Tempo and Mode in Evolution Genetics and Paleontology 50 Years After Simpson (1995) / Chapter Skim
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Tempo and Mode in Human Evolution
Tempo and Mode in Human Evolution
Pages 169-186
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From page 169... ...
the paleontological record of Hominidae has improved more than a 100-fold. The improvements include precise geological dating and rich collections of well-preserved fossil hominids.
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From page 170... ...
A second hypothetical common ancestor appears in Figure 1B to account for the numerous derived traits shared by A robustus, A
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171 ~ 2 _ ~ Cal · ~ Q)
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The most significant features for bipedalism include shortened iliac blades, lumbar curve, knees approaching midline, distal articular surface of tibia nearly perpendicular to the shaft, robust metatarsal I with expanded head, convergent hallux (big toe) , and proximal foot phalanges with dorsally oriented proximal articular surfaces.
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From page 174... ...
174 / Henry M McHenry Lumbar lordosis and sacral retroflexion Sacral ala expanded laterally Sacroiliac and hip joints closely approximated Pelvis with: · Mediolaterally expanded, supennfenorly shortened, and anteriorly rotated iliac blades · Robust anterior iliac spines · Distinct sciatic notch · Distinct iliopsoas groove · Rugose and large area for sacrotuberous ligament · Retroflexed auncular surface with extensive retroauncular area · Robust posterior superior iliac spine · Sigmoid curvature of iliac crest · Dorsoventrally thickened pubic symphysis · Retroflexion of hamstring tuberosity · Shortened ischial shank Femoroal neck long with human-like distribution of cortical and spongy bone Distal femur with: · High bicondylar angle · Elliptical lateral condyle · Deep patellar groove with high lateral lip Calcaneus with: · Massive body · Deep domoplanSar dimension · Ovoid transverse section · Honzontally oriented sustentacular shelf Midtarsal region is: · Stout · Anteropostenorly expanded · Strong transverse and longitudinal arch ~\~\ Relative small forelimbs Proximal humerus with open and shallow bicipital groove Distal humerus with: · Rounded lateral well of olecranon fossa · Greale lateral epicondyle · Moderate-sized and cranially facing medial epicondyle · Moderate development of supracondylar ridge Radiocarpal joint perpendicular to shaft axis Capitate with: · Proximodistally shortened axis · Single and elongated facet for MCII A\ · Shallow excavations for \\\ MCIII articulations Metacarpals Il-V relatively short with no dorsal transverse ridge on heads Phalanges relatively short Tibia with straight shaft Distal tibia with articular surface nearly perpendicular to shaft axis Metatarsal I with: · Robust and triangular diaphysis · Expanded head Metatarsals Il-V with: · Heads expanded superiorly · MTV powerfully built with large tuberosity Hallux is convergent Toes relatively short Proximal phalanges with dorsally oriented proximal articular surfaces FIGURE 2A Derived postcranial traits shared by A
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From page 175... ...
Body size remains relatively small in all species of Australopithecus, including the surprisingly petite bodies of the "robust" australopithecines (McHenry, 1992, 1994b; Ruff and Walker, 1993, Table 1, column 3~. Sexual dimorphism in body s~ze decreases from A
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~ length · Prominent palmer beak / l l ·Waisted neck / l l Middle phalanges relatively longl I I Proximal phalanges: I l l Curved ~ ~ ~C · Broad-based ~ ~ Knee with: · Narrow bodied in dorsal view I I · Mediolateral flare of body for flexor I I · Rectangular sheath l l · Wide inter · More highly circumferential trochle: I condylar Metatarsal I with rounded head I notch Navicular with: I · Marked · Low maximum dorsoplantar height asymmetry · Large cuboid facet which faces at right condyles angles to the lateral cuneiform · Single Lateral cuneiform with pongid-like I attachment planter tuberosity for lateral meniscus / Distal tibia with posterior tilt / Distal fibula with: <~ · Proximal border of distal articular surface running obliquely · Articular surface facing inferomedially · Less acute angle between distal articular and subcutaneous surfaces · Broad and deep peroneal groove Midthoracic vertebrae with ventrallyexpanded contra Lumbar and sacral contra relatively small in cross-section iliac blades face posteriorly Ischium relatively long with hamstring surface area facing mostly inferiorly Acetabulum with diminutive anterior horn FIGURE 2B Primitive postcranial traits of A afarensis shared with the reconstructed common ancestor of African apes and humans.
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From page 177... ...
Most notable primitive traits include large central and small lateral upper incisors, projecting upper canine with marginal attrition facets, small metaconid of the lower first premolar and parallel or convergent tooth rows. The positions of the masticatory muscles are also primitive, particularly the posterior placement of the main fibers of the temporalis.
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From page 178... ...
Occupation of a special food niche and the correlated adaptations have a particularly low taxonomic value." In fact, many of the same traits characteristic of A aethiopicus and the other "robust" australopithecines reappear in distantly related species adapted to heavy chewing.
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From page 179... ...
Body weight estimates may be off the mark, but the sample of postcranial specimens is sufficient to show that body weight remained at about the same relatively small size in all species of Australopithecus. This result implies that the apparent increase in brain size through time in species of Australopithecus is not due merely to an increase in body size.
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From page 181... ...
erectus has absolute brain volumes that do not increase through time and therefore represent a period of stasis (Rightmire, 1990~. It is difficult to establish whether relative brain sizes increased because there are very few postcranial fossils of H
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From page 182... ...
Relative brain size increased slightly among successively younger species of Australopithecus, expanded significantly with the appearance of Homo, but within early Homo remained at about half the size of Homo sapiens for almost a million years. Many apparent trends in human evolution may actually be due to the accumulation of relatively rapid shifts in successive species.
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(1982) The relativity of relative brain measures and hominid mosaic evolution.
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(1981) Relative brain size and basal metabolic rate in terrestrial vertebrates.
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(1994b) Behavioral ecological implications of early hominid body size.
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From page 186... ...
Analyse morpho-fonctionelle chez les primates et les hominides fossiles. (Presses du CNRS, Paris)
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