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Australopithecus sediba
#1
Ceph Wrote:Australopithecus sediba

[Image: ss13-2.jpg]

Temporal range: 1.98–1.977Ma Pleistocene

Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Order:Primates
Family:Hominidae
Genus:†Australopithecus
Species:Australopithecus sediba

The fossil skeletons of Au. sediba from Malapa cave are so complete that scientists can see what entire skeletons looked like near the time when Homo evolved. Details of the teeth, the length of the arms and legs, and the narrow upper chest resemble earlier Australopithecus, while other tooth traits and the broad lower chest resemble humans. These links indicate that Au. sediba may reveal information about the origins and ancestor of the genus Homo. Functional changes in the pelvis of Au. sediba point to the evolution of upright walking, while other parts of the skeleton retain features found in other australopithecines. Measurements of the strength of the humerus and femur show that Au. sediba had a more human-like pattern of locomotion than a fossil attributed to Homo habilis. These features suggest that Au. sediba walked upright on a regular basis and that changes in the pelvis occurred before other changes in the body that are found in later specimens of Homo. The Australopithecus sediba skull has several derived features, such as relatively small premolars and molars, and facial features that are more similar to those in Homo. However, despite these changes in the pelvis and skull, other parts of Au. sediba skeleton shows a body similar to that of other australopithecines with long upper limbs and a small cranial capacity. The fossils also show that changes in the pelvis and the dentition occurred before changes in limb proportions or cranial capacity.  

The combination of primitive and derived traits in Australopithecus sediba shows part of the transition from a form adapted to partial arboreality to one primarily adapted to bipedal walking. but the legs and feet point to a previously unknown way of walking upright. With each step, Australopithecus sediba turned its foot inward with its weight focused on the outer edge of the foot. This odd way of striding may mean that upright walking evolved on more than one path during human evolution.

Where Lived:  Southern Africa (South Africa)
When Lived:  Between 1.977 and 1.98 million years ago
[Image: sediba.jpg?1297322557]

Year of Discovery:  2008
History of Discovery: 
The first specimen of Australopithecus sediba, the right clavicle of MH1, was discovered on the 15th of August in 2008 by Matthew Berger, son of paleoanthropologist Lee Berger from the University of Witwatersrand, at the site of Malapa, South Africa. It was announced in Science in April 2010. 

Height & Weight Supplemental Information: 
MH1, a juvenile male around 12-13 years old, was a maximum of 1.3 meters (4’3”) tall. In general, Australopithecus sediba had small bodies with long arms. Australopithecus sediba had a level of sexual dimorphism similar to that found in modern humans. 

We don’t know everything about early humans—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.

Since Au. sediba was discovered recently, there are many unanswered questions about it. Below are some of the still unanswered questions about Australopithecus sediba that may be answered with future discoveries:

What is the time range and geographic range of Australopithecus sediba? This question can only be answered by the finds of more specimens.
Will the close relationship between Au. sediba and Homo be confirmed by future finds? 
The first paper:

Berger, L.R., de Ruiter, D.J., Churchill, S.E., Schmid, P., Carlson, K.J., Dirks, P.H.G.M., Kibii, J.M., 2010. Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa. Science 328, 195-204.

[Image: imagen-karabo.jpg]

Other recommended readings:

Balter, M., 2010. Candidate human ancestor from South Africa sparks praise and debate. Science 328, 154-155.

Dirks, P.G.H.M, Kibii, J.M., Kuhn, B.F., Steininger, C., Churchill, S.E., Kramers, J.D., Pickering, R., Farber, D.L., Mériaux, A.-S., Herries, A.I.R, King, G.C.P., Berger, L.R., 2010. Geological setting and age of Australopithecus sediba from Southern Africa. Science 328, 205-208.

Wong, K., 2010. Spectacular South African skeletons reveal new species from murky period of human evolution. Scientific American 8 April 2010 (Available a thttp://www.scientificamerican.com/article.cfm?id=south-african-hominin-fossil, 9 April 2010).

Wong, K., 2010. Fossils of our family. Scientific American June 2010.

