AAptaPK1cserokmtat.docx

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Available online at www.sciencedirect.com

Palaeoworld 17 (2008) 41–46
Research paper
The first described Arsinoitherium from the upper Eocene
Aydim
Formation of Oman: Biogeographic implications
Abdul Razak Al-Sayigh a, Sobhi Nasir a,∗ , Anne S. Schulp b,
Nancy J. Stevens c
a Department of Earth Sciences, P.O. Box 36, 123-Al-Khod,
Sultan Qaboos University, Oman
b Natuurhistorisch Museum Maastricht, De Bosquetplein 6-7,
NL6211KJ Maastricht, The Netherlands
c Department of Biomedical Sciences, College of Osteopathic
Medicine, 228 Irvine Hall, Ohio University, USA
Received 4 April 2006; received in revised form 8 March 2007;
accepted 18 July 2007
Available online 3 August 2007
bstract
A new fossiliferous locality is discovered from the upper
Eocene Aydim Formation, in Dhofar, Southern Sultanate of
Oman. A left ulna of
rsinoitherium is described, and cranial and postcranial
specimens found in close proximity are referred to the same
taxon. The locality is
romising for the recovery of additional fossil specimens.
Moreover, the presence of Arsinoitherium in Oman is of
biogeographic significance; as
he Red Sea did not exist during the late Eocene, these large-

bodied animals were able to freely travel between what is now
the Arabian Peninsula
nd continental Africa.
ublished by Elsevier Ltd on behalf of Nanjing Institute of
Geology and Palaeontology, CAS.
eywords: Arsinoitherium; Oman; Biogeography; Afro-Arabia;
Aydim Formation
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. Introduction
Cenozoic fossil vertebrates from the Arabian Peninsula
onvey an important contribution to palaeontological under-
tanding, representing vertebrates that occupied a myriad of
cological niches, large and small in body size, aquatic and ter-
estrial in habitat. Yet despite the important geographic position
f Arabia with respect to other landmasses, relatively little is
nown about its early Paleogene large-bodied terrestrial mam-
alian fauna. Arabian fossils are meaningful for unraveling
he Tertiary migrational patterns of different vertebrate clades

mong the landmasses of Africa, Europe and Asia. During
he Paleocene and Eocene, paleobiogeographic reconstructions
redict broad similarities between the terrestrial vertebrates of
ontinental Africa and the Arabian Peninsula. Subsequently,
arge-scale interchange of terrestrial faunas between Arabia and
urasia took place beginning in the early Miocene via the colli-
ion of Arabia and Asia (e.g., Whybrow and Clements, 1999).
∗ Corresponding author.
E-mail address: [email protected] (S. Nasir).
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871-174X/$ – see front matter. Published by Elsevier Ltd on
behalf of Nanjing Insti
oi:10.1016/j.palwor.2007.07.005
Until recently, regional biogeographic inferences were based
argely on Arabian marine sequences, and from terrestrial faunas
ocumented in the better-known palaeontological successions
n neighboring landmasses. As evidence of Mesozoic verte-
rates has grown rapidly in recent years from continental Africa,
adagascar, and India (e.g., Krause et al., 1997, 1999, 2006;
ay et al., 1999; Whybrow and Hill, 1999; Sanders et al.,
004; Sereno et al., 2004; Durand, 2005; O’Connor et al.,
006), vertebrate fossils (dinosaur, turtle and crocodile) have
lso been recovered from the Late Campanian–Maastrichtian
l-Khod Conglomerate of the Sultanate of Oman (Schulp et al.,
000; Nolan et al., 1990; Buscalioni et al., 2004). Yet whereas

ligocene mammals and other vertebrates have been described
rom the Dhofar region of Oman (e.g., Thomas et al., 1999), the
ajority of Tertiary vertebrate research on the Arabian Peninsula
as focused upon Miocene and later deposits in Saudi Arabia
Anon, 1975; Whybrow and Hill, 1999) and the United Arab
mirates (Whybrow and Hill, 1999).
The tropical shelf deposits of Oman offer a promising
rospect for documenting intermediate stages of mammalian
volution during the Eocene. In this paper we describe an
rsinoitherium specimen collected from within the Eocene
tute of Geology and Palaeontology, CAS.
mailto:[email protected]
dx.doi.org/10.1016/j.palwor.2007.07.005
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2 A.R. Al-Sayigh et al. / P
ydim rock Formation in Dhofar region of Southern Oman
Fig. 1). Oman’s location between Egypt and India provides
n important data point, facilitating more robust comparisons
ith Arsinoitherium and other Tethyan vertebrates known from
ontinental Africa. This discovery has implications for under-
tanding past environments and biotas, filling a gap in the
Eocene
fro-Arabian fossil record.
. Stratigraphy and geological setting of the Aydim
ocality

