Oldest evidence of abundant C4 grasses and habitat heterogeneity in eastern Africa.

The assembly of Africa's iconic C4 grassland ecosystems is central to evolutionary interpretations of many mammal lineages, including hominins. C4 grasses are thought to have become ecologically dominant in Africa only after 10 million years ago (Ma). However, paleobotanical records older than 10 Ma are sparse, limiting assessment of the timing and nature of C4 biomass expansion. This study uses a multiproxy design to document vegetation structure from nine Early Miocene mammal site complexes across eastern Africa. Results demonstrate that between ~21 and 16 Ma, C4 grasses were locally abundant, contributing to heterogeneous habitats ranging from forests to wooded grasslands. These data push back the oldest evidence of C4 grass-dominated habitats in Africa-and globally-by more than 10 million years, calling for revised paleoecological interpretations of mammalian evolution.

Ganciclovir-resistant cytomegalovirus retinitis in a 4-month-old infant.

We present a case of ganciclovir-resistant cytomegalovirus retinitis (CMV) in a 4-month-old boy with congenital CMV infection. This case highlights the potential utility of a combination of intermittent viral load monitoring and retinal examinations in cases of congenital CMV with retinitis.

Morphological affinities of a fossil ulna (KNM-WS 65401) from Buluk, Kenya.

The morphological affinities of a primate proximal ulna (KNM-WS 65401) recovered from the late Early Miocene site Buluk, Kenya, are appraised. Nineteen three-dimensional landmarks on ulnae from 36 extant anthropoid species (n = 152 individuals) and KNM-WS 65401, as well as a subset of 14 landmarks on six ulnae belonging to other East African Miocene catarrhine taxa, were collected. To quantify ulnar shape, three-dimensional geometric morphometric techniques were used and linear dimensions commonly cited in the literature were derived from the landmark data. KNM-WS 65401 is situated between monkeys and hominoids in the principal components morphospace. KNM-WS 65401 shares features such as a short olecranon process, broad trochlear notch, and laterally oriented radial notch with extant hominoids, whereas features such as an anteriorly directed trochlear notch and flat, proximodistally elongated, and anteroposteriorly narrow radial notch are shared with extant monkeys. Principal component scores and linear metrics generally align KNM-WS 65401 with both suspensors and arboreal quadrupeds, but quadratic and linear discriminant analyses of principal component score data provide posterior probabilities of 80% and 83%, respectively, for assignment of KNM-WS 65401 to the suspensory group. Compared with fossil ulnae from other Miocene primates, KNM-WS 65401 is morphologically most distinct from KNM-LG 6, attributed to Dendropithecus macinnesi, and morphologically most similar to KNM-WK 16950R, attributed to Turkanapithecus kalakolensis. The KNM-WS 65401 individual likely possessed more enhanced capabilities for elbow joint extension, perhaps during suspensory behaviors, compared with other Miocene primates in the sample.

New dentognathic fossils of Noropithecus bulukensis (Primates, Victoriapithecidae) from the late Early Miocene of Buluk, Kenya.

The late Early Miocene site of Buluk, Kenya, has yielded fossil remains of several catarrhine primates, including 16 dentognathic specimens of the stem cercopithecoid Noropithecus bulukensis. With the exception of the large sample of Victoriapithecus macinnesi from the middle Miocene of Maboko Island, Kenya, the majority of stem cercopithecoid taxa are represented by small sample sizes. We describe and analyze 91 new cercopithecoid fossils collected from Buluk between 2004 and 2018, including several previously undescribed tooth positions for N. bulukensis, and provide the first evaluation of dental metric and morphological variation in this sample. The results show that the expanded Buluk sample exhibits high levels of dental variation in the postcanine tooth row, similar to V. macinnesi at Maboko, but this variation is consistent with a single-species hypothesis. Subtle differences in the shape of the I1, breadth of the C1 and P3, relative breadth of M1, upper and lower molar distal shelf lengths, the degree of M2 basal flare, and a less-developed lower molar distal lophid differentiate the dentition of N. bulukensis from V. macinnesi. Although differences exist between the N. bulukensis and V. macinnesi dental samples, the high degree of variation within each sample complicates the identification of many individual specimens. New partial maxillae and mandibles allow reassessment of previously described diagnostic differences between N. bulukensis and V. macinnesi, negating upper molar arcade shape as a diagnostic feature and confirming the existence of differences in mandibular symphyseal morphology. Overall, new fossils from Buluk provide new evidence of the dentognathic anatomy of a medium-sized cercopithecoid that coexisted with a diverse group of noncercopithecoid catarrhines at the end of the early Miocene.

Author Correction: New infant cranium from the African Miocene sheds light on ape evolution.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Primitive Old World monkey from the earliest Miocene of Kenya and the evolution of cercopithecoid bilophodonty.

