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Paranthropus robustus
Ceph Wrote:Paranthropus robustus

Temporal range: Pleistocene, 2–1.2 Ma

Scientific classification
Species:Paranthropus robustus

Paranthropus robustus is an example of a robust australopithecine; they had very large megadont cheek teeth with thick enamel and focused their chewing in the back of the jaw. Large zygomatic arches (cheek bones) allowed the passage of large chewing muscles to the jaw and gave P. robustus individuals their characteristically wide, dish-shaped face. A large sagittal crest provided a large area to anchor these chewing muscles to the skull. These adaptations provided P. robustus with the ability of grinding down tough, fibrous foods. It is now known that ‘robust’ refers solely to tooth and face size, not to the body size of P. robustus.

[Image: robustus_illustration_kc_head_sq_0.jpg]
Image Credit: Karen Carr Studio

Where Lived:  Southern Africa (South Africa)
When Lived: About 1.8 to 1.2 million years ago
[Image: robustus_timeline.png?1267763117]

Year of Discovery:  1938

History of Discovery: 
When scientist Robert Broom bought a fossil jaw fragment and molar in 1938 that didn’t look anything like some of the Au. africanus fossils he’d found during his career, he knew he was on to something different. After exploring Kromdraai, South Africa, the site where the curious fossils came from, Broom collected many more bones and teeth that together convinced him he had a new species which he named Paranthropus robustus (Paranthropus meaning “beside man”).

Males: average 3 ft 9 in (1.2 m) tall; Females: average just under 3 ft 3 in (1 m)
Males: average 119 lbs (54 kg); Females: average 88 lbs (40 kg)
Height & Weight Supplemental Information: 
This species had a relatively high level of sexual dimorphism.

We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas with groundbreaking technology, and continually filling in some of the gaps about our understanding of human evolution. 

Below are some of the still unanswered questions about Paranthropus robustus that may be answered with future discoveries:

Which species did Paranthropus robustus evolve from? Did P. robustus evolve from P. aethiopicus, or were there regionally distinct robust australopithecine lineages - meaning P. robustus evolved from the other southern African species Au. africanus?
Bone tools presumably used by P. robustus to dig into termite mounds have been found at several South African sites. Was this tool-making, termite-mound-digging behavior something shared by all populations of this species, or was it a regional behavior?
First paper:

Broom, R., 1938. The Pleistocene anthropoid apes of South Africa. Nature 142, 377-379.

 Other recommended readings:

Scott, R.S., Ungar, P.S., Bergstrom, T.S., Brown, C.A., Grine, F.E., Teaford, M.F., Walker, A., 2005. Dental microwear texture analysis shows within-species dietary variability in fossil hominins. Nature 436, 693–695.

Sponheimer, M., Passey, B.H., de Ruiter, D.J., Guatelli-Steinberg, D., Cerling, T.E., Lee-Thorp, J.A., 2006. Isotopic evidence for dietary variability in the early hominin Paranthropus robustus. Science 314, 980-982.

Wood, B., Strait, D., 2004. Patterns of resource use in early Homo and Paranthropus. Journal of Human Evolution 46, 119–162.

How They Survived:
Robust species like Paranthropus robustus had large teeth as well as a ridge on top of the skull, where strong chewing muscles attached. These features allowed individuals to crush and grind hard foods such as nuts, seeds, roots, and tubers in the back of the jaw; however, P. robustus didn’t just eat tough foods. This early human species may have been more of a dietary generalist, also eating variety of other foods such as soft fruits and possibly young leaves, insects, and meat.

While scientists have not found any stone tools associated with Paranthropus robustus fossils, experiments and microscopic studies of bone fragments show that these early humans probably used bones as tools to dig in termite mounds. Through repeated use, the ends of these tools became rounded and polished. Termites are rich in protein, and would have been a nutritious source of food for Paranthropus.

