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Preliminary report of trilobites from the Hanonet Formation (Eifelian – Givetian transition), southern border of Dinant Synclinorium, Belgium

Authors:
  • Natuurhistorisch Museum Maastricht

Abstract and Figures

The macrofauna of the Hanonet Formation is well documented with the exception of trilobites. Recent investigation of the basal layers of this formation (Polygnathus ensensis conodont Zone) at Resteigne has allowed identification of six trilobite taxa, comprising Calycoscutellum goolaertsi n. sp., Nyterops hollandi n. sp., Hypsipariops? sp., Gerastos cf. prox, Dohmiella sp. 2, and Dechenella sp. The taxa Calycoscutellum cf. goolaertsi n. sp. and Cornuproetus cornutus n. ssp. 1 are recorded from the same formation at Couvin.
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Preliminary report of trilobites from the Hanonet Formation (Eifelian
Givetian transition), southern border of Dinant Synclinorium, Belgium
by Allart P. VAN VIERSEN
VIERSEN, A.P. VAN, 2007 Preliminary report of trilobites from
the Hanonet Formation (Eifelian Givetian transition), southern
border of Dinant Synclinorium, Belgium. Bulletin de l’Institut
royal des Sciences naturelles de Belgique, Sciences de la Terre,
77: 15-29, 3 gs, 3 pls, Brussels, October 15, 2007 – ISSN 0374-
6291.
Abstract
The macrofauna of the Hanonet Formation is well documented
with the exception of trilobites. Recent investigation of the basal
layers of this formation (Polygnathus ensensis conodont Zone)
at Resteigne has allowed identication of six trilobite taxa,
comprising Calycoscutellum goolaertsi n. sp., Nyterops hollandi
n. sp., Hypsipariops? sp., Gerastos cf. prox, Dohmiella sp. 2, and
Dechenella sp. The taxa Calycoscutellum cf. goolaertsi n. sp.
and Cornuproetus cornutus n. ssp. 1 are recorded from the same
formation at Couvin.
Keywords: Trilobites, Hanonet Formation, Middle Devonian,
Belgium.
Résumé
La macrofaune de la Formation de Hanonet est bien documentée, à
l’exception des trilobites. Des fouilles récentes de la partie basale
de cette formation (Zone à conodontes Polygnathus ensensis)
à Resteigne ont permis d’identier six taxons de trilobites, y
compris Calycoscutellum goolaertsi n. sp., Nyterops hollandi
n. sp., Hypsipariops? sp., Gerastos cf. prox, Dohmiella sp. 2 et
Dechenella sp. Les taxons Calycoscutellum cf. goolaertsi n. sp. et
Cornuproetus cornutus n. ssp. 1 ont été decouverts dans la même
formation à Couvin.
Mots-clefs: Trilobites, Formation d’Hanonet, Dévonien moyen,
Belgique.
Introduction
The Hanonet Formation is a major source of latest
Eifelian to early Givetian trilobites that outcrops on
the southern and southeastern borders of the Dinant
Synclinorium. Contrary to most other macrofaunal
constituents, the trilobites of this formation are very
poorly documented. There are few publications in
which they are mentioned (see, e.g., BLONDIEAU,
1995; BULTYNCK & HOLLEVOET, 1999) and there are
no descriptions available except for one species (see
VAN VIERSEN, 2006b).
The present paper describes trilobite specimens
from the basal part of the Hanonet Formation in
the southwestern part of the abandoned quarry
of Resteigne. Several additional specimens were
collected from the Hanonet Formation in quarry “La
Couvinoise” north of Couvin.
Locations and stratigraphy
ABANDONED QUARRY OF RESTEIGNE (Loc002, southern
border of Dinant Synclinorium, Belgium; Fig. 1)
This quarry is occasionally nicknamed “Carrière de la
Lesse”. It has received much attention in sedimentological
and palaeontological studies (see, e.g., MAMET & PREAT,
1983; PREAT et al., 1984; COEN-AUBERT et al., 1986;
COEN-AUBERT, 1988, 1996, 2003; CASIER & PREAT, 1990,
1991; SIX, 1991; BLONDIEAU, 1995; VAN VIERSEN, 2006b).
A nearly uninterrupted sequence of late Eifelian to early
Givetian strata is exposed here, chiey comprising the
Hanonet, Trois-Fontaines and Terres d’Haurs formations.
At Resteigne there is a hiatus near the base of the
Hanonet Formation, just above contact with the lower
Jemelle Formation, and the unit attains a thickness of 70
m here (PREAT & TOURNEUR in BULTYNCK et al., 1991;
BULTYNCK & DEJONGHE, 2001). A detailed account of the
stratigraphic units in this quarry was provided by COEN-
AUBERT et al. (1986).
Trilobites were collected from the predominantly
argillaceous limestones that constitute the basal part of the
Hanonet Formation in the southwestern part of the quarry,
just below the Eifelian Givetian boundary (Polygnathus
BULLETIN DE L’INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE
BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN
SCIENCES DE LA TERRE , 77: 15-29, 2007
AARDWETENSCHAPPEN, 77: 15-29, 2007
ensensis conodont Zone). They are represented by the
genera Calycoscutellum, Dechenella, Dohmiella, Gerastos,
Hypsipariops?, Nyterops and Otarioninae gen. & sp. indet.
QUARRY LA COUVINOISE (Loc021, southern border of
Dinant Synclinorium, Belgium; LECOMPTE, 1960, gs. 3,
7, pl. 4, gs. 1-4; BULTYNCK & HOLLEVOET, 1999, g. 1)
An actively exploited quarry 400 m northeast of the
Couvin railway station which has previously been called
“Carrière Haine” and “Carrière Collard et Guillaume”.
