CSU East Bay Hominids Biological Anthropology Discussion

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California State University - East Bay

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Hypothetical: A researcher claims to have found a hominin in a South African cave site that dates to the Early Pleistocene (~2.5-2 mya). They present an argument that this specimen showed evidence of a strict herbivorous diet that mostly comprised roots and grasses. They also suggest that, despite having a full suite of bipedal adaptations (including the convergent hallux), this animal was well-adapted to climbing trees. For the following response I would like you to:

              -Explain how the researchers may have obtained the late Pliocene date

-What methods could be employed in this environment/region and why other methods would not work

                                            -how do the methods work?

              -Explain the craniofacial & dental morphologies that justify the dietary claim

                             -What are the traits and what are the functions of them?

-Explain what evidence might support the assertion that these animals were still adapted to climbing trees

              -What are the traits and what are the functions of them?

-If you were to attribute this to a species (or even a grade), what would it be?

              -Briefly contrast this specimen with other hominin forms at the time

Question #2

The emergence and success of our genus can be attributed to a variety of factors that likely began during the time of Late Australopithecus. This is most strongly associated with a shift in diet that not only influenced greater brain development but also a burgeoning tool culture. Furthermore, once this shift occurred, our ancestors became increasingly more mobile and rapidly refined stone tool technologies. This trend marks the story of our genus and leads to the continued success of our species, Homo sapiens.

First:

Explain the climatic conditions that may have influenced this dietary shift

Second:

Utilizing the hominin fossil record and your knowledge of the adaptive significance of each new morphology and technology, discuss:

-the presumed impacts of this diet on brain structure and function

-the original tool culture (structure and function) that emerged in response to this

Third:

Discuss the next wave of technological achievement and the Hominins associated with it. How did the development of Acheulean tools reflect a new way of hominin thinking?

Finally:

The pinnacle of hominin cognitive development is reflected only in Homo sapiens. What did this new material culture look like? Why do you think that this emerged only in African Homo sapiens and not in Neanderthals? Remember that the two populations had comparable cranial capacities.

