Paleontological Reconnaisance In Yemen

by Ian Tattersall, James M. Clark, Peter Whybrow.

Yemen Update 37 (1995):21-24

During September and October, 1991, a team representing the American Museum of Natural History, New York City, the British Museum (Natural History), London, and the Ministry of Oil and Mineral Resources of the Republic of Yemen, undertook a vertebrate paleontological survey of several areas in Yemen. Field personnel included the authors of this report, plus Dr Mustafaal-Saruri of the Minerals Exploration Board, Aden Office, Dr Mustafa Abdul Latif and Mr Mohammed Abdul Hamid, of the Ministry of Oil and Mineral Resources, Minerals Sector, Sanaa, and other Ministry staff as assigned. The fieldwork was sponsored and facilitated by His Excellency Ali Gabr Alawi, Deputy Minister of Oil and Mineral Resources of the Republic of Yemen and Chairman of the Minerals Exploration Board, and Mr Othman Noman, Vice-Chairman of the Minerals Exploration Board.

Our field research was initiated following the discovery by Mr Jamil Saif Raweh Al Dobai of a well-preserved fossil frog impression at the locality of Ar Rhyashia, southeast of Sanaa (see accompanying map). The Ar Rhyashia site represents a freshwater interbed in the Yemen Volcanic Series, the principal stratigraphic unit of north Yemen, and the anuran discovery was the first significant vertebrate fossil to be found in this stratigraphic context. The initial plan was simply to investigate Ar Rhyashia and the surrounding region in detail, and to collect at fossiliferouslocalities; but by the time that fieldwork commenced the union of the former YAR and PDRY had opened up new paleontological prospects in the southern part of the combined Republic of Yemen. Accordingly, several stratigraphic contexts of potential interest were identified in southern Yemen, and prospection of these was added to the objectives of an extended expedition.

Itinerary and Stratigraphic Contexts

The expedition's itinerary is shown in the map, and covered a wide area in both northern and southern Yemen. Our initial prospections were undertaken, as planned, in the region of Ar Rhyashia. Three freshwater interbeds were identified in the Yemen Volcanics at Ar Rhyashia: all were limey shales partly metamorphosed by overlying basalt flows. A layer was identified that contained numerous anuran and other impressions, and some ten complete anuran skeletons and one fish were collected in it. The Ar Rhyashia interbeds lie stratigraphically high in the Yemen Volcanic Series, and we estimate them to be of earliest Miocene age, upwards of 20 million years old. Samples of an underlying basalt we recollected for potential argon-argon dating, but proved contaminated. More extensive collecting and prospection at Ar Rhyashia were planned than were eventually achieved, since problems with unfriendly local elements rapidly curtailed our activities in the area.

The main object of our prospections was to locate Tertiary and Quaternary mammal sites, which previous reconnaissances had failed to identify in northern Yemen. We thus shifted our attention southwards, since several early Tertiary sedimentary basins had been mapped along the southern Yemen coast between Aden and Mukallah. The first region to be prospected was the Hamarah Basin (no. 4 on the map), approximately 300 km northeast of Aden. Here rocks of the Shihr Group are exposed: well-cemented red Oligocene sandstones that unconformably overlie mildly gypsiferous and less well consolidated yellow sandstones of Eocene age (Hadramawt Group). Fossil worm casts were identified in the Oligocene sediments, but no bone was found.

Next prospected were rocks exposed in the southeastern and southwestern parts of the Mayfa'ah Depression. In the former area, yellow playa clastics of the middle Eocene HabshiyaFormation near Al Qurayn (no. 5 on the map) produced plant fossils and invertebrates, plus some scraps of vertebrate bone. In the latter, the red sandstones of the Miocene Irqah Formation, and underlying yellowish sandstones probably belonging to the Oligocene Fuwwah Formation, both proved unfossiliferous.

