Olga Otero

A new hominid from the Upper Miocene of Chad, Central Africa

The search for the earliest fossil evidence of the human lineage has been concentrated in East Africa. Here we report the discovery of six hominid specimens from Chad, central Africa, 2,500 km from the East African Rift Valley. The fossils include a nearly complete cranium and fragmentary lower jaws. The associated fauna suggest the fossils are between 6 and 7 million years old. The fossils display a unique mosaic of primitive and derived characters, and constitute a new genus and species of hominid. The distance from the Rift Valley, and the great antiquity of the fossils, suggest that the earliest members of the hominid clade were more widely distributed than has been thought, and that the divergence between the human and chimpanzee lineages was earlier than indicated by most molecular studies.

Geology and palaeontology of the Upper Miocene Toros-Menalla hominid locality, Chad

All six known specimens of the early hominid Sahelanthropus tchadensis come from Toros-Menalla site 266 (TM 266), a single locality in the Djurab Desert, northern Chad, central Africa. Here we present a preliminary analysis of the palaeontological and palaeoecological context of these finds. The rich fauna from TM 266 includes a significant aquatic component such as fish, crocodiles and amphibious mammals, alongside animals associated with gallery forest and savannah, such as primates, rodents, elephants, equids and bovids. The fauna suggests a biochronological age between 6 and 7 million years. Taken together with the sedimentological evidence, the fauna suggests that S. tchadensis lived close to a lake, but not far from a sandy desert, perhaps the oldest record of desert conditions in the Neogene of northern central Africa.

Phosphate Lu–Hf geochronology

Abstract Igneous, metamorphic and biogenic apatite contains Lu and Hf in proportions that make this mineral suitable for dating by the 176Lu–176Hf method. We present a new method for separation of Lu and Hf from apatite that involves a single extraction column step for Hf and a second exchange column step for Lu. This procedure allows rapid sample processing prior to analysis by MC-ICP-MS. Results from the igneous Gardiner, Skaergaard and Khibina Intrusions indicate that the closure temperature for the Lu–Hf isotopic system in apatite is relatively high. The Lu–Hf isochron age of ∼60 Ma for the Skaergaard Intrusion, East Greenland, is older than the generally accepted emplacement age, but does not appear to be a product of mixing. A centimeter-sized apatite from the Otter Lake area, Grenvillian Province, yields high and variable 176Lu/177Hf ratios showing that metamorphic apatite may, in some cases, allow for mono-mineral dating. The most important application of the method is undoubtedly its potential use for dating sedimentary formations. Although we find biogenic apatite in porous matrix highly susceptible to post-depositional resetting of the Lu–Hf isotopic system, the preservation of a near-depositional age for a shark tooth from the impermeable London Clay and recent work on crystalline authigenic phosphorites [Earth Planet. Sci. Lett. 201 (2002) 203] show the Lu–Hf system to be a promising tool for direct dating of sedimentary formations.

New Oligocene vertebrate localities from Northern Kenya (Turkana basin)

STÉPHANE DUCROCQ,*,1 JEAN-RENAUD BOISSERIE,1 JEAN-JACQUES TIERCELIN,2 CYRILLE DELMER,3 GÉRALDINE GARCIA,1 MANTHI FREDERICK KYALO,4 MEAVE G. LEAKEY,5 LAURENT MARIVAUX,6 OLGA OTERO,1 STÉPHANE PEIGNÉ,7 PASCAL TASSY,7 and FABRICE LIHOREAU6; 1IPHEP, UMR CNRS 6046, Faculté des Sciences de Poitiers, 40 avenue du Recteur Pineau, F-86022 Poitiers cedex, France, stephane.ducrocq@univ-poitiers.fr, geraldine.garcia@univ-poitiers.fr, olga.otero@univ-poitiers.fr; jean.renaud.boisserie@univ-poititers.fr; 2UMR CNRS 6118 Géosciences Rennes, Université de Rennes 1, Campus de Beaulieu, Bât. 15, F-35042 Rennes cedex, France, jean-jacques.tiercelin@ univ-rennes1.fr; 3Palaeontology Department, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom; 4Palaeontology Section, NMK HQ Museum Hill, P.O. Box 40658, 00100, Nairobi, Kenya, fkmanthi@museums.or.ke; 5Stony Brook University, Turkana Basin Institute, N511 Social and Behavioral Sciences, Stony Brook, New York 11794-4364, U.S.A, meave.leakey@stonybrook.edu; 6ISEM, UMR CNRS 5554, Université Montpellier II, c.c. 064, Place Eugène Bataillon, F-34095 Montpellier cedex 5, France, Laurent.Marivaux@univ-montp2.fr, fabrice.lihoreau@univ-montp2.fr; 7UMR CNRS 7207, Muséum national d’Histoire naturelle, 8, rue Buffon CP 38, F-75231 Paris cedex 05, France, peigne@mnhn.fr; ptassy@mnhn.fr

