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The geological and faunal context of Late Miocene hominid remains from Lukeino, Kenya
C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 332 (2001) 145–152 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS. Tous droits réservés S1251-8050(01)01528-2/FLA Paléontologie / Palaeontology (Paléontologie humaine / Human Palaeontology)
The geological and faunal context of Late Miocene hominid remains from Lukeino, Kenya Martin Pickforda,∗ , Brigitte Senutb a Chaire de paléoanthropologie et de préhistoire du Collège de France, UMR 8569 et GDR 983 du CNRS, 8, rue Buffon,
75005 Paris, France
b Laboratoire de paléontologie du Muséum national d’histoire naturelle, UMR 8569 et GDR 983 du CNRS, 8, rue Buffon,
75005 Paris, France Received 16 January 2001; accepted 22 January 2001 Communicated by Yves Coppens
Abstract – Hominid fossils have been recovered from four localities within the Late Miocene Lukeino Formation, Tugen Hills, Kenya. The sediments from which the fossils came consist of fluvial and shallow lacustrine deposits. Some of the specimens are coated in a thin layer of carbonate of organic origin, suggesting deposition and preservation in slightly alkaline water, while others are riddled with superficial cracks indicating exposure at the surface prior to burial. Radioisotopic age determinations from lavas underlying and overlying the Lukeino Formation, and from crystals from the sediments themselves, indicate an age of ca 6 Ma for these hominids. 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS hominid / Late Miocene / Kenya / stratigraphy / depositional environment Résumé – Contexte géologique et faunique des restes d’hominidés du Miocène supérieur de Lukeino, Kenya. Des hominidés fossiles ont été trouvés dans quatre localités de la formation de Lukeino, du Miocène supérieur, dans les collines Tugen au Kenya. Les sédiments qui ont livré les restes fossiles consistent en des dépôts lacustres et fluviatiles. Certains spécimens sont recouverts d’une mince pellicule de carbonate d’origine organique, suggérant que le dépôt et la conservation ont eu lieu dans un milieu aquatique alcalin, tandis que d’autres présentent des craquelures à la surface qui indiquent qu’il y a eu exposition à l’air libre avant l’enfouissement. Les déterminations radioisotopiques de l’âge, faites sur les laves sous-jacentes et sus-jacentes à la formation de Lukeino et à partir des cristaux des sédiments eux-mêmes, indiquent un âge de 6 Ma pour ces hominidés. 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS hominidé / Miocène supérieur / Kenya / stratigraphie / milieu de dépôt
Version abrégée 1. Introduction 1.1. Géologie La formation de Lukeino au Kenya ( figure 1) [3, 22, 24] consiste en des sédiments entrecoupés par le sill de
dolérite Rormuch, daté de 5,65 ± 0,5 Ma ( figure 2). Ces derniers reposent sur la surface altérée du Trachyte de Kabarnet, daté de 6,2 ± 0,19 Ma, et sont recouverts par les basaltes de la formation de Kaparaina, dont l’âge est calculé à 5,65 ± 0,07 [13, 14] ( figure 2). Les dépôts sont donc vieux de 6 Ma, âge confirmé par les associations de mammifères. Des données complémentaires concernant
∗ Correspondence
and reprints. E-mail addresses: [email protected] (M. Pickford), [email protected] (B. Senut).
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l’âge de la formation de Lukeino sont indiqués dans les références [1, 2, 4, 24, 25, 27, 29–33, 35, 36]. 1.2. Localités à hominidés Quatre sites sur les 44 localités fossilifères reconnues dans la formation de Lukeino [24] ont livré des restes d’hominidés fossiles. Une molaire isolée (KNM LU 335) a été trouvée à Cheboit 1974 (00◦ 46 38,5 N : 35◦ 52 19,6 E). Ce spécimen a été au centre d’un débat intense (Andrews in [25]), [6, 9–11, 15, 23, 43, 45], qui a été résumé par Senut [37] et par Hill [12]. Les trois autres sites sont Kapcheberek (00◦ 45 03,2 N : ◦ 35 52 12,9 E), Aragai (00◦ 34 45,1 N : 35◦ 50 42,0 E) et Kapsomin (00◦ 45 10,5 N : 35◦ 52 29,9 E) ( figures 3–6). Les descriptions des hominidés fossiles sont données dans la référence [38].
2. Stratigraphie Les coupes stratigraphiques mesurées à Kapsomin, Kapcheberek et Aragai ( figures 4–6) indiquent que les hominidés proviennent de niveaux différents dans la formation de Lukeino. La découverte in situ de plusieurs spécimens, leurs positions stratigraphiques variées, les caractères de conservation des hominidés fossiles similaires à ceux du reste de la faune, ainsi que le fait que les os sont recouverts de pellicules de carbonate synsédimentaire d’origine organique excluent la possibilité que les os aient été enterrés dans les sédiments de Lukeino à une date postérieure à celle de la période de sédimentation. On en conclut donc que les 13 pièces d’hominidés fossiles se sont déposées avec les sédiments et la faune du Miocène supérieur qu’ils contiennent.
