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TAPHONOMY AND AFFINITY OF AN ENIGMATIC
SILURIAN VERTEBRATE, JAMOYTIUS KERWOODI
WHITE
by ROBERT S. SANSOM* , KIM FREEDMAN*� , SARAH E. GABBOTT* ,
RICHARD J. ALDRIDGE* and MARK A. PURNELL**Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK; e-mails [email protected], [email protected], [email protected],
�6 Wescott Road, Wokingham, Berkshire RG40 2ES, UK; e-mail [email protected]
Typescript received 14 July 2009; accepted in revised form 23 April 2010
Abstract: The anatomy and affinities of Jamoytius kerwoodi
White have long been controversial, because its complex
taphonomy makes unequivocal interpretation impossible
with the methodology used in previous studies. Topological
analysis, model reconstruction and elemental analysis, fol-
lowed by anatomical interpretation, allow features to be
identified more rigorously and support the hypothesis that
Jamoytius is a jawless vertebrate. The preserved features of
Jamoytius include W-shaped phosphatic scales, 10 or more
pairs of branchial openings, optic capsules, a circular, subter-
minal mouth and a single terminal nasal opening. Interpreta-
tions of paired ‘appendages’ remain equivocal. Phylogenetic
analysis places Jamoytius and Euphanerops together (Jamoytii-
formes), as stem-gnathostomes rather than lamprey related
or sister taxon to Anaspida.
Key words: Jamoytius, Euphanerops, phylogeny, taphonomy,
Vertebrata, Gnathostomata, Silurian.
White (1946) first described Jamoytius kerwoodi on the
basis of two specimens from a Lower Silurian (Llando-
very) horizon of the Lesmahagow inlier of Lanarkshire,
Scotland, and considered it to be the most primitive
known vertebrate. Numerous subsequent authors have
disputed this conclusion or have disagreed with aspects of
White’s (1946) interpretation (Data S1). Evidence from
additional specimens collected at Lesmahagow localities
(see Ritchie 1968, 1985 for synopses of locality and stra-
tigraphy details) prompted Ritchie (1960, 1963, 1968,
1984) to redescribe Jamoytius as an ‘unspecialized anas-
pid’, possibly related to the extant jawless vertebrates. As
shown by Plate 1, most of Ritchie’s (1960, 1968) interpre-
tations of the anatomical features of Jamoytius differ from
those of White (1946).
Despite Ritchie’s treatment, Jamoytius continued to
generate debate. Various authors challenged Ritchie’s
work (e.g. Janvier 1981; Forey and Gardiner 1981) or sug-
gested affinities with a range of subsequently discovered
fossils (e.g. Janvier and Busch 1984; Briggs and Clarkson
1987). Cladistic analyses of the jawless vertebrates (e.g.
Janvier 1981, 1996a, b; Forey 1984, 1995; Forey and Jan-
vier 1993) have also failed to clarify the affinities of
Jamoytius; the lack of agreement regarding its anatomical
homologies has meant that different analyses have used
different character codings. In addition to coding, choice
of the in-group taxa included in the phylogenetic investi-
gation has affected the placement of Jamoytius (Donoghue
et al. 2000; Donoghue and Smith 2001; Gess et al. 2006).
The position of Jamoytius on cladograms has conse-
quently not stabilized, though Jamoytius usually appears
as a sister taxon to the lampreys, the anaspids, or Eupha-
nerops longaevus Woodward, 1900.
Janvier and Lund (1983 2, p. 412) wrote, ‘These various
interpretations cause one to wonder about the degree of
imagination involved in the study of Jamoytius and other
fossils preserved as tarry impressions.’ So why has it
proved so difficult to produce a definitive interpretation
of Jamoytius and to determine its affinities? The principal
problem is one that affects interpretation of many prob-
lematic fossils – disentangling the different aspects of the
process of anatomical reconstruction. The selection of an
appropriate anatomical comparator upon which to base
hypotheses of homology (comparisons being drawn either
directly to a specific extant organism or clade, or indi-
rectly through a fossil intermediate) can be especially
problematic (Donoghue and Purnell 2009); the choice of
interpretative model needs careful justification on the
basis of characters present, preferably unequivocally, in
the fossils. In the case of Jamoytius, almost all workers
have considered it as a jawless vertebrate without explicit
justification, and consequently, anatomical interpretations,
P A L A 1 0 1 9 B Dispatch: 15.10.10 Journal: PALA CE: Archana
Journal Name Manuscript No. Author Received: No. of pages: 17 PE: Raymond
[Palaeontology, 2010, pp. 1–17]
ª The Palaeontological Association doi: 10.1111/j.1475-4983.2010.01019.x 1
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homology statements and phylogenetic analyses are all at
risk of circularity. Jamoytius is generally preserved in two
dimensions, and investigations have often concentrated
on relating the shape of its features to the three-dimen-
sional anatomical parts of presumably related organisms.
Different workers have alternatively described the same
circular features in Jamoytius as mouth, eyes and nasal
structures (Pl. 1 and Data S1). These interpretations are
thus inherently equivocal. Anatomical and phylogenetic
claims, and counterclaims, will continue to be insecure
without further information about the topology, compo-
sition and taphonomic history of anatomical features,
combined with explicit articulation of the methodology
used to reach anatomical interpretations.
MATERIALS AND METHODS
Topological reconstruction and comparative anatomy. In
order to address the problems of circularity and equivo-
cal interpretations, a stepwise methodology separating
topological considerations from anatomical interpreta-
tion was applied as advocated by Donoghue and Purnell
(2009). First, the features of the fossils were identified
and described (i.e. number and shape of distinct body
parts, and the topological relationship between those
body parts). By comparing specimens preserved in dif-
ferent orientations, three-dimensional reconstruction was
possible (cf. Briggs and Williams 1981; Purnell and
Donoghue 1999). Throughout this process of interpreta-
tion and reconstruction, no assumptions were made
about the affinities of the organism or the homology of
its features.
Following topological description, an explicitly justified
interpretative model was selected upon which to base
anatomical hypotheses. Putative homologies were identi-
fied through the consideration of topological relationships
between body parts (Rieppel and Kearney 2002) and were
informed by evolutionary and potential taphonomic
transformational sequences (i.e. assessing whether the
appearance of a feature, or its absence, represents the ori-
ginal anatomical condition, or the results of post-mortem
processes of decay and preservation). The intrinsic
properties and composition of the body parts provided
additional constraints on interpretations.
