Footprint evidence of early hominin locomotor diversity at Laetoli, Tanzania

Abstract

Bipedal trackways discovered in 1978 at Laetoli site G, Tanzania and dated to 3.66 million years ago are widely accepted as the oldest unequivocal evidence of obligate bipedalism in the human lineage1–3. Another trackway discovered two years earlier at nearby site A was partially excavated and attributed to a hominin, but curious affinities with bears (ursids) marginalized its importance to the paleoanthropological community, and the location of these footprints fell into obscurity3–5. In 2019, we located, excavated and cleaned the site A trackway, producing a digital archive using 3D photogrammetry and laser scanning. Here we compare the footprints at this site with those of American black bears, chimpanzees and humans, and we show that they resemble those of hominins more than ursids. In fact, the narrow step width corroborates the original interpretation of a small, cross-stepping bipedal hominin. However, the inferred foot proportions, gait parameters and 3D morphologies of footprints at site A are readily distinguished from those at site G, indicating that a minimum of two hominin taxa with different feet and gaits coexisted at Laetoli.

Coordination of trunk motion during bipedal walking in the frontal plane: A comparison between Homo sapiens, Macaca fuscata, and an exploratory study on a gibbon

“…Our results support the notion the safety ratio can be used to estimate mediolateral CoM motion from footprints in early hominins (Thompson et al, 2018), such as the Laetoli site G trackways (Tuttle et al, 1990). Another hominin footprint was found at Laetoli site A (McNutt et al, 2021), but those are ‘cross‐stepping gait‘, unfortunately, making it difficult to estimate the mediolateral CoM motion. The macaques utilized in O'Neill et al (2018) showed that the locomotor kinematics in the pelvis are similar among non‐human primates, indicating that bipedal walking in the human and chimpanzee LCA involved non‐human‐like pelvic (and presumably lower limb) motion.…”

From footprint morphometrics to the stature of fossil hominins: A common but uncertain estimate

“…However, these uncertainties due to intraindividual variation must be weighed because they are only valid in particular substrate conditions: loose and easily deformed sand. Even if several hominin footprints have been discovered in similar conditions, others have been left in different substrates such as clayey mud (Manolis et al, 2000, Onac et al, 2005, Citton et al, 2017, Ledoux et al, 2017 or volcanic ash (Leakey and Hay, 1979, Mietto et al, 2003, Masao et al, 2016, McNutt et al, 2021 having a lesser capacity for deformation; the footprints made in these substrates are morphologically closer to the anatomy of the foot and present a less important intraindividual dispersion.…”

“…Hominin footprints represent a particular remain in paleoanthropology. While they were scarce in the fossil record until the 2010s (Leakey and Hay, 1979, Bennett et al, 2009, Lockley et al, 2009, they have become in the last ten years a more and more common material thanks to discoveries in all regions and for periods ranging from the Upper Miocene to the Holocene (Ashton et al, 2014, Masao et al, 2016, Gierliński et al, 2017, Ledoux et al, 2017, Altamura et al, 2018, Bustos et al, 2018, Helm et al, 2018, Duveau et al, 2019, Stewart et al, 2020, Mayoral et al, 2021, McNutt et al, 2021, Zhang et al, 2021.…”

“…Thanks to this particular temporal scale, footprints provide many original information. They inform on the locomotor behaviour (Bennett and Morse, 2014, Bennett et al, 2016, Hatala et al, 2016a, Hatala et al, 2016b, Hatala et al, 2016c, McNutt et al, 2021 but also the functional anatomy (Duveau et al, 2019, Wiseman et al, 2020 of the individuals who made them. The famous Laetoli trackways are the most telling example since they represent the first direct evidence of human bipedalism used by fossil hominins (Leakey and Hay, 1979, Masao et al, 2016, McNutt et al, 2021.…”

“…They inform on the locomotor behaviour (Bennett and Morse, 2014, Bennett et al, 2016, Hatala et al, 2016a, Hatala et al, 2016b, Hatala et al, 2016c, McNutt et al, 2021 but also the functional anatomy (Duveau et al, 2019, Wiseman et al, 2020 of the individuals who made them. The famous Laetoli trackways are the most telling example since they represent the first direct evidence of human bipedalism used by fossil hominins (Leakey and Hay, 1979, Masao et al, 2016, McNutt et al, 2021. However, the most common information estimated from the footprints are body characteristics such as body mass (Robbins, 1986, Dingwall et al, 2013, Bennett and Morse, 2014, Domjanic et al, 2015, Ruff et al, 2021 and especially and more commonly the stature of individuals (Ashton et al, 2014, Masao et al, 2016, Altamura et al, 2018, Bustos et al, 2018, Helm et al, 2018, Duveau et al, 2019, Mayoral et al, 2021, Zhang et al, 2021.…”