The Origin and Evolution of Mammals - Moodle

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Minimal divergence of tribosphenidans Bs V H Bm Ap Ab Ce T C S Ca Ma Pa Eo 145 135 125 115 105 95 85 75 65 55 45 Minimal divergence eutherians-metatherians Kielantherium Aegialodon Crown ungulates Aspanlestes Eoungulatum Tribotherium Protungulatum Zalambdalestes Gypsonictops Cimolestes Kennalestes Asioryctes Ukhaatherium Daulestes Montanalestes Murtoilestes Prokennalestes Eomaia Sinodelphys Holoclemensia Deltatheridium Atokatheridium Sulestes Marsasia Kokopellia Asiatherium Albertatherium Anchistodelphys Turgidodon Pediomys Didelphodon famously by Gregory (1947) and more recently on the basis of some molecular evidence. However, there is general agreement now that marsupials and placentals are related as crown-group Theria, to the exclusion of Monotremata. As well as numerous cranial and dental characters, an increasing preponderance of molecular evidence supports this view (Killian et al. 2001). The relationship of monotremes to the Mesozoic mammal groups is considerably less clear, and the development of views about this problem has had Crown marsupials THE MESOZOIC MAMMALS 175 Figure 5.20 Dates of occurrences, and a possible phylogeny of Cretaceous Tribosphenida (Modified from Luo et al. 2003). an extraordinarily chequered history. At one time it was believed by almost everyone that monotremes had a separate origin from pre-mammalian therapsids, implying convergent evolution of their mammalian characters. The discovery of the Late Triassic mammals of South Wales quickly altered that view because similarities were seen between, on the one hand Morganucodon and the monotremes, and on the other Kuehneotherium and the living therians. Yet the dental similarities between the two fossil forms was such that there was no longer any
176 THE ORIGIN AND EVOLUTION OF MAMMALS reason to doubt that they shared a common mammalian ancestor (Hopson and Crompton 1969; Kermack and Kielan-Jaworowska 1971). There were two characters quoted in support of a relationship between Morganucodon and monotremes. The first was an alleged similarity between the molar teeth. In fact, echidnas completely lack teeth and Ornithorhynchus only possesses them as a juvenile, shedding them and replacing them with horny ridges, shortly after emerging from the burrow. These juvenile teeth are three in number and are large, thinly enamelled and have a crown pattern consisting of two or three high, transverse ridges or lophs connecting labial with lingual cusps. They were interpreted as based on a linear arrangement of three cusps, and hence derivable from the ‘non-therian’ molar teeth of a Morganucodon-like ancestor, but specialised by extreme transverse widening. The second supposedly shared character was the structure of the sidewall of the braincase. In living therians this is formed largely from the alisphenoid bone, in monotremes from an anterior lamina of the petrosal bone. In Morganucodon both these bones are present but, as in monotremes, the anterior lamina constitutes the sidewall itself. Thus, relying on these two similarities, an early dichotomy into non-therian and therian mammals was envisaged, with monotremes and therians the respective living members of the two. In due course, however, it was shown that the differences between the two groups in the structure of the sidewall of the braincase were quite trivial. In both cases the bone that forms it is an intramembranous ossification that later in development simply fuses with either the periotic bone behind as in monotremes, or the alisphenoid bone below as in therians. Furthermore, the alleged similarities in tooth structure came to be recognised as far too vague to carry much weight. Compared to this very weak evidence for a monotreme–Morganucodon relationship, there are several characters shared by monotremes and therians that can be demonstrated to be more derived than in Morganucodon (Kemp 1983). These include the loss of contact of postdentary bones to the dentary to form ear ossicles, the fusion of the elements of the first vertebra to form a complete atlas ring and of the cervical ribs to the vertebrae, and the enlargement of the cerebellum. All cladistic analyses now place monotremes closer to living therians than to morganucodontids. Up to this point, the fossil record of monotremes had not proved helpful. Apart from Pleistocene remains, the only fossil known was Obdurodon (Fig. 5.21(a)), a Miocene ornithorhynchid that had retained an adult dentition. Even the beautiful, complete skull found in 1985. (Archer et al. 1992; Musser and Archer 1998) added nothing useful to the debate on monotreme relationships, for the teeth (Fig. 5.21(b)) are very similar to the juvenile teeth of Ornithorhynchus, and equally difficult to compare with those of other taxa. A palaeontological breakthrough came with the description of a fragment of lower jaw bearing three molar teeth that had been found in the opal mine of Lightning Ridge, New South Wales (Archer et al. 1985). Steropodon (Fig. 5.21(c)) dates from the Albian stage of the Early Cretaceous. Its molars have a pattern of cusps that can be identified as equivalent to the three trigonid and three talonid cusps of a tribosphenic lower tooth, although modified in a monotremelike fashion by development of strong transverse ridges (Kielan-Jaworowska et al. 1987; Rich et al. 2001b). Whether the dentition of Steropodon was a modified tribosphenic tooth as such, or evolved from a pre-tribosphenic stage was debatable (Kielan- Jaworowska et al. 1987). At any event, not only was