Preliminary report on new echinoderm Lagerstätten from the Upper
Ordovician of the eastern Anti-Atlas, Morocco
A. W. Hunter, B. Lefebvre, & E. Nardin,
UMR CNRS 5561, Biogéosciences, Université de Bourgogne, 6 boulevard Gabriel, F-21000, Dijon, France.
P. Van Roy
Department of Geology & Soil Science, Ghent University, Krijgslaan 281/S8, B-9000, Ghent, Belgium.
S. Zamora
Área y Museo de Paleontologia Paleontología, Departamento de Ciencias de la Tierra, Universidad de
Zaragoza, E-50009, Zaragoza, Spain.
S. Régnault
Muséum d’Histoire naturelle, 12 rue Voltaire, F-44000, Nantes, France.
ABSTRACT: Four distinct echinoderm Lagerstätten have recently been discovered in the Upper Ordovician of the eastern Anti-Atlas, Morocco. They have yielded hundreds of exquisitely preserved specimens.
Their taphonomy and associated lithology both suggest rapid, in situ burial. Here we discuss the diverse range
of assemblages represented and their significance to the diversity of echinoderms in the Lower Palaeozoic.
The oldest assemblage (Izegguirene Formation, lowermost Caradoc) is dominated by eocrinoids, large
ophiuroids, and mitrate stylophorans associated with rare crinoids. It shows strong similarities with slightly
older faunas described from the underlying Ouine-Inirne Formation (Llandeilian) in the Central Anti-Atlas.
The second assemblage (lower part of the Lower Ktaoua Formation, lower-middle Caradoc) is composed of
eocrinoids (Cardiocystites) and small ophiuroids (encrinasterid indet.). The third assemblage was collected in
the upper part of the Lower Ktaoua Formation (lowermost Ashgill). This ‘starfish’ bed is dominated by ophiuroids and large solutes, associated with common diploporites and rhombiferans, and rare crinoids and mitrates. Finally, the youngest assemblage (lower part of Upper Tiouririne Formation, lower Ashgill) has
yielded abundant remains of edrioasteroids and rhombiferans.
1. INTRODUCTION
Four distinct echinoderm Lagerstätten, yielding
hundreds of exquisitely preserved specimens, have
recently been discovered in the Upper Ordovician of
the eastern Anti-Atlas, Morocco in the El Caïd Rami
area (Figure 1). Fossils are preserved as fully articulated individuals with even the most delicate skeletal
elements, such as brachioles, arms and aulacophores
preserved. This preliminary study briefly overviews
the taxonomic diversity of these organisms, their taphonomy and their palaeoecology. This investigation is intended to be a taxonomic survey of all the
different echinoderm groups represented. However,
more detailed systematic descriptions of the fossils
are in progress and will be published elsewhere.
Here we discuss the diverse range of assemblages
represented and their significance to the diversity of
echinoderms in the Lower Palaeozoic and what can
be deduced about their palaeoecology and community structure.
Figure 1, Map of the Anti Atlas region showing the El Caïd
Rami area.
1
2. STRATIGRAPHY AND ENVIRONMENTAL
SETTING
Although the various assemblages are all primarily
preserved in clastic rich sediments, the formation of
these deposits took place in different environments,
representing more than one facies type. However, it
is clear that these are life assemblages from relatively shallow palaeoenvironments such as distal
upper offshore, their preservation probably resulting
from rapid, storm influenced burial. The four fossil
assemblages are considered Upper Ordovician in age
(Figure. 2).
This is the first record of Ascocystites in the Ordovician of Morocco. This genus was already described
in the Middle Ordovician of Brittany (Chauvel 1941,
Régnault 1990) and Portugal (Young & Donovan
1993), and in the lower Caradoc of Bohemia (Barrande 1887, Prokop & Petr 1999).
Figure 2, Stratigraphic Framework for the Anti Atlas region
showing the position of the assemblages from localities "CRF1" (Tizi n'Mouri), "CRF-2", "CRF-3", "CRF-4" (Bou Nemrou),
and "CRT" (piste de Tinejdad).
