Exam 2 Flashcards
Which traits used to diagnose a fossil species as a hominin have also been seen in late Miocene hominids and present day gibbons and short-nosed monkeys, and what is the implication of this?
Traits:
- Reduced canine size in combination with partial or complete loss of uppercanine/lower third premolar honing and less apparent canine sexual dimorphism. These changes are inferred to indicate changes in social structure as well.
- Anteriorly positioned and horizontally oriented foramen magnum
- Pelvic and other postcranial features that are typically indicators of bipedalism.
Implication: Many of these traits are seen in Miocene hominids and present day gibbons and short-nosed monkeys, but they don’t always serve the same function as they do for hominins. If non-hominins share supposedly unique hominin characteristics, and utilize those characteristics in very different ways, it is important for researchers to look beyond the suite of hominin characteristics and consider various explanations for the presence of such characteristics.
What is a synapomorphy? Give examples of synapomorphies in earlier hominins and discuss possible morphological implications of these synapomorphies for early hominins.
Synapomorphy: a shared derived similarity.
Examples of synapomorphies in earlier hominins (sp. Ar. Ramidus) include: an anteriorly positioned foramen magnum, small canines that do not dramatically differ between males and females, and a pelvis with a mediolaterally broad ilium, abbreviated iliac isthmus, inferosuperiorly short pubic symphysis, prominent anterior inferior iliac spine, and discrete sciatic notch.
Possible morphological implication: these earlier hominins were bipedal. The lack of a dramatic difference between male and female canines suggests that they were not a very sexually dimorphic species. Thus, their social structure probably didn’t involve as much aggressive competition between males, and men and women may have engaged in monogamous relationships.
Who were Ramapithecus and Oreopithecus and discuss the controversy surrounding each find.
Ramapithecus: Ramapithecus punjabicus was a late Miocene hominoid from South Asia. When originally discovered, Ramapithecus was believed to be an early hominin. The Paleoanthropologists who made that conclusion did so using homoplasies between Ramapithecus and hominins as evidenced from fossil remains. These homoplasies included a short face, robust jaws, small canines, and thick-enameled bunodont molars.
In the 1980s, more fossil material from Ramapithecus was recovered. Researchers analyzed this material in combination with DNA evidence to create a better picture of what they were looking at and when it existed. They discovered that Ramapithecus was actually Sivapithecus, a close relative to the orangutan.
Oreopithecus: Oreopithecus bambolii was a late Miocene hominoid. Its’ remains have been extracted from fossil sites in Tuscany and Sardinia, the first discovery taking place in 1872. In the late 1950’s Johannes Hurzeler classified Oreopithecus as a fossil hominin. He reasoned that Oreopithecus shared several features with fossil hominins, many of which are tied to bipedalism (often thought to be a uniquely human trait). Today, a near complete skeleton of Oreopithecus indicates that it is not a member of the hominin clade. The characteristics that Oreopithecus shares with hominins are mere homoplasies or retained primitive hominid features. Oreopithecus had dental, cranial, hand, hip, and hindlimb structures matching those of hominins, but they developed them independently in a non-hominin lineage.
The cases of Ramapithecus and Oreopithecus point to limitations in current methodology, and the importance of carefully considering various interpretations of each find. They point caution in classifying fossil hominins using a suite of structural-functional characteristics.
What do we know about Ardi’s methods of locomotion?
Ardi was what the authors call a “facultative biped.” She walked upright when on the ground, and on all fours when up in the trees. Ardi had an opposable big toe for grasping tree limbs, but she did not swing from trees or knuckle-walk.
What evidence currently exists to suggest that Ardipithecus *is* an ancestor to Au. Anamensis?
Australopithecus Anamensis appeared in the Middle Awash region 200,000 years after Ardi. The authors claim that this is the only evidence in support of a relationship between the two.
How does Ardi’s existence interfere with the hypothesis that grassland habitats were the origin for bipedal hominins?
Fossilized plant and animal specimens found in nearby localities of the same age as Ardi suggest that Ardi lived in the woodland environment. Ardi ate woodland plants and shared a habitat with monkeys, kudu antelopes, and peafowl. If Ardi was bipedal and lived in woodlands, it doesn’t seem that living in grasslands was a precursor to bipedalism.
We learned that primates are diagnosed primates when they possess a suite of traits. When considering hominins, can this concept be applied here as well? Why or why not?