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Australopithecus Savanna Adapted Hominins Early Bipeds  There is very little evidence regarding the earliest bipedal hominins Sahelanthropus tchadensis  Sahelanthropus tchadensis  Orrorin tugenensis  Ardipithecus ramidus  Besides Ardipithecus, these fossil hominins are still debatable  Either due to fragmentary remains or poor context Orrorin tugenensis Earliest Bipeds  Ardipithecus ramidus (“Ardi”) is proven to be a biped  Dated between 4.5 and 4.2 mya  Anterior placement of foramen magnum  Iliac blades shaped and oriented for bipedal balance  Also retains primitive arboreal traits  Divergent hallux (big toe)  Disproportional hand/finger lengths  Good for climbing Exiting the forest  Evidence from Ardipithecus suggests that bipedalism first evolved in a woodland environment  Arboreal and dietary adaptations  Generalized dental toolkit  Proportional incisors, canines, premolars, and molars  No specializations  Isotopic analysis shows that it consumed forest and grassland resources  Lived in a mixed environment Exiting the forest  Once hominins left the forest, they needed to adapt to a new resources base  Lack of soft resources to consume  Fruit/young leaves  Moving to savanna grasslands necessitated a diet of grasses, roots, seeds, or other tough resources  Dentition and masticatory abilities needed to toughen up Australopithecus  Australopithecus is a fossil genus of hominin ancestors adapted to savanna resources  More of a grade than a clade  No clear phylogenetic relationships  The grade is identifiable through a set of traits  Enlarged post-canine dentition  Premolars and molars  Thickened tooth enamel  Some degree of cranial traits associated with heavy chewing  As they relate to the temporalis and masseter muscles Australopithecus  In addition to the dietary adaptation's australopithecines display a full suit of bipedal traits  Not as efficient as modern humans  But more so than Ardipithecus  Slow, lumbering bipedalism  Walking and standing  Not running  Some arboreal associated traits as well  Longer arms than legs  Long hands/fingers  Robust Ischia for hamstring muscle attachment Australopithecus  The aforementioned traits are used to broadly identify members of this grade  Diversity exists within the grade  These hominins are dated between 4.9-1.2 mya  More than 3.5 million years  Multiple species existed through this time  All had the general suite of traits  Varied in modifications Australopithecus Diversity  The span of Australopithecus can be divided into early and late phases  Early phase includes transitional species and the archetype for a generalized savanna dweller  Australopithecus anamensis  Australopithecus afarensis  Late phase illustrates a divergence in the grade with species specializing to different savanna resources  Robust Australopithecines  Gracile Australopithecines Savanna Resources  Savannas are a type of seasonal grassland  Punctuated sparse woodlands and gallery forests  Sharp contrast to the environments characterizing most of primate evolution  Available resources are tough to chew and to digest  Grasses are abrasive  Roots and tubers are tough to chew  Seeds and nuts can damage teeth Savanna Resources  Meat is another resource plentiful on the savanna  Primates have never been carnivorous  Insectivorous  Omnivorous with minimal meat inclusion (small vertebrates maybe)  Was not immediately accessible or desirable  Savanna vegetation was preadapted to  Fallback foods  Not entirely nutritious, but plentiful Early phase Australopiths  The earliest member of this genus is Australopithecus anamensis  Relatively fragmented fossil assemblage  Dates between 4.2-3.9 mya  There are a few elements that suggest this was a biped  Anteriorly placed foramen magnum  Robust distal Tibia  Teeth tell a story of transitionary diet Australopithecus anamensis  Au. anamensis is interesting due to its relatively broad incisors with enlarged postcanine teeth and thick enamel  Broad incisors are uncharacteristic of the Australopithecus grade  Similar to Chimpanzees  Frugivore adaptation  The large post-canine teeth and thick enamel suggest the inclusion of more fallback foods  Abrasive diet  Au. anamensis is a mosaic fossil  Mix of primitive and derived traits Australopithecus afarensis  Au. afarensis is the best-known Australopithecus species  Lucy  Also, the longest lived  3.9-2.9 mya  Archetype of the grade  Best example of Australopithecus adaptations  Post-canine teeth adapted to abrasive resources  Bipedal with some arboreal adaptions  Brain size on par with chimpanzee (~400-500 cc cranial capacity) Australopithecus afarensis  Au. afarensis was a savanna generalist  Adapted to exploit various resources in its environment  Likely contributes to its 1-million-year existence  Towards the end of the time of Au. afarensis, different specialized versions begin to appear  Likely divergence from within Au. afarensis  Divergence stresses resource specialties Australopithecus divergence  Generalized populations have much flexibility in generating specialists  Remember patterns of selection  Directional and disruptive selection  Acting on a range of variation  Some Australopithecus populations began to heavily emphasize their reliance on abrasive resources  Grasses, roots, seeds  Others found softer food sources  Though these required some ingenuity to