Essay, Pages 29 (7237 words)
INVESTIGATIONS INTO THE EVOLUTION OF AUSTRALIAN MAMMALS WITH A FOCUS ON MONOTREMATA
This thesis began as an investigation into evolution of the platypus family (Ornithorhynchidae, Monotremata), now known from both Australia and South America.
The thesis broadened its scope with inclusion of non-ornithorhynchid Mesozoic monotremes from Lightning Ridge, NSW. This change in direction brought an unexpected result: a fossil mammal from Lightning Ridge investigated for this thesis (presumed to be monotreme: Flannery et al. , 1995) appears to be a new and unique type of mammal.
Specimens were procured through Queensland Museum (Riversleigh material); Australian Museum (Lightning Ridge material); and Museum of Victoria and the South Australian Museum (fossil ornithorhynchids).
Specimens were examined under a light microscope and scanning electron microscope; specimens were photographed using light photography and a scanning electron microscope; and illustrations and reconstructions were done with a camera lucida microscope attachment and photographic references. Parsimony analysis utilised the computer programs PAUP and MacClade.
Major conclusions: 1) analysis and reconstruction of the skull of the Miocene platypus Obdurodon dicksoni suggest this robust, large-billed platypus was a derived northern offshoot off the main line of ornithorhynchid evolution; 2) the well-preserved skull of Obdurodon dicksoni shows aspects of soft anatomy previously unknown for fossil ornithorhynchids; 3) two upper molars from Mammalon Hill (Etadunna Formation, late Oligocene, central Australia) represent a third species of Obdurodon; 4) the South American ornithorhynchid Monotrematum sudamericanum rom the Paleocene of Argentina is very close in form to the Oligocene-Miocene Obdurodon species from Australia and should be considered congeneric; 5) a revised diagnosis of the lower jaw of the Early Cretaceous monotreme Steropodon galmani includes the presence of two previously undescribed archaic features: the probable presence of postdentary bones and a meckelian groove; 6) morphological evidence is presented supporting a separate family Steropodontidae; and 7) analysis of new fossil material for Kollikodon ritchiei suggests that this taxon is not a monotreme mammal as originally identified but is a basal mammal with close relationships to allotherian mammals (Morganucodonta; Haramiyida).
Kollikodon is provisionally placed as basal allotherian mammal (Allotheria sensu Butler 2000) and is unique at the ordinal level, being neither haramiyid nor multituberculate. A new allotherian order – Kollikodonta – is proposed. i ORIGINALITY STATEMENT I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged. ’
Anne Marie Musser 31 August 2005 ii TABLE OF CONTENTS Abstract Originality Statement Table of Contents List of Figures List of Tables Acknowledgments i ii iii viii x xi Introduction to the thesis Mammalian evolution in the southern hemisphere Australia’s role: a key player General aims and approach of this thesis Chapter aims and results References 1 2 3 4 5 7 CHAPTER 1: A review of the monotreme fossil record and comparison of palaeontological and molecular data. Abstract Introduction Early mammalian evolution Mesozoic mammals from the southern hemisphere Mesozoic monotremes Cainozoic monotremes The relationship between platypus and echidnas ‘Molecules vs. orphology’: consensus or disagreement? Prototherian-therian dichotomy The Marsupionta hypothesis 14 16 16 17 20 21 22 23 24 24 25 iii A trichotomy Future directions Summary Acknowledgements References 27 28 28 29 29 CHAPTER 2: Furry egg-layers: monotreme relationships and radiations Introduction Living monotremes Echidnas Monotreme morphology Skull structure Postcranial skeleton Soft anatomy and physiology