Scanning Electron Microscopy Volume 1986 Number 4 Article 35 10-9-1986 The Enamel Ultrastructure of Multituberculate Mammals: A Review D. W. Krause State University of New York S. J. Carlson University of California, Davis Follow this and additional works at: https://digitalcommons.usu.edu/electron Part of the Life Sciences Commons Recommended Citation Krause, D. W. and Carlson, S. J. (1986) "The Enamel Ultrastructure of Multituberculate Mammals: A Review," Scanning Electron Microscopy: Vol. 1986 : No. 4 , Article 35. Available at: https://digitalcommons.usu.edu/electron/vol1986/iss4/35 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Scanning Electron Microscopy by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. SCANNING ELECTRON MICROSCOPY /1986/IV (Pages 1591-1607) 0586-5581/86$1.00+05 SEM Inc., AMF O'Hare (Chicago), IL 60666-0507 USA THE ENAMELULTRASTRUCTURE OF MULTITUBERCULATEMAMMALS: A REVIEW 1* 2 D. W, Krause and S. J, Carlson 1Department of Anatomical Sciences, State UnivP.rsity of New York, Stony Brook, New York 11794 2Museum of Paleontology and Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan 48109 2Present address: Department of Geology, University of California Davis, CA 95616 (Received for publication May 09, 1986, and in revised form October 09, 1986) Abstract Introduction The enamel ultrastructure of multituber­ The enamel ultrastructure of multituber­ culate mammals has been sampled extensively and culate mammals has been sampled extensively and studied intensively and is better known than for studied intensively; it is better known than for any other group of early mammals. The enamel of any other group of early mammals, and perhaps for the earliest multituberculates, those of the Late any other group of fossil mammals save hominoids. Triassic-Early Jurassic suborder Haramiyoidea and Only recently, with the advent of technological the Late Jurassic-early Early Cretaceous suborder advances in scanning electron microscopy, have Plagiaulacoidea, is "preprismatic." With only concerted efforts been made to investigate two exceptions, all Late Cretaceous and early systematically the enamel ultrastructure of Tertiary genera of multituberculates examined mammals for the purpose of providing a new and have prismatic enamel. Prisms are either small independent data set with which to test phylo­ with circular (complete) boundaries or large with genetic hypotheses based on gross morphological arc-shaped (incomplete) boundaries. There is a characters alone (e.g., Gantt et al. 1977; Boyde remarkably consistent relationship between enamel 1978; Vrba and Grine 1978; Gantt 1980, 1983; von ultrastructural type and subordinal taxa in that Koenigswald 1982; Boyde and Martin 1984a, b; small, circular prisms are usually found within Grine et al., 1986a). Historically, multituber­ the suborder Ptilodontoidea and large, arc-shaped culate phylogeny has been determined almost prisms are usually found in the suborder Taenio­ exclusively on the basis of a few gross dental labidoidea and in six Late Cretaceous-Early characters that have proven inadequate to dis­ Tertiary genera of indeterminate subordinal criminate consistently between higher taxa. status. Cranial and postcranial characters are imprac­ Research currently in progress suggests that tical to employ in phylogenetic analyses of both small, circular prisms and large, arc-shaped multituberculates because adequate material is prisms are homologous in all multituberculates in rare. Thus, multituberculates have served as the which they occur, with one exception. Neolio­ focus of considerable research on enamel ultra­ tomus, a taeniolabidoid, appears to have evolved structure because, even though they were among small, circular prisms independently. In addi­ the most evolutionarily successful and taxonom­ tion, it appears that large, arc-shaped prisms ically long-lived of early mammals, their taxon­ represent the primitive condition in multituber­ omy and systematics have been, and still are, in culates with prismatic enamel, not small, circ­ disarray. ular prisms as has been proposed previously. The objectives of this paper are to review and discuss what has been learned from past studies about the enamel ultrastructure of the Multituberculata, to re-evaluate some of that work in the light of previously unpublished data, and to present some preliminary conclusions concerning the homology and polarity of multi­ tuberculate enamel ultrastructural characters. In addition, we wish to suggest some areas for KEY WORDS: Enamel ultrastructure, multituber­ future research on these subjects. But first it culates, mammals, phylogeny, cladistics, homo­ is necessary to provide, as