Mammals from the Age of Dinosaurs

Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure

Zofia Kielan-Jaworowska
Richard L. Cifelli
Zhe-Xi Luo
Copyright Date: 2004
Pages: 700
  • Cite this Item
  • Book Info
    Mammals from the Age of Dinosaurs
    Book Description:

    The fossil record on Mesozoic mammals has expanded by orders of magnitude over the past quarter century. New specimens, some of them breathtakingly complete, have been found in nearly all parts of the globe at a rapid pace. Coupled with the application of new scientific approaches and techniques, these exciting discoveries have led to profound changes in our interpretation of early mammal history.

    Mesozoic mammals have come into their own as a rich source of information for evolutionary biology. Their record of episodic, successive radiations speaks to the pace and mode of evolution. Early mammals were small, but they provide key information on the morphological transformations that led to modern mammals, including our own lineage of Placentalia. Significant and fast-evolving elements of the terrestrial biota for much of the Mesozoic, early mammals have played an increasingly important role in studies of paleoecology, faunal turnover, and historical biogeography. The record of early mammals occupies center stage for testing molecular evolutionary hypotheses on the timing and sequence of mammalian radiations.

    Organized according to phylogeny, this book covers all aspects of the anatomy, paleobiology, and systematics of all early mammalian groups, in addition to the extant mammalian lineages extending back into the Mesozoic.

    eISBN: 978-0-231-50927-5
    Subjects: Paleontology, Ecology & Evolutionary Biology, Biological Sciences, Zoology

Table of Contents

  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-vi)
    (pp. vii-x)
    Jason A. Lillegraven and William A. Clemens

    When most of us think about mammals from the Mesozoic Era we use our imaginary time-viewing machines to see furry little creatures with relatively large beady eyes and warm wiggly noses. We see them scampering through moonlit forests capturing insects, tearing apart fruits from early flowering plants, sometimes lapping nectar, and universally marking their territories with diverse body exudates. We think of them as denizens of a world much different from ours of today. The food chains of their generally warmer ecosystems are seen to be capped by dinosaurs, crocodiles, and birds, all of which were foraging within forests and...

    (pp. xi-xviii)
  5. CHAPTER 1 Introduction
    (pp. 1-18)

    The first 155 million years (Ma) of mammalian history occurred during the Mesozoic. During this vast time span, mammals diversified into many lineages and underwent enormous anatomical evolution. Humans are primates; primates are placentals; placentals are eutherians; and stem eutherians have a long history, which extends well back into the Early Cretaceous. Mesozoic mammals include the trunk and a bewildering bush of basal branches for the entire mammalian family tree. Their fossil records are indispensable for our understanding of the deep history that gave rise to extant mammals, including our own lineage of placentals.

    Mammals have thrived in the world’s...

  6. CHAPTER 2 Distribution: Mesozoic Mammals in Space and Time
    (pp. 19-108)

    Following our traditional concept of Mammalia, and thus including a number of forms known only by fossils of the Mesozoic, the earliest mammals are from the Late Triassic, a bit over 220 Ma old (figure 2.1). The Mesozoic record thus spans about 155 Ma of mammalian history—more than twice the duration of the entire Cenozoic. Yet the Mesozoic record is frustratingly sparse.¹ Reasonably complete specimens—skulls and skeletons—are rare and are known for only a few taxa, while for many groups the discovery of a partial jaw is a notable occurrence. The record is also discontinuous, being punctuated...

  7. CHAPTER 3 Origin of Mammals
    (pp. 109-160)

    Mammals are distinctive from nonmammalian vertebrates in many derived features that, in turn, are correlated with important biological adaptations. They are unique among vertebrates, for example, in having fur, which provides insulation for maintaining an elevated (homeothermic) metabolism, and mammary glands, which provide milk for neonates. The important reproductive feature of nursing the neonate by mother’s milk is correlated with mammalian growth patterns and numerous apomorphies of the dentition and skull, as discussed by Pond (1977),Tyndale-Biscoe and Renfree (1987), Jenkins (1990), and Zeller (1999a).

    The origin of mammals was accompanied by the evolution of a number of derived osteological and...