Sedimentology of the Hanonet Formation here has been
described by BULTYNCK (1970) and PREAT (1989), among
others. BULTYNCK & HOLLEVOET (1999, g. 2) provided
an overview of the stratigraphic succession of the upper
part of the Jemelle Formation, the Hanonet Formation,
and the lower part of the Trois-Fontaines Formation in the
Couvin area. These workers also positioned the Eifelian
Givetian boundary within the lower part of the Hanonet
Formation based on the rst occurrence of the conodont
Polygnathus hemiansatus.
During an excursion to the quarry of the Société
Géologique de Belgique and the Société belge de Géologie,
de Paléontologie et d’Hydrologie in 1959, a rich macrofauna
was recovered from the “Upper Couvinian, niveau Co2d à
Cyrtoceras nodulosum(LECOMPTE, 1960). This horizon is
now considered to belong to the Hanonet Formation (see, e.g.,
PREAT & TOURNEUR in BULTYNCK et al., 1991, p. 45) and
is of a late Eifelian or early Givetian age. LECOMPTE (1960,
p. 52) recorded trilobites from a level within this horizon
“Co2d” that he assigned to Scutellum alutaceum, Scutellum
abelliferum, Harpes macrocephalus and Phacops latifrons
(a repository for the original material was not named and
thus none of the identications can be corroborated). Two
additional trilobite taxa, Dechenella aff. verneuili and
Scutellum, were recorded together with Stringocephalus
burtini from what was considered by LECOMPTE (1960,
pp. 54-55) to be the summit of “Co2d.” Assuming that
LECOMPTEs (1960) specimens of Stringocephalus burtini
were correctly identied and considering the stratigraphic
range of this brachiopod (see STRUVE, 1961; BULTYNCK et
al., 2000, g. 6), these records may be considered to be of
early Givetian age and probably come from a basal horizon
in the Trois-Fontaines Formation.
Preliminary collections at this locality comprise
trilobite specimens from the Hanonet Formation but that
were not found in situ. Hence, their age is approximately
late Eifelian or early Givetian. Trilobites include the genera
Calycoscutellum, Cornuproetus, Dechenella, Gerastos,
Hypsipariops, Nyterops, and, assuming that LECOMPTEs
(1960) record is congeneric, Harpes.
While focus is currently on trilobites from Resteigne, the
trilobite faunas of the Hanonet Formation at both localities
are very similar at the genus level. Calycoscutellum,
Dechenella, Gerastos, Nyterops, and probably also
Hypsipariops are mutually represented. Specimens of at
least Nyterops and Calycoscutellum are closely related
at the species level and possibly conspecic. Other taxa,
which are known only from one of these sites, are Harpes
and Cornuproetus (Couvin) and Dohmiella and Otarioninae
gen. & sp. indet. (Resteigne). The separate occurrences of
these trilobites may be easily explained by the fact that they
are very rare at their respective localities. Furthermore,
similar relative rarities of these taxa are known from coeval
strata in the adjacent Eifel (see, e.g., BASSE, 2002; BASSE
& MÜLLER, 2004).
Location of abandoned quarry of Resteigne (Loc002) in southern Belgium. Square on overview map indicates
position of local map within Belgium.
Fig. 1 —
16
Allart P. VAN VIERSEN
Phacops cf. imitator STRUVE, 1970 (IRSNB
a12449); Jemelle Formation, Chavées Member,
middle Eifelian, from embankment south of
the Jemelle railway station (see VAN VIERSEN,
2007 for further details on locality). Dorsal and
oblique lateral views on silicone cast of partial
external mould of cephalon, x 5.
Fig. 2 —
Systematic palaeontology
All trilobites described below are deposited
in the Institut royal des Sciences naturelles de
Belgique (Brussels), abbreviated IRSNB, except
for one specimen which is in the collections of
Forschungsinstitut und Naturmuseum Senckenberg
(Frankfurt am Main), abbreviated SMF. All specimens
were coated with ammonium chloride sublimate prior
to photography. Terminology follows WHITTINGTON
& KELLY (1997).
Family Phacopidae HAWLE & CORDA, 1847
Subfamily Phacopinae HAWLE & CORDA, 1847
Remarks
Phacops latifrons (BRONN, 1825) is a notorious species
that has a persistent history of claimed records from the
Belgian Lower to Middle Devonian (e.g. DEWALQUE,
1880; MAILLIEUX, 1904, 1919, 1933, 1938; VAN
TUIJN, 1927; FOURMARIER, 1954; LECOMPTE, 1960)
and especially from early Eifelian strata in the area
between Treignes and Vireux-Molhain (see STRUVE,
1982 for remarks). Most of these records come
without descriptions or illustrations but MAILLIEUX
(1933, pl. 5, g. 89) provided a line drawing of an
outstretched specimen. The depiction is a chimaera,
comprising features that typify different phacopines.
It may be assumed that this reconstruction was based
on multiple specimens belonging to different species
and it eloquently illustrates how broad the concept
of Phacops latifrons was at the time. What is more
is that the high amount of records of Phacops from
the Ardennes creates a skewed reection of its actual
occurrence. The genus is a rare component of Eifelian
trilobite faunas here, the phacopid part of which
appears to be predominated by Geesops STRUVE, 1972
and Pedinopariops STRUVE, 1972 during the lower
Eifelian (see, e.g., VAN VIERSEN, 2006a) and middle
Eifelian, and Nyterops STRUVE, 1972 during the upper
Eifelian and lower Givetian (see CRÔNIER & VAN
VIERSEN, in press, for preliminary data). According
to BASSE (1998, 2006) Phacops latifrons is in fact
known exclusively from late half Eifelian strata in the
Eifel and Sauerland (Rhenish Slate Mountains). Only
Phacops cf. imitator STRUVE, 1970 (middle Eifelian,
Jemelle; see Fig. 2) and Phacops sartenaeri STRUVE,
1985 (upper Eifelian, Petigny; see STRUVE, 1985) are
currently known from the Ardennes with certainty.
