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Geol. Mag. 147 (6), 2010, pp. 860–870.
c
Cambridge University Press 2010 860
doi:10.1017/S0016756810000348
A Middle–Late Eocene vertebrate fauna (marine fish
and mammals) from southwestern Morocco; preliminary
report: age and palaeobiogeographical implications
SYLVAIN ADNET
∗
, HENRI CAPPETTA &RODOLPHE TABUCE
UMR 5554: Institut des Sciences de l’Evolution de Montpellier, Universit
´
e de Montpellier 2, Place E. Bataillon,
34095 Montpellier cedex 5, France
(Received 23 September 2009; accepted 1 March 2010; first published online 4 May 2010)
Abstract – Recent field work in the southern Moroccan Sahara (‘Western Sahara’), south of the city
of ad-Dakhla, has led to the discovery of several new fossiliferous sites with fossil vertebrates in
sedimentary deposits previously reported for the Mio-Pliocene. The sedimentology and geological
setting of the studied area are briefly reported here, and at least three units have been identified
in successive stratigraphical sequences according to their fossil content. The first preliminary list of
vertebrate associations is reported and consists mainly of isolated teeth belonging to selachian and bony
fishes, a proboscidean tooth currently assigned to ?Numidotherium sp. and many remains of archaeocete
whales (Basilosauridae). At least 48 species of selachians are presently identified; many of them are new
and others are recorded in the late Middle Eocene (Bartonian) and Late Eocene (Priabonian) of Wadi
Al-Hitan (Egypt) or Wadi Esh-Shallala Formation (Jordan) as in other African localities (e.g. Otodus
cf. sokolowi, ‘Cretolamna’ twiggsensis, Xiphodolamia serrata, Misrichthys stromeri, Hemipristis
curvatus, Galeocerdo cf. eaglesomi, Propristis schweinfurthi), probably indicating a Late Eocene
age for unit 2 of the bedrock successions. The evolutionary trend noticeable on the proboscidean tooth
is in agreement with such an assumption, by comparison with the close relative species known from
the Eocene of Egypt, Libya and Algeria. Indeed, the faunal associations from the Dakhla area clearly
demonstrate the erroneous age of these deposits, previously thought to be Mio-Pliocene. It suggests a
correlation in age (late Middle Eocene–Late Eocene) and a similar environment with the famous marine
deposits from Egypt and Jordan. It opens new opportunities to understand the biogeography and the
surprising similarity of landscape between West and Northeast Africa during the Bartonian–Priabonian
period.
Keywords: southwestern Morocco, Eocene, selachians, mammals, stratigraphy, palaeobiogeography.
1. Introduction
Since the 19th century, northern Morocco (north of the
Anti-Atlas) has been famous for its abundant and diver-
sified fossil vertebrate faunas, ranging from Palaeozoic
to Pliocene. For the Palaeogene, major fossils of both
marine (e.g. Noubhani & Cappetta, 1997; Cavin et al.
2000; Gheerbrant et al. 1993; Hua & Jouves, 2004)
and terrestrial vertebrates (e.g. Gheerbrant et al. 2002,
2006; Gheerbrant, Domning & Tassy, 2005; Bourdon,
2006) have been discovered, including, for example,
the oldest evidence of Afrotheria (Gheerbrant, Sudre
& Cappetta, 1996; Gheerbrant, 2009).
In contrast, and probably due to the difficult access,
little attention has been paid to the Cenozoic depos-
its cropping out along the southwestern Moroccan
Sahara (‘Western Sahara’) and observed until the
1950s by Spanish, French and Moroccan geologists,
successively. Mainly composed of clastic deposits,
geological formations in the south of the Dakhla–
Boujdour–Laayoune basin (Fig. 1a) were until now
usually mapped as Mio-Pliocene (Saadi, 1988; Rjimati
et al. 2008). No evidence of fossil vertebrates older
∗
Author for correspondence: sylvain.adnet@univ-montp2.fr
than the Neogene has been reported in previous
literature (Joleaud, 1907; Arambourg in Choubert
et al. 1966) until the recent discovery of shark teeth
and bone remains of archaeocete whales by local
people. Thanks to their information, an exploratory
field trip in 2009 in the south of the Dakhla peninsula
allowed us to locate these fossiliferous levels and to
discover many vertebrate fossils, collected in several
close localities. Dating interest becomes obvious,
considering that all taxa display many characteristics
of the Middle–Late Eocene assemblages known from
other African fossiliferous localities. The purpose of
this paper is to provide the first detailed sedimentary
log of the new fossiliferous localities, a preliminary
account of the taxa recovered, and to compare this
assemblage to other known Eocene assemblages that
have been reported elsewhere. In addition, we discuss
the stratigraphy and palaeoecological significance of
the new assemblages.