  8. CHAPTER 4 The Earliest-Known Stem Mammals
    (pp. 161-186)

    Mammals are defined by the common ancestry of Sinoconodon and extant mammals¹ (see chapter 3). Mammals so defined include those synapsids that are more closely related to monotremes, marsupials, and placentals than to tritheledontids (“ictidosaurs”), tritylodontids, probainognathids, dromatheriids, or any combination of these cynodont groups. The Mammalia under this stem-based definition can be diagnosed by the derived characters of a craniomandibular joint formed by the dentary condyle and the squamosal glenoid, a promontorium in the petrosal, a well-developed separation of the jugular foramen from the hypoglossal foramen (except for Ornithorhynchus), and a host of other characters. A number of stem...

  9. CHAPTER 5 Docodontans
    (pp. 187-201)

    Docodontans are a monophyletic group defined by the common ancestor of Docodon, Simpsonodon, and all other Mesozoic mammal taxa more closely related to Docodon and Simpsonodon than to morganucodontans, Shuotherium, and cladotherians (stem “eupantotherians”). This group consists of mole-sized or smaller mammals. Uncontested docodontans are known from the Middle Jurassic to Early Cretaceous of the Laurasian continents. One putative taxon may extend their range to the Late Triassic (Sigogneau-Russell and Godefroit, 1997, an assignment challenged by Butler, 1997). On the other hand, Pascual et al. (2000) reported a docodontan dentary with three molars in the Late Cretaceous of Argentina. We...

  10. CHAPTER 6 Australosphenidans and Shuotherium
    (pp. 202-215)

    Some of the most important new paleontological discoveries of the past two decades have been made on the southern continents. The first of these was the 1985 discovery of the first Mesozoic mammal from Australia—the Early Cretaceous toothed monotreme Steropodon galmani, represented by a partial dentary with three molar teeth (Archer et al., 1985). The authors stated that the dental terminology used by them for S. galmani (p. 363): “assumes that the teeth are tribosphenic and the cusps are homologues of topographically analogous cusps in therian mammals” (see chapter 11 for a discussion on the origin of tribosphenic molars)....

  11. CHAPTER 7 Eutriconodontans
    (pp. 216-248)

    Eutriconodontans comprise a diverse, well-known group of Mesozoic mammals. Molar structure and other craniodental features indicate a strictly animalivorous diet; body size spanned a considerably broader range than most other groups and included some of the largest of all mammals known from the entire Mesozoic (figure 7.1).As a taxonomic group, Eutriconodonta are named after the most conspicuous, albeit primitive, characteristic of their dentition: a molar pattern consisting of three main cusps placed in anteroposterior alignment on a crown that is somewhat compressed transversely (figure 7.2). The distinctiveness of these characteristics was formally recognized by early workers (e.g., Marsh, 1887; Osborn,...

  12. CHAPTER 8 Allotherians
    (pp. 249-342)

    Marsh (1880) proposed the order Allotheria¹ (from Greek allos—other, different, therion—wild animal) to include two Late Jurassic genera, Plagiaulax and Ctenacodon, based on well-preserved dentaries with teeth, and he assigned Allotheria to Marsupialia. The dentaries superficially resembled those of rodents, but the teeth designated as molars were different, covered with numerous cusps of subequal height, arranged in longitudinal rows. Moreover, the lower premolars were unusual in being bladelike, covered on their labial and lingual sides by oblique ridges. Four years later Cope (1884) proposed the Multituberculata as a suborder of Marsupialia, including three families: Tritylodontidae, Polymastodontidae (= Taeniolabididae),...

  13. CHAPTER 9 “Symmetrodontans”
    (pp. 343-370)

    “Symmetrodontans” are poorly known, rare, and mainly small mammals, characterized by a simple reversed-triangle molar pattern. Functionally, the pattern represents a fundamental step in the evolution of mammalian molar design (e.g., Crompton and Sita-Lumsden, 1970): it is structurally intermediate between the cusp-in-line “triconodont” molar (chapters 4, 7) and the more elaborate molars of tribosphenic mammals and their precursors among “eupantotheres” (Patterson, 1956; Crompton and Jenkins, 1967, see chapters 10, 11). Formal recognition of “symmetrodontans,” in concept as well as name, stems from the work of Simpson (1925e, 1928a, 1929a), who placed then-known taxa (all from the Late Jurassic and earliest...

  14. CHAPTER 10 “Eupantotherians” (Stem Cladotherians)
    (pp. 371-407)

    “Eupantotherians” (= “eupantotheres”; “Eupantotheria” Kermack and Mussett, 1958) represent a very important assemblage of Mesozoic mammal clades that are placed between the plesiomorphic “symmetrodontans” (chapter 9) and the more advanced boreosphenidan mammals with tribosphenic molars (chapter 11). The three main groups traditionally assigned to “eupantotherians” are peramurids and their kin, amphitheriids, and dryolestoids, including paurodontids and dryolestids.