In the eastern part of the Gulf of Aden, rifting of the Afro-
rabian plate began during the Oligocene and continued until
arly Miocene, followed by oceanization (Lepvrier et al., 2002).
fter the final regression of the Cretaceous sea, a new major
ransgressive–regressive series was deposited during the Ter-
iary in southern Oman (Platel et al., 1992). This depositional
eries involves three sedimentary groups (Platel et al., 1992;
latel and Roger, 1989; Lepvrier et al., 2002) corresponding to
re-rift, syn-rift and post-rift stages of deposition (Fig. 2): the
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Fig. 1. Location of t
world 17 (2008) 41–46
adramawt, Dhofar and Fars groups, respectively. Specimens
etailed herein were discovered within the Hadramawt Group,
brief description of which follows.
The Hadramawt Group, Paleocene (Thanetian) to late Eocene
Priabonian) in age, rests unconformably upon Cretaceous strata.
n its type area, the Hadramawt Group constitutes an exten-
ive sequence of typical carbonate shelf deposits comprising
our formations. The Umm Er Radhuma Formation (Beydoun,
964), up to 600 m thick, is a late Thanetian–middle Iler-
ian limestone with shale intercalations and chert nodules. The
atest early Lutetian–Bartonian Dammam Formation, and the
artonian–Priabonian Aydim Formation each reach more than
00 m in thickness. The thin (60 m) dolomitic and evaporitic

idal-flat deposits of the Rus Formation (late Ilerdian to Cuisian)
eveloped in between. The Aydim Formation was defined in
hofar in order to distinguish the upper Eocene limestone that
verlies the Dammam Formation (Platel et al., 1987; Roger et al.,
989, 1992; Lepvrier et al., 2002). The marine limestone of the
ydim Formation, 100–120 m thick, has very few equivalents in
he Arabian Peninsula, as much of the region was emerged dur-
he study area.
A.R. Al-Sayigh et al. / Palaeoworld 17 (2008) 41–46 43
relate
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Fig. 2. Mesozoic and Cenozoic stratigraphic units and rift-
ng the late Eocene (Platel et al., 1987). In Somalia these
deposits
orrespond to the Karkar Formation (Merla et al., 1979). The
ype-section for the Aydim Formation has been established in
he Aydim area (Platel et al., 1987; Roger et al., 1992) where
he formation consists of four members of contrasting lithol-
gy: the Heiron, Moosak, Tagut and Haluf members (Fig. 3).
he basal very thin (1–5 m) Heiron Member comprises a soft
reen marl, occasionally transitioning into beds of very fine,
reen mudstone and pink sandy siltstone (2 m). Above this is
he Moosak Member, a 20–30 m thick unit of thin-bedded beige,
ioclastic limestone, with an interval of cross-bedded yellowish
iltstone and calcarenite, rich in Nummulites. The macrofauna
Fig. 3. Lithostratigraphic log of the Aydim Formation.
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d sequences in Southern Dhofar (after Roger et al., 1989).
f these lagoonal facies comprises branched and solitary corals,
astropods, bivalves, and echinoids. The calcarenitic base of the
agut Member, some 6 m thick, is easily recognizable and con-
ains numerous foraminifera, particularly Nummulites. Above
his is a thick sequence (50 m) of thin-bedded, whitish, bioclas-
ic or micritic, generally strongly recrystallized limestone, rich
n echinoids, corals and foraminifera. The overlying Haluf Mem-
er, about 25 m thick, consists of alternating soft, white to
yellow
halky marl, and fairly indurated beige to brown biomicritic
imestone. In this area, the upper part of the Aydim Formation
has
characteristic stepped morphology. Brown algal laminations
re abundant at the top of the formation.
. Arsinoitherium: an intriguing herbivore

Arsinoitherium is an extinct mammalian taxon known pri-
arily from the late Eocene and early Oligocene of Egypt and
thiopia (e.g., Andrews, 1906; Sanders et al., 2004). The genus
s a member of the enigmatic group, the Embrythopoda, of which
he phylogenetic relationships with other early Cenozoic mam-
alian groups remain poorly understood (e.g., Tabuce et al.,
007). Once allied with hyraxes (Andrews, 1906), more recent
tudies group the embrythopods most closely with either the pro-
oscideans (Court, 1993) or the tethytheres (Gheerbrant et al.,
005). The genus Arsinoitherium was first described by Beadnell
1902) from the Jebel Qatrani Formation, Fayum Depression
f Egypt, a geologic unit comprised of ∼350 m of fluvial
andstones, mudstones, siltstones and conglomerates, and esti-
ated at 31 Ma of age (Seiffert, 2006). Subsequent discoveries
f Arsinoitherium indicate that this animal lived throughout
frica browsing in warm, humid, highly vegetated environments
Moseley, 1988; Kappelman et al., 2003). This taxon has been
econstructed as a massive, graviportal herbivore with forelimbs
dapted for strong forelimb retraction rather than adduction, fea-
ures consistent with occupying a semi-aquatic habitat in which
orelimbs provide strong forward propulsion during locomotion
Court, 1993).
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. Systematic palaeontology
lass Mammalia Linnaeus, 1758
uperorder Paenungulata Simpson, 1945
rder Embrithopoda Andrews, 1906
amily Arsinoitheriidae Andrews, 1904
enus Arsinoitherium Beadnell, 1902
Arsinoitherium sp.
.1. Material
Well-preserved partial left ulna (SQU-287). Fragmentary cra-
ial elements (SQU-289) and pedal phalanges (SQU-288) found
n close proximity (∼distance; e.g., 0.5 m) to the ulna are here
onservatively referred to the same taxon. Specimens are housed

