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Latest Emsian (Early Devonian) sediments at the famous mud−mound− and trilobite−locality Hamar Laghdad (Tafilalt, Morocco) yielded some red−coloured remains of phacopid trilobites. Closer examination revealed that the eyes of these phacopids are often greenish in colour. EDX−analyses showed that the lenses retained their original calcitic composition, possibly greenish due to Fe−impurities, while most of the exoskeleton was silicified. The silicified parts contain elevated concentrations of iron which causes the red colour. This phenomenon is explained by the porosity of the exoskeleton in contrast to the homogeneous and massive construction of the lenses and their Mg−content. These incompletely silicified trilobites enabled a reconstruction of the silicification process in trilobites. Their diagenetic alteration probably occurred as a result of events associated with the Cretaceous transgression.
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Red Devonian trilobites with green eyes from Morocco
and the silicification of the trilobite exoskeleton
Klug, C., Schulz, H., and De Baets, K. 2009. Red Devonian trilobites with green eyes from Morocco and the silicification
of the trilobite exoskeleton. Acta Palaeontologica Polonica 54 (1): 117–123.
Latest Emsian (Early Devonian) sediments at the famous mud−mound− and trilobite−locality Hamar Laghdad (Tafilalt,
Morocco) yielded some red−coloured remains of phacopid trilobites. Closer examination revealed that the eyes of these
phacopids are often greenish in colour. EDX−analyses showed that the lenses retained their original calcitic composition,
possibly greenish due to Fe− and Mn−impurities, while most of the exoskeleton was silicified. The silicified parts contain
elevated concentrations of iron which causes the red colour. This phenomenon is explained by the porosity of the
exoskeleton in contrast to the homogeneous and massive construction of the lenses and their Mg−content. These incom
pletely silicified trilobites enabled a reconstruction of the silicification process in trilobites. Their diagenetic alteration
probably occurred as a result of events associated with the Cretaceous transgression.
Key words: Trilobita, taphonomy, diagenesis, silicification, transgression, mud−mounds, Devonian, Morocco.
Christian Klug [], Kenneth DeBaets [], Paläontologisches Institut und
Museum der Universität Zürich, Karl Schmid−Str. 4, CH−8006 Zürich, Switzerland;
Hartmut Schulz [hartmut.schulz@uni−], Institut für Geowissenschaften, Eberhard−Karls−Universität Tübingen,
Sigwartstr. 10, D−72076 Tübingen, Germany.
Trilobite eyes always attracted the attention of palaeonto−
logists and biologists, partially because of their often large
size compared to body size but also because of the sheer fact
that such a sense organ can be preserved in such detail: Even
the quality and optical properties of its lenses could be exam
ined (Clarkson and Levi−Setti 1975; Bruton and Haas 2003
and references therein; Fortey and Chatterton 2003). Espe
cially phacopid eyes were often discussed in numerous arti
cles, partially because of the abundance of this trilobite group
and partially because of the large size of the eyes and their
lenses, respectively, of some members of the Phacopidae
(Bruton and Haas 2003 and references therein).
Because of its usually strongly mineralised cuticle, it is
often well preserved and thus, the ultrastructure of the trilo
bite cuticle could be studied in detail in various groups (e.g.,
Teigler and Towe 1975; McAllister and Brand 1989; Daling
water et al. 1991, 1993, 1999). As we show in thisarticle, the
physical properties required for optical functionality of the
eyes and their Mg−content (Lee et al. 2007) influenced the
diagenesis of this part of the trilobite exoskeleton. We exam
ined a number of well−preserved phacopid trilobites from
Hamar Laghdad (Tafilalt, eastern Anti−Atlas, Morocco) be
cause of their peculiar preservation. At this locality, we
found several enrolled specimens of Barrandeops cf. granu
lops (Chatterton, Fortey, Brett, Gibb, and McKellar, 2006)
(e.g., PIMUZ 27077), a species formerly described from the
DraValley (Chatterton et al. 2006). In these specimens, the
exoskeleton is red except for the lenses which are green. Im−
ages of one of these extraordinary fossils (PIMUZ 27077)
were used for the cover of the April 2008−edition of the Jour−
nal “Geology”, but without an accompanying article. In this
article we want to (1) show why the eyes of these trilobites
are green and (2) discuss how this phenomenon can be ex−
Institutional abbreviation.—PIMUZ, Paläontologisches Insti
tut und Museum, Zürich University, Switzerland (PIMUZ
27075–27077, 27080–27083).