Rocks of the Wadi Fuwwah (no. 6 on the map)and of the nearby Wadi Ambakhah, near Mukallah, included poor exposures of the Habshiya Formation. These were unfossiliferous, as were the Oligocene and possibly earlier sandstones and siltstones of the Wadi Brum (no. 7 on the map), 10 km to the southwest of Mukallah, and the lagoonal marly shales of the Wadi Buwaysh (no. 8 on the map),20 km to its northeast. Similarly unproductive were the greennearshore shales of the Paleocene Umm Ar Radamah Formation (no. 9 on the map), about 100 km northeast of Mukallah, and deposits of the Shihr Group in the Wadi Huwayrah (no. 10 on the map, page 13), 50 km from Mukallah. The same disappointing situation prevailed in the Shihr Group deposits exposed near 'Irs (no. 11 on the map) in the Wadi Haj'r, and in the Jurassic Kohlan Sandstones of the same region.

More fossiliferous were the rocks exposed in the Wadi Kaninah, where the middle Eocene Habshiya Formation is well exposed. These are near shore marine sands and sandy silts with ahematitic surface litter and numerous fossil wood fragments and other plant fossils. Mollusks and gastropods were found here as well as wood. To the east of Kaninah village (no. 12 on the map), further exposures of the poorly consolidated yellow near shore sands of the Habshiya Formation, stratigraphically above the principal fossil wood zone, yielded Turritella and oyster fossils, plus some more fossil wood. These rocks also produced our first discoveries of significant vertebrate bone in this stratigraphic context, including parts ofteleosts, rays, chelonians, cetaceans and sirenians.

Everywhere they were exposed in the Mayfa'ah trough, sediments of the early to middle Eocene Jiza and Rus Formations proved unfossiliferous. However, in this area the Kaninah-Jizwal sequence (no. 13 on the map) of the later HabshiyaFormation did produce some plant and invertebrate fossils. In the Wadi Haj'r, limestones of the Shuqrah Formation (early late Jurassic)are exposed above the Kohlan sandstones. Near Jabal Zulma Ba-Thalab(no. 14 on the map), 40 km to the north of the main Aden-Mukallahroad, a partial crocodylian skeleton was found. Unfortunately, this significant find was embedded in a block that had fallen from high on a cliff face, so extensive prospection of the deposits from which ithad come was not practicable.

Fossils Recovered (by locality)

1. Zulma Ba-Thalab, southern Yemen.

At this locality in the Wadi Haj'r, some40 km to the north of the Aden-Mukallah road, a crocodylian fossilwas found in limestones of the early late Jurassic Shuqrah Formation. This 165 million year-old partial skeleton consists of parts of the posterior postcranium of a teleosaurid thalattosuchian crocodile and includes the diagnostic osteoderms. It is the oldest vertebrate fossil currently known from the entire Arabian peninsula, and is chiefly of importance on this account. This marine crocodile, estimated to have been about three meters long when alive, belongs to a family which is common in early late Jurassic marine deposits worldwide. The block of limestone in which it was found embedded has been recovered and transported to the premises of the Minerals Exploration Board in Aden, where it awaits study and installation in a proposed museum.

2. Ar Rhyashia, northern Yemen.

At Ar Rhyashia, approximately 23 km south of Rada', limey and partly metamorphosed shaley freshwater interbeds in the Yemen Vocanic Series have yielded a fauna consisting principally of well-preserved anuran skeleton impressions. This is the first significant vertebrate fauna to have been discovered anywhere in the Yemen Volcanics, the principal stratigraphic unit of northern Yemen. Circumstances unfortunately prevented detailed mapping of the Ar Rhyashia localities, and basalt samples collected for argon-dating were, as noted, contaminated. However, the Ar Rhyashiyainter beds lie stratigraphically quite high in the Volcanic Series, and are estimated to be of earliest Miocene age. Some ten anuran specimens in an excellent state of preservation have been collected, and have been submitted to Ms Amy Henrici of the Carnegie Museum of Natural History for detailed study. This study has not as yet been completed, but preliminary analysis suggests that all specimens belong to the same frog species, an undescribed member of Pipidae that is apparently closely related to species of the living genus Xenopus. One fish skeleton was also collected, and is currently under study by Dr John Maisey of the American Museum of Natural History. It appears to be a neopterygian amiid or a teleost of undetermined affinity; more certain identification must await further study.

