalized at the University of Uppsala Field work was funded ´ by the Departement Histoire de la Terre of the Museum National d’Histoire Naturelle, Paris Ta Hoa Phuong and Tong Dzuy Thanh are grateful to the National Foundation for Sciences and Technology Development of Viet Nam for the effective support to the Projects 105.01.79.09 and 105.06.60.09 The authors thank Elga Mark-Kurik (Institute of Geology, Tallinn University ´ of Technology, Estonia) and Daniel Goujet (Departement His´ toire de la Terre, Museum National d’Histoire Naturelle, Paris, France) for their reviews, comments, and corrections LITERATURE CITED FIGURE Relationships among Placodermi (modified after Janvier, 1996:fig 4.57) The numbers to are related to the possible phylogenetic position of Hagiangella goujeti (branch in dashed lines) ` ` ` partie Barrande, J 1872 Systeme silurien du centre de la Boheme 1ere ´ ´ Recherches paleontologiques, supplement au vol i., 647 pp ă Broili, F 1930 Uber Gemundina Sturtzi Traquair Abhandlungen ă der Bayerischen Akademie der Wissenschaften Mathmatischnaturwissenschaftliche Abteilung 6:1–24 Brotzen, F 1934 Die silurischen und devonischen Fischvorkommen in Westpodolien II Paleobiologica 6:111–131 Burrow, C J., and S Turner 1999 A review of placoderm scales, and their significance in placoderm phylogeny Journal of Vertebrate Paleontology 19:204–219 Cope, E D 1885 The position of Pterichthys in the system American Naturalist 19:289–291 Downloaded by [Aston University] at 11:58 18 January 2014 538 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL 31, NO 3, 2011 Denison, R H 1978 Placodermi; 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SKULL OF HAGIANGELLA FROM DEVONIAN OF VIETNAM to suggest that the anterior ventrolateral plate of Hagiangella and the possibly fused interolateral and anterior ventrolateral... The skull roof of Hagiangella goujeti Janvier, 2005, displays a typical acanthothoracid set of characters (e.g., stellate ornamentation, two pairs of central and paranuchal plates), but also features... Acanthothoraci on the basis of the morphology of its fused anterolateral, spinal and anterior ventrolateral plates, and the characteristic stellate ornamentation of the group Isolated plates of
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Xem thêm: DSpace at VNU: The skull of Hagiangella goujeti Janvier, 2005, a high-crested acanthothoracid (Vertebrata, Placodermi) from the Lower Devonian of northern Vietnam, DSpace at VNU: The skull of Hagiangella goujeti Janvier, 2005, a high-crested acanthothoracid (Vertebrata, Placodermi) from the Lower Devonian of northern Vietnam

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