Following translation of topological structures into
anatomical interpretations, taxonomic assessments and
phylogenetic analyses were employed to investigate the
placement of the organism in an evolutionary context.
Elemental analysis. Topological data were complemented
by determination of the chemistry and preservation of
particular features to provide evidence of original histol-
ogy and ⁄or composition (e.g. Butterfield 2002; Gabbott
et al. 2004). Elemental mapping of some features of Ja-
moytius was performed on a LEO 435 VP Scanning Elec-
tron Microscope with an Oxford Instruments ISIS 300
EDX spectrometer operating in variable pressure mode at
10 Pascals with an accelerating voltage of 10 kV and a
beam current of 500 picoamps for 1000 frames (approxi-
mately 14 h of run time). The specimens analysed in this
study have not been subjected to hydrofluoric acid treat-
ment (Ritchie 1963, 1968); smaller specimens were
selected because of SEM chamber size limits.
Phylogenetic analysis. Data matrices were constructed in
MacClade 4.06 (Maddison and Maddison 2003). Heuristic
searches were performed using PAUP 4.0 (Swofford 2002)
with 1000 random sequence addition replicates and TBR
(Tree bisection and reconnection) branch swapping.
Where appropriate, characters were reweighted according
to their rescaled consistency indices. To investigate the
alternative topologies that satisfy phylogenetic relation-
ships proposed on the basis of molecular data, heuristic
searches were conducted using backbone constraint trees
constructed in MacClade 4.06 (see below).
Institutional abbreviations and publicly held material. NHM, Nat-
ural History Museum, London, P11284 (holotype), P11285,
P47784-7; AMS, Australian Museum, Sydney, F64401, F102841-
6; NMS National Museum of Scotland, Edinburgh, 1959.1,
1966.3.1-3; BGS, British Geological Survey, Keyworth, 11882-3;
Hunterian Museum, Glasgow, V.7792, V.8036V.8141, V.8148,
GLHAM101382; UOE, University of Edinburgh, FR1628,
FR1476, 20129-32, 20145, 20159-62.
BODY PARTS, TOPOLOGICALANALYSIS AND RECONSTRUCTION
Body shape
In general aspect, Jamoytius has an elongate lozenge-
shaped body exhibiting a size range of 140–180 by 30–
EXPLANATION OF PLATE 1
Jamoytius kerwoodi White holotype (NHM P11284a) immersed in 90 per cent ethanol with incident polarized light and filter,
illustrating the conflicting interpretations of White (1946), in bold, and Ritchie (1960, 1963, 1968, 1984) in plain text. Scale bar
represents 10 mm.
2 PALAEONTOLOGY
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SANSOM et al., Jamoytius kerwoodi
eye
mouth
intermuscle spaces
(myocommata)
interscale spaces
displaced skin
lateral �n fold
basal supports
of anal �n
not interpreted
lateral �n fold
ventral termination
of body scales
notochord
one margin
of intestine
rays of
dorsal �n
not interpreted
bifurcation of
notochord
branchial basket
eye
eye
basal supports
of dorsal �n
not interpreted
intestine
one margin
of intestine
not interpreted
eye
lateral �n fold
branchial basket
muscle blocks
(with muscle �bres)
unmineralized scales
(with ornamentation)
COLOUR
PLATE 1
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40 mm. The body is preserved with a varying degree of
curvature (range of 40–90 degrees through the long axis
of the body). One end of the body of Jamoytius shows a
greater degree of morphological differentiation, contain-
ing multiple different substructures. This is provisionally
taken to be the head (see later discussion), thus indicating
anterior. Through comparison of paired and symmetrical
body parts, specimens are identified as collapsed remains
of a bilaterally symmetrical organism preserved in differ-
ent orientations (some are dorso-ventrally collapsed, some
laterally and others intermediate).
There is not enough evidence to determine the original
shape of the posterior of the organism, as most slabs do
not possess the most posterior portion. When present,
the posterior is preserved much more faintly than the rest
of the body, sometimes too faintly to be discerned clearly.
NHM P47784a exhibits what could be interpreted as two
posterior lobes, but the region is poorly preserved and
heavily prepared, thus obscuring the original body out-
line.
Body parts
Anterior subcircles. Four subcircles occur in the anterior
region. From comparison of specimens preserved in dif-
ferent orientations, it is apparent that they are coincident
with the body margin. Two distinct types of subcircle
occur. Two have broad, dark margins and form a lateral,
symmetrical pair, close to either the dorsal or ventral
body margin (Text-fig. 1). Comparison of the shapes of
these structures in dorso-ventral and laterally collapsed
specimens indicates that their original shape was either a
laterally flattened spheroid, or an outwardly opening cup-
like structure roughly equating to half or two-thirds of a
sphere (e.g. Text-fig. 1A). The other two subcircles have
narrower margins and lie along the sagittal plane, one ter-
minal, one subterminal in position (Text-fig. 1C,D). Irre-
spective of the orientations of the body, these axially
located rings are preserved as approximately circular out-
lines. This indicates either that they were originally spher-
ical, or that they were discs with sufficient rigidity at the
time of body collapse to reorient into a bedding parallel
attitude.
Elemental mapping analysis performed on the anterior
region of NHM P47787a shows a clear correlation of car-
bon with one of the paired, broader margined, anterior
subcircles (Text-fig. 2B).
Serial subrectangles. Towards the anterior end, many
specimens preserve a pair of linear features composed of
serially repeated, contiguous, subrectangular shapes
A B
C
A B C D
D
TEXT -F IG . 1 . 8Anterior subcircles of
Jamoytius (A–D) with corresponding
graphic interpretations (below), where
darker grey represents laterally paired
subcircles with broader margins, lighter
grey represents subterminal ring and
medium grey represents terminal ring.
A, NHM P11284a. B, NMS 1966.3.2. C,
NHM P11285. D, NMS 1966.3.1. Scale
bars represent 5 mm.
LOW
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4 PALAEONTOLOGY
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(Text-fig. 3A,B). The central areas of the subrectangles
have the same coloration as the body but their perime-
ters are darker. Like the anterior subcircles, the lines of
subrectangles are coincident with the body margin. The
subrectangles are arranged in a ladder-like line, which
lies at a shallow angle to the antero-posterior axis of
the body.
