The Origin and Evolution of Mammals - Moodle

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(a) Purgatorius (c) are part of the super-order Euarchontoglires is not doubted, but within it they could be stem-group Primates (Bloch and Silcox 2001; Bloch and Boyer 2003a,b), basal members of the Dermoptera (Beard 1993), or have no sister-group relationship with (b) Plesiadapis Carpolestes LIVING AND FOSSIL PLACENTALS 233 Figure 7.5 Plesiadapiformes. (a) Isolated upper molar of Purgatorius in occlusal view (Savage and Long 1986). (b) Carpolestes skeleton, restoration, and hind foot to show grasping structure. Presacral length of skeleton approx. 12 cm (Bloch and Boyer 2002). (c) Plesiadapis skull, occlusal views of upper and lower dentitions, and skeleton. Length of skull approx. (Savage and Long 1986 and Romer 1966 after Simpson). anyone of the other euarchontogliran orders (Kirk et al. 2003). Plesiadapiforms were a relatively abundant, diverse part of the Palaeocene radiation of North America and Europe. The dentition (Fig 7.5(c)) is
234 THE ORIGIN AND EVOLUTION OF MAMMALS superficially rodent-like, with enlarged incisors and reduced canines. The molars are rectangular and the cusps blunt, indicating an omnivorous, or perhaps frugivorous diet. Most plesiadapiforms were small, such as Carpolestes (Fig. 7.5(b)) whose head and body length is about 15 cm (Bloch and Boyer 2003a), and skeleton adapted for an arboreal existence. Others, notably Plesiadapis, were relatively large in body size, weighing up to 5 kg (Fig. 7.5(c)). The skeleton of this particular genus has been variously interpreted as either terrestrially adapted on the basis of the length of the limbs, or alternatively arboreally adapted as suggested by the well-developed claws and the structure of the ankle joint (Szalay and Delson 1979). ‘Condylarthra’ The concept of ‘Condylarthra’ as a group of basal ungulate herbivores has been very important in the development of ideas about Palaeocene placental evolution. It contains a variety of small, primitive members, but more importantly a number of lineages of specialised and significantly larger herbivores, and secondary carnivores are included. Furthermore, the ancestral roots of all the later, specialised ungulate orders of placentals have been assumed to lie within the group. Thus the ‘condylarths’ are profoundly paraphyletic, and the interrelationships of this mixture of ancestral and derived condylarths are practically impossible to disentangle. Most agree that, while the term has long since outlived any formal usefulness, it is still virtually impossible to do without it: hence its retention but with quotation marks, or alternatively use of the synonymous expression ‘archaic ungulates’. The characteristics of ‘condylarths’ are simply the ancestral features of ungulates generally (Archibald 1998; Nessov et al. 1998). The molar have evolved a crushing action in place of the primitive shearing function. They are low-crowned, with bunodont cusps. The uppers are rectangular in occlusal view with a fourth cusp, the hypocone, developed. The trigonid of the lower molar is shortened from front to back and bears a prominent metaconid cusp. The second feature of ‘condylarths’ concerns the terminal phalanges of the digits. They are elongated and are not grooved or fissured, and are therefore at least incipiently hoof-like rather than claw-like. The distinction between ‘condylarth’ molars and those of the presumed ancestral grade seen in zhelestids are not marked, and nor are there clear differences between the most progressive ‘condylarths’ and stem members of some of the ungulate placental orders. Nevertheless, accepting ‘condylarths’ as a grade of primitive ungulates, several groups can be distinguished at least some of which are probably monophyletic (Archibald 1988; Prothero et al. 1998). The great majority are from the Palaeocene of North America, where more than half the Early and Middle Palaeocene mammal species are ‘condylarths’. Many are herbivorous and include species of large body size. Others have a modified dentition suitable for an omnivorous, or a carnivorous diet, and amongst the latter are the first placental mammals to enter the medium to large body-sized carnivorous habitat. Protoungulatum. Protungulatum (Fig. 7.6(a)) is the earliest and most primitive ‘condylarth’, a genus that occurs in North America at the base of the Early Palaeocene. Apart from a few cranial and postcranial fragments, it is only represented by teeth and jaws, which have the ancestral ‘condylarth’ form. The dental formula is I3/3: C1/1: PM4/4: M3/3, there is no diastema behind the incisors, and the premolar teeth show only a slight tendency to become more molariform. The cusps of the molars are relatively tall, and the upper molars are transversely wide. The hypocone is barely developed. Arctocyonidae. Several families of ‘condylarths’ appear in the Early Palaeocene, distinguished mostly by details of the dentition. The most primitive are the Arctocynonidae, which occur in North America and Europe. Protoungulatum is sometimes included as the most basal member, although it shares only ancestral characters with them. Arctocyonid molar teeth are relatively low-crowned, and there is a fully developed hypocone cusp on the uppers, indicating that the crushing function had fully evolved. A virtually complete skull of Arctocyon (Fig. 7.6(b)) from Europe shows lower canines, a deep sagittal crest, and a low position of the mandibular articulation. All these characters indicate an ability to take significant live prey, even though there was no tendency to develop any form of carnassial, or specialised shearing teeth. Thus, arctocyonids seem to
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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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Page 202 and 203: (d) (a) pa A Dasyuromorphia B C pr
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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
Page 226 and 227: (f) (g) Wakaleo Diprotodon optatum
Page 228 and 229: fossil mammals, which might help cl
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Page 236 and 237: effectively absent. However, increa
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Page 248 and 249: (a) (f) (e) Hyopsodus Phenacodus (d
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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
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Page 262 and 263: continuously growing, and form a gr
Page 264 and 265: navicular facet, 19 or more thoraci
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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
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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
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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
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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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