3. Habshiya Formation, southern Yemen.

Rocks of the Paleocene through Eocene Hadramawt Group are widely if not extensively exposed in a series of depressions that lie perpendicular to the shoreline in the Shawba and Hadramawt Governorates of southern Yemen. Of these rocks, only those of the middle Eocene Habshiya Formation proved at all fossiliferous, and then only at two localities among the many that were prospected. Near Al Qurayn, in the southeastern part of the Mayfa'ah Depression, Habshiya exposures yielded some plant and invertebrate fossils, but only scraps of vertebrate bone. More important was a locality east of Kaninah village, which lies in the Wadi Kaninah, approximately 25km north of Jawl Ba-Hawa, the principal town of the Wadi Haj'r. Here a coarse yellow unconsolidated sandstone of nearshore facies produced plant, invertebrate and vertebrate fossils.

Plant fossils comprise the first fossil flora known from southern Yemen, and include internal casts of fruits of a genus cf. Anona (custard apples or magnolids), fruits that may be in the waterlily family, and a fruit possibly in theCucurbitacea (cucumbers), as well as numerous fragments of fossil wood. Together these fossils indicate the proximity of a tropical rainforest, suggesting an onshore environment similar to that inferred from isolated mammal teeth for the late Eocene of southwestern Oman, and equivalent to the renowned Eocene-Oligocene Fayum fauna and flora of Egypt.

Invertebrates include oysters and Turritella, and a substantial list of vertebrates includes the teeth of a ray (possibly Myliobatis), cranial and dental elements of large teleost fish, chelonian bones, dugong ribs and scapula, and a cetacean rib. This fauna includes the first fossil mammals known from anywhere in Yemen. All elements of the flora and fauna agree with the notion that this facies of the HabshiyaFormation was deposited in a nearshore marine environment that interfaced with a tropical rainforest environment onshore via a marshy, lagoonal shoreline.

Summary and Prospects

The reconnaisance reported here has produced the oldest vertebrate fossil yet known from the Arabian peninsula, the only vertebrate fauna yet known from deposits associated with the Tertiary Yemen Volcanic Series, the first mammal fossils known from Yemen, and the first fossil flora to be reported from southern Yemen. It has also pointed towards the best prospects for future paleontological prospection in Yemen by mammalian paleontologists. Our surveys indicate that onshore and near shore deposits of earlier Tertiary age become thicker and better-exposed as one moves northeast along the southern Yemen shoreline, toward Oman. Given that nearshore marine deposits in the area of Oman that borders on Yemen has recently started to produce mammal teeth that are comparable with those found in the remarkable late Eocene to Oligocene deposits of Egypt's Fayum, we would predict that the best prospects that Yemen offers for significant finds in Paleogene mammalian paleontology lie further to the east than we were able to explore on this occasion, in the area between Ash Shihr and the frontier with Oman. This area is remote, little visited, logistically difficult, and geologically not well known; but extrapolation of the observations we made along the coast to the southwest of Ash Shihr suggests that exploration of this region would be highly worthwhile.

Acknowledgments

The authors wish to thank the National Geographic Society for its generous financial support of the research reported here. We would also like to record our gratitude to Deputy Minister Ali Gabr Alawi and Deputy Chairman Othman Noman for their enthusiastic sponsorship and facilitation of this work. Our other colleagues at the Ministry of Oil and Mineral Resources, especially Dr Mustafa As-Saruri, but also Mr Mohamed Mukrid, Mr Mohammed Abdul Hamid, Dr Mustafa Abdul Latif, and Dr Iqbal Al Jailani, are also deserving of our warmest thanks, as is Dr Hamed El-Nakhal, of Sanaa University, whose advice and support have been invaluable throughout our researches in Yemen. And yet again we wish to register our appreciation to the American Institute for Yemeni Studies and to Dr Jeffrey Meissner for providing logistical support and invaluable advice.

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