2.1 Repositories
The material referred to in this paper is deposited
in the following public institutions: Muséum
d'Histoire naturelle de Lyon (ML), Muséum
d'Histoire naturelle de Marseille (MHNM), Muséum
d'Histoire naturelle de Nantes (MHNN), Muséum
d’Histoire naturelle de Toulouse (MHNT) and
Museo Paleontólogico de la Universidad de
Zaragoza, Spain. (MPZ)
3. THE FOSSIL ASSEMBLAGES.
The Ordovician is widely represented in the Palaeozoic outcrops of Morocco, mainly in the AntiAtlas (Destombes et al. 1985), where fossiliferous
rocks appear very rich in echinoderm fossils (Chauvel 1966).
3.1 Assemblage from locality CRF-4 (Bou Nemrou)
The most diverse of the four principal assemblages is found within the Izegguirene Formation at
locality CRF-4 (Bou Nemrou), and is earliest Caradoc in age. These massive deposits are dominated by
the eocrinoid Ascocystites (Figure 3) and large ophiuroids (protasterid nov. gen. nov. sp. Figure 11j).
Figure 3, Ascocystites sp., Bou Nemrou (CRF-4), eastern AntiAtlas, Morocco; Izegguirene Formation (lower Caradoc). A:
Adult specimen (MHNN.P.047504); B - C: probable juvenile
(MHNM.15406-31.1 & MHNM.15406-38). Scale bar: 1cm.
The asterozoans are entirely composed of members of the class Ophiuroidea. These specimens have
ambulacra typical of Ordovician groups represented
in most major Lagerstätten. Protasterids, which are
also recorded from the Lower Ordovician of the
Montagne Noire (Hunter & Vizcaïno 2006) and the
Middle Ordovician of Bohemia (Petr 1989) and Brittany (Hunter et al. in press) are the most common
asterozoan group, both at Bou Nemrou and in the
2
next assemblage. The assemblage also exhibits a
high diversity of mitrate stylophorans, including
Anatifopsis, Aspidocarpus, and Eumitrocystella, as
well as rare crinoids. The mitrate assemblage shows
strong similarities with slightly older faunas described from the underlying Ouine-Inirne Formation
(Llandeilian) in the central Anti-Atlas (Chauvel
1971, Cripps 1990, Beisswenger 1994). Within mitrates, the genus Eumitrocystella is endemic to the
Anti-Atlas, but closely related forms (e.g., Mitrocystella) are widespread in peri-Gondwanan regions
(Bohemia, France, Spain, Portugal). Aspidocarpus is
a genus of relatively generalized, primitive mitrocystitid mitrates, that is known from the western
margin of Gondwana from the Middle Ordovician
(Morocco, and Brittany) to the Caradoc (Brittany,
and Bohemia). Anatifopsis is a genus of kirkocystid
mitrate with a world-wide distribution, known from
the Tremadoc to the Ashgill.
Figure 4. MHNM.15406.1.1: Large slab with ophiuroids, mitrates (Eumitrocystella sp.) and large solutes (Dendrocystites
sp.), Tizi n'Mouri (CRF-1), eastern Anti-Atlas, Morocco. Upper part of Lower Ktaoua Formation, lower Ashgill. Scale bar:
4cm.
3.2 Assemblage from locality CRF-3
This assemblage, which is found in the lower part
of the Lower Ktaoua Formation, is presumed to be
early-middle Caradoc in age. The echinoderm community is primarily composed of eocrinoids (Cardiocystites) (Figure 11a), mitrates (Eumitrocystella
sp.) (Figure 11 d-f), and ophiuroids (Figure 6). This
is the first record of Cardiocystites in the Ordovician
of the Anti-Atlas. This genus was previously described in coeval deposits from Bohemia (Barrande
1887) and Wales (Dean & Smith 1998). Within the
assemblage, two distinct starfish beds can be recognised; one of these beds is characterized by the presence of two small ophiuroid taxa (Figure 11g-h) including a new genus within the encrinasterids
(Shackleton, 2005).