3. La faune de Lukeino La faune de Lukeino est riche et diversifiée (tableau) [5, 7, 8, 16–18, 21, 25, 26, 28, 34, 39–42, 44].
4. Le milieu de dépôt 4.1. Bassin de Lukeino La formation de Lukeino est constituée de shales lacustres dans les parties centrales du bassin et de faciès de bords de lac, de plaine alluviale et fluviatiles à la périphérie
1. Introduction 1.1. Geology and age The Lukeino Formation, which crops out extensively in the eastern foothills of the Tugen Hills, west of Lake Baringo, Kenya ( figure 1) [3, 22, 24] consists of lacustrine and fluvial sediments, which are over 130 m thick. They have been intruded by the Ror-
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du bassin. Les hominidés fossiles proviennent de dépôts de lac peu profonds à Kapsomin et de sédiments fluviatiles et de plaine alluviale à Cheboit, Kapcheberek et Aragai. 4.2. Les affleurements de Kapsomin Les dépôts de Kapsomin comprennent des alternances de shales d’eau peu profonde et de silts, avec des intercalations de concrétions carbonatées de 50 cm de diamètre et des conglomérats intraformationnels dans des chenaux peu profonds, déposés à proximité d’une falaise basse de basalte ( figure 4). La principale concentration en vertébrés fossiles provient du pied de la falaise de basalte, puissante de 2 à 3 m.
5. Taphonomie de Kapsomin De nombreux fossiles sont recouverts d’une fine pellicule d’origine bactérienne ou algaire, suggérant qu’ils sont tombés dans l’eau, où ils ont été recouverts d’algues, avant d’être ensevelis dans les sédiments. D’autres fossiles, dont la mandibule fragmentaire, présentent d’importantes craquelures à la surface de l’os, indiquant une phase de dessiccation avant enfouissement. L’assemblage faunique de Kapsomin (423 entrées au catalogue) est dominé par Aepyceros, par d’autres bovidés de taille moyenne à petite ainsi que par des Colobinae de petite taille. Des marques de morsure sur plusieurs os, dont les fémurs d’Hominidés, indiquent qu’un carnivore de grande taille a probablement été responsable de la concentration des os au pied de la falaise.
6. Paléoenvironnement à Kapsomin La prédominance des impalas dans l’association faunique de Kapsomin suggère qu’aux abords du site, il y a probablement eu un pays boisé ouvert, alors que la présence de nombreux colobes indique des concentrations denses d’arbres.
7. Conclusion La formation de Lukeino, vieille de 6 Ma, a livré 13 hominidés, récoltés dans des dépôts fluviatiles et lacustres dont l’âge est compris entre 6,2 et 5,65 Ma. Les hominidés de Lukeino sont donc les plus anciens connus de la famille.
much Dolerite Sill aged 5.625 ± 0.5 Ma ( figure 2). The outcrops occur in a north–south oriented belt in the eastern foothills of the Tugen Hills, between latitudes 0◦ 45 N and 1◦ 30 N and longitudes 35◦ 50 E to 36◦ E. The sediments repose on a weathered surface of Kabarnet Trachyte dated 6.2 ± 0.19 Ma and are capped by basalts of the Kaparaina Formation aged 5.65 ± 0.07 Ma [13, 14] ( figure 2). The sediments are ca 6 Ma old, an age confirmed by the mammal fauna,
M. Pickford, B. Senut / C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 332 (2001) 145–152
mation are to be found in [1, 2, 4, 24, 25, 27, 29–33, 35, 36]. 1.2. Hominid localities Four sites out of the 44 fossiliferous localities mapped within the Lukeino Formation [24] have yielded hominid remains. An isolated lower molar (KNM LU 335) was collected at Cheboit (00◦ 46 38.5 N: 35◦ 52 19.6 E) in 1974. The specimen has been the subject of debate (Andrews in [25]) [6, 9–11, 15, 23, 43, 45], which was summarised by Senut [37] and Hill [12]. Similarities to both chimpanzees and humans have been pointed out. The other three hominid sites are Kapcheberek (00◦ 45 03.2 N: 35◦ 52 12.9 E), Aragai (00◦ 34 45.1 N: 35◦ 50 42.0 E), and Kapsomin (00◦ 45 10.5 N: 35◦ 52 29.9 E) (all GPS readings were taken on the WGS 84 datum) ( figures 3–6). Descriptions of the hominid fossils are to be found in [38].
Figure 1. Geomorphic setting of the Lukeino Formation at the time of deposition.
2. Stratigraphy
Figure 1. Situation géomorphologique de la formation de Lukeino à l’époque du dépôt.