Material and geological setting
The recently discovered, seemingly perfectly preserved pha
copid trilobites were eroded from marls from close to the
Emsian/Eifelian boundary from the Moroccan locality Hamar
The specimens of Barrandeops cf. granulops included in
this study were discovered in a rich benthic fauna of latest
Emsian age (391.9 ± 3.4 Ma; Kaufmann 2006) at the “red
cliff” (Klug 2002) at Hamar Laghdad (Fig. 1). This Moroccan
locality (18 km east−southeast of Erfoud; N 31°22’37'' W
4°03’28”) gained fame for its perfectly exposed mud−mounds
(e.g., Roch 1934; Massa et al. 1965; Hollard 1974; Alberti
1982; Brachert et al. 1992; Wendt 1993; Belka 1994, 1998;
Bultynck and Walliser 2000; Aitken et al. 2006; Cavalazzi et
al. 2007). In addition to this impressive occurrence of carbon−117.pdf
Acta Palaeontol. Pol. 54 (1): 117–123, 2009
ate build−ups, Hamar Laghdad is well−known for its rich inver
tebrate faunas. Especially cephalopods (Töneböhn 1991; Klug
2002; Klug et al. 2008) and arthropods (e.g., Alberti 1969,
1980, 1982) have been described from the Early and Middle
Devonian strata of this locality. Late Emsian biostratigraphy at
Hamar Laghdad can be summarised as follows: The upper
most layer of most mud−mounds yielded Mimagoniatites
fecundus (Barrande, 1865), the index of the basal Dalejan
(Late Emsian). According to Klug (2002: 10), the “marls and
claystones above contain a diverse fauna (Alberti 1980) with
ammonoids including Gyroceratites cf. gracilis (Barrande,
1865), Latanarcestes latisellatus Erben, 1953, and L. noe
ggerathi (von Buch, 1832)”. At the top of the Emsian succes
sion at Hamar Laghdad, a rich benthonic assemblage occurs. It
contains bivalves, inarticulate and articulate brachiopods, var
ious rugose and tabulate corals, crinoids, cystoids (Eucystis),
gastropods, hyolithids, rare rostroconchs, well−preserved trilo
bites (corynexochids, harpetids, lichids, phacopids, proetids)
and goniatites. Among the latter, Anarcestes cf. latissimus
Chlupáč and Turek, 1983, Chlupacites praeceps (Chlupáč and
Turek, 1983), and Amoenophyllites doeringi Klug, 2002 were
identified. The nodular limestones above contain numerous
specimens of Foordites veniens Chlupáč and Turek, 1983.
This layer represents the base of the section published by Klug
(2002: fig. 10).
In order to learn more about the origin of this coloration, we
examined the chemical composition of the red trilobites from
Hamar Laghdad. For this purpose, we produced thin−sections
(PIMUZ 27075, 27081; Fig. 2D–H). These thin−sections and
an isolated phacopid cephalon (PIMUZ 27076) were sub−
jected to a series of elemental micro analyses using a scan−
ning electron microscope SEM LEO 1450 VP at the Institut
für Geowissenschaften Tübingen (Fig. 3). Operating para−
meters were 17 kV with a working distance of 29 mm. The
chemical composition of sample points was measured using
an energy−dispersive X−ray analyser EDX (Oxford Instru
ments INCA EDS 200). Measuring time was 90 seconds.
These examinations clearly showed that the cuticle of the
isolated cephalon (PIMUZ 27076) is silicified except for the
lenses, which retained their calcitic composition (Fig. 3; 45.3
paved roads
dirt roads
20 km
Erg Chebbi
T a f i l a l t
Hamada du Guir
High Atlas
Middle Atlas
Atlantic Ocean
100 km
Middle Atlas
Hamar Laghdad
Fig. 1. Geologic map of Morocco and the Tafilalt (eastern Anti−Atlas),
showing the position of the “red cliff” at Hamar Laghdad (modified after
Klug 2007).
Fig. 2. Phacopid trilobite Barrandeops cf. granulops (Chatterton, Fortey, Brett, Gibb, and McKellar, 2006), Early Devonian (Emsian/ Eifelian boundary),
Hamar Laghdad (Tafilalt, eastern Anti−Atlas, Morocco). A. PIMUZ 27077, the cephalon is 10.2 mm across. A1, anterior view showing the red exoskeleton
and the green lenses; A2, lateral view; A3, dorsal view of the cephalon; note the well preserved ornamentation; A4, detail of A2to show the slightly corroded
surface of the lenses and the partially still calcitic, partially silicified intralensar sclera. B. PIMUZ 27082, the cephalon is 9.9 mm across and 7 mmin length.
B1, detail of B2showing the calcitic lenses with the silicified intralensar sclera (the eye is 3.1 mm long); B2, lateral view of the entire specimen. C. PIMUZ
27083, broken fragments of the exoskeleton of a cephalon (length of largest fragment 6.3 mm). C1, mesial view from oblique below showing the interior of
the eye and the green lenses with the red interlensar sclera; C2, same specimen, different fragment (4.5 mm long), view of the fracture surface; C3, detail of
C1, showing the fracture surface of two recrystallised but still calcitic lenses. D,E,G,H. Details of a thin section through specimen PIMUZ 27081 (width
19.3 mm). D. Detail of the eye and adjacent librigena. D1, image taken under incident light, both the bend in the growth lines of the intralensar sclera and the
surface of the librigena are silicified (red) while the rest is still calcitic (greenish); D2, same detail as in D1under transmitted light. E. Detail of the
exoskeleton under transmitted light. Note the manganese and iron minerals which filled the pore canals from the inside of the trilobite (width 1.6 mm).
