The Origin and Evolution of Mammals - Moodle

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z (a) (c) a.pt.m. M B PO P P SQ P M p.add.m. a.keel PO apo. PO SQ SQ ext.add.m. (d) EVOLUTION OF MAMMALIAN BIOLOGY 91 M P PO temp. fen B M SQ temp. fen. apo. (b) apo. p.pt.m. p.add.m. p.pt.m. Figure 4.2 Origin and functioning of the pelycosaur-grade jaw musculature. (a) Dorsal view, coronal section and lateral view of the posterior region of an ancestral amniote skull based on Westlothiana. (b) The same for the basal pelycosaur Eothyris. (c) Lateral view of a eupelycosaur skull with the lower temporal bar cut away (top). The same to show the deeper musculature (middle). Orientation of force of adductor mandibuli muscle (M). (d) Lateral and medial views of lower jaw of the sphenacodontine Dimetrodon. Orientation of force of adductor mandibuli muscle (bottom) a.keel, angular keel; apo, aponeurotic sheet; a.pt.m, anterior pterygoideus muscle; ext.add.m, external adductor muscle; M, muscle; P.parietal; PO, postorbital; p.add.m, posterior pterygoideus muscle; SQ, squamosal; temp.fen, temporal fenestra; z, zone of weakness.
92 THE ORIGIN AND EVOLUTION OF MAMMALS and the skull table as a whole narrowed. Reduction in cranial width reduced the medially directed component of the adductor mandibuli, and so increased the net bite force available. Sphenacodontine grade Several important mammal-like innovations are evident in Dimetrodon and the other sphenacodontines. To start with, the dentition had become differentiated to some extent. The anterior, incisor teeth are large and round in cross-section for grasping and possibly ripping up prey. They are followed by an enlarged canine in both upper and lower jaws for an initial disabling bite. Behind these are the smaller postcanines, laterally compressed, sharp and slightly recurved, which would have aided in retaining the still struggling prey of these top-carnivore animals. The morphology and functioning of the jaw musculature of eupelycosaurs (Fig. 4.2(c)) has been analysed in most detail by Barghusen (1973). By analogy with modern primitive amniotes, he assumed that the main jaw-closing muscle, the adductor mandibuli, was divided into separate slips. An external adductor mandibuli originated from the edges of the temporal fenestra and from an aponeurotic sheet of connective tissue covering the fenestra. It inserted into both faces of a vertical aponeurotic sheet attached to the dorsal edge of the jaw. A posterior adductor mandibuli originated from the posterior part of the temporal fenestra and inserted into the hind region of the vertical aponeurosis and adjacent areas of the jaw. Third, an anterior pterygoideus muscle originated from the dorsal surface and posterior edge of the palate, especially from the large lateral pterygoid processes and massive quadrate rami of the pterygoid further back. Insertion of the anterior pterygoideus muscle was low down on the internal surface of the lower jaw. While this basic arrangement no doubt also occurred in more primitive pelycosaurs, important innovations in the form of processes on the lower jaw had evolved in the sphenacodontines, which increased the effectiveness of the muscle action (Fig. 4.3(d)). The dentary and surangular bones had extended dorsally to form a prominent coronoid eminence, the forerunner of the mammalian coronoid process; the angular had expanded ventrally as a large keel-like structure below the level of the jaw articulation. These processes have a dual effect. One is simply to increase the area available for the insertion of muscle. The other is to create lever arms so that the torque generated by the muscles on the jaw increased. In the case of the coronoid eminence, the adductor mandibuli muscle ran from it in a postero-dorsal direction and so had a longer lever arm with respect to the jaw articulation than if it had been attached to the dorsal edge of a jaw without a coronoid eminence. The effect is further increased by the ventral reflection of the articular bone, depressing the position of the jaw hinge. In the case of the enlarged angular keel, here a ventral extension of the lower jaw creates a larger lever arm for a muscle that runs antero-dorsally, which is the orientation of the anterior pterygoideus muscle. A curious morphological effect follows from the combination of the development of the large angular keel with the ventral deflection of the articular region of the jaw. A space exists between the keel laterally and the articular region medially. It is unencumbered below, and part of the pterygoideus muscle may have wrapped around the ventral edge of the main part of the jaw to insert within it. Although not very prominent at this stage, the space is the forerunner of the therapsid condition discussed shortly, where a much larger recess is bounded by the reflected lamina of the angular. Given this arrangement of the major jaw-closing muscles, a further consequence arises, although not of great importance at this stage of evolution. The adductor mandibuli has a posteriorly directed component to its line of action, while the anterior pterygoideus has an anteriorly directed component. These will tend to cancel out, and therefore the tendency for the lower jaw to be pulled either backwards or forwards during the bite is reduced. Not only would this have relieved some of the stress acting at the jaw hinge, but it also endows the potential to control precisely any antero-posterior shifts of the jaw. As it happens, the jaw articulation of Dimetrodon indicates that there were still large stresses, and no possibility of such propalinal movement of the jaw, but this potential property was to be realised in the subsequent evolution of the mammalian jaw mechanism. The sphenacodontian jaw articulation is complex. There are two quadrate condyles in the form of elongated cylinders. The outer one is at a higher
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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
Page 52 and 53: (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 104 and 105: (b) a.pt.m. temp.m. a.pt.m. temp.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
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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
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
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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
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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