access Robust vs Gracile Australopithecines  The are all Australopithecus  Some discuss robust australopithecines in terms of Paranthropus  Can only make such claims if you can prove that they are related (and thus belong in the same genus)  We cannot do this  We keep them in the Grade Australopithecus  This is especially true given the flexibility of the traits used to define the robust forms Lumpers vs Splitters: What are you? Robust Australopithecines  There are three recognized robust Australopithecine species  Australopithecus aethiopicus  ~2.5 mya  Ethiopia  Australopithecus boisei  ~1.4-2.3 mya  Tanzania  Australopithecus robustus  ~2-1.2 mya  South Africa Robust Australopithecines  Robust Austrlopithecines accentuated traits associated with tough to process resources  Post-Canine Megadontia  Increased size of Premolars and molars relative to Au. afarensis  Diminutive Incisors  Massive muscle attachments  Large, flared Zygomatics  Prominent Sagittal Crest  Post-Orbital Constriction/large Temporal Foramen Robust Craniofacial traits Robust Australopithecines  The prominent sagittal crest and postorbital constriction relate to enlarged Temporalis Muscles  The enlarged Zygomatics provide greater surface area for the Masseter Muscles  Both muscle groups associated with chewing force  The Post-Orbital Constriction and Enlarged Temporal Foramen provide the need space for the giant temporalis muscles stretching from the sagittal crest to the mandible Gracile Australopithecines  Robust Australopithecines exploited their niche successfully for more than a million years  During this time, they co-existed with other, less-robust hominins  Both in the genus Australopithecus and Homo  These gracile forms shared many similarities with Au. afarensis but tended to have a smaller build, smaller incisors, and a larger brain Gracile Australopithecines  There are a handful of tentative gracile forms  Au. garhi  Au. africanus  Au. sediba  Some even place Au. afarensis in this group  Essentially anything lacking the specialized traits of the robust forms  We can be a bit more narrow, however, to illustrate a change in form Gracile Australopithecus  The only strong evidence for a new gracile form is found in Australopithecus africanus  Raymond Dart’s original find  ~2.9-2.1 mya  Australopithecus sediba would also qualify but seems to be the same species as Au. africanus  Variation Gracile Australopithecus  Compared with Au. afarensis:  Smaller build  Slightly smaller cheek teeth  Larger cranial capacity  ~430-520  Smaller body with larger brain?  Increased encephalization  Why?  Brain growth facilitated by nutrient intake  New food source?  Likely inclusion of animal protein Meat Eating and Encephalization  Higher energy yield  Easier to digest  Reduction in intestinal tract  Energy conservation in digestion  More nutritious diet paired with reduced energy requirement  Difficult to acquire  One strong benefit of being bipedal is having free hands  Use of implements  Prior to the development of stone tool culture (seen in genus Homo), gracile australopithecines likely used stones as tools to access bone marrow  Influenced lighter build and bigger brain. The Genus Homo Brain Changes  Gracile Australopithecines mostly encompass two species  Australopithecus africanus  Australopithecus sediba  The likely inclusion of animal protein resulted in  A smaller body (shorter digestive tract)  Smaller teeth (easier to chew food)  A larger brain (more energy to fuel brain growth)  These traits trend into the genus Homo Our Genus  The genus Homo emerges during the Australopithecus existence  ~2.4-2.3 Ma  Co-exists with multiple Australopithecus species  Primarily recognized as having a smaller build, smaller teeth, and larger brains  Morphologically very similar to later gracile Australopithecines  Differentiated via stones tools Genus Homo  Characterized by a rapid increase in encephalization and the accompaniment of recognizable stone tool cultures  Tool culture vs. tools?  Some degree of uniformity  Method of development taught and learned socially  Early tool culture (Oldowan) still pretty crude  Function? Oldowan Tools  Relatively simple tools  Hard to identify unless you have a large sample  Stone core  Flakes removed  Creates an edge  Oldowan choppers  Simple tasks  Bone breaking?? Marrow extraction?? Genus Homo  Homo habilis  Morphological and temporal overlap with many Australopiths  ~2.3-1.5 mya  Tanzania  Encephalization jump  510-630 cc  Au. africanus @ 430-520  Gracile skull  Reduced dentition Finding Homo  H. habilis might be controversial but still represents the start of a change  Somewhere around 2.5 mya:  Stone tools appear  Gracile austalopithecines disappear-ish  New gracile forms emerge with a larger cranial capacity Genus Homo  Homo rudolfensis  N. Kenya  1.9-1.8 mya  700-750 cc  Both early homo species associated with stone tools  +expanding encephalization  Meat consumption offered as an explanation Variation  How many species?  H. habilis vs. H. rudolfensis  Minor morphological differences  Sexual dimorphism??  