The Origin and Evolution of Mammals - Moodle

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(c) (d) (a) (b) Kayentatherium EVOLUTION OF MAMMAL-LIKE REPTILES 71 (e) Oligokyphus Bocatherium Figure 3.23 Tritylodontids. (a) Skull of Oligokyphus in four views. Skull length approx. 9 cm (Kühne 1956). (b) Postcanine dentition of Oligokyphus major, uppers (top) and lowers (bottom) anterior to the right (Kühne 1956). (c) Postcranial skeleton of Oligokyphus. Postsacral length approx. 28 cm (Kühne 1956). (d) Skull of Kayentatherium. Skull length approx. 22 cm (Carroll 1988, from Sues 1983). ((e) Lateral view of skull of Bocatherium mexicanum. Skull length approx. 4.2 cm (Clark and Hopson 1985).
72 THE ORIGIN AND EVOLUTION OF MAMMALS The tritylodontid skull has a strong look of a mammal about it because of the loss of the postorbital bar so that the orbit and temporal fenestra are confluent, and the extremely large temporal fenestrae separated from one another by a very deep sagittal crest. The dentary bone occupies almost the whole of the lower jaw and has enormous coronoid and angular processes, while the postdentary bones are reduced to a delicate compound rod set into a groove on the medial side. However, there is still no contact between the dentary and the squamosal, the jaw hinge consisting of the tiny articular and the weakly supported quadrate bone. The superficially rodent-like dentition is highly specialised for a herbivorous diet. Canines are absent but have been functionally replaced by an enlarged pair of second incisors. In primitive members such as Oligokyphus (Fig. 3.23(a)) this is the largest of the three pairs present but in other forms such as Kayentatherium (Fig. 3.23(d)) it is the sole remaining pair. After a long diastema in both the upper and the lower jaws, there is a row of large, complex postcanine teeth (Fig. 3.23(b)). The crowns of the upper postcanines have three longitudinal rows of sharp, crescentic cusps, while the lowers have two such rows. The tooth rows are parallel and when the jaws closed, occlusion occurred on both sides simultaneously. The two rows of cusps of the lower teeth fitted into the troughs formed by the three rows of cusps of the uppers, and the action consisted of powerfully dragging the lower jaws backwards while the teeth were in contact. The individual crescentic cusps of the upper teeth had the concave edge facing forwards, while those of the lower teeth faced backwards, and so the net effect was a filing action between the two opposing occlusal surfaces, allowing very fine shredding of even quite tough vegetation. The complete postcranial skeleton of Oligokyphus is known (Kühne 1956; Kemp 1983) and is virtually mammalian in form (Fig. 3.23(c)). The shoulder girdle is modified by reduction of the coracoid bone and a large, laterally reflected acromion. The humerus is extremely slender. In the pelvis (Fig. 4.8(b)), the ilium has almost lost the posterior process, and the extensive anterior process has a lateral ridge of mammalian form separating dorsal from ventral regions. The femur has an inturned spherical head and discrete trochanter major and trochanter minor, and is thus fully mammalian in structure. Tritheledonta Tritheledontans (Fig. 3.24) constitute another highly derived group of non-mammalian cynodonts. They are very small, presumably insectivorous forms occurring from the early Upper Triassic Carnian stage through to the Lower Jurassic (Lucas and Hunt 1994). The skull and, to the limited degree it has been described, the postcranial skeleton are remarkably mammalian in general appearance. As in the tritylodontids, the prefrontal and postorbital bones have been lost, and therefore there is no postorbital bar separating the orbit from the temporal fenestra. Unlike the tritylodontid condition, the temporal fenestra is long, the sagittal crest low and broad, and the zygomatic arch slender, characters probably correlated with the small size of the animals. Other mammalian features include the virtual disappearance of the lateral pterygoid processes of the palate. One of the phylogenetically most significant derived features of all is a contact between the articular process of the dentary and the squamosal, and therefore the presence of the new, secondary jaw articulation immediately lateral to the quadrate-articular hinge. This critical feature (Fig. 3.24(d)) was first claimed for Diarthrognathus (Crompton 1963) but not universally accepted. However, it has been amply confirmed subsequently in Pachygenelus (Allin and Hopson 1992; Luo and Crompton 1994). The tritheledontid dentition also possesses certain otherwise uniquely mammalian characters. One is that the histological structure of the enamel is prismatic. A second is that wear facets are present on the inner faces of the upper and the outer faces of the lower postcanines, indicating not only that they had a direct, shearing occlusion, but also that, as in primitive mammals, there was a unilateral action of the jaws, only one side of the dentition being active during any one instant. However, unlike mammals generally, the upper and lower wear facets do not match exactly, so the occlusion cannot have involved the precise action between specific parts of opposing teeth that distinguishes the more advanced group. Little can yet be said of the postcranial skeleton for want of a description of material whose existence has been
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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
Page 32 and 33: (b) (c) (a) Casea rutena Casea broi
Page 34 and 35: (Fig. 3.2(f)), is actually an ophia
Page 36 and 37: the first one is enlarged, often to
Page 38 and 39: Even at their initial appearance in
Page 40 and 41: (a) Nikkasaurus (b) (d) Reiszia (e)
Page 42 and 43: Nikkasauridae The family Nikkasauri
Page 44 and 45: has figured large in discussions of
Page 46 and 47: (c) Figure 3.9 (continued). Syodon
Page 48 and 49: a mixture of progressively more spe
Page 50 and 51: 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 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 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
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(a) (b) (i) (ii) (iii) (iv) (v) a g
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cold stress, the part that usually
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conducted the experiment of wrappin
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mammals themselves that the enlarge
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elevation of maximum aerobic activi
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a mammal. The difficulty with all s
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collection, ingestion, and assimila
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were edaphosaurid and caseid pelyco
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CHAPTER 5 The Mesozoic mammals The
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(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
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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
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
Page 342:
Tulerpeton 14, 18 Tylopoda 264 Ukha
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The Origin and Evolution of Mammals - Moodle

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