Steropodon the first Australian Mesozoic mammal to be discovered, but also it is one of the best examples of that rare phenomenon of a new fossil intermediate resolving an existing dispute about relationships. Monotremes are highly derived tribosphenidans. A few more monotremes have been discovered. Teinolophos (Fig. 5.21(d)) is also from the Albian of Australia, and the sole specimen to date consists of a single antero-posteriorly compressed molar tooth in a minute partial lower jaw. Rich et al. (2001b) interpreted it as closely related to Steropodon. The first monotreme to be discovered outside Australia is Monotrematum (Fig. 5.21(e)). It is of Palaeocene age and occurs in Patagonia. So far only isolated molar teeth have been found, but these resemble quite closely those of Obdurodon, indicating that it is an ornithorhynchid (Pascual et al. 1992, 2002). To this point in the story of the origin of tribosphenidans, the timing of the appearance in the fossil record of the different degrees of expression
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The Origin and Evolution of Mammals
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The Origin and Evolution of Mammals
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Preface This book arose from twin a
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For Mal /gosia with love and thanks
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Contents 1 Introduction The definit
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CHAPTER 1 Introduction There are ab
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transversely occluding molar teeth
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the Mesozoic mammals, is to do with
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a hierarchy of committees under the
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it means that a 200 Ma igneous rock
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een a more fundamental impact than
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Table 2.3 Classification of marsupi
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(a) (b) (c) humerus radius aquatic
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(a) Westlothiana Limnoscelis PO Wes
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the ankle bones to form an astragal
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(b) (c) (a) Casea rutena Casea broi
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(Fig. 3.2(f)), is actually an ophia
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the first one is enlarged, often to
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Even at their initial appearance in
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(a) Nikkasaurus (b) (d) Reiszia (e)
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Nikkasauridae The family Nikkasauri
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has figured large in discussions of
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(c) Figure 3.9 (continued). Syodon
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a mixture of progressively more spe
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animal with interdigitating, but no
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(e) (a) Anomocephalus Ulemica (b) S
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mandibulae musculature. This, as in
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To date the postcranial skeleton of
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ecognised four subgroups, based mai
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the presence of a deep, longitudina
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collected from the Lystrosaurus Ass
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(a) (d) (c) (b) Leontocephalus V PA
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(a) (c) Lycosuchus Oliveria (d) EVO
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separate families. Lycosuchidae (Fi
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consist of a large labial cusp and
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Procynosuchus (d) Procynosuchus (a)
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They constitute the monophyletic gr
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Although there is no mammal-like co
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Cynognathidae Cynognathus (Fig. 3.2
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(e) (f) Figure 3.22 (continued). Ma
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(c) (d) (a) (b) Kayentatherium EVOL
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Pachygenelus (e) (a) (c) Therioherp
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palatal, and orbitosphenoid bones,
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Wible and Hopson 1993). The interor
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published a cladogram based on rece
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310-320 Ma. By this time, the great
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are forms such as Casea itself, var
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lakes and swamps in the low-lying l
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urrowing and subsisting on a diet o
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Eothyris Haptodus sphenacodontine B
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z (a) (c) a.pt.m. M B PO P P SQ P M
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(b) a.pt.m. temp.m. a.pt.m. temp.m.