It is not inconceivable that Phacops latifrons occurs
here as well but evidence for it remains elusive.
Genus Nyterops STRUVE, 1972
Type species: Phacops (Phacops) nyter STRUVE,
1970, from the Cürten Formation (Givetian) of the
Eifel, Germany.
Nyterops hollandi n. sp.
Pl. 1, Figs 1-6
1995 — Phacops sp. BLONDIEAU, pl. 12, g. 6.
Derivation of name
After Dieter Holland, who generously prepared the
material of this species.
Holotype
Cephalon IRSNB a12430 (Pl. 1, Figs 1-4).
Type locality
Southwestern slope of quarry of Resteigne (Loc002),
Belgium.
Type horizon
Basal part of Hanonet Formation, uppermost
Eifelian.
Material
Three cephala (IRSNB a12430-a12432), two pygidia
(IRSNB a12433-12434), from type locality and
horizon.
Diagnosis
A species of Nyterops with the following characteristic
features: Wide (tr.) cephalon with weakly sloped genal
17
Trilobites from the Hanonet Formation, Belgium
elds and genal corners protruding far abaxially.
Visual surface comprising fteen dorsoventral
les with maximally four lenses per le. Smallest
distance between eye and lateral border about equal to
maximum height of eye.
Description
Cephalic doublure bearing ne terrace ridges.
Vincular furrow medially shallow; distally rmly
impressed. Preglabellar furrow continuous; medially
distinct; ne and weakly impressed anterolaterally
near eye. Cephalic border rounded in section; bearing
ne terrace ridges that disappear posterolaterally near
sharp genal angle. Glabella anteriorly overhanging;
strongly vaulted (tr.); bearing evenly spaced, coarse
tubercles except anteriorly where tubercles are
transversally expanded, narrow (sag., exsag.), and
grouped into ridge-like structures. Highest point of
glabella is lateral to γ and about equal to highest point
of occipital ring when latter is held in the vertical
plane. In dorsal view, eyes remain at a clear distance
from lateral cephalic margin (easily obscured by
tectonic deformation). Visual surface is comprised of
15 dorsoventral les of lenses, counting in examined
specimens (from front to back): 3; 4; 4; 4; 4; 4; 3 or 4; 4;
3 or 4; 4; 4; 3; 2 or 3; 2 or 3; 2 lenses per le. Lenses in
anterior and posterior few les usually protrude above
sclera; remaining lenses slightly to deeply embedded.
Intercalating ring accentuated by one or more large
tubercles. Reniform palpebral lobe bearing tubercles
that remain at a distance from abaxial margin of this
lobe, especially in the middle (exsag.). Palpebral
furrow anteriorly broad and shallow; posteriorly deep.
Palpebral area of xigena inated, bearing up to about
six tubercles. Axial furrows diverging at around 60°.
Small, deep pits on genal eld near lateral border that
disappear posterolaterally. In anterior view, a wide
genal eld is visible lateral to the eye. Abaxial half
of posterior border bearing a row of coarse, slightly
acuminate tubercles with closely spaced smaller ones
in front of them. Posterior border furrow reaching
abaxially until posterior (exsag.) to abaxial margin
of eye. Occipital furrow medially (tr.) slightly more
distinct than distally. Several faint tubercles present
medially (tr.) on occipital ring.
Thorax (based on examination of specimens in
private collections): similar to that of Nyterops nyter.
Pygidium: similar to that of Nyterops nyter.
Comparison
Nyterops nyter from the lower Givetian of the Eifel
differs from Nyterops hollandi n. sp. as follows:
maximum number of lenses per dorsoventral le varies
from ve to six; maximum height of eye clearly exceeds
minimal distance between eye and lateral border;
gena is steep and its abaxial development is strongly
reduced as if this part of the cephalon is folded strongly
ventrally; genal corner protrudes more posteriorly.
BASSE (2006) described a new species Nyterops
yetieiiensis from the upper Eifelian of the Eifel.
The German species differs from Nyterops hollandi
n. sp. as follows: glabella slightly protrudes medially
anteriorly; coarse, independent tubercles present on
frontal part of glabella (instead of the “ridge complex”
of transversally expanded tubercles that characterises
Nyterops nyter and Nyterops hollandi n. sp.); genal
eld exceedingly rich in coarse tubercles.
Genus Hypsipariops STRUVE, 1982
Type species: Pedinopariops (Hypsipariops) lyncops
Struve, 1982, from the Loogh Formation (Givetian)
of the Eifel, Germany.
Remarks
STRUVE (1982, p. 488) erected Hypsipariops (=
eurycaulus species group of Phacops (Pedinopariops)
sensu STRUVE, 1972) as a new subgenus of
Pedinopariops STRUVE, 1972. According to BASSE
(2006, p. 106), the holotype of Liolophops sublevatus
(STRUVE, 1970) (type species of Liolophops STRUVE,
1972) is exceedingly similar to Hypsipariops. STRUVE
(1972, 1995) regarded the weak curvature (tr.) of L0 as
one of the main characteristic features of Liolophops.
BASSE (2006) however, suggested that this a feature
that occurs in a late ontogenetic stage and, given the
strong similarities between them, that both genera
might be considered synonyms. Despite this, BASSE
(2006) maintained Hypsipariops because both genera
may have distinct phylogenetic origins: There seem to
be two groups of a possibly paraphyletic Pedinopariops
in the Eifelian of the Eifel, each of which with a
distinct ontogeny but similar adult morphology (see
ibid., p. 106). Liolophops was placed in one group,
characterised by transformation of granules into ne
granules to more or less at bladders during post-
larval ontogeny, while Hypsipariops was tentatively
placed in the other group, characterised by hardly
any changes in prosopon during post-larval ontogeny.