2. Geological setting
The sub-horizontal stratigraphical sequences visible
near Dakhla (Fig. 1b) show a slight syntectonic activity,
only marked at the top by some clastic dykes of yellow
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New Eocene vertebrates from southwestern Morocco 861
Figure 1. (a) Location of the new fossiliferous deposits (star), south of the city of ad-Dakhla, Moroccan Sahara, Morocco. Principal
geological structures simplified from Von Raad & Wissmann (1982), Saadi (1988) and Villeneuve (2005). (b) Outcrop on beach
illustrating the stratigraphical sequence as observed south of El Argoub (23
◦
21
17.76
N, 16
◦
01
55.28
W). Lithology is detailed in
text.
sandstone intersecting the underlying silt–chert suite.
This field observation is in agreement with that of
Labails et al. (2009), who noticed thick sedimentary
deposits offshore of Daklha, as indicated by seismic re-
flection data. This suggests a slight subsidence process
on this passive continental margin as a result of a tec-
tonic inheritance of the great Western African Craton
(Fig. 1a, anteclise of Reguibat; see Villeneuve, 2005).
The stratigraphical sequences (Fig. 2) crop out on
cliffs along the shoreline in a succession of beaches
from south of El Argoub to the commonly named
‘Garitas’ in a restricted military area. The bedrock
succession studied here is entirely observable from
the beach core (Fig. 1b) and accessible in few track
roads used by the local fishermen. Lateral variations of
facies are obvious, especially regarding the thickness
of sequences (see Fig. 2). We have divided these
sequences into three lithological units. Their ages,
mainly based on fossil marine vertebrates, will be
discussed hereafter.
The lower part of the sequences (unit 1; see
Figs 1b, 2) consists of a thick sequence of marly
siltstone, regularly interrupted by grey chert and black
coprolite-supported conglomerates. This alternating
succession sometimes displays composite marl or yel-
low sand beds, particularly towards the top of the unit.
The boundary between units 1 and 2 is easily detectable
and occurs over a distinctive irregular black quartzite
(except in the south where it disappears), and below
a yellowish-white marly siltstone with micro-remains
of fish. Burrows and flaser bedding are sometimes
observable inside this layer, mixing the fossiliferous
sand coming from the overlying bedrock B1. The
thickness of this layer seems to decrease from north
to south where it sometimes disappears. Unit 2 begins
with the previous bed, followed by the first fossiliferous
bed (B1) that in fact consists of two successive
layers: a fine compact conglomeratic sandstone at
the base (irregularly distributed), with imbedded teeth
and larger allochthonous elements which are badly
preserved; and a 0.8–1.2 m thick medium sandstone
with clay and phosphate grain elements. No calcareous
fossil was found in this sandstone, which can range
from grey to brown or reddish colour. The contact
between B1 and the upper strata is a distinctive irregular
erosion surface, emphasized by many burrows and/or
interbedded pockets of B1. Over a massive bedrock of
5–10 m of composite white siltstone–chert, the upper
fossiliferous bed (B2) consists of a muddy sandstone,
sometimes with a gypsum element present. The contact
between B2 and the overlying series is badly defined
in the sandstone thickness and seems irregular, but B2
always overlies a sandy layer with a high concentration
of gypsum. Unit 2 ends with yellow muddy sandstone
softly consolidated with irregular pockets of red muddy
sandstone. The boundary between units 2 and 3 is not
very distinctive and occurs below white calcareous
cemented sandstone. The upper part of the sequence
(unit 3) consists of a massive sandy to bioclastic
limestone, with ripple stratification (particularly in the
Dakhla peninsula), partially replaced by dolomite and
containing numerous invertebrate fossils or tracks. This
perched bedrock, laterally irregular, caps the sediment-
ary series and constitutes the accessing headland that
runs along the coast line. Many rhizoliths occur in the
calcareous sandstone, just below the sandy limestone
boundary. This unit is thin further south, as observed
in ‘Garitas’.
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862 S. ADNET, H. CAPPETTA & R. TABUCE
Figure 2. Stratigraphical section, position of the main fossil ver-
tebrate levels (B1, B2 and intermediate) and unit interpretation
of study area. Lithology is detailed in text. Location of section
is indicated by distance south from the centre of Dakhla.
Deposits in the lower part of the sequence (unit 1) are
entirely marine, as indicated by the numerous silicate
beds, chert and coprolite-supported conglomerates
dispersed along the column. Very scarce fossil shells
or teeth have been discovered from the visible base of
unit 1 to the top of unit 2. A metre-sized bed with large
black nodules occurs at the extreme base of the series,
when accessible under the beach sand dune.
The upper part of the sequence (unit 3) was mainly
formed by marine processes as well, as it consists of
a thick sandstone complex in the studied area, with
marine fossils (echinids, bivalves and gastropods) from
the base to at least 1 m below the massive sandy
limestone. The presence of a dense root system and/or
burrows in this level may suggest the mangrove soil
(vertical pneumatophores) of a tropical area, overlain
by a coastal deposit, as indicated by the presence
of numerous tracks of marine organisms inside the
massive sandy limestone.
