Palaeontologia Electronica palaeo-electronica.org Deciduous dentition and dental eruption sequence of Bothriogenys fraasi (Anthracotheriidae, Artiodactyla) from the Fayum Depression, Egypt Hesham M. Sallam, Afifi H. Sileem, Ellen R. Miller, and Gregg F. Gunnell ABSTRACT Paleogene anthracotheres are poorly documented from Afro-Arabian localities. This is due, in large part, to the fragmentary nature of the specimens that have been described. However, sediments in the Jebel Qatrani Formation, Fayum Depression, Egypt, preserve the richest anthracothere assemblage in all of Afro-Arabia. Unlike other samples, the Fayum collection includes many complete dentitions, skulls, and partial skeletons. Based on these extensive collections, this study provides the first description of the complete deciduous dentition and dental eruption sequence for the early Oligocene anthracothere Bothriogenys fraasi. A detailed discussion concerning the pattern and timing of dental growth in B. fraasi is provided, and the ontogenetic sequence documented for B. fraasi is compared with those available for suoids and hippos, the two extant groups currently considered as possible sister taxa to anthraco- theres. Results show that anthracotheres and suoids share a more similar dental emer- gence pattern, and one that may be close to the primitive condition for artiodactyls, while hippos have a very different dental eruption sequence as a consequence of their highly divergent life history pattern. As a growing body of life history research indicates that taxa in close phylogenetic proximity may be expected to share features of their dental developmental pattern, this finding suggests a useful test of competing hypothe- ses of a relationship between Anthracotheriidae and either Hippopotamidae or Suiformes can potentially be developed based on eruption patterns. Hesham M. Sallam, Mansoura University Vertebrate Paleontology Center, Department of Geology, Mansoura University, Mansoura, 35516, Egypt, and Department of Evolutionary Anthropology, Duke University, Durham, NC 27708, USA [email protected] Afifi H. Sileem, Vertebrate Paleontology Section, Cairo Geological Museum, Cairo, Egypt, [email protected] Ellen R. Miller, Department of Anthropology, Wake Forest University, Winston-Salem, NC 27106, USA, [email protected] Gregg F. Gunnell, Division of Fossil Primates, Duke Lemur Center, Durham, NC 27705, USA, [email protected] Keywords: Fayum; Egypt, Oligocene; juvenile; dentition; Artiodactyla Submission: 13 February 2016 Acceptance: 16 August 2016 Sallam, Hesham M., Sileem, Afifi H., Miller, Ellen R., and Gunnell, Gregg F. 2016. Deciduous dentition and dental eruption sequence of Bothriogenys fraasi (Anthracotheriidae, Artiodactyla) from the Fayum Depression, Egypt. Palaeontologia Electronica 19.3.38A: 1-17 palaeo-electronica.org/content/2016/1595-anthracotheriidae-from-egypt Copyright: Palaeontological Association October 2016 SALLAM ET AL.: ANTHRACOTHERIIDAE FROM EGYPT INTRODUCTION Anthracotheriidae is an extinct family of artio- dactyls known from Eocene – Miocene deposits The terrestrial mammal-bearing localities of across Laurasia and into Africa (but not elsewhere the Jebel Qatrani Formation, Fayum Depression, in Gondwana). Behaviorally, they are thought to Egypt, including the well-known quarries L-41, A, have occupied a range of browsing niches over B, E, V, I, and M, are among the most productive both their long temporal and broad geographic Paleogene fossil localities known anywhere in ranges, although whatever their specific feeding Africa (Figure 1). The Jebel Qatrani deposits range ecologies were they are widely acknowledged to in age from late Eocene through early Oligocene have been semi-aquatic based on skeletal propor- (~34 to ~30 Ma) (Kappelman et al., 1992; Seiffert, tions and inferred habitats where fossils are found 2006; Seiffert et al., 2008), and fossils recovered (e.g., Black, 1978; Pickford, 1991; Holroyd et al., from the Jebel Qatrani have profoundly influenced 2010; Miller et al., 2014). As a group, identification our understanding of primate (e.g., Seiffert et al., of the closest living anthracothere relative within 2010; Seiffert, 2012), and mammalian evolution Artiodactyla is contested, with some researchers (e.g., Simons and Rasmussen, 1990; Simons, favoring a suiform affiliation (e.g., Pickford, 2007), 2008). However, relatively few of these mammalian and others supporting a closer relationship with studies have focused on anthracotheres (Andrews, extant Hippopotamidae (e.g., Black, 1978; Bois- 1906; Schmidt, 1913; Black, 1978; Holroyd et al., serie and Lihoreau, 2006; O’Leary et al., 2012). 