From the Late Eocene and Early Oligocene of Egypt
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Craniodental Morphology and Systematics of a New Family of Hystricognathous Rodents (Gaudeamuridae) from the Late Eocene and Early Oligocene of Egypt Hesham M. Sallam1*, Erik R. Seiffert2, Elwyn L. Simons3 1 Department of Geology, Faculty of Sciences, Mansoura University, Mansoura, Egypt, 2 Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York, United States of America, 3 Division of Fossil Primates, Duke Lemur Center, Durham, North Carolina, United States of America Abstract Background: Gaudeamus is an enigmatic hystricognathous rodent that was, until recently, known solely from fragmentary material from early Oligocene sites in Egypt, Oman, and Libya. Gaudeamus’ molars are similar to those of the extant cane rat Thryonomys, and multiple authorities have aligned Gaudeamus with Thryonomys to the exclusion of other living and extinct African hystricognaths; recent phylogenetic analyses have, however, also suggested affinities with South American caviomorphs or Old World porcupines (Hystricidae). Methodology/Principal Findings: Here we describe the oldest known remains of Gaudeamus, including largely complete but crushed crania and complete upper and lower dentitions. Unlike younger Gaudeamus species, the primitive species described here have relatively complex occlusal patterns, and retain a number of plesiomorphic features. Unconstrained parsimony analysis nests Gaudeamus and Hystrix within the South American caviomorph radiation, implying what we consider to be an implausible back-dispersal across the Atlantic Ocean to account for Gaudeamus’ presence in the late Eocene of Africa. An analysis that was constrained to recover the biogeographically more plausible hypothesis of caviomorph monophyly does not place Gaudeamus as a stem caviomorph, but rather as a sister taxon of hystricids. Conclusions/Significance: We place Gaudeamus species in a new family, Gaudeamuridae, and consider it likely that the group originated, diversified, and then went extinct over a geologically brief period of time during the latest Eocene and early Oligocene in Afro-Arabia. Gaudeamurids are the only known crown hystricognaths from Afro-Arabia that are likely to be aligned with non-phiomorph members of that clade, and as such provide additional support for an Afro-Arabian origin of advanced stem and basal crown members of Hystricognathi. Citation: Sallam HM, Seiffert ER, Simons EL (2011) Craniodental Morphology and Systematics of a New Family of Hystricognathous Rodents (Gaudeamuridae) from the Late Eocene and Early Oligocene of Egypt. PLoS ONE 6(2): e16525. doi:10.1371/journal.pone.0016525 Editor: Anjali Goswami, University College London, United Kingdom Received August 26, 2010; Accepted January 4, 2011; Published February 22, 2011 Copyright: ß 2011 Sallam et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This research has been funded by a series of grants from the U.S. National Science Foundation as well as The Leakey Foundation, Gordon and Ann Getty, Margot Marsh, Verna Simons, the Smithsonian Foreign Currency Program, and the Boise Fund of Oxford University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: [email protected] Introduction and the ‘‘Upper Fossil Wood Zone’’ [8], now called the ‘‘lower sequence’’ and ‘‘upper sequence’’, respectively [9]. The sediments The Jebel Qatrani area of northern Egypt, which is located of the Jebel Qatrani Formation consist primarily of variegated north-northwest of Birket Qarun (the largest lake in North Africa), alluvial deposits [9], and overlie the nearshore marine and fluvial preserves the richest terrestrial mammal-bearing Paleogene expo- beds of the late Eocene Qasr el-Sagha Formation. Almost all of the sures in Egypt, if not the entire Afro-Arabian landmass [1,2]. The area’s major vertebrate fossil quarries, such as quarries A, B, E, V, I, eastern part of this protected area is situated approximately 85 km M, and L-41 occur in the Jebel Qatrani Formation (Figure 2). Of southwest of Cairo (Figure 1), and takes its name (Egyptian Arabic these, only L-41 is likely to be late Eocene in age, and is probably gebel = mountain, qatrani = tar) from the Widan el-Faras basalt, very close to the Eocene-Oligocene boundary [6,7]. which unconformably caps the Oligocene succession. The geology Fieldwork in the Jebel Qatrani area in 1983 led to the discovery of of the Jebel Qatrani area is uncomplicated, consisting of a series of the oldest and most productive quarry, Locality 41 (L-41) (Figure 1C– escarpments of late Eocene, early Oligocene, and Miocene