Fossil monotremes Cretaceous forms Ornithorhynchids Fossil tachyglossids Biogeography Monotreme relationships Relationships within Monotremata Relationships with other mammals Gondwanan radiation Evolutionary trends Summary Acknowledgements References 39 3 35 36 37 41 44 46 48 48 52 58 63 65 65 66 67 67 68 68 68 74 CHAPTER 3: New information about the skull and dentary of the Miocene platypus Obdurodon dicksoni and a discussion of ornithorhynchid relationships Introduction Materials and methods 76 77 iv Referred specimens Abbreviations Results Dorsal view Ventral view Lateral view Foramina Discussion of the differences in cranial morphology separating Ob. dicksoni from Or. anatinus Development of the bill in ornithorhynchids Comparisons involving the crania and dentaries Dental evolution in ornithorhynchids Relationships within Monotremata Relationships within Ornithorhynchidae Addendum References 7 77 77 79 81 82 83 87 88 89 90 90 90 CHAPTER 4: Evolution, biogeography and palaeoecology of the Ornithorhynchidae Abstract Fossils and evolutionary relationships Morphology Dental morphology Cranial morphology Postcranial morphology Biogeography, distribution and palaeoecology Factors limiting distribution of ornithorhynchids A conservation message Acknowledgements References CHAPTER 5: Kollikodon ritchiei: Description, relationships and reassessment of affinities 93 96 96 99 100 100 102 103 107 107 108 108 112 v Abstract Introduction Geological and palaeontological setting Opalisation: processes, timing and preservation of fossils Associated flora and fauna
Materials and methods Description Maxilla 122 Palatine Lower jaw Upper dentition Lower dentition Occlusion and dental function 139 Comparisons and discussion Tritylodontoidea Morganucodonta Docodonta Haramiyida Multituberculata Monotremata Other Gondwanan Mesozoic mammals Phylogenetic analysis Data sets and character coding Results General discussion Summary of morphology and function Relationship hypotheses A model for derivation of molar form 181 114 115 115 118 119 121 122 126 128 132 137 140 140 145 148 151 153 157 159 160 160 167 169 167 175 vi ‘Prototheria’ revisited Conclusions Taxonomic relationships Future directions Acknowledgements Literature cited Appendices 183 184 186 187 187 188 206 Thesis Conclusions References Appendices 228 240 -1- vii LIST OF FIGURES CHAPTER 1 Figure 1: The geological timescale and the monotreme fossil record 19 CHAPTER 2
Figure 1: The eastern New Guinea long-beaked echidna Zaglossus bartoni Figure 2: The skull and dentary of the living platypus Ornithorhynchus anatinus Figure 3: Skull and dentary of the Short-beaked Echidna Tachyglossus aculeatus Figure 4: The skeleton of the Short-beaked Echidna Tachyglossus aculeatus Figure 5: Shoulder girdle of the Short-beaked Echidna Tachyglossus aculeatus Figure 6: Steropodon galmani: right dentary fragment with M/1-M/3 in place and an alveolus for the last premolar (anterior is to the right) Figure 7: Kollikodon ritchiei, right maxillary fragment and right dentary fragment Figure 8: Teinolophos trusleri: comparison between the penultimate molar of T. rusleri and the M/2 of S. galmani Figure 9: Molar teeth of Steropodon galmani and Ornithorhynchidae Figure 10: Reconstruction of the skull and dentary of the Miocene platypus Obdurodon dicksoni Figure 11: Skulls of fossil Australian long-beaked echidnas Figure 12: A restoration of the giant Western Australian echidna ‘Zaglossus’ hacketti Figure 13: Map of Australia showing the present and historic distribution of ornithorhynchids plus S. galmani 64 59 61 52 57 51 50 49 46 45 43 38 40 CHAPTER 3 viii Figure 1: Reconstruction of the skull and dentary of Obdurodon dicksoni Figure 2: The skull and dentary of Ornithorhynchus anatinus 78 80 CHAPTER 4