n the collections of the Sultan Qaboos University (SQU).
.2. Description
SQU-287 is a partial left ulna, robust in form, and mea-
uring 38 cm in length (Fig. 4). The proximal portion of the
pecimen exhibits a wide semilunar notch. A large rugosity is
resent on the posterior aspect of the olecranon process, asso-
iated with strong muscle attachments in life, although what
emains of the proximal aspect of the process is badly abraded.
ortions of the facets supporting both the medial and lateral
umeral condyles are present, creating a saddle-shaped sur-
ace separated by a V-shaped notch for the articulation with
he radius. As in other Arsinoitherium specimens (e.g., Court,
993), the proximal radius does not appear to have been fused
ith the ulna. The ulnar diaphysis is flat anteriorly, but triangular
n cross-section owing to the prominent ridge running distally
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Fig. 4. Left ulna of Arsinoitherium (A) medial view; (B) an
world 17 (2008) 41–46
rom the olecranon process. The midshaft narrows, then expands
istally; however, epiphyseal articulations for the carpus are
ot preserved. SQU-287 differs from the similarly sized Paleo-
astodon in having a more robust ulnar shaft that dramatically
xpands distally. Moreover, SQU-287 also lacks the deep radial
roove running nearly the length of the diaphysis as observed in

aleomastodon. Although lacking in specific autapomorphies,
he specimen is consistent in size and morphology with other
pecimens attributed to the genus Arsinoitherium (Andrews,
906).
.3. Remarks
Currently there are two recognized species of Arsinoitherium,
. zitteli from the Fayum of Egypt, and the larger A. gigan-
eum recovered from the Chilga region of northwestern Ethiopia.
n additional species (“A. andrewsi”) has also been proposed,
ased on molar size differences within the Fayum sample (e.g.,
ankester, 1903; Andrews, 1906). However, Sanders et al.
2004) argued that the range of variation in Fayum arsinoithere
ooth size could comfortably be encompassed in a single, sexu-
lly dimorphic extant herbivore species, and relegated all Fayum
pecimens to A. zitteli. Due to the incomplete nature of SQU-
87, no attempt is made to assign it beyond the level of the genus
t this time. Approximately 30 fragmentary specimens referable
o Arsinoitherium have been recovered from the Aydim locality
o date, only three of which are identifiable to element. Impor-
antly, more complete bones remain in situ and await continued
xcavation. Hence more precise taxonomic placement of the
mani arsinoithere material awaits the recovery of additional
lements.
terior view; and (C) lateral view. Scale bar = 50 mm.

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.4. Occurrence
The specimens described herein were discovered in the upper

ocene calcarenite beds of the Moosak Member of the Aydim
ormation (Fig. 3), west of Salalah; approximately 46 km from
he Yemen border close to Aydim (Fig. 1).
. Discussion and biogeographic implications
The location of Oman between Africa and Asia undoubt-
dly made it an important portal for the global dispersal of early
enozoic mammals. During the Cretaceous, the vertebrate com-
osition of Oman included taxa reflecting clades that arose prior
o the breakup of Gondwanan landmasses (e.g., crocodyliforms:
uscalioni et al., 2004). Still attached to Africa during the Creta-
eous and Paleogene, the Arabian Peninsula was mainly a broad,
hallow, carbonate-dominated tropical shelf, similar to the South
hina Sea today. Much of the region was covered by water
ntil the late Eocene (Alsharhan and Nairn, 1997; Abed, 2005).
eparation from what is now continental Africa began during
he Oligocene and continued until the early Miocene (Beydoun,
964, 1966, 1970, 1982; Abbate et al., 1988; Bosellini, 1992;
antozzi, 1996; Fantozzi and Sgavetti, 1998; Lepvrier et al.,
002). Southern Yemen, Oman, and northern Somalia together
omprise the site of an Oligo-Miocene extension, related to rift-
ng in the Gulf of Aden (Beydoun, 1964; Lepvrier et al., 2002).
quivalent rift-related deposits are exposed along the conjugate
argins of these regions today. As such, the period of rifting and
ctive faulting in the central part of Gulf of Aden lasted about
5 Ma, starting approximately 35 Ma in the late Eocene-early
ligocene, climaxing around 5 Ma later and reaching comple-
ion with the deposition of the post-rift sediments beginning
round 18 Ma (Lepvrier et al., 2002).
The recovery of Arsinoitherium from the Aydim Formation of