G. Details of the pleura (width of detail 6.6 mm) showing beginning silicification. G1, transmitted light, silicified parts brownish; G2, incident light, silici
fied parts redish; silicification begins at the outer surface. H. Detail of the rhachis (width 1.9 mm). H1, transmitted light, silicified parts brownish forming
pouches; manganese and iron minerals deposits on the internal parts of the pore canals; H2, incident light, silicified parts redish. Silicification begins at the
outer surface and along the pore canals. F. Details of a thin section through the cephalon of specimen PIMUZ 27075 (width 25.4 mm, length 13.9 mm).
F1, detail of F2to show the red colour of the bends in the growth lines of the intralensar sclera and the green lenses; the lens on the left shows horizontal frac
tures, indicating recrystallisation of this lens; F2, the complete eye under incident light. Note the greenish colour of the lenses and the red colour of the bends
in the growth lines of the intralensar sclera. Most of the exoskeleton is red (silicified). F3, like F2, but under transmitted light.
wt. % calcium, 54.0 wt. % oxygen). On the glabella of the
measured specimen, five analyses rather uniformly revealed
the presence of approximately 1.9 wt. % iron (which explains
the red color), 1.0 wt. % calcium, 2.0 wt. % aluminum and
0.7 wt. % potassium (Fig. 3).
Not all specimens from this locality are preserved identi−
cally. The degree of silicification and iron−staining is highly
variable. This is reflected in exoskeleton colours ranging
from greenish−yellowish (when still more or less calcitic) to
red (when silicified). One enrolled specimen which was
thin−sectioned (PIMUZ 27081) retained much of its original
calcitic mineralogy with a clear predominance of calcium
and oxygen, reflected in its more greenish to yellowish col
our. The element of iron was detected by the EDX in traces
only and in some places not at all. Hassan (1978) analysed
the composition of a greenish calcite from Egypt and found
impurities of manganese and iron [“Mn(IV) and Fe(II)”].
Based on these findings, he concluded that the calcite was
precipitated “in an environment that was more acidic and
with a very low oxidation potential” (Hassan 1978: 732).
The EDX−analyses in specimens PIMUZ 27075 and
27076 clearly showed that all red parts of the exoskeleton are
silicified while the yellowish to greenish parts such as the
lenses retained the calcitic composition with low contents of
iron and magnesium. The examinations of the thin−sectioned
cephalons revealed that the replacement of calcite by silica
commenced at the outer surface (Fig. 2G, H) of the sclerites
and following pore canals (Fig. 2E, H) as well as the bend in
the growth lines of the intralensar sclera (Fig. 2D, F; cf.
Bruton and Haas 2003). More or less simultaneously, man
ganese and iron minerals were deposited from the ventral
side (i.e., from within the enrolled trilobite) in the pore canals
(Fig. 2E, H). The sediment matrix visible in the thin−sections
(Fig. 2D–H) is partially silicified (red areas) and partially
carbonatic (light coloured under incident light). The lenses
locally are well preserved with the primary small crystal size
while adjacent lenses can be already recrystallised, forming a
single or few crystals (Fig. 2C, D, F).
Remarks on the local diagenesis
We found evidence for two diagenetic processes which have
occurred directly next to each other at the “red cliff” (Hamar
Dolomitisation.—A thin section of red−coloured Late Eife
lian limestones from the top of the “red cliff” is composed of
relatively large, unmistakable dolomite crystals (< 2 mm). The
Late Eifelian rocks contain also dolomitised fossils such as
various cephalopods. Dolomitisation occurs abundantly in the
carbonates of the Anti−Atlas which characteristically have a
reddish colour due to iron compounds (compare Kaufmann
1997, 1998). At Hamar Laghdad, this reddish facies is largely
restricted to the more elevated parts of the Hamar Laghdad
ridge (Fig. 4).
Silicification.—The mineralogy of both the trilobite exo
skeletons and their sediment matrix indicate a local and par
tial silicification. Silicified trilobites occur (usually in associ
ation with silicified ostracods) also in other localities of the
Anti−Atlas such as in the Taouz− and Ouidane Chebbi regions
in roughly the same stratigraphic position. As far as we
know, Hamar Laghdad is the only locality where the silici
fied trilobite exoskeletons carry the red colour.
Fig. 3. SEM−SE image of cephalon PIMUZ 27076 and results of the element analyses (“EDX−spektrum X”). A. SEM−SE image of the eye and result of the
element analysis of a lense (“EDX−spektrum 1”). Note the absence of iron and silica. B. SEM−SE image of the glabella and result of the element analysis
(“EDX−spektrum 9”). Iron and silica are present. C. Analysis performed in the intralensar area (“EDX−spektrum 2”) of the glabella(see A). Iron and silica
are present.
