The Origin and Evolution of Mammals - Moodle

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Titanoides (pantodont) (a) (c) (b) LIVING AND FOSSIL PLACENTALS 239 Onychodectes (taeniodont) Stylinodon (taeniodont) Figure 7.8 Taeniodonts and pantodonts. (a) The taeniodont Onychodectes skull and occlusal views of upper and lower dentitions. Skull length approx. 10 cm (Lucas et al. 1998). (b) The taeniodont Stylinodon skeleton and skull. Skull length approx. 25 cm (Lucas et al. 1998). (c) The pantodont Titanoides skull, occlusal views of upper and lower dentitions, and skeleton. Length of skull approx. 15 cm (Lucas 1998 after Simons).
240 THE ORIGIN AND EVOLUTION OF MAMMALS was the size of a large dog, with a skull about 20 cm in length. In North America, the group makes its appearance in the middle of the Palaeocene, and it survived into the Middle Eocene as represented by Coryphodon. Teeth of pantodonts also occur in the Palaeocene Tiupampan fauna of South America (Muizon and Marshall, 1987, 1992) and the Eocene of Antarctica (Reguero et al. 2002). The dentition of pantodonts is complete, with modest canines and no diastema. The most characteristic feature is the development of lophs on the postcanine teeth. In the more primitive bemalambdids of Asia, the lophs are V-shaped, but in all other forms, collectively classified as Eupantodonta, the molar tooth lophs have evolved a W-shape (Lucas 1993). The postcranial skeleton varies from that of the lightly built, possibly arboreal genus Archaeolambda, which is known from a complete Late Palaeocene skeleton from China, to the massive, graviportal Barylambda that is often likened to a giant ground sloth, complete with a massive pelvis and heavy tail that suggest a habit of browsing on high vegetation. Despite their large body size and herbivorous habit, there are no dental or postcranial features suggesting that pantodonts are related to the ‘condylarths’ as was once believed. McKenna (1975) followed more recently by Lucas (1993, 1998) proposed that, like the taeniodonts, pantodonts are possibly related to the palaeoryctid group of small Cretaceous insectivorous mammals, on the basis of features of the dentition shared by the primitive pantodonts and a form such as Didelphodus. Tillodonta The tillodonts are another group of mainly Palaeocene herbivores, whose most primitive members such as Lofochaius occur in the Early Palaeocene of China, where they survived until the Late Eocene (Lucas 2001). They make their appearance in North America in the latest Palaeocene, where they underwent a brief radiation in the Early to Middle Eocene before becoming extinct. Early Eocene tillodonts are also found in Europe, but so far none have turned up in South America (Lucas and Schoch 1998a). Tillodonts varied from small, with a skull length of only 5 cm, to large mammals such as the bearlike Trogosus (Fig. 7.9(a)), which has a 35 cm skull and an estimated body weight of about 150 kg. The tillodont dentition (Fig. 7.9(b)) is highly distinctive, particularly due to the enlarged, chisel-like second incisors in which the enamel is restricted to the anterior edge. The other incisors, canines and anterior premolars tended to be lost, leaving only the square, hypsodont molars with a dilambdodont pattern of crests, which rapidly wore down. The teeth are carried in powerfully built jaws, and the body as a whole was heavily built, with well-developed and recurved claws. All the indications are of a ground grubbing mammal feeding on roots and tubers. At one time tillodonts were regarded as derivatives of ‘condylarths’, but there are no clear ungulate characters. The similarity of the dilambdodont molars of tillodonts and pantodonts has suggested to several authors that the two are sister groups (Chow and Wang 1979; Lucas 1993), though the evidence is not very convincing: the similarities may be convergent in two groups independently derived from palaeoryctid-like ancestors. The biogeography of the group has been investigated by Schoch and Lucas (1982; Schoch 1986), who argue that it probably had an Asian origin. The similarity between the Chinese Meiostylodon and the North American Esthonyx can be explained by a dispersal into North America by the Late Palaeocene. They also suggested that the relatively early demise of the group in North America was due to competition from the similarly adapted taeniodonts. Dinocerata The dinoceratans include the largest of all the archaic Palaeocene–Eocene herbivores, ranging in estimated body weight from 175 kg to 4.5 tonnes. The earliest record of this short-lived group is Prodinoceros from the latest Palaeocene of both China and North America (Lucas and Schoch 1998), and none survived beyond the Middle Eocene. Although massively built, Prodinoceros (Fig. 7.9(c)) was relatively small for the group and lacked the bony protuberances of the skull so characteristic of the later members, such as the huge mid-Eocene Uintatherium (Fig. 7.9(d)), which occurred in North America and Asia, although not in Europe. The dentition of dinoceratans shows a tendency to reduce and eventually lose the upper incisors, but to retain and enlarge the upper canine. The premolars
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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
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Procynosuchus (d) Procynosuchus (a)
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They constitute the monophyletic gr
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Although there is no mammal-like co
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Cynognathidae Cynognathus (Fig. 3.2
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(e) (f) Figure 3.22 (continued). Ma
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(c) (d) (a) (b) Kayentatherium EVOL
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Pachygenelus (e) (a) (c) Therioherp
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palatal, and orbitosphenoid bones,
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Wible and Hopson 1993). The interor
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published a cladogram based on rece
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310-320 Ma. By this time, the great
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are forms such as Casea itself, var
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lakes and swamps in the low-lying l
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urrowing and subsisting on a diet o
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Eothyris Haptodus sphenacodontine B
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z (a) (c) a.pt.m. M B PO P P SQ P M
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(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
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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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Page 208 and 209: (b) (d) (a) Glasbius Alphadon (c) D
Page 210 and 211: elieved to be Late Cretaceous in ag
Page 212 and 213: (Fig. 6.5(c)). The dentition exhibi
Page 214 and 215: (d) Figure 6.6 (continued). Thylaco
Page 216 and 217: (a) (c) Caroloameghina and Procarol
Page 218 and 219: (a) (e) (d) Proargyrolagus Groeberi
Page 220 and 221: (a) (b) Djarthia Thylacotinga (c) (
Page 222 and 223: LIVING AND FOSSIL MARSUPIALS 211 M
Page 224 and 225: Extinct Notoryctemorphia At present
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Page 228 and 229: fossil mammals, which might help cl
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Page 232 and 233: the Diprotodontia also included gen
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Page 246 and 247: (a) (d) (e) (g) Protoungulatum Meso
Page 248 and 249: (a) (f) (e) Hyopsodus Phenacodus (d
Page 252 and 253: (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
Page 262 and 263: continuously growing, and form a gr
Page 264 and 265: navicular facet, 19 or more thoraci
Page 266 and 267: (a) (c) Phosphatherium Numidotheriu
Page 268 and 269: coexist with other characters that
Page 270 and 271: The salient feature of Widanelfasia
Page 272 and 273: 1 (a) 1. Perissodactyla 2. Titanoth
Page 274 and 275: (a) (b) BUNODONTIA or SUIFORMES SUI
Page 276 and 277: time, which suggests that it was on
Page 278 and 279: condition. This particular combinat
Page 280 and 281: etween Primates, Dermoptera (colugo
Page 282 and 283: have postcranial adaptations for ar
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Page 288 and 289: The Late Cretaceous mammal record i
Page 290 and 291: interordinal divergences in the Lat
Page 292 and 293: diversity on Earth (Janis 1993). Fu
Page 294 and 295: effect of the surrounding sea. Trop
Page 296 and 297: was high. It lasted from 5 to 3 Ma
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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
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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