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.

Gorjanović-Kramberger Hypothesis: Took 99 Years, But We Finally Tested It

Anatomy, Human Evolution, Palaeoanthropology, Palaeobiology, Paleoanthropology, Paleobiology, Science, Statistics

You meet Homo neanderthalensis in a dark alley……………….What do you do?

Homo neanderthalensis is one of the best understood species of hominin today. One that lasted many hundreds of thousands of years throughout Europe. Despite what we know through the lens of science, there is still much that we want to know about this species of human. Interrogating the subtle pieces of evidence is the task of palaeoanthropologists, archaeologists, palaeoenvironmental scientists throughout the world. Contrary to what you may see on your average human evolution documentary, the kind of research conducted can be much more subtle. Here I will draw your attention to a difficult question. If we could fill the Great Hall of the South Kensington Museum with a few hundred individuals of our extinct cousin, what differences would we see in the upper chest and neck. The answer to that, at the beginning of 2015: We are not happy that we really know enough to give an answer.

Range_of_Homo_neanderthalensis
Range of Homo neanderthalensis

H. neanderthalensis is a well represented species of human in the fossil record, but the post-cranial anatomy is less well accounted for than the skulls. Not ideal for an investigation into the chest and abdominal regions of the human body. Nevertheless, it is vital we exhaustively examine what we have, to reveal potential clues to the kind of morphology these populations once exhibited. To that end, ten palaeobiologists from various Spanish academic institutions presented evidence that may be useful here. The mechanics of the breathing system, constrained by the rib cage and not the evolution of the species, is the focus here. Research continues to be a work in progress, new technologies arrive and they help further our understanding of the past. This research is no exception. Two year into the new millennium a new form of analysis that gauged quantity within a structure was applied to a collection of isolated ribs from an individual codenamed Shanidar 3. This individual had a more splayed lower rib cage compared to the more barrel-like form of our lower rib cage. Thus started a series of papers that suggested the lower rib cage of Homo neanderthalensis was generally less like ours. Comparatively less investigative research has been given to the upper end of the rib cage. This latest academic paper sets out to help understand just that.

Title and Authors of the Paper in Question
Title and Authors of the Paper in Question
640px-Krapina_-_Dragutin_Gorjanovic_Kramberger
Dragutin Gorjanović-Kramberger (1856 – 1936)

In 1906 and a time when ancient humans were Anti or Post Diluvian Era (Noah’s Great Flood), Dragutin Gorjanović-Kramberger suggested that the superior ribs are an important facet of an upper thoracic orchestra of components, that together control upper thoracic breathing, separate from diaphragmatic breathing. It was not until 2015 that this hypothesis was put to the test on six hominin first-ribs from the cave site of El Sidrón, Asturias, northern Spain. The six first-rib fragments may represent, at most, four individuals. The first step was to identify the bone fragments and place them in their correct anatomical position. Below is a re-organisation of the information given about the sample itself. The first-rib of Kebara 2 was found to be similar in shape space and form space (both terms used in a statistical analysis of shape, known as Procrustes Least Squares (PLS)) to SD-1767 and SD-1699, indeed H. neanderthalensis exhibits straighter first-ribs than modern day Homo sapiens. What could this mean? The scalene muscles are the ones that give your neck, its shape. They run from the Rib 1 and Rib 2 up the side of your neck attaching to the vertebrae. Alteration in shape of the first ribs, and the attached muscles will have to operate differently, but may help explain the differences we see between H. sapiens and H. neanderthalensis. The principle component analysis (PCA) reveals some overlap in the linearity of the rib shaft. Such results are reflected in analysis of the specimens of Krapina Cave, Croatia and ATD6-108 representing Homo antecessor, from Gran Dolina Cave, Atapuerca, Spain. So, the straightness of the first-ribs may affect the movement of the upper torso during breathing.

Juvenile 1: SD-2148 (Right) and SD-2172 (Left)

Juvenile 2: SD-417 (Left) and SD-1225 (Right)

Large Adolescent / Small Adult: SD-1767 (Left)

Large Adult: SD-1699 (Right)

Looking at the juveniles, it is important to understand costal cartilage development. Understanding adult H. neanderthalensis individuals is easier, as there are more post-cranial fossils, but the El Sidrón hominins will be useful in understanding the ontogeny of costal cartilage in future fossil ribs of  juveniles. The El Sidrón juveniles confirm a tighter upper chest for H. neanderthalensis. The first-ribs are smaller, but feature larger attachments at the rib heads, whereas the lower ribs have smaller attachment points. Therefore, a H. neanderthalensis individual, exhibited a smaller upper torso, which was further from the cranium thanks to the slightly longer neck vertebrae. First-ribs that are straighter would have to project out from the skeleton more and Gorjanović-Kramberger proposed that the rest of the rib-cage would project outward, just as much. The scientific team added to this, that a change in the first ribs would in turn affect the rest of the rib-cage, because the ribs are latched together with intercostal muscle, preventing individual ribs from varying in shape, that ultimately allows coordination of muscle, chest wall and breathing action. Upper ribs connect directly with the sternum and so, result in distinctive rib shape compared with the lower thorax.

Association of Intercostal Muscle and Rib Bone
Association of Intercostal Muscle and Rib Bone

To summarise, the first ribs appear to determine the shape of the upper thorax ribs, but straightness of the first rib is linked with the straightness of the upper ribs. Together, this suggests the existence of different rib shape and functions between the upper and lower thorax. When you look at a particular fossil specimen, it is important you are aware of what bones, muscles, cartilage was associated with it. They all interact in subtle ways which we are piecing together in hominins, with the variety in body forms available going back 7 million years. In examination of the monophyly of Paranthropus, cladistical statistics showed us that the skeletal points used, should not be linked with eachother. An example of that, would be the masticatory system in Paranthropus comprising numerous points, all interacting with one another. This is a shame because the crania and mandibles are predominantly all we have of that genus. Currently, most are happy that Paranthropus boisei, Paranthropus aethiopicus and Paranthropus robustus are part of the same family – they are monophyletic. The rib cage, is similar to the masticatory system but it is a single unit with two functions, one  is upper thoracic respiration and the other is diaphragmatic respiration. H. neanderthalensis evolved a more restrictive respiratory system and highly developed arm muscles, evolutionarily more important for the condition in which it lived. So, if you were to meet our ancient ancestor in a dark alley, what should you do? It would have been prone to breathlessness, but could rearrange your face easier. Moral of the story, RUN!

The costal remains of the El Sidrón Neanderthal site (Asturias, northern Spain) and their importance for understanding Neanderthal thorax morphology