Pleistocene footprints show intensive use of lake margin habitats by Homo erectus groups

Abstract

Reconstructing hominin paleoecology is critical for understanding our ancestors’ diets, social organizations and interactions with other animals. Most paleoecological models lack fine-scale resolution due to fossil hominin scarcity and the time-averaged accumulation of faunal assemblages. Here we present data from 481 fossil tracks from northwestern Kenya, including 97 hominin footprints attributed to Homo erectus. These tracks are found in multiple sedimentary layers spanning approximately 20 thousand years. Taphonomic experiments show that each of these trackways represents minutes to no more than a few days in the lives of the individuals moving across these paleolandscapes. The geology and associated vertebrate fauna place these tracks in a deltaic setting, near a lakeshore bordered by open grasslands. Hominin footprints are disproportionately abundant in this lake margin environment, relative to hominin skeletal fossil frequency in the same deposits. Accounting for preservation bias, this abundance of hominin footprints indicates repeated use of lakeshore habitats by Homo erectus. Clusters of very large prints moving in the same direction further suggest these hominins traversed this lakeshore in multi-male groups. Such reliance on near water environments, and possibly aquatic-linked foods, may have influenced hominin foraging behavior and migratory routes across and out of Africa.

Crevasse‐splay and associated depositional environments of the hominin‐bearing lower Okote Member, Koobi Fora Formation (Plio‐Pleistocene), Kenya

“…Footprint‐marked levels suggest secession of deposition and landscape stability; however, if the pauses in sedimentation were long, then sub‐aerial processes (e.g., soil formation, wind abrasion) would have obliterated the footprints, which is not the case. The multiple, well‐defined impressions (Bennett et al ., ) indicate that sedimentation resumed and the footprints were buried not too long after they were made (Roach et al ., ).…”

“…Many of the coarse units have a massive fabric, parallel laminations or wavy laminations. Convolute bedding and mammal footprints, including those of hominins, are preserved locally by the mudstones (Vondra & Bowen, 1978;Bennett et al, 2009;Roach et al, 2016). Medium-to fine-grained sandstones and tuffs preserve cross-stratifications and planar laminations interstratified with small-scale cross strata (Vondra & Burggraf, 1978;Bennett et al, 2009).…”

“…Refining these interpretations is not only key for addressing this possibility but also for further understanding the depositional environments in which the Okote Member's hominin record was formed and preserved. Further sedimentological and stratigraphic study of the member will help to provide additional palaeoenvironmental constraints on the evolutionary data being gleaned from the H. erectus footprints (Bennett et al ., 2016a; Hatala et al ., ; Roach et al ., ) and comparisons with hominin footprints from elsewhere in eastern Africa (Bennett et al ., 2016b; Liutkus‐Pierce et al ., ; Masao et al ., ). The new data presented here argue that a number of the Okote Member's hominin‐bearing strata are best interpreted as the products of crevasse‐splay and crevasse‐channel sedimentation (Table ).…”

“…Behrensmeyer et al . 's () observations come at a time when the Okote Member's footprints are being interpreted as indicative of ‘intensive use of lake‐margin habitats by Homo erectus groups’ (Roach et al ., ). This is a fairly novel supposition, as definitive evidence of hominin group behaviour in a lake‐margin setting is rare.…”

These feet were made for walking

“…Looking back, 2016 has been a banner year for trace fossils in human evolution (e.g., Bennett et al, 2016; Liutkus-Pierce et al, 2016; Roach et al, 2016), and these new sets of footprints from Laetoli are a fitting capstone to the year. To judge by the profound scientific impact of the first set of Laetoli footprints, we can expect the new ones to figure prominently in future narratives of the origins of humans.…”