Figure 1: Left lower first molar, holotype of Obdurodon insignis (SAM P18087), illustrating the blade structures of ornithorhynchid molars Figure 2: Comparison of the bill and marginal cartilage between Obdurodon dicksoni and Ornithorhynchus anatinus Figure 3: Map of ornithorhynchid distribution 105 101 97 CHAPTER 5 Figure 1: Position of Lightning Ridge in Early Cretaceous Figure 2: Extent of incursion of Eromanga Sea Figure 3: Occlusal view, maxilla and dentary Figure 4: Lateral view, maxilla and dentary Figure 5: Medial view, maxilla and dentary Figure 6: Posterior view of maxilla Figure 7: Details of palatal region Figure 8: Posterior views of dentaries of K. ritchiei and Steropodon almani Figure 9: SEMs of apical pits on molar cusps Figure 10: Upper and lower teeth in occlusion Figure 11: Cladogram of phylogenetic relationships Figure 12: Hypothesis for derivation of multicuspid teeth in Kollikodon Figure 13: Comparisons between molar teeth of various taxa 116 117 124 125 127 128 129 131 135 139 168 182 179 ix LIST OF TABLES CHAPTER 1 Table 1: A glossary of terms highlighted in boldface in the text, taken from the sources cited 18 CHAPTER 3 Table 1: Abbreviations for figures 1a-c and 2a-c Table 2: Abbreviated table of thegotic terms relevant to dental structures in ornithorhynchids Table 3: Table of synonyms for the major foramina of the skull and dentary in Ornithorhynchus anatinus and Obdurodon dicksoni 84 82 79 CHAPTER 4
Table 1: The present composition of Ornithorhynchidae, with estimated ages, localities and a listing of recovered material Table 2: A list of some of the differences between the crania of Obdurodon dicksoni and Ornithorhynchus anatinus (modified from Archer et al. 1002, 1993a) 101 97 CHAPTER 5 Table 1: Vertebrate fauna of the Griman Creek Formation Table 2: Abbreviations used in Figures 3-10 Table 1, Appendix: Craniomandibular comparisons Table 2, Appendix: Comparisons of dental characters 120 130 203 206 x ACKNOWLEDGMENTS The thesis presented here is my own work, but it was only made possible through the contributions and support of many people and organisations both in Australia and abroad. I extend my sincerest thanks to you all.
Firstly I would like to thank Professor Michael Archer for proposing my doctoral project and for providing fossil material, support and guidance. For much-appreciated financial support I thank the Australian Research Council Small Grants Scheme; the Fulbright Commission; the University of New South Wales; the Linnean Society of New South Wales; the American Museum of Natural History and Richard Tedford; Harvard University and Profs. Farish A. Jenkins, Jr. and Alfred W. Crompton; the Paleobiological Fund; and the Royal Zoological Society of New South Wales. Special thanks go to the Australian Museum (my employer from 1998-2005); this institutional support was crucial to the success of my project and is gratefully acknowledged. For supporting Prof.
Archer’s research at Riversleigh, I thank the Australian Research Council Grant Scheme; the National Estate Grants Scheme (Queensland); the University of New South Wales; the Commonwealth Department of Environment, Sports and Territories; the Queensland National Parks and Wildlife Service; the Commonwealth Heritage Unit; ICI Australia; the Australian Geographic Society; the Queensland Museum; the Australian Museum; the Royal Zoological Society of New South Wales; the Linnean Society of New South Wales; Century Zinc; Mount Isa Mines; Surrey Beatty and Sons; and the Riversleigh Society. For providing space and material resources I thank the University of New South Wales School of Biological, Earth and Environmental Sciences (Palaeontology Laboratory, Prof. Michael Archer) and the Australian Museum (Palaeontology, Robert Jones; and Materials Conservation, David Horton-James and Colin MacGregor).