The second starfish bed contains a large asterozoan which is thought to be a new species of Protaster (Figure 11i) (Shackleton, 2005). This assem-
blage also contains small Dendrocystites-like
solutes, with a relatively long and slender brachiole.
They are the first solutes to be recorded in the Upper
Ordovician of Morocco. Dendrocystites is an abundant and well-known solute in the Caradoc of Bohemia, where two species have been described: D.
sedgwicki and D. barrandei (Barrande 1887, Bather
1913, Prokop & Petr 1999).
Figure 5. Large solute (Dendrocystites sp.) MHNM.15406.33,
showing the external mould (left) and the latex cast (right).
Tizi n'Mouri (CRF-1), eastern Anti-Atlas, Morocco. Upper part
of Lower Ktaoua Formation, lower Ashgill. Scale bars: 4cm
(left) & 1cm (right).
3.3 Assemblages from Tarhia region (CRF-1,CRF-2)
In the Tarhia region, two distinct echinoderm assemblages were collected close to the limit between
the Lower Ktaoua Formation and the overlying Upper Tiouririne Formation. The presence of the trilobite Mucronaspis zagoraensis and biostratigraphic
data (Villas et al. 2006) indicate a Pusgillian age for
the Tizi n'Mouri assemblage (See Figure 2) The first
echinoderm assemblage (locality CRF-1, Tizi
n'Mouri) appears in a thin level of yellowish, medium-grained sandstone (quartzitic sandstone). It is
mainly composed of the rhombiferan Homocystites
sp. (Figures 7(right)) and large Dendrocystites-like
solutes, associated with mitrocystitid mitrates
(Eumitrocystella sp.) (Figure 4-5). The specimens in
these deposits, as in most of the faunas described in
this study, appear complete and articulated. They are
preserved as natural moulds coated by extremely
thin films of limonite. Homocystites is a relatively
widely distributed rhombiferan (Figure 11c), which
was described in the Middle Ordovician of Baltica
(Russia; Kesling 1967), the Caradoc of several western Gondwanan regions (Bohemia, Portugal, Spain;
3
Barrande 1887, Delgado 1908, Gil Cid et al. 1996),
and in the Ashgill of Avalonia (Wales; Donovan et
al. 1996) and Laurentia (North America, Scotland;
Kesling 1967; Paul 1984; Donovan et al. 1996). The
large Dendrocystites have short and stout brachioles.
As their morphology is clearly distinct from that of
the small solutes from the CRF-3 assemblage, the
large forms from Tizi n'Mouri very likely belong to
another species.
Figure 6. MHNM.15406.23.1a-b, Ophiuroid (Protaster sp. left)
and mitrate (right; Eumitrocystella sp.), locality CRF-3, eastern
Anti-Atlas, Morocco. Lower part of Lower Ktaoua Formation,
lower-middle Caradoc. Scale bar: 1.5cm (left) & 2cm (right).
Figure 7, Asterocystis sp. (left, MHNT.PAL.20005.0.141.1)
and Homocystites sp. (right, MNHM.15406.18.1), localities
CRF-1 (Tizi n'Mouri) and CRF-2, respectively, eastern AntiAtlas, Morocco. Upper part of Lower Ktaoua Formation, lower
Ashgill. Scale bars: 1cm
The second assemblage, sampled in locality CRF2, can be classified as a ‘starfish’ bed (see Goldring
& Stephenson, 1972) as it is dominated by a new
genus of ophiuroid belonging to the eophiurids
(Shackleton, 2005). Like all of the ophiuroids from
these assemblages, they require formal taxonomy
beyond the scope of this paper, being left in open
families until the entire asterozoan fossil record is
better understood. This assemblage is also packed
with large solutes (Dendrocystites sp.), associated
with common diploporites (Asterocystis nov. sp.). It
is the first time that Asterocystis is recorded outside
of Baltica (see Kesling 1967). The new species of
Asterocystis is a diploporan with recumbent ambu-
lacra, bearing weak and slender brachioles. The
theca is highly organised and the thecal plates bear
numerous covered diplopores (Figure 11b). The
rhombiferan Homocystites is common in the Tizi
n'Mouri assemblage but rare and poorly preserved in
the starfish bed (Figure 9).