The precise number of subrectangles is difficult to
establish and possibly varies between individuals. Jamoy-
tius has been reported to have had as many as 17 subrec-
tangles in each series (Ritchie 1984) and as few as seven
(Forey and Gardiner 1981). In the case of the specimen
discussed by the latter, the body is incomplete and the
posterior portion of the region with subrectangles may be
missing. On all specimens for which the entire length of
the line of subrectangle rows is present, at least 10 can be
identified, and on several, at least 14 (e.g. Text-fig. 3).
W-shaped structures. Although they are not preserved in
all specimens, among the most conspicuous features of
Jamoytius are W-shaped, serially repeated structures.
Their disposition indicates that they were coincident with
the body outline, or at least very nearly so (Pl. 1; Text-
fig. 4A). Each W extends around the majority of the lat-
eral body margin, leaving a gap on one body surface,
either dorsal or ventral (Pl. 1; Text-fig. 4D; Ritchie 1968,
pl. 4, fig. 1). The series of Ws does not extend along the
entire antero-posterior axis of the body; they are absent
from the anterior (e.g. Pl. 1) and their posterior limit is
uncertain. The Ws consist of alternating narrow and
broad zones.
The narrow zones are prominent and generally show
relief. They normally have a central area (200–300 lm
wide), the same colour as the matrix of the siltstone in
which the fossils are preserved, with very dark borders (c.
50 lm wide) on either side (Text-fig. 4C). In some
instances, the narrow zones also exhibit a tuberculate tex-
ture (Text-fig. 4E; Ritchie 1968, pl.4, fig. 3), which is best
observed on fragmentary specimens.
The broad zones (1–3 mm wide) lack relief, but are
darker in colour than other parts of the body. Within the
broad zones are linear features, lighter in colour; some of
these lines form dendritic patterns (Text-fig. 4C).
Elemental mapping of the W-shaped stripes of speci-
men GLAM V8141c shows that the borders of the narrow
zones and the whole of the broad zones contain associa-
tions of Ca and P (Text-fig. 2A) but not the other ele-
ments making up the matrix. Carbon is also present, but
appears to have an inverse distribution to that of Ca and
P; the W-shaped features are, therefore, interpreted as
being composed of calcium phosphate, possibly with an
organic component.
Axial lines and rounded structures. In the holotype (NHM
P11284a, Pl. 1, Text-fig. 5) and FR 1601 (Ritchie 1968; pl.
4, fig. 2, pl. 6, fig. 1), a pair of parallel, axial lines are
noted in the middle of the trunk (each approximately
2 mm width). Upon closer inspection, the lines are com-
posed of contiguous lozenge- or oval-shaped units, each
slightly longer than wide (Text-fig. 6B). In FR 1601, the
region between the axial lines preserves the W-shaped
structures from both the near and far side of the body,
whilst the region outside of the axial lines preserves the
Ws from only one side of the body (Text-fig. 6A). In
NHM P11284a, one of the axial lines bifurcates towards
the anterior. Towards the posterior of NHMP11284a, the
lines become less clear. Aligned with the axial lines are a
parallel and paired posterior series of dark, rounded
structures, which exhibit positive relief (Text-fig. 6B).
A C
PCa
CB
TEXT -F IG . 2 .9 SEM back scatter and elemental maps. A, W-
shaped structures of GLAM V8141c (back scatter; C, Carbon;
Ca, Calcium; P, Phosphorous). B, Anterior subcircle NHM
47787A (back scatter; C, Carbon).
LOW
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SANSOM ET AL . : TAPHONOMY AND AFFINITY OF AN ENIGMATIC SILURIAN VERTEBRATE 15
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Their periodicity is approximately the same as that of the
W-shaped structures. The alignment of the axial rounded
structures with the axial lines, combined with the loz-
enge-shaped units of the lines, suggests that the rounded
structures and axial lines may comprise the same struc-
ture.
Paired longitudinal ‘folds’. A pair of parallel linear features
resembling collapsed folds is observed on the same sur-
face of the body as the gap between the W-shaped struc-
tures (Pl. 1, Text-fig. 3). They originate posterior to the
serial subrectangles and continue posteriorly until they
become indistinct. They are generally straight and exhibit
wrinkling in some instances.
Reconstruction
The general two-dimensional form of fossils of Jamoytius
is presumed to be a result of the collapse of a soft body
A
C
D
B A
B
TEXT -F IG . 3 . 10Anterior subrectangles
with corresponding graphic
interpretations (A, B) and ventro-lateral
‘folds’ (C, D). A, NMS 1966.3.2. B, NMS
1965.59a. C, NMS 1966.3.2. D, NHM
P11285. Scale bars represent 5 mm.
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6 PALAEONTOLOGY
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during decay rather than compaction, and body fossils in
different orientations can thus be equated to two-dimen-
sional views of a three-dimensional organism (Briggs and
Williams 1981). Most of the preserved features are evi-
dent in almost all the dorso-ventrally and laterally col-
lapsed specimens that retain the appropriate portion of
the body, and the three-dimensional architecture and
position of these features can therefore be confidently
modelled. Whilst the model is a simplification of some
features (e.g. anterior subcircles), it corresponds well with
all known specimens of Jamoytius, including those that
are obliquely collapsed (Text-fig. 7). The accuracy of the
model can be tested by its ability to predict the position
of features in any newly discovered specimens.
The antero-posterior axis and dorso-ventral and axis
are identified on the basis of the anatomical differentia-
tion in the ‘head’ and symmetrical disposition of surface
structures (e.g. paired subcircles and W-shaped struc-
tures), respectively; distinguishing dorsal and ventral
remains problematic in the absence of a phylogenetic
context. The model indicates that the paired axial lines
and allied rounded structures are likely to be interior
structures. They are preserved in only two specimens
(NHMP11284, oblique; FR1601, lateral) but it seems that
both lines occur in the sagittal plane. Towards the ante-
rior, one of the axial lines is very close to the surface with
no gap in Ws towards the anterior; towards the posterior,
the axial lines approach the midline.
