The Origin and Evolution of Mammals - Moodle

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pubis is excluded from the acetabulum. Krebs (1991) believed that Henkelotherium was adapted for an arboreal existence, as indicated by the long, flexible tail, the relative length of the penultimate phalanges, and the recurved claws. The dryolestidans were abundant and diverse during the Upper Jurassic and Early Cretaceous of Europe and North America. More unexpectedly, they underwent a considerable radiation into several indigenous families during the South American Late Cretaceous (Fig. 5.15(d)), where they form the dominant part of the mammalian fauna of the Campanian-aged Los Alamitos Formation of Patagonia (Bonaparte 1990, 1994). One of the earliest ‘eupantotheres’, and also the first to be discovered is Amphitherium, from the Middle Jurassic Stonesfield slate of Oxfordshire (Fig. 5.16(d)). As yet it is only known from lower jaws and teeth. What the lower molar teeth show is a relatively large protoconid and smaller metaconid and paraconid cusps, forming a roughly equilateral triangle. The talonid is more developed than in dryolestidans, to the extent of bearing a distinct cusp and extending backwards to overlap the next molar behind. Vincelestes (Fig. 5.16(a)) is known from several skulls and postcranial remains from the Early Cretaceous of Argentina (Hopson and Rougier 1993). It was a relatively large form, with a short, robustly built skull about 7 cm long. The side wall of the braincase is composed of more or less equal sized anterior lamina of the petrosal and alisphenoid, which more closely resembles the condition in the basal mammal Morganucodon than the tribosphenidans. No description of the postcranial skeleton has yet been published (Rougier 1993). The dentition is unusual, with reduction of the dental formula to I4/1: C1/1: PM2/2: M3/3. The upper canine is huge, the first and last postcanines small. The lower molars have low cusps and a small talonid with only a single cusp. The upper molars are a curious shape, being very wide laterally, and narrow medially. The phylogenetic position of Vincelestes is not certain because of the specialisation of its dentition, and the lack of cranial material in most other ‘eupantotheres’ for comparison. The dentition of the Upper Jurassic Peramus (Fig. 5.16(b) and (d)) is very well known, and is important as the ‘eupantothere’ stage whose teeth are most similar to those of the Tribosphenida (Clemens and Mills 1971). There are eight postcanine teeth, but whether four or five of these should be regarded as premolars is debated, with a growing consensus that the primitive number of premolars is actually five (Novacek 1986b; Martin 2002). The lower molars have a talonid that bears two cusps, the hypoconid and hypoconulid, connected by an oblique crest. In view of developments to come, the talonid is described as incipiently basined. The upper molars are triangular and although no protocone has evolved, there is a narrow cingulum on the lingual side of the crown that is the incipient homologue of the protocone. The functional effect of these changes was to enhance the shearing action between the hinder part of the upper tooth and the talonid of the lower tooth, as analysed by Crompton (1971). Tribosphenida THE MESOZOIC MAMMALS 167 Aegialodontidae If the discovery of such an oddity as Shuotherium illustrates the unexpectedness of Mesozoic mammal research, then the discovery of a single, worn, and incomplete molar tooth referred to as Aegialodon illustrates the rewards of patience (Kermack et al. 1965). It emerged from a very large volume of the Early Cretaceous Wealden deposits of Cliff End in Sussex, and its importance lies in the small, but distinctly basined talonid on the back of the tooth. All the advanced holotherian mammals, including the modern marsupials and placentals as well as several extinct Mesozoic taxa possess a new large cusp on the upper molar teeth called the protocone, which occluded with an enlarged talonid on the corresponding lower molar. The talonid is described as basined because crests on all sides enclose it. This new arrangement adds a crushing action to the largely shearing action of more primitive therian teeth such as those of Amphitherium and Peramus, in which the smaller talonid is still open on the lingual side. Although no upper molar of Aegialodon is yet known, a protocone must have been present, for in no other way could the pattern of wear facets on the talonid be explained (Crompton 1971). A couple of decades later, Dashzeveg and Kielan-Jaworowska (1984) described a very similar form from the Early
168 THE ORIGIN AND EVOLUTION OF MAMMALS (d) (a) Vincelestes (b) Peramus Amphitherium Peramus Kielantherium (c) Kielantherium Figure 5.16 (a) Lateral view of the skull of Vincelestes neuqueniams. Length approx. 7.5 cm (Hopson and Rougier 1993). (b) Occlusal view of the upper and lower postcanine dentition of Peramus in occlusion (Clemens and Mills 1971). (c) Labial view of lower jaw with four molars of Kielantherium gobiensis. Length illustrated approx. 0.7 cm (Kielan-Jaworowska and Dashzeveg 1984). (d) Stages in the evolution of lower molars illustrated by a lower molar of Amphitherium, upper and lower molars of Peramus, and a lower molar of Kielantherium (Kemp 1982). (e) Simplified views of a fully evolved tribosphenid upper and lower molars, separated, and at the start and completion of occlusion (Pough et al. 2001). (e)
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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
Page 128 and 129: (a) (c) (d) PMX (f) V n.turb mx.tur
Page 130 and 131: ol.b (a) (b) cer.hem gorgonopsian t
Page 132 and 133: (a) (b) (i) (ii) (iii) (iv) (v) a g
Page 134 and 135: cold stress, the part that usually
Page 136 and 137: conducted the experiment of wrappin
Page 138 and 139: mammals themselves that the enlarge
Page 140 and 141: elevation of maximum aerobic activi
Page 142 and 143: a mammal. The difficulty with all s
Page 144 and 145: collection, ingestion, and assimila
Page 146 and 147: were edaphosaurid and caseid pelyco
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
Page 174 and 175: (a) 1 (b) (d) me (c) me.d 3 styl st
Page 176 and 177: (a) (c) Henkelotherium Crusafontia
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 186 and 187: Minimal divergence of tribosphenida
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
Page 196 and 197: of feasibility that a taxon of endo
Page 198 and 199: mammals, by creating environmental
Page 200 and 201: the 11 species of marsupial, of whi
Page 202 and 203: (d) (a) pa A Dasyuromorphia B C pr
Page 204 and 205: earing two huge claws on digits thr
Page 206 and 207: that contains the independent ances
Page 208 and 209: (b) (d) (a) Glasbius Alphadon (c) D
Page 210 and 211: elieved to be Late Cretaceous in ag
Page 212 and 213: (Fig. 6.5(c)). The dentition exhibi
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
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fossil mammals, which might help cl
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30 40 50 60 Figure 6.13 Southern Go
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the Diprotodontia also included gen
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1. Placentalia 2. Edentata 3. Epith
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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
Page 306 and 307:
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
Page 318 and 319:
cladogenesis in dasyurid marsupials
Page 320 and 321:
(eds) Evolution of Tertiary mammals
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McKenna, M.C. and Bell, S.K. 1997.
Page 324 and 325:
(ed) The phylogeny and classificati
Page 326 and 327:
Ray, S. 2000.Endothiodont dicynodon
Page 328 and 329:
Rubidge, B.S., Kitching, J.W., and
Page 330 and 331:
Simpson, G.G. 1970. The Argyrolagid
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Thewissen, J.G.M. 1990. Evolution o
Page 334 and 335:
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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The Origin and Evolution of Mammals - Moodle

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