Diversity in the later Paleogene proboscidean radiation: a small barytheriid from the Oligocene of Dhofar Governorate, Sultanate of Oman

Abstract

Despite significant recent improvements to our understanding of the early evolution of the Order Proboscidea (elephants and their extinct relatives), geographic sampling of the group's Paleogene fossil record remains strongly biased, with the first ~30 million years of proboscidean evolution documented solely in near-coastal deposits of northern Africa. The considerable morphological disparity that is observable among the late Eocene and early Oligocene proboscideans of northern Africa suggests that other, as yet unsampled, parts of Afro-Arabia might have served as important centers for the early diversification of major proboscidean clades. Here we describe the oldest taxonomically diagnostic remains of a fossil proboscidean from the Arabian Peninsula, a partial mandible of Omanitherium dhofarensis (new genus and species), from near the base of the early Oligocene Shizar Member of the Ashawq Formation, in the Dhofar Governorate of the Sultanate of Oman. The molars and premolars of Omanitherium are morphologically intermediate between those of Arcanotherium and Barytherium from northern Africa, but its specialized lower incisors are unlike those of other known Paleogene proboscideans in being greatly enlarged, high-crowned, conical, and tusk-like. Omanitherium is consistently placed close to late Eocene Barytherium in our phylogenetic analyses, and we place the new genus in the Family Barytheriidae. Some features of Omanitherium, such as tusk-like lower second incisors, the possible loss of the lower central incisors, an enlarged anterior mental foramen, and inferred elongate mandibular symphysis and diminutive P(2), suggest a possible phylogenetic link with Deinotheriidae, an extinct family of proboscideans whose origins have long been mysterious.

A new early Oligocene mammal fauna from the Sirt Basin, central Libya: Biostratigraphic and paleobiogeographic implications

“…In addition to the ongoing debate over its correlation, the faunal content of the Jebel Qatrani Formation differs in some ways from that of other broadly contemporary rock units in Afro-Arabia. This is exemplified by the presence of cricetid and anomaluroid rodents, strepsirhine primates, and the unusual proboscidean Omanitherium in early Oligocene sites in Oman, taxa that have yet to be reported from the more thoroughly sampled and studied early Oligocene faunas known from Egypt (Gheerbrant et al, 1993;Thomas et al, 1999;Seiffert et al, 2012). Despite important recent progress in documenting later Oligocene faunas in Afro-Arabia (e.g., Kappelman et al, 2003;Stevens et al, 2008, 2013; Rasmussen and Gutierrez, 2009;Ducrocq et al, 2010Ducrocq et al, , 2011Zalmout et al, 2010), the African early Oligocene record remains inadequately sampled, especially from a biogeographic and biostratigraphic perspective.…”

A middle Eocene mesoeucrocodylian (Crocodyliformes) from the Kaninah Formation, Republic of Yemen

“…Until recently, the continental record of Palaeogene vertebrates from the Arabian Peninsula extended no earlier than the Oligocene, with anurans described from the late Oligocene Yemen Volcanic Group (Henrici & Baez, 2001), and a more diverse fauna recovered from early Oligocene deposits in the Ashawq Formation of Oman (e.g., Thomas et al, 1989;Seiffert et al, 2012). More recently, an anthropoid primate was described from the mid-late Oligocene Shumaysi Formation of Saudia Arabia (Zalmout et al, 2010), and the discovery of a large-bodied mammal in the Aydim Formation of Oman has for the first time revealed continental mammals from as early as the late Eocene (Al-Sayigh et al, 2008).…”

Large Mammals from the Rupelian of Oman – Recent Finds

“…The alternating sequences of clastic and carbonate beds of the formation contain Nummulites, and numerous types of gastropods (Text-fi gs 6, 7), bivalves, echinoids, sponges, corals, fi sh remains and other vertebrate bones, the latter including turtles, crocodiles, proboscideans, primates, anthracotheriids, Arsinoitherium, hyracoids, bats and rodents (e.g. Thomas et al 1989, 1991, Otero and Gayet 2001, Al-Sayigh et al 2008, Seiffert et al 2012, Pickford 2015a, b, c, Sigé et al 1994.…”

“…There are also many enamel fragments. The following descriptions deal only with the more complete dental elements, comprising some rather complete lower incisors, and a reasonable sample of upper cheek teeth, which were poorly represented in previously available samples (Seiffert et al 2012, Pickford 2015b.…”

“…The Palaeogene fossil record of the Arabian Peninsula is of interest for several reasons, not least of which is its geographic position in the northeastern part of the Afro-Arabian land mass, south of the Tethys Seaway but not far from Asia to the northeast and from Europe to the northwest. In addition to the physical barrier of the Tethys Seaway that stood between the northern land mass and Afro-Arabia during the Eo-Oligocene, which tended to hinder dispersal of land mammals between the two continental land masses, there was a latitudinal effect which possibly played a role in restricting biotic interchanges, just as it does today, are limited in diversity and quantity, and because of this, interpretations of the taxonomy, systematics and phylogeny of some of the taxa remain ambiguous or incomplete (Seiffert et al 2012, Zalmout et al 2012, Pickford 2015a. Medium-sized mammals are generally poorly represented in the peninsula, but include a diversity of primates (Thomas et al 1991, Zalmout et al 2010 and hyracoids ), many of which remain unidentifi ed on account of the fact that most of the fossils comprise isolated or fragmentary teeth.…”