Old World monkeys (Cercopithecoidea) are a highly successful primate radiation, with more than 130 living species and the broadest geographic range of any extant group except humans. Although cercopithecoids are highly variable in habitat use, social behavior, and diet, a signature dental feature unites all of its extant members: bilophodonty (bi: two, loph: crest, dont: tooth), or the presence of two cross-lophs on the molars. This feature offers an adaptable Bauplan that, with small changes to its individual components, permits its members to process vastly different kinds of food. Old World monkeys diverged from apes perhaps 30 million years ago (Ma) according to molecular estimates, and the molar lophs are sometimes incompletely developed in fossil species, suggesting a mosaic origin for this key adaptation. However, critical aspects of the group's earliest evolution remain unknown because the cercopithecoid fossil record before ∼18 Ma consists of only two isolated teeth, one from Uganda and one from Tanzania. Here we describe a primitive Old World monkey from Nakwai, Kenya, dated at ∼22 Ma, that offers direct evidence for the initial key steps in the evolution of the cercopithecoid dentition. The simple dentition and absence of bilophodonty in the Nakwai monkey indicate that the initial radiation of Old World monkeys was first characterized by a reorganization of basic molar morphology, and a reliance on cusps rather than lophs suggests frugivorous diets and perhaps hard object feeding. Bilophodonty evolved later, likely in response to the inclusion of leaves in the diet.

Fossil lemurs from Egypt and Kenya suggest an African origin for Madagascar's aye-aye.

In 1967 G.G. Simpson described three partial mandibles from early Miocene deposits in Kenya that he interpreted as belonging to a new strepsirrhine primate, Propotto. This interpretation was quickly challenged, with the assertion that Propotto was not a primate, but rather a pteropodid fruit bat. The latter interpretation has not been questioned for almost half a century. Here we re-evaluate the affinities of Propotto, drawing upon diverse lines of evidence to establish that this strange mammal is a strepsirrhine primate as originally suggested by Simpson. Moreover, our phylogenetic analyses support the recognition of Propotto, together with late Eocene Plesiopithecus from Egypt, as African stem chiromyiform lemurs that are exclusively related to the extant aye-aye (Daubentonia) from Madagascar. Our results challenge the long-held view that all lemurs are descended from a single ancient colonization of Madagascar, and present an intriguing alternative scenario in which two lemur lineages dispersed from Africa to Madagascar independently, possibly during the later Cenozoic.

New infant cranium from the African Miocene sheds light on ape evolution.

The evolutionary history of extant hominoids (humans and apes) remains poorly understood. The African fossil record during the crucial time period, the Miocene epoch, largely comprises isolated jaws and teeth, and little is known about ape cranial evolution. Here we report on the, to our knowledge, most complete fossil ape cranium yet described, recovered from the 13 million-year-old Middle Miocene site of Napudet, Kenya. The infant specimen, KNM-NP 59050, is assigned to a new species of Nyanzapithecus on the basis of its unerupted permanent teeth, visualized by synchrotron imaging. Its ear canal has a fully ossified tubular ectotympanic, a derived feature linking the species with crown catarrhines. Although it resembles some hylobatids in aspects of its morphology and dental development, it possesses no definitive hylobatid synapomorphies. The combined evidence suggests that nyanzapithecines were stem hominoids close to the origin of extant apes, and that hylobatid-like facial features evolved multiple times during catarrhine evolution.

Deep time and the search for anthropoid origins.

Recent fossil discoveries, phylogenetic analyses, revised reconstructions of continental drift, and accumulating molecular evidence have all yielded new information relating to anthropoid origins within the broader context of primate evolution. There is an emerging consensus among molecular studies that four superorders of eutherian mammals can be recognized: Afrotheria, Euarchontoglires (to which primates belong), Laurasiatheria, and Xenarthra. Overall, molecular phylogenies for mammals agree with some statistical analyses of the primate fossil record in indicating an early origin for primates around 85 Ma ago, and the divergence of haplorhines and strepsirrhines at ca. 77 Ma. Such an ancient date for the origin of haplorhines is some 17 Ma prior to the first known possible primate, and some 22 Ma before the earliest fossil evidence of undoubted euprimates. Because anthropoid fossils date back at least to the late Eocene and perhaps to the middle Eocene, and given indications of an early origin for primates, it is unlikely that ancestral anthropoids arose within any other currently known clade of fossil primates (adapiforms, omomyiforms, strepsirrhines, or tarsiiforms). Implications of new molecular, morphological, and biogeographic lines of evidence are explored with respect to the likely time and place of the origin of anthropoids. Four competing, testable hypotheses are reviewed in detail: 1) the Paratethyan hypothesis, 2) the continental Asian hypothesis, 3) the Indo-Madagascar hypothesis, and 4) the African hypothesis. A case is made that current evidence best supports a relatively ancient Gondwanan origin for primates, as well as a Gondwanan (African or Indo-Madagascan) origin for anthropoids at least as old as that of any other currently documented major primate clade. Available fossil evidence at present seems to be most compatible with the African hypothesis, but it is noteworthy that primates are included not in Afrotheria but in Euarchontoglires.

Developmental processes and canine dimorphism in primate evolution.

Understanding the evolutionary history of canine sexual dimorphism is important for interpreting the developmental biology, socioecology and phylogenetic position of primates. All current evidence for extant primates indicates that canine dimorphism is achieved through bimaturism rather than via differences in rates of crown formation time. Using incremental growth lines, we charted the ontogeny of canine formation within species of Eocene Cantius, the earliest known canine-dimorphic primate, to test whether canine dimorphism via bimaturism was developmentally canalized early in primate evolution. Our results show that canine dimorphism in Cantius is achieved primarily through different rates of crown formation in males and females, not bimaturism. This is the first demonstration of rate differences resulting in canine dimorphism in any primate and therefore suggests that canine dimorphism is not developmentally homologous across Primates. The most likely interpretation is that canine dimorphism has been selected for at least twice during the course of primate evolution. The power of this approach is its ability to identify underlying developmental processes behind patterns of morphological similarity, even in long-extinct primate species.