The Origin and Evolution of Mammals - Moodle

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mandibulae musculature. This, as in the dicynodonts, would have provided the necessary posteriorly directed force on the mandible during occlusion (Rybczynski 2001). The form and evident action of the teeth indicate a committed herbivorous animal. Dromasauroidea There are three genera of small, primitive anomodonts from the Late Permian of South Africa generally included in a taxon Dromasauria. They are represented by a total of four specimens, each one of which is preserved as a natural sandstone cast of the skull and postcranial elements (Brinkman 1981). Galeops (Fig. 3.11(d)) shows features otherwise restricted to the dicynodonts, leading to the view that among the dromasaurs it is the dicynodont sistergroup (Modesto and Rybczynski 2000; Rybczynski 2000). The characters in question include further shortening of the preorbital region of the skull, absence of anterior teeth on either premaxilla or dentary, and the remaining posterior dentition reduced to a short row of small, peg-like teeth. The arrangement implies that dicynodont-like horny tooth plates had evolved at the front of the jaws. Other features of dicynodonts that are found are fusion of the paired dentaries at the symphysis, and a quadrate condyle divided by a longitudinal groove into lateral and medial condyles, corresponding to elongated articular condyles. According to King (1994), the structure of the jaw articulation would have permitted propalinal movement of the lower jaw. The preserved specimens of neither of the other two genera of dromasaurs, Galepus and Galechirus (Fig. 3.11(c)) are as revealing. They are much the same size as Galeops, and look superficially very similar. However, there are differences in the dentition which justifies at least the generic distinction between the three (Brinkman 1981). Galechirus possesses premaxillary teeth, which are decidedly procumbent, but the situation of the lower teeth is unclear. Galepus has at least six small lower teeth, but in this case the nature of the upper dentition is unclear. Dicynodontia The great majority of anomodonts belong to the very well-defined group Dicynodontia, which makes its appearance in the Eodicynodon Assemblage Zone EVOLUTION OF MAMMAL-LIKE REPTILES 43 contemporary with the earliest of the primitive African anomodonts described above. Indeed, it is the eponymous Eodicynodon itself that first represents the group (Rubidge 1984, 1990a). Eodicynodon The trends in cranial evolution seen in the primitive anomodonts up to the stage represented by Galeops reach their culmination in the fully dicynodont form of Eodicynodon (Fig. 3.12(a)). All the incisor teeth are absent, there is an enlarged caniniform upper tusk, and its postcanine dentition is reduced to a small number of relatively minute teeth. (Rubidge, 1990b, described a specimen of Eodicynodon, which lacks the caniniform tooth; he attributed it to a different species). The triturating surface of the jaws consisted virtually exclusively of a horny beak. Cox (1998) concluded from the structure of the bony surfaces that there were three parts to the beak. A medial anterior dentary beak bit within the front margins of the palate, presumably with a cropping function. Further back, a pad on the dentary table acted against a palatal pad medial to the caniniform process. Third, a posterior horny blade on the dentary bit against a palatine pad behind the caniniform process. In some specimens the lower blade also carries a row of small teeth. In order to operate these biting structures, the external adductor musculature had a much enlarged lateral component, originating from the horizontally flattened and dorsally bowed zygomatic arch and inserting at least partially on a lateral shelf on the dentary. The temporal fenestra as a whole is elongated, while the lateral pterygoid processes are reduced. These point to the increased importance of a posteriorly directed power stroke during the closing phase of the jaw action, accompanied by a reduction in the importance of the anterior pterygoideus musculature with its anteriorly directed component (Fig. 3.12(c)). The jaw articulation (Fig. 3.12(d)) has the uniquely dicynodont structure of more or less equal lateral and medial convex condyles on the quadrate and corresponding but elongated articular condyles on the lower jaw. King et al. (1989) believed that the feeding mechanism of Eodicynodon had achieved the essential dicynodont arrangement but that the degree of propaliny was still less than occurred in later dicynodonts, a view reiterated by King (1994) and Cox (1998).