outhern Oman supports the notion that during the late Eocene,
he Red Sea did not yet provide a significant barrier to prevent
nimals from freely crossing between the Arabian Peninsula and
frica. The subsiding area between Dhofar and Somalia in the
ate Eocene provided a first stage in the opening of the Gulf of
den due to rifting processes. This scenario explains the persis-
ence of marine deposits in this area, despite the general marine
egression associated with a global fall in sea level beginning at
he close of the middle Eocene (Roger et al., 1992, 1993). Until
his time, the mammalian fauna is essentially African in char-
cter (Whybrow and Hill, 1999), with subsequent increases in
sian components, such as rodents (Whybrow and Hill, 1999).
. Conclusions
Based on a fairly complete left ulna and several associ-
ted elements, the genus Arsinoitherium is reported from the
aleogene Aydim Formation of Oman. This newly discovered
ertebrate assemblage offers promise for comparisons among
aleogene Afro-Arabian faunas. Moreover, exposures in Wadi
ydim vary from bioclastic limestone to calcareous sandstone,
udstone and siltstones similar to those of the Fayum Depres-
ion of Egypt. These discoveries suggest that the Aydim locality
G
world 17 (2008) 41–46 45
n Dhofar preserves an Arabian snapshot of a littoral Fayum-like
nvironment. At almost 36 Ma, the Omani mammal is perhaps
ne of the older arsinoitheres in the world.

cknowledgments
We wish to thank Samir Hanna for his assistance with this
ork. Thanks are also due to William Sanders for his help with
dentification of the specimen. We thank Marcelo Reguero, Eric
oberts, Chen Siwei and an anonymous reviewer for construc-
ive comments.
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1989. Donnees
nouvelles sur la stratigraphie et I’histoire geologique du Dhofar
(Sultanat
d’Oman). Bull. Soc. Geol. France 8 (Serie V), 265–277.
1992. Geology of
Dhofar (Sultanate of Oman). Stratigraphy and Geodynamic
Evolution Since
the Mesozoic. Oman Ministry of Petroleum and Minerals,
Document No. 1,
252 pp.
oger, J., Sen, S., Thomas, H., Cavelier, C., Al-Sulaimani, Z.,
1993. Strati-
graphic, palaeomagnetic and palaeoenvironmental study of the
Early
Oligocene vertebrate locality of Taqah (Dhofar, Sultanate of
Oman).
Newslett. Stratigr. 28, 93–119.
anders, W., Kappelman, J., Rasmussen, D.T., 2004. New large-
bodied mam-
mals from the late Oligocene site of Chilga, Ethiopia. Acta
Palaeont. Pol.
49, 365–392.
chulp, A.S., Hanna, S., Hartman, A.F., Jagt, J.W., 2000. A Late
Cretaceous
theropod caudal vertebra from the Sultanate of Oman.
Cretaceous Res. 21,
851–856.

eiffert, E.R., 2006. Revised age estimates for the later
Paleogene mammal
faunas of Egypt and Oman. Proc. Natl. Acad. Sci. 103 (13),
5000–5005.
ereno, P.C., Wilson, J.A., Conrad, J.L., 2004. New dinosaurs
link southern
landmasses in the mid-Cretaceous. Proc. Roy. Soc. Lond.,
Series B 271,
1325–1330.
impson, G.G., 1945. The principles of classification and a
classification of
mammals. Bull. Am. Mus. Natl. Hist. 85, 1–350.
abuce, R., Delmer, C., Gheerbrant, E., 2007. Evolution of the
tooth enamel
microstructure in the earliest proboscideans (Mammalia). Zool.
J. Linn. Soc.
149 (4), 611–628.
homas, H., Roger, J., Sen, S., Pickford, M., Gheerbrant, E., Al-
Sulaimani,
Z., Al-Busaidi, S., 1999. Oligocene and Miocene terrestrial
vertebrates in
the southern Arabian Peninsula (Sultanate of Oman) and their
geodynamic
and palaeogeographic settings. In: Whybrow, P.J., Hill, A.
(Eds.), Fossil
Vertebrates of Arabia. Yale University Press, New Haven, pp.
430–442.
hybrow, P.J., Clements, D., 1999. Arabian Tertiary fauna, flora,
and locali-
ties. In: Whybrow, P.J., Hill, A. (Eds.), Fossil Vertebrates of
Arabia. Yale

University Press, New Haven, pp. 460–472.
hybrow, P.J., Hill, A., 1999. Introduction to fossil vertebrates
of Arabia, sum-
mary and overview of palaeontological research in the Emirate
of Abu Dhabi,
United Arab Emirates. In: Whybrow, P.J., Hill, A. (Eds.), Fossil
Vertebrates
of Arabia. Yale University Press, New Haven, pp. 1–4.
Aydim Formation of Oman: Biogeographic
implicationsIntroductionStratigraphy and geological setting of
the Aydim localityArsinoitherium: an intriguing
herbivoreSystematic
palaeontologyMaterialDescriptionRemarksOccurrenceDiscussio
n and biogeographic
implicationsConclusionsAcknowledgmentsReferences
Running Head: EARTH SCIENCE
1
EARTH SCIENCE
2
Earth Science
Student’s Name
Institutional Affiliation

