The Origin and Evolution of Mammals - Moodle

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(a) Westlothiana Limnoscelis PO Westlothiana Protorothyris Eothyris (d) (e) (f) (b) (c) PO Westlothiana Protorothyris Archaeothyris Figure 3.2 Early amniotes. (a) Skull of the stem amniote Westlothiana lizziae in dorsal and lateral views with occipital view of Limnoscelis (Westlothiana from Smithson et al. 1994; Limnoscelis from Laurin and Reisz 1995). (b) Dorsal, occipital, and lateral views of the skull of Protorothyris (Carroll 1964; Panchen 1972). (c) Dorsal, occipital, and lateral views of Eothyris (Romer and Price 1940; Panchen 1972). (d) Postcranial skeleton of Westlothiana lizziae. Presacral length approx. 11 cm (Smithson et al. 1994). (e) Postcranial skeleton of Protorothyris. Presacral length approx. 12 cm (Carroll 1964). (f) Postcranial skeleton of Archaeothyris florensis. Presacral length approx. 30 cm (Reisz 1972). PO, postorbital. Supratemporal stippled; Tabular cross-hatched. PO
18 THE ORIGIN AND EVOLUTION OF MAMMALS Tulerpeton (Lebedev and Coates 1995), which, if correctly interpreted, indicates that the living Amniota must have separated from their closest living relatives, the Amphibia, at least 360 Ma. If Tulerpeton is rejected, the next candidate for earliest stem-amniote is the 333 Ma Lower Carboniferous Westlothiana (Fig. 3.2(a) and (d)), which is known from complete skeletons (Smithson et al. 1994). It was a small, short-limbed, superficially very reptile-like animal with a number of amniote characters such as the structure of the vertebral column and certain details of the skull bone pattern. There is a considerable diversity of later Carboniferous tetrapods that are widely, if not universally considered stem-group amniotes (Clack and Carroll 2000; Heatwole and Carroll 2000). The seymouriids, once believed to be the ancestral reptile group, include quite large highly terrestrially adapted forms. Probably the majority view at present is that the apparently herbivorous diadectids along with the large, crocodilelike limnoscelids together constitute the closest relatives of amniotes (Laurin and Reisz 1995, 1997; Berman et al. 1997; Gauthier et al. 1988). Other analyses place the diadectomorphs as the sister group of the Synapsida alone, and therefore regard them as actual members of the Amniota (Panchen and Smith 1988; Berman 2000). Whatever the exact relationships might be, it is clear that Amniota was the one lineage within the complex radiation of early tetrapods that achieved a high level of terrestrial adaptation. Assuming that the protorothyridids and synapsids are indeed the two sister groups constituting a monophyletic Amniota, the structure of the hypothetical common ancestor of the two can be inferred from a comparison of the most primitive, Carboniferous members such as Hylonomus and Archaeothyris, respectively. It was a relatively small, superficially lizard-like animal, with a presacral body length of maybe 10 cm. The classic view of the evolution of the skull in amniotes was that the synapsid skull such as that of Archaeothyris evolved from an anapsid skull such as that of a protorothyridid by little more than opening of a temporal fenestra low down behind the orbit (e.g. Carroll 1970b). However, Kemp (1980b, 1982) noted that the protorothyridid skull also possessed uniquely derived characters, absent from the synapsids. Notably, the postorbital, supratemporal, and tabular bones were all reduced in size. The implication is that the common ancestral amniote skull must have combined the absence of a temporal fenestra with large postorbital, supratemporal, and tabular bones. This configuration is found in certain early tetrapods such as the limnoscelids and probably Westlothiana (Fig. 3.2(a)), both considered stemgroup amniotes. Significantly, in both these latter cases the posterior part of the skull appears to have retained at least some degree of flexibility between the skull table and the postorbital cheek region. This in turn is probably part of a type of cranial kinetism found in the most primitive of tetrapods, which is associated with suction feeding in water. Thus the hypothetical ancestral amniote was by inference as much an aquatic feeder as a fully evolved terrestrial one. The strengthening of the hind part of the skull that is necessary for an actively biting animal feeding on land must have evolved subsequently, differently, and therefore independently in the two respective amniote groups, explaining the difference in cranial structure between them. In addition to the repatterning of the temporal bones, other features of the evolution of the amniote skull are related to strengthening of the skull. The back of the skull, the occiput, was braced firmly against the cheek to resist the increasing forces generated by the increased jaw closing musculature, whilst elaboration of the tongue and hyoid apparatus in the floor of the mouth may well have occurred to assist in the capture and oral manipulation of food (Lauder and Gillis 1997). To judge by the homodont dentition of sharp teeth rounded in cross-section, insects and other invertebrates constituted the principal diet. There were new features of the postcranial skeleton of the ancestral amniote, although as Sumida (1997) shows, evolution of the characteristic amniote postcranial skeleton was quite gradual, with characters accumulating in several of the stem-amniote groups, and leading eventually to a highly terrestrially adapted form (Fig. 3.2(e)). Early on there was the evolution of the typical amniote vertebral structure in which the spool-shaped pleurocentral element and neural arch are firmly connected, and small ventral intercentra lie between adjacent pleurocentra. The limbs became relatively larger. The most characteristic postcranial feature acquired at the fully amniote level is the fusion of three of
Page 2 and 3: The Origin and Evolution of Mammals
Page 4 and 5: The Origin and Evolution of Mammals
Page 6 and 7: Preface This book arose from twin a
