The Origin and Evolution of Mammals - Moodle

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(b) a.pt.m. temp.m. a.pt.m. temp.m. z.ang.m z.ang.m level in the skull than the lower. They correspond to two equally elongated glenoid fossae of the articular bone. Thus the jaw hinge was strongly built, and restricted movements to a simple orthal opening (a) r Q ART Q m palate Skull roof occiput m EVOLUTION OF MAMMALIAN BIOLOGY 93 temp.m. a.pt.m. r a.pt.m. temp.m. refl.lam. Figure 4.3 Basal therapsid jaw musculature and function. (a) Lateral view of the skull and main jaw muscles of a basal therapsid. (b) The jaw musculature of a therocephalian, based on Therioognathus in lateral view, dorsal view, and a coronal section throughy the zygomatic arch and reflected lamina of the angular (c). The streptostylic action of the therocephalian quadrate: top left, dorsal view of the paired lower jaws showing direction of net muscle force (m) and jaw hinge reaction (r); top right and bottom left, the effect of attempting to open the jaws without allowing quadrate movement; bottom right, the rotation of the quadrate as seen from behind that enables the jaws to open. (Kemp 1972a). a.pt.m, anterior pterygoideus muscle; ART, articular; Q, quadrate; refl.lam, reflected lamina of the angular; temp.m, temporalis muscle; z.ang.m, zygomatico-angularis muscle. and closing of the jaw. It was also designed to resist the tendency for the lower jaw to be pulled inwards towards the midline of the skull by the medially directed net component of the muscle force. (c)
94 THE ORIGIN AND EVOLUTION OF MAMMALS Biarmosuchian grade The next stage is the primitive therapsid, or biarmosuchian grade (Fig. 3.8(a) and 4.3(a)). Relatively little innovation had occurred, but rather an exaggeration of the novelties that had evolved by the sphenacodontine-grade condition. The principle of well-developed incisors, large canines, but lessprominent postcanines was retained, but with even greater distinction between them. The canines were relatively enormous and must have been used in a kinetic fashion in which the lower jaw was accelerated from a widely open position and the kinetic energy so generated was dissipated by the teeth sinking into the prey. The reason for thinking this, apart from the size of the canines, is that the jaw adductor musculature still acted at the posterior end of the jaw, so no great static force could have been generated between teeth situated towards the front of the jaw. The incisors, in addition to being well developed, were probably capable of interdigitating, lowers between uppers, which increased the effectiveness of their biting action. The overall mass of the adductor musculature had certainly increased considerably, as indicated by the increased size of the temporal fenestra. It extends further dorsally, ventrally, and posteriorly than in the sphenacodontine stage, thereby providing a larger area of connective sheet over it, and bony edging around it for the attachment of muscle. There is still no development of a discrete coronoid process of the dentary rising above the dorsal margin of the jaw, although the coronoid eminence is prominent. The most striking change in the lower jaw was the evolution of a full-sized reflected lamina of the angular. Instead of being merely the keel of that bone separated by a notch from the depressed articular region of the jaw as in the sphenacodontines, it has become a very large, thin sheet enclosing laterally a deep, narrow space between itself and the main body of the jaw. The exact function of this prominent structure in basal therapsids has never been fully agreed upon. Despite a number of earlier suggestions that it housed a gland, or an air-filled diverticulum associated with hearing, there is little doubt now that its primary function was for muscle insertion. In Biarmosuchus (Fig. 3.8(a)), Ivakhnenko’s (1999) reconstruction indicates a pattern of ridges on the external surface of the lamina indicative of strengthening against muscle-generated forces. The most plausible general explanation for the form of the reflected lamina is that it served as the insertion site for a complex set of muscles running in a variety of different directions. At the biarmosuchian grade, this may have included tongue and hyoid musculature inserted on the lower part of the lamina, and jaw-opening musculature running from the posterior region backwards towards the shoulder girdle region. In the more advanced carnivorous groups, gorgonopsians, and therocephalians, the strengthening ridges are more strongly developed, although in quite different patterns respectively. Certainly in gorgonopsians and possibly in therocephalians, there is evidence for an invasion of part of the reflected lamina by adductor mandibuli musculature. However, this could not have been true of biarmosuchians because their zygomatic arch was not expanded laterally to create room for the attachment of such a muscle. The jaw articulation of Biarmosuchus is a simple roller and groove system, restricting the jaw to strictly orthal movements. Thus, the biting mechanism at this stage was little more sophisticated, although more powerful than in