How They Survived: 
Due to the mixture of derived features in the pelvis and primitive features in other areas of the skeleton, it is unclear to some researchers the extent to which Au. sediba used arboreal habitats or remained on the ground using terrestrial bipedal locomotion. Relatively long arms and a small body may have allowed Au. sediba to utilize arboreal habitats. Derived features in the pelvis and the pattern of diaphyseal strength in the humerus and femur suggest that Au. sediba might have regularly walked upright in a way that was more similar to modern humans than to earlier members of Australopithecus.

The possible increasing emphasis on upright walking is accompanied by differences in the skull and teeth compared with other australopithecines.  The relatively small dentition of Au. sediba may signal a dietary change. As more features of the environment and functional morphology of Australopithecus sediba are discovered, their way of life will become clearer.


Evolutionary Tree Information: 
Australopithecus sediba’s mixture of primitive traits found in other australopithecines and derived traits also found in Homo makes the evolutionary position of Au. sediba an interesting question. Similar to other australopithecine species, Au. sediba is small in size, with long arms and small cranial capacity. Its features are more derived than those of Au. anamensis and Au. afarensis. Australopithecus sediba bears a strong resemblance to Au. africanus, a fossil species that is also found in South Africa. They have similar skull, facial and dental features. The species differ in features such as the shape of the cranium and the face, showing that Au. sediba was more derived compared with Au. africanus. The combination of similarities and differences led Berger and his colleagues to conclude that Au. sediba was descended from Au. africanus.

The traits Australopithecus sediba shares with Homo may indicate a closer relationship between this species and Homo than between other australopithecines and Homo. Berger and his colleagues proposed that Au. sediba is ancestral to the genus Homo or is closely related to the ancestral species. However, there are earlier and contemporaneous fossils attributed to Homo, making it difficult to think of Au. sediba as an ancestor to Homo.  The time range for the species Au. sediba is currently unknown. It is not known where in that time span the current sample falls and how it fits with the time ranges of other species. Another possibility is that Au. sediba is closely related to another, still unknown species that was ancestral to the genus Homo. While that species evolved into Homo, Au. sediba may have persisted leading to the overlap in time between Homo and Au. sediba.

Other researchers question the idea that Au. sediba and Homo are closely related at all, citing the possibility that the juvenile MH1 may not reflect the adult post-cranial characteristics of Au. sediba or that the postcranial features of Au. sediba may not be unique to the taxon, but may be found in other australopithecines. Another possibility raised by researchers is that the Malapa finds belong in the genus Homo. The number of different ideas about the placement of the Malapa finds stems from the debate on how early members of the genus Homo should be recognized and which fossils belong in it. There is a question of whether cranial and dental features or the advent of modern postcranial body proportions are most important in defining Homo, since some fossils, such as the Australopithecus sediba remains, contain a combination of features. 
http://humanorigins.si.edu/evidence/huma...cus-sediba
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MH1 is a juvenile australopithecine

MH1 is a juvenile australopithecine, about 12-13 years old. It was the first specimen of Au. sediba found at Malapa Cave. Both cranial and postcranial remains have been recovered from this individual. The mixture of primitive and derived traits may help link the genus Australopithecus with the genus Homo. 

[Image: a_sediba_MH1_p_34_LB.jpg]
Image Credit: Courtesy of Lee Berger
MH1
Code interpretation:  Malapa Hominin 1
Site:  Malapa
Date of discovery:  2008
Discovered by:  Matthew Berger
Age:  Between 1.95 and 1.78 million years old
Species:  Australopithecus sediba
Text: 
Between 1.95 and 1.78 million years old
http://humanorigins.si.edu/evidence/huma...ossils/mh1
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The Mosaic Nature of Australopithecus sediba
Lee R. Berger

he site of Malapa, South Africa, has yielded perhaps the richest assemblage of early hominin fossils on the continent of Africa. The fossil remains of Au. sediba were discovered in August of 2008, and the species was named in 2010 (1) and given a provisional age of ∼1.78 to 1.95 Ma (2). In 2011, detailed studies of four critical areas of anatomy of these remains were published (3–6), and a refined date of ∼1.977 to 1.98 Ma was proposed (7). The six articles presented in full in the online edition of Science (www.sciencemag.org/site/extra/sediba), with abstracts in print (pp. 164–165), complete the initial examination of the prepared material attributed to three individuals: the holotype and paratype skeletons, commonly referred to as MH1 and MH2, and the adult isolated tibia referred to as MH4. They, along with the cumulative research published over the past 3 years, provide us with a comprehensive examination of the anatomy of a single species of early hominid.

