[Show abstract][Hide abstract] ABSTRACT: Australopithecus fossils were regularly interpreted during the late 20th century in a framework that used living African apes, especially chimpanzees, as proxies for the immediate ancestors of the human clade. Such projection is now largely nullified by the discovery of Ardipithecus. In the context of accumulating evidence from genetics, developmental biology, anatomy, ecology, biogeography, and geology, Ardipithecus alters perspectives on how our earliest hominid ancestors--and our closest living relatives--evolved.
Full-text · Article · Apr 2015 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Although the suid genus Kolpochoerus is well known from the Plio-Pleistocene of Africa, the evolutionary history of one of its constituent species, K. majus, remained obscure until substantial fossil evidence accumulated during the last 20 years, largely from sites in Ethiopia. Here, we describe Kolpochoerus phillipi sp. nov., based on a fairly complete skull and the remains of additional individuals from ~2.5 Ma deposits at Matabaietu, in the Middle Awash study area of Ethiopia. Based on a phylogenetic analysis, we suggest that K. phillipi sp. nov. belongs to a clade of “bunolophodont suines” including K. majus and the extant giant forest hog Hylochoerus meinertzhageni. Within this clade, K. phillipi sp. nov. likely represents a potential ancestor of K. majus, based on its morphology and stratigraphic position.
Full-text · Article · Mar 2015 · Acta Palaeontologica Polonica
[Show abstract][Hide abstract] ABSTRACT: The early Pliocene African hominoid Ardipithecus ramidus was diagnosed as a having a unique phylogenetic relationship with the Australopithecus + Homo clade based on nonhoning canine teeth, a foreshortened cranial base, and postcranial characters related to facultative bipedality. However, pedal and pelvic traits indicating substantial arboreality have raised arguments that this taxon may instead be an example of parallel evolution of human-like traits among apes around the time of the chimpanzee-human split. Here we investigated the basicranial morphology of Ar. ramidus for additional clues to its phylogenetic position with reference to African apes, humans, and Australopithecus. Besides a relatively anterior foramen magnum, humans differ from apes in the lateral shift of the carotid foramina, mediolateral abbreviation of the lateral tympanic, and a shortened, trapezoidal basioccipital element. These traits reflect a relative broadening of the central basicranium, a derived condition associated with changes in tympanic shape and the extent of its contact with the petrous. Ar. ramidus shares with Australopithecus each of these human-like modifications. We used the preserved morphology of ARA-VP 1/500 to estimate the missing basicranial length, drawing on consistent proportional relationships in apes and humans. Ar. ramidus is confirmed to have a relatively short basicranium, as in Australopithecus and Homo. Reorganization of the central cranial base is among the earliest morphological markers of the Ardipithecus + Australopithecus + Homo clade.
Preview · Article · Jan 2014 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Evolutionary biologists created a large twentieth-century literature about delimiting biological species. Paleontologists contributed the unique complications of deep time. Toward century's end, one participant wrote: "In all probability more paper has been consumed on the questions of the nature and definition of the species than any other subject in evolutionary and systematic biology."