Chapter Summary
Cenozoic fossil originates from the Arabian Peninsula. It is
used to convey an important role in paleontological
understanding. However, it represents an origin that is occupied
with a myriad of ecological niches. It is generally large in
quantity but small in body size. Cenozoic fossil is also both
aquatic and terrestrial in habitat. Although this mineral fossil is
located in a good geographical area, it is little known by many
people especially in its early paleogene. Most of the fossils in
Arabian geographical landmasses are very important. They are
mostly used in unveiling the patterns of tertiary migration of
different vertebrates amongst the Asian, Europe, and African
landmasses. The pale biographic reconstructions predict a wide
range of similarities amongst the three landmasses during the
Paleocene and Eocene. However, there was an interchange of
terrestrial faunas that took place in large scales between the
Eurasia and Arabia. These processes occurred at the beginning
of Miocene through which the landmass of Arabia colluded with
Asian landmass
Initially, the regional biographic assumptions were
made based on the Arabian marine series. However, from the
terrestrial faunas were recorded in a well-known paleontological
succession on the nearest landmasses. The Mesozoic vertebrates
have rapidly grown from different continental landmasses
including India and Africa. This acts as evidence that the
Mesozoic vertebrates have grown rapidly over the years. There
are also more discoveries of vertebrate fossils in different parts
of the world including the Sultanate of Oman and the late
Campanian of the sultanate of Oman. More discoveries of the

areas rich in the Cenozoic fossils include the United Arab
Emirates and Saudi Arabia. These are the main areas in which
this research on the Arabian Peninsula is based. The fossil
deposits of Oman are very capable for keeping the records of
intermediate phases of mammalian evolution during the early
Eocene. Therefore, the specimen for the research was collected
from the Eocene.
There is a rock formation in a region called Dhofar. This
is a place that India provides as an important data point because
it facilitates a more robust comparison of Arsinoitherrioum and
Tethyan vertebrates that are known from the continent of
Africa. The discovery of these rock formations has helped in
understanding environments in the past and fills up the gap in
the Eocene African and Arabian fossils records. The process
continued from the early Miocene and later was followed by
oceanization. During the last regression of cretaceous sea, there
was a new transigressive series of deposits which was
discovered at the tertiary time in southern Oman. The specimen
of Dhofar formation is detailed in the discoveries within the
hadramawt which briefly describes the entire process. In this
area, there is an extensive series of carbonate layers that is
deposited in different formations.
The middle limestone layer which has intercalations between
the layers and a chart of nodules is the latest formation in the
limestone. However, each layer of the limestone has more than
400m in thickness. The aydim formation was characterized by
Dhofar which distinguishes it from the upper layer of Eocene
that extensively overlies the damman formation. The marine
limestone formed with the aydim has a width ranging from 100-
120 m. However, it has an equivalent peninsula in which the
region was discovered during the limestone formation. The thin
dolomitic and evaporitic tidal flat deposits have a thickness of
60m. The arsinotherium is an extinct mammalian taxon that is
primarily known for the late Eocene and the early Oligocene of
both Ethiopia and Egypt. The genus is amongst the members of
the enigmatic group. This group has phylogenetic relationships

with the formation of early Cenozoic mammalian groups.
However, this relationship has always remained poorly
understood over the years.
Running Head: EARTH SCIENCE
1
Earth Science
Student’s Name
Institutional Affiliation

Palaeoworld 17 (2008) 41–46
Research paper
Aydim
Formation of Oman: Biogeographic implications
Abdul Razak Al-Sayigh a, Sobhi Nasir a,∗ , Anne S. Schulp b,
Nancy J. Stevens c
a Department of Earth Sciences, P.O. Box 36, 123-Al-Khod,
Sultan Qaboos University, Oman
b Natuurhistorisch Museum Maastricht, De Bosquetplein 6-7,
NL6211KJ Maastricht, The Netherlands
c Department of Biomedical Sciences, College of Osteopathic
Medicine, 228 Irvine Hall, Ohio University, USA
Received 4 April 2006; received in revised form 8 March 2007;
accepted 18 July 2007
Available online 3 August 2007
bstract
A new fossiliferous locality is discovered from the upper
Eocene Aydim Formation, in Dhofar, Southern Sultanate of
Oman. A left ulna of
rsinoitherium is described, and cranial and postcranial
specimens found in close proximity are referred to the same
taxon. The locality is
romising for the recovery of additional fossil specimens.
Moreover, the presence of Arsinoitherium in Oman is of
biogeographic significance; as

