Thursday, July 5, 2007

Lothagam: The Dawn of Humanity in Eastern Africa

Lothagam: The Dawn of Humanity in Eastern Africa

Badgley, Catherine

Lothagam: The Dawn of Humanity in Eastern Africa. Meave G. Leakey and John M. Harris (eds). 2003. Columbia University Press, New York, 688 p., cloth, ISBN 0-231-11870-8.

The fossil site known as Lothagam lies west of the southern end of Lake Turkana (formerly Lake Rudolf) in northern Kenya. The Turkana Basin is famous for its paleontological, paleoanthropological, and archeological records from both east and west of this large lake in the eastern part of the rift system. The PlioPleistocene outcrops have been the focus of important research in early hominid taxonomy and evolution, subsistence behavior of early hominids, the tempo and mode of evolution in lacustrine gastropods, vertebrate taphonomy, and mammalian faunal turnover, as well as basic systematic paleontology of terrestrial and aquatic vertebrates. Lothagam is a more restricted area (~60 km^sup 2^ of outcrop) and its strata are older-late Miocene to early Pliocene, overlain unconformably by Quaternary sands, gravels, and coquinas. Only a handful of African sites document this time period that includes the Messinian salinity crisis and major floral and faunal changes in many parts of the world. Thus, this monograph is a welcome publication for those who work on the later Neogene, and for paleoanthropologists interested in the ecological context of basal hominids.

Paleontological work began at Lothagam in 1967 under Bryan Patterson and continued sporadically until 1989, when Meave Leakey and John Harris co-led interdisciplinary research teams in five field seasons to document the geology, geochronology, paleontology, paleoanthropology, and isotope geochemistry of the sediments and faunas. This monograph covers primarily the results of these field seasons from 1989 to 1993, although there are frequent references to results from the earlier field work. The early field seasons retrieved over 500 specimens, including many vertebrate fossils. The fauna documented in the monograph is based on about 1,500 described specimens, out of a cumulative total of 2,150 specimens (excluding fish specimens, which number ~7,000). Over 100 species of mammals, as well as birds, crocodilians, turtles, fishes, and crabs are recorded from the Lothagam sequence. It is the type site for 10 vertebrate genera and 28 vertebrate species.

The book covers geology, geochronology, the invertebrate and vertebrate fauna, and isotope geochemistry of soil carbonates and mammalian teeth. These subjects are organized into 13 sections, most having two or more chapters. Each chapter has a short abstract, a helpful attribute in a volume covering such diverse subjects. Many chapters have lovely half-tone illustrations of restored animals or landscapes, by the talented artist Mauricio Anton. His appendix explaining the scientific basis of his reconstructions adds credibility to his work and also documents the important collaboration between artist and scientist. Most chapters are followed by tables of data about rocks or fossils; these data tables make up about 20 percent of the book and are critical to the lasting value of the monograph. Contributors include accomplished specialists in geology, paleontology, and paleoanthropology. The editors are authors or coauthors on a number of the chapters and were clearly involved in all aspects of the research about Lothagam.

Geology.-Eastern-rift tectonics tilted a 900 m sequence of alluvial sediments, volcaniclastics, and lavas into a horst structure, which is Lothagam today. Feibel establishes the stratigraphic framework. Four formations range in age from Middle Miocene to Holocene. The middle two formations and their fossils are the focus of this monograph. The Late Miocene Nawata Formation consists of sandstones, mudstones, and tephras in facies interpreted as fluvial. Most of the fossils come from this formation. The Late Miocene-Early Pliocene Nachukui Formation consists of sandstones, mudstones, claystones, diatomites, and coquinas. This formation has an older fluvial phase and a younger lacustrine phase. Most vertebrate fossils come from the fluvial beds. The lacustrine phase is part of a transgression within the entire Turkana Basin.

Wynn's chapter on paleosols describes several paleosol types in the Nawata and Nachukui formations. Paleosols can be indicative of depositional and postdepositional processes, paleovegetation, and paleoclimate. Wynn infers that the ancient moisture regimes were quite seasonal, with a dry season of at least four months' duration. Based on modern analogs of the paleosols, he infers an older interval (before 6.7 Ma) of "relatively lush semideciduous and thorntree savanna" (p. 37). Between about 6.7 and 5.0 Ma, a drier regime prevailed and the floodplain bore grassy and thornbush savanna interlaced by gallery woodlands along ephemeral channels. A more mesic regime returned after 5 Ma, with more wooded savannas. This chapter suffers a bit from unfamiliar paleosol terminology. Since the monograph is not aimed primarily at paleopedologists, it would have been helpful for such critical terms as "vertisols" and "luvisols" to be defined.