3. Systematic palaeontology
The previously described vertebrate fauna from the Dakhla–
Boujdour area (‘Rio de Oro’ in Joleaud, 1907; Arambourg
in Choubert et al. 1966) probably comes from the massive
limestone or lateral equivalents (formerly molasse; Joleaud,
1907), which sporadically turn into a shelly limestone
(pectinid) in the Dakhla peninsula. These authors cited
‘Galeocerdo aduncus, Sphyrna prisca, Odontaspis con-
tortidens, O. cuspidata, Oxyrhina hastalis, Carcharodon
megalodon, C. rondeletii, Myliobatis faujasi, Diodon sp.
and Chrysophrys sp.’ The accurate Mio-Pliocene age
attributed to these fossil vertebrates was in agreement with
the contemporaneous geological literature (Font y Sague,
1911; Deperet, 1912; Hernandez et al. 1949) and with
observations of the invertebrate palaeontologists (Lecointre,
1962, 1963a,b, 1966a,b; Roman, 1963) who considered the
massive limestone of ‘Rio de Oro’ (up to 10 km south of
Dakhla) as Pliocene (or younger) in age. The age of the
underlying deposits (white calcareous sandstone with fossil
root mark, unit 3) is currently unknown but we provisionally
propose a Miocene age, as suggested by the presence of
several Miocene equatorial fossil woods discovered in the
Dakhla area (Lecointre & Koeniguer, 1965; Koeniguer, 1967;
updated in Dup
´
eron-Laudoueneix & Dup
´
eron, 1995). The
lower part of the sequence (units 1–2) has never been of
particular interest to palaeontologists. Only Ortlieb (1975)
reported several observations in the ‘Garitas-Amtal’ area,
where he collected fossil shark teeth (sent to one of us, HC)
and bone fragments in ‘the yellow calcareous or muddy sand-
stone, located over (northward) or below (southward) some
marly sand deposits with gypsum’. While this author pointed
out the helpful regularity of the fossiliferous deposit from
‘Garitas’ to ‘Amtal’ towards the south, he only considered
one level and could not propose any age for these layers.
New fossils were collected by surface collecting and
screen-washing. A total of seven samples of sediment were
taken during a short field trip in 2009. Every sample varied
between 2 kg and 20 kg of residue previously concentrated
by screen-washing (mesh width down to 0.4 mm). In a
further step, the insoluble residue was disaggregated by
immersion in diluted acetic acid (6 %) or fresh water. The
selachians represent the largest part of the fossil vertebrate
remains recovered in unit 2, with several thousand specimens
collected, equally distributed in samples. The majority of
the fossil material consists of isolated teeth (plus partial
tooth plates and caudal spines of myliobatid rays, and
undetermined vertebrae) representing at least 48 species of
sharks and rays. A preliminary list is given in Table 1. Some of
them are new and will be described in detail in a forthcoming
work devoted to this vertebrate group. Discussions on
significant taxa regarding dating and correlation have been
favoured in the present study. Isolated teeth, rostral elements
and disarticulated bones of bony fish recovered along unit 2
will not be treated here, awaiting supplementary samples
of matrix. Two other taxonomic groups of vertebrates were
discovered in unit 2 (B1 and B2). These comprise some
remains of archaeocete whales and one broken tooth of
a terrestrial mammal. The former are often reduced to
isolated and badly preserved bones and teeth (DAK.5, Fig. 3j)
that clearly belong to Basilosauridae, but some complete
skeletons, partially disarticulated, were observed in situ.Itis
beyond the scope of this paper to report on this promising
discovery for cetacean palaeobiogeography and, concerning
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New Eocene vertebrates from southwestern Morocco 863
Table 1. Preliminary list of fossil vertebrates recovered in study
area
Taxa B1 B2
Selachians
O. Lamniformes
Otodus cf. sokolovi ++
‘Cretolamna’ twiggsensis +++ +++
Macrorhizodus praecursor +++ +++
Carcharias sp. +++
‘Carcharias’ koerti ?reworked
Alopias aff. alabamensis ++ ++
Xiphodolamia serrata +
O. Orectolobiformes
Nebrius cf. obliquus ++
Chiloscyllium spp. +
O. Carcharhiniformes
Scyliorhinus spp. ++
Carcharhinus frequens +++ +++
Carcharhinus spp. ++++ ++++
Rhizoprionodon sp. +++ +++
Misrichthys stromeri ++
Abdounia spp. ++ ++
Galeocerdo cf. eagleasomi ++ ++
Galeocerdo sp. ++
Physogaleus sp. ++ ++
Hemipristis curvatus ++ ++
Paragaleus sp. ++ ++
Galeorhinus spp. ++
Sphyrna sp. ++
O. Rajiformes
Rhynchobatus sp. ++ ++
Rhinobatos spp. (+ oral teeth of pristids) ++ +
Pristis cf. lathami (rostral teeth) ++
Propristis schweinfurthi (rostral teeth) ++
Anoxypristis sp. (rostral teeth) ++
O. Torpediniformes
cf. Narcine sp. +
O. Myliobatiformes
Dasyatis spp. +++ +++
Himantura spp. +
Gymnura sp. +
Ouledia sp. +
Aturobatis sp. +
Myliobatis spp. +++ +++
Rhinoptera sp. +++ +++
Aetobatus cf. irregularis ++
Garabatis sp. +
Archaeomanta sp. +
Burnhamia sp. +
Mobula sp. ++
Selachian incertae sedis
Odontorhytis sp. ++
Actinopterygians
O. Perciformes
Sphyraena sp. ++ ++
Trichiurides sp. ++ ++
Cyladrincanthus sp. +
Mammals
Archaeocete indet. ++ ++
?Numidotherium sp. ?reworked
Number of ‘+’ symbols indicates the relative abundance in B1 and
B2.
the mammalian remains, we have only focused on the
primitive proboscidean tooth (GTS.1) found in B1.