For preparation of materials and technical support I thank Anna Gillespie and Karen Black (preparators of the Riversleigh material, University of New South Wales); Robert Jones (Collection Manager, Australian Museum); Henk Godthelp (Laboratory Manager, Palaeontology, UNSW); Robyn Murphy xi (UNSW Photography Dept. ); Sue Lindsay (SEM laboratory, Australian Museum); and Carl Bento and Stuart Humphries (Australian Museum Photography Dept). For procurement or loan of specimens I would like to thank Joanne Wilkinson (Queensland Museum); Robert Jones (Australian Museum Palaeontology Dept); Sandy Ingleby (Australian Museum Mammalogy Dept); Wayne Longmore and Lina Frigo (Museum of Victoria Mammalogy Dept); Neville Pledge (South Australian Museum); Tom Rich (Museum of Victoria); Andrew Cody; and Elizabeth Smith.
I am indebted to the following individuals for discussion, comment, technical assistance and, last but not least, friendship and support. Many thanks to Kathy Belov, Karen Black, Patrick Filmer-Sankey, David Goldney, Tom Grant, the late Mervyn Griffiths, Jim Hopson, Farish A. Jenkins Jr. , Zerina Johanson, Robert Jones, Ernie Lundelius, Colin Macgregor, Peter Murray, Stewart Nicol, Tanya Rankin, Tom Rich, Alex Ritchie, Guillermo Rougier, Richard Tedford, and Peter Temple-Smith. Tom Grant took my on my first field trip to net platypuses, which will remain a high point of my life. David Goldney and Tanya Rankin have also generously taken me into the field and shared their knowledge of the ecology and biology of the platypus.
This thesis was examined by three anonymous reviewers who provided suggestions, corrections and additions to the content. Their contributions have considerably improved the thesis and are gratefully acknowledged. Special mention and the sincerest of thanks go to Desui Miao (for suggesting that I work on monotremes as a research topic); Hans-Peter Schultze (for encouraging me in this decision and supporting my nomination for a Fulbright grant); Mike Augee (for an invitation to Australia and for many fine long lunches); and Steve Wroe (for our many discussions and debates and for his unflagging support). Last but certainly not least, I thank my great friend Louise Berg for her limitless help, support and good humour. xii INTRODUCTION TO THE THESIS
This thesis presents a series of investigations into mammalian evolution in Australia from the Mesozoic to the present. The primary focus is on Monotremata (the platypus and echidnas and their extinct relatives); the origins of these unusual and archaic mammals have been obscure since their discovery by the western world over 200 years ago. The thesis also examines the affinities of the recently discovered Early Cretaceous mammal Kollikodon ritchiei, originally described as a monotreme mammal (Flannery et al. , 1995) but whose relationships are reinterpreted here. The thesis is primarily in the form of published papers (Chapters 1-4) but includes an unpublished manuscript (Chapter 5). Additional studies (reported as abstracts) are included in appendices.
The purpose of this thesis was to investigate the available fossil monotreme material or material deemed to be monotreme (much of which is recently discovered and highly significant); to compare these fossils to mammals and near-mammals from both southern and northern continents; and to formulate hypotheses on relationships and origins. The origin of mammals – and of southern hemisphere mammals in particular – is a dynamic and contentious area of palaeontology. Mesozoic mammals from Gondwanan continents have only recently been recovered and figure prominently in current debates on mammalian origins (see below). Methods employed include analysis of fossil material using a binocular microscope and scanning electron microscope; comparison of this material to that of non-mammalian cynodonts and basal mammals (taken from the literature); and parsimony analysis utilising the computer programs PAUP and MacClade.