Page 8 and 9: For Mal /gosia with love and thanks
Page 10 and 11: Contents 1 Introduction The definit
Page 12 and 13: CHAPTER 1 Introduction There are ab
Page 14 and 15: transversely occluding molar teeth
Page 16 and 17: the Mesozoic mammals, is to do with
Page 18 and 19: a hierarchy of committees under the
Page 20 and 21: it means that a 200 Ma igneous rock
Page 22 and 23: een a more fundamental impact than
Page 24 and 25: Table 2.3 Classification of marsupi
Page 26 and 27: (a) (b) (c) humerus radius aquatic
Page 30 and 31: the ankle bones to form an astragal
Page 32 and 33: (b) (c) (a) Casea rutena Casea broi
Page 34 and 35: (Fig. 3.2(f)), is actually an ophia
Page 36 and 37: the first one is enlarged, often to
Page 38 and 39: Even at their initial appearance in
Page 40 and 41: (a) Nikkasaurus (b) (d) Reiszia (e)
Page 42 and 43: Nikkasauridae The family Nikkasauri
Page 44 and 45: has figured large in discussions of
Page 46 and 47: (c) Figure 3.9 (continued). Syodon
Page 48 and 49: a mixture of progressively more spe
Page 50 and 51: animal with interdigitating, but no
Page 52 and 53: (e) (a) Anomocephalus Ulemica (b) S
Page 54 and 55: mandibulae musculature. This, as in
Page 56 and 57: To date the postcranial skeleton of
Page 58 and 59: ecognised four subgroups, based mai
Page 60 and 61: the presence of a deep, longitudina
Page 62 and 63: collected from the Lystrosaurus Ass
Page 64 and 65: (a) (d) (c) (b) Leontocephalus V PA
Page 66 and 67: (a) (c) Lycosuchus Oliveria (d) EVO
Page 68 and 69: separate families. Lycosuchidae (Fi
Page 70 and 71: consist of a large labial cusp and
Page 72 and 73: Procynosuchus (d) Procynosuchus (a)
Page 74 and 75: They constitute the monophyletic gr
Page 76 and 77: 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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that contains the independent ances
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(b) (d) (a) Glasbius Alphadon (c) D
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elieved to be Late Cretaceous in ag
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(Fig. 6.5(c)). The dentition exhibi
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(d) Figure 6.6 (continued). Thylaco
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(a) (c) Caroloameghina and Procarol
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(a) (e) (d) Proargyrolagus Groeberi
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(a) (b) Djarthia Thylacotinga (c) (
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LIVING AND FOSSIL MARSUPIALS 211 M
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Extinct Notoryctemorphia At present
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(f) (g) Wakaleo Diprotodon optatum
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fossil mammals, which might help cl
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30 40 50 60 Figure 6.13 Southern Go
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the Diprotodontia also included gen
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1. Placentalia 2. Edentata 3. Epith
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effectively absent. However, increa
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Asioryctes (a) (b) (d) Cimolestes p
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and Prokennalestes, although it doe
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(a) Leptictidium Palaeoryctidans we
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(a) Purgatorius (c) are part of the
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(a) (d) (e) (g) Protoungulatum Meso
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(a) (f) (e) Hyopsodus Phenacodus (d
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Titanoides (pantodont) (a) (c) (b)
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(a) (b) (d) Trogosus (tillodont) Es
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Mioclaenus Paulacoutoia (didolodont
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their presence. The five orders may
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Xenungulata. Only two Late Palaeoce
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(a) (b) (d) (c) Oxyaena Patriofelis
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continuously growing, and form a gr
Page 264 and 265:
navicular facet, 19 or more thoraci
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(a) (c) Phosphatherium Numidotheriu
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coexist with other characters that
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The salient feature of Widanelfasia
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1 (a) 1. Perissodactyla 2. Titanoth
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(a) (b) BUNODONTIA or SUIFORMES SUI
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time, which suggests that it was on
Page 278 and 279:
condition. This particular combinat
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etween Primates, Dermoptera (colugo
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have postcranial adaptations for ar
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undoubtedly related at a supraordin
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indisputably to occur prior to the
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The Late Cretaceous mammal record i
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interordinal divergences in the Lat
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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
Page 300 and 301:
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
Page 336 and 337:
Index Note: Page numbers in italics
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Equoidea 262 Equus 262 Erethizon 28
Page 340 and 341:
Overkill hypothesis 289, 290 Oxyaen
Page 342:
Tulerpeton 14, 18 Tylopoda 264 Ukha
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The Origin and Evolution of Mammals - Moodle

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