The material is housed in the Laboratory of Paleontology,
Institut des Sciences de l’Evolution, Montpellier. Abbre-
viations: DAK – collection number for material from the
Dakhla area, GTS – collection number for material from the
Dakhla area, locality of ‘Garitas’.
3.a. Fish fauna
The fish fauna currently consists of 48 fossil species of
elasmobranches and 4 fossil species of bony fishes. Forty
genera and seven orders are represented, ranking this fossil
site in the top ten of the most diversified selachian faunas
from the Cenozoic in Africa. Most of these species are
new and under study, awaiting careful comparisons with
those from the contemporaneous deposits of the Whale
Valley (Fayum, Egypt; see Case & Cappetta, 1990) that are
currently undergoing revision (C. Underwood & D. Ward,
pers. comm.). Only a limited sample of selachian taxa having
an interest for correlation is figured and briefly discussed
here.
Locality. Unit 2, B1 and B2 from all sites, ?Samlat Fm.,
?Gerran member (Ratschiller, 1967).
Class CHONDRICHTHYES
Several modern orders of selachians (sensu Compagno,
2005) are represented in the fossil deposits (see Table 1).
However, Hexanchiformes, Squatiniformes, Heterodonti-
formes and Squaliformes are completely lacking.
Lamniformes: Numerous complete and well-preserved
teeth recovered in L1 and L2 (DAK.2–3; Fig. 3c, d) belong to
‘Cretolamna’ twiggsensis (Case, 1981), the youngest species
of the genus which was discussed and adequately illustrated
by Case & Cappetta (1990, pp. 9–10, pl. 3). This species
is easily recognizable by a pair of double flat cusplets on
anterior (Fig. 3c) and on lateral teeth (Fig. 3d). The range of
this species is restricted to the Middle–Late Eocene interval
and its geographical distribution extends to palaeotropical
seas between the Caribbean, western Tethys (Case, 1981;
Case & Borodin, 2000) and oriental Tethys (Casier, 1971;
Case & Cappetta, 1990; Case & West, 1991; Adnet et al.
2007).
Complete teeth of Otodus cf. sokolowi (Jaekel, 1895)
(often called ‘Carcharocles’) are less common in B1 and
B2 but relatively well preserved also. The teeth can reach
up to 10 cm in height, displaying a large triangular cusp
with a well-marked and regular serration on the cutting
edges (DAK.1; Fig. 3a), and a pair of lateral cusplets,
not very high and often divergent in lateral teeth to less
developed in anterior teeth. Case & Cappetta (1990, pp. 6–7)
have extensively discussed the taxonomic ambiguity within
other Eocene species, and particularly in the smaller species
Otodus auriculatus (Blainville, 1818), commonly recorded
in Eocene deposits worldwide (e.g. Ward & Wiest, 1990;
Dutheil, 1991; Long, 1992; Cappetta & Stringer, 2002).
The occurrence of ‘Carcharias’ koerti (Stromer, 1910)
(genus status unclear, see Strougo, Cappetta & Elnahas,
2007) is quite surprising because this large pelagic shark is
only known from Lutetian deposits widely distributed around
Northern and Western Africa (Strougo, Cappetta & Elnahas,
2007; Cappetta, Pfeil & Schmidt-Killer, 2000; Cappetta,
1987; Cappetta & Traverse, 1988; Noubhani & Cappetta,
1997; White, 1955; Dartevelle & Casier, 1959). However, all
the teeth belonging to ‘C.’ koerti were found in situ inside
the hard bone bed (as DAK.4; Fig. 3i) at the base of B1,
and their state of preservation is clearly different from all the
other taxa, showing a worn patina, blunted cutting edges and
sometimes many marks that suggest a reworking from older
deposits (Fig. 3i2).
The species Xiphodolamia serrata (GTS.2, Fig. 3b),
recently described from Priabonian deposits of Jordan, Iran
and Angola (Adnet et al. 2009), is probably one of the most
important elements for dating of the Dakhla deposits.
Carcharhiniformes: One of the unnamed species of
Carcharhinus (DAK2B.1; Fig. 3g) belongs to the ‘bull-
shark’ group among Requiem sharks (see Adnet et al.