Evolutionary Tree Information:
From 1940s through 1970s, lots of debate whether this species represented the males of Au. africanus. Eventually, scientists recognized that the 'robust' forms were different enough to be in their own species, originally called Australopithecus robustus. Later, the three robust species (aethiopicus, boisei, and robustus) were recognized as being different enough from the other australopithecines - and similar enough to each other - to be placed into a separate genus, Paranthropus.


SK 46

SK 46 preserves the left half of the braincase and the nearly complete palate of Paranthropus robustus. The cheek teeth are nearly perfectly preserved; although the incisors and one canine tooth have been lost, their alveoli (the bony pits that hold the tooth roots) remain. Because these alveoli are still preserved, paleoanthropologists are able to reconstruct the size of the cheek teeth (molars and premolars) relative to the incisors and canines. This information can give clues about the dietary habits of this early human species. The large size of the cheek teeth relative to the front teeth suggests that Paranthropus robustus had a diet dominated by coarse vegetable matter. The large teeth provided a large occlusal area (the area where the upper and lower teeth contact each other during chewing). Think about a cow, or a horse, both of which eat large amounts of grass and other coarse plant foods. These animals have large cheek teeth and large chewing surfaces. By this kind of analogy and by direct study of microscopic wear on the tooth surfaces, scientists have determined that the large cheek teeth of robust australopiths were used for grinding tough, fibrous foods.

The preserved portion of the cranium has other features typical of P. robustus, including large zygomatic arches and a prominent sagittal crest. These features are associated with large chewing muscles used in grinding tough foods.

[Image: robustus_SK46_skull_CC_lt_s_l.jpg]
Image Credit: Chip Clark, Smithsonian Institution
SK 46
 Exhibit item
Site:  Swartkrans, Republic of South Africa
Date of discovery:  1936
Discovered by:  local quarryman
Age:  Between 1.8 and 1.5 million years old
Species:  Paranthropus robustus

SK 48

Discovered in the debris pile at a cave site commercially mined for calcite, this skull represented until recently the best preserved skull of any member of this species. SK 48 is the cranium of an adult robust australopith. Most of the skull (minus the lower jaw) is preserved and is relatively undistorted by the fossilization process, although some damage did occur when the specimen was dynamited out of the limestone deposits by miners. Preserved in the cranium were the right canine tooth and first premolar and all three left molars, indicating the individual was an adult at death.

The flat face, caused by the anterior (frontward) position of the cheekbones, and the extremely large molars and premolars are typical traits of robust australopithecines. These traits are linked to the development of a chewing complex designed to process tough, fibrous foods. The anterior position of the cheekbones created more space for large chewing muscles to pass behind the zygomatic arch. The large molars and premolars provided large surfaces for grinding tough foods.

The fossil was originally described by Robert Broom of the Transvaal Museum of South Africa. He inferred that the individual was a female based on the presence of a very small sagittal crest.

[Image: robustus_SK48_skull_CC_lt_3qtr_l_0.jpg]
Image Credit:
SK 48
 Exhibit item
Site:  Swartkrans, Republic of South Africa
Date of discovery:  1950
Discovered by:  Fourie (a local quarryman)
Age:  Between 1.8 and 1.5 million years old
Species:  Paranthropus robustus
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2-million-year-old fossils reveal hearing abilities of early humans

Date: September 25, 2015
Source: Binghamton University
Research into human fossils dating back to approximately two million years ago reveals that the hearing pattern resembles chimpanzees, but with some slight differences in the direction of humans.

[Image: 150925142702_1_900x600.jpg]
Lateral view of the Paranthropus robustus skull SK 46 from the site of Swartkrans, South Africa showing the 3D virtual reconstruction of the ear and the hearing results for the early hominins.
Credit: Rolf Quam

Research into human fossils dating back to approximately two million years ago reveals that the hearing pattern resembles chimpanzees, but with some slight differences in the direction of humans.