Thus, assuming this hypothesis is true, the similarities
between adults of both genera might be regarded as
homoplasies. While BASSEs (2006) suggestion seems
credible, the accommodation of Hypsipariops and
Liolophops in separate, as yet formally unrecognised
18
Allart P. VAN VIERSEN
Line drawing of pygidium of Calycoscutellum
goolaertsi n. sp.
Fig. 3 —
Pedinopariops groups does not imply monophyly for
either Hypsipariops or Liolophops. All three taxa, as
currently perceived, are ambiguous and should be
subjected to a cladistic analysis. Following BASSE
(2006) Hypsipariops is maintained here, although
provisionally.
Hypsipariops? sp.
Pl. 1, Figs 7-9
Material
One partially exfoliated cephalon (IRSNB a12435),
from locality Loc002, Resteigne, basal part of
Hanonet Formation.
Discussion
The preservation of the single cephalon that is available
for study is inadequate to permit a detailed description
or comparison. It is easily distinguished from co-
occurring Nyterops hollandi n. sp. in Resteigne in
having much larger eyes (18 dorsoventral les with
maximally 7 lenses per le) that are positioned close
to lateral border.
Specimens of this taxon from the Resteigne quarry
can attain considerable sizes and are the largest
trilobites known from the Belgian Devonian (with the
exception of some Early Devonian homalonotids). The
present author has examined several well-preserved
cephala [similar to Hypsipariops eurycaulus (STRUVE,
1970)] in private collections that are as wide (tr.) as 80
mm. These sizes strongly remind of large phacopid
Drotops species described by STRUVE (1995) from the
Moroccan Devonian.
BASSE (2006, pl. 23, fig. 228) illustrated a plaster
cast of a cephalon from the Couvinoise quarry
(site Loc021) that he assigned to Hypsipariops cf.
eurycaulus. This cast is housed by the Senckenberg
Museum; according to the latter author the original
specimen is in the collections of the IRSNB.
Family Styginidae VOGDES, 1890
Subfamily Scutelluinae RICHTER & RICHTER, 1955
Genus Calycoscutellum ARCHINAL, 1994
Type species: Brontes abellifer GOLDFUSS, 1839,
from the Junkerberg Formation (Eifelian) of the Eifel,
Germany.
Calycoscutellum goolaertsi n. sp.
Pl. 2, Figs 2, 5-7; Pl. 3, Fig. 3; Fig. 3
Derivation of name
After Stijn Goolaerts, who generously provided the
holotype.
Holotype
Pygidium IRSNB a12436 (Pl. 2, Fig. 5).
Type locality
Southwestern slope of quarry of Resteigne (Loc002),
Belgium.
Type horizon
Basal part of Hanonet Formation, uppermost
Eifelian.
Material
One pygidium (IRSNB a12436), one partially
exfoliated pygidium (IRSNB a12437), one
fragmentary pygidium (IRSNB a12438), one
cranidium (IRSNB a12439), one partial librigena
(IRSNB a12440), from type locality and horizon. One
tentatively assigned incomplete pygidium (IRSNB
a12441) (Pl. 3, Fig. 6), from locality Loc021, Couvin,
Hanonet Formation.
Diagnosis
A species of Calycoscutellum with the following
characteristic features: Pygidial median rib gradually
19
Trilobites from the Hanonet Formation, Belgium
narrowing towards anterior; proximally slightly
widened and connected to axis. Pygidial pleurae
distally slightly wider (tr.) than adjacent interpleural
furrows.
Discussion
Calycoscutellum species from the Middle Devonian
of the Rhenish Slate Mountains are morphologically
similar enough for previous workers (e.g. ARCHINAL,
1994; BASSE & MÜLLER, 2004) to have restricted
their descriptions to diagnostic features alone.
Especially the pygidial median rib has been attributed
signicant diagnostic value and the present author
follows this view. In addition to this, two closely
related species from the Eifel that are similar in age
to Calycoscutellum goolaertsi n. sp. are contrasted
below.
The pygidium of the type species of
Calycoscutellum, C. abelliferum, from the middle
Eifelian of the Eifel is very similar yet distinctly
differs from that of the new species in having a
median rib that is proximally rudimentary and
disappears before reaching the axis; more compacted
(sag.) pygidial contour; wider interpleural furrows
relative to pleurae.
The pygidium of Calycoscutellum capitellum
ARCHINAL, 1994 from the lower Givetian of the Eifel
comes close to the new taxon but is distinct in having
a much more rounded outline of axis; proximally
strongly widened (tr.) median rib; generally more
strongly curved pleural ribs; denser tuberculation
(also on cranidium).
Family Proetidae SALTER, 1864
Subfamily Proetinae SALTER, 1864
Genus Gerastos GOLDFUSS, 1843
Type species: Proetus cuvieri STEININGER, 1831,
from the Ahrdorf Formation (Eifelian) of the Eifel,
Germany.
Gerastos cf. prox (RICHTER & RICHTER, 1956)
Pl. 3, Figs 1, 2, 4, 5, 7-9, 11
Material
Two cranidia (IRSNB a12442-a12443), one pygidium
(IRSNB a12444), one incomplete pygidium (IRSNB
a12445), from locality Loc002, Resteigne, basal part
of Hanonet Formation.
Discussion
The specimens from the upper Eifelian of Resteigne
are exceedingly similar to topotypical material of
Gerastos prox recorded from the Ahbach Formation
(Eifelian Givetian transition) of the Eifel by RICHTER
& RICHTER (1956). BASSE (2002) reviewed Gerastos
prox and reassigned a collection of early Givetian
specimens from the Eifel to his new species Gerastos
eiiensis. According to this last author Gerastos
eiiensis is principally different from the slightly
younger Gerastos prox in having smaller eyes; less
distinct abaxial demarcation of subocular ridge; larger
librigenal eld usually bearing denser granulation;
more rmly impressed pygidial border furrow (ibid.,
p. 22). The pygidia from Resteigne show the weakly
impressed pygidial border furrow that was considered
to be characteristic of coeval Gerastos prox by BASSE
(2002), which suggests that they are conspecic.