ANATOMICAL INTERPRETATION ANDCHARACTER HOMOLOGY
Establishing a phylogenetic context
Historically, Jamoytius has been interpreted as a jawless
vertebrate, but it lacks any unequivocal vertebrate synapo-
morphies (e.g. sensory canals, brain, skull, muscular phar-
ynx, multi-chambered heart, liver, kidney etc.) or, for
that matter, any unequivocal chordate synapomorphies
(e.g. dorsal nerve chord, notochord, myomeres, endo-
style ⁄ thyroid, pharyngeal arches, postanal tail). Paired
sense organs can be reasonably interpreted as present in
Jamoytius, but these are not unique to chordates
(although within chordates, they are a vertebrate synapo-
morphy). Previous interpretations of Jamoytius as a verte-
brate or even chordate have, therefore, not been
adequately justified: anterior anatomical differentiation,
serial stripes, axial lines, and a fusiform and curved body
shape are not sufficient in themselves to support a chor-
date model. Such general conditions could be noted in a
broad range of metazoan taxa, for example, articulated
A
C D E
B
TEXT -F IG . 4 . W-shaped serially repeating stripes on the trunk of Jamoytius. A, NHM P11284a illustrating coincidence of stripes
with the left body margin. B, GLAM 101283 ⁄ 1. C, GLAM V8141. D, NHM P47784a. E, NHM P11284a. Scale bars represent 5 mm
(A–D) or 1 mm (E).
SANSOM ET AL . : TAPHONOMY AND AFFINITY OF AN ENIGMATIC SILURIAN VERTEBRATE 17
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soft-bodied fossils such as the purported polychaete Piec-
konia (e.g. Fitzhugh et al. 1997, fig. 7A.18). We can, how-
ever, compare Jamoytius with fossil or extant taxa that
possess the particular topological features outlined above.
Following redescription of Euphanerops (Janvier and
Arsenault 2007), it is clear that it shares with Jamoytius
the following features: dark anterior subcircles (specifi-
cally, a lateral pair, one terminal ring and one subtermi-
nal ring) and ladder-like rows of contiguous serially
repeating anterior subrectangles (Text-fig. 8). Two other
structures are comparable between the two genera but are
not present in exactly the same condition: serially repeat-
ing antero-posterior stripes and paired ventro-lateral
‘folds’. Unlike Jamoytius, Euphanerops also preserves some
unequivocal chordate synapomorphies (postanal tail,
terminal subcircle
subterminal subcirclelateral subcircle (l)
serial sub-
rectangles (l)
serial sub-
rectangles (r)
lateral subcircle (r)
ventro-lateral
folds
W-shaped
structures
axial line
(l/d)
axial line
(r/v)
linear rounded
structures
TEXT -F IG . 5 . Body parts and topological interpretation of the
holotype (NHM P11284a) of Jamoytius. Scale bar represents
10 mm.
ventralaxialline
dorsalaxialline
Ws on right(proximal)surface
Ws on left(distal) surface
dorsalaxialline
ventralaxialline
anteriorbifurcation
axial roundedstructures
Ws on dorso-lateralsurface
A A
B B
TEXT -F IG . 6 . Axial structures of Jamoytius. A, Trunk of FR
1601 with reconstruction illustrating paired axial lines. B, Trunk
of NHM P12284a with reconstruction illustrating paired axial
lines and axial rounded structures. A1 from Ritchie (1968, pl. 6,
fig. 1). Scale bars represent 5 mm.
8 PALAEONTOLOGY
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notochord) and vertebrate synapomorphies (mineralized
endoskeleton, anal fin with fin supports) (Janvier and
Arsenault 2007). Given the similarities between Jamoytius
and Euphanerops in body parts and their topological
relations, it is reasonable to infer that Jamoytius also
possessed a postanal tail and notochord, which are not
A B
C
TEXT -F IG . 7 . Different perspectives of the three-dimensional model compared with two-dimensional fossil specimens of Jamoytius
preserved in different orientations. A, Dorsal perspective with NHM P11284a. B, Ventral perspective with NMS 1966.3.2. C, Lateral
perspective (anterior-posterior axis slightly oblique) with NHM P11285. Scale bar represents 5 mm.
A
B
C
contiguous
subrectangles
median sub-
terminal subcircle
lateral
subcircles
TEXT -F IG . 8 . Anatomy of
Euphanerops and Jamoytius. A, MHNM
01-02 drawing illustrating some of the
features shared with Jamoytius. B,
Reconstruction of Euphanerops. C.
Reconstruction of Jamoytius in light of
new data. A from Janvier and Arsenault
(2007, fig. 3B2), B from Janvier and
Arsenault (2002, fig. 1b).Scale bar
represents 10 mm (A).
SANSOM ET AL . : TAPHONOMY AND AFFINITY OF AN ENIGMATIC SILURIAN VERTEBRATE 19
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preserved in known specimens. We reject the alternative
hypothesis that the similarities between Jamoytius and
Euphanerops are mere coincidences, on grounds of parsi-
mony. A chordate context for the interpretation of the
body parts of Jamoytius is thus justified, and topology can
be translated into anatomy in the light of this compara-
tive model (Table 1).
Anterior subcircles and subrectangles
Anatomical interpretation. Given a chordate model, the
lateral paired anterior subcircles are best interpreted as
optic capsules. The positions of the optic capsules of
Jamoytius can be interpreted as dorso-lateral given that in
all chordates with eyes they are located on either lateral
or dorso-lateral surfaces (rare exceptions include the ven-
tro-lateral eyes of the bighead carp, Hypophthalmichthys
nobilis). The dorsal and ventral surfaces of Jamoytius are
thereby identified – the optic capsules are dorsal, and the
gap between the W-shaped structures is along the ventral
surface.
Of the median anterior subcircles, the large rounded
subterminal ring, which is now clarified as being located
on the ventral body surface, is best interpreted as the oral
opening. Its position and architecture are consistent with
its interpretation as an annular cartilage (e.g. Ritchie
1963, 1968), such as that found in the extant lampreys.
There are, however, no associated structures preserved
that might support that hypothesis (e.g. circum oral teeth,
copular cartilages, oral papillae). The smaller, terminal
subcircle is comparable to the single nasal opening
observed in a number of jawless vertebrates, both extant
and extinct. Its terminal position indicates that it is unli-
kely to be a pineal organ.
The paired, serially repeating subrectangles compare
closely to the branchial openings observed in fossil jawless
vertebrates such as Euphanerops, osteostracans, and, to a
lesser extent, extant jawless vertebrates such as lampreys.
These animals possess a series of external branchial
openings, which originate in the head region and descend
ventrally towards the posterior. In Jamoytius, the subrec-
tangles have previously been interpreted as internal, akin
to the branchial basket of lampreys (Ritchie 1963, 1968;
Forey and Gardiner 1981; Janvier 1981) and as such
would be lateral to the gills. The coincidence of the struc-
tures with the body margin makes them more comparable
with cartilaginous trematic rings surrounding the external
branchial openings. The Jamoytius subrectangles are, how-
ever, contiguous and numerous, unlike the trematic rings
of lampreys.
