Terrifying Upright Apes? Monkeys?

Throughout human history, creatures that resemble us have often inspired unease and caution. Tales of humanoid beings living in remote mountains appear across many cultures. In ancient Chinese legends there are the mysterious xingxing; in Australian mythology the Yowie; in Tibetan traditions the Yeti; and in modern folklore the well-known Bigfoot. These stories reveal a persistent human fascination with, and fear of, beings that resemble ourselves. But do such upright, human-like animals actually exist in the natural world, or are they merely products of imagination shaped by ancient storytelling?

Fig. 1. Fragmentary upper and lower jaw fossils of Paradolichopithecus (圖片來源：Masanaru Takai, Yingqi Zhang, Takeshi D Nishimura ，採用 CC BY-NC-SA 4.0 授權。)

The short answer is that non-human animals capable of walking on two legs have indeed existed. However, our own ancestors—at least the species Homo sapiens—never encountered such creatures. The animal in question belongs to the baboon lineage of Old World monkeys. Palaeontologists have given it the name Paradolichopithecus. These primates lived from the Middle Pliocene to the Early Pleistocene across the Eurasian steppes. Fossils have been discovered from western Europe, including Spain and France, through the Balkan Peninsula, and as far east as Tajikistan and China. Ecologically they appear to have resembled modern baboons, inhabiting open grassland environments rather than dense forests.

Fig. 2. AI-assisted reconstruction of Paradolichopithecus, manually verified to match the morphology used in current mainstream reconstructions.

What makes these animals remarkable lies in the structure of their skeleton. Fossils reveal unusually robust fibulae and a square-shaped ankle structure. Even more striking is the morphology of the talus bone, which shows similarities to the ankle structure found in Australopithecus. Among primates, this type of configuration is highly unusual. It is typically associated with members of the human lineage rather than with monkeys. The ankle joint appears to distribute body weight more evenly across the talar surface and involves a greater contribution from the fibular side of the leg. Such features suggest that this primate may have been capable of frequent upright locomotion across the Eurasian plains.

The forelimbs of Paradolichopithecus were also distinctive. Fossil specimens indicate powerful arms with a robust humerus and radius. The humerus reached roughly 22.2 centimetres in length, while the radius extended to about 25.2 centimetres—longer than those of modern mandrills or baboons. The humerus also bears a deep and wide groove for the tendon of the biceps muscle, together with a broad joint surface at the shoulder. These features imply strong arm musculature and a highly mobile shoulder joint. Such anatomical traits suggest that these monkeys possessed arms capable of flexible manipulation, potentially allowing them to grasp and carry objects or collect food with both hands.

Although the fossil record does not provide direct evidence explaining how Paradolichopithecus evolved this locomotor pattern, palaeontologists suspect that environmental change played a key role. During the late Neogene, Eurasia underwent a gradual transition toward drier climates and more open landscapes. The rising Himalayan mountain system altered atmospheric circulation patterns, reducing moisture across large regions of the continent. Dense forests gradually gave way to shrublands and grass-dominated steppe environments.

Under these changing ecological conditions, the ancestors of Paradolichopithecus may have experienced increasing pressure to descend from trees and adapt to terrestrial life. Moving across open grasslands likely exposed them to new challenges, including greater predation risk and longer travel distances in search of food. Natural selection may therefore have favoured anatomical traits that allowed more efficient upright or semi-upright movement. Over evolutionary time, this pressure could have produced skeletal adaptations supporting a form of habitual bipedal locomotion.

Despite these discoveries, many aspects of the biology of Paradolichopithecus remain mysterious. For example, researchers still do not know whether these primates possessed the cognitive or anatomical ability to manufacture and use tools. Another unresolved question concerns their eventual disappearance. Did environmental shifts drive them to extinction, or might their decline have been linked to the arrival of early humans such as Homo erectus on the Eurasian steppes? At present, the fossil evidence is still too limited to provide definitive answers.

Future discoveries may yet illuminate the life and fate of this unusual primate—an animal that hints at an evolutionary experiment in upright movement outside the human lineage.

Author: Rodrigo

References:

1. Van Der Greer, A. A. E.; (2002) The postcranial elements of Paradolichopithecus arvernensis (Primates, Cercopithecidae, Papionini) from Lesvos, Greece

2. Y. Sondaar, Paul; Van der Geer, Alexandra (January 2006). "The unique postcranial of the Old World monkey Paradolichopithecus: more similar to Australopithecus than to baboons" . Hellenic Journal of Geosciences. 1: 19–28 – via users.uoa.gr.