NEW DATA ON THE SKULL AND DENTITION IN THE MONGOLIAN LATE CRETACEOUS EUTHERIAN MAMMAL ZALAMBDALESTES JOHN R. WIBLE Section of Mammals, Carnegie Museum of Natural History, 5800 Baum Boulevard, Pittsburgh, PA 15206 e-mail: [email protected] MICHAEL J. NOVACEK Division of Paleontology, American Museum of Natural History e-mail: [email protected] GUILLERMO W. ROUGIER Department of Anatomical Sciences and Neurobiology, School of Medicine, University of Louisville, Louisville, KY 40292 e-mail: [email protected] BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 281, 144 pp., 58 ®gures, 3 tables Issued January 9, 2004 Copyright q American Museum of Natural History 2004 ISSN 0003-0090 2 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 281 CONTENTS Abstract ....................................................................... 3 Introduction .................................................................... 3 Materials and Methods .......................................................... 5 History of Investigations ......................................................... 7 Comparative Morphology ....................................................... 17 Dentition ................................................................... 17 Upper Incisors ............................................................ 18 Upper Canine ............................................................. 21 Upper Premolars .......................................................... 22 Upper Molars ............................................................. 25 Lower Incisors and Canine ................................................. 28 Lower Premolars .......................................................... 31 Lower Molars ............................................................. 32 Dental Formula ........................................................... 32 Lower Jaw .................................................................. 33 Skull ....................................................................... 37 Nasal-Facial Region ....................................................... 39 Palate .................................................................... 42 Orbitotemporal Region ..................................................... 47 Basicranium and Auditory Region ........................................... 65 Occiput .................................................................. 84 Endocranial Cast .......................................................... 86 Vascular Reconstruction ...................................................... 88 Veins .................................................................... 90 Arteries .................................................................. 91 Discussion .................................................................... 96 Previous Phylogenetic Analyses ............................................... 96 Hu (1993) ................................................................ 96 Archibald (1996) and Nessov et al. (1998) ................................... 97 Rougier et al. (1998) ....................................................... 99 Meng and Wyss (2001) ................................................... 103 Archibald et al. (2001) .................................................... 106 Ji et al. (2002) ........................................................... 109 Comparisons ............................................................... 112 Within Zalambdalestes .................................................... 112 With Barunlestes butleri ................................................... 114 With Kulbeckia kulbecke .................................................. 116 With Leptictids and Insectivorans ........................................... 118 With Rodents, Lagomorphs, and Elephant Shrews ............................ 120 With Asioryctitheres ...................................................... 124 With Zhelestids .......................................................... 129 Conclusions .................................................................. 129 Acknowledgments ............................................................ 131 References ................................................................... 131 Addendum ................................................................... 140 Appendix 1: List of Anatomical Terms .......................................... 141 2004 WIBLE ET AL.: ZALAMBDALESTES 3 ABSTRACT Exquisitely preserved specimens of the Late Cretaceous eutherian Zalambdalestes recently collected from the Djadokhta Formation (Early Campanian) of the Gobi Desert by the Mon- golian Academy of Sciences±American Museum of Natural History Expeditions are the cen- terpiece of a thorough redescription of this taxon's craniodental morphology. Resolved and amended are uncertainties and errors in prior descriptions based on poorer preserved specimens collected by earlier expeditions to the Gobi. Preserved and described for the ®rst time in Zalambdalestes is the basicranium, including an ectotympanic bone and portions of the hyoid arch. Zalambdalestes with a skull length of nearly 50 mm is large compared with other Cretaceous eutherians. It is also highly specialized with a long, thin, tubular snout, large diastemata in the anterior upper dentition, and an elongated mesial lower incisor with restricted enamel. These specializations, though less extreme, are also present in the zalambdalestids Barunlestes from the slightly younger Barun Goyot Formation of the Gobi and Kulbeckia from the late Turonian and Coniacian of Uzbekistan and the Santonian of Tadjikistan. No phylogenetic analysis published to date includes enough taxonomic and morphological breadth to evaluate the relationships of Zalambdalestes. Nevertheless, we investigate the im- pact of our observations on seven phylogenetic analyses published since 1993 that include Zalambdalestes. A comprehensive phylogenetic analysis testing the relationships of Zalamb- dalestes is not included here, but it is expected to result from our ongoing efforts to produce a phylogeny of basal tribosphenic and therian mammals. Currently, zalambdalestids are viewed either as stem eutherians or as having af®nities to Glires (lagomorphs and rodents). Our comparisons with other extinct and extant taxa support a position for Zalambdalestes within Eutheria but outside the crown-group Placentalia. Sup- porting this basal position for Zalambdalestes are such primitive features as the last upper incisor in the maxilla, nasals broadly expanded posteriorly to contact the lacrimals, pterygoids meeting on the midline, and the position of the glenoid fossa on the zygoma and not the braincase proper, in addition to the occurrence of epipubic bones reported previously. Za- lambdalestes shares a number of apomorphies with Asioryctitheria, the clade including the Mongolian Late Cretaceous Asioryctes, Ukhaatherium, and Kennalestes. Among the unusual specializations supporting a zalambdalestid-asioryctithere clade are: the postglenoid foramen anterior rather than posterior to the postglenoid process; the postglenoid and entoglenoid pro- cesses of the squamosal continuous; a fusiform ectotympanic expanded laterally and contacting the entoglenoid process; a suprameatal foramen in the squamosal; a crista interfenestralis connecting from the petrosal promontorium to a ®ngerlike tympanic process behind the round window; a large piriform fenestra in the anterior roof of the tympanic cavity, which transmitted the ramus inferior of the stapedial artery endocranially to the orbit; a foramen ovale between the alisphenoid and squamosal; and a medially positioned internal carotid artery. All but the last two of these specializations are reminiscent of those occurring in various extant lipotyph- lans, including taxa placed by recent DNA sequence analyses within Afrotheria and Eulipo- typhla, and may provide a link between the Mongolian Cretaceous eutherians and lipotyphlans. The available sample of Zalambdalestes exhibits a remarkable degree of individual varia- tion, including the incidence of the upper maxillary incisor, the ®rst upper premolar, and the second lower premolar. The possibility exists that more than a single species, Z. lechei,is represented. INTRODUCTION etons occur in the Upper Cretaceous se- Therian mammals are known from Lower quences of the Gobi Desert in Mongolia. Cretaceous deposits by isolated teeth, jaw These fossil beds were ®rst discovered in the fragments, and petrosals (Slaughter, 1965, 1920s by the American Museum of Natural 1971; Kielan-Jaworowska and Dashzeveg, History Central Asiatic Expeditions (CAE) 1989; Cifelli, 1993, 1999; Wible et al., 1997, led by Roy Chapman Andrews (Gregory and 2001) and now by a nearly complete skeleton Simpson, 1926a, 1926b; Simpson, 1928a, with crushed skull (Ji et al., 2002). However, 1928b). The specimens collected were re- the oldest, nearly complete skulls and skel- ferred by Gregory and Simpson (1926a) to 4 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 281 two new families of Insectivora, the Delta- high in the quality of representative material. theridiidae, including Deltatheridium, Delta- This is largely due to new specimens of Za- theroides, and Hyotheridium, and the Za- lambdalestes and the closely related genus lambdalestidae, including Zalambdalestes. Barunlestes recovered by the Polish±Mon- Of these, Deltatheridium and Deltatheroides golian Expeditions between 1963 and 1971