However, since no librigenae were recovered of the
Belgian taxon, a more detailed comparison with the
German species is impossible and thus the rst is
provisionally treated under open nomenclature.
Although some of the differences between
Gerastos prox and Gerastos eiiensis may seem
subtle, samples taken by the present author from a
lower Givetian horizon in the Resteigne quarry that
include a librigena exhibit a morphology close to
that of Gerastos eiiensis and are distinctly different
from the late Eifelian Gerastos specimens from this
same site. This suggests that the differences between
Gerastos prox and Gerastos eiiensis that were
described by BASSE (2002) are correct and that both
taxa are valid. The early Givetian specimens from
Resteigne will be treated in a later paper.
Genus Dohmiella LÜTKE, 1990
Type species: Proetus (Euproetus) dohmi RICHTER
& RICHTER, 1918, from the Junkerberg Formation
(Eifelian) of the Eifel, Germany.
Remarks
Dohmiella has been considered a junior subjective
synonym of Gerastos by ADRAIN (1997) and JELL &
ADRAIN (2003). VAN VIERSEN (2006b) subsequently
retained Dohmiella and suggested that the presence of
distinct median nodes on at least the pygidial axis is
a potential synapomorphy. This author also emended
the generic diagnosis.
20
Allart P. VAN VIERSEN
Dohmiella sp. 2
Pl. 3, Fig. 10
v 2006 — Dohmiella sp. 2 VAN VIERSEN, p. 234, pl. 2, g. 10.
Material
One librigena (SMF 58587), from locality Loc002,
Resteigne, basal part of Hanonet Formation.
Discussion
This species is extremely rare and also represents
the stratigraphically latest known occurrence of
Dohmiella in Belgium. No new material has been
recovered of Dohmiella sp. 2 and it is also absent
among numerous trilobite specimens from Resteigne
in private collections that have been investigated by
the present author. Dohmiella has not been reported
from the Couvinoise quarry (site Loc021).
Subfamily Dechenellinae PŘIBYL, 1946
Genus Dechenella KAYSER, 1880
Type species: Phillipsia verneuili BARRANDE, 1852,
from the Givetian of the Eifel, Germany.
Remarks
According to BASSE (2002) the stratigraphically
earliest records of Dechenella from Germany are of
latest Eifelian age. In Belgium Dechenellinae possibly
appear as early as in the middle Eifelian. BLONDIEAU
(1995, pl. 12, g. 3) illustrated a pygidium from
the Jemelle Formation at the old railway section
between Jemelle and Rochefort (see GODEFROID,
1968, pp. 60-62; GODEFROID in BULTYNCK et al.,
1991, p. 31; BLONDIEAU, 1995, p. 39) that may be
tentatively assigned to Dechenellinae. Unfortunately,
BLONDIEAUs (1995) specimen is a damaged
internal mould lacking most of the axis and better
preserved material will be required to make a denite
identication.
Dechenella sp.
Pl. 3, Fig. 12
Material
One incomplete pygidium (IRSNB a12446), from
locality Loc002, Resteigne, basal part of Hanonet
Formation.
Discussion
A substantial amount of Dechenella species has been
described from latest Eifelian to Givetian strata in
the Rhenish Slate Mountains (see, e.g., STRUVE,
1992; BASSE, 2002). At least two Dechenella species
occur in the upper Eifelian to lower Givetian of
the Resteigne quarry. The inadequately preserved
pygidium that is illustrated here reveals little about
the morphology of this species and it is unfeasible
to compare it with the broad variety of species from
Germany. New collections of this comparatively
rare genus at Resteigne will be required to properly
describe it.
Subfamily Cornuproetinae RICHTER, RICHTER &
STRUVE in MOORE, 1959
Genus Cornuproetus RICHTER & RICHTER, 1919
Type species: Gerastos cornutus GOLDFUSS, 1843,
from the Ahrdorf Formation (Eifelian) of the Eifel,
Germany.
Cornuproetus cornutus (GOLDFUSS, 1843)
Assigned taxa
Five subspecies are included in this species, namely
cornutus cornutus (middle Eifelian, Eifel, Ardennes);
cornutus pruemensis BASSE, 2002 (upper Eifelian,
Eifel); cornutus n. ssp. A of BASSE, 1997 (lower
Eifelian, Sauerland); ssp. cf. cornutus pruemensis of
BASSE, 2002 (middle Eifelian, Eifel); n. ssp. 1 herein
(upper Eifelian or lower Givetian, Ardennes).
Cornuproetus cornutus n. ssp. 1
Pl. 2, Figs 1, 3, 4
Material
One librigena (IRSNB a12447), one incomplete
pygidium (IRSNB a12448), from locality Loc021,
Couvin, Hanonet Formation.
Description
Librigena. Lateral border somewhat dorsally attened;
adaxially more vaulted than abaxially; anteriorly
broader than posteriorly. In dorsal view, four border-
parallel terrace ridges are visible anteriorly on lateral
border which backwards disappear one by one,
starting with the innermost ridge and abaxially; only
the outermost ridge is extended posteriorly on the
genal spine. Fine, short, asymmetric terrace ridges are
present on lateral border where border-parallel ridges
are absent, posterior border, genal spine and genal
eld. Posterior border as broad (exsag.) as anterior
part of lateral border; bearing several granules. Genal
eld with coarse granules concentrated medially on
21
Trilobites from the Hanonet Formation, Belgium
posterior half and several additional granules anterior
to these. Posterior border furrow medially (tr.)
somewhat broader (exsag.) and indenting librigenal
eld here. Adaxial half of genal spine bearing a single
terrace ridge similar to, but slightly ner than those on
lateral border.
Pygidial axis is comprised of four axial rings plus
terminal axial piece, each of which remains of equal
width (sag., exsag.) throughout their length (tr.).
