New stem giraffoid ruminants from the early and middle Miocene of Namibia Jorge MORALES Departamento de Paleobiologia, Museo Nacional de Ciencias Naturales, CSIC, José Gutierrez Abascal 2, E-28006, Madrid (Spain) Dolores SORIA Departamento de Paleobiologia, Museo Nacional de Ciencias Naturales, CSIC, José Gutierrez Abascal 2, E-28006, Madrid (Spain) Martin PICKFORD Chaire de Paléoanthropologie et de Préhistoire, Collège de France, 11 place Marcelin-Berthelot, F-75005, Paris (France) Laboratoire de Paléontologie, UMR 8569 du CNRS, Muséum national d'Histoire naturelle 8 rue de Button, F-75231 Paris cedex 05 (France) Morales J., Soria D. & Pickford M. 1999. — New stem giraffoid ruminants from the early and middle Miocene of Namibia. Geodiversitas (21)2: 229-253. ABSTRACT At the early and middle Miocene localities of the Sperrgebiet, Namibia, new material of climacoceratid tuminants have been collected recently. From Elisabethfeld we describe new material belonging to Propalaeoryx austroafri- canus Stromer, 1926, together with a new genus and species of climacocera­ tid Sperrgebietomeryx wardi n. gen., n. sp., a species without frontal appendages close to Propalaeoryx and to primitive early Miocene European ruminants such as Andegameryx. From the locality of Arrisdrift, we define another new genus and species of climacoceratid with frontal appendages, KEYWORDS Ruminantia, Orangemeryx bendey n. gen., n. sp., characterized by its complex tined frontal Giraffoidea, apophyses. Comparison of the dentition and postcranial skeleton of this Climacoceratidae, genus and those of Sperrgebietomeryx suggests a close phylogenetic relation­ Miocene, Namibia. ships between them. 1999 • 21 (2) 229 Morales J., Soria D. & Pickford M. RESUME Nouveaux ruminants giraffoïdes du Miocène ancien et moyen de Namibie. Dans les localités du Miocène inférieur et moyen de la Sperrgebiet en Namibie, de nouveaux restes de ruminants Climacoceratidae ont été récem­ ment técoltés. Un nouveau matériel provenant d'Elisabethfeld appartenant à Propalaeoryx austroafricanus Stromer, 1926 est décrit, ainsi qu'un nouveau gente et une nouvelle espèce du Climacocetatidae, Sperrgebietomeryx wardi n. gen., n. sp., espèce ne possédant pas d'appendices frontaux, proche de Propalaeoryx et des ruminants primitifs du Miocène inférieur européen, comme Andegameryx. A Arrisdrift, nous décrivons un autte genre et une autte espèce de Climacoceratidae avec des appendices frontaux, Orangemeryx MOTS CLÉS Ruminantia, bendeyi, qui se catactérise par ses apophyses frontales complexes. Les compa­ Giraffoidea, raisons entte la dentition et le squelette postctânien de ce genre et de ceux de Climacoceratidae, Sperrgebietomeryx suggètent une proche parenté phylogénétique entre les Miocène, Namibie. deux. INTRODUCTION This is the second tepott on the ruminants of the early and middle Miocene of Namibia collected by the Namibia Palaeontology Expedition. The first paper dealt with the small bovid Namibiomeryx senuti Motales et ai, 1995. In this article we describe the giraffoids from the same region. Two new genera of giraffoids recovered from the sites of Elisabethfeld and Arrisdrift in southern Namibia (Fig. 1) reveal a great deal about the origins of this superfamily of ruminants. The new climacoceratid giraffoids lack frontal apo­ physes, and occut in the early Miocene deposits at Elisabethfeld and other sites in the northern part of the Sperrgebiet. Sperrgebietomeryx is clo­ sely related to primitive late Oligocène European ruminants such as Andegameryx Ginsburg et ai, 1994, and lies close to the root of the group which subsequently developed apophyses, the Giraffoidea. Sperrgebietomeryx occurs in the same strata as another sperrgebietometycine, the genus Propalaeoryx Stromer, 1926. Basal middle Miocene deposits at Arrisdrift have yielded abundant remains of a new genus of cli­ FIG. 1. — Geographical location of Arrisdrift (early middle macoceratid, Orangemeryx, a climacoceratine Miocene) and Langental and Elisabethfeld (early Miocene) in the Sperrgebiet, southern Namibia. 230 GEODIVERSITAS • 1999 • 21 (2) Miocene giralioids from Namibia with fined apophyses. Examination of the skull removed, principally by sand-blasting, since the and postcranial skeleton of this genus and those photographs had been taken two months pre­ of Sperrgebietomeryx suggests that the Arrisdrift viously. A mandible with the cheekteeth in place species may well be the descendant of the in June had eroded so that only the ventral mar­ Elisabethfeld one. gin of the jaw was left in August. The transition from primitive pecorans to climaco- The associated fauna indicates that the ceratids with apophyses thus appears to have Elisabethfeld skeleton is of early Miocene age. occurred in Africa subsequent to colonization of The site correlates broadly with the localities of this continent by pecorans from Eurasia. Songhor and Koru, Kenya, and is thus interpret­ ed to be about 20-21 Ma old (Faunal Set I of Pickford 1981). GEOLOGICAL SETTING ARRISDRIFT ELISABETHFELD The site of Arrisdrift occurs in a lateral channel