Rolf Quam, assistant professor of anthropology at Binghamton University, led an international research team in reconstructing an aspect of sensory perception in several fossil hominin individuals from the sites of Sterkfontein and Swartkrans in South Africa. The study relied on the use of CT scans and virtual computer reconstructions to study the internal anatomy of the ear. The results suggest that the early hominin species Australopithecus africanus and Paranthropus robustus, both of which lived around 2 million years ago, had hearing abilities similar to a chimpanzee, but with some slight differences in the direction of humans.

Humans are distinct from most other primates, including chimpanzees, in having better hearing across a wider range of frequencies, generally between 1.0-6.0 kHz. Within this same frequency range, which encompasses many of the sounds emitted during spoken language, chimpanzees and most other primates lose sensitivity compared to humans.

"We know that the hearing patterns, or audiograms, in chimpanzees and humans are distinct because their hearing abilities have been measured in the laboratory in living subjects," said Quam. "So we were interested in finding out when this human-like hearing pattern first emerged during our evolutionary history."

Previously, Quam and colleagues studied the hearing abilities in several fossil hominin individuals from the site of the Sima de los Huesos (Pit of the Bones) in northern Spain. These fossils are about 430,000 years old and are considered to represent ancestors of the later Neandertals. The hearing abilities in the Sima hominins were nearly identical to living humans. In contrast, the much earlier South African specimens had a hearing pattern that was much more similar to a chimpanzee.

In the South African fossils, the region of maximum hearing sensitivity was shifted towards slightly higher frequencies compared with chimpanzees, and the early hominins showed better hearing than either chimpanzees or humans from about 1.0-3.0 kHz. It turns out that this auditory pattern may have been particularly favorable for living on the savanna. In more open environments, sound waves don't travel as far as in the rainforest canopy, so short range communication is favored on the savanna.

"We know these species regularly occupied the savanna since their diet included up to 50 percent of resources found in open environments" said Quam. The researchers argue that this combination of auditory features may have favored short-range communication in open environments.

That sounds a lot like language. Does this mean these early hominins had language? "No," said Quam. "We're not arguing that. They certainly could communicate vocally. All primates do, but we're not saying they had fully developed human language, which implies a symbolic content."

The emergence of language is one of the most hotly debated questions in paleoanthropology, the branch of anthropology that studies human origins, since the capacity for spoken language is often held to be a defining human feature. There is a general consensus among anthropologists that the small brain size and ape-like cranial anatomy and vocal tract in these early hominins indicates they likely did not have the capacity for language.

"We feel our research line does have considerable potential to provide new insights into when the human hearing pattern emerged and, by extension, when we developed language," said Quam.

Ignacio Martinez, a collaborator on the study, said, "We're pretty confident about our results and our interpretation. In particular, it's very gratifying when several independent lines of evidence converge on a consistent interpretation."

How do these results compare with the discovery of a new hominin species, Homo naledi, announced just two weeks ago from a different site in South Africa?

"It would be really interesting to study the hearing pattern in this new species," said Quam. "Stay tuned."

The study was published on Sept. 25 in the journal Science Advances.

Story Source: Binghamton University. "2-million-year-old fossils reveal hearing abilities of early humans." ScienceDaily. (accessed September 26, 2015).

Journal Reference:
Rolf Quam et al. Early hominin auditory capacities. Science Advances, September 2015 DOI: 10.1126/sciadv.1500355

Studies of sensory capacities in past life forms have offered new insights into their adaptations and lifeways. Audition is particularly amenable to study in fossils because it is strongly related to physical properties that can be approached through their skeletal structures. We have studied the anatomy of the outer and middle ear in the early hominin taxa Australopithecus africanus and Paranthropus robustus and estimated their auditory capacities. Compared with chimpanzees, the early hominin taxa are derived toward modern humans in their slightly shorter and wider external auditory canal, smaller tympanic membrane, and lower malleus/incus lever ratio, but they remain primitive in the small size of their stapes footplate. Compared with chimpanzees, both early hominin taxa show a heightened sensitivity to frequencies between 1.5 and 3.5 kHz and an occupied band of maximum sensitivity that is shifted toward slightly higher frequencies. The results have implications for sensory ecology and communication, and suggest that the early hominin auditory pattern may have facilitated an increased emphasis on short-range vocal communication in open habitats. 
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Height and weight evolved at different speeds in the bodies of our ancestors