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the dentary bone above the level of
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the therocephalian grade was not on
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A balance was also achieved in the
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Locomotion Ancestral amniote grade
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screw-shaped: the front part faces
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For the recovery phase, the relativ
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SC PRC p.i.f.i tr.min (c) dp.cr ect
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the therocephalian pelvis and hindl
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spc s.sp s.sp SC PRC (d) delt T AST
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no significant novelties to what ha
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(a) (c) (e) (g) D D ex. au.m C tym
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(a) (c) (d) PMX (f) V n.turb mx.tur
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ol.b (a) (b) cer.hem gorgonopsian t
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(a) (b) (i) (ii) (iii) (iv) (v) a g
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cold stress, the part that usually
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Page 138 and 139: mammals themselves that the enlarge
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Page 142 and 143: a mammal. The difficulty with all s
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Page 148 and 149: CHAPTER 5 The Mesozoic mammals The
Page 150 and 151: (a) (d) AL condylar foramina are se
Page 152 and 153: evidence to relate the haramiyidans
Page 154 and 155: postcranial skeleton, and Graybeal
Page 156 and 157: side of the head can be in action a
Page 158 and 159: the lower molars is relatively high
Page 160 and 161: morganucodontan teeth. However, des
Page 162 and 163: adjacent lower molars. A small exte
Page 164 and 165: (a) (b) (d) P4 P4 Plagiaulax P4 Pau
Page 166 and 167: American Morrison Formation genus C
Page 168 and 169: a self-sharpening property. As the
Page 170 and 171: near parasagittal gait (Fig. 5.11(e
Page 172 and 173: pass through the birth canal. Relat
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Page 176 and 177: (a) (c) Henkelotherium Crusafontia
Page 178 and 179: pubis is excluded from the acetabul
Page 180 and 181: Cretaceous, (Aptian or Albian) of M
Page 182 and 183: eautifully preserved placentals fro
Page 184 and 185: subsequent specimens revealed that
Page 188 and 189: (c) (a) M 1 M 1 M 2 Steropodon M 2
Page 190 and 191: (b) (a) (c) pa.d pr.d me.d Ambondro
Page 192 and 193: crown-group therians) is accepted b
Page 194 and 195: form of the tooth, must reflect sub
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Page 198 and 199: mammals, by creating environmental
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Page 202 and 203: (d) (a) pa A Dasyuromorphia B C pr
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Page 208 and 209: (b) (d) (a) Glasbius Alphadon (c) D
Page 210 and 211: elieved to be Late Cretaceous in ag
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Page 214 and 215: (d) Figure 6.6 (continued). Thylaco
Page 216 and 217: (a) (c) Caroloameghina and Procarol
Page 218 and 219: (a) (e) (d) Proargyrolagus Groeberi
Page 220 and 221: (a) (b) Djarthia Thylacotinga (c) (
Page 222 and 223: LIVING AND FOSSIL MARSUPIALS 211 M
Page 224 and 225: Extinct Notoryctemorphia At present
Page 226 and 227: (f) (g) Wakaleo Diprotodon optatum
Page 228 and 229: fossil mammals, which might help cl
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effectively absent. However, increa
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Asioryctes (a) (b) (d) Cimolestes p
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and Prokennalestes, although it doe
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(a) Leptictidium Palaeoryctidans we
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(a) Purgatorius (c) are part of the
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(a) (d) (e) (g) Protoungulatum Meso
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(a) (f) (e) Hyopsodus Phenacodus (d
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Titanoides (pantodont) (a) (c) (b)
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(a) (b) (d) Trogosus (tillodont) Es
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Mioclaenus Paulacoutoia (didolodont
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their presence. The five orders may
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Xenungulata. Only two Late Palaeoce
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(a) (b) (d) (c) Oxyaena Patriofelis
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continuously growing, and form a gr
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navicular facet, 19 or more thoraci
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(a) (c) Phosphatherium Numidotheriu
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coexist with other characters that
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The salient feature of Widanelfasia
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1 (a) 1. Perissodactyla 2. Titanoth
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(a) (b) BUNODONTIA or SUIFORMES SUI
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time, which suggests that it was on
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condition. This particular combinat
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etween Primates, Dermoptera (colugo
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have postcranial adaptations for ar
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undoubtedly related at a supraordin
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indisputably to occur prior to the
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The Late Cretaceous mammal record i
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interordinal divergences in the Lat
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diversity on Earth (Janis 1993). Fu
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effect of the surrounding sea. Trop
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was high. It lasted from 5 to 3 Ma
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and thus remain in their preferred
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agreement about exactly when within
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References Abdala, F. Redescription
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Ax, P. 1987. The phylogenetic syste
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Bramble, D. M. 1978. Origin of the
Page 308 and 309:
Colbert, E.H. 1948. The mammal-like
Page 310 and 311:
Duvall, D. 1986. A new question of
Page 312 and 313:
Gow, C.E. 1980. The dentitions of t
Page 314 and 315:
Ivakhnenko, M.F. 1990. The late Pal
Page 316 and 317:
Kemp, T.S. 1988a. A note on the Mes
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cladogenesis in dasyurid marsupials
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(eds) Evolution of Tertiary mammals
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McKenna, M.C. and Bell, S.K. 1997.
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(ed) The phylogeny and classificati
Page 326 and 327:
Ray, S. 2000.Endothiodont dicynodon
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Rubidge, B.S., Kitching, J.W., and
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Simpson, G.G. 1970. The Argyrolagid
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Thewissen, J.G.M. 1990. Evolution o
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Novacek, M.J., and McKenna, M.C. (e
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Index Note: Page numbers in italics
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Equoidea 262 Equus 262 Erethizon 28
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Overkill hypothesis 289, 290 Oxyaen
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Tulerpeton 14, 18 Tylopoda 264 Ukha
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