Figure 8, Edrioasteroids (MPZ2006/565-569) from the youngest assemblage, lower part of the Upper Tiouririne Formation,
lower Ashgill (locality CRT, piste de Tinejdad). Scale bar:
1cm.
3.4 Assemblage from locality CRT (piste de
Tinejdad)
The youngest assemblage is from the lower part
of Upper Tiouririne Formation (lower Ashgill). It
has yielded abundant remains of edrioasteroids (Figure 8) and rhombiferans (Echinosphaerites sp.). This
assemblage is preserved in a green, fine-grained
sandstone, possibly a greywacke. The trilobite association of Mucronaspis zagoraensis and Kloucekia
(Phacopidina) aff. solitaria associated with the
echinoderm material indicates a Pusgillian age
(Destombes, 1972). Echinosphaerites is a widely
distributed fistuliporite rhombiferan, documented in
the Middle to Late Ordovician of Baltica, China,
Iran, Sibumasu, as well as in various western periGondwanan regions (see Kesling 1967, Bockélie
1981, Parsley 1998, Lefebvre et al. 2005).
Figure 9, Homocystites sp. (MPZ 2006/26-28, 30-31, 42).
From the Upper part of Lower Ktaoua Formation. Scale bar:
1.5cm.
4
PALAEOECOLOGY
The taphonomy of these assemblages is complex,
but broadly speaking these are life assemblages
which did not undergo considerable transportation.
This is evidenced by the fact that both the filter feeding echinoderms and the asterozoans have all of
their appendages intact and articulated.
Features such as intact ophiuroid disks, complete
articulation of appendages and a weakly disarticulated theca, (attached to the proximal stem), suggest
a rapid burial between 2 days to 1 week (Brett et al.
1997), with transport limited to a short distance
close to where the animal lived. Complete and articulated arms in all the asterozoans suggest preservation state 2 (Kerr & Twitchett 2004) that is, all
skeleton parts, excluding the mouthparts, are articulated. Eocrinoids, mitrates and ophiuroids are also
classified as type 1 echinoderms according to the
classification of Brett et al. (1997). The mitrates are
frequently preserved with their aulacophore in extended position (See figure 11d-f for numerous examples) which is further evidence of rapid burial as
the aulacophore typically tends to retract quickly after death.
Along with rhombiferans, diploporans are assigned to type 2 echinoderms according to the taphonomic classification of Brett et al. (1997). Such
excellent preservation of all the thin elements fully
articulated (for example brachioles and thecal plates)
suggests that these diploporans also experienced a
relatively rapid burial. There is an obvious alignment of the specimens of Asterocystis indicated by
the brachioles arranged like a plume (alignment of
the theca with the stem and the brachioles) (for example see Figure 7). This could indicate the influence of unidirectional current in preservation and
even in mode of life. Further evidence comes from
the ophiuroids and mitrates in the CRF-3 assemblage. It is observed that almost all aulacophores of
the mitrates are directed in the same direction; the
arms of co-occurring ophiuroids also show a similar
unidirectional orientation, all pointing in the same
general direction (Figure 10). In Asterocystis, the
stem is alternating in its most proximal part and it
seems to have an attachment surface in its distal end.
The last feature could indicate that the specimens of
Asterocystis lived fixed to the substrate. The columnal alternation could have eased movements of the
stem in response to the hydrodynamic conditions.
The Ascocystites population seems to comprise
juveniles and adults. This differentiation between
juveniles/adults (Figure 3) is based on the difference
in the total length of the theca (from 2 cm to more
than 20 cm), and on the number of thecal plates and
brachioles that increases during the growth. The
numerous specimens of Homocystites in the CRF-1
(Tizi n'Mouri) assemblage could also be juvenile or
immature forms. Evidence comes from their rela-
tively small thecal size, their tiny brachioles, the reduced size and ornamentation of the plates in each
circlet. Their large proximal stem could indicate a
certain ability to move or to react with the current.