1996; Ducrocq, 1997; Sileem et al., 2015; Sileem Much of the recent work on anthracotheres et al., 2016), despite the fact that anthracotheres has been concerned with establishing their alpha are among the most abundant fossils recovered taxonomy, as reflected in observable differences from Fayum deposits. FIGURE 1. 1, location map of the Jebel Qatrani area, Fayum Depression. 2, stratigraphic positions and age esti- mates for major mammal-bearing fossil localities, following Seiffert (2006), EOB is abbreviation for Eocene Oligocene Boundary. 3, map of Jebel Qatrani area, showing different rock units, common landmarks and the approximate posi- tion of anthracothere-bearing fossil localities. 2 PALAEO-ELECTRONICA.ORG 1 among adult dental morphologies (e.g., Lihoreau material, there is no evidence for P /1 replacement and Ducrocq, 2007, but for exceptions see Pick- 1 suggesting that Bothriogenys fraasi retained a dP /1 ford, 2006; 2008). However, many of these investi- into adulthood. Morphology is not especially helpful gations have been conducted without adequate to determine whether or not the retained tooth is material. The mandibular and maxillary material deciduous or permanent because, unlike dP3/ and available in many museum collections preserves 3 4 2 jaws with only molars and premolars, while many dP /4, dP /2 is neither molariform or of an exagger- 2 of the most striking differences among anthracoth- ated form but more like permanent P /2 suggesting ere taxa are manifest in their anterior dentition that the first deciduous premolar would be simple (e.g., presence/absence of diastemata, reduced v. as well. caniniform canines, relative size, and orientation of It is not uncommon for mammals (some pigs, incisors), even when the morphology of the cheek hippopotamus, horses, hyraxes) to retain decidu- teeth remains more conservative. ous first premolars that are not replaced (Zeigler, In contrast, the collection of anthracothere 1971; Luckett, 1993; Smith, 2000). Only Tapirus material from the Jebel Qatrani Formation is com- and maybe some archaeocete whales show evi- prised of a large number of anthracothere speci- dence of replacement of the first premolar among mens (N= ~2270, including isolated teeth and mammals and in the case of the latter the evidence postcranial elements), that are currently recog- is not compelling (Luckett, 1993; Uhen, 2000). nized as representing six species in three genera. Therefore, the first upper and lower premolars of A fairly large proportion of these preserve at least Bothriogenys fraasi are here considered to be part of the anterior dentition and 12% (N=33/270) retained deciduous teeth. of the specimens attributed to B. fraasi are juve- All specimens are cataloged in the Duke University niles. Lemur Center, Division of Fossil Primates and desig- Here we provide the first documentation of the nated with the prefix DPC. The studied materials were deciduous dentition and dental eruption sequence scanned using a Nikon XT H 225 ST micro-CT scanner of the anthracothere, Bothriogenys fraasi, a taxon housed at Duke University’s Shared Materials Instru- known from the early Oligocene upper sequence in mentation Facility, and three-dimensional reconstruc- the Jebel Qatrani Formation. This work represents tions were rendered in Avizo v.8. Dental measurements the first detailed account of an ontogenetic were taken from digital surface models (in Stanford “ply” sequence for any anthracothere taxon and is made format). All three dimensional (3D) digital materials are possible by the decades of fieldwork in the Fayum available for viewing and direct download at www.mor- that recovered such a large sample of remarkably phosource.org, (morphosource.org/index.php/Detail/Pro- well-preserved juvenile specimens. Results from jectDetail/Show/project_id/224). See also Table 1 for this investigation into the pattern and timing of den- digital object identifiers, DOIs that directly link to 3D dig- tal growth in B. fraasi will serve as a reference for ital media associated with each specimen. More details comparison with other anthracothere species, and yet are provided in Supplemental Material. Reuse of provides empirical information from growth and these data should cite MorphoSource, the DOI and this development towards resolving the phylogenetic paper. relationships within anthracotheres, and between anthracotheres and other artiodactyl groups. DESCRIPTION Upper Deciduous Teeth MATERIAL AND METHODS A complete upper and lower deciduous pre- Tooth position is referenced as dI, dC, dP, P, molar dentition for Bothriogenys fraasi is available and M (for deciduous incisors, canine, premolars, as a composite from specimens recovered from and permanent premolars and molars, respec- Fayum Quarries I, M, and O. DPC 5167 (Figure tively), with upper and lower teeth designated by 3.1-4, Table 1) is a right maxillary fragment