Date: November 8, 2017
Source: University of Cambridge
The largest study to date of body sizes over millions of years finds a 'pulse and stasis' pattern to hominin evolution, with surges of growth in stature and bulk occurring at different times. At one stage, our ancestors got taller around a million years before body mass caught up.

[Image: 171108092241_1_900x600.jpg]
Femoral head bones of different species illustrating the size range in the hominin lineage. From top to bottom: Australopithecus afarensis (4-3 million years; ~40 kg, 130 cm); Homo ergaster (1.9-1.4 million years; 55-60 kg; ~165 cm); Neanderthal (200.000-30.000 years; ~70 kg; ~163 cm).
Credit: University of Cambridge

A wide-ranging new study of fossils spanning over four million years suggests that stature and body mass advanced at different speeds during the evolution of hominins -- the ancestral lineage of which Homo sapiens alone still exist.

Published today in the journal Royal Society Open Science, the research also shows that, rather than steadily increasing in size, hominin bodies evolved in "pulse and stasis" fluctuations, with some lineages even shrinking.

The findings are from the largest study of hominin body sizes, involving 311 specimens dating from earliest upright species of 4.4m years ago right through to the modern humans that followed the last ice age.

While researchers describe the physical evolution of assorted hominin species as a "long and winding road with many branches and dead ends," they say that broad patterns in the data suggest bursts of growth at key stages, followed by plateaus where little changed for many millennia.

The scientists were surprised to find a "decoupling" of bulk and stature around one and a half million years ago, when hominins grew roughly 10cm taller but would not consistently gain any heft for a further million years, with an average increase of 10-15kgs occurring around 500,000 years ago.

Before this event, height and weight in hominin species appeared to evolve roughly "in concert," say the authors of this first study to jointly analyse both aspects of body size over millions of years.

"An increase solely in stature would have created a leaner physique, with long legs and narrow hips and shoulders. This may have been an adaptation to new environments and endurance hunting, as early Homo species left the forests and moved on to more arid African savannahs," says lead author Dr Manuel Will from Cambridge's Department of Archaeology, and a Research Fellow at Gonville and Caius College.

"The higher surface-to-volume ratio of a tall, slender body would be an advantage when stalking animals for hours in the dry heat, as a larger skin area increases the capacity for the evaporation of sweat."

"The later addition of body mass coincides with ever-increasing migrations into higher latitudes, where a bulkier body would be better suited for thermoregulation in colder Eurasian climates," he says.

However, Dr Will points out that, while these are valid theories, vast gaps in the fossil record continue to mask absolute truths. In fact, Will and colleagues often had to estimate body sizes from highly fragmented remains -- in some cases from just a single toe bone.

The study found body size to be highly variable during earlier hominin history, with a range of differently shaped species: from broad, gorilla-like Paranthropus to the more wiry or 'gracile' Australopithecus afarensis. Hominins from four million years ago weighed a rough average of 25kg and stood at 125-130cm.

As physicality morphs over deep time, increasingly converging on larger body sizes, the scientists observe three key "pulses" of significant change.

The first occurs with the dawn of our own defined species bracket, Homo, around 2.2-1.9m years ago. This period sees a joint surge in both height (around 20 cm) and weight (between 15-20kg).

Stature then separated from heft with a height increase alone of 10cm between 1.4-1.6m years ago, shortly after the emergence of Homo erectus. "From a modern perspective this is where we see a familiar stature reached and maintained. Body mass, however, is still some way off," explains Will.

It's not until a million years later (0.5-0.4m years ago) that consistently heavier hominins appear in the fossil record, with an estimated 10-15kg greater body mass signalling adaptation to environments north of the Mediterranean.