The apparent variability in the number of paired bran-
chial openings (10 or more pairs) may be because of the
nature of preservation of these features but could also
reflect real differences in the number of branchial struc-
tures; intraspecific variation in the number of branchial
units occurs in some jawless vertebrates (i.e. hagfishes).
Taphonomy and composition. Since Ritchie’s (1963)
description of Jamoytius, the features of the anterior have
generally been accepted as components of a cartilaginous
endoskeleton in part because of their inferred decay resis-
tance and similarity to that of lampreys. Jawless vertebrate
cartilages are quite varied in composition, both within
and between clades (e.g. Wright et al. 1998; Zhang et al.
2006), and this variability seemingly affects their decay
resistance (R. Sansom, pers. obs.). There are no definite
fossil precedents for the preservation of cartilage as
organic films (Euphanerops remains equivocal (Janvier
and Arsenault 2002, 2007), whilst interpretations for con-
odonts (e.g. Aldridge and Theron 1993) have been made
through comparison with Jamoytius). This does not in
itself rule out Ritchie’s (1963, 1968) interpretation of a
cartilaginous endoskeleton in Jamoytius, however. With-
out analytical determination of the biomolecular compo-
sition of these features (which may be impossible in these
fossils), their interpretation must rely solely on compara-
tive anatomy and comparative taphonomy.
The uniform preservation of the anterior structures as
dark, flat films, coupled with their carbonaceous compo-
sition, is consistent with organic preservation. Further-
more, their wrinkles and folds indicate flexibility at the
time of collapse; the absence of evidence of brittle defor-
mation indicates they were not rigid. Ductile deformation
need not rule out their interpretation as cartilaginous
supports for body openings (e.g. annular and trematic
rings), because cartilage, including that of jawless
vertebrates, can exist in both rigid and flexible forms,
but it does prompt consideration of other potential
body margin-related biomolecules. For example, high
concentrations of melanin are found in association with
TABLE 1 . Topological features identified in Jamoytius and
their anatomical interpretations based upon a chordate compar-
ator.
Topological feature Anatomical interpretation
Anterior subcircles
(paired, lateral)
Optic capsules
Anterior subcircle
(terminal)
Single, terminal, nasal
opening
Anterior subcircle
(subterminal)
Round ventral mouth
Anterior subrectangles Multiple external branchial
openings
W-shaped structures Rigid (probably mineralised)
scales
Axial lines with subunits Axial skeleton
Ventro-lateral paired ‘folds’ Lateral fin folds?
10 PALAEONTOLOGY
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photosensory structures of lampreys (e.g. optic capsules,
pineal organ, lateral line system (Young 1981)) and other
body openings (e.g. branchial (Bagenal 1973)). The distri-
bution of melanin in lampreys is, therefore, consistent
with the interpretation of the anterior structures of
Jamoytius having originally had a high melanin content.
Currently, we are unable to determine whether the
anterior structures of Jamoytius were melanin or cartilage.
Regardless of whether they represent cartilaginous sup-
ports for body openings or skin pigment surrounding the
body openings, the anterior subcircles and subrectangles
are still best interpreted as a mouth, nasal opening, eyes
and external branchial openings.
W-shaped structures
Anatomical interpretations. A number of fossil jawless ver-
tebrates exhibit serial V-, W- or Z-shaped bands along
the body. These have been interpreted either as myomeres
(e.g. Haikouichthys, conodonts) or external dermoskeletal
scales (osteostracans, certain anaspids). Similarly, the W-
shaped structures of Jamoytius have been interpreted as
muscle blocks (Forey and Gardiner 1981; White 1946)
and as scales, either mineralized (Ritchie 1960) or unmin-
eralized, ‘horny’ and carbonized (Ritchie 1968, 1984).
Others regard any interpretations of these structures as
equivocal (Janvier 1981).
The Ws of Jamoytius appear to be single units, rather
than a series of subunits arranged in a W-shape, as is the
case in the scales of most vertebrates. Euphanerops also
shows long, undivided structures that run the height of
its flank, yet it is uncertain whether they are scales or
myomeres (Janvier and Arsenault 2007).
Taphonomy and composition. The narrow zones of the W-
shaped structures have undergone brittle deformation in
the form of fracturing and displacement in several speci-
mens (Text-fig. 4D), thus indicating that they were rigid
prior to collapse or compaction. Interpretation of the Ws
as scales is supported by their rigid nature, tubercular
ornamentation, preservation in relief and coincidence
with the body margin.
The W-shaped structures are phosphatic and rigid,
demonstrating a very different taphonomic history to the
anterior features (carbonaceous composition and ductile
deformation). It is important to consider whether the
phosphate of the Ws is primary or secondary. Within the
Jamoytius horizon, primary phosphate occurs, for exam-
ple, in the dermal denticles of the thelodont Loganellia
(Marss and Ritchie 1998) and secondary phosphate is
known in the form of fibrous mineralized muscle in the
arthropod Ainiktozoon (Van Der Brugghen et al. 1997).
The texture and colour of the phosphate of Jamoytius
does not directly compare to either of these phosphates,
so its nature remains unclear. The fracturing of the scales
does, however, support the hypothesis that the scales were
biomineralized in vivo, prior to their deformation.
No evidence is found for the muscle fibres identified
by White (1946). It seems likely that this was a misinter-
pretation of the dendritic pattern of the broad zone
(Ritchie 1968), which cannot be reconciled with any fea-
ture of a myomere (Text-fig. 4C). The dendritic pattern
occurs on specimens that have not been treated with hy-
droflouric acid (contra Forey and Gardiner 1981), but not
on any specimen that exhibits tubercles. The variation in
the appearance of scales among specimens may, therefore,
relate to the level of the splitting of the scale passing
through different hard tissues. This is observed in some
osteostracans (R. Sansom, pers. obs.), in which the mid-
dle layer of the dermoskeleton can be exposed revealing a
dendritic pattern of ‘intra-areal’ canals (e.g. Denison
1947; Janvier 1996a; Sansom 2008). The relative thinness
of the scales of Jamoytius, however, is difficult to reconcile
with the hypothesis that the broad zone dendritic pattern
represents a canal system. Alternatively, the pattern could
be an artefact caused by taphonomic processes such as
fracture because of post-mortem shrinkage of the broad
zones.