pelycosaurs, with a disabling bite delivered by the canines, a tearing action using the incisors, and a finer tearing, or food retention by the modest-sized postcanines. Therocephalian grade The next definable stage is the therocephalian grade (Fig. 4.3(b)), in which the principal innovation is enlargement of the temporal fenestra by extreme medial extension. This has occurred to such an extent that the intertemporal region of the skull roof is reduced to a narrow girder, the sagittal crest. The midline of the crest tends to be sharp and the sides face dorso-laterally, providing an area for the origin of the innermost part of the adductor mandibuli musculature. This area of muscle attachment continues smoothly round on to the front face of the occiput, while the almost horizontal temporal fenestra, covered by its connective tissue sheet, gives further origin for the muscle. By this stage, a large part of the adductor musculature is distinguishable as a medial component, namely a true temporalis muscle. A coronoid process of the dentary had evolved, as a postero-dorsal extension of
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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
Page 54 and 55: mandibulae musculature. This, as in
Page 56 and 57: To date the postcranial skeleton of
Page 58 and 59: ecognised four subgroups, based mai
Page 60 and 61: the presence of a deep, longitudina
Page 62 and 63: collected from the Lystrosaurus Ass
Page 64 and 65: (a) (d) (c) (b) Leontocephalus V PA
Page 66 and 67: (a) (c) Lycosuchus Oliveria (d) EVO
Page 68 and 69: separate families. Lycosuchidae (Fi
Page 70 and 71: consist of a large labial cusp and
Page 72 and 73: Procynosuchus (d) Procynosuchus (a)
Page 74 and 75: They constitute the monophyletic gr
Page 76 and 77: Although there is no mammal-like co
Page 78 and 79: Cynognathidae Cynognathus (Fig. 3.2
Page 80 and 81: (e) (f) Figure 3.22 (continued). Ma
Page 82 and 83: (c) (d) (a) (b) Kayentatherium EVOL
Page 84 and 85: Pachygenelus (e) (a) (c) Therioherp
Page 86 and 87: palatal, and orbitosphenoid bones,
Page 88 and 89: Wible and Hopson 1993). The interor
Page 90 and 91: published a cladogram based on rece
Page 92 and 93: 310-320 Ma. By this time, the great
Page 94 and 95: are forms such as Casea itself, var
Page 96 and 97: lakes and swamps in the low-lying l
Page 98 and 99: urrowing and subsisting on a diet o
Page 100 and 101: Eothyris Haptodus sphenacodontine B
Page 102 and 103: z (a) (c) a.pt.m. M B PO P P SQ P M
Page 106 and 107: the dentary bone above the level of
Page 108 and 109: the therocephalian grade was not on
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
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postcranial skeleton, and Graybeal
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side of the head can be in action a
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the lower molars is relatively high
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morganucodontan teeth. However, des
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adjacent lower molars. A small exte
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(a) (b) (d) P4 P4 Plagiaulax P4 Pau
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American Morrison Formation genus C
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a self-sharpening property. As the
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near parasagittal gait (Fig. 5.11(e
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pass through the birth canal. Relat
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(a) 1 (b) (d) me (c) me.d 3 styl st
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(a) (c) Henkelotherium Crusafontia
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pubis is excluded from the acetabul
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Cretaceous, (Aptian or Albian) of M
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eautifully preserved placentals fro
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subsequent specimens revealed that
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Minimal divergence of tribosphenida
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(c) (a) M 1 M 1 M 2 Steropodon M 2
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(b) (a) (c) pa.d pr.d me.d Ambondro
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crown-group therians) is accepted b
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form of the tooth, must reflect sub
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of feasibility that a taxon of endo
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mammals, by creating environmental
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the 11 species of marsupial, of whi
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(d) (a) pa A Dasyuromorphia B C pr
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earing two huge claws on digits thr
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that contains the independent ances
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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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