The Origin and Evolution of Mammals - Moodle

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spc s.sp s.sp SC PRC (d) delt T AST sbc.sc B (a) delt s.sp CL spc acr PRC pect delt PU IL dp.cr ob.f FIB CALC t.ca (f) sbc.sc sc.tric c.br c.tric COR s.ac.but tr.maj tr.int ISC p.i.f.i l.dor IL tr.maj CL R (e) il.fem U p.i.f.i EVOLUTION OF MAMMALIAN BIOLOGY 111 p.i.f.i ob.f (c) ISC PU PU PU p.i.f.e (b) il.fem isc.tro ISC il.fem isc.tro Figure 4.8 Cynodont-grade limb function. (a) Left scapulo-coracoid and humerus of a eucynodont in anterior and lateral views showing orientation and major shoulder musculature, and (inset) section through the scapula blade. (b) Diagram of the shapes of the corresponding glenoid and humerus articulating surfaces. Successive points of the humerus head in contact with the glenoid are x-a, y-b, and z-c as it rolls backwards. (c) Orientation of the forelimb at the start and finish of a stride. (d) Left pelvis and hindlimb of the eucynodont Cynognathus in lateral view. (e) Left pelvis and femur of the traversodontid cynodont Luangwa in side view at the start (upper) and end (lower) of the stride, showing the mammal-like musculature and gait. (f) Left pelvis and femur of the tritylodontid Oligokyphus. acr, acromion process; AST, astragalus, CALC, calcaneum; c.br, coraco-brachialis muscle; CL, clavicle; c.tric. coracoid slip of triceps; delt, deltoideus muscle; dp.cr, deltopectoral crest; FIB, fibula; H, humerus; IL, ilium; il.fem, ilio-femoralis muscle; ISC, ischium; isc.tro, ischio-trochantericus muscle; l.dor, latissimus dorsi muscle; ol.pr, olecranon process; pect, pectoralis muscle; p.i.f.e, pubo-ischio femoralis externus muscle; p.i.f.i, pubo-ischio femoralis internus muscle; PRC, procoracoid; PU, pubis; R, radius; s.ac.but, supra-acetabular buttress; sbc.sc, subcoraco-scapularis muscle; SC, scapula; sc.tric, scapular slip of the triceps muscle; spc, supracoracoideus; s.sp, supraspinatus muscle; T, tibia; tr.int, trochanter internus; t.ca, tuber calcis; tr.maj, trochanter major; U, ulna (Kemp 1982). H a x ol.pr b y z CL c H SC p.i.f.e R U ol.pr
112 THE ORIGIN AND EVOLUTION OF MAMMALS acromion process above and the coracoid bone below leads to the forward-facing internal face of the scapula. The area of origin of the supracoracoideus muscle of primitive therapsids had expanded upwards and forwards through the gap, to spread over this part of the internal face of the scapula, which is the equivalent of the supraspinatus fossa of mammals. A similar eversion of the hind edge of the scapula blade has also occurred, and so the posterior part of the inner scapula blade faces largely posteriorly. This is the area of origin of the retractor muscle, the subcoraco-scapularis. Even though the shoulder joint, and also the humerus, are still primitive in structure, the musculature controlling the limb had increased in size. This is explicable by recalling that the function of the forelimb is to support the front of the animal off the ground; enlargement of both the retractor and protractor muscles would have increased the strength of the support, and also the manoeuvrability of the forelimbs in an animal increasingly able to accelerate and rapidly change direction. In contrast to the primitive nature of the forelimb, the hindlimb of eucynodonts demonstrates the transition to the more or less fully mammalian mode of action, involving loss of the ability to undergo the sprawling gait. The bulbous, inturned head of the femur fits comfortably into the deep, hemispherical acetabulum only when the femur is held in a virtually parasagittal orientation (Fig. 4.8(d)). In this position, the very prominent, mammal-like trochanter major lies on the postero-lateral part of the femoral head, in exactly the right position to accept the insertion of a large ilio-femoralis muscle. To a varying extent in different eucynodont taxa, the ilium has extended further forwards, the pubis been reduced and turned backwards, and the ischium turned more horizontally (Fig. 4.8(e)). These pelvic girdle features are correlated with an increasing development of the gluteal (ilio-femoralis) and psoas–iliacus (puboischio-femoralis internus) musculature as the prime motivators of the locomotory cycle, in the mammalian fashion. Tritylodontid and tritheledontid grade The postcranial skeleton of tritheledontids is as yet insufficiently known to base a reconstructed stage on that group. Although, as far as it goes, the partial postcranial skeleton of Pachygenelus described by Gow (2001) is similar to those of both tritylodontids and early mammals. The postcranial skeleton of tritylodontids is known in practically every detail from the description of Oligokyphus (Fig. 3.23(c)) by Kühne (1956), and the as yet unpublished material of the North American form Kayentotherium. It closely resembles the basal mammalian stage represented by the morganucodontans (Jenkins and Parrington 1976). At last the forelimb had evolved a mammalian mode of action. The coracoid plate is very small and the glenoid fossa is widely open. The humerus is relatively slender with a bulbous head that can move quite freely in the glenoid as a ball-and-socket joint instead of the rolling joint characterising the earlier stages. Adduction– abduction as well as protraction–retraction movements were freely possible. The elbow was turned backwards and the forelimb is placed more or less below the body, as in modern small mammals (Jenkins 1971a). The anterior edge of the scapula and acromion process are even more extremely everted, and the supraspinatus muscle was very well developed, as indicated by a large depression on the now fully anterior-facing part of the internal scapula surface. In the hindlimb, the trend towards losing the posterior process of the ilium and elongating the anterior process was completed, with the latter bearing the characteristically mammalian longitudinal ridge separating gluteal musculature above from iliacus musculature below (Fig. 4.8(f)). The pubis is fully turned back to a level entirely behind the acetabulum, and the obturator fenestra in the pubo-ischiadic plate is full sized. In short, the pelvic girdle is completely mammalian in form, as too is the femur, with the head separated by a short neck from the distinct trochanter major and trochanter minor. Actually, the two trochanters and femoral head are in line with each other, rather than set off at an angle as in typical mammals, a feature that Gow (2001) attributed to fossorial adaptations specific to tritylodontids. Mammalian grade At this rather generalised level of discussion, there is little to add to the story of the origin of mammalian locomotor mechanics, as directly inferred from the preserved skeletons. The morganucodontans added
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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
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 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 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 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
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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
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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
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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