Susanne Cote

VERTEBRAL DEVELOPMENT IN THE DEVONIAN SARCOPTERYGIAN FISH EUSTHENOPTERON FOORDI AND THE POLARITY OF VERTEBRAL EVOLUTION IN NON-AMNIOTE TETRAPODS

Abstract Study of a growth series of twenty-seven specimens from the Upper Devonian of Escuminac Bay, Québec documents a complex pattern of vertebral development in the osteolepiform fish Eusthenopteron foordi. Ossification begins with elements associated with the caudal, anal, and second dorsal fins. Development of the haemal arches, caudal radials, and caudal neural arches continues anteriorly and posteriorly from near the level of the anterior margin of the caudal fin. Trunk neural arches ossify later than the caudal neural arches and as a separate sequence. Trunk intercentra most likely begin ossification posteriorly and continue forward after the ossification of haemal arches is complete. Comparisons of many different patterns of vertebral development within the modern actinopterygians demonstrates that the sequence of development in Eusthenopteron foordi is unique. The diverse patterns of vertebral development observed in fossil and modern fish presumably result from an interplay between the inherent anterior to posterior sequence of development controlled by the Hox genes, and varying selective forces imposed by the physical and biological environment in which the fish develop. Initiation of vertebral development in the caudal region of Eusthenopteron foordi can be attributed to selection for early function of the tail in propulsion. In contrast, vertebral development in Carboniferous amphibians typically proceeds from anterior to posterior. This may reflect development in the still water of ponds and lakes in contrast with the coastal environment inhabited by the hatchlings of Eusthenopteron foordi. The sequences of vertebral development seen in Carboniferous labyrinthodonts and lepospondyls are divergently derived from that observed in Eusthenopteron foordi.

Stratigraphic interpretation of the Kulu Formation (Early Miocene, Rusinga Island, Kenya) and its implications for primate evolution.

Early Miocene fossils from Rusinga Island, Kenya, provide some of the best evidence for catarrhine evolution and diversification, and, together with more than eighty-five other mammalian species, form an important comparative reference for understanding faunal succession in East Africa. While there is consensus over the stratigraphic position of most of Rusingas volcaniclastic deposits, the lacustrine Kulu Formation has been placed in various parts of the geological sequence by different researchers. To resolve this discrepancy, we conducted detailed geological analyses which indicate that the Kulu Formation was formed in the Early Miocene during a period of volcanic inactivity and subsidence following the early, mainly explosive hyper-alkaline phase of the Kisingiri complex and prior to the final eruptions of nephelinitic lavas. The underlying Hiwegi and older formations were locally deformed and deeply eroded before sedimentation began in the Kulu basin, so that the Kulu sediments may be significantly younger than the 17.8 Ma Hiwegi Formation and not much older than the overlying Kiangata Agglomerata-Lunene Lava series, loosely dated to ca. 15 Ma. The overall similarities between Kulu and Hiwegi faunas imply long-term ecological stability in this region. Our stratigraphic interpretation suggests that the Kulu fauna is contemporaneous with faunas from West Turkana, implying that differences between these assemblages-particularly in the primate communities--reflect paleobiogeographic and/or paleocological differences. Finally, the position of the Kulu Formation restricts the time frame during which the substantial faunal turnover seen in the differences between the primate and mammalian communities of Rusinga and Maboko Islands could have occurred.

Additional material of the enigmatic Early Miocene mammal Kelba and its relationship to the order Ptolemaiida

Kelba quadeemae, a fossil mammal from the Early Miocene of East Africa, was originally named on the basis of three isolated upper molars. Kelba has previously been interpreted as a creodont, a pantolestid, an insectivoran, and a hemigaline viverrid. The true affinities of this taxon have remained unclear because of the limited material and its unique morphology relative to other Miocene African mammals. New material of Kelba from several East African Miocene localities, most notably a skull from the Early Miocene locality of Songhor in Western Kenya, permits analysis of the affinities of Kelba and documents the lower dentition of this taxon. Morphological comparison of this new material clearly demonstrates that Kelba is a member of the order Ptolemaiida, a poorly understood group whose fossil record was previously restricted to the Oligocene Fayum deposits of northern Egypt. Phylogenetic analysis supports the monophyly of the Ptolemaiida, including Kelba, and recovers two monophyletic clades within the order. We provide new family names for these groups and an emended diagnosis for the order. The discovery of ptolemaiidans from the Miocene of East Africa is significant because it extends the known temporal range of the order by >10 million years and the geographic range by >3,200 km. Although the higher-level affinities of the Ptolemaiida remain obscure, their unique morphology and distribution through a larger area of Africa (and exclusively Africa) lend support to the idea that Ptolemaiida may have an ancient African origin.

Additional mandibles of Rangwapithecus gordoni, an early Miocene catarrhine from the Tinderet localities of Western Kenya

Two catarrhine mandibles and five isolated teeth have been discovered from Early Miocene localities in Western Kenya. One mandible comes from the well-known locality of Songhor whereas the other is from a newly discovered locality, Lower Kapurtay, located near Songhor. The mandibles both can clearly be assigned to the species Rangwapithecus gordoni based on molar morphology, which is unique among Early Miocene catarrhines. The isolated specimens can be assigned to Rangwapithecus based on their similarities in morphology to the homologues preserved in the two mandibles. These specimens provide important new information about the dentognathic morphology of Rangwapithecus, which is described in detail. The mandible from Songhor (KNM-SO 22228) represents the first definitive female mandible of Rangwapithecus. The Lower Kapurtay mandible (KNM-KT 31234) appears to be male but is much smaller than another recently described male mandible of this species (KNM-SO 17500) and the type maxilla (KNM-SO 700). These specimens enable a reassessment of the attributions of all other mandibles and isolated lower teeth of Rangwapithecus, and we present a complete hypodigm of the mandibular and lower dental material for the species. Finally, we provide some additions to the diagnosis of Rangwapithecus gordoni based on previously unknown morphology.

The Fishes of Bukwa, Uganda, a Lower Miocene (Burdigalian) Locality of East Africa

ABSTRACT Renewed research at the early Miocene fossil site of Bukwa in northeastern Uganda has resulted in new fossil finds, including fish, with representatives of two families, Cichlidae and Alestidae. Although the two families were previously briefly reported from Bukwa, we here give a more detailed account of the fishes based on newly collected material. The cichlid material, mainly composed of vertebrae, can be tentatively assigned to one or more species of Pseudocrenilabrinae. The alestid material, comprising a diversity of teeth, likely represents several different species of Alestes, Brycinus, and/or Bryconaethiops. Although the ichthyofaunal diversity of Bukwa is low, the fishes are important for indicating the paleoenvironment and hydrographic connections of Bukwa. The early Miocene was a critical time for African faunas, because it was during this time that the Afro-Arabian and Eurasian plates came into contact with one another, ending the long isolation of Africa, which, along with rifting in East Africa, created new terrestrial and hydrological connections allowing faunal interchanges. Bukwa is one of only a few African early Miocene localities known that sample fish and, based on these fish, the site probably represents an area of interconnected lakes and large rivers, including floodplains.