The Origin and Evolution of Mammals - Moodle

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(a) (f) (e) Hyopsodus Phenacodus (d) (g) (b) (c) Ectoconus LIVING AND FOSSIL PLACENTALS 237 Mioclaenids Meniscotherium Periptychius Figure 7.7 Herbivorous ‘condylarths’. (a) Hyopsodus skeleton, skull, upper molars in occlusal view and lower molars in occlusal view. Length of skull approx. 6 cm (Archibald 1998 after Gazin and Romer 1966 after Matthew). (b) Comparison of mioclaenid lower teeth in occlusal view. From the top Abdounodus from North Aftica; Promioclaenus from North America; Tiuclaenus from South America; Molinodus from South America; Pucanodus from South America (Gheerbrant et al. 2001). (c) Skull of the periptychid Ectoconus. Length approx. 16 cm (Archibald 1998, figure 20.2 after Gregory 1951). (d) Occlusal views of upper and lower dentition of Periptychius (Archibald 1998 after Matthews). (e) Phenacodus skeleton. Presacral length approx. 1.5 m (Archibald 1998, after Gregory). (f) Skull and occlusal views of upper and lower dentition of Phenacodus. Skull length approx. 22 cm (Romer 1966, after Cope and Matthew). (g) Meniscotherium upper teeth in occlusal view (Romer 1966, after Matthew).
238 THE ORIGIN AND EVOLUTION OF MAMMALS with five widely spaced digits bearing small hooves, and probably associated with a semi-plantigrade stance. The Phenacodontidae were the most specialised herbivorous family of all. They appeared in the Middle Palaeocene of North America and survived into the Eocene. Phenacodus (Fig 7.7(e) and (f) also occurs in the Early Eocene of Europe, and there is a possible specimen of similar age from Morocco (Gheerbrant et al. 2001), but the group is not represented for certain in Asia (Thewissen 1990). Taxonomically, the phenacodontids are not usually included with the more conservative herbivorous families, but as a separate group of more progressive ungulates, possibly related to the Tethytheria (Prothero et al. 1988; Janis et al. 1998a), a question returned to later. Phenacodontids show the extreme of ‘condylarth’ specialisation for herbivory of both the dentition and the postcranial skeleton. The posterior premolars are the most molariform of all. The molars are very low-crowned with the cusps developed into crescents or lophs of various patterns in the different genera. The limbs are well-designed for cursorial locomotion: elongated, slender, and bearing reduced first and fifth digits. Phenacodus (Fig. 7.7(e) and (f)), with a presacral body length up to 2 m, had the least specialised version of phenacodontid teeth; others such as the 60 cm long Meniscotherium (Fig. 7.7(g)) reached the zenith of ‘condylarth’ herbivorous dentition, with its fully expressed pattern of crescents and lophs on the crowns. The phenacolophids are a poorly known, but phylogenetically very important group of Asian ‘condylarths’ because they have been variously implicated in the origins of the embrithopod, tethythere, and perissodactyl ungulate orders (McKenna and Manning 1977; Prothero et al.1988). They are known from little more than teeth of Mid- Late Palaeocene age, the molars of which are dilophodont, having two transverse lophs or crests. Eocene ‘condylarths’ from Morocco have been mentioned. There are also Palaeocene ‘condylarths’ from the Ouarzazate Basin of Morocco (Gheerbrant 1995), but the affinities of these specimens are unclear. Given the molecular evidence for the origin of the African ungulate orders as part of a geographically isolated radiation of Afrotheria, it will be very important to discover whether these African ‘condylarths’ are members of groups existing elsewhere, or are actually basal members of Afrotheria, related perhaps to the Proboscidea and Hyracoidea. Taeniodonta The taeniodonts were omnivorous mammals occurring exclusively in the North American Palaeocene and Eocene (Schoch 1986; Lucas et al. 1998). In body size they vary from 5 kg to over 100 kg. The most primitive member is the Early Palaeocene Onychodectes (Fig. 7.8(a)), in which there is a moderately large canine followed by widely spaced, interlocking premolars. The molars are high crowned with low, bunodont cusps and a roughly rectangular occlusal surface. The postcranial skeleton is that of a fairly generalised, non-cursorial mammal perhaps able to climb well, and Lucas et al. (1998) suggest that it had a mode of life comparable to that of the Virginia Opossum. Later taeniodonts, notably Stylinodon (Fig. 7.8(b)), were larger and had evolved a much shorter, powerfully built skull. The canines and upper incisors were greatly enlarged, open-rooted, and the enamel only covered the anterior faces, giving them a chiselling function. The anterior premolars had evolved into cutting blades while the posterior teeth were simplified crushing pegs of dentine. The whole skeleton had become heavily built, and the powerful forelimbs bore large, flattened claws, presumably adapted for digging out and consuming roots and tuberous parts of plants. The relationships of taeniodonts are obscure. There is no evidence at all to relate them to ‘condylarths’, but rather to one of the more conservative primitive insectivorous taxa. McKenna and Bell (1997) classify them with palaeoryctids. A more precise possibility is that they are related to the otterlike pantolestids, which are themselves believed to have palaeoryctid affinities. Pantodonta The pantodonts (Fig. 7.8(c)) include the very first of the large, herbivorous placental mammals to evolve after the Cretaceous, although others were much smaller, less than 10 kg. The earliest and most primitive forms are from the Early Palaeocene of China, where Bemalambda and Hypsilolambda occur in the Shanghuan Formation (Wang et al. 1998). Bemalambda
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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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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 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 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
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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
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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
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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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The Origin and Evolution of Mammals - Moodle

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