The upper limb of Paranthropus boisei from Ileret, Kenya

Anatomy, Archaeology, Archeology, Evolution, Geology, Human Evolution, Human Origins, Journal of Human Evolution, Lithic Analysis, Lithics, Palaeoanthropology, Palaeobiology, Palaeontology, Paleobiology, Paleontology

Figure 3. Stratigraphic section (left) shown with the image (right) of the outcrop highlighting the positions of the three major tuffs. All hominin fossils were found on the surface or in secondarily deposited sediment below the Ileret Tuff (1.52 ± 0.01 Ma). Some of the remains were found above the Lower Ileret Tuff (1.53 ± 0.01 Ma) indicating that the bones must have been buried above it. The large excavation area is visible on the right side of the outcrop and gully; the lower footprint level (Bennett et al., 2009Dingwall et al., 2013Hatala et al., 2017) is exposed on the left side of the image. All fragments of KNM-ER 47000 were located on the surface of the lower portion of the outcrop or secondarily buried in sediment eroded from the drainage that extends up the slope from the excavation site toward the right margin of the picture.

Paranthropus boisei was first described in 1959 based on fossils from the Olduvai Gorge and now includes many fossils from Ethiopia to Malawi. Knowledge about its postcranial anatomy has remained elusive because, until recently, no postcranial remains could be reliably attributed to this taxon. Here, we report the first associated hand and upper limb skeleton (KNM-ER 47000) of P. boisei from 1.51 to 1.53 Ma sediments at Ileret, Kenya. While the fossils show a combination of primitive and derived traits, the overall anatomy is characterised by primitive traits that resemble those found in Australopithecus, including an oblique scapular spine, relatively long and curved ulna, lack of third metacarpal styloid process, gracile thumb metacarpal, and curved manual phalanges. Very thick cortical bone throughout the upper limb shows that P. boisei had great upper limb strength, supporting hypotheses that this species spent time climbing trees, although probably to a lesser extent than earlier australopiths. Hand anatomy shows that P. boisei, like earlier australopiths, was capable of the manual dexterity needed to create and use stone tools, but lacked the robust thumb of Homo erectus, which arguably reflects adaptations to the intensification of precision grips and tool use. KNM-ER 47000 provides conclusive evidence that early Pleistocene hominins diverged in postcranial and craniodental anatomy, supporting hypotheses of competitive displacement among these contemporaneous hominins.

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Figure 1. Right upper limbs of a modern human (left), chimpanzee (center), and KNM-ER 47000 (right), which preserves lateral portions of the scapula, the distal portion of the humerus, most of the ulna, and most of metacarpals (MCs) 1-3 and proximal phalanges 2-4. KNM-ER 47000 has primitive traits including a gracile thumb MC, lack of MC 3 styloid process, curved phalanges with prominent flexor sheaths, a long and curved ulna, a humerus with thick cortical bone and a prominent brachioradialis flange, and obliquely oriented scapular spine. Derived traits include a relatively long thumb, short manual phalanges, and a lateral scapular glenoid orientation. Scale bar at right is 10 cm.

Discovery of the Paranthropus of Peninj

Geology, Human Evolution, Human Origins, Palaeoanthropology, Paleoanthropology, Radiometric Dating

This evening on the 11th of January 1964, fossil hunter Kamoya Kimeu (1940-Present) was crossing what had been an Early Pleistocene delta to the western side of Lake Natron, Arusha, Tanzania. He was there with a team led by Richard Leakey in search of our earliest ancestors. Barely a few days into the expedition, Kimeu found a hominin mandible, not one of our ancestors, but just an intriguing. It is 1964 and by this time, OH 5, representative of Paranthropus boisei was already gracing the covers of magazines throughout the world. Thought to be the first human that used stone tools for the first time, the Nutcracker Man was not all he was cracked up to be. As more hominin fossils from the Late Pliocene and early Pleistocene began to show, it became more and more clear, that while P. boisei may have been found on an archaeological layer, this is not enough evidence to support a “he’s the first human” hypothesis.

Lengai_from_Natron

Ol Doinyo Lengai: A View from Lake Natron

Kimeu had found another representative of P. boisei at Peninj and it was a remarkably complete hominin mandible. The right condyle was missing and so too were the left and right coronoid processes, despite that the fossil had its complete set of teeth and that was particularly key. The teeth showed a great deal of wear  to the point that you could see the dentine beneath the enamel. This individual must have eaten alot of sedges and grasses throughout its life to give that sort of result. Grasses and sedges that you could find around deltas like that one that would have entered Lake Natron, when it wasn’t quite as salty. But when exactly did our hominin friend give up its spirit along the shores of the Lake. The stratigraphic layers in the region are like the pages of a picture book, no words, but pictures that can tell better narratives that Twilight could ever even dream of. The mandible was uncovered in a sedimentary layers, comprising the deltas alluvial deposits, sandwiched between two volcanic layers. The volcanic Tuff atop the layer that contained the fossil was previously dated to between 1.6 and 1.4 million years of age, while the basalt below was dated to 1.7 million years of age. You may think that the fossil is probably going to be between 1.7 and 1.4 million years of age, but the team of geologists at the site conducted further analysis at the site to help get a more accurate result. They settled on an age for the mandible of between 1.5 and 1.3 million years of age. Enough time for the ph of a lake to reach beyond 12.

Peninj

View of Lake Natron and a superimposed graphic of the hypothetical organisation of the layers around the fossil.

Since the discovery of the Peninj 1 mandible in 1964, another hominin with similar characteristics to P. boisei was found. Paranthropus aethiopicus now joined a trio of hominin species that became the Paranthropines, comprising boisei, robustus (South African hominin) and aethiopicus. Most of what we have collected of these creatures are crania and mandibles, though some postcranial remains have been found. Thankfully the teeth survive well and can tell us a great deal about their diet and the subtle, yet important questions of how they chew their greenery. There was a long drawn out debate over whether these three hominins deserved to live in a separate group – the Paranthropines. Originally, these hominins were classified as robust australopithecines and the palaeoanthropological community decided that a change was needed. The complete anatomy of the Peninj Hominin was never recovered and given that the mandible survived so well, this individual may have fallen to a carnivore in the delta. Below is a summary of the discovery that was made on the 11th of January 1964.