    Cladotheria (McKenna, 1975) is a stem-based clade defined by the common ancestor of boreosphenidans (including marsupials and placentals) and the fossil taxa more closely related to Crown Theria than to the more plesiomorphous Spalacotheriidae. By current prevailing hypotheses of cladistic relationships from the...

  15. CHAPTER 11 “Tribotherians” (Stem Boreosphenidans)
    (pp. 408-424)

    In 1936 Simpson introduced the term “tribosphenic molars” in reference to a pattern common to both basal eutherians and metatherians. These teeth had previously been referred to as tritubercular (upper) molar and tritubercular sectorial or tuberculosectorial (lower) molars (Osborn, 1907). The tribosphenic molar (from Greek tribein, to grind; and sphen, wedge) is, as described by Simpson (1936a: 797): “suggestive of the mortar and pestle, opposing action of protocone and talonid of the wedge-like, alternating and shearing action of trigon and trigonid.”During occlusion the upper tribosphenic molar shears posterior to its lower counterpart (figure 11.1C). Simpson’s term tribosphenic molar succinctly highlighted...

  16. CHAPTER 12 Metatherians
    (pp. 425-462)

    Marsupials and their putative fossil relatives, collectively termed Metatheria, have long been of general interest among evolutionary biologists. Like eutherians—and in contrast to monotremes—living marsupials give live birth; however, their reproductive biology is distinctly different (e.g., Tyndale-Biscoe, 1973; Renfree, 1981, 1983, 1993; Tyndale-Biscoe and Renfree, 1987; Zeller and Freyer, 2001). Living marsupials are mainly restricted to southern landmasses (though this is not the case for fossil relatives), and the origin and biogeographic deployment of the group have been widely discussed (e.g., Simpson, 1953; Hoffstetter, 1972; Lillegraven, 1974; Marshall, 1980, and references therein).

    There are nearly 80 genera of...

  17. CHAPTER 13 Eutherians
    (pp. 463-516)

    Eutheria are the most successful group of mammals and are of special interest in that they have dominated Tertiary mammal faunas of all major continents except Australia and South America. Eutherians are a clade consisting of all extant placentals plus all extinct mammals that are more closely related to extant placentals (such as humans) than to extant marsupials (such as kangaroos). The extant placentals are a subgroup of the Eutheria. Placentals have some 18 extant orders, comprise the vast majority of about 4,600 modern living mammal species (see chapter 1), and many more fossil representatives have been described.

    Within the...

  18. CHAPTER 14 Gondwanatherians
    (pp. 517-519)

    Gondwanatheria are an enigmatic group of Late Cretaceous and early Paleocene mammals from Gondwana landmasses (figures 14.1, 14.2). The two South American gondwanatherian genera, characterized by hypsodont molars and very thick enamel (the Late Cretaceous Gondwanatherium and the early Paleocene Sudamerica) were initially assigned to Edentata (e.g., Scillato-Yané and Pascual, 1984, 1985; Bonaparte, 1986a,b, 1990). Bonaparte (1986a) described m2 of a brachyodont Late Cretaceous taxon, Ferugliotherium, which he assigned to Multituberculata. Mones (1987) proposed an edentate order Gondwanatheria for Gondwanatherium and Sudamerica, but Krause and Bonaparte (1990) erected suborder Gondwanatheria within Multituberculata, to include hypsodont Sudamericidae (Sudamerica and Gondwanatherium) and...

  19. CHAPTER 15 Interrelationships of Mesozoic Mammals
    (pp. 520-538)

    Phylogenetic relationships are the foundation for understanding the diversification of Mesozoic mammals. A phylogeny with extensive sampling of taxa and characters is absolutely crucial for establishing the framework in which to clarify the taxic evolution of Mesozoic mammals. Mesozoic mammals also underwent great anatomical evolution in dentition, skull, and skeleton, as best reflected by the vast differences between the basal taxa from the Late Triassic or Early Jurassic and the more derived taxa of the Late Cretaceous. The most basic approach to the understanding of the Mesozoic mammalian evolution is to map the pattern of anatomical evolution within a well-supported...

    (pp. 539-556)
    (pp. 557-606)
    (pp. 607-608)
    (pp. 609-610)
  24. INDEX
    (pp. 611-630)