Stratigraphic sections measured at Kapsomin, Kapcheberek and Aragai ( figures 4–6) reveal that the hominid fossils were derived from different levels within the Lukeino Formation. At Aragai ( figure 5), a fragment of femur came from intraformational conglomerates ca 5 m above the base of the formation. At Cheboit [24] a hominid lower molar came from fluvial sands with manganese nodules near the base of the formation. The Kapsomin assemblage is from lacustrine and lake margin silts and shales from the middle part of the formation, about 100 m above its base, but 55 m below the Rormuch Sill ( figure 4), while the phalanx from Kapcheberek came from fluvial sands/silts ca 30 m above the top of the Rormuch Sill ( figure 6). The depositional settings at four separate localities, the in situ discovery of several of the specimens, their varied stratigraphic positions and the preservation characters of the hominid fossils similar to those of the rest of the fauna, and the fact that some of the material is coated in syndepositional carbonate of organic origin, exclude the possibility that the remains were buried into Lukeino sediments at a date later than the period of sedimentation. It is concluded that all Lukeino fossil hominid pieces are coeval with the sediments and the Late Miocene fauna that they contain.
Figure 2. Radioisotopic age determinations (Ma) Kabarnet, Lukeino and Kaparaina Formations. Figure 2. Datations radio-isotopiques (Ma) des formations de Kabarnet, de Lukeino et de Kaparaina.
in particular the suids and proboscideans, which are typical of this period. Additional basic data concerning the determination of the age of the Lukeino For-
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Figure 4. Stratigraphic section at Kapsomin, Tugen Hills, Kenya. Figure 3. Sketch map of Kapsomin, Tugen Hills, Kenya, showing provenience of hominid and other important fossils. 1 = proximal femur (in situ); 2 = humerus; 3 = femur lacking head (in situ); 4 = upper canine (in situ); 5 = I1 ; 6 = P4 ; 7 + 8 = left and right mandible fragments; 9 = primate dI1 ; 10 = left M3 ; 11 = right M3 ; A = galagid mandible; B = rhinocerotid skeleton (in situ); C = bovid frontal with horn cores (in situ) + colobine humerus (in situ); D = colobine mandible with three molars; E = colobine M3 ; F = colobine maxilla; G = bovid mandible. Figure 3. Carte de Kapsomin, collines Tugen, Kenya, montrant la localisation des fossiles d’hominidés et d’autres spécimens importants. 1 = fémur proximal (in situ) ; 2 = humérus ; 3 = fémur sans tête (in situ) ; 4 = canine supérieure (in situ) ; 5 = I1 ; 6 = P4 ; 7 + 8 = fragments de mandibule gauche et droite ; 9 = dI1 du primate ; 10 = M3 gauche ; 11 = M3 droite ; A = mandibule de galagidé ; B = squelette de rhinocéros (in situ) ; C = massacre de bovidé (in situ) + humérus de colobiné (in situ) ; D = mandibule avec trois molaires de colobiné ; E = M3 de colobiné ; F = maxillaire de colobiné ; G = mandibule de bovidé.
3. Lukeino fauna The fauna from the Lukeino Formation is rich and diverse, with an abundance of ruminants and proboscideans (table). Several additions to previously published faunal lists are made, based on the new collections. Primary descriptions of Lukeino faunal
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Figure 4. Coupe stratigraphique à Kapsomin, collines Tugen, Kenya.
elements are to be found in [5, 7, 8, 16–18, 21, 25, 26, 28, 34, 39–42, 44].
4. Depositional environment 4.1. Lukeino basin The Lukeino Formation contains a great variety of sedimentary facies ranging from fully lacustrine shales in the central parts of the basin to lake margin, floodplain and fluvial facies, often with intraformational conglomerates, around the periphery of the basin ( figure 1) [19, 20, 24]. Near the top of the section there are airfall and water lain tuffs. The hominid fossils came from shallow lake deposits at Kapsomin and fluvial, floodplain deposits at Cheboit, Kapcheberek and Aragai. 4.2. Kapsomin outcrops The fossiliferous deposits at Kapsomin ( figure 3) comprise intercalations of shallow water shales and silts with 50 cm diameter, plate-like, carbonate concretions and intraformational conglomerates in shal-
M. Pickford, B. Senut / C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 332 (2001) 145–152
Figure 5. Stratigraphic section at Aragai, Tugen Hills, Kenya. Figure 5. Coupe stratigraphique à Aragai, collines Tugen, Kenya.
low channels (up to 1 m thick) deposited adjacent to a low basalt cliff which the sediments eventually buried ( figure 4). The lacustrine deposits contain algal or bacterial stromatolites covering plant stems and shells of the aquatic snail Melanoides as well as some of the mammalian fossils. The main concentration of vertebrate fossils occurs at the foot of a 2–3 m basalt cliff, in green to buff and black silts containing boulders of basalt derived from the cliff ( figures 3 and 4).
