Location and Chronology

The geo-plaeontological site of Laetoli is situated in the Enduleni ward of Ngorongoro District, Arusha Region, northern Tanzania. It lies at a latitude of 2°59'46.39" S and longitude of 35°21'8.64" E, within the southern part of the eastern branch of the East African Rift Valley. The site extends over a vast plateau, approximately 1,799 m above sea level, to the west of the volcanic complex comprising Sadiman (2,870 m), Lemagrut (3,135 m), and Oldeani (3,200 m). This position places it between the southeastern limits of the Serengeti plains and the Lake Eyasi basin [1][23]. Sediments are exposed along the margin of the Eyasi Plateau, which forms the divide between the Lake Eyasi and Olduvai Gorge drainage basins [24].

The Laetoli Beds sits atop the Precambrian Basement, with a clear unconformity separating the two geological formations. The Laetoli Beds are subdivided into two lithological units: the upper and lower units. The lower unit is characterized by aeolian tuffs interbedded with air-fall and water-worked tuffs [4][2].

The age of the Laetoli fossil beds were estimated using two dating methods: potassium-argon dating and stratigraphic analysis [1]. Radiometric dating of the sediments indicated an age between 3.8 Ma and older than 4.32 Ma. However, considering the estimated sedimentation rates at Laetoli, the base of the sequence could be as old as 4.6 Ma [7].

While the Lower Laetoli Beds have yielded only a limited number of fauna fossils, with no hominin discoveries, the Upper Laetoli Beds have provided significant finds. Dated to approximately 3.5 to 3.8 million years ago [7], this layer is notable for containing all of the Australopithecus afarensis fossils found to date. Within the Upper Laetoli Beds, Tuff 8 is of particular interest. This layer has preserved valuable information about the mammalian paleocommunity of the time in the form of tracks preserved in ashfall deposits [6][3]. Notably, Tuff 7, the layer in which the famous Site G footprints were discovered, has been dated more precisely to 3.56±0.2 Ma [2][25][26][7].

History

The site of Laetoli was first brought to the attention of western science in 1935 by a man named Sanimu. He persuaded archaeologist Louis Leakey to investigate the area, which led to the collection of several mammalian fossils. One of these finds, a left lower canine tooth, was initially identified as belonging to a non-human primate. However, it was later revealed in 1979 by Andrews and White to be the first fossil hominin discovered at the site [1].

German archaeologist Ludwig Kohl-Larsen extensively studied the Laetoli site in 1938 and 1939, identifying several hominin remains. Despite a 1959 excavation yielding no new hominin finds, the 1974 discovery of a hominin premolar by George Dove renewed interest in Laetoli [1].

The 1975 and 1976 field seasons at Laetoli focused on studying the area’s geology and collecting and excavating fossils, including vertebrates and mollusks, from the Laetoli Beds and later deposits. The upper, fossiliferous part of the Laetoli Beds was dated to 3.6 – 3.5 Ma [6]. The Laetoli fossils, which include teeth, jaws, and fragmentary infant skeleton from at least 23 individuals, date to a period between 3.76 and 3.46 Ma [27].

While visiting the Laetoli camp in 1976, Dr. Andrew Hill noticed several depressions in the surface of a fine-grained tuff exposed in the river bed of what is now known as Site G. These proved to be footprints of birds and mammals, including elephants, rhinoceros, carnivores, and hares, preserved in volcanic ash. The footprints, which had been revealed by natural erosion and weathering, also included trails of remarkably humanlike prints [6][1][28][27].

Site G Footprints

The Laetoli Site G offers a remarkable 24-meter (75-foot) record of footprints left in volcanic ash around 3.66 million years ago. These prints were made by three hominin individuals walking in the same direction across a humid layer that was later cemented. The exceptional preservation of the footprints, totaling around 70 impressions, is attributed to a unique combination of climatic, volcanic, and mineralogic conditions. As undeniable evidence of upright bipedalism in early human ancestors, this discovery holds great significance in the study of fossil tracks and trackways [6][22][29][30][31].

In 1978, Mary Leakey’s team discovered footprints at Laetoli Site G (Locality 8). These prints. Left by three individuals referred to as G1, G2, and G3, provide a unique glimpse into the past. The smallest individual (G1) walked alongside the largest (G2), while the intermediate-sized individual (G3) stepped into G2’s footprints [15][32][23][30][22]. G1 and G3 followed parallel paths behind G2, suggesting they walked side by side [22].

The hominin fossil footprints discovered at Laetoli have been the subject of extensive research into the locomotion, speed, body size, and behavior of the track-makers [22]. These footprints are of great importance, contributing significantly to the understanding of human evolution [8][9].

While the species responsible for the Laetoli footprints is much debated among researchers, there is tentative agreement that Australopithecus afarensis is the most likely candidate. This conclusion is supported by the recovery of actual A. afarensis fossils from the upper Laetoli Beds, which have been dated to the same timeframe as the footprints [22]. Furthermore, the height range calculated for the Laetoli track-makers in this study aligns with the stature range of A. afarensis as determined from skeletal remains, which falls between 1.1 and 1.6 meters [33][22].

Sources

Environmental Change within the Laetoli Fossiliferous Sequence. Vegetation Catenas and Bovid Ecomorphology. In Paleontology and Geology of Laetoli. Human Evolution in Context. Volume 1 - Geology, Geochronology, Paleoecology and Paleoenvironment

Gignos Citations