The Origin and Evolution of Mammals - Moodle

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(a) (d) (e) (g) Protoungulatum Mesonyx (c) (b) (f) Chriacus Mesonyx Harpagolestes Andrewsarchus Arctocyon Figure 7.6 Basal and carnivorous ‘condylarths’. (a) Protoungulatum skull and occlusal views of upper and lower dentition. Skull length approx. 6 cm (Archibald 1998, after Szalay and Sloan and Van Valen). (b) Arctocyon skull in lateral view. Length approx. 26 cm (Romer 1966, after Russell). (c) Postcranial skeleton of Chriacus. Presacral length approx. 50 cm (Rose 1987). (d) Skeleton and (e) skull of the mesonychid Mesonyx. Skull length approx. 28 cm (Romer 1966 after Scott). (f) Skull of the mesonychid Harpagolestes. Length approx. 40 cm. (g) Skull of the giant mesonychid Andrewsarchus. Skull length approx. 83 cm (Carroll 1988, after Osborn).
236 THE ORIGIN AND EVOLUTION OF MAMMALS have been generalist omnivores. In body size, they ranged up to that of a small bear, and probably had a comparably cosmopolitan diet. Chriacus (Fig. 7.6(c)) was a very lightly built, agile form. Carnivorous ‘condylarths’. Arctocyonids were common in the Early Palaeocene and structurally represent the base of the ‘condylarth’ radiation, from which various more specialised groups diverged. Some became more adapted for carnivory, with a tendency to evolve molar teeth with higher, sharper cusps, and shearing edges, in place of the bunodont cusps of the arctocyonid-grade (Szalay 1969). These constituted the very first radiation of relatively large, predaceous mammals. Three groups of ‘condylarths’ exhibiting an increasing expression of this trend are usually combined into a taxon Cete (Archibald 1998; Prothero et al. 1988). The triisodontids are the most primitive members of this group, and include one of the very earliest ‘condylarths’. Isolated 5 mm long molars of Ragnarok occur at the base of the Palaeocene 65 Ma. Carnivorous characteristics of the dentition are only incipiently developed. The later group Hapalodectidae are more progressive in this respect, having higher, sharper cusps. Hapalodectes was a small, rat-sized animal, not found until the Eocene in North America, but already present in the Late Palaeocene of Asia. The Mesonychidae express to the greatest extent the tendency towards specialised carnivory. The molar teeth are laterally compressed, and shearing edges have developed on the front of the lower teeth, which acted against edges on the back of the uppers. This condition is described as prevallidpostvallum shearing, a system that is only analogous to the postvallid-prevallum shearing system of the carnivorous teeth that evolved in the later specialist carnivore groups Creodonta and Carnivora. Some Mesonyx such as Mesonyx itself (Fig. 7.6(d) and (e)) were the size of a wolf and had lightly built, digitigrade limbs. Others, such as Harpagolestes (Fig. 7.6(f)) were even larger, heavily built with powerful jaws and teeth and were probably scavengers rather than hunters. The mesonychids are also known from Asia, where they occur in the Early Palaeocene Shanghuan and the Late Palaeocene Nonshanian faunas (Wang et al. 1998; Lucas 2001). One of the last forms, Andrewsarchus (Fig. 7.6(g)), is from the Late Eocene of Mongolia, and is often claimed to be the largest terrestrial carnivorous mammal ever discovered. Its skull was over 80 cm in length. Herbivorous ‘condylarths’. Other lineages of ‘condylarths’ evolved increasingly specialised herbivorous adaptations from an arctocyonid-like ancestry. To varying degrees the premolar teeth enlarged and became more molar like, and the molars evolved broader, six-cusped occlusal surfaces. The limbs tended to become digitigrade, with well developed hooves on each of the digits. Four main families are recognised (Archibald 1998) and all of them first occur in the Early Palaeocene of China as well as North America (Wang et al. 1998; Lucas 2001). The hyopsodontids (Fig. 7.7(a)) were small, rabbit-sized animals with short limbs. The canines were very small, and the last premolar is slightly enlarged. The paraconule and metaconule cusps of the upper molars had enlarged to give the sixcusped condition. Hyopsodus extended into the Eocene and is therefore one of the last surviving ‘condylarths’. The family Mioclaenidae (Fig. 7.7(b)) were also relatively small, incipiently specialist herbivores. The premolars were more molarised, and the occlusal surfaces of the molar teeth were simplified by having less distinct cusps, suggesting a more continuous grinding action of tougher food. Mioclaenids, or at least close relatives of this family occur in the Early Palaeocene Tiupampan fauna of the Santa Lucia Formation of Bolivia, where they have been implicated in the origin of the indigenous South American ungulate orders. Gheerbrant et al. (2001) have described ‘condylarth’ teeth of Early Eocene age from Morocco in North Africa, one of which, Abdounodus (Fig. 7.7(b)), is comparable to mioclaenids. Periptychids varied from small, squirrel-sized mammals to Ectoconus (Fig. 7.7(c)), which was the size of a sheep. In this family, the premolars were more or less fully molarised, and crescentic crests had developed from the cusps of these and the molars (Fig. 7.7(d)). Archibald (1998) interpreted the tooth structure as an adaptation for dealing with tough, fibrous vegetation that was first shredded by the swollen premolars and then pulverised by the molars. The skeleton of periptychids is rather heavily built and the limbs short. The feet too are short,
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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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Page 200 and 201: the 11 species of marsupial, of whi
Page 202 and 203: (d) (a) pa A Dasyuromorphia B C pr
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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
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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
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 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
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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
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
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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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