There is a specific set of traits that are used to identify species as hominins, however, caution must be used when doing this. Sometimes traits are interpreted as Synapomorphies, or derived traits, when in actuality, they are homoplasies. Sometimes species who share the same traits utilize those traits differently. This is exemplified in gibbons, which have an anteriorly positioned and horizontally oriented foramen magnum (a feature that has been considered a “uniquely”bipedal trait). Gibbons are not bipedal, and this finding suggests that the feature is more generally associated with differences in head carriage and facial length.
Shared similarities associated with bipedal behaviour include an anteriorly situated foramen magnum, short and broad iliac blades,infero-superiorly short pubic symphysis, a well-developed anterior inferior iliac spine, a large ischial spine, medial and lateral condyles of the distal femur similar in size, possibly associated with a bicondylar angle. The impressive suite of shared features with fossil hominins led Hürzeler to deduce (not unreasonably) that Oreopithecus
was a fossil hominin, but these features are most parsimoniously interpreted as either homoplasies or retained primitive hominid features. Oreopithecus
is a classic example of how a late Miocene hominid can independently acquire a suite of structural–functional complexes of the dentition, cranium, hand, hip and hindlimb that closely parallel the specialized features uniquely associated with the hominin lineage,and thereby encourage researchers to generate erroneous
assumptions about evolutionary relationships.
Oreopithecus highlights the dangers inherent in uncritically assuming that shared similarities
are a secure indication of relationship or that extant primates are an adequate guide to the potential behavioural diversity of extinct taxa.
Why do the authors feel that it is important for students and researchers to understand the implications behind each hominin fossil find, and understand the hypotheses of each find?
Because homoplasy can be a confounding influence when reconstructing ancestral morphotypes.
Oreopithecus
is a classic example of how a late Miocene hominid can independently acquire a suite of structural–functional complexes of the dentition, cranium, hand, hip and hindlimb that closely parallel the specialized features uniquely associated with the hominin lineage,and thereby encourage researchers to generate erroneous
assumptions about evolutionary relationships.
Oreopithecus highlights the dangers inherent in uncritically assuming that shared similarities
are a secure indication of relationship or that extant primates are an adequate guide to the potential behavioural diversity of extinct taxa.
Features considered to be hominin specializations can be shown to have been acquired independently in a non-hominin lineage in association with inferred behaviours that are functionally related to, but not necessarily narrowly restricted to, terrestrial bipedalism
What factors would have prompted Ardi to have an omnivorous diet?
The team suggests that Ar. ramidus was “more omnivorous” than chimpanzees, based on the size, shape, and enamel distribution of its teeth. It probably supplemented woodland plants such as fruits, nuts, and tubers with the occasional insects, small mammals, or bird eggs. Carbon-isotope studies of teeth from five individuals show that Ar. ramidus ate mostlywoodland, rather than grassland, plants
What arguments could be made to suggest that Ardi is not on the direct human lineage?
The pelvis was crushed and is only suggestive of bipedality
The knee was not positioned above the ankle, which makes some researchers skeptical of whether or not it was bipedal…
Due to the limited nature of fossils, we’re only allowed a limited clue on vital aspects of early hominids such as locomotion. Do you think that this specimen’s gait was representative of the rest of the species? (Au. sediba)
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What about dentition? Why dentition before brain development?
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There was the possiblity of injury found in the fossil. How might that impact the research of the species when there is a limited amount of resources to work with?
It seems reasonable to consider the possibility that the remains could belong to an individual who had a bone disorder, or even perhaps a muscular disorder.
The fact that there is a limited amount of resources to work with can make it difficult to determine if the trait is typical or atypical of the species, thus making it even more dificult to make conclusions based on those traits.
At the same time, the female sample of Au. sediba (MH2) had an “extreme” bony protrusion on her knee that may have prevented dislocation of the kneecap as well as discomfort…this could mean that the protrusion is an adaptation to walking in a hyperpronated fashion. Adaptations like that do not occur within one person’s lifetime, so it seems more likely that the gait of MH2 is the norm for Au. sediba. If this is true, it would provide us with more solid conclusions
The chimpanzee-esque heel was interesting. What purpose did it serve, if any?
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If we were to recover the missing phalanges as well, what more would that tell us about the species?
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