The best chapter on the geologic setting is by McDougall and Feibel. They succinctly describe the geologic setting and lucidly discuss the methods used for radiometric dating using K-Ar and Ar-Ar methods. Absolute-age estimates based on volcanic minerals constrain the ages of the formations, of particular marker units, and of fossils from the sequence. The chapter contains a useful composite stratigraphic section illustrating lithostratigraphic units, prominent marker layers, isotopic age-estimates from the sampled horizons, and paleomagnetic stratigraphy (fig. 2.18). The distribution of unconformities, isotopic dates, and paleosols indicate that extended hiatuses occurred in the depositional history of the Lothagam area.

Fauna.-Most of the book is devoted to the animal remains from Lothagam. These are more varied and environmentally informative than I expected. About one-third of the way through the faunal chapters, I realized that Rudyard Kipling would have loved this site as living ecosystems, especially that of the Lower Nawata Formation. The richness and ecological diversity of the fauna challenge and delight the imagination.

The ancient rivers and lakes were teeming with life, a far cry from the dry moonscape of the site today. Fossil crabs, discussed by Martin and Trautwein, imply a well-oxygenated river system. Stewart documents over 20 species of fish, including lungfish, electric fish, large minnows, catfish, Nile perch, and rare cichlids. The changes in species, richness, and body sizes of fish assemblages signify changes in the size and swiftness of the river system and eventually large lake. Appearances of three taxa known from older sites in the western rift and of two from the Nile drainage signify hydrological contact with these drainage systems during the Pliocene. Exquisite fossil chelonians, described by Wood, include members of extinct genera, extinct species of surviving genera, and at least one extant species. At least six species, including a giant tortoise, are represented. Lothagam exhibits greater taxonomic richness of turtles than any other Neogene African site. Only the Paleogene Fayum sequence has comparable taxonomic diversity of turtles. Abundant remains of the pelomedusid Turkanemys pattersoni are proposed to represent a congregation of nesting females. Storrs reviews five species of crocodilians that lurked in the rivers, swamps, and lakes. The Lothagam crocodilians exhibited greater taxonomic diversity than in any other Neogene African fossil site and today. Lothagam contains the earliest record of Crocodylus niloticus, the dominant living crocodilian in East Africa. Living C. cataphractus is also represented by fossils. A new East African record of gavial, Eogavialis andrewsi, is documented. One skull of Euthecodon, of uncertain phylogenetic placement, implies a body length of 10 m! The robust crocodylid Rimasuchus would have served Kipling well in "How the elephant got its trunk," and there were plenty of "elephants" available for such a skirmish. These crocodilians showed considerable trophic diversity, with the longirostrine species acting as piscivores, the brevirostrine species as hunters of terrestrial vertebrates, and the intermediate ecomorph as a generalist animal consumer.

Avian postcranials and eggshell fragments represent species from 10 bird families, reviewed by Harris and Leakey. Two ratiteshell pore patterns are attributed to Struthionidae (ostriches) and Aepyornithidae (elephant birds). Most of the postcranial elements belong to continental waterbirds, including pelicans, anhingas, herons, storks, ducks, and rails. A bustard and owl were also present.

Semiaquatic mammals include otters and hippos. The otter Vishnuonyx (from the carnivore chapter) is represented by a single upper premolar; this genus occurs at other Late Miocene, East African sites and in the Siwalik sequence of the Indian subcontinent. Hippos are among the most remarkable mammals from Lothagam. Hippo fossils, covered by Weston, constitute 27 percent of the mammalian fossil assemblage, with over 300 specimens, including complete crania and associated postcranials. Several species were present, all in the genus Hexaprotodon. H. harvardi is the best-represented species, with nine partial skulls. Slightly smaller than the extant Hippopotamus amphibius, H. harvardi had slender long bones and rnetapodials and is thought to have been highly cursorial. Variation in limb morphology and abundance of fossils is the basis for inferring seraiaquatic to more terrestrial habits among the hippo species.