In the Tafilalt, dolomitised rocks are often reddish in col−
our, certainly due to their iron compounds−content. These
dolomites occur mainly in two situations: near faults (Bernd
Kaufmann, personal communication 2008; Graz and Kauf−
mann 1997) and close to the erosional surface at the base of
the Cretaceous transgression. To our knowledge, these dia−
genetic phenomena have not been examined in detail in the
study area yet and thus, a full sedimentological interpretation
of these diagenetic processes is not available yet.
At Hamar Laghdad, the red facies is at least partially re
lated to the erosional processes prior and during the Creta
ceous transgression because it occurs predominantly in ele
vated parts of the Hamar Laghdad−ridge, i.e., close to the ero
sional surfaces, and it occurs also in other parts of the Tafilalt
where the Devonian sediments reach close to the Cretaceous
transgression surface (e.g., Ouidane Chebbi, Achguig). At the
red cliff, some red−coloured erosional remnants of the Creta
ceous transgression conglomerate containing coarse silici
clastics are preserved. We suggest, tentatively, that at least the
dolomitisation but potentially also the silicification at the “red
cliff” were caused by the penetration of silicium−, aluminium−
and iron−bearing fluids after the uplift, during the later erosion
of the Devonian sediments and during the Cretaceous trans
gression. The silicification is not surprising since the Creta
ceous transgressive sediments contain sandstones, conglomer
ates (both with siliceous components and sometimes with a si
licified matrix) and thin chert−layers. The locally limited oc
currence of this preservation is not surprising since the Late
Emsian to earliest Eifelian marls are less resistant towards ero
sion than, e.g., the massive mud−mound−limestones and thus,
sediments of this stratigraphic intervals which were altered by
transgression−related diagenetic phenomena are rare.
We also considered that the silica might have originated
from the local hydrothermal activity (cf. Belka 1998; Aitken
et al. 2002). This appears unlikely, however, because this
phenomenon does not occur everywhere in Hamar Laghdad
but only on the red cliff while hydrothermal activities proba
bly occurred in the entire Hamar Laghdad region.
Trilobite exoskeleton diagenesis
The above described patterns of the selective and partial sili
cification of the trilobite exoskeleton were probably caused
by differences in porosity (pore canals in most of the exo
skeleton in contrast to the homogeneous lenses) and compo
sition (primary magnesium content of the lenses; see Lee et
al. 2007). For the silicification of the trilobites, the following
sequence of events is evident from the thin−sectioned speci
(1) Silicification began at the outer surface of the exo
skeleton as well as in pore canals and along the bend of growth
lines within the intralensar sclera.
(2) The exoskeleton became fully silicified including the
intralensar sclera while the lenses stayed calcitic but may
have become recrystallised.
(3) Ultimately, the lenses became silicified, too.−117.pdf
Hamar Laghdad ridge
red cliff
erosional relics
of the Cretaceous
Fig. 4. Map of Hamar Laghdad showing the mud−mounds, the distribution of the red facies, the position of the red cliff, erosional remnants of the Cretaceous
transgression conglomerate and the distribution of outcrops of Middle Devonian sediments (map based on satellite images, the topographic map sheet
“Erfoud, feuille NH−30−XX−2, Carte du Maroc 1/100000”, and Berkowski 2006: fig. 1).
Phacopid trilobites from the latest Emsian of Hamar Laghdad,
Morocco are silicified to varying degrees. This fact allows a
reconstruction of details of the silicification process. Silicifica
tion started at the outer surface of the exoskeleton as well as in
pore canals and along the bend of growth lines within the
intralensar sclera. From these silicification centres, this pro
cess continued until only the lenses remained calcitic. Addi
tional to the homogeneity of the calcite crystals of the lenses,
needed for their optimal optical functionality, and their higher
magnesium−content (Lee et al. 2007), the absence of pore−ca
nals in the lenses accounts for the fact that the eyes retained the
greenish calcite (this colour is also encountered in various
other invertebrate fossils from the red cliff as well as brachio
pod shells such as the thick−shelled Middle Devonian Devono
gypa and Ivdelinia from the Maïder Basin; Kaufmann 1998)
while the rest of the trilobite exoskeleton is silicified and red
because of a sufficiently high content of iron compounds. The
greenish colour of the lenses might have been caused by man
ganese and iron−impurities which could not be detected with
certainty with the EDX because the content was too low. This
differential replacement also explains why the lenses are
slightly corroded while the rest of the exoskeleton is rather
well preserved. So far, this differential replacement of calcite
is only known from the eyes of phacopids. Other trilobite taxa
from the same strata have holochroal eyes and thus much
smaller lenses which were probably more rapidly replaced by
silica. The lenses of these holochroal eyes are preserved in the
red, iron−stained silica exactly like the exoskeletons. The sili−
cification probably happened in relation to the Cretaceous
transgression because (1) the silicification occurs at the only
one place at Hamar Laghdad, the red cliff, where the latest
Emsian marls reach close to the transgression surface (they are
more deeply eroded otherwise because of their higher clay
content and thus lower erosion−resistance), (2) the Cretceous
sediments display the same colour, (3) the Cretaceous sedi
ments are rich in silica (siliciclastic conglomerates and cherts),
(4) this phenomenon does not occur in other parts of Hamar
Laghdad in the same stratigraphic position, and (5) silicified
arthropods from other localities in the Anti−Atlas do not show
this coloration.