Specimens were photographed using light photography and a scanning electron microscope; and illustrations and reconstructions were done with a camera lucida microscope attachment and photographic references. Fossil taxa studied (or in some cases restudied) for this thesis include the Early Cretaceous Steropodon galmani, the first Mesozoic mammal from Australia (Archer et al. , 1985; KielanJaworowska et al. , 1987; Musser, in press; Luo et al. , 2001, 2002; abstract, Musser, 2005); the Early Cretaceous Kollikodon ritchiei, described as a monotreme based on the lower jaw and dentition (Flannery et al. , 1995; Chapter 5, this thesis); the first non-Australian monotreme, the Paleocene South American platypus Monotrematum sudamericanum (Pascual et al. , 1992 a, b; abstract, Musser and Archer, 1998; Pascual et al. 2002; Forasiepi and Martinelli, 2003); Tertiary ornithorhynchids in the genus Obdurodon (Woodburne and Tedford, 1975; Archer et al. , 1978, 1992, 1993a; Musser and 1 Archer, 1998; abstract, Musser, 1999); Pleistocene platypus material referable to the living Platypus Ornithorhynchus anatinus (De Vis, 1885; Archer et al. , 1978; Musser, 1998; Musser, in press); Tertiary echidnas in the genus Megalibgwilia (Dun, 1895; Murray, 1978a, b; Griffiths et al. , 1991; Musser, in press); and the living Short-beaked Echidna Tachyglossus aculeatus (Jenkins and Musser, unpub. ; Musser and Jenkins, 1992; Musser, in press). Mammalian evolution in the southern hemisphere Mesozoic mammals from the southern hemisphere are exceedingly rare.
Most of what is known about the earliest mammals has come from evidence found in the northern hemisphere, in part because of more extensive work on northern continents and in part because of lack of exposure of fossil-bearing outcrops of the right age (Triassic-Early Jurassic) on southern continents. Mammals evolved from advanced mammal-like reptiles (cynodonts) near the close of the Triassic and radiated into the earliest types during the first part of the Jurassic (e. g. , Hopson and Crompton, 1969; Clemens et al. , 1979; Crompton and Jenkins, 1979; Miao, 1991; Kielan-Jaworowska, 1992; Cifelli, 2001). The oldest mammals are about 225 million years old (Late Triassic of North America: Lucas and Luo, 1993).
These archaic, non-therian mammals (early mammals not closely related to Theria: marsupials and placentals and their extinct relations) comprised early mammalian faunas, which generally gave way to more advanced types as these evolved. Marsupial and placental mammals (advanced therians) have only been in existence since the Early Cretaceous (e. g. , Ji et al. , 2002; Luo et al. , 2003). Although debated (e. g. , Rich et al. , 1997, 1999a, Woodburne et al. , 2003) the current consensus is that advanced therians evolved on northern continents, replacing older mammal faunas during the latter part of the Mesozoic. In recent years there have been several key discoveries of Mesozoic mammals and nearmammals from the southern hemisphere: Australia (Archer et al. , 1985; Flannery et al. , 1995; Clemens et al. 2003); South America (Bonaparte 1986a, 1986b, 1987, 1990; Bonaparte and Rougier 1987; Kielan-Jaworowska and Bonaparte, 1996; Pascual et al. , 2000; Rauhut et al. , 2002; Rougier et al. , 2000); Madagascar (Krause et al. , 1994, 1997a, b, 1999; Krause and Grine 1996; Flynn et al. , 1999); India (Datta 1981; Yadagiri 1985; Prasad and Sahni 1988; Prasad et al. , 1995; Datta and Das 2001; Rana and Wilson 2003); and Africa (Heinrich 1998, 1999; Sigogneau-Russell et al. , 1998; Krause et al. , 2003). No Mesozoic mammals have yet been found in either Antarctica or New Zealand although they were certainly present in those regions (early Tertiary mammals are now known from Antarctica: e. g. , Woodburne and Zinsmeister, 1982).