Irish et al. examine highly heritable nonmetric dental traits in Au. sediba. The species appears phylogenetically distinct from East African australopiths but close to Au. africanus, forming a southern African australopith clade. The latter shares some derived states with a clade comprising four fossil samples of the genus Homo. This result has implications for our present understanding of hominin phylogeny through the terminal Pliocene and suggests a possibility that Au. sediba, and perhaps Au. africanus, did not descend from the Au. afarensis lineage. De Ruiter et al. examine mandibular material attributable to MH2, including the previously unknown mandibular incisors and premolars of Au. sediba. As seen elsewhere in the cranium and skeleton, these mandibular remains share similarities with those of other australopiths but differ from Au. africanus in both size and shape, as well as in their ontogenetic growth trajectory. These results further support the claim that Au. sediba is taxonomically distinct from Au. africanus. Where the Au. sediba mandibles differ from those of Au. africanus, they appear most similar to those of representatives of early Homo.

[Image: F1.medium.gif]
Composite reconstruction of Au. sediba based on recovered material from MH1, MH2, and MH4 and based on the research presented in the accompanying manuscripts. Because all individuals recovered to date are approximately the same size, size correction was not necessary. Femoral length was established by digitally measuring a complete femur of MH1 still encased in rock. For comparison, a small-bodied female modern H. sapiens is shown on the left and a male Pan troglodytes on the right.
CREDIT: LEE R. BERGER AND THE UNIVERSITY OF THE WITWATERSRAND

Churchill et al. explore the upper limb elements of Au. sediba, describing the most complete and undistorted humerus, radius, ulna, scapula, clavicle, and manubrium yet described from the early hominin record, all associated with one individual. With the exception of the hand skeleton (3), the upper limbs of the Malapa hominins are largely primitive in their morphology. Au. sediba thus shares with other australopiths an upper limb that was well suited for arboreal climbing and possibly suspension, although perhaps more so than has previously been suggested for this genus.

Remains of the rib cage of Au. sediba are described by Schmid et al. and reveal a mediolaterally narrow upper thorax like that of the large-bodied apes and unlike the broad cylindrical chest seen in humans. In conjunction with the largely complete remains of the shoulder girdle, the morphological picture that emerges is one of a conical thorax with a high shoulder joint (producing an ape-like “shrugged” shoulder appearance) and thus a configuration that is perhaps uniquely australopith and would not have been conducive to human-like swinging of the arms during bipedal striding and running. The less well-preserved elements of the lower rib cage suggest a degree of human-like mediolateral narrowing to the lower thorax, indicating a rather unsuspected mosaic anatomy in the chest that is not like that observed in Homo erectus or H. sapiens.

Williams et al. analyze elements of the cervical, thoracic, lumbar, and sacral regions of the vertebral column, showing that Au. sediba had the same number of lumbar vertebrae as modern humans but possessed a functionally longer and more flexible lower back. Morphological indicators of strong lumbar curvature suggest that Au. sediba was derived in this regard relative to Au. africanus and was more similar to the Nariokotome H. erectus skeleton.

Finally, DeSilva et al. describe the lower limb anatomy of Au. sediba and propose a specific biomechanical hypothesis for how this species walked. In isolation, the anatomies of the heel, midfoot, knee, hip, and back are unique and curious, but in combination they are internally consistent for a biped walking with a hyperpronating gait. The implications are that multiple forms of bipedalism were once practiced by our early hominin ancestors.

