final chap 9 Flashcards
lumpers
Researchers who prefer to lump variable specimens into a single species or taxon and who feel high levels of variation is biologically real.
splitters
Researchers who prefer to split a highly variable taxon into multiple groups or species.
Savannah Hypothesis (or Aridity Hypothesis)
It suggests that the expansion of the savannah (or less densely forested, drier environments) forced early hominins from an arboreal lifestyle (one living in trees) to a terrestrial one where bipedalism was a more efficient form of locomotion
Forest Hypothesis
hypothesized that forested environments, rather than savannahs, were a key influence on the development of bipedalism in hominin
Variability Selection Hypothesis
states that hominin groups would experience varying degrees of natural selection due to continually changing environments and potential group isolation. This would allow certain groups to develop genetic combinations that would increase their ability to survive in shifting environments. These populations would then have a genetic advantage over others that were forced into habitat-specific adaptations
Pulsed Variability Selection Hypothesis
East African Rift System (EARS) and changes in deep lakes are key drivers of diversification during early human evolution.
Several proposed selective pressures for bipedalism:
- Energy conservation
- Thermoregulation
- Bipedalism freed up our ancestors’ hands
Sahelanthropus tchadensis
- The initial discovery was made in 2001 by Ahounta Djimdoumalbaye in Chad
- Closed forest patch, palm groves, and mixed grasslands
- Most likely ate plants
- Arboreal locomotor modes
- Average brain case: 320-380cc
*small cranial capacity (360 cc) and has canines smaller than those in extant great apes, yet still larger and pointier than those in humans.
*A short cranial base and a foramen magnum (the hole through which the spinal cord enters the cranium) that is more humanlike in positioning have been argued to indicate upright walking.
- exhibits a set of a set of derived features, including a long, low cranium; a small, ape-sized brain case; and relatively reduced prognathism.
Orrorin tugenensis
- dated to between 6 mya and 5.7 mya
- was discovered near Tugen Hills in Kenya in 2000 by Brigitte Senut + Mark Pickford
*Smaller cheek teeth (molars and premolars) than those in even more recent hominins (i.e., derived), thick enamel, and reduced, but apelike, canines characterize this species.
*First species that clearly indicates adaptations for bipedal locomotion, with fragmentary leg, arm, and finger bones having been found but few cranial remains
- femur that was found: indicates that Ororrin was bipedal, and recent studies suggest that it walked in a similar way to later Pliocene hominins.
- Shape of femur neck and cross-section of bone
Ardipithecus:
Ardipithecus ramidus
(Ar. ramidus)
- best known of the earliest hominins
- large sample size of over 110 specimens from Aramis alone.
- Wooded woth higher water budget
- Rich flora + fauna
*Found in Ethiopia, Kenya (in the Middle Awash region and in Gona by White et.al in 1992
*opposable big toe (hallux)
*pelvis and hip show that she could walk upright (i.e., it is derived), supporting her hominin status
*small brain (300 cc to 350 cc)
*midfacial projection, and slight prognathism show retained primitive cranial features, but the cheek bones are less flared and robust than in later hominins.
*Researchers believe that Ardipithecus ramidus was able to walk upright, although not as efficiently as later humans. It possessed the musculature required for tree climbing, and while moving quadrupedally, it likely placed weight on the palms of the hands rather than on the knuckles.
- Faculative biped terrestrial/ palmigrade climber/ clamberer arboreally
- Foramen magnum beneath cranium, broad pelvis, primitive foot, no knuckle walk adaptation.
Ardipithecus:
Ardipithecus kadabba
- discovered in 1997 by paleoanthropologist Dr. Yohannes Haile-Selassie
Evolutionarily, partially in response to our increased reliance on our hands and brain, our teeth have reduced in size and our faces are flatter, or more orthognathic.
True
orthognathic
The face below the eyes is relatively flat and does not jut out anteriorly.
incisiform
An adjective referring to a canine that appears more incisor-like in morphology.
procumbent
In reference to incisors, tilting forward
canine diastema
A space between the teeth, usually for large canines to fit when the mouth is closed.
Large, short molars with thick enamel allowed these early cousins of ours to grind away at fibrous, coarse foods, such as sedges, which require plenty of chewing. This is further evidenced in the low cusps, or ridges, on the teeth, which are ideal for chewing.
True
Trends among early hominins include a reduction in procumbency, reduced hind dentition (molars and premolars), a reduction in canine size (more incisiform with a lack of canine diastema and honing P3), flatter molar cusps, and thicker dental enamel. All early hominins have the primitive dental formula of 2:1:2:3. These trends are all consistent with a generalist diet, incorporating more fibrous foods.
True
This pattern of larger posterior dentition (even relative to the incisors and canines), thick enamel, and cranial evidence for large chewing muscles is far more pronounced in a group known as the robust australopithecines, as opposed to their earlier contemporaries or predecessors, the gracile australopithecines, and certainly larger than those seen in early Homo, which emerges during this time. This pattern of incredibly large hind dentition (and very small anterior dentition) has led people to refer to robust australopithecines as megadont hominins.
True
gracile
Slender, less rugged, or pronounced features.
robust
Rugged or exaggerated features.
Australopithecus anamensis
- Currently found from sites in the Turkana region (Kenya) and Middle Awash (Ethiopia
*discovered by an Ethiopian herder named Ali Bereino
*A small brain size (370 cc), relatively large canines, projecting cheekbones, and primitive earholes show more primitive features as compared to those of more recent Australopithecines.
*indicates bipedalism is a fragment of a tibia (shinbone), which demonstrates features associated with weight transfer during bipedal walking.
Au. afarensis
- oldest and most well-known australopithecine species and consists of a large number of fossil remains.
- Discovered by: Hadar, 1974
- dated to between 2.9 mya and 3.9 mya and is found in sites all along the EARS system, in Tanzania, Kenya, and Ethiopia
*Lucy : found in 1974 by Donald Johanson and dates to approximately 3.2 mya
- The canines and molars of Au. afarensis are reduced relative to great apes but are larger than those found in modern humans
- prognathic face and robust facial features that indicate relatively strong chewing musculature (compared with Homo) but which are less extreme than in Paranthropus.
- large overall size variation indicates high levels of sexual dimorphism in this species
- Skeletal evidence indicates that this species was bipedal, primarily through examining the pelvis and lower limb, which demonstrate a humanlike femoral neck, a valgus knee, and bowl-shaped hip.
Australopithecus africanus
- 3.5-2.0 MYA
- Taung child (1924)
- currently dated to between 3.3 mya and 2.1 mya (Pickering and Kramers 2010), with discoveries from Sterkfontein, Taung, Makapansgat, and Gladysvale in South Africa
- relatively large brain (400 cc to 500 cc)
- small canines without an associated diastema, and more rounded cranium and smaller teeth than Au. afarensis indicate some derived traits.
- Similarly, the postcranial remains (in particular, the pelvis) indicate bipedalism
- sloping face and curved phalanges (indicative of retained arboreal locomotor abilities) show some primitive features.
- “Mrs. Ples” brain case is small in size (like apes) but has a less prognathic face and its foramen magnum is positioned more like modern humans than in African apes.