"From then onwards, average body height and weight stays more or less the same in the hominin lineage, leading ultimately to ourselves," says Will.

There are, however, a couple of exceptions to this grand narrative: Homo naledi and Homo floresiensis*. Recently discovered remains suggest these species swam against the tide of increasing body size through time.

"They may have derived from much older small-bodied ancestors, or adapted to evolutionary pressures occurring in small and isolated populations," says Will. Floresiensis was discovered on an Indonesian island.

"Our study shows that, other than these two species, hominins that appear after 1.4m years ago are all larger than 140cm and 40kg. This doesn't change until human bodies diversify again in just the last few thousand years."

"These findings suggest extremely strong selective pressures against small body sizes which shifted the evolutionary spectrum towards the larger bodies we have today."

Will and colleagues say evolutionary pressures that may have contributed include 'cladogenesis': the splitting of a lineage, with one line -- the smaller-bodied one, in this case -- becoming extinct, perhaps as a result of inter-species competition.

They also suggest that sexual dimorphism -- the physical distinction between genders, with females typically smaller in mammals -- was more prevalent in early hominin species but then steadily ironed out by evolution.

Study co-author Dr Jay Stock, also from Cambridge's Department of Archaeology, suggests this growth trajectory may continue.

"Many human groups have continued to get taller over just the past century. With improved nutrition and healthcare, average statures will likely continue to rise in the near future. However, there is certainly a ceiling set by our genes, which define our maximum potential for growth," Stock says.

"Body size is one of the most important determinants of the biology of every organism on the planet," adds Will. "Reconstructing the evolutionary history of body size has the potential to provide us with insights into the development of locomotion, brain complexity, feeding strategies, even social life."


*Both Homo naledi and Homo floresiensis are of a surprisingly young age, says Will: between ~300,000 and 100,000-60,000 years respectively

Story Source: University of Cambridge. "Height and weight evolved at different speeds in the bodies of our ancestors." ScienceDaily. (accessed November 8, 2017).

Journal Reference:
Manuel Will, Adrián Pablos, Jay T. Stock. Long-term patterns of body mass and stature evolution within the hominin lineage. Royal Society Open Science, 2017; 4 (11): 171339 DOI: 10.1098/rsos.171339

Body size is a central determinant of a species' biology and adaptive strategy, but the number of reliable estimates of hominin body mass and stature have been insufficient to determine long-term patterns and subtle interactions in these size components within our lineage. Here, we analyse 254 body mass and 204 stature estimates from a total of 311 hominin specimens dating from 4.4 Ma to the Holocene using multi-level chronological and taxonomic analytical categories. The results demonstrate complex temporal patterns of body size variation with phases of relative stasis intermitted by periods of rapid increases. The observed trajectories could result from punctuated increases at speciation events, but also differential proliferation of large-bodied taxa or the extinction of small-bodied populations. Combined taxonomic and temporal analyses show that in relation to australopithecines, early Homo is characterized by significantly larger average body mass and stature but retains considerable diversity, including small body sizes. Within later Homo, stature and body mass evolution follow different trajectories: average modern stature is maintained from ca 1.6 Ma, while consistently higher body masses are not established until the Middle Pleistocene at ca 0.5–0.4 Ma, likely caused by directional selection related to colonizing higher latitudes. Selection against small-bodied individuals (less than 40 kg; less than 140 cm) after 1.4 Ma is associated with a decrease in relative size variability in later Homo species compared with earlier Homo and australopithecines. The isolated small-bodied individuals of Homo naledi (ca 0.3 Ma) and Homo floresiensis (ca 100–60 ka) constitute important exceptions to these general patterns, adding further layers of complexity to the evolution of body size within the genus Homo. At the end of the Late Pleistocene and Holocene, body size in Homo sapiens declines on average, but also extends to lower limits not seen in comparable frequency since early Homo.

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