he Red Sea did not exist during the late Eocene, these large-
bodied animals were able to freely travel between what is now
the Arabian Peninsula
nd continental Africa.
ublished by Elsevier Ltd on behalf of Nanjing Institute of
Geology and Palaeontology, CAS.
eywords: Arsinoitherium; Oman; Biogeography; Afro-Arabia;
Aydim Formation
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. Introduction
Cenozoic fossil vertebrates from the Arabian Peninsula
onvey an important contribution to palaeontological under-
tanding, representing vertebrates that occupied a myriad of
cological niches, large and small in body size, aquatic and ter-
estrial in habitat. Yet despite the important geographic position
f Arabia with respect to other landmasses, relatively little is
nown about its early Paleogene large-bodied terrestrial mam-
alian fauna. Arabian fossils are meaningful for unraveling

he Tertiary migrational patterns of different vertebrate clades
mong the landmasses of Africa, Europe and Asia. During
he Paleocene and Eocene, paleobiogeographic reconstructions
redict broad similarities between the terrestrial vertebrates of
ontinental Africa and the Arabian Peninsula. Subsequently,
arge-scale interchange of terrestrial faunas between Arabia and
urasia took place beginning in the early Miocene via the colli-
ion of Arabia and Asia (e.g., Whybrow and Clements, 1999).
∗ Corresponding author.
E-mail address: [email protected] (S. Nasir).
h
(
E
p
e
A
871-174X/$ – see front matter. Published by Elsevier Ltd on
behalf of Nanjing Insti
oi:10.1016/j.palwor.2007.07.005
Until recently, regional biogeographic inferences were based
argely on Arabian marine sequences, and from terrestrial faunas
ocumented in the better-known palaeontological successions
n neighboring landmasses. As evidence of Mesozoic verte-
rates has grown rapidly in recent years from continental Africa,
adagascar, and India (e.g., Krause et al., 1997, 1999, 2006;
ay et al., 1999; Whybrow and Hill, 1999; Sanders et al.,
004; Sereno et al., 2004; Durand, 2005; O’Connor et al.,
006), vertebrate fossils (dinosaur, turtle and crocodile) have
lso been recovered from the Late Campanian–Maastrichtian
l-Khod Conglomerate of the Sultanate of Oman (Schulp et al.,

000; Nolan et al., 1990; Buscalioni et al., 2004). Yet whereas
ligocene mammals and other vertebrates have been described
rom the Dhofar region of Oman (e.g., Thomas et al., 1999), the
ajority of Tertiary vertebrate research on the Arabian Peninsula
as focused upon Miocene and later deposits in Saudi Arabia
Anon, 1975; Whybrow and Hill, 1999) and the United Arab
mirates (Whybrow and Hill, 1999).
The tropical shelf deposits of Oman offer a promising
rospect for documenting intermediate stages of mammalian
volution during the Eocene. In this paper we describe an
rsinoitherium specimen collected from within the Eocene
tute of Geology and Palaeontology, CAS.
mailto:[email protected]
dx.doi.org/10.1016/j.palwor.2007.07.005
4 alaeo
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ydim rock Formation in Dhofar region of Southern Oman
Fig. 1). Oman’s location between Egypt and India provides
n important data point, facilitating more robust comparisons
ith Arsinoitherium and other Tethyan vertebrates known from
ontinental Africa. This discovery has implications for under-
tanding past environments and biotas, filling a gap in the
Eocene
fro-Arabian fossil record.
. Stratigraphy and geological setting of the Aydim
ocality

In the eastern part of the Gulf of Aden, rifting of the Afro-
rabian plate began during the Oligocene and continued until
arly Miocene, followed by oceanization (Lepvrier et al., 2002).
fter the final regression of the Cretaceous sea, a new major
ransgressive–regressive series was deposited during the Ter-
iary in southern Oman (Platel et al., 1992). This depositional
eries involves three sedimentary groups (Platel et al., 1992;
latel and Roger, 1989; Lepvrier et al., 2002) corresponding to
re-rift, syn-rift and post-rift stages of deposition (Fig. 2): the
o
1
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Fig. 1. Location of t
world 17 (2008) 41–46
adramawt, Dhofar and Fars groups, respectively. Specimens
etailed herein were discovered within the Hadramawt Group,
brief description of which follows.
The Hadramawt Group, Paleocene (Thanetian) to late Eocene
Priabonian) in age, rests unconformably upon Cretaceous strata.
n its type area, the Hadramawt Group constitutes an exten-
ive sequence of typical carbonate shelf deposits comprising
our formations. The Umm Er Radhuma Formation (Beydoun,
964), up to 600 m thick, is a late Thanetian–middle Iler-
ian limestone with shale intercalations and chert nodules. The
atest early Lutetian–Bartonian Dammam Formation, and the
artonian–Priabonian Aydim Formation each reach more than