Significant difference in cranial capacity  510 vs. 770  Probably a single species  Modern humans vary by at least 400 cc’s on either side of the scale Last Morphological Shift  Homo erectus  Many traits that carry over from the initial trend  Broad brain case  Frontal and parietal development  Expanded brain:: 8001,250 cc  Next step in bipedal adaptations identifiable in post-crania Homo erectus  The development of modern proportions was the last big step in our morphological evolution  Thereafter evolution along trends  Nariokotome estimated at 5.3 ft tall  1.6-1.5 mya  Longer stride made for easier travel  Pursuit of prey  Regional and Continental travel  Tool kit becomes more sophisticated Homo erectus  As is the case with so many hominin fossils, there is considerable debate regarding the variation and/or diversity of this species  Some propose a divide between African and Asian populations  Homo erectus vs Homo ergaster  Throughout all of the debate, there is very poor evidence supporting the splitting of the one species into multiple  Best diagnosis is that they are all H. erectus and that this species was variable across time and space Acheulean Tools  Acheulean  Handaxes  Bilateral  Cognitive template  An idea of what the final outcome needs to look like  H. erectus & the Acheulean spanned distance and time.  More than 1.5 my  Africa, Europe, Asia Archaic Homo sapiens?  Aka post-erectus grade hominins  Homo heidelbergensis  ~600-800kya  Slightly increased cranial capacity  ~1,300 cc  Advanced Acheulean  More refined  Increased fine motor skills Neanderthal Split  Somewhere around 400-250kya populations of H. heidelbergensis migrated out of Africa  Colonized Europe during glaciation  Maintained advanced Acheulean tools  Mousterian  Developed physiological changes adapted to cold climate  Increased robusticity  Increased respiratory thermoregulation  Wider nasal aperture Homo sapiens  Populations of H. heidelbergensis that stayed in Africa continued evolving  ~300-200 kya  Homo sapiens  Developed more refined tool technology  Levallois::Prepared core  Something new  Art  Ochre at ~164 kya  Shell Beads at ~ 100 And then…?  H. sapiens developed more sophisticated tools and artistic expression in Africa  Neanderthals specialized to Ice Age climates in Europe  ~45 kya wave of H. sapiens migration into Europe  Not the first migration  But the first successful  Climate change + advanced culture likely to have influenced the replacement of Neanderthals Neanderthal DNA  Neanderthals are recent enough to have preserved Ancient DNA (aDNA)  Genetically distinct from African Homo sapiens  Of course they are, they were geographically separated  Genetically distinct does not mean separate species  Unique mutations occurred in Neanderthal populations  Among other things, these account for the different anatomy/physiology Homo sapiens neanderthalensis  Neanderthals represent a cross-roads in the difficulties of species identification  Paleospecies identified by observable morphology in the fossil record  Existing species identified via reproductive continuity  Biological Species Concept  The unique segments of Neanderthal DNA were inherited by modern H. sapiens  We bred with Neanderthals  Same with the so-called Denisovans  Homo sapiens was a variable population  Just as it is now
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Answer to Question 1
Basically, fossils have had played an important role in the study of ancient organisms and how
these organisms provided the understanding of the current extant species. To define, fossils are
ancient remains that had been preserved and thus are utilized by researchers to characterize and
describe the fossilized species. Initially, characterization occurs through dating the obtained fossil.
This is a key step to categorize at what point in time the fossilized species had been extant. One of
the commonly used methods in determining the age of rocks/fossils is radiometric dating.
Radiometric dating methods involve the measurement of the radioactive isotope found in the
investigated material relative to its daughter isotope. Since the length of time it takes for the
radioactive isotope to undergo decay and produce the daughter isotope is established, the rationale
of this chemistry provides the best method to estimate fossil age. In the hypothetical scenario, the
remains of the hominin found in the South African cave dated to the Early Pleistocene/Late
Pliocene. Since these geologic time epochs occurred approximately 2.5 to 2 mya, then carbon
dating would not be an effective method as the latter is only able to date rocks/fossils to
approximately 50,000 years ago. Because of this, it can be assumed that the radioactive dating
method used for the fossilized hominin includes potassium-argon dating as this method can date
rocks/fossils of about 100,000 years to 4 billion years before the present. However, volcanic
sediments that aid an effective argon dating method are absent in South Africa. This means that
the estimation of the age of the obtained hominin could only be achieved through stratigraphy.
This method makes use of time-diagnostic animal species to correlate events that had been
established through argon-dated evidence (Nawrot et al., 2018). To further note, paleontological
resources such as that of the hominin remains found in the South African cave site could occur in
two ways. First, the fossils that had been preserved within the rocks had been become exposed due
to the natural processes of cave formation. Second, the karst features of the cave allow the
accumulation of the fossils. Since the hominin had been protec...


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