The Origin and Evolution of Mammals - Moodle

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their presence. The five orders may be described briefly as follows. Litopterna. The litopterns were relatively conservative as far as the dentition is concerned, and the teeth of the earliest members of the group (Fig 7.10(c)) resemble those of ‘condylarths’, particularly the South American group Didolodontidae (Fig. 7.10(b)). Some authors have even included the latter in the Litopterna. The crowns are generally low, and the development of lophs weak. In contrast, the limbs were the most highly evolved of the ungulates, with a strong tendency to reduce the side toes leaving the third digit dominant. Of the two groups of litopterns, the proterotherioideans were remarkable for their horse-like build and the Miocene member Thoatherium (Fig. 7.11(a)) possessed a single-toed, extraordinarily equid-like condition of its limbs. The other group, the macrauchenioideans are invariably described as camel-like, with their elongated neck and limbs, and broad foot consisting of three almost equal toes. The group is also represented in the Eocene of Antarctica by teeth of Victorlemoinea. The Plio-Pleistocene Macrauchenia (Fig. 7.11(b)) has its nostril opening high up on its skull, which led to the belief that there was a proboscis present, although it might alternatively have been associated with a swampy habitat, or keeping the brain cool by evaporation. This genus also has the most derived molar teeth of all litopterns, having become highcrowned and lophodont. Notoungulata. The notoungulates were far the most diverse of the meridiungulate orders, with more than 100 genera in 13 families evolving in the course of the Cenozoic (Fig. 7.10(f)). At one time, it was believed that there were Palaeocene notoungulates in China and North America, which were placed in a primitive family Arctostylopidae (page 242). However, the dental similarities on which the proposed relationship was based are evidently convergent and the arctostylopids are properly placed in an entirely unrelated placental order of their own (Cifelli et al. 1989; Cifelli and Schaff 1998). This leaves notoungulates as exclusively South American, with the single exception of the Pleistocene Mixotoxodon, which briefly extended its range into central America. Notoungulates are categorised by a generally broad, flat skull, and unique features of the auditory LIVING AND FOSSIL PLACENTALS 245 region. The molar teeth tend to be strongly lophodont, and full hypsodonty is commonly developed. The most basal group, the Notioprogonia, were medium-sized, heavily built, and digitigrade animals (Fig. 7.12(a)). In the course of the Tertiary three groups evolved from notioprogonian-like ancestors. The toxodonts included the largest of all South American ungulates, with the late surviving Toxodon (Fig. 7.12(e)) the size and build of a large rhinoceros. Its incisor teeth were chisel-shaped and the molars hypsodont, indicating a low-level browsing and grazing habit. The typotheres (Fig. 7.12(b) and (c)) were rather like giant rodents, with loss of the anterior dentition except for broad, open-rooted, chisel shaped incisors, and again hypsodont molars. The third group, the hegetotheres (Fig. 7.12(d)), resembled the typotheres in dentition, but tended to develop elongated hind legs, giving them a rabbit-like appearance. Astrapotheria. The astropotheres were very large ungulates, with the best-known genus, the Oligocene Astrapotherium (Fig. 7.10(e) and 7.11(e)), some 3 m in length. The upper incisors of astropotheres are absent and presumably there was a horny pad against which the lower incisors bit. The upper canines are huge and tusk like while the lowers are less enlarged but still prominent. The last two molar teeth evolved enormous size. The nostrils have shifted to the top of the skull, suggesting the possibility of a proboscis as in the litoptern Macrauchenia. The postcranial skeleton was extremely peculiar. The forelegs were very stout and strongly built, but the hindlegs relatively slender. Romer (1966) suggested the possibility of an amphibious mode, perhaps comparable to hippos. Astropotheres survived into the Late Miocene, and are one of the two ungulate orders represented by teeth in the Eocene of Antarctica. Pyrotheria. The pyrotheres (Fig. 7.10(g) and 7.11(d)) were also very large and elephant-like in general form (MacFadden and Frailey 1984). The similarity is enhanced by the tusk-like incisors, two upper and one lower on either side. The six cheek teeth resembled those of primitive proboscideans in the transversely expanded, bilophodont condition. Compared to other South American ungulate orders, pyrotheres were short-lived, appearing in the early Eocene and disappearing during the Oligocene.
246 THE ORIGIN AND EVOLUTION OF MAMMALS (c) (a) (e) Toxodon Miocochilius (typothere) Notostylops (notioprogonian) (b) (d) Pachyrukhos (hegetothere) Mesotherium (typothere) Figure 7.12 Meridungulates: notoungulates. (a) Skull of the notioprogonian Notostylops. Length approx. 14 cm (Savage and Long 1986, after Simpson). (b) Skull of the Pleistocene typothere Mesotherium. Length approx. 27 cm (Savage and Long 1986, after Rovereto). (c) Skeleton of the Miocene typothere Miocochilius. Presacral length approx. 70 cm (Savage and Long 1986, after Stirton). (d) Skull and skeleton of the hegetothere Pachyrukhos. Skull length approx. 7 cm (Savage and Long 1986 after Scott). (e) Skeleton of Toxodon. Presacral length approx. 2.7 m (Savage and Long 1986 after Piveteau).
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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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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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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
Page 226 and 227: (f) (g) Wakaleo Diprotodon optatum
Page 228 and 229: fossil mammals, which might help cl
Page 230 and 231: 30 40 50 60 Figure 6.13 Southern Go
Page 232 and 233: the Diprotodontia also included gen
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Page 236 and 237: effectively absent. However, increa
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Page 240 and 241: and Prokennalestes, although it doe
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Page 248 and 249: (a) (f) (e) Hyopsodus Phenacodus (d
Page 250 and 251: Titanoides (pantodont) (a) (c) (b)
Page 252 and 253: (a) (b) (d) Trogosus (tillodont) Es
Page 254 and 255: Mioclaenus Paulacoutoia (didolodont
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
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
Page 284 and 285: undoubtedly related at a supraordin
Page 286 and 287: indisputably to occur prior to the
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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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
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(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
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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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