This examination of a large number of associated, often complete and undistorted elements gives us a glimpse of a hominin species that appears to be mosaic in its anatomy and that presents a suite of functional complexes that are different from both those predicted for other australopiths and those of early Homo. Such clear insight into the anatomy of an early hominin species will clearly have implications for interpreting the evolutionary processes that affected the mode and tempo of hominin evolution and the interpretation of the anatomy of less well-preserved species.
http://www.sciencemag.org/content/340/6129/163
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Dental Morphology and the Phylogenetic “Place” of Australopithecus sediba
Joel D. Irish1, Debbie Guatelli-Steinberg, Scott S. Legge, Darryl J. de Ruiter, Lee R. Berger

ABSTRACT
To characterize further the Australopithecus sediba hypodigm, we describe 22 dental traits in specimens MH1 and MH2. Like other skeletal elements, the teeth present a mosaic of primitive and derived features. The new nonmetric data are then qualitatively and phenetically compared with those in eight other African hominin samples, before cladistic analyses using a gorilla outgroup. There is some distinction, largely driven by contrasting molar traits, from East African australopiths. However, Au. sediba links with Au. africanus to form a South African australopith clade. These species present five apomorphies, including shared expressions of Carabelli’s upper first molar (UM1) and protostylid lower first molar (LM1). Five synapomorphies are also evident between them and monophyletic http://carnivoraforum.com/topic/10285935/1/Homo habilis[/url]/rudolfensis + H. erectus. Finally, a South African australopith + Homo clade is supported by four shared derived states, including identical LM1 cusp 7 expression.
http://www.sciencemag.org/content/340/6129/1233062
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Mandibular Remains Support Taxonomic Validity of Australopithecus sediba
Darryl J. de Ruiter, Thomas J. DeWitt, Keely B. Carlson, Juliet K. Brophy, Lauren Schroeder, Rebecca R. Ackermann, Steven E. Churchill, Lee R. Berger

ABSTRACT
Since the announcement of the species Australopithecus sediba, questions have been raised over whether the Malapa fossils represent a valid taxon or whether inadequate allowance was made for intraspecific variation, in particular with reference to the temporally and geographically proximate species Au. africanus. The morphology of mandibular remains of Au. sediba, including newly recovered material discussed here, shows that it is not merely a late-surviving morph of Au. africanus. Rather—as is seen elsewhere in the cranium, dentition, and postcranial skeleton—these mandibular remains share similarities with other australopiths but can be differentiated from the hypodigm of Au. africanus in both size and shape as well as in their ontogenetic growth trajectory. http://www.sciencemag.org/content/340/6129/1232997
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The Upper Limb of Australopithecus sediba
Steven E. Churchill, Trenton W. Holliday, Kristian J. Carlson, Tea Jashashvili, Marisa E. Macias, Sandra Mathews, Tawnee L. Sparling, Peter Schmid, Darryl J. de Ruiter, Lee R. Berger

ABSTRACT
The evolution of the human upper limb involved a change in function from its use for both locomotion and prehension (as in apes) to a predominantly prehensile and manipulative role. Well-preserved forelimb remains of 1.98-million-year-old Australopithecus sediba from Malapa, South Africa, contribute to our understanding of this evolutionary transition. Whereas other aspects of their postcranial anatomy evince mosaic combinations of primitive (australopith-like) and derived (Homo-like) features, the upper limbs (excluding the hand and wrist) of the Malapa hominins are predominantly primitive and suggest the retention of substantial climbing and suspensory ability. The use of the forelimb primarily for prehension and manipulation appears to arise later, likely with the emergence of Homo erectus.
http://www.sciencemag.org/content/340/6129/1233477
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The Lower Limb and Mechanics of Walking in Australopithecus sediba
Jeremy M. DeSilva, Kenneth G. Holt, Steven E. Churchill, Kristian J. Carlson, Christopher S. Walker, Bernhard Zipfel, Lee R. Berger

ABSTRACT
The discovery of a relatively complete Australopithecus sediba adult female skeleton permits a detailed locomotor analysis in which joint systems can be integrated to form a comprehensive picture of gait kinematics in this late australopith. Here we describe the lower limb anatomy of Au. sediba and hypothesize that this species walked with a fully extended leg and with an inverted foot during the swing phase of bipedal walking. Initial contact of the lateral foot with the ground resulted in a large pronatory torque around the joints of the foot that caused extreme medial weight transfer (hyperpronation) into the toe-off phase of the gait cycle (late pronation). These bipedal mechanics are different from those often reconstructed for other australopiths and suggest that there may have been several forms of bipedalism during the Plio-Pleistocene.
http://www.sciencemag.org/content/340/6129/1232999

Ceph Wrote:Not much size difference between male and female Australopithecines

Date: April 28, 2015
Source: Penn State
Summary: Lucy and other members of the early hominid species Australopithecus afarensis probably were similar to humans in the size difference between males and females, according to new research.