Future studies should continue by analysing the alteration
of sediments below the Cretaceous transgression and analy
ses of the green colour in brachiopods and trilobite eyes as
well as other fossils from the red cliff.
The field work in Morocco was kindly supported by the Swiss National
Science Foundation (project No. 200021−113956/1 to CK). We thank
Frowin Pirovino (Geologisches Institut, Eidgenössische Technische
Hochschule, Zürich, Switzerland) for the production of thin sections,
Mike Pirie as well as Laura Wilson for proof−reading and Thomas
Galfetti (all Zürich University, Switzerland) for the impetus to produce
this study. Raimund Feist (Université Montpellier 2, France) and an
anonymous reviewer helped much to improve the manuscript. Alan W.
Owen (University of Glasgow, UK) and Jarosław Stolarski (Institute of
Paleobiology, Polish Academy of Sciences, Warsaw, Poland) also dis
cussed the matter with us and gave some valuable information. Allart P.
Van Viersen (Born, Belgium) and Harald Prescher (Kerpen, Germany)
kindly shared their opinion on phacopid taxonomy with us.
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... Scanning electron microscopy in combination with energydispersive X-ray spectrometry (SEM-EDX) is one of the most powerful and versatile techniques that enables the determination of the inorganic chemical composition of different materials (e.g., metal, alloy, ceramic, etc.). During the last decades, SEM-EDX has proved useful to the study of the chemistry associated with different preservation modes of fossil remains (e.g., Kohn et al., 1999;Klug et al., 2009;Lin and Briggs, 2010;Benavente et al., 2014). ...
... Applications of semi-quantitative EDX analysis to the study of fossil materials have proven to be very reliable, providing reproducible results (e.g., Klug et al., 2009;Lin and Briggs, 2010;Previtera et al., 2013;Benavente et al., 2014). The absolute or standardless method used (as opposed to a relative method), does not need standards (e.g., Vázquez et al., 1988;1990;Barrea and Mainardi, 1998;D'Angelo et al., 2002) and the samples provide all the experimental information required, since well-known physical processes are involved. ...
... Differences in the chemical preservation of trilobite pygidia occurring in a single stratigraphic position (as it is the case in this study; thickness of the collection interval was approximately 20 cm) have been recorded (e.g., Klug et al., 2009), and this could be regarded as a general rule rather than an exception in the preservation of trilobite exoskeletons. ...
Selected pygidia of the middle Cambrian corynexochid trilobite Athabaskia anax (Walcott 1916) from the Miaolingian Series of San Isidro (Precordillera, Mendoza, Argentina) are analyzed for the first time using scanning electron microscopy in combination with energy-dispersive X-ray spectrometry (SEM-EDX). Pygidia occur in a single stratigraphic level composed of fine-grained calcareous sandstones and show four types of morphological preservations. The purpose this case study is threefold: (1) to analyze in detail the sample types by means of SEM-EDX in order to explore the chemical changes of the exoskeleton induced by diagenesis; (2) to use principal component analysis (PCA) to focus on groupings as a function of the chemical composition; and (3) to analyze the possible systematic implications of the chemical data. Results show that PCA supports the distinction among the four types of morphological preservations, based mainly on differences in the contents of Ca, Al, and K, as well as Si and Mg. This suggests that diagenesis followed distinct taphonomic pathways in the single stratigraphic level and resulted in contrasting chemical compositions of the four types of morphological preservations. It is interpreted that some morphological characteristics of the pygidia are the result of chemical and structural changes taking place during fossilization and do not represent real morphological differences in the living organisms. Our results dictate caution when using some morphological characteristics of the exoskeletons to erect new taxa, which, in turn, could be used to draw erroneous conclusions on their biostratigraphy, biogeography, and palaeoecology.
... Specimens of Cyphaspides were collected from three localities in southeastern Morocco: Talawarite, northeast of Erg Chebbi; a small section west of the village of Jorf (west of Erfoud); and the 'Red-Green' locality (located in the area of the Hamar Laghdad mud mound complex, see Fig. 1; Klug et al., 2009). The specimens are assigned to three new species of Cyphaspides. ...
... These descriptions are based mainly on articulated, complete carapaces. However, we have also obtained silicified sclerites of Chatterton et al.-Aulacopleurid trilobite Cyphaspides from Morocco this genus from the mined trilobite interval at Talawarite (complete adult carapaces that are the types of Cyphaspides ammari new species were collected from this bed) and from the locality that is known informally as the Red-Green bed at Hamar Laghdad (see Klug et al., 2009). Cyphaspides is a sufficiently distinct genus of aulacopleurid trilobite that it is classified in a subfamily with only one other similar, closely related genus, Protocyphaspides Přibyl and Vanek, 1977 and possibly the much younger Namuropyge. ...