age. E). Annual excavations at L-41 undertaken by Duke University and Four formations, ranging in age from the late Eocene to the early the Cairo Geological Museum over the course of the subsequent 26 Miocene, are exposed, and the most fossiliferous, the Jebel Qatrani years have significantly increased the number of fossil vertebrate Formation [3], previously known as the ‘‘Fluvio-Marine Series’’ [4] species known from the Fayum area. Species known from the L-41 underlies the Miocene Khashab Formation and is late Eocene and are often represented not only by dental and mandibular remains, but early Oligocene in age [5,6,7]. The formation has been divided into also by complete crania and postcranial remains, though the latter are two zones, previously referred to as the ‘‘Lower Fossil Wood Zone’’ often badly crushed and distorted [10,11,12,13]. PLoS ONE | www.plosone.org 1 February 2011 | Volume 6 | Issue 2 | e16525 Gaudeamuridae from the Paleogene of Egypt Figure 1. Location and overview of Quarry L-41. A, Location map of the Fayum Depression; B, close up map of Jebel Qatrani area, showing major land marks mentioned here; C, general view of Quarry L-41; D, quarrying process at L-41; E, workers exposing a new area of L-41. doi:10.1371/journal.pone.0016525.g001 Although hystricognathous rodents are often among the most being over four decades old, Albert Wood’s analysis of Fayum abundant components of the Jebel Qatrani Formation’s terrestrial rodents [14] remains the most significant publication on the group, mammal faunas, little has been published about the group. Despite though newer discoveries were subsequently dealt with in an PLoS ONE | www.plosone.org 2 February 2011 | Volume 6 | Issue 2 | e16525 Gaudeamuridae from the Paleogene of Egypt PLoS ONE | www.plosone.org 3 February 2011 | Volume 6 | Issue 2 | e16525 Gaudeamuridae from the Paleogene of Egypt Figure 2. Stratigraphic positions and age estimates for major mammal-bearing fossil quarries, approximate position of Eocene- Oligocene boundary, following Seiffert [6], and distribution of hystricognathous rodents in the Jebel Qatrani area. doi:10.1371/journal.pone.0016525.g002 unpublished doctoral dissertation [15]. The oldest hystricognaths very similar parsimony analysis to that of Sallam et al. [16], and from Egypt, ,37 Ma Protophiomys aegyptensis and Waslamys attiai, argued that Gaudeamus might be an African caviomorph. were recently described by Sallam et al. [16], but more derived Here we present new fossil evidence from Quarry L-41 that members of this rodent suborder have been discovered at helps to illuminate the origin of the genus Gaudeamus. This new numerous levels between the oldest (BQ-2, ,37 Ma) and youngest material provides the basis for the erection of a new higher taxon, (I and M, ,30 Ma) major terrestrial mammal-bearing localities in Gaudeamuridae — the first new family of Fayum rodents to be the area. The rodents from the ,34 Ma Quarry L-41 include named in over half a century. In addition, two new species of evolutionarily intermediate forms that provide an important Gaudeamus are documented here by nearly complete crania and source of information not only for understanding the group’s almost complete upper and lower dentitions. The new species systematic position, but also for the evolution and biogeographic represent the oldest records of the genus Gaudeamus to date. More history of Hystricognathi. fragmentary material of Gaudeamus from L-41 was described in the Among other taxa, the extensive collection of hystricognathous unpublished Ph.D. dissertation of Holroyd [15], and one species rodents from L-41 includes numerous specimens of the genus that she named in that work, Gaudeamus hylaeus, was used in a Gaudeamus, including not only mandibles and maxillae, but also subsequent publication [17] despite not yet having been nearly complete crania. Gaudeamus is the most hypsodont rodent of adequately described and figured according to the requirements the lower sequence, and bears molars with tall lophs and a highly of the International Code of Zoological Nomenclature (ICZN); derived, but relatively simple, occlusal pattern. Gaudeamus is this species has since been listed as a nomen nudum by Pickford et al. intermediate in size when compared with other Fayum rodents [25]. A further complication is that we recognize an additional such as the tiny genus Phiocricetomys and the relatively large genus new species, Gaudeamus aslius, within Holroyd’s G. hylaeus Metaphiomys [17]. Remains of specimens that would ultimately be hypodigm. In order to prevent further confusion in the literature, placed in the