2007) and displays upper teeth with a modern morphology
compared to those of species known in the worldwide
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864 S. ADNET, H. CAPPETTA & R. TABUCE
Figure 3. Fossil selachians from Dakhla area. (a) O. cf. sokolowi (DAK.1), 1 – labial view, 2 – lingual view; (b) X. serrata (GTS.2),
1–profile,2–labialview;(c,d)‘C.’ twiggsensis (DAK.2–3), 1 – labial view, 2 – lingual view; (e) G. cf. eaglesomi (DAK1.1), 1 –
labial view, 2 – lingual view; (f) M. stromeri (upper tooth) (DAK2A.1), 1 – labial view, 2 – lingual view; (g) Carcharhinus sp. (upper
tooth) (DAK2B.1), 1 – labial view, 2 – lingual view; (h) P. schweinfurthi (rostral tooth) (GTS.3), 1 – basal view, 2 – upper view; (i)
‘C.’ koerti (partially embedded) (DAK.4), 1 – labial view, 2 – lingual view; (j) posterior (lower) tooth of Basilosauridae (DAK.5).
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New Eocene vertebrates from southwestern Morocco 865
Eocene seas, including those from the Late Eocene of the
southern USA (e.g. C. gilmorei: White, 1956; M
¨
uller, 1999).
If the upper teeth (from B1 and B2) are reminiscent of
the Late Eocene and Oligocene specimens from Pakistan
(Adnet et al. 2007), Egypt (Case & Cappetta, 1990, figs
164, 165; Murray, 2004) or Oman (Thomas et al. 1989),
there are important differences in crown and root shape
(more rectangular) that will require further comparisons.
Nevertheless, the presence of such modern Carcharhinus
species in the Late Eocene of Western Tethys brings into
question the palaeobiogeographical scenarios proposed in
Adnet et al. (2007) about the modern rise of large Requiem
sharks.
The peculiar carcharhinid Misrichthys stromeri (Case &
Cappetta, 1990) seems to be restricted to the Bartonian and
Priabonian of Egypt (Fayum, gebel Mokattam and Western
Desert: pers. obs.) and Priabonian of Jordan (Mustafa &
Zalmout, 2002). This is the first occurrence (DAK2A.1,
Fig. 3f) outside the Near East. Relatively scarce, teeth of
this species have been found in B1 and B2 of unit 2.
Teeth of Galeocerdo cf. eaglesomi (DAK1.1, Fig. 3e)
are similar in shape to G. eaglesomi (White, 1955) but are
two times larger than the type Lutetian material coming
from Ameki, Nigeria (White, 1926, pl. 6 and White, 1955,
holotype included), the upper bone bed (BBR) from Togo
(Cappetta & Traverse, 1988) and from the Western desert in
Egypt (Strougo, Cappetta & Elnahas, 2007). As this material
may be considered to be younger in age (both B1 and
B2), an increase of size in the ‘lineage’ eaglesomi is thus
conceivable and this is the reason we only refer this species
to G. eaglesomi.
Two Carcharhiniform taxa are presently recorded for the
first time in the Eocene: Paragaleus and Sphyrna.Thefirst
is the earliest occurrence for this genus which was unknown
before the Miocene, and the second has been confidently
known since the Lower Oligocene (Adnet et al. 2007).
Rajiformes: Rostral teeth (GTS.3; Fig. 3h) of the sawfish
Propristis schweinfurthi (Dames, 1883) are unusual and
easily distinguishable from other fossil or living Pristidae.
This species is known from the Middle–Late Eocene of
the Tethyan realm from the Caribbean (Case, 1981; Case
& Borodin, 2000; Cappetta & Stringer, 2002) to Egypt
(Case & Cappetta, 1990) and in the north (D. Kemp, unpub.
Ph.D. thesis, Univ. Portsmouth, 1994) and south Atlantic
coasts (White, 1926; Dartevelle & Casier, 1959; Cappetta &
Traverse, 1988).
All the fossil batoids recovered here display an occurrence
compatible with a Bartonian–Priabonian age, except two
fossil Myliobatiformes that were previously unknown after
the middle Eocene: Aturobatis (Ypresian of USA, Lutetian
of southwestern France) and Garabatis (Thanetian–Lutetian
of Morocco).
Selachian incertae sedis: Occurrence of the enigmatic
genus Odontorhytis (see Cappetta, 1987) is not surprising
because it is relatively common in the Eocene coastal deposits
of the Tethyan Realm, from North Morocco (Cappetta, 1981)
to Egypt (Case & Cappetta, 1990; Strougo, Cappetta &
Elnahas, 2007; T. Cook & A. Murray, pers. comm.) and
Pakistan (Case & West, 1991). Recorded in B1 and B2, these
teeth seem different, however, from those of the Bartonian–
Priabonian Egyptian species O. pappenheimi B
¨
ohm, 1926 in
having a more slender cusp and less massive root.
Class ACTINOPTERYGII
Currently restricted to isolated teeth and broken bones,
fossil material of marine bony fishes (Perciformes) has
been identified as Sphyraena sp. (Sphyraenidae), Trichiurides
sp. (Trichiuridae incertae sedis) and Cylindracanthus sp.