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Three new species of Cyphaspides are proposed: C. ammari, C. nicoleae , and C. pankowskiorum . These species are based on specimens obtained from Middle Devonian (Eifelian) strata of the Bou Tchrafine Group, near Erfoud, in the Province of Errachidia, southeastern Morocco. The present contribution enhances our knowledge of Cyphaspides by providing details of three new species that are based on well-preserved, complete, and articulated types. The genus Cyphaspides is discussed, and an emended diagnosis is provided. The paleobiogeography, ontogeny, and relationships of the genus are discussed. UUID:
... The oldest ones are the studies undertaken in the framework of the geological mapping of this area, corresponding to 1/200 000 map sheet of Tafilalet-Taouz (Destombes and Hollard, 1986) recently revised by Destombes, (2006). Numerous works have been consecrated to the lithostratigraphic, pleontologic and sedimentoligical studies (Destombes et al., 1962;Destombes, 1963;Hollard, 1974a;Klug, 2001Klug, , 2007Klug et al., 2009;Becker et al., 2018aBecker et al., , 2018bBecker et al., , 2018cKlug and Pohle, 2018;Pohle and Klug, 2018). In addition, several tectonic and metallogenic works have been documented in many publications (Makkoudi, 1995;Baidder et al., 2008Baidder et al., , 2016Essalhi et al., 2016Essalhi et al., , 2018Ait Daoud et al., 2020;Saidi et al., 2020) and in the National Geological Mapping Program [Programme National de la Cartographie Géologique (PNCG)]. ...
... alensar bowl) remained. K. Complete visual unit of G. schlotheimi. Note the widened base of the unit, supposedly containing neural networks (white arrow). L. Synchrotron scan of a visual unit of Barrandeops cf. granulops (Chatterton,Fortey, Brett, Gibb, and McKellar, 2006), Phacopida, Emsian, Early Devonian, Hamar Laghdad (Tafilalt, Morocco), comp.Klug et al., (2009) (Schoenemann and Clarkson, 2013), and explanatory diagram. M. Harpes macrocephalus Goldfuss, 1839, Harpetida, Ahrdorf Fm., Lower Middle Devonian, Auberg, Eifel, Germany, benthic trilobite. N. Reduced compound eye of M. O. Brim of M with pores, forming a 'compound ear' or 'compound nose'. P. Unspecified harpetid trilobite. Note the pores ...
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Great progress has been made during the last decades in understanding visual systems of arthropods living today. Thus it seems worthwhile to review what is known about structure and function of the eyes of trilobites, the most important group of marine arthropods during the Paleozoic. There are three types of compound eyes in trilobites. The oldest and most abundant is the so-called holochroal eye. The sensory system represents a typical apposition eye, and all units are covered by one cornea in common. The so-called abathochroal eye (only in eodiscid trilobites) consists of small lenses, each individually covered by a thin cuticular cornea. The schizochroal eye is represented just in the suborder Phacopina, and probably is a highly specialized visual system. We discuss the calcitic character of trilobite lenses, the phylogenetic relevance of the existence of crystalline cones in trilobites, and consider adaptations of trilobite's compound eyes to different ecological constraints. The aim of this article is to give a resumé of what is known so far about trilobite vision, and to open perspectives to what still might be done.
... There was a turnover in dacryoconarids, from Nowakia faunas to the dominance of Viriatellina ( Fig. 16; ALBERTI 1980ALBERTI , 1981a. The thin marl unit with still relatively rich neritic fauna grades upwards into greenish-grey, hypoxic shales with principially the same deep-water (dominantly pelagic), goethitic fauna as at Bou Tchrafine KLUG et al. 2009 Since the mudmounds thrived in subphotic facies and kept up with steady transgression through the lower Emsian, their eventual dismiss by eustatic rise seems questionable. As noted by AITKEN et al. (2002) it is likely that the combined effects of reduced hydrothermal supplies for bacterially meditated carbonate formation and eustatic drowning terminated the mound growth. ...
... Based on the colour, host sediments and surface patterns (such as crystal structures and visible suture lines), preservation in different minerals is inferred for vertebrate and invertebrate fossils from the arid eastern Anti-Atlas (Fig. 1). Although their actual mineralogical composition was rarely tested (Klug et al. 2009, the mineralogy of a given fossil has commonly been inferred based on speculation rather than actual mineralogical examinations . Consequently, the analysis of the mineral composition of fossils of various ages and localities from the Devonian of the Anti-Atlas is crucial. ...