5. Kapsomin taphonomy Many of the fossil specimens have a thin carbonate coating of algal or bacterial origin, suggesting that they fell into water where they were covered in algae prior to being buried by sediments. Others, including the hominid mandible fragments, are severely cracked, presumably due to desiccation prior to burial. The faunal assemblage at Kapsomin (423 catalogue entries) is dominated by Aepyceros and other medium to small bovids (tragelaphines, neotragines) and small colobines. Tooth marks on several of the bones, including the hominid femora, indicate that a large carnivore was probably responsible for concentrating the bones near the foot of the cliff. The prey size, type of damage to the bones and the Kapsomin mammalian assemblage as a whole (dominated by medium to small ruminants and colobus monkeys) suggest that
Figure 6. Stratigraphic section at Kapcheberek, Tugen Hills, Kenya. Figure 6. Coupe stratigraphique à Kapcheberek, Collines Tugen, Kenya.
the predator may well have been a leopard-like cat, a phalanx of which was found at the site.
6. Kapsomin palaeoenvironment The predominance of impalas in the Kapsomin faunal assemblage suggests that the surroundings of the site were probably open woodland, while the presence of several specimens of colobus monkeys indicate that there were denser stands of trees in the vicinity, possibly fringing the lake margin and streams that drained into the lake. The lake waters were probably alkaline, as suggested by the abundance of carbonate oncoliths and concretions of algal or bacterial origin deposited
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Table. Faunal list, Lukeino formation. Tableau. Liste faunique, formation de Lukeino. Crustacea Mollusca
Ostracoda Bivalvia Gastropoda
Pisces
Reptilia
Crocodilia
Chelonii
Squamata Aves Mammalia
Rodentia
Lagomorpha Carnivora
Proboscidea
Hyracoidea Tubulidentata Primates
Perissodactyla
Mutelidae Thiariidae Cichlidae Cyprinidae Clariidae Crocodylidae
Pelomedusidae Trionychidae Testudinidae Varanidae Ophidea Hystricidae Muridae Bathyergidae Thryonomyidae Leporidae Amphicyonidae Mustelidae Viverridae Hyaenidae Felidae Gomphotheriidae Elephantidae
Deinotheriidae Procaviidae Orycteropodidae Galagidae Cercopithecoidea Hominoidea Equidae Rhinocerotidae
Artiodactyla
Chalicotheriidae Hippopotamidae Suidae Giraffidae Bovidae
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Indet. 2 spp. Indet. Melanoides tuberculata Indet. Indet. Indet. Crocodylus lloydi Crocodylus sp. cf Euthecodon sp. Indet. Indet. Indet. Varanus sp. Indet. Indet. Hystrix sp. Saidomys sp. Indet. Thryonomys sp. Indet. Amphicyon sp. Lutrinae sp. cf Herpestes sp. Indet. Large sp. Small sp. Anancus kenyensis Primelephas gomphotheroides Stegotetrabelodon orbus Loxodonta Lukeino stage Deinotherium bozasi Indet. Orycteropus large sp. Orycteropus small sp. Indet. Colobinae Hominidae Hipparion cf sitifense Hipparion turkanense ?Diceros sp. Ceratotherium praecox Ancylotherium hennigi Hippopotamus s.l. large sp. Hippopotamus s.l. small sp. Nyanzachoerus tulotos Giraffa cf jumae Cephalophus sp. Kobus aff. porrecticornis Aepyceros sp. Neotragini Ugandax cf gautieri Tragelaphus cf spekei
M. Pickford, B. Senut / C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 332 (2001) 145–152
around plant stems, gastropod shells and some of the mammalian specimens.
7. Conclusions The Lukeino Formation, aged ca 6 Ma, has yielded 13 hominid fossils and a rich and diverse vertebrate fauna. The material occurs in fluvial and lacustrine
deposits at diverse stratigraphic levels, both below and above the Rormuch Sill. Age determinations of lavas that underlie and overlie the sediments indicate that the sediments are between 6.2 and 5.65 Ma, while volcanogenic crystals collected within it yielded an age of 6.06 Ma. The radio-isotopic age estimate is in agreement with biochronology, especially of suids and proboscideans. The Lukeino hominids are thus the oldest known members of the family.
Acknowledgements. The Kenya Palaeontology Expedition thanks the Community Museums of Kenya (E. Gitonga) for local affiliation and the Kenyan Office of the President for research permission to M.P. (OP/13/001/28C 212) and B.S. (OP/13/001/29C 139). Funding was provided by the Collège de France (Prof. Y. Coppens), the Laboratoire de paléontologie du Muséum national d’histoire naturelle, UMR 8569 (Prof. P. Taquet) and the CNRS (GDR 983 and UPR 2147). The help of Drs P. Mein (University of Lyon) and D. Gommery (CNRS) is gratefully acknowledged. The KPE is anxious to thank all the personnel of the Community Museums of Kenya for their indispensable aid. We thank our field team (K. Cheboi, N. Kiptalam, E. Kiptalam, D. Chebor, S. Chetalam and J. Chebet) and local inhabitants for logistic aid. We thank the Chief of Kipkata Location (I. Tobole) and the Sub-Chief and villagers of Rondinin for their cheerful support and efficient help. Thanks to F. Pilard for draughting the map of Kapsomin.