Second inter-ring furrow (counting from anteriorly)
is broadest (sag., exsag.). Prosopon on axial rings
consists of short terrace ridges on anterior half with
medially (tr.) several granules; posterior half bears
a transversal row of small tubercles. Terminal axial
piece anteriorly demarcated by a transversal row of
short transversal terrace ridges that laterally almost
touch one another so that they verge to forming an
uninterrupted ridge. Terminal axial piece covered
with closely spaced granules. Three weakly curved
pleurae are discernible on the pleural eld that are
covered with faint terrace ridges; several randomly
scattered granules are present on anterior two pleurae.
Border medially much broader (exsag., sag.) than
distally (tr.); its ornament consists of granules and
short terrace ridges. Pygidial margin with one or two
border-parallel terrace ridges visible dorsally.
Comparison
Morphologically closest to Cornuproetus cornutus n.
ssp. 1 is coeval Cornuproetus cornutus pruemensis
from the Eifel. Among shared features is the
proximally broad and distally narrow pygidial border.
The German subspecies is clearly different in having
the rst pygidial inter-ring furrow broadest (sag.,
exsag.) and a posteriorly more strongly tapered (tr.)
pygidial axis. BASSE (2002) did not give a detailed
description with his subspecies and his illustrations
are of inadequate quality to discern details of
prosopon. This impedes further comparison of both
subspecies at this time.
Well-preserved topotypical material of the
nominal subspecies has been described and illustrated
by previous workers (e.g. RICHTER & RICHTER,
1956; LÜTKE, 1990; BASSE, 1997, 2002) which is
principally different from the subspecies from Couvin
in having predominantly nely granulose librigenal
and pygidial prosopon rather than the richer mixture
of terrace ridges and granules in the latter.
Cornuproetus cornutus n. ssp. 1 shows some
resemblance to Diademaproetus rhenanus BASSE,
2002 regarding its dorsal prosopon. Recently,
CHATTERTON et al. (2006) emended the diagnosis
of Diademaproetus on the basis of well-preserved
specimens from Germany and Morocco. None of
the characters that were listed by the latter authors
are exhibited by Diademaproetus rhenanus and
the species is probably more suitably placed in
Cornuproetus.
Acknowledgements
S. Goolaerts (Geo-Instituut, Universiteit Leuven) has donated
trilobite material. D. Holland (Ilsede) has prepared some of the
specimens. P. Budil (Czech Geological Survey) and S.M. Gon
III (The Nature Conservancy of Hawaii) have reviewed the
manuscript. G. Cremers (Venlo) and R. Leunissen (Wollersheim)
have donated additional phacopid trilobite material from the
Eifel for comparison. E. Defour (Heusden-Zolder) has created a
silicone cast of an external mould. A. Schulp (Natuurhistorisch
Museum Maastricht) and H. Prescher (Kerpen) have helped with
preparations to whiten the illustrated specimens. I am greatly
indebted to these persons for their help.
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R.L., ed. Treatise on invertebrate paleontology, Part O,
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Order Agnostida, Order Redlichiida. Geological Society of
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Allart P. VAN VIERSEN
Graaf van Loonstraat 25
NL-6121 JS Born
The Netherlands
E-mail: apvanviersen@hotmail.com
Typescript submitted: April 1, 2007
Revised typescript received: April 27, 2007
25
Trilobites from the Hanonet Formation, Belgium
Fig. 1
Fig. 2
Figs 3-4
Figs 5-7
Figs 1-2
Fig. 3
Figs 4-5
Fig. 6
Figs 7-9
Fig. 10
Fig. 11
Fig. 12
Figs 1-4
Figs 5-6
Figs 7-9
PLATE 2
Cornuproetus cornutus n. ssp. 1; incomplete pygidium (IRSNB a12448); Couvin Loc021; Hanonet
Fm.; dorsal view, x 18.
Calycoscutellum goolaertsi n. sp.; partially exfoliated cranidium (IRSNB a12439); Resteigne
Loc002; Hanonet Fm.; ventral view (inversed photograph), x 4.
Cornuproetus cornutus n. ssp. 1; librigena. (IRSNB a12447); Couvin Loc021; Hanonet Fm.; 3:
dorsal view, x 16; 2: oblique frontal view, x 11.
Calycoscutellum goolaertsi n. sp.; Resteigne Loc002; Hanonet Fm.; 5: Holotype, pygidium
(IRSNB a12436); dorsal view, x 4; 6: Mostly exfoliated pygidium with abnormal right lateral to
posterolateral outline (IRSNB a12437); dorsal view, x 3; 7: pygidium (IRSNB a12438); dorsal
view x 4.
PLATE 3
Gerastos cf. prox (RICHTER & RICHTER, 1956); pygidium (IRSNB a21444); Resteigne Loc002;
Hanonet Fm.; 1: dorsal view, x 12; 2: lateral view, x 12.
Calycoscutellum goolaertsi n. sp.; incomplete librigena (IRSNB 12440); Resteigne Loc002;
Hanonet Fm.; dorsal view, x 4.
Gerastos cf. prox (RICHTER & RICHTER, 1956); incomplete pygidium (IRSNB a12445); Resteigne
Loc002; Hanonet Fm.; 4: dorsal view, x 9; 5: oblique lateral view, x 11.
Calycoscutellum cf. goolaertsi n. sp.; partial pygidium (IRSNB a12441); Couvin Loc021;
Hanonet Fm.; dorsal view, x 3.
Gerastos cf. prox (RICHTER & RICHTER, 1956); cranidium (IRSNB a12442); Resteigne Loc002;
Hanonet Fm.; 7: lateral view, x 8; 8: dorsal view, x 8; 9: frontal view, x 8.