00 m in thickness. The thin (60 m) dolomitic and evaporitic
idal-flat deposits of the Rus Formation (late Ilerdian to Cuisian)
eveloped in between. The Aydim Formation was defined in
hofar in order to distinguish the upper Eocene limestone that
verlies the Dammam Formation (Platel et al., 1987; Roger et al.,
989, 1992; Lepvrier et al., 2002). The marine limestone of the
ydim Formation, 100–120 m thick, has very few equivalents in
he Arabian Peninsula, as much of the region was emerged dur-
he study area.
A.R. Al-Sayigh et al. / Palaeoworld 17 (2008) 41–46 43
relate
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Fig. 2. Mesozoic and Cenozoic stratigraphic units and rift-
ng the late Eocene (Platel et al., 1987). In Somalia these
deposits
orrespond to the Karkar Formation (Merla et al., 1979). The
ype-section for the Aydim Formation has been established in
he Aydim area (Platel et al., 1987; Roger et al., 1992) where
he formation consists of four members of contrasting lithol-
gy: the Heiron, Moosak, Tagut and Haluf members (Fig. 3).
he basal very thin (1–5 m) Heiron Member comprises a soft
reen marl, occasionally transitioning into beds of very fine,
reen mudstone and pink sandy siltstone (2 m). Above this is
he Moosak Member, a 20–30 m thick unit of thin-bedded beige,
ioclastic limestone, with an interval of cross-bedded yellowish
iltstone and calcarenite, rich in Nummulites. The macrofauna
Fig. 3. Lithostratigraphic log of the Aydim Formation.
c
l
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d sequences in Southern Dhofar (after Roger et al., 1989).
f these lagoonal facies comprises branched and solitary corals,
astropods, bivalves, and echinoids. The calcarenitic base of the
agut Member, some 6 m thick, is easily recognizable and con-
ains numerous foraminifera, particularly Nummulites. Above
his is a thick sequence (50 m) of thin-bedded, whitish, bioclas-
ic or micritic, generally strongly recrystallized limestone, rich
n echinoids, corals and foraminifera. The overlying Haluf Mem-
er, about 25 m thick, consists of alternating soft, white to
yellow
halky marl, and fairly indurated beige to brown biomicritic
imestone. In this area, the upper part of the Aydim Formation
has
characteristic stepped morphology. Brown algal laminations
re abundant at the top of the formation.

. Arsinoitherium: an intriguing herbivore
Arsinoitherium is an extinct mammalian taxon known pri-
arily from the late Eocene and early Oligocene of Egypt and
thiopia (e.g., Andrews, 1906; Sanders et al., 2004). The genus
s a member of the enigmatic group, the Embrythopoda, of which
he phylogenetic relationships with other early Cenozoic mam-
alian groups remain poorly understood (e.g., Tabuce et al.,
007). Once allied with hyraxes (Andrews, 1906), more recent
tudies group the embrythopods most closely with either the pro-
oscideans (Court, 1993) or the tethytheres (Gheerbrant et al.,
005). The genus Arsinoitherium was first described by Beadnell
1902) from the Jebel Qatrani Formation, Fayum Depression
f Egypt, a geologic unit comprised of ∼350 m of fluvial
andstones, mudstones, siltstones and conglomerates, and esti-
ated at 31 Ma of age (Seiffert, 2006). Subsequent discoveries
f Arsinoitherium indicate that this animal lived throughout
frica browsing in warm, humid, highly vegetated environments
Moseley, 1988; Kappelman et al., 2003). This taxon has been
econstructed as a massive, graviportal herbivore with forelimbs
dapted for strong forelimb retraction rather than adduction, fea-
ures consistent with occupying a semi-aquatic habitat in which
orelimbs provide strong forward propulsion during locomotion
Court, 1993).
4 alaeo
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. Systematic palaeontology
lass Mammalia Linnaeus, 1758
uperorder Paenungulata Simpson, 1945
rder Embrithopoda Andrews, 1906
amily Arsinoitheriidae Andrews, 1904
enus Arsinoitherium Beadnell, 1902
Arsinoitherium sp.
.1. Material
Well-preserved partial left ulna (SQU-287). Fragmentary cra-
ial elements (SQU-289) and pedal phalanges (SQU-288) found
n close proximity (∼distance; e.g., 0.5 m) to the ulna are here

onservatively referred to the same taxon. Specimens are housed
n the collections of the Sultan Qaboos University (SQU).
.2. Description
SQU-287 is a partial left ulna, robust in form, and mea-
uring 38 cm in length (Fig. 4). The proximal portion of the
pecimen exhibits a wide semilunar notch. A large rugosity is
resent on the posterior aspect of the olecranon process, asso-
iated with strong muscle attachments in life, although what
emains of the proximal aspect of the process is badly abraded.
ortions of the facets supporting both the medial and lateral
umeral condyles are present, creating a saddle-shaped sur-
ace separated by a V-shaped notch for the articulation with
he radius. As in other Arsinoitherium specimens (e.g., Court,
993), the proximal radius does not appear to have been fused
ith the ulna. The ulnar diaphysis is flat anteriorly, but triangular
n cross-section owing to the prominent ridge running distally
t
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Fig. 4. Left ulna of Arsinoitherium (A) medial view; (B) an
world 17 (2008) 41–46
rom the olecranon process. The midshaft narrows, then expands
istally; however, epiphyseal articulations for the carpus are
ot preserved. SQU-287 differs from the similarly sized Paleo-
astodon in having a more robust ulnar shaft that dramatically
xpands distally. Moreover, SQU-287 also lacks the deep radial