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[43] Ungar P.S., Walker A., Coffing K., Reanalysis of the Lukeino molar (KNM LU 335), Amer. J. Phys. Anthrop. 94 (1994) 165–173. [44] Winkler A., Systematics and biogeography of Neogene rodents from the Baringo District, Kenya, PhD thesis, Southern Methodist Univ. Dallas, 1990, pp. 1–172. [45] Wood B., Plio–Pleistocene hominins from the Baringo Region, Kenya, in: Andrews P.J., Banham P. (Eds.), Late Cenozoic Environments and Hominid Evolution: a tribute to Bill Bishop, Geological Society, London, 1999, pp. 113–122.
The geological and faunal context of Late Miocene hominid remains from Lukeino, Kenya Martin Pickforda,∗ , Brigitte Senutb a Chaire de paléoanthropologie et de préhistoire du Collège de France, UMR 8569 et GDR 983 du CNRS, 8, rue Buffon,
75005 Paris, France
b Laboratoire de paléontologie du Muséum national d’histoire naturelle, UMR 8569 et GDR 983 du CNRS, 8, rue Buffon,
75005 Paris, France Received 16 January 2001; accepted 22 January 2001 Communicated by Yves Coppens
Abstract – Hominid fossils have been recovered from four localities within the Late Miocene Lukeino Formation, Tugen Hills, Kenya. The sediments from which the fossils came consist of fluvial and shallow lacustrine deposits. Some of the specimens are coated in a thin layer of carbonate of organic origin, suggesting deposition and preservation in slightly alkaline water, while others are riddled with superficial cracks indicating exposure at the surface prior to burial. Radioisotopic age determinations from lavas underlying and overlying the Lukeino Formation, and from crystals from the sediments themselves, indicate an age of ca 6 Ma for these hominids. 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS hominid / Late Miocene / Kenya / stratigraphy / depositional environment Résumé – Contexte géologique et faunique des restes d’hominidés du Miocène supérieur de Lukeino, Kenya. Des hominidés fossiles ont été trouvés dans quatre localités de la formation de Lukeino, du Miocène supérieur, dans les collines Tugen au Kenya. Les sédiments qui ont livré les restes fossiles consistent en des dépôts lacustres et fluviatiles. Certains spécimens sont recouverts d’une mince pellicule de carbonate d’origine organique, suggérant que le dépôt et la conservation ont eu lieu dans un milieu aquatique alcalin, tandis que d’autres présentent des craquelures à la surface qui indiquent qu’il y a eu exposition à l’air libre avant l’enfouissement. Les déterminations radioisotopiques de l’âge, faites sur les laves sous-jacentes et sus-jacentes à la formation de Lukeino et à partir des cristaux des sédiments eux-mêmes, indiquent un âge de 6 Ma pour ces hominidés. 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS hominidé / Miocène supérieur / Kenya / stratigraphie / milieu de dépôt
Version abrégée 1. Introduction 1.1. Géologie La formation de Lukeino au Kenya ( figure 1) [3, 22, 24] consiste en des sédiments entrecoupés par le sill de
dolérite Rormuch, daté de 5,65 ± 0,5 Ma ( figure 2). Ces derniers reposent sur la surface altérée du Trachyte de Kabarnet, daté de 6,2 ± 0,19 Ma, et sont recouverts par les basaltes de la formation de Kaparaina, dont l’âge est calculé à 5,65 ± 0,07 [13, 14] ( figure 2). Les dépôts sont donc vieux de 6 Ma, âge confirmé par les associations de mammifères. Des données complémentaires concernant
∗ Correspondence
and reprints. E-mail addresses: [email protected] (M. Pickford), [email protected] (B. Senut).
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l’âge de la formation de Lukeino sont indiqués dans les références [1, 2, 4, 24, 25, 27, 29–33, 35, 36]. 1.2. Localités à hominidés Quatre sites sur les 44 localités fossilifères reconnues dans la formation de Lukeino [24] ont livré des restes d’hominidés fossiles. Une molaire isolée (KNM LU 335) a été trouvée à Cheboit 1974 (00◦ 46 38,5 N : 35◦ 52 19,6 E). Ce spécimen a été au centre d’un débat intense (Andrews in [25]), [6, 9–11, 15, 23, 43, 45], qui a été résumé par Senut [37] et par Hill [12]. Les trois autres sites sont Kapcheberek (00◦ 45 03,2 N : ◦ 35 52 12,9 E), Aragai (00◦ 34 45,1 N : 35◦ 50 42,0 E) et Kapsomin (00◦ 45 10,5 N : 35◦ 52 29,9 E) ( figures 3–6). Les descriptions des hominidés fossiles sont données dans la référence [38].
2. Stratigraphie Les coupes stratigraphiques mesurées à Kapsomin, Kapcheberek et Aragai ( figures 4–6) indiquent que les hominidés proviennent de niveaux différents dans la formation de Lukeino. La découverte in situ de plusieurs spécimens, leurs positions stratigraphiques variées, les caractères de conservation des hominidés fossiles similaires à ceux du reste de la faune, ainsi que le fait que les os sont recouverts de pellicules de carbonate synsédimentaire d’origine organique excluent la possibilité que les os aient été enterrés dans les sédiments de Lukeino à une date postérieure à celle de la période de sédimentation. On en conclut donc que les 13 pièces d’hominidés fossiles se sont déposées avec les sédiments et la faune du Miocène supérieur qu’ils contiennent.