The stem in all Homocystites and Ascocystites
gradually decreases in diameter until it becomes
slender. Moreover, no holdfasts have been observed
at the end of the complete stems. Thus, it is suggested a mode of life could be with the stem pushed
into the substrate, although it not clear whether the
fine-grained sandstones represent the substrate occupied by the echinoderms.
Figure 10, Large slab (MHNM.15406.23.1a-b) showing ophiuroids and mitrates on the bedding plain with a preferred orientation. CRF-3, eastern Anti-Atlas, Morocco. Lower part of
Lower Ktaoua Formation, lower-middle Caradoc. Scale bar:
10cm.
The stem of the Cardiocystites bohemicus (Barrande, 1887) occurring in the CF3 assemblage is
very long and constant in diameter, with an apparent
synostosial articulation. It seems to be relatively robust and rigid, yet with sufficient flexibility for high
amplitude movements. These features seem to indicate that the specimen could filtrate at least 20 cm
above the substrate in the water column. The stem
could serve as a mooring cable to maintain the theca
in the currents. The highly flattened body form of
Cardiocystites could be an adaptation to floating in
the high currents in shallow water (as expected for
other flattened eocrinoids; Nardin In-press).
It is clear that in all the horizons there is trophic
tiering with distinct separation between epibenthic
feeders (ophiuroids, solutes, and mitrates) found in
different associations as the medium to high suspension feeders (eocrinoids rhombiferans, and diploporans). This is particularly apparent in the CRF-3 assemblage, where the gregarious ophiuroid-mitrates
assemblage predominates. Gregarious ophiuroid assemblages are commonplace in the fossil record and
can be observed today (see Blaber et al. 1987, Fujita
& Ohta 1990). The other extreme is the Bou Nemrou
assemblage, which, although having a large ophiuroid component, is dominated by eocrinoids, with mitrates also being common here. A notable observation is that communities tend to have two principle
components. At Bou Nemrou, there is a clear distinction between the filter feeding eocrinoids and the
large ophiuroids, whereas in the CRF-3 assemblage,
5
mitrates and ophiuroids form the dominating association, while the Tizi n'Mouri assemblages are solute and eocrinoid based communities with ophiuroids occurring in much lower numbers. This
mitrate/ophiuroid association in observed throughout
the Lower Palaeozoic (see Hunter et al. in press).
This trend continues with Bou Nemrou showing a
clear distinction between the filter feeding eocrinoids and the large ophiuroids. Apart from the obvious association between taxa these assemblages are
notable in that they have many other palaeoecological associations, including the apparent alignment
with current conditions (explained above), and the
density patterns shown in some of the echinoderms,
although it is difficult to document whether this is an
actual phenomenon or simply a taphonomic artefact.
Most significant is the apparent ontogeny identified
in the eocrinoids and the other filter feeding echinoderms, with immature forms even predominating in
certain assemblages, e.g. Tizi n'Mouri, with uncommon adults occurring in locality CRF-2. It is clear
that each of the assemblages could represent a different palaeo-depth, necessitating a more extensive
comparison with other regions and facies of the
western peri-Gondwana margin, where palaeoenvironmental conditions are better established.