Archaic mammals remained on southern continents well past the point at which they disappeared from more northern areas and these relict groups had in many cases become highly 2 specialised (e. g. , Bonaparte, 1990; Heinrich, 1999; Pascual et al. , 2000). Late Cretaceous Gondwanan mammals are overwhelmingly non-therian, non-tribosphenic or pre-tribosphenic (e. g. , Bonaparte, 1990; Pascual et al. , 2000; Krause et al. , 1997a, b). At least one group of Jurassic-Cretaceous Gondwanan mammals with primitive lower jaws developed advanced, therian-like tribosphenic teeth (Ausktribosphenos nyktos and Bishops whitemorei: Rich et al. , 1997, 1999a, 2001a; Ambondro mahabo: Flynn et al. , 1999; and Asfaltomylos patagonicus: Rauhut et al. 2002; Martin and Rauhut, 2005). Although their relationships to other mammals are contested (Rich et al. , 1997, 1999a; Kielan-Jaworowska et al. , 1998; Musser and Archer, 1998; Archer et al. , 1999; Luo et al. , 2001, 2002; Rich et al. , 2002; Woodburne et al. , 2003) these southern tribosphenic mammals (‘Australosphenida’ of Luo et al. , 2001, 2002 [who include monotremes in this group]) have generated great interest in Gondwanan Mesozoic mammals and the part they may have played in mammalian evolution. Australia’s role: a key player Today Australia is home to all three groups of living mammals: monotremes, marsupials and placental mammals.
It is the only continent to have such a fauna, the result of past geographical position, long since obliterated polar dispersal routes, and long periods of isolation during which relict types (monotremes) persisted and emigrants (predominantly marsupials) flourished in the absence of more extreme competition faced on other continents. Monotreme mammals have traditionally been seen by many palaeontologists as sole Australian survivors of the Triassic-Jurassic early radiation of mammals (see Musser, 2003 for a review). The highly specialised living monotremes have undoubtedly diverged in many ways from what must have been a more generalised ancestor (e. g. , Musser, in press) and their origins are a source of great interest as well as debate. The 1985 discovery of Steropodon, described by Archer et al. 1985) as a possible tribosphenic therian mammal because of its therian-like molars, galvanised debate about monotreme origins because this suggested a much more advanced position for monotremes than previously believed. Subsequent studies place monotremes in more basal positions (e. g. , Kielan-Jaworowska et al. , 1987; Rowe, 1988; Wible, 1991; Meng and Wyss, 1995; Luo et al. , 2001, 2002; Pascual et al. , 2002; Rich et al. , 2005) but without consensus about relationships. Prior to the discovery of Steropodon galmani from Lightning Ridge in New South Wales (Archer et al. , 1985) there was no record of any Australian mammal older than the late Oligocene (Rich et al. , 1991).
Australia lacks Late Cretaceous and earliest Tertiary vertebrate sites (aside from some fragmentary remains from the early Late Cretaceous; see below), leaving a ‘black hole’ of over 3 50 million years from the Early Cretaceous (110-115 myo) to the early Eocene (the approximately 55 myo Murgon fossil site in southeast Queensland: Godthelp et al. , 1992). Murgon records the first known Australian marsupials, several of which have ties to South American types (e. g. , Archer et al. , 1993b) and which were descendants of the mainly arboreal South American marsupials that spread across Antarctica to Australia during the latest Cretaceous-earliest Tertiary (e. g. , Case, 1989).
Australian Mesozoic mammals have now been recovered from three Early Cretaceous sites: Lightning Ridge; Flat Rocks, Victoria; and the Toolebuc Formation (abstract, Godthelp, 2005) as well as from the early Late Cretaceous Winton Formation (abstract, Salisbury, 2005). Lightning Ridge deposits are middle Aptian in age (approx. 110 mybp: Burger, 1988) and have produced Steropodon galmani (Archer et al. , 1985); Kollikodon ritchiei (Flannery et al. , 1995); and an edentulous maxilla (Rich et al. , 1989). Several edentulous jaws that appear to be monotreme have also been recovered (Musser, in prep. ). Remarkably, a single tooth has recently been described that may either be that of a traversodont cynodont or dryolestoid mammal (Clemens et al. , 2003).
