Erik R. Seiffert

Fossil evidence for an ancient divergence of lorises and galagos

Morphological, molecular, and biogeographic data bearing on early primate evolution suggest that the clade containing extant (or ‘crown’) strepsirrhine primates (lemurs, lorises and galagos) arose in Afro-Arabia during the early Palaeogene, but over a century of palaeontological exploration on that landmass has failed to uncover any conclusive support for that hypothesis. Here we describe the first demonstrable crown strepsirrhines from the Afro-Arabian Palaeogene—a galagid and a possible lorisid from the late middle Eocene of Egypt, the latter of which provides the earliest fossil evidence for the distinctive strepsirrhine toothcomb. These discoveries approximately double the previous temporal range of undoubted lorisiforms and lend the first strong palaeontological support to the hypothesis of an ancient Afro-Arabian origin for crown Strepsirrhini and an Eocene divergence of extant lorisiform families.

Oligocene mammals from Ethiopia and faunal exchange between Afro-Arabia and Eurasia

Afro-Arabian mammalian communities underwent a marked transition near the Oligocene/Miocene boundary at approximately 24 million years (Myr) ago. Although it is well documented that the endemic paenungulate taxa were replaced by migrants from the Northern Hemisphere, the timing and evolutionary dynamics of this transition have long been a mystery because faunas from about 32 to 24 Myr ago are largely unknown. Here we report a late Oligocene fossil assemblage from Ethiopia, which constrains the migration to postdate 27 Myr ago, and yields new insight into the indigenous faunal dynamics that preceded this event. The fauna is composed of large paenungulate herbivores and reveals not only which earlier taxa persisted into the late Oligocene epoch but also demonstrates that one group, the Proboscidea, underwent a marked diversification. When Eurasian immigrants entered Afro-Arabia, a pattern of winners and losers among the endemics emerged: less diverse taxa such as arsinoitheres became extinct, moderately species-rich groups such as hyracoids continued into the Miocene with reduced diversity, whereas the proboscideans successfully carried their adaptive radiation out of Afro-Arabia and across the world.

Convergent evolution of anthropoid-like adaptations in Eocene adapiform primates

Adapiform or ‘adapoid’ primates first appear in the fossil record in the earliest Eocene epoch (∼55 million years (Myr) ago), and were common components of Palaeogene primate communities in Europe, Asia and North America. Adapiforms are commonly referred to as the ‘lemur-like’ primates of the Eocene epoch, and recent phylogenetic analyses have placed adapiforms as stem members of Strepsirrhini, a primate suborder whose crown clade includes lemurs, lorises and galagos. An alternative view is that adapiforms are stem anthropoids. This debate has recently been rekindled by the description of a largely complete skeleton of the adapiform Darwinius, from the middle Eocene of Europe, which has been widely publicised as an important ‘link’ in the early evolution of Anthropoidea. Here we describe the complete dentition and jaw of a large-bodied adapiform (Afradapis gen. nov.) from the earliest late Eocene of Egypt (∼37 Myr ago) that exhibits a striking series of derived dental and gnathic features that also occur in younger anthropoid primates—notably the earliest catarrhine ancestors of Old World monkeys and apes. Phylogenetic analysis of 360 morphological features scored across 117 living and extinct primates (including all candidate stem anthropoids) does not place adapiforms as haplorhines (that is, members of a Tarsius–Anthropoidea clade) or as stem anthropoids, but rather as sister taxa of crown Strepsirrhini; Afradapis and Darwinius are placed in a geographically widespread clade of caenopithecine adapiforms that left no known descendants. The specialized morphological features that these adapiforms share with anthropoids are therefore most parsimoniously interpreted as evolutionary convergences. As the largest non-anthropoid primate ever documented in Afro-Arabia, Afradapis nevertheless provides surprising new evidence for prosimian diversity in the Eocene of Africa, and raises the possibility that ecological competition between adapiforms and higher primates might have played an important role during the early evolution of stem and crown Anthropoidea in Afro-Arabia.

Palaeontological evidence for an Oligocene divergence between Old World monkeys and apes

Apes and Old World monkeys are prominent components of modern African and Asian ecosystems, yet the earliest phases of their evolutionary history have remained largely undocumented. The absence of crown catarrhine fossils older than ∼20 million years (Myr) has stood in stark contrast to molecular divergence estimates of ∼25–30 Myr for the split between Cercopithecoidea (Old World monkeys) and Hominoidea (apes), implying long ghost lineages for both clades. Here we describe the oldest known fossil ‘ape’, represented by a partial mandible preserving dental features that place it with ‘nyanzapithecine’ stem hominoids. Additionally, we report the oldest stem member of the Old World monkey clade, represented by a lower third molar. Both specimens were recovered from a precisely dated 25.2-Myr-old stratum in the Rukwa Rift, a segment of the western branch of the East African Rift in Tanzania. These finds extend the fossil record of apes and Old World monkeys well into the Oligocene epoch of Africa, suggesting a possible link between diversification of crown catarrhines and changes in the African landscape brought about by previously unrecognized tectonic activity in the East African rift system.