The early Miocene site of Elisabethfeld (Stromer of the Proto-Orange located about 1 km east of 1926) occupies one of a series of pre-Miocene the present-day channel of the river. Fossiliferous valleys which used to drain into the Atlantic sediments lie at an altitude of about 41 m above Ocean from the region of the present-day Namib mean sea-level, infilling a low channel carved Sand Sea. As a result of a worldwide rise in sea- into the Gariep Group of Late Proterozoic age. level during the early Miocene the transient sedi­ The channel is filled with a complex cut-and-fill ments in the valleys stopped moving, and further sequence of sediments ranging in grain size from sedimentation occurred in the drowned valleys. conglomerates to clays, the latter representing At Elisabethfeld, fine-grained red limey silts clay-drapes deposited during periods when the accumulated in a plain that lay between the Arrisdrift channel was cut off from the main Grillental and one of its southern tributaries river. During periods of high water, the channel which had cut through Proterozoic rocks. These would be active, so that numerous scour and fill red silts, which are often overprinted with pedo- episodes occurred, and can be seen in superposi­ genic features, were incised and then buried by tion in the excavation. green silts, sands and conglomerates. These flu- During periods of low water level, the channel viatile beds are overlain by a fine-grained palaeo- was effectively isolated from the main stream and dune sequence (Greenman 1966, 1970; Corbett would have been a quiet pool of water. This 1989). Unconformably overlying the early channel lay close to sea-level, as indicated by the Miocene sediments is a two metre thick traverti­ presence of serpulid worm tubes in abundance, ne which has invaded the upper portion of the even to the extent of forming serpulid reefs. aeolianite. Fragments of this travertine have been Today these invertebrates live in brackish water incorporated into a younger set of aeolianites in estuarine settings. There can be little doubt which crop out extensively in the area, often that at the beginning of the Middle Miocene, filling palaeo-valleys cut into the early Miocene some 17.5-17 Ma ago, sea-level was some 41 m sediments. above present day levels. At the base of one of the green, pebbly-sand The site of Arrisdrift, like the earlier ones in the channel infillings cropping out as a low cliff and northern Sperrgebiet, owes its formation to the immediately overlying the basal red limey silts, world-wide rise in sea-level that occurred at the the partial skeleton of a ruminant was observed end of the early Miocene, which caused the by Drs J. Ward and I. Corbett in June, 1993. back-ponding of sediments within the Proto- The specimen was photographed and left in situ Orange valley. The difference in ages of the fossil for later excavation. In August, 1993, Drs sites in the northern and southern Sperrgebiet M. Pickford and B. Senut visited the site with indicate that the rise in sea-level was relatively J. Ward and excavated the skeleton. It was evi­ slow, the highest stand being reached some 2- dent that at least 1 cm of sediment had been 3 Ma later than the onset of rising sea-levels. GEODIVERSITAS • 1999 • 21 (2) 231 Morales J., Soria D. 6V. Pickford M. FIG. 2. — Atlas of Sperrgebietomeryx wardin. gen., n. sp. (EF 37'92); A, dorsal view; B, ventral view. Scale bar: 20 mm. This scenario is confirmed by the discovery of DIAGNOSIS. — Ruminants of medium to large size early Miocene mammals at Auchas, another chatacterised by the tendency - in relation to other ruminants of the same age - for elongation of the Proto-Orange deposit, in sediments 32-37 m neck (including the atlas) and limbs. Distal epiphysis above present-day mean sea-level, or some 10 m of the metatatsal with open gully. Dentition with a lower than the deposits at Arrisdrift. cleat hypsodont tendency. Palaeomeryx fold in lower By the time that sea-levels dropped again later in molars moderate or suppressed, hypoconid isolated the middle Miocene, the Proto-Orange river had and lobe of m3 simple. abandoned some of its meander loops and was following a less sinuous course towards the coast. When incision occurred following lowering of Sl'ERRGEBIETOMERYCINAE n. subfam. base-levels, the early and middle Miocene sedi­ ments deposited in many of the abandoned loops TYPF. GENUS. — Sperrgebietomeryx n. gen. wete left high and dry. DIAGNOSIS. — Climacoceratidae without ctanial pro- The fauna associated with Omngemeryx is early tubetances. Cranium with wide frontals, sagittal crest middle Miocene in age, correlating closely with and nuchals strongly defined. Dentition moderately European zone MN4 (De Bruijn et al. 1992) hypsodont. Premolar series elongate. Lower molars with strong stylids and moderate paleometyx fold. and with the sites of Buluk and Maboko in Upper molats with very strong styles and late union of Kenya, assigned to Faunal Set PHI (Pickford the intetnal lobes with the outet wall. 1981). It is probably about 17.5-17 Ma (Pickford 1994).