(Xiphiidae) with very similar morphologies to those pub-
lished by Case & Borodin (2000), who reported
Sphyraena
sp., Trichiurides sagittidens (Winkler) and Cylindracanthus
cf. rectus (Dixon) from the Late Eocene of the Irwinton Sand
Member, Georgia.
3.b. Class MAMMALIA
The unique tooth comes from the base of B1 and belongs to
a terrestrial mammal. Due to its rarity and importance, it is
here described in detail.
Mirorder TETHYTHERIA McKenna, 1975
Order PROBOSCIDEA Illiger, 1811
Genus Numidotherium Mahboubi et al. 1986
?Numidotherium sp.
Referred specimen. GTS.1; left M
1or2
(Fig. 4) (length =
41 mm; width = 36 mm)
Locality. Unit 2, brown hard ground of the B1 north of
‘Garitas’. ?Samlat Formation, ?Gerran member (Ratschiller,
1967).
Description. The crown is brachyodont and rectangular
in occlusal view; its morphology is characterized by a
bilophodont pattern and a typical true lophodonty without
any trace of conules (Fig. 4a). Protoloph and metaloph are
slightly anteriorly convex. The metaloph does not reach
the top of the acute metacone. Wear affects the mesial
wall of both lophs. The hypocone and the protocone are
labially situated on the crown and their lingual walls are
sloping toward the base of the tooth; the paracone and
metacone are smaller than the lingual cusps. Despite the
poor preservation of the specimen in its external margins,
a mesial cingulum and a small style at the lingual side of
the interloph are visible. The preservation does not allow the
observation of the potential occurrence of both the parastyle
and postentoconule; the number and morphology of the roots
are also unknown. The distocrista reaches the hypocone to the
distal cingulum; there is no postmetacrista or metastyle. The
postparacrista and the crista obliqua are tenuous. The enamel
microstructure, studied according to the method described
by Tabuce, Delmer & Gheerbrant (2007), is characterized by
a schmelzmuster composed of 3-D enamel (thick bundles of
prisms decussate in all directions) (Fig. 4). In large areas the
vertical component of the decussation is attenuated, evoking
Hunter-Schreger bands (Fig. 4b).
Comments. The true lophodont molar morphology and
the bilophodonty of this specimen suggest affinities with
some deinotheriines or ‘barytherioid’ prosboscideans. The
deinotheriines Prodeinotherium and Deinotherium share
with the Dakhla proboscidean a one-layered schmelzmuster
composed of 3-D enamel (Tabuce, Delmer & Gheerbrant,
2007), in addition to their bilophodont M2 (their M1 is
trilophodont). These deinotheriines differ, however, in having
a complete distocrista linking the hypocone to the top of the
metacone. The earliest putative deinotheriid, Chilgatherium
from the Late Oligocene of Ethiopia (Sanders, Kappelman &
Rasmussen, 2004), differs in the bunolophodont morphology
of its cheek teeth. The ‘barytherioids’, which include one
of the oldest representatives of the proboscideans, are
possibly paraphyletic taxa (see Gheerbrant et al. 2005);
they are composed of Numidotherium koholense (Mahboubi
et al. 1986; Noubhani et al. 2008) and Daouitherium
rebouli (Gheerbrant et al. 2002) from the Early Eocene
of Algeria and Morocco, respectively, plus Barytherium
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866 S. ADNET, H. CAPPETTA & R. TABUCE
Figure 4. Dakhla proboscidean, left M
1or2
(GTS.1) in occlusal view (a); vertical section of the enamel under the paracone (b).
Figure 5. Measurements of the M
1or2
of the Dakhla proboscidean
compared with Numidotherium koholense and Barytherium
grave.
grave from the Late Eocene to Early Oligocene of Fayum
(Egypt) and Dor El Talha (Libya) (see Shoshani et al.
1996; C. Delmer, unpub. Ph.D. thesis, MNHN Paris, 2005),
and possibly Phosphatherium escuilliei from the Early
Eocene of Morocco (Gheerbrant, Sudre & Cappetta, 1996;
Gheerbrant et al. 2005). Within ‘barytherioids’, GTS.1 is
intermediate in size between Barytherium grave and N.
koholense or Daouitherium (Fig. 5). Other comparisons with
Daouitherium, unknown by its upper molars, are impossible.
Daouitherium,asPhosphatherium, differs from the Dakhla
proboscidean, however, in having a distinct schmelzmuster
composed of true Hunter-Schreger bands (Tabuce, Delmer
& Gheerbrant, 2007). Phosphatherium differs in addition
in having a much smaller size (nearly four times), a
mesostyle and a premetacrista. Numidotherium koholense
and Barytherium grave are more like the specimen studied
here, with their larger size, a more advanced lophodonty,
and by the schmelzmuster composed of 3-D enamel. The
occurrence of incipient Hunter-Schreger band-like structures
in the enamel microstructure of N. koholense is peculiarly
similar to the morphology observed in the Dakhla specimen.