background infor­ logy, polarity, Mesozoic, Paleogene, variability mation, a brief account of the evolutionary history and paleobiological attributes of multi­ tuberculates. *Address for correspondence: David W. Krause, Department of Anatomical What Are Multituberculates? Sciences, State University of New York, Stony Brook, New York 11794 The Multituberculata is the longest-lived Phone No. (516) 444-3117 order of mammals. Their known geologic record is 1591 D, W. Krause and S. J. Carlson from the Late Triassic to the early Oligocene, an Table 1. Classification of multituberculates interval of over 150 million years. Multituber­ (Hahn and Hahn 1983). culates, unlike their dinosaurian contemporaries, survived the Cretaceous-Tertiary boundary with Order MULTITUBERCULATA little apparent ill effect (Archibald 1983). Suborder HARAMIYOIDEA Representatives of the order have been found only Family HARAMIYIDAE on northern continents: in the Late Jurassic to Haramiya, Thomasia, ?Hypsiprymnopsis early Oligocene of North America, in the Late Suborder PLAGIAULACOIDEA Triassic to early Eocene of Europe, and in the Family ARGINBAATARIDAE Early Cretaceous to early Eocene of Asia (Clemens Arginbaatar and Kielan-Jaworowska 1979; Hahn and Hahn 1983). Family Paulchoffatiidae The Order Multituberculata is both a taxonomical­ Subfamily Kuehneodontinae ly diverse and numerically abundant group that Bolodon, Guimarotodon, Henkelodon, includes 57 named genera and over 140 named Kuehneodon, Plioprion species (Hahn and Hahn 1983). During the Late Subfamily Paulchoffatiinae Cretaceous, they comprised as much as 75% of the Paulchoffatia, Pseudobolodon individuals in mammalian local faunas (Van Valen Subfamily indeterminate and Sloan 1966). They appear to have attained Parendotherium peak species diversity in the middle Paleocene, Family Plagiaulacidae approximately 60 million years before present Ctenacodon, Loxaulax, Plagiaulax, (Van Valen and Sloan 1966; Krause 1980). Psalodon The relationships of multituberculates to Suborder PTILODONTOIDEA other higher taxa of mammals are obscure. They Family BOFFIIDAE have long been grouped with docodonts, tricono­ Boffius donts, and monotremes as nontherian mammals, a Family CIMOLODONTIDAE taxonomic arrangement that has recently been Anconodon, Cimolodon, Liotomus challenged (e.g., Presley 1981; Kemp 1982, 1983; Family NEOPLAGIAULACIDAE Archer et al. 1985). Ectypodus, Mesodma, Mimetodon, The Order Multituberculata is generally Neoplagiaulax, Parectypodus, divided into three suborders: Plagiaulacoidea, Xanclomys Ptilodontoidea, and Taeniolabidoidea. Most Family PTILODONTIDAE workers (e.g., Hahn 1973; McKenna 1975; Sloan Kimbetohia, Prochetodon, Ptilodus 1979) also include an enigmatic and poorly known Suborder TAENIOLABIDOIDEA Late Triassic and Early Jurassic (possibly middle Family EUCOSMODONTIDAE Jurassic) group from Europe, the suborder Hara­ Subfamily BUGINBAATARINAE miyoidea, in the Multituberculata (a possible Buginbaatar haramiyid has been described recently from the Subfamily EUCOSMODONTINAE Late Triassic/Early Jurassic of North America Bulganbaatar, Chulsanbaatar, (Jenkins et al. 1983)). The Plagiaulacoidea are Eucosmodon, Kryptobaatar, a Late Jurassic to Early Cretaceous group con­ Nemegtbaatar, Neoliotomus, Stygimys, taining 13 genera, the Ptilodontoidea a Late Tugrigbaatar, ?Xyronomys Cretaceous to early Oligocene group also con­ Subfamily MICROCOSMODONTINAE taining 13 genera, and the Taeniolabidoidea a Acheronodon, Microcosmodon, Late Cretaceous to early Eocene group containing Pentacosmodon 20 genera. Eight Late Cretaceous and early Subfamily SLOANBATAARIDAE Tertiary genera (Allacodon, Cimexomys, Cimolomys, Sloanbaatar Essonodon, Hainina, Meniscoessus, Paracimexomys, Family TAENIOLABIDIDAE and Viridomys), most of which, until recently, Catopsalis, Kamptobaatar, were included in either the Ptilodontoidea or Lambdopsalis, Prionessus, Taeniolabidoidea, are currently placed in Sub­ Sphenopsalis, Taeniolabis order incertae sedis. Table 1, based upon a Suborder indeterminate compilation by Hahn and Hahn (1983), presents the Family CIMOLOMYIDAE most recent comprehensive classification of all Cimolomys, Meniscoessus, ?Essonodon genera currently allocated to the Multitubercu­ Family indeterminate lata. Allacodon, Cimexomys, Hainina, Multituberculates are so-named because of Paracimexomys, Viridomys the possession of multiple cusps, arranged in longitudinal rows, on the molars. Plagiaulacoids are characterized by a greater number of incisors fragmentary cranial material of ptilodontoids and premolars than later forms, ptilodontoids by from North America suggests that these forms were an enlarged, blade-like