Evidence for a convergent slowdown in primate molecular rates and its implications for the timing of early primate evolution

A long-standing problem in primate evolution is the discord between paleontological and molecular clock estimates for the time of crown primate origins: the earliest crown primate fossils are ∼56 million y (Ma) old, whereas molecular estimates for the haplorhine-strepsirrhine split are often deep in the Late Cretaceous. One explanation for this phenomenon is that crown primates existed in the Cretaceous but that their fossil remains have not yet been found. Here we provide strong evidence that this discordance is better-explained by a convergent molecular rate slowdown in early primate evolution. We show that molecular rates in primates are strongly and inversely related to three life-history correlates: body size (BS), absolute endocranial volume (EV), and relative endocranial volume (REV). Critically, these traits can be reconstructed from fossils, allowing molecular rates to be predicted for extinct primates. To this end, we modeled the evolutionary history of BS, EV, and REV using data from both extinct and extant primates. We show that the primate last common ancestor had a very small BS, EV, and REV. There has been a subsequent convergent increase in BS, EV, and REV, indicating that there has also been a convergent molecular rate slowdown over primate evolution. We generated a unique timescale for primates by predicting molecular rates from the reconstructed phenotypic values for a large phylogeny of living and extinct primates. This analysis suggests that crown primates originated close to the K–Pg boundary and possibly in the Paleocene, largely reconciling the molecular and fossil timescales of primate evolution.

A radiation of arboreal basal eutherian mammals beginning in the Late Cretaceous of India

Indias Late Cretaceous fossil mammals include the only undisputed pre-Tertiary Gondwanan eutherians, such as Deccanolestes. Recent studies have suggested a relationship between Deccanolestes and African and European Paleocene adapisoriculids, which have been variably identified as stem euarchontans, stem primates, lipotyphlan insectivores, or afrosoricids. Support for a close relationship between Deccanolestes and any of these placental mammal clades would be unique in representing a confirmed Mesozoic record of a placental mammal. However, some paleogeographic reconstructions place India at its peak isolation from all other continents during the latest Cretaceous, complicating reconstructions of the biogeographic history of the placental radiation. Recent fieldwork in India has recovered dozens of better-preserved specimens of Cretaceous eutherians, including several new species. Here, we incorporate these new specimens into an extensive phylogenetic analysis that includes every clade with a previously hypothesized relationship to Deccanolestes. Our results support a robust relationship between Deccanolestes and Paleocene adapisoriculids, but do not support a close affinity between these taxa and any placental clade, demonstrating that Deccanolestes is not a Cretaceous placental mammal and reinforcing the sizeable gap between molecular and fossil divergence time estimates for the placental mammal radiation. Instead, our expanded data push Adapisoriculidae, including Deccanolestes, into a much more basal position than in earlier analyses, strengthening hypotheses that scansoriality and arboreality were prevalent early in eutherian evolution. This comprehensive phylogeny indicates that faunal exchange occurred between India, Africa, and Europe in the Late Cretaceous-Early Paleocene, and suggests a previously unrecognized ∼30 to 45 Myr “ghost lineage” for these Gondwanan eutherians.

Fossil and molecular evidence constrain scenarios for the early evolutionary and biogeographic history of hystricognathous rodents

The early evolutionary and paleobiogeographic history of the diverse rodent clade Hystricognathi, which contains Hystricidae (Old World porcupines), Caviomorpha (the endemic South American rodents), and African Phiomorpha (cane rats, dassie rats, and blesmols) is of great interest to students of mammalian evolution, but remains poorly understood because of a poor early fossil record. Here we describe the oldest well-dated hystricognathous rodents from an earliest late Eocene (≈37 Ma) fossil locality in the Fayum Depression of northern Egypt. These taxa exhibit a combination of primitive and derived features, the former shared with Asian “baluchimyine” rodents, and the latter shared with Oligocene phiomorphs and caviomorphs. Phylogenetic analysis incorporating morphological, temporal, geographic, and molecular information places the new taxa as successive sister groups of crown Hystricognathi, and supports an Asian origin for stem Hystricognathi and an Afro-Arabian origin for crown Hystricognathi, stem Hystricidae, and stem Caviomorpha. Molecular dating of early divergences within Hystricognathi, using a Bayesian “relaxed clock” approach and multiple fossil calibrations, suggests that the split between Hystricidae and the phiomorph-caviomorph clade occurred ≈39 Ma, and that phiomorphs and caviomorphs diverged ≈36 Ma. These results are remarkably congruent with our phylogenetic results and the fossil record of hystricognathous rodent evolution in Afro-Arabia and South America.