Moreover, the latter and N. koholense share lophs that are
less convex relative to Barytherium grave. N. koholense also
differs from Barytherium in the occurrence of a parastyle
and postentoconule; unfortunately, these characters cannot
be checked on GTS.1 due to the preservation of the specimen.
According to C. Delmer (unpub. Ph.D. thesis, MNHN Paris,
2005), N. koholense and Barytherium share the occurrence
of a postparacrista II. This structure is lacking in GTS.1,
but we consider that this trait is too variable and tenuous,
at least on N. koholense, to reject the attribution of GTS.1
to ?Numidotherium. Comparisons are also necessary with
Arcanotherium savagei, another bilophodont species from
the Late Eocene to Early Oligocene of Dor El Talha
(Court, 1995). Initially related to N. koholense, notably
based on its bilophodonty, Arcanotherium savagei was
recently excluded from the ‘barytherioid’ proboscideans by
Delmer (2009). This author considers that this taxon is
in fact more related to the bunolophodont proboscideans
such as Moeritherium and Elephantiformes. It differs from
the specimen studied here in having crenulated enamel, a
paraconule, a postprotocrista, and an incipient convolute that
pre-dates the third loph observed on the upper molars of
the elephantiforms Phiomia and Palaeomastodon. The three-
layered schmelzmuster of Arcanotherium savagei is also
reminiscent of these genera (Tabuce, Delmer & Gheerbrant,
2007) and clearly differs from that observed on GTS.1.
To conclude, the molar morphology of GTS.1, notably
its slightly convex lophs compared to Barytherium and
its enamel microstructure, suggests more affinities with
Numidotherium than with the other proboscideans. Some
critical characters that define N. koholense (parastyle and
postentoconule) need to be checked on more preserved
material. If these characters were absent, GTS.1 could
represent a new taxon. Its size (intermediate between
N. koholense and Barytherium) and its Middle/Upper Eocene
age (compared to the Ypresian age of N. koholense) could
support this hypothesis.
4. Dating and palaeoenvironment
No mention of outcropping Palaeogene deposits has
been noted in the literature concerning the Dakhla
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New Eocene vertebrates from southwestern Morocco 867
area and the Palaeogene is only mentioned in a core
sample from the offshore basin (C. Labails, unpub.
Ph.D. thesis, Univ. Brest, 2007) or limited to the
northeastern part of the Dakhla–Laayoune–Tarfaya
basins where Palaeogene deposits (Samlat Formation
in Ratschiller, 1967) overlie the Cretaceous, and consist
of marine siliceous chalk (Davison, 2005). Within
this unit, the Eocene Guerran Member (Ratschiller,
1967) is mainly characterized by clastic sediments with
calcareous and marl intercalations, probably belonging
to the clastic event of the Priabonian suggested by
Swezey (2009) for Western North Africa (clastic
dominance between marine mudstone and gypsum
or gypsiferous mudstone). The stratigraphical age of
this member must be pondered, but it seems to be
capped by a regional unconformity, which is labelled
‘end-Eocene’ in Swezey (2009) and ‘Base Oligocene
Unconformity’ in Guiraud et al. (2005). Overlying this
unconformity, the Oligocene Morcba member (in the
Samlat Formation: Ratschiller, 1967) reaches up to
300 m in thickness and consists mainly of continental
sandstone and conglomerate in the Aaiun area. This
member is possibly missing in the Dakhla area. The
Neogene is generally thin (< 100 m) and is only
exposed onshore in the western part of the basin. Sandy
limestone and oyster beds are the main lithologies
reported, as observed in the Dakhla area.
No foraminifera or nannoplankton assemblages were
detected in the sampled clastic sediments along the
observed series, excluding more precise biostratigraph-
ical correlations. However, there is no doubt that units 1
and 2 are Palaeogene in age because unit 2 is currently
dated from the late Middle Eocene (Bartonian) or Late
Eocene (Priabonian) according to its palaeontological
content and evidence as exposed below. Units 1–2
are probably the southwestern equivalent in age of
the Itgui–Gerran members of the Samlat Formation
(‘Boujdour-Aaiun’ area in Ratschiller, 1967). It is
noteworthly that this author mentioned a similar fossil
association with fossil shark teeth, coprolites, fish re-
mains and invertebrates in clastic deposits of the Gerran
Member (dated to Eocene) near Samlat Amgrash. The
majority of taxa recovered in B1 and B2 are known
elsewhere in Bartonian and Priabonian deposits, such
as the Basilosauridae which worldwide are recovered
exclusively in these stages (Uhen, 2008). Only one
taxon, Xiphodolamia serrata Adnet et al. 2009 (GTS.2,
Fig. 3b) is currently restricted to the Late Eocene period
only (Adnet et al. 2009). The other part of the fauna
either (1) shows a stratigraphical range spanning more
Palaeogene stages or (2) has not yet been recorded
in the fossil state until now. Besides this strong clue,
the modern occurrence of some taxa (e.g. presence
of Mobulidae, modern Carcharias and Carcharhinus,
very large ‘C.’ twiggsensis and G. aff. eaglesomi,
many Hemipristis curvatus), as well as the faunal
association type (abundance of Carcharhiniformes,
especially Carcharhinus, few Orectolobiforms) rather
support a Priabonian age, even if we cannot definitively
exclude a late Middle Eocene age for unit 2 also.