Flat Rocks is roughly 115 million years of age (the base of the Aptian: Rich et al. , 1997) and has produced a diverse Mesozoic fauna, including the oldest known monotreme (Teinolophos trusleri: Rich et al. , 1999, 2001b, 2005) as well as Ausktribosphenos nyktos and Bishops whitmorei, two new mammals described as archaic placentals and assigned to the newly erected order Ausktribosphenida (Rich et al. , 1997, 1999, 2001a; see above). Tertiary Australian mammals come from several sites, including the late Oligocene central Australian Etadunna Formation and the Oligocene-Miocene Riversleigh World Heritage Fossil Deposits in northwest Queensland.
The first toothed fossil ornithorhynchid (Obdurodon insignis: Woodburne and Tedford, 1975) was recovered from Etadunna Formation sediments. The early Miocene platypus Obdurodon dicksoni (Archer et al. , 1992, 1993; Musser and Archer, 1998) and thylacine Nimbacinus dicksoni (Wroe and Musser, 2001) were both produced from Riversleigh limestones; their exceptional preservation as well as taxonomic importance are testament to the outstanding nature of the material being recovered at this site. General aims and approach of this thesis The original aim of this thesis was an investigation of Tertiary platypus material; it has since grown into a much broader project as new fossil material has come to hand.
In particular, several Mesozoic mammalian specimens from Lightning Ridge, NSW have recently been recovered and added to this study: a maxilla with upper dentition of the bunodont mammal Kollikodon ritchiei Flannery et al. , 1995 and a series of edentulous monotreme jaws (abstract, Musser, 2003a; Musser in 4 prep. ). In addition, the holotype lower jaw of the Early Cretaceous Steropodon galmani has been reexamined, revising the original diagnosis of Archer et al. (1985). Steropodon is compared to the recently discovered Victorian Early Cretaceous monotreme Teinolophos trusleri (abstracts, Musser, 2003, 2005), recently shown to possess a very archaic lower jaw with trough for possible accessory jaw bones (Rich et al. , 2005). This thesis also examines the biogeography, palaeoecology and distributions of monotremes (Musser, 1998).
The aims of these investigations were to 1) describe and identify fossil material provided for the thesis; 2) analyze and assess affinities and intrafamilial relationships of fossil platypuses within Ornithorhynchidae; 3) determine relationships of the Early Cretaceous mammal Kollikodon ritchiei; and 4) put the evolution, palaeoecology and biogeography of these fossil mammals into a regional and global context. Chapter aims and results All thesis chapters except for Chapter 5 have been or are about to be published in peer-reviewed scientific journals or books. Chapter 5 is presented as an unpublished manuscript. Chapter 1 (Musser, 2003) reviews the monotreme fossil record, the literature on monotreme anatomy and palaeontology, and the debates – historical and ongoing – over monotreme relationships. Estimates of divergence times between monotremes and other mammals and relationship hypotheses as determined by molecular studies are compared with the monotreme fossil record.
This paper was published as part of the conference proceedings of a symposium on monotreme biology (a Satellite Symposium of the International Congress of Comparative Physiology and Biochemistry) held at Lemonthyme Lodge, Tasmania in February 2003 (Comparative Biochemistry and Physiology Part A [Molecular and Integrative Physiology], Volume 136A, 2003). Chapter 2 (Musser, in press) is a chapter in a forthcoming book on Australasian vertebrates, Evolution and Biogeography of Australasian Vertebrates, due to be published later this year (2005). It is a comprehensive overview of both extant and extinct monotremes and includes discussion of monotreme anatomy (internal, external and skeletal), physiology, ecology, biogeography, and the fossil record.
Original investigations presented here but otherwise unpublished include comparison of ornithorhynchid dentitions and a preliminary, revised diagnosis of the lower jaw of Steropodon galmani. Chapter 3 (Musser and Archer, 1998) presents a study of the skull of the Miocene platypus Obdurodon dicksoni. This paper was part of a special volume on platypus biology published in Philosophical Transactions of the Royal Society of London, Series B (Volume 353, 1998). An 5 osteological reconstruction of the skull and dentary is described and illustrated along with a description of the cranial and mandibular foramina. Comparisons are made with the skull of the living platypus, Ornithorhynchus anatinus.