Freshwater fish δ18O indicates a Messinian change of the precipitation regime in Central Africa

Tracking terrestrial environmental change throughout the Neogene is a challenge, notably in areas such as Central Africa where the few available data consist of a few vertebrate fossil assemblages. Here we aim to quantify the evolution of the δ 18 O of the main water body between four Neogene wet episodes in the Chad basin, ranging from the Late Miocene to the early Pliocene. The δ 18 O of the open water body was inferred from oxygen isotope measurements of phosphate in the apatite of open water fish tooth enamel. The more open the fish habitat, the lower the δ 18 O, as revealed by the teeth of the large tiger fish ( Hydrocynus ) sampled in the four available Chadian vertebrate fossiliferous areas, i.e., Toros-Menalla (anthracotherid unit), Kossom Bougoudi, Kolle, and Koro Toro, all located in the Djurab Desert (Chad) and dated at 7.04 ± 0.18 Ma, 5.26 ± 0.23 Ma, 3.96 ± 0.48 Ma, and 3.58 ± 0.27 Ma, respectively. The δ 18 O values increased by ∼2‰ between the two sites having ages that bracket the Messinian time period, and there was a slight increase of ∼0.6‰ difference between the three Pliocene sites. These results reflect unambiguously change in the water cycle in Central Africa during the late Neogene, interpreted as a constant drying trend between the four successive wet episodes registered in the Djurab and a shift during the Messinian.

Cretaceous characiform fishes (Teleostei: Ostariophysi) from Northern Tethys: description of new material from the Maastrichtian of Provence (Southern France) and palaeobiogeographical implications

Abstract The order Characiformes (Teleostei: Otophysi) is one of the most diverse freshwater fish groups. It contains around 1400 living species in South and Central America and Africa. Their fossil record starts in the Cretaceous on both continents and also in Europe. Here, we describe and discuss the occurrences of new characiform fish teeth from Provence (Maastrichtian, S. France). Five morphological types are recognized. They belong to possibly three different taxa, and they are regarded as Characiformes indet. However, two of them have resemblances to alestin fishes and could be related to the African family Alestidae. The characiform fishes from Provence are among the oldest known in Europe, together with a freshwater characiform fish occurring in Romania, and the recently described marine fish Sorbinicharax from Italy. The biogeographical history of characiform fishes has been intensively discussed during the last three decades. The group is generally accepted to be Gondwanan and its diversification linked with the break-up of this continent, with two main scenarios depending on whether the group is archaeo- or telolimnic. Some authors also propose a Pangaean origin. The recent discoveries of Sorbinicharax and of the fossils from Provence change our view on the Cretaceous characiform diversity and their early ecology, and they also enable us to re-evaluate the proposed biogeographical scenarios, reinforcing the hypothesis of the telolimny of the group.

A NEW CLAROTEID CATFISH (SILURIFORMES) FROM THE UPPER MIOCENE OF TOROS-MENALLA, CHAD: AUCHENOGLANIS SOYE, SP. NOV

Abstract Three specimens of a fossil catfish, collected from the Upper Miocene of Toros-Menalla (Western Djurab, Chad), are identified as members of Auchenoglanis (Claroteidae, Auchenoglanidinae) based on the shape and the ornamentation of the bones of the skull, including a markedly developed parieto-supraoccipital broadly connected with the first nuchal plate. The description is based on a comparison with living specimens of the two valid species of the genus, providing details on their bony anatomy. The fossil fish is a new species, Auchenoglanis soye sp. nov. Original features include supraoccipital process more than twice as wide as long, straight posterolateral border of the sphenotic, parurohyal with a median anterior process, and lateral articular surfaces of the second dorsal spine lateral to the foramen. Auchenoglanis fish are known since the Late Miocene and are endemic to the Nilo-Sudanese province. The fossil record was previously limited to a few isolated spines identified as Auchenoglanis sp., and A. soye sp. nov. is the first fossil species described for the genus. On the basis of preliminary observations of the ichthyofauna from Toros-Menalla, the scarcity of Auchenoglanis in the fossil record might be due to the low abundance of a fish with a rather high ecological valence.