The terrestrial environment was likewise populated by diverse and charismatic animals. Fifteen species of lagomorphs and rodents are reviewed by Winkler. Notably, some of these records are among the oldest in Africa, including two genera of bunnies, Alilepus and Serengetilagus, and the Old World porcupine, Hystrix. Squirrels (scuirids), cane rats (thryonomyids), gerbils (gerbillines), and mice (murines) are known from the smaller fossils. The chapter contains a good summary of the biogeographic affinities of the small mammals; in addition to regional affinities, some species show north African, others south African, and others southern Eurasian affinities. Small mammals were recovered through surface collecting and some dry screening. Wet-screening at Lothagam has not been done because of the scarcity of water; it would likely increase the remains of small mammals substantially to include insectivores, bats, and additional rodents.

Monkeys, described by Leakey, Teaford, and Ward, are well represented as fossils, both in quantity and quality. Both Cercopithecinae, including the earliest fossils of this group, and Colobinae were present. Three species of baboons and several large leaf monkeys are recognized. Notably, the postcrania of these fossil cercopithecines and colobines are quite similar (unlike the situation today) and suggest semi-terrestrial habits. Evidence for extreme arboreal adaptations found in living colobines did not occur until the Late Pliocene, suggesting a recent evolution of these features in African colobines. A valuable aspect of this chapter is the section on molar microwear features, indicative of what the animal ate in the last few days of its life. Colobine and cercopithecine fossil teeth show fine scratches and small pits in statistically indistinguishable patterns. While the fossil colobine microwear resembles microwear on modern colobine molars, the fossil cercopithecine microwear resembles the colobine pattern, not that of extant cercopithecines. The Lothagam material demonstrates that modern African cercopithecines and colobines have both changed considerably in their ecological habits since the late Miocene.

Hominoids consist of seven dental and gnathic specimens, reviewed by Leakey and Walker. Although slightly rarer in the overall fossil assemblage than aardvarks, until the publication of this monograph, the hominoid fossils put Lothagam on the map. Three teeth from the Late Miocene Upper Nawata Formation are named as hominid indet.-the specimens are the age of the estimated divergence time between humans and chimps, but are not diagnostic of phylogenetic position. The mid-Pliocene specimens most closely match fossils of Australopithecus afarensis.

The most impressive mammalian material from Lothagam is the fossil carnivores, described by Werdelin. Carnivores show high taxonomic and ecological diversity. Among the 21 taxa recognized are the youngest amphicyonids (bear dogs) known anywhere, a new genus of gigantic cursorial mustelid possibly related to the extant honey badger Mellivora, an otter, a civet, genets, four species of hyena, a new genus of sabertooth cat, and other felids. Several lineages make first African appearances in the Lothagam record. Most Miocene carnivoran taxa have close relatives in the Miocene of Eurasia rather than elsewhere in Africa. Anton's illustrations include the reconstructed skeleton, musculature, and full-coat views of selected species.

Proboscideans, reviewed by Tassy, include elephantoids and deinotheres, and also show high taxonomic diversity. Eleven taxa include the new species, Elephas nawatensis, a primitive member of the genus and the first Miocene record of Elephas; contemporaneous species of Loxodonta and Elephas in the early Pliocene; and rare but persistent deinotheres. The Lothagam fossils indicate that evolutionary differentiation among elephantines began in the late Miocene rather than mid-Pliocene.

Milledge describes fossil aardvarks, known from a partial skeleton and a dozen postcranials. Two species are known from the Nawata Formation, both slightly smaller than the extant aardvark.

Harris and Leakey review the rhinos, represented by cranial, dental, and postcranial fossils. The large, heavy-bodied Brachypotherium lewisi, is the common one in the fossil assemblage. Ceratotherium praecox, related to the extant white rhino, and Diceros bicornis, the oldest record of the extant black rhino, co-occurred with B. lewisi in the Upper Nawata Formation. Imagine a landscape inhabited by several kinds of elephantoids, deinotheres, three species of rhino, two species of hippo, and two species of giraffe (below). This diversity of mammalian megaherbivores, while known from other Late Miocene sites (e.g., Siwalik faunas of Pakistan), has not existed anywhere since the latest Miocene.