Early primate evolution in Afro-Arabia

The peculiar mammalian fauna that inhabited Afro‐Arabia during the Paleogene first came to the attention of the scientific community in the early part of the twentieth century, when Andrews 1 and Schlosser 2 published their landmark descriptions of fossil mammals from the Fayum Depression in northern Egypt. Their studies revealed a highly endemic assemblage of land mammals that included the first known Paleogene records of hyraxes, proboscideans, and anthropoid primates, but which lacked ancestors of many iconic mammalian lineages that are found in Africa today, such as rhinos, zebras, bovids, giraffes, and cats. Over the course of the last century, the Afro‐Arabian Paleogene has yielded fossil remains of several other endemic mammalian lineages, 3 as well as a diversity of prosimian primates, 4 but we are only just beginning to understand how the continents faunal composition came to be, through ancient processes such as the movement of tectonic plates, changes in climate and sea level, and early phylogenetic splits among the major groups of placental mammals. These processes, in turn, made possible chance dispersal events that were critical in determining the competitive landscape–and, indeed, the survival–of our earliest anthropoid ancestors. Newly discovered fossils indicate that the persistence and later diversification of Anthropoidea was not an inevitable result of the clades competitive isolation or adaptive superiority, as has often been assumed, but rather was as much due to the combined influences of serendipitous geographic conditions, global cooling, and competition with a group of distantly related extinct strepsirrhines with anthropoid‐like adaptations known as adapiforms. Many of the important details of this story would not be known, and could never have been predicted, without the fossil evidence that has recently been unearthed by field paleontologists.

Afrotherian origins and interrelationships: new views and future prospects.

Publisher Summary This chapter discusses a number of issues related to afrotherian origins and interrelationships. Particular attention is given to the apparent conflict between molecular and morphological evidence for afrotherian monophyly and the evolutionary or interpretive bases underlying the apparent absence of morphological characters. The phylogenetic position and time of origin of afrotheria, the implications they hold for competing views of a southern versus northern origin for afrotherians, and other extant placental mammals are discussed. Representative species of the six orders of mammals comprising the Afrotheria are: (1) elephant, (2) manatee, (3) hyrax, (4) golden mole, (5) elephant-shrews, and (6) aardvark. The recognition of afrotherian monophyly has exposed a number of unique phylogenetic patterns in the morphology and physiology of the peculiar mammals. Phylogenetic analyses of mitochondrial genomes often support a nested placement for afrotheria within Placentalia. The chapter concludes that the possible inability of sequence data to conclusively resolve many of the evolutionary relationships within afrotheria and propose that an emphasis on the identification of so-called rare genomic changes (RGCs) may ultimately provide the most convincing resolution of afrotherian supraordinal phylogeny.

Geology, Paleoenvironment, and Age of Birket Qarun Locality 2 (BQ-2), Fayum Depression, Egypt

Vertebrate paleontological research in the Fayum Depression began in 1879, with Georg Schweinfurth’s recovery of whale and fish fossils on the island Geziret el-Qarn in Birket Qarun (Dames, 1883; Schweinfurth, 1886). In later years Schweinfurth worked north of the lake, in part within the uppermost levels of the Birket Qarun Formation that are exposed to the south of (and stratigraphically below) the site of the Qasr el-Sagha Temple, but he is not known to have collected any vertebrate fossils from those beds. Subsequent exploration by Hugh Beadnell, and later Richard Markgraf, led to the discovery of fragmentary remains of the cetacean Basilosaurus isis from near this stratigraphic horizon on the northwest side of Birket Qarun (Andrews, 1904; Stromer, 1908; see also Gingerich, 2008), but no vertebrate fossils were reported from sediments exposed on the northeast side of the lake until late in the 20th century, when a single premolar of the proboscidean Moeritherium was described (Holroyd et al., 1996). In the year 2000, paleontological reconnaissance in the sediments exposed along the ‘‘plain of Dime’’ led to the identification of a number of new vertebrate fossil localities (Fig. 1), most of which preserve fragmentary remains of proboscideans (Barytherium and Moeritherium), sirenians, and whales. One locality situated on the northeast side of Birket Qarun, now called Birket Qarun Locality-2 or BQ-2, initially produced surface finds of creodont postcrania, a basicranium and partial mandible of Barytherium, a partial mandible and postcrania of Moeritherium, and a small placental petrosal. Subsequent quarrying anddry screening at BQ-2 from2001 to 2005 has revealed craniodental and postcranial remains of numerous small mammals, including primates, hyracoids, herodotiines, ptolemaiids, anomaluroid and hystricognathous rodents,