Axial lines with subunits
Anatomical interpretation. The linear, dorsal and ventral
axial lines and their continuation posteriorly as lines of
rounded axial features should be assessed through com-
parison with antero-posterior axial structures known in
vertebrates, i.e. notochord, dorsal nerve cord, gut and
vertebral elements. The contiguous lozenge ⁄oval subunits
are not consistent with previous interpretations as a noto-
chord and a gut (White 1946), or margins of a gut
(Ritchie 1968). A further inconsistency is the anterior
bifurcation of one of the lines (dorsal) that, contra to
Ritchie (1968), is not part of the branchial basket (Text-
fig. 5).
The internal pattern of subunits within the lines is
more in keeping with interpretation as an axial skeleton.
The contiguous nature of the subunits towards the ante-
rior and increasing separation towards the posterior is
comparable to the condition of the arcualia in lampreys
(Marinelli and Strenger 1954). The rounded or lozenge
shape of the elements in Jamoytius does not, however,
match the irregularly shaped cartilaginous arcualia of
either lampreys (a single series dorsal to notochord) or
Euphanerops (dorsal and ventral series, Janvier and Ar-
senault 2007: fig. 16). Rather, they are more comparable
to the ‘haemal series’ of Euphanerops, more specifically,
the lozenge-shaped subunits of the posterior haemal ser-
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ies. Although the notochord of modern jawless vertebrates
(hagfish and lampreys) is wide, the gap between the dor-
sal and ventral axial lines of Jamoytius is proportionally
far larger, potentially making interpretation as dorsal and
ventral arcualia problematic. Furthermore, the anterior
bifurcation of the dorsal line in NHM P12284 is inconsis-
tent with interpretation as arcualia.
Whilst it is not possible to determine precise homology
of the dorsal and ventral axial lines because of their unu-
sual shape and position, it is likely that they are formed
by subunits of some form of axial skeleton, either arcualia
in a previously unobserved condition or a ‘haemal series’
comparable to that of Euphanerops (Janvier and Arsenault
2007).
Taphonomy and composition. If interpretation of the dor-
sal and ventral axial lines of Jamoytius as axial skeleton is
accepted, then comparison with extant jawless vertebrates
indicates the subunits were likely composed of cartilage.
The seemingly different nature of the preservation of the
axial lines from that of the anterior subcircles ⁄ subrectan-
gles does not mean that they cannot both be composed
of cartilage: lamprey branchial cartilages have a different
composition from arcualial and neurocranial cartilages
(Fernandes and Eyre 1999; Robson et al. 1997).
Notochords interpreted in fossil jawless vertebrates
such as Gilpichthys (Bardack and Richardson 1977) and
conodonts (Aldridge et al. 1993) have a banded appear-
ance, seemingly because of overprinting of the myomeres.
In Jamoytius, evidence of myomeres is not preserved.
Whilst the W-shaped scales have a periodicity similar to
that of the axial line subunits, there are instances of the
narrow zones overlying the subunits. The subunits of the
axial lines of Jamoytius are, therefore, unlikely to be a
taphonomic artefact because of scales or myomere over-
printing. In FR 1601, the region between the dorsal and
ventral axial lines is the only region of the body to pre-
serve the W-shaped scales from both lateral sides of the
body (Text-fig. 6A). A similar pattern is observed in late-
stage decay of larval lampreys (e.g. Sansom et al. 2010),
which, when viewed laterally, reveal myomeres from both
lateral sides of the body within the region occupied by
the wide notochord, but not the dorsal and ventral sec-
tions of the body (R. Sansom, pers. obs.).
Paired longitudinal ‘folds’
Anatomical interpretation. The paired parallel ‘folds’ on
the ventro-lateral body margins (Text-fig. 3) have been
the source of conflicting interpretations. Some authors
regard them as ‘lateral fin folds’ (Janvier 1981; Ritchie
1968; White 1946), whilst others find no evidence to sup-
port that view (Forey and Gardiner 1981; Westoll 1958).
Long, thin, paired appendages (lateral fin folds) do not
occur in any form in extant vertebrates (Bemis and
Grande 1999), so we have compared the structures in
Jamoytius to those known in fossil jawless vertebrates.
Pharyngolepis (an anaspid) and Euphanerops possess long,
thin, paired ‘appendages’, which extend along the ventro-
lateral surfaces from the head to the anal region (Janvier
and Arsenault 2007; Ritchie 1964). In both of these taxa,
there are mineralized components of the ventro-lateral
appendages. Jamoytius lacks such mineralized structures,
and the ventro-lateral ‘folds’ are probably simple folds of
the skin.
Taphonomy and composition. Interpretation of the dorso-
ventral ‘folds’ as folds of skin without any form of
mineralized supports raises the question whether the
paired features are true anatomical features or a tapho-
nomic artefact. If the majority of the body surface was
covered with rigid scales (W-shaped structures), the more
flexible ventral surface in the gap between scales would be
prone to deformation during collapse. This hypothetical
taphonomic scenario is perhaps supported by the wrin-
kling that occurs within in the ventro-lateral folds of
some specimens but their paired nature argues against it
(Text-fig. 3). It is therefore unclear whether these folds
are distinct anatomical structures or merely a conse-
quence of body collapse; homologizing them with the
‘appendages’ of Pharyngolepis and Euphanerops is thus
currently problematic.
PHYLOGENETIC ANALYSIS
The evidence presented above indicates that Jamoytius is a
jawless vertebrate of uncertain affinities, so we have used
the most recent and comprehensive analysis of early ver-
tebrate interrelationships (Gess et al. 2006) as a basis to
investigate its precise phylogenetic position. The matrix of
Gess et al. (2006) is based upon earlier matrices (Janvier
1996b; Donoghue et al. 2000; Donoghue and Smith
2001), updated and expanded to include subsequently dis-
covered soft-bodied vertebrates, namely Haikouichthys
and Myllokunmingia (Shu et al. 1999; Donoghue et al.
2003; Hou et al. 2002), Mesomyzon (Chang et al. 2006)
and Priscomyzon (Gess et al. 2006) as well as oral charac-
ters relating to cyclostome monophyly.
Coding. The coding used for Jamoytius by Donoghue
et al. (2000) and subsequently by Donoghue and Smith
(2001) and Gess et al. (2006) was based upon an earlier
unpublished version of the data presented here (Freed-
man 1999), not all of which has survived subsequent
scrutiny. Thus, the coding has been modified to reflect
the interpretations herein (e.g. Table 1; Appendix S1).