3. La faune de Lukeino La faune de Lukeino est riche et diversifiée (tableau) [5, 7, 8, 16–18, 21, 25, 26, 28, 34, 39–42, 44].
4. Le milieu de dépôt 4.1. Bassin de Lukeino La formation de Lukeino est constituée de shales lacustres dans les parties centrales du bassin et de faciès de bords de lac, de plaine alluviale et fluviatiles à la périphérie
1. Introduction 1.1. Geology and age The Lukeino Formation, which crops out extensively in the eastern foothills of the Tugen Hills, west of Lake Baringo, Kenya ( figure 1) [3, 22, 24] consists of lacustrine and fluvial sediments, which are over 130 m thick. They have been intruded by the Ror-
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du bassin. Les hominidés fossiles proviennent de dépôts de lac peu profonds à Kapsomin et de sédiments fluviatiles et de plaine alluviale à Cheboit, Kapcheberek et Aragai. 4.2. Les affleurements de Kapsomin Les dépôts de Kapsomin comprennent des alternances de shales d’eau peu profonde et de silts, avec des intercalations de concrétions carbonatées de 50 cm de diamètre et des conglomérats intraformationnels dans des chenaux peu profonds, déposés à proximité d’une falaise basse de basalte ( figure 4). La principale concentration en vertébrés fossiles provient du pied de la falaise de basalte, puissante de 2 à 3 m.
5. Taphonomie de Kapsomin De nombreux fossiles sont recouverts d’une fine pellicule d’origine bactérienne ou algaire, suggérant qu’ils sont tombés dans l’eau, où ils ont été recouverts d’algues, avant d’être ensevelis dans les sédiments. D’autres fossiles, dont la mandibule fragmentaire, présentent d’importantes craquelures à la surface de l’os, indiquant une phase de dessiccation avant enfouissement. L’assemblage faunique de Kapsomin (423 entrées au catalogue) est dominé par Aepyceros, par d’autres bovidés de taille moyenne à petite ainsi que par des Colobinae de petite taille. Des marques de morsure sur plusieurs os, dont les fémurs d’Hominidés, indiquent qu’un carnivore de grande taille a probablement été responsable de la concentration des os au pied de la falaise.
6. Paléoenvironnement à Kapsomin La prédominance des impalas dans l’association faunique de Kapsomin suggère qu’aux abords du site, il y a probablement eu un pays boisé ouvert, alors que la présence de nombreux colobes indique des concentrations denses d’arbres.
7. Conclusion La formation de Lukeino, vieille de 6 Ma, a livré 13 hominidés, récoltés dans des dépôts fluviatiles et lacustres dont l’âge est compris entre 6,2 et 5,65 Ma. Les hominidés de Lukeino sont donc les plus anciens connus de la famille.
much Dolerite Sill aged 5.625 ± 0.5 Ma ( figure 2). The outcrops occur in a north–south oriented belt in the eastern foothills of the Tugen Hills, between latitudes 0◦ 45 N and 1◦ 30 N and longitudes 35◦ 50 E to 36◦ E. The sediments repose on a weathered surface of Kabarnet Trachyte dated 6.2 ± 0.19 Ma and are capped by basalts of the Kaparaina Formation aged 5.65 ± 0.07 Ma [13, 14] ( figure 2). The sediments are ca 6 Ma old, an age confirmed by the mammal fauna,
M. Pickford, B. Senut / C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 332 (2001) 145–152
mation are to be found in [1, 2, 4, 24, 25, 27, 29–33, 35, 36]. 1.2. Hominid localities Four sites out of the 44 fossiliferous localities mapped within the Lukeino Formation [24] have yielded hominid remains. An isolated lower molar (KNM LU 335) was collected at Cheboit (00◦ 46 38.5 N: 35◦ 52 19.6 E) in 1974. The specimen has been the subject of debate (Andrews in [25]) [6, 9–11, 15, 23, 43, 45], which was summarised by Senut [37] and Hill [12]. Similarities to both chimpanzees and humans have been pointed out. The other three hominid sites are Kapcheberek (00◦ 45 03.2 N: 35◦ 52 12.9 E), Aragai (00◦ 34 45.1 N: 35◦ 50 42.0 E), and Kapsomin (00◦ 45 10.5 N: 35◦ 52 29.9 E) (all GPS readings were taken on the WGS 84 datum) ( figures 3–6). Descriptions of the hominid fossils are to be found in [38].
Figure 1. Geomorphic setting of the Lukeino Formation at the time of deposition.
2. Stratigraphy
Figure 1. Situation géomorphologique de la formation de Lukeino à l’époque du dépôt.
