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
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The skull of Hagiangella goujeti Janvier, 2005, a high-crested acanthothoracid (Vertebrata, Placodermi) from the Lower Devonian of northern Vietnam
Vincent Dupret af , Ta Hoa Phuong b , Tong-Dzuy Thanh b , Nguyen Duc Phong c , Philippe Janvier de & Gặl 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 & Gặl 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
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Trang 2ARTICLE
THE SKULL OF HAGIANGELLA GOUJETI JANVIER, 2005, A HIGH-CRESTED
ACANTHOTHORACID (VERTEBRATA, PLACODERMI) FROM THE LOWER DEVONIAN OF
NORTHERN VIETNAM
VINCENT DUPRET,∗,1,†TA HOA PHUONG,2TONG-DZUY THANH,2NGUYEN DUC PHONG,3PHILIPPE JANVIER,4,5
and GA ¨EL CL ´EMENT4
1Universit ´e Lille 1—Sciences et Technologies, FRE 3298 G ´eosyst `emes du CNRS, 59655 Villeneuve d’Ascq cedex, France;
2Department of Geology, Vietnam National University, 334 Nguyen Trai street, Thanh Xuan District, Ha Noi City, Viet Nam,
tahoaphuong@gmail.com; tongdzuythanh@gmail.com;
3Vietnam Institute of Geosciences and Mineral Resources (VIGMR), Km9+300, Nguyen Trai Street, Thanh Xuan District, Ha Noi
City, Viet Nam, phongcs@gmail.com;
4Mus ´eum National d’Histoire Naturelle, UMR 7207 du CNRS, CP38, 47 rue Cuvier 75231 Paris cedex 05, France, janvier@mnhn.fr;
gclement@mnhn.fr;
5Palaeontology Department, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom
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
INTRODUCTION The Placodermi McCoy, 1848, (‘armored fishes’) are the most
diversified vertebrates of the entire Devonian period (Janvier,
1996) Among them, the Acanthothoraci Stensi ¨o, 1944, is
con-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
Palaeacan-thaspididae Stensi ¨o, 1944, ‘Radotina’ prima is the sister group
to the Arthrodira Woodward, 1891 (including the Phyllolepida
Stensi ¨o, 1934), on one hand, and to the Petalichthyida Jaekel,
1911, plus the Ptyctodontida Gross, 1932, on the other (see
Jan-vier, 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
en-semble comprising Radotina kosorensis Gross, 1950, Kosoraspis
Gross, 1959, and Kimaspis Mark-Kurik, 1973a, is more closely
related to the Rhenanida Broili, 1930 The supposedly
mono-phyletic family Weejasperaspididae White, 1978, would be the
sister group of a large clade that includes the
Palaeacanthas-pididae, Arthrodira, Petalichthyidae, and Ptyctodontida More
recently, Goujet and Young (2004) have considered the
Acan-thothoraci monophyletic Given the present work, we follow a
non-monophyletic hypothesis
Evolution-ary Organismal Biology, University of Uppsala, Norbyv ¨agen 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 mate-rial 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
Gi-ang 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 de-scribed herein all come from Tung Vai 2, from which also comes
the holotype of the species They are referred to H goujeti
be-cause 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 elas-tomer cast of the natural mould was made and whitened with magnesium oxide for photography
Institutional Abbreviation—BT, Geological Museum, Hanoi,
Vietnam
531
Trang 3532 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL 31, NO 3, 2011
FIGURE 1 Geographic location of Tung Vai 1 and 2 in northern
Viet-nam (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,
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, post-marginal 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 Order ACANTHOTHORACI Stensi ¨o, 1944 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)
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 gir-dle is expanded medially As in other acanthothoracids, the or-namentation of the armor consists of stellate tubercles The ros-tral 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 orna-mented
DESCRIPTION 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 an-imal (as occurs in most acanthothoracids and other ‘loose-nose’
placoderms; e.g., Kujdanowiaspis, in which the postethmoid
ossi-fication is most often preserved), rather than having been simply absent Nevertheless, the ornamented anterior surface of the pre-orbital 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 tuber-cles along plate sutures (likely due to the differential growth of the plates), was used to identify the plate boundaries The sen-sory 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,
Trang 4FIGURE 2 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 1 mm.
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FIGURE 3 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
(sec-ond) 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
do 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
Ki-maspis but contrary to Hagiangella.
The skull roof of H goujeti is shorter than in any other
Acan-thothoraci, 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 Acanthotho-raci (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 supraor-bital sensory line grooves (soc, Fig 2) that extend until the level
of the radiation center of the nuchal plate (N, Fig 2) They con-tact 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
Trang 6Hagiangella because the boundary between the postorbital and
marginal plates is not discernible In other words, there is a
possi-bility 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
observ-able 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
infraor-bital 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
pro-cesses, 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
bound-ary 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
con-tacts 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
proba-bly converged at this point Because the course of these
sen-sory 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,
infraor-bital, 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
cross-commissure, which cross the posterior central, anterior, and
pos-terior paranuchal and nuchal plates Moreover, determining
ho-mologies 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
ma-terial of Hagiangella goujeti, we consider that the latter lacks the
central sensory groove and the median pit line
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 radia-tion 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 Wuttagoonaspi-didae)
The occipital cross-commissure is documented in acanthotho-racids (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 cross-commissure in Acanthothoraci is situated posteriorly in the pos-terior extension of the pospos-terior 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
cen-ters (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) poste-rior pit line always runs between the nuchal and the anteposte-rior
paranuchal plates Nevertheless, in the basal arthrodire
Yimi-naspis 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
be-cause the supraorbital groove has been identified and the cen-tral 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 cross-commissure
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
en-tailing 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 con-fluence 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
cen-ter 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
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medial transverse sensory grooves in Hagiangella goujeti can be
homologized with the first and second posterior pit lines of
Yim-inaspis shenme.