In some Devonian strata in the eastern Anti‐Atlas, fossil invertebrates are abundant, display a high taxonomic diversity and indicate many shifts in palaeoecology. This is reflected in changes in faunal composition of invertebrates and vertebrates. Fossils of jawed vertebrates of late Lochkovian and younger age have been recorded and are relatively common with their abundance and diversity increasing towards the Late Devonian. Environmental changes in the Devonian also left their mark in the preservation of vertebrates and invertebrates from the Anti‐Atlas, which varies strongly through time and regionally. This variation partially reflects environmental changes linked with the evolution of small marine basins during the disintegration of the continental shelf of Gondwana in this region, fluctuations of the regional sea level and other environmental changes. To improve our understanding of these ecological changes, of shifts in preservation through the succession and of the formation of Fossil‐Lagerstätten, we analysed the mineral composition of some invertebrate and vertebrate samples of Devonian and Early Carboniferous age by Raman spectroscopy and X‐ray diffraction. Additionally, we characterized some of these Fossil‐Lagerstätten using palaeontological and sedimentological parameters. We examined eight Devonian Konzentrat‐Lagerstätten and two Konservat‐Lagerstätten with soft‐tissue preservation (the Famennian Thylacocephalan Layer and the Hangenberg Black Shale of the southern Maïder). The last two are the first Konservat‐Lagerstätten described from the Devonian of North Africa. The taphonomic and oceanic settings suggest that these Konservat‐Lagerstätten are formed because of stagnation (related to vertical restriction of water exchange and water depth rather than limited spatial water exchange and a lateral restriction) in the relatively small Maïder Basin with limited water exchange with the neighbouring Tafilalt Basin. The temporally low oxygen levels in the Maïder Basin are a possible reason for the reduced chondrichthyan diversity (missing demersal and shallow water species) compared to the Tafilalt Platform.
Taking advantage of the exceptional record of Devonian trilobites in North Africa, a new dataset was compiled in order to reveal their long-term evolutionary history leading to their extinction. This dataset comprises 1171 trilobite occurrences from 168 different localities, within 22 consecutive and discrete chronostratigraphic intervals (substage temporal scale), representing 556 species, 179 genera, and 15 families scattered among nine North African basins. The reconstructed palaeobiodiversity trajectories by means of various biodiversity estimators of taxonomic richness are consistent and highlight a progressive and continuous diversification throughout the Early Devonian to reach a maximum of diversity at the end of the Emsian. Most families encountered in North Africa contribute to this increase of diversity. This regional diversification shows the same trends as the global one. Thereafter, the trilobite diversity began to decline due to extinction rates higher than origination rates during the Eifelian (Middle Devonian). From the middle Givetian to the late Frasnian, the trilobite diversity remained low. After this major decline, and the Frasnian events, a faunal change occurred, especially in phacopid and proetid trilobites, which were the only two families crossing the Frasnian/Famennian boundary. Indeed, the Kellwasser Event impacted an already impoverished diversity leading to a major faunal renewal associated with quick taxonomic changes at the genus level. A larger proportion of deeper water and reduced-eye/blind trilobites who acted as opportunists characterized the Famennian recovery. Finally, these palaeobiodiversity trends are compared to those of ammonoids from the same area.
Modularity and integration are variational properties expressed at various levels of the biological hierarchy. Mismatches among these levels, for example developmental modules that are integrated in a functional unit, could be informative of how evolutionary processes and trade‐offs have shaped organismal morphologies as well as clade diversification. In the present study, we explored the full, integrated and modular spaces of two developmental modules in phacopid trilobites, the cephalon and the pygidium, and highlight some differences among them. Such contrasts reveal firstly that evolutionary processes operating in the modular spaces are stronger in the cephalon, probably due to a complex regime of selection related to the numerous functions ensured by this module. Secondly, we demonstrate that the same pattern of covariation is shared among species, which also differentiate along this common functional integration. This common pattern might be the result of stabilizing selection acting on the enrolment and implying a coordinate variation between the cephalon and the pygidium in a certain direction of the morphospace. Finally, we noticed that Austerops legrandi differs slightly from other species in that its integration is partly restructured in the way the two modules interact. Such a divergence can result from the involvement of the cephalon in several vital functions that may have constrained the response of the features involved in enrolment and reorganized the covariation of the pygidium with the cephalon. Therefore, it is possible that important evolutionary trade‐offs between enrolment and other functions on the cephalon might have partly shaped the diversification of trilobites.
Late Emsian (early Dalejan, Polygnathus inversus Zone) brachiopods from Hamar Laghdad (eastern Anti-Atlas, Morocco) are examined on the basis of a collection of over 540 specimens coming from the Kess-Kess Formation. Two entirely different assemblages (no shared species) corresponding to mud mound and inter-mound carbonates are recorded. The assemblage A (inter-mound carbonates) includes 15 species and is dominated by Kyrtatrypa cf. balda, Brachyspirifer? sp., and Sieberella? sp. Other brachiopods include Stenorhynchia ulrici Halamski & Baliñski n. sp., Eoglossinotoechia marocanensis and Reticulariopsis? sp. The assemblage A is a mixture of quieter water species and of brachiopods adapted to high energy environments. The assemblage D from cavities and small caves occurring within the Kess-Kess mud mounds is nearly monospecific, dominated (98%) by Septatrypa tumulorum Baliñski & Halamski n. sp. This species was probably adapted to live around the outlets of active or inactive venting chimneys. Precise biogeographic analysis of the fauna is hampered by inadequate preservation and the necessity of using the open nomenclature resulting therefrom, but Bohemian affinities of the described brachiopods are clear. © 2018 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.