No preview · Article · Jan 2014 · Evolutionary Anthropology Issues News and Reviews
[Show abstract][Hide abstract] ABSTRACT: Beginning in the 1960s, geological and paleoanthropological exploration of the Ethiopian rift system’s basins have led to the discovery and assembly of the most comprehensive record of human biological and technological change during the last 6 million years. The hominid fossils, including partial skeletons, were primarily discovered in the Afar Rift, the Main Ethiopian Rift, and in the Omo Basin of the broadly rifted zone of SW Ethiopia. The paleoanthropological research areas within the SW Afar Rift that have yielded many diverse hominid species and the oldest stone tools are, from north to south, Woranso-Mille (aff. Ardipithecus and Au. afarensis), Hadar (Au. afarensis, Homo sp.), Dikika (Au. afarensis), Gona (Ar. kadabba, Ar. ramidus, H. erectus, and oldest stone tools), Middle Awash (Ar. kadabba, Ar. ramidus, Au. anamensis, Au. afarensis, Au. garhi, H. erectus, H. rhodesiensis, H. sapiens idaltu, and the oldest paleo-butchery locality), and Galili (Au. afarensis). Additional hominid remains were discovered at Melka Kunture on the banks of the Awash River near its source along the western margin of the central part of the Main Ethiopian Rift (H. erectus), at Konso (H. erectus and A. boisei), and at the southern end of the MER, and in the Omo Basin (Au. anamensis, Au. afarensis, Au. aethiopicus, Au. boisei, H. habilis, and H. erectus).Distal and sometimes proximal tephra units interbedded within fossilifeous sedimentary deposits have become key elements in this work by providing chronological and correlative control and depositional contexts. Several regional tephra markers have been identified within the northern half of the eastern African rift valley in Ethiopia and Kenya, and in marine sediments of the Gulf of Aden Rift and the NW Indian Ocean. Out of the many regional tephra stratigraphic markers that range in age from the early Pliocene (3.97 Ma) to the late Pleistocene (0.16 Ma), the Sidi Hakoma Tuff (SHT) has been more widely identified and thoroughly characterized than any of the others.An age of 3.446 ± 0.041 Ma was determined on the SHT according to the most recent calibration, and it is the only regional stratigraphic marker whose source has been traced to a buried caldera in the central sector of the Main Ethiopian Rift. This paper describes new SHT occurrences and presents chemical and chronological results in the context of a broader review of the importance of this key marker. Moreover, the geographic distributions, probable dispersal mechanisms, and importance of regional tephra units in determining the tectonic and sedimentological processes in the different rift basins of the eastern African rift valleys are considered.
Full-text · Article · Jan 2013 · Journal of African Earth Sciences
[Show abstract][Hide abstract] ABSTRACT: Cerling et al. contest our interpretation of the woodland habitat preference of Ardipithecus ramidus. However, their reconstruction of a predominantly open grassy environment with riparian woodlands is inconsistent with the
totality of the fossil, geological, and geochemical evidence. In the Middle Awash, Ar. ramidus fossils are confined to the western portion of the sampled Pliocene landscape where the species is associated with woodland
to grassy woodland habitat indicators.
[Show abstract][Hide abstract] ABSTRACT: We assigned Ardipithecus to the Hominidae based on numerous dental, cranial, and postcranial characters. Sarmiento argues that these characters are
not exclusive to hominids, contending that Ardipithecus is too old to be cladistically hominid. His alternative phylogeny, however, is unlikely because it requires tortuous, nonparsimonious
[Show abstract][Hide abstract] ABSTRACT: The femur and pelvis of Ardipithecus ramidus have characters indicative of both upright bipedal walking and movement in trees. Consequently, bipedality in Ar. ramidus was more primitive than in later Australopithecus. Compared with monkeys and Early Miocene apes such as Proconsul, the ilium in Ar. ramidus is mediolaterally expanded, and its sacroiliac joint is located more posteriorly. These changes are shared with some Middle
and Late Miocene apes as well as with African apes and later hominids. However, in contrast to extant apes, bipedality in
Ar. ramidus was facilitated by craniocaudal shortening of the ilium and enhanced lordotic recurvature of the lower spine. Given the predominant
absence of derived traits in other skeletal regions of Ar. ramidus, including the forelimb, these adaptations were probably acquired shortly after divergence from our last common ancestor
with chimpanzees. They therefore bear little or no functional relationship to the highly derived suspension, vertical climbing,
knuckle-walking, and facultative bipedality of extant African apes.
[Show abstract][Hide abstract] ABSTRACT: The Middle Awash Ardipithecus ramidus sample comprises over 145 teeth, including associated maxillary and mandibular sets. These help reveal the earliest stages
of human evolution. Ar. ramidus lacks the postcanine megadontia of Australopithecus. Its molars have thinner enamel and are functionally less durable than those of Australopithecus but lack the derived Pan pattern of thin occlusal enamel associated with ripe-fruit frugivory. The Ar. ramidus dental morphology and wear pattern are consistent with a partially terrestrial, omnivorous/frugivorous niche. Analyses show
that the ARA-VP-6/500 skeleton is female and that Ar. ramidus was nearly monomorphic in canine size and shape. The canine/lower third premolar complex indicates a reduction of canine
size and honing capacity early in hominid evolution, possibly driven by selection targeted on the male upper canine.