Part of the problem here is that you're looking at human evolution in isolation. It is unfortunate that the fossil record is sparse for apes (for reasons explained in your quote), but when the available evidence is compared with the more complete fossil lineages of many other creatures (including other mammals) it's clearly consistent with such patterns.Well, lets just say these comments never cease to keep that question in my mind:
"Molecular evidence indicates that the lineage of gibbons (family Hylobatidae), the "lesser apes", diverged from that of the great apes some 18–12 million years ago, and that of orangutans (subfamily Ponginae) diverged from the other great apes at about 12 million years. There are no fossils that clearly document the ancestry of gibbons, which may have originated in a still-unknown South East Asian hominoid population; but fossil proto-orangutans, dated to around 10 million years ago, may be represented by Sivapithecus from India and Griphopithecus from Turkey.[10] Species close to the last common ancestor of gorillas, chimpanzees and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Molecular evidence suggests that between 8 and 4 million years ago, first the gorillas (genus Gorilla), and then the chimpanzees (genus Pan) split off from the line leading to the humans. Human DNA is approximately 98.4% identical to that of chimpanzees when comparing single nucleotide polymorphisms (see human evolutionary genetics).[11] The fossil record, however, of gorillas and chimpanzees is limited; both poor preservation—rain forest soils tend to be acidic and dissolve bone—and sampling bias probably contribute most to this problem.
Other hominins probably adapted to the drier environments outside the African equatorial belt; and there they encountered antelope, hyenas, elephants and other forms becoming adapted to surviving in the East African savannas, particularly the regions of the Sahel and the Serengeti. The wet equatorial belt contracted after about 8 million years ago, and there is very little fossil evidence for the divergence of the hominin lineage from thaDiscussion and Debatet of gorillas and chimpanzees—which split was thought to have occurred around that time. The earliest fossils argued by some to belong to the human lineage are Sahelanthropus tchadensis (7 Ma) and Orrorin tugenensis (6 Ma), followed by Ardipithecus (5.5–4.4 Ma), with species Ar. kadabba and Ar. ramidus."
It's a far more complex lineage with many more branches and interbreeding of subspecies than was ever expected, but in the light of other mammalian lineages, it is just a more fragmented record. The clincher is the genetic record that clarifies the relationships between the primate branches and shows evidence of the interbreeding between hominid subspecies.
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