The El Caïd Rami assemblages show strong relationships with Middle to Late Ordovician faunas of
other areas of the Gondwanan margin, and especially with Bohemia. From an asterozoan point of
view these assemblages are significant as they establish that protasterids have a much wider distribution
within peri-Gondwana and in particular outside of
Bohemia (see Petr 1989). Unfortunately, such palaeogeographic considerations are complicated by
the obvious stratigraphic variations found in the faunas. Asterozoan assemblages in the CRF-4 (Bou
Nemrou) communities contain protasterids that are
recorded from the Lower to the Middle Ordovician
(Spencer 1950, 1951). However, the Tarhia assemblages consist entirely of new asterozoans, likely to
be endemic to the region. Observations and data
from the other echinoderm groups suggest a gradual
transition from a late Middle Ordovician-like fauna
(Bou Nemrou) not very different from that of the
underlying Ouine-Inirne Formation, to a more typical Late Ordovician fauna (Tarhia). The composition
of early Ashgill (Pusgillian) assemblages from the
Anti-Atlas of Morocco is very different from that of
coeval faunas from other peri-Gondwanan regions,
which are dominated by rhombiferans with Baltic affinities, and adapted to temperate to warm seawaters. In other Gondwanan regions (e.g., Algeria,
Brittany, Carnic Alps, Montagne Noire (France),
Sardinia and Spain), forms adapted to cold water
(e.g., solutes, mitrates, etc.) are absent or extremely
rare in pre-Hirnantian Ashgill deposits.
CONCLUSIONS
The echinoderms are exceptionally preserved and
are likely to have been entombed by an obrution deposit.
Many taxa are documented for the first time in the
Upper Ordovician of the Anti-Atlas: the eocrinoids
Ascocystites and Cardiocystites, the diploporan Asterocystis, the mitrates Anatifopsis, Aspidocarpus,
and Eumitrocystella, protasterid and encrinasterid
ophiuroids, and the solutes.
The horizons clearly show trophic tiering with
epibenthic feeders (ophiuroids and mitrates) and
medium to high suspension feeders (eocrinoids,
rhombiferans, and diploporans).
Several specific palaeoecological observations can
be made; these include faunal associations (e.g.
ophiuroids and mitrates), alignment with current
conditions, density of fauna and ontogeny.
It is established there is a relationship between El
Caid Rami assemblages and other faunas of the
Gondwana margin and especially Bohemia. A gradual transition can be observed from a Middle Ordovician-like fauna (Bou Nemrou) to a fauna more
typical of the Upper Ordovician (CRF-3), which,
contrary to the situation in other peri-Gondwanan
regions, persists in the early Ashgill (CRF-1, CRF-2,
CRT).
ACKNOWLEDGEMENTS
Thanks go to Joseph Botting and D. Van Damme for
their help in the field. We also wish to thank the curators of the following collections for access to important specimens: Muséum d'Histoire naturelle de
Lyon (ML), Muséum d'Histoire naturelle de Marseille (MHNM), Muséum d'Histoire naturelle de
Nantes (MHNN), and Muséum d’Histoire naturelle
de Toulouse (MHNT). This work would not have
been possible without the group of local experts including Véronique and Roland Reboul.
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Figure 11, A, Cardiocystites sp., adult form CRF3 eastern
Anti-Atlas, Morocco. Lower part of Lower Ktaoua Formation,
lower-middle Caradoc (MHNM.15406.13.1). B, Asterocystis
sp., adult form (MHNT.PAL.2005.0.154). C, Homocystites
sp., (MHNM.15406-15-1) probable juvenile forms CRF1 eastern Anti-Atlas, Morocco. Upper part of Lower Ktaoua Formation, lower Ashgill. D-F Eumitrocystella sp. CRF3 eastern
Anti-Atlas, Morocco. Lower part of Lower Ktaoua Formation,
lower-middle Caradoc. (D) ML20 269457 (E-F)
MHNN.P.035380. G-H, Two new encrinasterids like ophiuroids from the CRF3 assemblage G (MHNM.15406.25.1
(3945)) H (MHNM.15406.14.1 (3905)).I, Protaster sp.
(MHNN.P.035380) CRF3 eastern Anti-Atlas, Morocco. Lower
part of Lower Ktaoua Formation, lower-middle Caradoc. J,
protasterid nov. gen. nov. sp. (MHNM.15406.32.2 (3930))
CRF4 eastern Anti-Atlas, Morocco. Lower part of Lower
Ktaoua Formation, lower-middle Caradoc. Scale bars 1cm.
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