[Image: 150428151512_1_540x360.jpg]
Two femora, on the left is a large, presumably male specimen and on the right is Lucy. The difference between these two gives the impression of a large size differences between the sexes. However, inclusion of the many intermediately sizes specimens from this species indicates that the size variation is similar to moderately dimorphic humans.
Credit: Philip Reno, Penn State

Lucy and other members of the early hominid species Australopithecus afarensis probably were similar to humans in the size difference between males and females, according to researchers from Penn State and Kent State University.

"Previous convention in the field was that there were high levels of dimorphism in the Australopithecus afarensis population," said Philip Reno, assistant professor of anthropology, Penn State. "Males were thought to be much larger than females." Sexual dimorphism refers to differences between males and females of a species. These can show up, for example, in body size and weight or in the size of the canine teeth. For Australopithecines, canines of males and females are about the same size, but it was assumed their body sizes differed. Other primates have varying degrees of sexual dimorphism. Gorillas are highly dimorphic, with males weighing as much as 200 pounds more than females. Chimpanzees are only moderately sexually dimorphic with males weighing about 18 pounds more than females on average. Humans are moderately sexually dimorphic. Previously, researchers assumed that A. afarensis was similar to or even more dimorphic than gorillas in sexual size differences.

Lucy is probably the most famous example of A. afarensis, a supposed female who measures 3.5 feet in height. Also often used as an example of this species is A.L. 128/129, another small specimen assumed to be female. However, A. afarensis existed long before brains in the human line became large enough to require the alteration in the pelvic structure that both allows for large-headed baby births and easy identification of female specimens. "There is no reason why Lucy, if female, would have the wide notched pelvic bone of a human female," said Reno. "We can't really sex Australopithecines."

While Lucy may not be female, she is the earliest discovered and most well preserved example of A. afarensis and so has been used as a model for the study of other specimens. Recently, another reasonably intact A. afarensis, Kadanuumuu, was uncovered and he stood 5 to 5.5 feet tall. Reno and C. Owen Lovejoy, distinguished professor of human evolutionary studies, Kent State, developed the Template Method to compare different skeletons and determine the range and dimorphism of A. afarensis. They report their results in the April 28th issue of PeerJ.

The pair used both Lucy and Kadanuumuu as templates for the method, which compares similar parts of the skeleton from partial remains to the nearly complete remains of the template. For example, the researchers compared the size of 41 specimens from different parts of the skeleton to that of Lucy. By determining the ratio of these specimens to Lucy, they could then calculate the relative size of partial bones from incomplete skeletons and better determine the size variation in the species.

Another method of determining sexual dimorphism is the Geometric Mean Method, which uses 11 characteristics to estimate size. Unfortunately, in this method, because Lucy is so complete a skeleton, she supplies seven or eight of the metrics; A.L. 128/129 supplies an additional three. So two very small individuals supply ten of the eleven metrics.

"In essence, Lucy is counted multiple times in the Geometric Mean Method, which gives her a skewed impact on the size of individuals," said Reno. "In our method, Lucy is weighted only once. The range shows intermediate moderate levels of sexual dimorphism, A. afarensis is within the human dimorphic range."

Another problem in comparing various A. afarensis skeletons is that except for those found in A.L. 333 -- a geologically contemporaneous group -- individuals could be 10 thousand to 100 thousand years apart in age. During that time, the overall size of the species could have changed. Neither method can accommodate this potential time warp, but the researchers acknowledge that the time range is another variable that must be considered. Because Lucy was the first discovered specimen, it was easy to assume that she was a typical size specimen, but it now appears that Lucy is at the lower edge of A. afarensis size and that Kadanuumuu may be an outlier at the upper edge of the range with many intermediate sized specimens between the two, according to Reno.