44 THE ORIGIN AND EVOLUTION OF MAMMALS (a) (b) Eodicynodon lat.add.ext. Robertia m.add.ext. refl.lam. (c) (d) Figure 3.12 Primitive dicynodonts. (a) Skull of Eodicynodon oosthuizeni in dorsal, ventral, lateral, and posterior views (Rubidge 1990). (b) Reconstruction of the postcranial skeleton of Robertia broomiana (King 1981(b)). (c) Reconstruction of the adductor jaw musculature of Dicynodon: left, superficial lateral view; right, deep lateral view. lat.add.ext, lateral adductor externus muscle. m.add.ext, medial adductor externus muscle. refl.lam, reflected lamina of the angular. (d) Jaw articulation of a dicynodont showing lower jaw in protracted (above) and retracted (below) postions. (King 1981a).
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The Origin and Evolution of Mammals
Page 4 and 5: The Origin and Evolution of Mammals
Page 6 and 7: Preface This book arose from twin a
Page 8 and 9: For Mal /gosia with love and thanks
Page 10 and 11: Contents 1 Introduction The definit
Page 12 and 13: CHAPTER 1 Introduction There are ab
Page 14 and 15: transversely occluding molar teeth
Page 16 and 17: the Mesozoic mammals, is to do with
Page 18 and 19: a hierarchy of committees under the
Page 20 and 21: it means that a 200 Ma igneous rock
Page 22 and 23: een a more fundamental impact than
Page 24 and 25: Table 2.3 Classification of marsupi
Page 26 and 27: (a) (b) (c) humerus radius aquatic
Page 28 and 29: (a) Westlothiana Limnoscelis PO Wes
Page 30 and 31: 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 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 104 and 105:
(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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the therocephalian grade was not on
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A balance was also achieved in the
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Locomotion Ancestral amniote grade
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screw-shaped: the front part faces
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For the recovery phase, the relativ
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SC PRC p.i.f.i tr.min (c) dp.cr ect
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the therocephalian pelvis and hindl
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spc s.sp s.sp SC PRC (d) delt T AST
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no significant novelties to what ha
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(a) (c) (e) (g) D D ex. au.m C tym
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(a) (c) (d) PMX (f) V n.turb mx.tur
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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
Page 184 and 185:
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
Page 224 and 225:
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
Page 242 and 243:
(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
Page 254 and 255:
Mioclaenus Paulacoutoia (didolodont
Page 256 and 257:
their presence. The five orders may
Page 258 and 259:
Xenungulata. Only two Late Palaeoce
Page 260 and 261:
(a) (b) (d) (c) Oxyaena Patriofelis
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continuously growing, and form a gr
Page 264 and 265:
navicular facet, 19 or more thoraci
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(a) (c) Phosphatherium Numidotheriu
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coexist with other characters that
Page 270 and 271:
The salient feature of Widanelfasia
Page 272 and 273:
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
Page 278 and 279:
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
Page 288 and 289:
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
Page 300 and 301:
agreement about exactly when within
Page 302 and 303:
References Abdala, F. Redescription
Page 304 and 305:
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
Page 320 and 321:
(eds) Evolution of Tertiary mammals
Page 322 and 323:
McKenna, M.C. and Bell, S.K. 1997.
Page 324 and 325:
(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
Page 332 and 333:
Thewissen, J.G.M. 1990. Evolution o
Page 334 and 335:
Novacek, M.J., and McKenna, M.C. (e
Page 336 and 337:
Index Note: Page numbers in italics
Page 338 and 339:
Equoidea 262 Equus 262 Erethizon 28
Page 340 and 341:
Overkill hypothesis 289, 290 Oxyaen
Page 342:
Tulerpeton 14, 18 Tylopoda 264 Ukha
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