This study synonymises the major foramina of the skull and dentary for both Ornithorhynchus and Obdurodon using as a guide the landmark study of the skull of Ornithorhynchus by Zeller (1989a). The phylogenetic importance of features of the skull, dentary and dentition is discussed and possible differences between the diets and lifestyles of Obdurodon and Ornithorhynchus are proposed. Chapter 4 (Musser, 1998) discusses evolutionary trends within the platypus family, putting this into a biogeographical and palaeoecological context. This paper was published as part of a special issue of Australian Mammalogy (Volume 20, Number 2) following the first National Symposium of Platypus Biology held at Charles Sturt University, Bathurst NSW in November, 1996.
Keystone discoveries (Obdurodon dicksoni and the South American platypus Monotrematum sudamericanum) are used to illustrate morphological change as ornithorhynchids evolved from toothed forms to the edentate and highly specialised living platypus Ornithorhynchus anatinus. Chapter 5 (unpublished manuscript) describes new material for the enigmatic Early Cretaceous mammal Kollikodon ritchiei, known initially from a fragmentary lower jaw with bunodont molar teeth and described as a highly specialised monotreme (Flannery et al. , 1995). Flannery et al. (1995) base their identification on perceived similarities between the lower molars of Kollikodon and monotremes. Newly acquired material (a maxillary fragment with four upper molariform teeth and a single premolar) is studied for this thesis and an alternative interpretation of the affinities of Kollikodon is presented.
Results of these investigations are summarised (Thesis Conclusions) and conclusions drawn on the evolutionary trends, relationships, ecology and biology of the taxa studied. Thesis appendices contain 1) additional papers in which I was either author or co-author (Rich et al. , 2005; Wroe and Musser 2001; Musser, 1999; Archer et al. , 1999); and 2) conference abstracts from papers or posters presented at palaeontological meetings. Announcement of the first occurrence of possible postdentary bones in a fossil monotreme, the Early Cretaceous Teinolophos trusleri, is made by in a groundbreaking paper by Rich et al. (2005), a discovery of global importance.
In Wroe and Musser (2001) the well-preserved skull of a comparatively basal marsupial carnivore, the Miocene thylacinid Nimbacinus dicksoni (the only fossil thylacine known from a nearly complete skeleton) is described. A short summary of the monotreme fossil record is presented by Musser (1999) as part of a series of papers on the evolution of the Australian mammal faunas (Archer et al. , 6 1999). Archer et al. (1999) is a jointly authored paper on Australian fossil mammals of uncertain affinities. References ARCHER, M. , PLANE, M. D. & PLEDGE, N. S. , 1978. Additional evidence for interpreting the Miocene Obdurodon insignis Woodburne and Tedford, 1975, to be a fossil platypus (Ornithorhynchidae: Monotremata) and a reconsideration of the status of Ornithorhynchus agilis De Vis, 1885. Australian Zoologist 20, 9-27. ARCHER, M. , FLANNERY, T. F. , RITCHIE, A. MOLNAR, R. E. , 1985. First Mesozoic mammal from Australia – an early Cretaceous monotreme. Nature 318, 363-366. ARCHER, M. , JENKINS, F. A. JR. , HAND, S. J. , MURRAY, P. & GODTHELP, H. , 1992. Description of the skull and non-vestigial dentition of a Miocene platypus (Obdurodon dicksoni n. sp. ) from Riversleigh, Australia, and the problem of monotreme origins. In Platypus and Echidnas, edited by M. L. Augee, pp. 15-27. Sydney: Royal Zoological Society of New South Wales. ARCHER, M. , MURRAY, P. , HAND, S. & GODTHELP, H. , 1993a. Reconsideration of monotreme relationships based on the skull and dentition of the Miocene Obdurodon dicksoni.
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