Bernor and Harris describe the three species of hipparionine equids found at Lothagam. Two species in the genus Eurygnathohippus include a large robust horse considered to be a woodland dweller and a smaller, slender-limbed, cursorial species. Hippotherium cf. H. primigenium may be a late survivor of the first sub-Saharan hipparion immigration in the early Late Miocene. Phylogenetic interpretations are very cautious.

Harris and Leakey review over half a dozen pre-Pleistocene suids, including several species of the tetraconodontine genus Nyanzochoerus and the peccary-like Cainochoerm africanas estimated to weigh less than 10 kg. The Lothagam record documents as many as five contemporaneous species of pigs.

Giraffids, described by Harris, are represented by two species of Paleotragus in the Nawata Formation and by two Asian immigrants, a species of Giraffa and one of Sivatherium, in the Nachukui Formation. All of the giraffids were browsers, according to isotope ecology.

After hippos, bovids are the most abundant group of mammalian fossils. Harris reviews 17 species in nine tribes as represented by numerous horn cores, some skulls, and dental and postcranial specimens. The Lothagam record contains the first members of eight bovid tribes, although this situation may reflect the paucity of Late Miocene sites in Africa. Lothagam also contains the youngest African members of the boselaphines, today known only from Asia. The most common bovid species through the Nawata and Nachukui formations is the impala relative, Aepyceros premelampus.

Isotope ecology.-Two chapters about stable-isotope ecology, both by Cerling and coauthors, follow the faunal chapters. The first covers present conditions in the Turkana Basin, an arid semi-desert landscape vegetated by dwarf shrubland. This chapter contains a good introduction to the methods and significance of stable-isotope ecology, based on [delta]^sup 18^O and [delta]^sup 13^C. Samples of soil carbonates, water, plants, and mammals were analyzed and compared from two northern and one central Kenyan locality. Much of the discussion concerns the relative proportions of C^sub 3^ and C^sub 4^ plants, and their distinctive isotopic ratios under a range of modern climatic conditions. C^sub 4^ plants, mainly tropical grasses and sedges, are known from warm, seasonally arid ecosystems; C^sub 3^ plants include trees, shrubs, and cool-season grasses and generally occur in cool, mesic, or humid environments. The modern shrubland east of Lake Turkana has a lower fraction of C^sub 4^ biomass than do the Serengeti grasslands, even though East Turkana is much more arid than the Serengeti, so the fraction of C^sub 4^ biomass is not a simple index of aridity per se.

The chapter on isotope paleoecology focuses on stable isotopes of oxygen and carbon from paleosol carbonates, fossil enamel, and fossil eggshell from the Lothagam sequence. Paleosol carbonates give [delta]^sup 13^C values indicating the presence of C^sub 3^-dominated and mixed C^sub 3^/C^sub 4^ vegetation. For much of the Lothagam sequence, C^sub 3^-plants constituted more than 50 percent of plant biomass. There is no paleosol evidence for pure C^sub 4^ vegetation. [delta]^sup 18^O values are depleted, compared to modern values, over much of the Lothagam sequence, indicating higher precipitation, lower evaporation, or a different precipitation source than in the Lake Turkana Basin today. Both [delta]^sup 13^C and [delta]^sup 18^O values are reported for most herbivorous mammal groups. The raw data are not graphed (a notable omission, because the range and variability are as interesting as the means). While some herbivorous taxa (e.g., Deinotheriwn) maintained a C^sub 3^-diet throughout the Lothagam sequence, many herbivorous taxa (equids, Nyanzochoerus, elephantoids) shifted from a mixed C^sub 3^/C^sub 4^ diet to a diet dominated by C^sub 4^-grasses in the Upper Nawata Formation or in the Apak (oldest) Member of the Nachukui Formation. [delta]^sup 18^O values from mammalian enamel and ostrich eggshell are all significantly depleted compared to their modern counterparts, consistent with the results from paleosols. The authors mistakenly use the term "enriched" when they mean "depleted" on at least two occasions, a confusing error for even a patient reader.