roove running nearly the length of the diaphysis as observed in
aleomastodon. Although lacking in specific autapomorphies,
he specimen is consistent in size and morphology with other
pecimens attributed to the genus Arsinoitherium (Andrews,
906).
.3. Remarks
Currently there are two recognized species of Arsinoitherium,
. zitteli from the Fayum of Egypt, and the larger A. gigan-
eum recovered from the Chilga region of northwestern Ethiopia.
n additional species (“A. andrewsi”) has also been proposed,
ased on molar size differences within the Fayum sample (e.g.,
ankester, 1903; Andrews, 1906). However, Sanders et al.
2004) argued that the range of variation in Fayum arsinoithere
ooth size could comfortably be encompassed in a single, sexu-
lly dimorphic extant herbivore species, and relegated all Fayum
pecimens to A. zitteli. Due to the incomplete nature of SQU-
87, no attempt is made to assign it beyond the level of the genus
t this time. Approximately 30 fragmentary specimens referable
o Arsinoitherium have been recovered from the Aydim locality
o date, only three of which are identifiable to element. Impor-
antly, more complete bones remain in situ and await continued
xcavation. Hence more precise taxonomic placement of the
mani arsinoithere material awaits the recovery of additional
lements.
terior view; and (C) lateral view. Scale bar = 50 mm.

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A.R. Al-Sayigh et al. / P
.4. Occurrence

The specimens described herein were discovered in the upper
ocene calcarenite beds of the Moosak Member of the Aydim
ormation (Fig. 3), west of Salalah; approximately 46 km from
he Yemen border close to Aydim (Fig. 1).
. Discussion and biogeographic implications
The location of Oman between Africa and Asia undoubt-
dly made it an important portal for the global dispersal of early
enozoic mammals. During the Cretaceous, the vertebrate com-
osition of Oman included taxa reflecting clades that arose prior
o the breakup of Gondwanan landmasses (e.g., crocodyliforms:
uscalioni et al., 2004). Still attached to Africa during the Creta-
eous and Paleogene, the Arabian Peninsula was mainly a broad,
hallow, carbonate-dominated tropical shelf, similar to the South
hina Sea today. Much of the region was covered by water
ntil the late Eocene (Alsharhan and Nairn, 1997; Abed, 2005).
eparation from what is now continental Africa began during
he Oligocene and continued until the early Miocene (Beydoun,
964, 1966, 1970, 1982; Abbate et al., 1988; Bosellini, 1992;
antozzi, 1996; Fantozzi and Sgavetti, 1998; Lepvrier et al.,
002). Southern Yemen, Oman, and northern Somalia together
omprise the site of an Oligo-Miocene extension, related to rift-
ng in the Gulf of Aden (Beydoun, 1964; Lepvrier et al., 2002).
quivalent rift-related deposits are exposed along the conjugate
argins of these regions today. As such, the period of rifting and
ctive faulting in the central part of Gulf of Aden lasted about
5 Ma, starting approximately 35 Ma in the late Eocene-early
ligocene, climaxing around 5 Ma later and reaching comple-
ion with the deposition of the post-rift sediments beginning
round 18 Ma (Lepvrier et al., 2002).

The recovery of Arsinoitherium from the Aydim Formation of
outhern Oman supports the notion that during the late Eocene,
he Red Sea did not yet provide a significant barrier to prevent
nimals from freely crossing between the Arabian Peninsula and
frica. The subsiding area between Dhofar and Somalia in the
ate Eocene provided a first stage in the opening of the Gulf of
den due to rifting processes. This scenario explains the persis-
ence of marine deposits in this area, despite the general marine
egression associated with a global fall in sea level beginning at
he close of the middle Eocene (Roger et al., 1992, 1993). Until
his time, the mammalian fauna is essentially African in char-
cter (Whybrow and Hill, 1999), with subsequent increases in
sian components, such as rodents (Whybrow and Hill, 1999).
. Conclusions
Based on a fairly complete left ulna and several associ-
ted elements, the genus Arsinoitherium is reported from the
aleogene Aydim Formation of Oman. This newly discovered
ertebrate assemblage offers promise for comparisons among
aleogene Afro-Arabian faunas. Moreover, exposures in Wadi
ydim vary from bioclastic limestone to calcareous sandstone,
udstone and siltstones similar to those of the Fayum Depres-
ion of Egypt. These discoveries suggest that the Aydim locality
G
world 17 (2008) 41–46 45
n Dhofar preserves an Arabian snapshot of a littoral Fayum-like
nvironment. At almost 36 Ma, the Omani mammal is perhaps
ne of the older arsinoitheres in the world.

cknowledgments
We wish to thank Samir Hanna for his assistance with this
ork. Thanks are also due to William Sanders for his help with
dentification of the specimen. We thank Marcelo Reguero, Eric
oberts, Chen Siwei and an anonymous reviewer for construc-
ive comments.
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Aydim Formation of Oman: Biogeographic
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