Dohmiella sp. 2 of VAN VIERSEN, 2006b; librigena with postdepositionally crushed eye (SMF
58587); Resteigne Loc002; Hanonet Fm.: Lateral view, x 7.
Gerastos cf. prox (RICHTER & RICHTER, 1956); small incomplete cranidium (IRSNB a12443);
Resteigne Loc002; Hanonet Fm.; dorsal view, x 14.
Dechenella sp.; incomplete pygidium (IRSNB a12446); Resteigne Loc002; Hanonet Fm.; dorsal
view, x 7.
Explanation of the plates
PLATE 1
Nyterops hollandi n. sp.; holotype cephalon (IRSNB a12430); Resteigne Loc002; Hanonet Fm.;
1: dorsal view, x 5; 2: oblique lateral view, x 7; 3: lateral view, x 7; 4: frontal view, x 5.
Nyterops hollandi n. sp.; Resteigne Loc002; Hanonet Fm.; 5: cephalon (IRSNB a12431), frontal
view, x 3.
Hypsipariops? sp.; cephalon (IRSNB a12435); 7: frontal view, x 2; lateral view, x 2; 9: dorsal
view x 2.
26
Allart P. VAN VIERSEN
PLATE 1
27
Trilobites from the Hanonet Formation, Belgium
PLATE 2
28
Allart P. VAN VIERSEN
PLATE 3
29
Trilobites from the Hanonet Formation, Belgium
... Rest-G1 and Jemelle ( van Viersen 2007b). The Mixed association does not appear to be restricted to a specific member of the Jemelle Formation. ...
... Nevertheless, the Treignes sample is well integrated in the Mixed association described in the HCA (Fig. 3) and DCA (Fig. 4). Moreover, the occurrence of Geesops, a genus characteristic of the Eifelian faunas ( van Viersen 2007b), strengthens the assumption that this sample comes from the lower part of the Hanonet formation before or during the Kačák event (House 1985). The remaining samples (Cou-G1, Rest-G1, and Roch-G1) are included in the Scutellum-Goldius association in the HCA. ...
... Moreover, the diversity indexes for these communities (Fig. 5) are high and similar to the Mixed association values. The trilobites from Resteigne were sampled in the lower part of the Hanonet Formation ( van Viersen 2007b) before the Kačák interval end. We may reasonably assume that the samples of Couvin and Rochefort come from similar layers before the substitution of the Eifelian fauna by the Givetian one. ...
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... Most of the material consists of internal moulds of cephala and pygidia of a representative of the subfamily Phacopinae Hawle and Corda, 1847. Phacopine taxonomy is based also on the sculpture of the dorsal exoskeleton of the cephalon; since the latter is rather thick in most species, internal moulds differ strongly from the calcified exoskeleton and thus comparison of the present material with taxa described on the basis of better preserved specimens from the Late Eifelian to Early Givetian beds of the Rhenohercynian Zone (Belgian Ardennes; German Eifel Synclines and western Sauerland region; e.g., van Viersen, 2007;Basse, 1998Basse, , 2006, is unfeasible. The remaining features are in good agreement with the "forme grande" [sensu Kielan, 1954; Fig. 18D, E, H-Q; an undescribed new species different from the name-bearing "forme petite" of Phacops schlotheimi skalensis Kielan, 1954 = Nyterops skalensis (Kielan, 1954)]. ...
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This is the third part of a tripartite survey on Devonian trilobites of the Rhenohercynian. Paleontology Region of the Oberbergische Land/Sauerland (shelf): 18 taxa (as mentioned above) are introduced as new ones. Till now, Kayserops has not been recorded later than in Emsian. In the northwestern Rhenish Mts last steps of development in this group can be identified in upper Eifelian. In early Givetian this species group is "replaced" by the similar Rheicops grevensteinensis g. & sp.n. which is characterized by some features reminding of "Comura". Almost synchronously and in a comparable mode development in late "Comura" species takes place, resulting in organisms called Gudralisium g.n., which are hardly to distinguish from Rheicops. Postlarval ontogenesis in two "populations" of Eifliarges is characterized by individualisation of segments in the pleural fields of the PYG. These two "populations" are similar to each other in the mode of this development, but they differ in its result, i.e. in the maximum number of individualized ribs and spines. Charybdaspis comes g. & sp.n., type species of this genus is morphologically closely related to Radiaspis radiata, type species of Radiaspis. But they clearly differ from each other in features of the THO: In comes the paired lateral spines of pleura 1-7 might have a common base in the convexe median pleural band, respectively. In radiata the anterior spine originates in the anterior pleural band, whereas the posterior spine comes from the median band. Both taxa have a similar and unique arrangement of the spines of pleura 8 and 9, which differs strongly from pleura 1-7. Kellerwald area ("trough"): Well preserved taxa (as mentioned above) are present. - Generally, Givetian odontopleurines are rare. Such a taxon is genus (?novum) ex Koneprusiinae sp.n. W, characterized by 3 + 1 individualized rings in the pygidial rhachis. Harz Mts (shelf): Upper Emsian taxa of Phacops, Acastellina, Treveropyge, Comura, and Malladaia are discussed. - The pygidial border of tiny holaspids in a "population" of Acastellina errabunda sp.n. is incised. In the course of the postlarval ontogenesis an almost entire margin occurs. - Malladaia festenburgensis sp.n. is the first finding of this genus in Germany. Lahn-Dill region ("trough"): Upper Emsian trilobites (as mentioned above) may resemble taxa of the same age or slightly younger from the Eifel hills and the eastern Sauerland. - A species of the "blind" phacopine Illaenula is reconstructed. Eifel area (shelf): Taxa from Wiltz, Heisdorf, Lauch, and Freilingen strata (late Upper Emsian, early Eifelian, and early Givetian) are discussed briefly to enlight similarities and differences with the situation east of the river Rhine. Stratigraphy Oberbergisches Land/Sauerland: In the eastern Sauerland the position of the p-b (partitus boundary) seems to be lower situated than assumed. - Of stratigraphic importance in the western Sauerland should be the chronology of some Asteropyginae close to the otomari Event. Here a lithologic change takes place, accompanied by the onset of the new Rheicops and