These chapters on isotope ecology add considerable value to the monograph, but I was puzzled by some of the environmental interpretations. In particular, the authors argue on several occasions that the [delta]^sup 13^C values from the mammalian herbivores indicate that the paleovcgetation of "the Lothagam ecosystem" was a dwarf shrubland, like the vegetation around Lake Turkana today. I find this intepretation implausible, and it is inconsistent with data from sedimentology, paleosols, and faunas. The presence of such high taxonomic and ecological diversity of mammals, including a dozen contemporaneous megaherbivores, is not compatible with semi-desert dwarf shrubland, but with a more lush if heterogeneous vegetation mosaic. In addition, there was more than one Lothagam ecosystem documented by the totality of the data presented in the monograph.

The final chapter by Leakey and Harris presents an admirable summary of all the preceding chapters, paragraph by paragraph, in the first section. The paleoenvironmental summary characterizes the climatic conditions of the Lower Nawata Formation as having seasonal rainfall in excess of 1,000 mm/yr; the Upper Nawata as having less precipitation in the lower part, then a return to wetter conditions that persist into the Apak. The Apak then provides evidence of pronounced aridity, corresponding to the Messinian crisis. Later in the chapter, the fauna of the Lower Nawata is described as consistent with a relatively lush closed woodland with wet swamps; the Upper Nawata as more open; the Apak as woodland with nearby grassland; and the Kaiyumung as more open, with increased grassland and bushland. Three landscape drawings by Anton present visual images of these differences. These paleoenvironmental inferences are again inconsistent with the notion of a single Lothagam ecosystem and with dwarf shrubland vegetation, which grows today under

Finally, the authors present their scenario for habitat change at Lothagam in relation to early human evolution. During the time of the Nawata Formation, ancestral hominids were restricted mainly to forests, and "the dwarf shrubland and dry thornbush" of the Upper Nawata lacked forests with tall trees. By the time of the earliest appearance of hominids (late in the Upper Nawata Formation), their bipedal gait and some form of manual defense against all the fierce predatory animals were efficient enough to allow foraging in more open habitats. This scenario suffers from lack of testability as well as unlikely vegetation. The rarity of hominid remains at all early hominid sites means that the absence of hominid fossils from most of the Nawata Formation could just as likely be a sampling effect.

Assessment and summary.-It was useful to review the Lothagam monograph while pondering the format of a future monograph by my research group about Miocene Siwalik sediments and faunas of Pakistan. Aspects I would choose to emulate include the broad coverage of the fauna, including invertebrates and nonmammalian vertebrates, as well as all of the mammalian groups; extensive data tables with each chapter so that readers have access to a substantial amount of primary data; the abstract at the beginning of each chapter; the half-tone illustrations; and the chapters on isotope ecology. For a monographic treatment of a rich fossil site, the balance between data and evaluation is good. While I often was interested in more analysis of phylogeny, functional morphology, biogeography, and ecology of particular animal groups, addition of these aspects for all groups could have added another 200 pages to an already large volume. The main purpose of a monograph is to document the major features of a site as part of the permanent record of the field, museum, and laboratory work, and the contributors focused on this goal well. Aspects of the book that I would do differently include illustrating all of the important taxa with either photographs or drawings (or providing an optional CD with such figures); achieving a more uniform quality of photographs and drawings (e.g., photographs in the fish chapter are poor, but those in the crocodile chapter are good); and adding biostratigraphic range charts and maps to the introductory and concluding chapters (oddly, there is no detailed map of the site anywhere in the book).

The positive aspects of the book outweigh the negative aspects by a large margin. I had long been aware of Lothagam as an older hominid site in the Turkana Basin, but little more. This monograph demonstrates that the fossil assemblage is remarkable for the high quality of preservation of many specimens, leading to species-level identification of much of the collection. Many taxa add new phylogenetic, biogeographic, or paleoecological information about their respective lineages. The faunas are ecologically and taxonomically diverse and unlike anything else known from the last five million years. This volume elevates Lothagam to the high status it deserves as a detailed window into late Miocene and early Pliocene ecosystems of the Old World tropics. I recommend this book to anyone interested in continental records from this time.


Museum of Paleontology

University of Michigan

Ann Arbor, Michigan 48109

Copyright Paleontological Society Sep 2004
Provided by ProQuest Information and Learning Company. All rights Reserved

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