Stratigraphic sections measured at Kapsomin, Kapcheberek and Aragai ( figures 4–6) reveal that the hominid fossils were derived from different levels within the Lukeino Formation. At Aragai ( figure 5), a fragment of femur came from intraformational conglomerates ca 5 m above the base of the formation. At Cheboit [24] a hominid lower molar came from fluvial sands with manganese nodules near the base of the formation. The Kapsomin assemblage is from lacustrine and lake margin silts and shales from the middle part of the formation, about 100 m above its base, but 55 m below the Rormuch Sill ( figure 4), while the phalanx from Kapcheberek came from fluvial sands/silts ca 30 m above the top of the Rormuch Sill ( figure 6). The depositional settings at four separate localities, the in situ discovery of several of the specimens, their varied stratigraphic positions and the preservation characters of the hominid fossils similar to those of the rest of the fauna, and the fact that some of the material is coated in syndepositional carbonate of organic origin, exclude the possibility that the remains were buried into Lukeino sediments at a date later than the period of sedimentation. It is concluded that all Lukeino fossil hominid pieces are coeval with the sediments and the Late Miocene fauna that they contain.
Figure 2. Radioisotopic age determinations (Ma) Kabarnet, Lukeino and Kaparaina Formations. Figure 2. Datations radio-isotopiques (Ma) des formations de Kabarnet, de Lukeino et de Kaparaina.
in particular the suids and proboscideans, which are typical of this period. Additional basic data concerning the determination of the age of the Lukeino For-
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Figure 4. Stratigraphic section at Kapsomin, Tugen Hills, Kenya. Figure 3. Sketch map of Kapsomin, Tugen Hills, Kenya, showing provenience of hominid and other important fossils. 1 = proximal femur (in situ); 2 = humerus; 3 = femur lacking head (in situ); 4 = upper canine (in situ); 5 = I1 ; 6 = P4 ; 7 + 8 = left and right mandible fragments; 9 = primate dI1 ; 10 = left M3 ; 11 = right M3 ; A = galagid mandible; B = rhinocerotid skeleton (in situ); C = bovid frontal with horn cores (in situ) + colobine humerus (in situ); D = colobine mandible with three molars; E = colobine M3 ; F = colobine maxilla; G = bovid mandible. Figure 3. Carte de Kapsomin, collines Tugen, Kenya, montrant la localisation des fossiles d’hominidés et d’autres spécimens importants. 1 = fémur proximal (in situ) ; 2 = humérus ; 3 = fémur sans tête (in situ) ; 4 = canine supérieure (in situ) ; 5 = I1 ; 6 = P4 ; 7 + 8 = fragments de mandibule gauche et droite ; 9 = dI1 du primate ; 10 = M3 gauche ; 11 = M3 droite ; A = mandibule de galagidé ; B = squelette de rhinocéros (in situ) ; C = massacre de bovidé (in situ) + humérus de colobiné (in situ) ; D = mandibule avec trois molaires de colobiné ; E = M3 de colobiné ; F = maxillaire de colobiné ; G = mandibule de bovidé.
3. Lukeino fauna The fauna from the Lukeino Formation is rich and diverse, with an abundance of ruminants and proboscideans (table). Several additions to previously published faunal lists are made, based on the new collections. Primary descriptions of Lukeino faunal
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Figure 4. Coupe stratigraphique à Kapsomin, collines Tugen, Kenya.
elements are to be found in [5, 7, 8, 16–18, 21, 25, 26, 28, 34, 39–42, 44].
4. Depositional environment 4.1. Lukeino basin The Lukeino Formation contains a great variety of sedimentary facies ranging from fully lacustrine shales in the central parts of the basin to lake margin, floodplain and fluvial facies, often with intraformational conglomerates, around the periphery of the basin ( figure 1) [19, 20, 24]. Near the top of the section there are airfall and water lain tuffs. The hominid fossils came from shallow lake deposits at Kapsomin and fluvial, floodplain deposits at Cheboit, Kapcheberek and Aragai. 4.2. Kapsomin outcrops The fossiliferous deposits at Kapsomin ( figure 3) comprise intercalations of shallow water shales and silts with 50 cm diameter, plate-like, carbonate concretions and intraformational conglomerates in shal-
M. Pickford, B. Senut / C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 332 (2001) 145–152
Figure 5. Stratigraphic section at Aragai, Tugen Hills, Kenya. Figure 5. Coupe stratigraphique à Aragai, collines Tugen, Kenya.
low channels (up to 1 m thick) deposited adjacent to a low basalt cliff which the sediments eventually buried ( figure 4). The lacustrine deposits contain algal or bacterial stromatolites covering plant stems and shells of the aquatic snail Melanoides as well as some of the mammalian fossils. The main concentration of vertebrate fossils occurs at the foot of a 2–3 m basalt cliff, in green to buff and black silts containing boulders of basalt derived from the cliff ( figures 3 and 4).