12 PALAEONTOLOGY
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The matrix has also been updated to include additional
data for Euphanerops (Janvier and Arsenault 2007), Hai-
kouichthys (Zhang and Hou 2004), Arandaspida (Sansom
et al. 2005) and Galeaspida (Wang et al. 2005). Euphaner-
ops is taken to include Legendrelepis and Endiolepis (Jan-
vier 1996c; Janvier and Arsenault 2007). Two taxa from
the Middle Devonian of Scotland that have been pro-
posed to have affinities with Jamoytius have been added
to the matrix: Cornovichthys (Newman and Trewin 2001)
and Achanarella (Newman 2002).
Gess et al. (2006) employed presence ⁄ absence coding.
Such coding methodology violates the requirements of
logical independence of characters and can lead to false
support for a cladogram (Strong and Lipscomb 1999;
Forey and Kitching 2000). For example, absence of a nas-
ohypophyseal opening is counted twice in two different
characters (15 ⁄ 16), as is absence of dentine (80 ⁄ 81). The
matrix presented here therefore utilizes contingent coding,
which necessitates the erection of additional characters
(Appendix S1: characters 100–109). Furthermore, revision
of the coding and coding strategy for the characters relat-
ing to the relationships of extant cyclostomes reveals that
many of the physiological and miscellaneous characters
are uninformative (P. C. J. Donoghue, unpublished data).
These characters are removed here, whilst some of the
neurological characters are revised (e.g. cerebellar primor-
dia, retina).
Results. Heuristic searches, including all taxa, found two
most parsimonious trees of branch length 185 (Text-
fig. 9B). Jamoytius is placed as sister taxon to Euphaner-
ops, united by a ventral mouth and annular cartilage
(both homoplastic characters). These taxa (which could
together be termed Jamoytiiformes Tarlo, 1967) are
resolved as stem-gnathostomes because of their trunk der-
mal skeleton, separate anal fin and paired fin folds.
Ostraco/Jawed
Ostraco/Jawed
Tunicata
Cephalochordata
Myxinoidea
Myxinikela
Haikouichthys
Petromyzontida
Mesomyzon
Priscomyzon
Mayomyzon
Euconodonta
Jamoytius
Euphanerops
Anaspida
Loganellia
Turinia
Heterostraci
Arandaspida
Astraspis
Galeaspida
Osteostraci
Jawed Vertebrates
1
1
1
1
1
1
2
2
2
1
1
1
3
1
Achanarella
Cornovichthys
1
1
2
Myxinoidea
Petromyzontida
Anaspida
Jamoytius
Ostraco/Jawed
Myxinoidea
Petromyzontida
Anaspida
Jamoytius
Ostraco/Jawed
Euphanerops
Myxinoidea
Petromyzontida
Anaspida
Jamoytius
Ostraco/Jawed
Euphanerops
Euconodonta
Pteraspidimorphi
Myxinoidea
Petromyzontida
Anaspida
Jamoytius
Euphanerops
Euconodonta
Myxinoidea
Petromyzontida
Anaspida
Jamoytius
Euphanerops
Euconodonta
Pteraspidimorphi
Myxinoidea
Petromyzontida
Anaspida
Jamoytius
Ostraco/Jawed
Euphanerops
Euconodonta
Forey 1995 Janvier 1996b Donoghue et al. 2000 Donoghue et al. 2001 Shu et al. 2003 Gess et al. 2006A
B C Tunicata
Cephalochordata
Myxinoidea
Myxinikela
Haikouichthys
Petromyzontida
Mesomyzon
Priscomyzon
Mayomyzon
Euconodonta
Jamoytius
Euphanerops
Anaspida
Loganellia
Turinia
Heterostraci
Arandaspida
Astraspis
Galeaspida
Osteostraci
Jawed Vertebrates
1
1
1
1
1
1
1
1
2
1
1
1
2
1
Achanarella
Cornovichthys
1
1
2 1
1
TEXT -F IG . 9 . Phylogenetic relationships of Jamoytius. A, simplified versions of previous cladistic analyses of Forey (1995), Janvier
(1996b), Donoghue et al. (2000), Donoghue and Smith (2001), Shu et al. (2003), and Gess et al. (2006) where Ostraco ⁄ Jawed
represents other ostracoderms and jawed vertebrates. B, single most parsimonious tree from the unconstrained phylogenetic analysis
with decay support indices. C, Strict consensus of trees resulting from analysis constrained for cyclostome monophyly with decay
indices.
SANSOM ET AL . : TAPHONOMY AND AFFINITY OF AN ENIGMATIC SILURIAN VERTEBRATE 113
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46
47
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49
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Whether Jamoytius preserves these latter two characters is
uncertain, but the same topology results when the paired
appendages of Jamoytius are coded as unknown. Jamoytii-
formes are placed closer to the root of total-group gnat-
hostomes than Anaspida because of an absence of dermal
head covering, dentine and lamellar aspidin. Close rela-
tionships between Jamoytius and Euphanerops have been
reconstructed in previous phylogenetic studies (Janvier
1996a–c; Donoghue et al. 2000; Donoghue and Smith
2001; Shu et al. 2003), but always as part of a clade with
Anaspida (Text-fig. 9A).
Of the other taxa proposed to have jamoytiiform
affinities, Cornovichthys is placed as a stem-vertebrate
(in the sense that Petromyzontida and Gnathostomata
comprise Vertebrata, whilst vertebrates and Myxinoidea
constitute Craniata (Janvier (1981)), whilst Achanarella
is placed as a stem-gnathostome in a more basal posi-
tion than (Jamoytius + Euphanerops). Neither taxon is,
therefore, resolved as part of a monophyletic Jamoytii-
formes.
The revisions incorporated in the data matrix used here
also led to other changes in relationships among jawless
vertebrates. Changing the coding strategy for dentine and
odontodes has led to the thelodonts (represented here by
Loganellia and Turinia) being identified as closer to the
root of total-group gnathostomes than the pteraspidimor-
phi (represented here by Heterostraci, Arandaspida and
Astraspis) on the gnathostome stem lineage. Furthermore,
eucondonts are placed as sister taxon to fossil and extant
lampreys, making conodonts stem-petromyzontids. Lam-
preys and euconodonts are united by possession of trans-
versely biting teeth.
Morphological evidence, both neontological and palae-
ontological, consistently finds lampreys (Petromyzontida)
as more closely related to jawed vertebrates than hagfishes
(Myxinoidea), as is the case here (Løvtrup, 1977; Janvier,
1981; Forey, 1984; Khonsari et al. 2009). Molecular inves-
tigations, however, identify the lampreys as more closely
related to the hagfishes and thus support cyclostome
monophyly (e.g. Delarbre et al. 2002; Delsuc et al. 2006).