The age of the base of unit 2, displaying the brown
hard bone bed (with evidence of reworked early Middle
Eocene sharks and one terrestrial mammal), remains
unclear even if we suspect a Priabonian age as well,
remixing a few older elements coming from areas
nearby (e.g. ‘C.’ koerti). This peculiar deposit is not
laterally continuous and no evidence of unconformity
was detected. The local presence of early Middle Eo-
cene fossiliferous sediment is only suspected, because
of the very large number of remixed elements that
we found in situ. Further detailed sedimentological
analysis and palaeontological elements must confirm
this assumption. The difference in age between B1
and B2 is not at all obvious, as they display the same
fossil species assemblages (see Table 1). Only future,
precise analyses of fossil samples can resolve this
point. Scarce fossil vertebrates have been discovered
in unit 1 and none in unit 3 of the study area but
the age of the top of the series (unit 3) was largely
discussed in the description of the geological setting
(Section 2). This probably corresponds to the Graret
Fartet member, mapped southwest of El Argoub by
Rjimati et al. (2008) and probably equivalent to the
Aaiun Formation (Ratschiller, 1967).
The selachian association shows great similarity
with those previously published from the Qasr el-
Sagha Formation and Birket-el-Qurun, Egypt (Stromer,
1905; Case & Cappetta, 1990; C. Underwood &
D. Ward, pers. comm.), Qa’Faydat ad Dahikiya in
the Wadi Esh-Shallala Formation, Jordan (Mustafa &
Zalmout, 2002; HC, pers. observ.), or the Dash-I-Goran
Formation, Pakistan (Adnet et al. 2007). It clearly
indicates marine deposits (B1 to B2) with elements of
tropical environment (e.g. numerous Carcharhinidae,
Pristidae, Mobulidae and other Myliobatiforms), an
assumption consistent with its past geographical
position, considering that the African plate moved
northwards and anticlockwise to reach a position during
the Late Eocene of approximately 6–8
◦
latitude south of
its current position (Swezey, 2009), namely at latitude
15–18
◦
N.
The slight differences in faunal composition and
preservation observed laterally or between B1 and
B2 are probably related to local change of tidal
environment, as observed in Wadi Al-Hitan, Egypt
(Peters et al. 2009). In this last work, most of the marine
vertebrate remains occur in condensed stratigraphical
intervals and the taxonomic composition changes
despite their proximity. The proximity of an emerged
land (that probably occurred in the Reguibat shield
to the east) with terrestrial fauna is now confirmed
by the occurrence of ?Numidotherium sp., even if it
is premature to correlate the terrestrial taxa with the
marine sandstone that yielded the main fish fauna.
5. Conclusions
Middle to Late Eocene marine deposits of the Near
East (northern Egypt, eastern Jordan) have yielded
numerous fossil vertebrates, mixing marine mammals
http://journals.cambridge.org Downloaded: 29 Sep 2010 IP address: 162.38.183.2
868 S. ADNET, H. CAPPETTA & R. TABUCE
and selachians (e.g. Case & Cappetta, 1990; Gingerich,
1992; Zalmout, Mustafa & Gingerich, 2000; Mustafa
& Zalmout, 2002). Wadi Al-Hitan (‘the Whale Valley’,
northern Egypt) has been classified as a World Heritage
site since 2005 (UNESCO), partly in recognition of
its palaeontological importance for the knowledge of
cetacean evolution (see Gingerich, 2007). Extensions
of a similar depositional environment and faunal
associations of the same age towards the Atlantic coast
are obviously linked to the high sea-level sequences
(e.g. Miller et al. 2005) and a lack of barrier during this
period (Meulenkamp & Sissingh, 2003; Guiraud et al.
2005). However, the remarkable similarity of tropical
and demersal taxa (e.g. Pristidae, Carcharhinidae,
Myliobatiformes) is noteworthy and implies a large
longitudinal marine faunal exchange along the south
coast of the Tethys and towards the Eastern Atlantic
at the end of the Eocene. Concerning the selachians,
there is no doubt that forthcoming taxonomical study
will strengthen the affinities presently observed with
the Fayum and will present a considerable potential
for broad-scale stratigraphical correlation between
Western North Africa and well-dated sites in the Middle
East. This preliminary report clearly confirms the
palaeontological interest of the Dakhla deposits which
greatly justifies further effort.
Acknowledgements. The authors are indebted to G
´
erard
Barbe and the local people who helped us during the field
trips, as well as B. Marandat and A. Ramdarshan for their
thorough review of the final manuscript. An anonymous
referee is thanked for his/her helpful suggestions to greatly
improve the quality of this paper. Contribution ISE-M no.
2010-007.
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