Story Source:

The above post is reprinted from materials provided by Penn State. Note: Materials may be edited for content and length.

Journal Reference:

Philip L. Reno, C. Owen Lovejoy. From Lucy to Kadanuumuu: balanced analyses ofAustralopithecus afarensisassemblages confirm only moderate skeletal dimorphism. PeerJ, 2015; 3: e925 DOI: 10.7717/peerj.925
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  • Claudiu Constantin Nicolaescu
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#2
Height and weight evolved at different speeds in the bodies of our ancestors

Date: November 8, 2017
Source: University of Cambridge
Summary:
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."

NOTE

*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. www.sciencedaily.com/releases/2017/11/171108092241.htm (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

Abstract
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.

Attached to this post:[Image: attach.png] Long_term_patterns_of_body_mass_and_stature_evolution_within_the_hominin_lineage.pdf (1.37 MB)
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#3
Scientists confirm pair of skeletons are from same early hominin species

January 17, 2019, New York University

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A life reconstruction of Au. sediba, commissioned by the University of Michigan's Museum of Natural History Credit: © Sculpture Elisabeth Daynes /Photo S. Entressangle

Separate skeletons suggested to be from different early hominin species are, in fact, from the same species, a team of anthropologists has concluded in a comprehensive analysis of remains first discovered a decade ago.

The research appears in a special issue of the journal PaleoAnthropology and is part of a series of articles that offers the most comprehensive accounting to date of Australopithecus sediba (A. sediba), a hominin species discovered in South Africa in 2008.

The fossil site of Malapa in the Cradle of Humankind, South Africa yielded two partial skeletons: a juvenile male individual—Malapa Hominin 1 (MH1)—and an adult female (MH2); each is more complete than the famous "Lucy" specimen from Ethiopia. The discovery of Malapa was made by Lee Berger, a professor in the Evolutionary Studies Institute at the University of the Witwatersrand in South Africa, who, with colleagues, dated the site to just under two million years old. They named a new hominin species, Australopithecus sediba, based on MH1 and MH2.

Over the past decade, researchers have been piecing together these skeletons; the culmination of their work appears in PaleoAnthropology, co-edited by New York University anthropologist Scott Williams and Dartmouth College anthropologist Jeremy DeSilva. The issue's nine papers, which analyze 135 fossils, outline A. sediba's skull, vertebral column, thorax, pelvis, upper limb, hand, and lower limb as well as its body proportions and walking mechanics.

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A life reconstruction of Au. sediba, commissioned by the University of Michigan's Museum of Natural History Credit: © Sculpture Elisabeth Daynes /Photo S. Entressangle

The papers' consensus is that A. sediba is a unique species distinct from both A. africanus, with which it shares a close geographic proximity, and from early members of the genus Homo (e.g., H. habilis) in both East and South Africa, but that it shares features with both groups, suggesting a close evolutionary relationship.

"Our interpretations in the papers suggest that A. sediba was adapted to terrestrial bipedalism, but also spent significant time climbing in trees, perhaps for foraging and protection from predators," says Williams, whose research in the issue centered on the axial skeleton (vertebrae, ribs, and sternum). "This larger picture sheds light on the lifeways of A. sediba and also on a major transition in hominin evolution, that of the largely ape-like species included broadly in the genus Australopithecus to the earliest members of our own genus, Homo."

A few years ago, a separate research group posited that the hominin fossils at Malapa belonged to two different species—in part due to differences in their lumbar vertebrae. However, an analysis by Williams and his colleagues, including two Ph.D. candidates in anthropology at NYU, Jennifer Eyre and Thomas Prang, indicates that both are from A. sediba and that distinctions are due to age.

"The differences in these vertebrae can simply be attributed to their developmental age differences: the juvenile individual's vertebrae have not yet completed growth, whereas the adult's vertebra growth is complete," he explains. "As it happens, the two Homo erectus skeletons we have are juveniles, so MH1 looks more similar to them because it too is a juvenile."