Gudralisium, which are frequent and easy to identify. Harz Mts/STP: A clear change in trilobite faunas reminds strongly of such taking place close to the p-b in its stratotype (Eifel area), but also of one happening in late Upper Emsian of the eastern Sauerland and the Dill region. Occurrence of Paralejurus intumescens in the Calceola shales and lack of typic Eifelian taxa might vote for an Emsian age of these shales, which formerly were regarded as early Eifelian. Faunal structure and geographic distribution Region of the Oberbergisches Land/Sauerland: Between Upper Emsian and Givetian different faunas are living on the shelf, each of them clearly differentiated., e.g. in hemipelagic and neritic ones. The frontier approx. between the western and the eastern Sauerland stands for such a break. Its pattern seems to be very constant for long periods of time. Widely distributed taxa occur especially in early Eifelian of the eastern Sauerland. - Upper Emsian trilobites are rare in the north-western Sauerland, but they are numerous in the eastern Sauerland and in the Rothaargebirge. Here close to the p-b the number of taxa decreases slightly to clearly. In the early Eifelian of the Rothaargebirge (transition shelf/"trough") trilobites are largely lacking, but in the eastern Sauerland and for the first time since Lochkovian in the western they are common. The north-western frontier of their distribution is now shifted clearly to north-west to the north-western Sauerland. Here is remains during Eifelian. In early Givetian this frontier is moving a little bit to the north-west. Synchronously, in the eastern Sauerland the number of taxa is strongly decreasing. Faunas of Upper Emsian age of the east Sauerland consist mainly of Phacopida, sometimes accompanied by Paralejurus, cornuproetids, lichids. Similar structures are known from the Lahn-Dill region and the Eifel area. Close to the p-b Cyphaspides and chotecopids occur, reminding of synchronous taxa of the Lahn region; initially, the geographic distribution of this new fauna in the Sauerland is restricted. Parallel existing Asteropyginae faunas seem to originate in Upper Emsian and they are replaced by e.g. Thysanopeltis, cornuproetids, and now more widespread Cyphaspides and chotecopids not before early Eifelian. The start of the early Eifelian in the western Sauerland/Bergisches Land seems to be characterized by few late Upper Emsian taxa coming from e.g. the Lahn-Dill region. In contrast to this the relations to the Eifel area are much clearer - as it can be stated for the whole Eifelian. In the elder Eifelian, fauna and lithofacies of shelf deposits (neritic to hemipelagic facies) in the eastern Sauerland contrast sharply with those of the west (neritic facies): in the Oberbergisches Land up to the east border of the western Sauerland, neritic fauna (scutelluids, proetids, large-eyed Phacopinae, Asteropyginae) with clear affinities to faunules of the Ardenno-Eifelian region (western Rhenohercynian) is dominating. Such neritic taxa are unknown in synchronously developed nearby "pelagic" deposits (Lahn-Dill, Kellerwald) (but possible forerunners occur here in assumed late Upper Emsian). In contrast to this, the faunules of the eastern Sauerland can clearly be influenced seemingly by pelagic faunas, reminding of synchronous taxa of the Kellerwald or of the Lahn-Dill region. Typical are thysanopeltids, certain cornuproetids, cyphaspidids, and chotecopoid phacopines, which seem to be absent or which are extremely rare west of the eastern Sauerland. But in some parts of the eastern Sauerland, neritic taxa of Upper Emsian age and western or southern provenience exist for a short period of time parallel to the mentioned pelagic organisms. In the course of the Eifelian in the western Sauerland remarquable changes in faunal structure take place frequently; they are mainly characterized by entrance of new taxa, e.g. dechenellids, but "never" by taxa coming from the eastern Sauerland. A clear alternation can be stated "shortly" after the otomari Event: now a reduced fauna lives in the west, mainly consisting of Proetidae, Phacopidae, Asteropyginae. There is no hint about clear influences from other regions. In the eastern Sauerland the "lack" of trilobites in post-event sediments indicates a much more drastic change. Trilobites of middle Givetian limestones from the transition shelf/"trough" of the eastern Sauerland remind weakly of species known from probably synchronously developed pelagic submarine rises of the Kellerwald region. Species related to those of back-reef deposits (Massenkalk, middle Givetian) have been identified in the Lahn-Dill region. A general lack of data about Givetian trilobites makes it difficult to judge about worldwide relations of faunas, but it looks like that there are close faunistic connections between English limestones and Rhenish Massenkalk. Kellerwald area: Re known species of late Emsian and early to middle Eifelian there should be close relations to taxa of the Lahn-Dill region. The Odershausen fm (± Eifelian/Givetian boundary) of Wildungen has yielded five species; one might occur in deposits of the western Sauerland, too. From Givetian cephalopod limestones of the Diemelsee area (Martenberg), from reef complexes of the Harz Mts, and from limestones of the Lahn-Dill region some organisms are known comparable with taxa of the Cheirurus limestone. These middle Givetian faunas of Wildungen remind of pelagic taxa of Eifelian age from the same area. In early Upper Devonian some organisms appear, which can be identified in Harz Mts and in the Lahn-Dill region, too. With this fauna of Wildungen, the lack of knowledge in the geographic distribution of certain trilobite associations of the pelagic facies is reduced. Harz Mts/STP: Two different faunas can be distinguished in late Upper Emsian: preferably neritic taxa in the speciosus beds, mainly seemingly pelagic ones in the overlaying Calceola shales. On generic level there are clear parallels to trilobites occuring in the Rhenish Mts, but most of the species differ evidently from the Rhenish ones. Moreover, comparable findings are made in some neritic influenced synchronously deposited sediments of Poland.