Phylogenetic analysis of our data matrix constrained for
cyclostome monophyly identifies a less parsimonious
solution (branch length 191) with a topology very similar
to that of the unconstrained analysis, differing only in
placement of the myxinoids and resolution amongst petr-
omyzontids (Text-fig. 9C). The Jamoytiiformes are still
recovered as stem-gnathostomes, whilst the euconodonts
are recovered as stem-cyclostomes.
EVOLUTIONARY IMPLICATIONS
Jamoytius is commonly considered to represent a primi-
tive member of a fossil or extant vertebrate clade, either a
primitive anaspid (e.g. Ritchie 1963) or an ancestral lam-
prey (e.g. Mallat 1984). Despite the fact that a number of
its characters are plesiomorphic for chordates or for ver-
tebrates, analysis here establishes sister taxon relationship
with Euphanerops. In our unconstrained analysis, Jamoyti-
iformes represent a new grade in the evolution of stem-
gnathostomes, after the evolution of a trunk dermal skele-
ton but before the evolution of lamellar aspidin and der-
mal head skeleton. Given the preservation of trunk
dermoskeleton of Jamoytius (W-shaped scales), it is rea-
sonable to assume that any head dermoskeleton would
also be preserved if it had existed. The coding for absence
of head dermoskeleton in Jamoytius, and subsequent
placement of Jamoytiiformes on the gnathostome stem,
therefore reflects phylogenetic absence rather than tapho-
nomic loss (see Donoghue and Purnell 2009 for a discus-
sion of alternative meanings of stem assignments). The
position of Cornovichthys as a stem-vertebrate is sup-
ported by only one character (anterior otic capsules), the
interpretation of which is equivocal in some taxa. The
stem placements of Cornovichthys and Achanarella are
likely to reflect taphonomic bias resulting from loss of
characters through post-mortem decay (Donoghue and
Purnell 2009; Sansom et al. 2010). To further resolve the
relationships of the Jamoytiiformes and putatively related
taxa, reinterpretation of the relevant fossils is required
using the same principles as applied here for Jamoytius.
The phylogenetic placement of conodonts as stem-lam-
preys or stem-cyclostomes is contrary to the hypotheses
from previous analyses in which conodonts are placed as
stem-gnathostomes (Donoghue et al. 2000; Donoghue
and Smith 2001). The new placement is not robust, but it
is the most parsimonious on the basis of the morphologi-
cal data analysed here. The instability of this result sug-
gests that addition of further soft-bodied taxa to
phylogenetic matrices of early vertebrates will potentially
affect hypotheses of euconodont affinity. Our phyloge-
netic analysis does not raise any doubts about the place-
ment of euconodonts within the vertebrates.
Other stem-gnathostome taxa such as Pteraspidomor-
phi, Galeaspida and Osteostraci are resolved to be closer
to the gnathostome crown than thelodonts. This proposal
differs from previous suggestions of thelodont sister
relationships with gnathostomes (Marss et al. 2007),
chondrichthyes (Turner 1991) or the group (Galeasp-
ida + Osteostraci + jawed vertebrates) (Donoghue and
Smith 2001). Given the limited number of thelodont taxa
included here, however, questions of thelodont affinity
remain open to further investigation.
Jamoytius has often been cited in defence of the lateral
fin fold theory (e.g. Jarvik 1980; Shubin et al. 1997), an
evolutionary developmental scenario in which the paired
appendages of jawed vertebrates derive from continuous
ventro-lateral fin folds of jawless vertebrates by the loss of
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the intermediate portion of the fin fold (Balfour 1876;
Thacher 1877; reviewed by Coates 1994; Bemis and
Grande 1999). The present study found no evidence for
any skeletal or muscular structures that would allow an
assessment of potential homologies with the paired fins of
jawed vertebrates. Furthermore, the antero-posterior skin
folds may represent taphonomic artefacts. Our results
indicate that the structures of anaspids, thelodonts and
potentially Jamoytius were acquired independently of
paired fins restricted to the pectoral region in Osteostraci
and Gnathostomata (Sansom 2009).
CONCLUSIONS
The study of the anatomy of problematic organisms can
be aided by the use of a methodology designed to sepa-
rate topological and morphological reconstruction from
anatomical interpretation and to gather as much informa-
tion as possible about the preserved features through
taphonomic analyses. The application to Jamoytius dem-
onstrates that it is a vertebrate, with preserved W-shaped
phosphatic scales, ten or more paired external branchial
openings, dorso-lateral optic capsules, a round ventral
mouth, a terminal nasal opening, and, potentially, dorsal
and ventral axial skeleton. Interpretations of paired fins
remain equivocal. Analyses of the phylogenetic affinity of
Jamoytius identify a sister taxon relationship with Eupha-
nerops. This clade, the Jamoytiiformes, is a primitive
group of stem-gnathostomes and does not form a clade
with the Anaspida.
Acknowledgements. This work was funded in part by a Natural
Environment Research Council grant (NE ⁄ E015336 ⁄ 1 to SEG
and MAP). KF was supported by an Overseas Research Student
award (ORS ⁄ 96014039) and by R. A. Freedman. Various people
are thanked for their assistance in enabling the study and loan of
material including Sir Frederick Stewart, Peder Aspen (University
of Edinburgh), Neil Clark (Hunterian Museum), Bobbie Paton,
Liz Hide and Mike Taylor (National Museum of Scotland), Sally
Young, Peter Forey and Martha Ritcher (Natural History
Museum, London), Robert Jones and Alex Ritchie (Australian
Museum) and Steve Tunnicliff (British Geological Survey). Tony
Milodowski and Paul Wetton (British Geological Survey) kindly
assisted with SEM analysis. We also appreciate the constructive
comments of three anonymous reviewers and Philip Donoghue,
which have allowed us to improve the manuscript.
Editor. Philip Donoghue
SUPPORTING INFORMATION
Additional Supporting Information may be found in the online
version of this article:
Data S1. Xxxxxxxx. 3
Appendix S1. Character list and matrix used in phylogenetic
analysis – an updated version of Gess et al. (2006) with neuro-
logical characters adapted according to P. Donoghue (unpub-
lished data).
Please note: Wiley-Blackwell are not responsible for the con-
tent or functionality of any supporting materials supplied by the
authors. Any queries (other than missing material) should be
directed to the corresponding author for the article.
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