Spine anatomy reveals the diversity of catfish through time: a case study of Synodontis (Siluriformes)

Synodontis (Mochokidae, Siluriformes) is a freshwater catfish endemic to Africa. The 118 extant species are present in almost all hydrographic basins. Some species are restricted to a single stream, whereas others have a vast distribution. Synodontis is known in the fossil record since the Miocene, and its history depends on the connections among African basins through time. The identification of species in the fossil record is essential to reconstruct this historical pattern. Catfish pectoral and dorsal spines are robust, they preserve well and they form most of the fossil remains for the genus Synodontis. Unfortunately, the criteria for the identification of extant Synodontis species are not applicable to fossil specimens. Here, we define 11 original morphological characters that permit to discriminate four extant species from the Chad-Chari hydrographic system. Six of these characters are defined on pectoral spines and five on dorsal spines. We then show that these characters can be used successfully for identifying fossil specimens. In particular, we present a case study in which we identify Synodontis cf. schall and Brachysynodontis cf. batensoda in the hominid-bearing sector Toros-Menalla (Late Miocene, northern Chad). We show that spine anatomy can be a powerful tool to recognise catfish species through time and thus to identify historical diversity pattern.

The Phylogenetic Intrarelationships of Spiny-Rayed Fishes (Acanthomorpha, Teleostei, Actinopterygii): Fossil Taxa Increase the Congruence of Morphology with Molecular Data

Acanthomorpha (spiny-rayed fishes) is a clade of teleosts that includes more than 15 000 extant species. Their deep phylogenetic intrarelationships, first reconstructed using morphological characters, have been extensively revised with molecular data. Moreover, the deep branches of the acanthomorph tree are still largely unresolved, with strong disagreement between studies. Here, we review the historical propositions for acanthomorph deep intrarelationships and attempt to resolve their earliest branching patterns using a new morphological data matrix compiling and revising characters from previous studies. The taxon sampling we use constitutes a first attempt to test all previous hypotheses (molecular and morphological alike) with morphological data only. Our sampling also includes Late Cretaceous fossil taxa, which yield new character state combinations that are absent in extant taxa. Analysis of the complete morphological data matrix yields a new topology that shows remarkable congruence with the well-supported molecular results. Lampridiformes (oarfishes and allies) are the sister to all other acanthomorphs. Gadiformes (cods and allies) and Zeiformes (dories) form a clade with Percopsiformes (trout-perches) and the enigmatic Polymixia (beardfish) and Stylephorus (tube-eye). Ophidiiformes (cusk-eels and allies) and Batrachoidiformes (toadfishes) are nested within Percomorpha, the clade that includes most of modern acanthomorph diversity. These results provide morphological synapomorphies and independent corroboration of clades previously only recovered from molecular data, thereby suggesting the emergence of a congruent picture of acanthomorph deep intrarelationships. Fossil taxa play a critical role in achieving this congruence, since a very different topology is found when they are excluded from the analysis.

A Fish Assemblage from the Middle Eocene from Libya (Dur At-Talah) and the Earliest Record of Modern African Fish Genera.

In the early nineteen sixties, Arambourg and Magnier found some freshwater fish (i.e., Polypterus sp., Siluriformes indet. and Lates sp.) mixed with marine members in an Eocene vertebrate assemblage at Gebel Coquin, in the southern Libyan Desert. This locality, aged ca 37–39Ma and now known under the name of Dur At-Talah, has been recently excavated. A new fish assemblage, mostly composed of teeth, was collected by the Mission Paléontologique Franco-Libyenne. In this paper, we describe freshwater fish members including a dipnoan (Protopterus sp.), and several actinopterygians: bichir (Polypterus sp.), aba fish (Gymnarchus sp.), several catfishes (Chrysichthys sp. and a mochokid indet.), several characiforms (including the tiger fish Hydrocynus sp., and one or two alestin-like fish), and perciforms (including the snake-head fish Parachanna sp. and at least one cichlid). Together with the fossiliferous outcrops at Birket Qarun in Egypt, the Libyan site at Dur At-Talah reduces a 10-Ma chronological gap in the fossil record of African freshwater fish. Their fish assemblages overlap in their composition and thus constitute a rather homogenous, original and significant amount of new elements regarding the Paleogene African ichthyofauna. This supports the establishment of the modern African freshwater fish fauna during this time period because these sites mostly contain the earliest members known in modern genera.