Scientists have revised the longstanding picture of “Nutcracker Man” — an extinct hominin, or human relative, nicknamed for its large teeth and powerful jaw muscles — thanks to fresh analysis of fossil footprints from a site in Kenya.
Nutcracker Man, whose species is scientifically known as Paranthropus boisei, lived in eastern Africa from about 2.3 million to 1.2 million years ago, and this new evidence suggests that P. boisei was taller and heavier and had more complex social relationships than once thought.
Prior estimates based on P. boisei fossil evidence hinted that males stood about 4.2 feet (131 centimeters) tall and weighed approximately 108 pounds (49 kilograms) on average. Updated calculations based on the length and width of 21 newly identified P. boisei footprints suggest that Nutcracker Man’s size was more humanlike, standing up to 6 feet (1.8 meters) tall and weighing as much as 165 pounds (75 kilograms).
Patterns in the footprints further indicate that the tracks belonged to eight P. boisei individuals who crossed through the site — East Turkana’s Koobi Fora Formation — at the same time, traveling as a group. These preserved prints provide clues about the complexity of their social structure in their lakeside habitat, researchers reported Monday in the journal PNAS.
“The site captures an amazing snapshot of hominin anatomy, locomotion, behavior, and environments,” said lead study author Kevin Hatala, an associate professor of biology at Chatham University in Pittsburgh and an associate researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
“Each set of footprints like this one provides a window to a moment in time when we can directly observe how hominins were living, and engaging with their environments,” Hatala told CNN in an email. “We think that the footprints may capture a group of adult males moving together along the lakeshore,” he said, adding that the threat of dangerous animals such as hippos could explain why the group included only adult males.
“Footprints are important fossils because they provide us with both anatomical and behavioral information,” said Patricia Kramer, a professor in the department of anthropology at the University of Washington in Seattle and an affiliate curator of archaeology at the Burke Museum. Kramer has previously studied these trackways but was not involved in the new research.
“I am excited that the authors have provided additional information and analysis about the trackways at Koobi Fora,” she told CNN in an email.
The tracks, which are about 1.4 million years old, are well-defined with depths reaching 0.4 inches (12 centimeters), and were probably pressed into mud in shallow lake water, the authors reported. Seven tracks were uncovered in 1978 through fieldwork led by senior study author Anna Katherine “Kay” Behrensmeyer, a senior research geologist and curator of vertebrate paleontology at the Smithsonian’s National Museum of Natural History in Washington, DC. Excavations in 2016 and 2023 later revealed 14 more hominin footprints, along with tracks left by animals such as antelope and hippos.
P. boisei wasn’t the only archaic human relative living near Lake Turkana. For hundreds of thousands of years, P. boisei coexisted alongside Homo erectus. Another study from 2024 led by Hatala reported the discovery of fossil footprints in Kenya’s Turkana Basin made no more than a few days apart by two different hominin species, and the researchers hypothesized that the prints belonged to H. erectus and P. boisei.