The late Early Devonian rostroconch fauna from the Amerboh Group of Bou Tchrafine in the Hamar Laghdad area is described. The few specimens are assigned to the genera Hoareicardia and Barrandeicardia within the Hippocardiidae of the Hippocardioidea. The material confirms the difficulties in recognizing different shell layer architecture in conocardiid rostroconchs, which is a prerequisite for specific determination. The presence of Hoareicardia in the late Early Devonian of Morocco denotes the distribution of the genus in both the northern (Laurussia) and southern (Gondwanan) shelf margins of the Rheic Ocean, and Barrandeicardia furthermore provides evidence of a probable connection with the highly diverse rostroconch assemblages of Perunica and Armorica. © 2018 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.
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Internal moulds of the relatively small- to moderate-size shells of Early Devonian ectocochleate cephalopods (typically <150 mm diameter) occasionally display traces of repaired shell damage. Presumably, these animals with their highly specialized buoyancy device, the phragmocone, lived in the water column. It is uncertain as to how the shells of these animals were damaged; one likely cause would be predatory attacks but the identity of the perpetrator remains uncertain. So far, no remains of arthropods capable of breaking or cutting shells have been found in the fossiliferous outcrops of this age in the Anti-Atlas (Morocco). The only macrovertebrate remains of this age are of acanthodian and placodermfish which probably lived a more or less benthonic life style. Additionally, a fish attack on these cephalopods would probably have destroyed most of the thin-shelled conch and killed the animal. Most of the repaired shell breaks are triangular in shape which is characteristic for cephalopod bite marks. Additionally, the paired arrangement of the fractures in over 70 bactritoids supports the hypothesis that it was a cephalopod attacking another cephalopod. It cannot be excluded with certainty that occasional vertebrate attacks left traces on their shells. Fossil evidence indicates that the development of tightly coiled conchs was a rapid evolutionary event in the Ammonoidea in the Early Devonian; however, the evolution of coiling is probably not directly related to predation pressures because the ratio of injured to healthy specimens is roughly the same in Zlíchovian bactritoids with orthoconic and ammonoids with coiled shells.
Hand specimens and polished sections of the cuticle of the trilobite Ellipsocephalus polytomus Linnarsson from the Middle Cambrian of Oland have been examined in incident light and, after etching, with the scanning electron microscope. Major subdivisions of Ellipsocephalus cuticle in life are proposed as: a very thin outermost epicuticle, an outer laminated layer, and a principal layer, the original structure of which is represented only by disc-like extensions on the perpendicular canals which pass across it. -from Authors
Perfectly exposed, carbonate mud buildups of Givetian age occur in the southern Ahnet Basin of the central Sahara. They are built of a massive core surrounded by mostly coarse-grained capping beds. The mud mounds and ridges are perfectly aligned along three directions that correspond exactly with the lineament and fault system known from the Pan-African (Precambrian) basement around the Ahnet Basin. It is suggested that the formation of mud ridges was favoured in those places where predominant currents were directed parallel to the orientation of venting fissures. -from English summary
Thin sections through the eye of a Phacops from the Middle Devonian, Germany, show a so-called mesodermal capsule below the lens. Organic lamellae within the lens indicate that its growth is closely related to that of the exoskeleton. There is no evidence for a Cartesian interface and intralensar bowl within the lens, here thought to be a gradient index (GRIN) lens. A keratometer for simulating identification of objects by the lenses, is described. There is no evidence for stereo vision and it is believed that overlap of the visual fields was to aid motion detection of other organisms. Comparison of the schizochroal eye of trilobites with that of the living Strepsiptera is discussed. Maculae of the hypostoma are considered to be homologous with the ventral eyes of Limulus.
Etched slices of the cuticle of the Silurian trilobite Homalonotus rhinotropis Angelin, 1854, from two localities in Skane, southern Sweden, have been examined with the scanning electron microscope. The two major subdivisions of the cuticle are a 'prismatic' (originally laminated) outer layer, about 20-30 μm thick, and a principal layer, 200-300 μm thick, which may be foliated dr roughly laminated. The original finely-laminated aspect of the outer layer may sometimes be seen as a continuous layer, but is more frequently detected as 'shaped inclusions' set in a prismatic background. These 'shaped inclusions' are considered to have been produced by accumulation of minerals around the apices of 3-6 μm perpendicular canals early in calcification and preferentially preserved because of subtle differences from the products of later stages of the process. It is possible that calcification started before ecdysis. The difficulties involved in ascertaining the original structure of the principal layer are outlined, and possible reasons for differences in its preservation from the outer layer are proposed.