5. Kapsomin taphonomy Many of the fossil specimens have a thin carbonate coating of algal or bacterial origin, suggesting that they fell into water where they were covered in algae prior to being buried by sediments. Others, including the hominid mandible fragments, are severely cracked, presumably due to desiccation prior to burial. The faunal assemblage at Kapsomin (423 catalogue entries) is dominated by Aepyceros and other medium to small bovids (tragelaphines, neotragines) and small colobines. Tooth marks on several of the bones, including the hominid femora, indicate that a large carnivore was probably responsible for concentrating the bones near the foot of the cliff. The prey size, type of damage to the bones and the Kapsomin mammalian assemblage as a whole (dominated by medium to small ruminants and colobus monkeys) suggest that
Figure 6. Stratigraphic section at Kapcheberek, Tugen Hills, Kenya. Figure 6. Coupe stratigraphique à Kapcheberek, Collines Tugen, Kenya.
the predator may well have been a leopard-like cat, a phalanx of which was found at the site.
6. Kapsomin palaeoenvironment The predominance of impalas in the Kapsomin faunal assemblage suggests that the surroundings of the site were probably open woodland, while the presence of several specimens of colobus monkeys indicate that there were denser stands of trees in the vicinity, possibly fringing the lake margin and streams that drained into the lake. The lake waters were probably alkaline, as suggested by the abundance of carbonate oncoliths and concretions of algal or bacterial origin deposited
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Table. Faunal list, Lukeino formation. Tableau. Liste faunique, formation de Lukeino. Crustacea Mollusca
Ostracoda Bivalvia Gastropoda
Pisces
Reptilia
Crocodilia
Chelonii
Squamata Aves Mammalia
Rodentia
Lagomorpha Carnivora
Proboscidea
Hyracoidea Tubulidentata Primates
Perissodactyla
Mutelidae Thiariidae Cichlidae Cyprinidae Clariidae Crocodylidae
Pelomedusidae Trionychidae Testudinidae Varanidae Ophidea Hystricidae Muridae Bathyergidae Thryonomyidae Leporidae Amphicyonidae Mustelidae Viverridae Hyaenidae Felidae Gomphotheriidae Elephantidae
Deinotheriidae Procaviidae Orycteropodidae Galagidae Cercopithecoidea Hominoidea Equidae Rhinocerotidae
Artiodactyla
Chalicotheriidae Hippopotamidae Suidae Giraffidae Bovidae
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Indet. 2 spp. Indet. Melanoides tuberculata Indet. Indet. Indet. Crocodylus lloydi Crocodylus sp. cf Euthecodon sp. Indet. Indet. Indet. Varanus sp. Indet. Indet. Hystrix sp. Saidomys sp. Indet. Thryonomys sp. Indet. Amphicyon sp. Lutrinae sp. cf Herpestes sp. Indet. Large sp. Small sp. Anancus kenyensis Primelephas gomphotheroides Stegotetrabelodon orbus Loxodonta Lukeino stage Deinotherium bozasi Indet. Orycteropus large sp. Orycteropus small sp. Indet. Colobinae Hominidae Hipparion cf sitifense Hipparion turkanense ?Diceros sp. Ceratotherium praecox Ancylotherium hennigi Hippopotamus s.l. large sp. Hippopotamus s.l. small sp. Nyanzachoerus tulotos Giraffa cf jumae Cephalophus sp. Kobus aff. porrecticornis Aepyceros sp. Neotragini Ugandax cf gautieri Tragelaphus cf spekei
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around plant stems, gastropod shells and some of the mammalian specimens.
7. Conclusions The Lukeino Formation, aged ca 6 Ma, has yielded 13 hominid fossils and a rich and diverse vertebrate fauna. The material occurs in fluvial and lacustrine
deposits at diverse stratigraphic levels, both below and above the Rormuch Sill. Age determinations of lavas that underlie and overlie the sediments indicate that the sediments are between 6.2 and 5.65 Ma, while volcanogenic crystals collected within it yielded an age of 6.06 Ma. The radio-isotopic age estimate is in agreement with biochronology, especially of suids and proboscideans. The Lukeino hominids are thus the oldest known members of the family.
Acknowledgements. The Kenya Palaeontology Expedition thanks the Community Museums of Kenya (E. Gitonga) for local affiliation and the Kenyan Office of the President for research permission to M.P. (OP/13/001/28C 212) and B.S. (OP/13/001/29C 139). Funding was provided by the Collège de France (Prof. Y. Coppens), the Laboratoire de paléontologie du Muséum national d’histoire naturelle, UMR 8569 (Prof. P. Taquet) and the CNRS (GDR 983 and UPR 2147). The help of Drs P. Mein (University of Lyon) and D. Gommery (CNRS) is gratefully acknowledged. The KPE is anxious to thank all the personnel of the Community Museums of Kenya for their indispensable aid. We thank our field team (K. Cheboi, N. Kiptalam, E. Kiptalam, D. Chebor, S. Chetalam and J. Chebet) and local inhabitants for logistic aid. We thank the Chief of Kipkata Location (I. Tobole) and the Sub-Chief and villagers of Rondinin for their cheerful support and efficient help. Thanks to F. Pilard for draughting the map of Kapsomin.
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