Read more at: https://phys.org/news/2019-01-scientists...n.html#jCp
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Statistical study finds it unlikely South African fossil species is ancestral to humans

by University of Chicago Medical Center

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Fossil casts of Australopithecus afarensis (left), Homo habilis (center), and Australopithecus sediba (right) Credit: Matt Wood, UChicago

Statistical analysis of fossil data shows that it is unlikely that Australopithecus sediba, a nearly two-million-year-old, apelike fossil from South Africa, is the direct ancestor of Homo, the genus to which modern-day humans belong.
The research by paleontologists from the University of Chicago, published this week in Science Advances, concludes by suggesting that Australopithecus afarensis, of the famous "Lucy" skeleton, is still the most likely ancestor to the genus Homo.
The first A. sediba fossils were unearthed near Johannesburg in 2008. Hundreds of fragments of the species have since been discovered, all dating to roughly two million years ago. The oldest known Homofossil, the jawbone of an as yet unnamed species found in Ethiopia, is 2.8 million years old, predating A. sediba by 800,000 years.
Despite this timeline, the researchers who discovered A. sediba have claimed that it is an ancestral species to Homo. While it is possible that A. sediba (the hypothesized ancestor) could have postdated earliest Homo (the hypothesized descendant) by 800,000 years, the new analysis indicates that the probability of finding this chronological pattern is highly unlikely.
"It is definitely possible for an ancestor's fossil to postdate a descendant's by a large amount of time," said the study's lead author Andrew Du, Ph.D., who will join the faculty at Colorado State University after concluding his postdoctoral research in the lab of Zeray Alemseged, Ph.D., the Donald M. Pritzker Professor of Organismal and Biology and Anatomy at UChicago.
"We thought we would take it one step further to ask how likely it is to happen, and our models show that the probability is next to zero," Du said.
Du and Alemseged also reviewed the scientific literature for other hypothesized ancestor-descendant relationships between two hominin species. Of the 28 instances they found, only one first-discovered fossil of a descendant was older than its proposed ancestor, a pair of Homo species separated by 100,000 years, far less than the 800,000 years separating A. sediba and earliest Homo. For context, the average lifespan of any hominin species is about one million years.
"Again, we see that it's possible for an ancestor's fossil to postdate its descendant's," Du said. "But 800,000 years is quite a long time."
Alemseged and Du maintain that Australopithecus afarensisis a better candidate for the direct ancestor of Homo for a number of reasons. A. afarensis fossils have been dated up to three million years old, nearing the age of the first Homo jaw. Lucy and her counterparts, including Selam, the fossil of an A. afarensis childthat Alemseged discovered in 2000, were found in Ethiopia, just miles from where the Homo jaw was discovered. The jaw's features also resemble those of A. afarensis closely enough that one could make the case it was a direct descendant.
"Given the timing, geography and morphology, these three pieces of evidence make us think afarensisis a better candidate than sediba," Alemseged said. "One can disagree about morphology and the different features of a fossil, but the level of confidence we can put in the mathematical and statistical analyses of the chronological data in this paper makes our argument a very strong one."

https://phys.org/news/2019-05-statistica...ecies.html


Journal Reference:

A. Du el al., "Temporal evidence shows Australopithecus sediba is unlikely to be the ancestor of Homo," Science Advances (2019). advances.sciencemag.org/content/5/5/eaav9038

Abstract
Understanding the emergence of the genus Homo is a pressing problem in the study of human origins. Australopithecus sediba has recently been proposed as the ancestral species of Homo, although it postdates earliest Homo by 800,000 years. Here, we use probability models to demonstrate that observing an ancestor’s fossil horizon that is at least 800,000 years younger than the descendant’s fossil horizon is unlikely (about 0.09% on average). We corroborate these results by searching the literature and finding that within pairs of purported hominin ancestor–descendant species, in only one case did the first-discovered fossil in the ancestor postdate that from the descendant, and the age difference between these fossils was much less than the difference observed between A. sediba and earliest Homo. Together, these results suggest it is highly unlikely that A. sediba is ancestral to Homo, and the most viable candidate ancestral species remains Australopithecus afarensis.

https://advances.sciencemag.org/content/5/5/eaav9038
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Oh my, a fossil that is 800,000 years older than our genus isn’t our ancestors?
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I never understood why A. sediba was considered a possible ancestor. Not only is it older, it also seems to have evolved a different form of walking to us .
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