Affinities of Hagiangella with the Ptyctodontida
Although the skull roof of Hagiangella goujeti is far from
dis-playing a typical ptyctodontid-like pattern, some of its features
compare to either this group or closely related ones:
1 The orbits are very large, as in the Ptyctodontida, and
rep-resent about one half of the skull roof length Large
or-bits, 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)
Never-theless, large orbits may represent a juvenile feature The
lat-ter inlat-terpretation 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
do not include the large orbits in the diagnosis
2 The skull roof of the Ptyctodontida is laterally composed by
slender blades (i.e., the marginal plates) that surround the
or-bits posteroventrally Such a feature is unknown in the
Acan-thothoraci A possible exception may be Romundina stellina,
in which a slight and tiny process surrounds the orbit
pos-teroventrally, 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
stel-lina does not appear to extend onto the orbital edge)
More-over, this area of the skull roof is not well preserved in
Hagian-gella 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
3 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
4 The sensory line system of the skull roof of Hagiangella
gou-jeti 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
der-mal bone layer has been partly destroyed during
fossiliza-tion (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
tien-shanica Mark-Kurik, 1973a (which Mark-Kurik considered as
close to “the hypothethical ancestor of placoderms”;
Mark-Kurik, 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
ances-tor, 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)
5 The supraorbital sensory groove and the two pairs of
pos-terior pit lines meet at the radiation center of the nuchal
plate in all Ptyctodontida, except in Rhamphodopsis
threipan-dli Watson, 1934 (attributed to a nuchal plate instead of
a postpineal plate by Long, 1997) This feature also
oc-curs 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 ‘cen-tronuchal’ 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 me-dial dermal element as a primitive condition for placoderms
6 No endolymphatic foramen or duct has been identified in the
skull material of Hagiangella This structure is absent
(pre-sumably lost) in the Ptyctodontida
7 The trunk armor is known from median dorsal plates, pos-sible posterior dorsolateral plates, and a single dermal ele-ment 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 ptyctodon-tid Rhamphodopsis and some high crested groenlandaspidid
arthrodires Recent phylogenetic analyses show the Groen-landaspididae 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
an-teroventral plates that were once considered typical for the actinolepidoid arthrodires (Miles, 1973) until their discov-ery 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
bre-vispinus 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 unorna-mented 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
(Mark-Kurik, 1977:fig 5), as in later ptyctodonts Lastly, the ventral
armor in Tollodus is composed of the possibly fused
interolat-eral and anterior ventrolatinterolat-eral plates (Mark-Kurik, 1977:fig 1), whereas it is considered that the later ptyctodonts only pos-sess a pair of interolateral plates (e.g., Long, 1997) The
ven-tral armor of Hagiangella shows a pair of well-developed
an-terior 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,
Trang 8to 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
be-yond the posterior edge of the anterior ventrolateral plate, and
belongs to a unit composed of this plate with the
anterolat-eral and the anterior ventrolatanterolat-eral 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.
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)
Alter-natively, 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
mem-bers 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
re-garded 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,
Hagian-gella may equally be considered as the sister group of this latter
group (including ‘Radotina’ prima) (Fig 4, hypothesis 4)
How-ever, a close relationship between ‘Radotina’ prima and
Hagian-gella seems unlikely (different skull roof, trunk armor, and
sen-sory line patterns; compare Fig 3A and C)
FIGURE 4 Relationships among Placodermi (modified after Janvier,
1996:fig 4.57) The numbers 1 to 4 are related to the possible phylogenetic
position of Hagiangella goujeti (branch in dashed lines).
Lastly, with regards to the stellate tubercle ornamentation, although considered for some time as exclusive to the acan-thothoracids, 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 charac-ter coding for the Placodermi in general (notably the large num-ber of non-applicable data), an extensive phylogenetic analysis will be the subject of a subsequent article The phylogeny pro-posed in Figure 4 has to be considered as showing provisional phylogenetic hypotheses described above
Regarding the familial attribution of Hagiangella, and
consid-ering 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 re-ferred provisionally to the family “Palaeacanthaspididae.” How-ever, as already stressed in Introduction, this family is consid-ered 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 ornamen-tation, two pairs of central and paranuchal plates), but also fea-tures 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
re-lationships 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 D ´epartement Histoire de la Terre of the Museum Na-tional 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 sup-port 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 (D ´epartement His-toire de la Terre, Mus ´eum National d’HisHis-toire Naturelle, Paris, France) for their reviews, comments, and corrections
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Submitted January 12, 2010; accepted January 22, 2011.
Handling editor: Zerina Johanson.