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

Abstract

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.

Revised age estimates for the later Paleogene mammal faunas of Egypt and Oman

“…For instance, the recently described late Oligocene paenungulates (hyracoids, embrithopods, and proboscideans) from Chilga, Ethiopia, bear great overall similarity to the paenungulates from the Jebel Qatrani Formation despite having been radioisotopically and magnetostratigraphically tied to Chron C9n (Ϸ28-27 Ma) (44). Indeed, as noted by Sanders et al (ref.…”

“…Unfortunately, the ages of many important Paleogene Afro-Arabian mammal faunas, such as those from Chambi (48) in Tunisia and the Hammadu du Dra region of Algeria (49), remain very poorly constrained, and this problem continues to hinder our understanding of early mammalian evolution in Africa. However, the precise dating of the Chilga mammal localities (44) and the recent discovery of a middle Eocene mammal fauna in Morocco (Aznag) that can be dated to 45.8-43.6 Ma based on associated foraminifera (50) represent major improvements to this situation. Placement of the Fayum and Dhofar mammals into an internally consistent biochronostratigraphic framework represents another major advance of the utmost importance, for this revised chronology will inform all future analyses of the taxa from these, the richest of all Paleogene Afro-Arabian mammal localities.…”

Genomic data support the hominoid slowdown and an Early Oligocene estimate for the hominoid–cercopithecoid divergence

“…Primates from the Fayum include Aegyptopithecus, a taxon plausibly inferred as ancestral to all living catarrhines, and neither hominoids nor cercopithecoids appear among the Fayum fauna, suggesting that 33 Mya is a reasonable upper limit to their divergence date (19,20). Sadly, much of the rest of this 33-to 21-Mya time span is so fossil poor in Africa, particularly for primates (21,22), that it is impossible to pinpoint when the divergence had not occurred. Given this scarcity of evidence, the fossil record is equally supportive of any divergence time between 32 and 21 Mya.…”

A proboscidean from the late Oligocene of Eritrea, a “missing link” between early Elephantiformes and Elephantimorpha, and biogeographic implications

“…The fossil site of Dogali (Eritrea, Fig. 1) described here and the Chilga site in Ethiopia (7,8) are in close proximity and are the only known late Oligocene mammal sites from the whole of Africa. The paleobiogeographical implications of these sites in the context of proboscidean evolution in Africa and across the Arabian Peninsula are discussed below.…”

“…Paleogene proboscidean fossils have been recovered from northern Africa (Algeria, Egypt, Libya, Mali, Morocco, Sudan, and Tunisia), western Africa (Senegal), central Africa (Angola) (1)(2)(3)(4)(5)(6), eastern Africa (Ethiopia) (7,8), and the Arabian Peninsula (Oman) (9). Aside from a small, isolated tusk fragment from Baluchistan, Pakistan, dated to the late Oligocene and showing ivory structural pattern consistent with attribution to gomphotheres, stegodons, or elephants (10), the fossil record of definitive Paleogene proboscideans and the evidence for the major early radiations of proboscideans (moeritheres, numidotheres, and palaeomastodonts) appear to be best documented in AfroArabia.…”