The Origin and Evolution of Mammals - Moodle

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the lower molars is relatively higher (Fig. 5.3(e)). The wear facets on the teeth indicate that there was a radical difference in the way in which occlusion occurred. Those on the lower teeth are almost vertical, but those on the upper tooth almost horizontal. This means that as a lower tooth worked against an opposing upper, the lower jaw must have rotated about its long axis to a much greater extent than in Morganucodon, causing the outer surface of the lower tooth to face almost upwards as it moved in a medial direction. The morphology of the lower jaw was modified in several ways to accommodate this rotation. First, the symphysis was mobile and almost horizontally orientated to permit a degree of differential movement between the paired jaw rami. Second, the ventral edge of the dentary is complex, with a process referred to by Jenkins et al. (1983) as a pseudoangular process lying well in front of the jaw hinge. There is also a flange developed below the jaw hinge, which may be equivalent to the true angular process of later mammals. These modifications indicate an elaboration of the masseter musculature in order to exaggerate the tendency that muscle already has to rotate the lower part of the jaw laterally. Docodonta Docodontans are characterised by molar teeth whose crowns have expanded to form complex occluding surfaces (Fig. 5.5(c)). Indeed, they are comparable to the tribosphenic teeth of the modern mammal groups, which achieved similar functional ends by entirely separate means. Docodontans are believed to occur only in Jurassic sediments, the earliest from the Middle Jurassic of the Isle of Skye (Waldman and Savage 1972), and the latest from several Upper Jurassic localities of North America and Europe. Pascual et al. (2000) described a jaw fragment bearing three teeth as a latest Cretaceous docodontan from South America. Named Reigitherium, it would indicate a remarkably long Gondwanan radiation of the group in isolation of the northern continents. However, the pattern of cusps of its very worn teeth is quite different from that of other docodontans, and therefore its inclusion in the group is regarded as very dubious by Kielan-Jaworowska et al. (2004). As with most THE MESOZOIC MAMMALS 147 Mesozoic mammal groups, docodontans were until relatively recently known only from teeth and jaw fragments. The discovery by Walter Kühne of a largely complete specimen of Haldanodon, from the Guimarota lignite mine in Portugal (Henkel and Krusat 1980) was actually the first discovery of any Upper Jurassic mammalian skeleton. Its postcranial bones have not yet been fully described, but Lillegraven and Krusat (1991) have given a very detailed account of the skull (Fig. 5.5(a) and (b)). The molar teeth of docodontans are expanded across the jaw to increase the area of occlusion between the uppers and the lowers. The result is that there is a crushing basin between the anterior lingual parts of the molars that worked analogously to the protocone-talonid system of tribosphenic teeth described later. A comparison of the dentition of Morganucodon, the primitive docodontan Haldanodon, and the advanced, Upper Jurassic Docodon (Fig. 5.5(d)) illustrates how docodontan teeth may have evolved from a hypothetical primitive condition (Crompton and Jenkins 1968). What in effect occurred was that the upper molars evolved a lingual extension that acted against the inner part of the crown of the lower molars. Instead of occlusion and therefore shearing being restricted to the sides of the main cusps, now the whole of the crown was involved. Exactly what diet this was adapted for can only be guessed at. Kron (1979) speculated that it involved a greater degree of simple crushing and grinding, associated perhaps with an omnivorous or frugivorous diet. This suggests that docodontans were one of the several superficially rodent analogues of the Mesozoic, incorporating a significant percentage of high-energy plant material into their hitherto largely insectivorous food. The limb bones of Haldanodon are stout and apparently horizontally oriented, which led Krusat (1991) to suggest that the animal was adapted for burrowing. Kielan-Jaworowska et al. (2004) proposed an alternative interpretation, that it was semiaquatic, living in a swampy environment that is preserved as the Guimarota Lignite mine. Views about the phylogenetic relationships of docodontans have shifted widely over the years. At one time the specialised, complex molar teeth were considered homologous with the triangulated molars of therians, and at another they were compared to
(c) (d) ant. (a) (b) ling. e Haldanodon b b E E B B a h? h? Docodon C A c d g Morganucodon a A x micc d b D D g E Upper teeth lower teeth Haldanodon b b h a D g g d g Haldanodon Docodon h micc h h h Figure 5.5 Docodontans. (a) Haldanodon expectatus skull in dorsal, ventral, and lateral views. Skull length approx. 3.5 cm (Lillegraven and Krusat 1991) and Lower jaw in lateral view (Krusat 1980). (b) Upper molars of Haldanodon expectatus in buccal view. Lower molar in lingual view; Upper molars in occlusal view. Lower molar in occlusal view (Krusat 1980). (c) Occlusal view of complete lower and upper postcranial dentition of Docodon. Approx. length of tooth rows 1.6 cm (Jenkins 1969). (d) Side and occlusal views of a hypothetical transition series from a Morganucodon-like ancestor through a primitive docodontan such as Haldanodon to an advanced form such as Docodon. Shaded areas are wear facets (Kron 1979, after Hopson and Crompton 1969). A E micc C h picc
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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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Page 110 and 111: A balance was also achieved in the
Page 112 and 113: Locomotion Ancestral amniote grade
Page 114 and 115: screw-shaped: the front part faces
Page 116 and 117: For the recovery phase, the relativ
Page 118 and 119: SC PRC p.i.f.i tr.min (c) dp.cr ect
Page 120 and 121: the therocephalian pelvis and hindl
Page 122 and 123: spc s.sp s.sp SC PRC (d) delt T AST
Page 124 and 125: no significant novelties to what ha
Page 126 and 127: (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 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 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 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
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(b) (d) (a) Glasbius Alphadon (c) D
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elieved to be Late Cretaceous in ag
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(Fig. 6.5(c)). The dentition exhibi
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(d) Figure 6.6 (continued). Thylaco
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(a) (c) Caroloameghina and Procarol
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(a) (e) (d) Proargyrolagus Groeberi
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(a) (b) Djarthia Thylacotinga (c) (
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LIVING AND FOSSIL MARSUPIALS 211 M
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Extinct Notoryctemorphia At present
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(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
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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
Page 328 and 329:
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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The Origin and Evolution of Mammals - Moodle

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