The Origin and Evolution of Mammals - Moodle

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They constitute the monophyletic group Epicynodontia, which includes three basal families plus the advanced Eucynodontia. Galesauridae The earliest of these more progressive cynodonts is the third kind of cynodont known to have existed (b) (a) (c) Galesaurus EVOLUTION OF MAMMAL-LIKE REPTILES 63 in the Late Permian. Cynosaurus is from the Dicynodon Assemblage Zone of South Africa, and is a member of the family Galesauridae, which is much better known from Galesaurus itself (Fig. 3.20(c)), which comes from the overlying, earliest Triassic Lystrosaurus Assemblage Zone fauna. Galesaurids are judged to be the most basal of the epicynodonts Platycraniellus Thrinaxodon Figure 3.20 Basal epicynodonts. (a) Skull of Thrinaxodon liorhinus in four views. Skull length approx. 7 cm (Parrington 1946). (b) Postcranial skeleton of Thrinaxodon liorhinus. Presacral length approx. 35 cm (Carroll 1988, from Jenkins 1984). (c) Skull of Galesaurus planiceps in dorsal view, with enlarged upper postcanine teeth. Skull length approx. 8.5 cm (Parrington 1934 and Broom 1932). (d) Dorsal view of skull of Platycraniellus elegans. Skull length approx. 10 cm (Abdala Unpublished Manuscript). (d)
64 THE ORIGIN AND EVOLUTION OF MAMMALS on the grounds of an incomplete secondary palate. Their most distinctive feature is the structure of the postcanine teeth. Compared to those of Procynosuchus, these have lost the cingular cusps. There is also no anterior accessory cusp as occurs in several other Triassic cynodont families, but a well-developed posterior accessory cusp lies immediately behind the somewhat recurved main cusp. Perhaps galesaurids were adapted for dealing with a more robust form of insect prey. Thrinaxodontidae Thrinaxodon (Fig. 3.20(a) and (b)) is far the commonest and most studied cynodont of the Lystrosaurus Assemblage Zone fauna of the Karoo. It also occurs in the Fremouw Formation of Antarctica (Colbert 1982). Structurally Thrinaxodon is the same grade as Galesaurus, which is to say intermediate in a number of its features between Procynosuchus on the one hand and the eucynodonts to follow. It was somewhat smaller than Procynosuchus, and the postcanine teeth were reduced in number. The more posterior, molariform postcanines have a sharp main cusp plus an anterior and a posterior accessory cusp in line with it, which developed from the enlarged end members of the row of cingulum cuspules along the internal base of the tooth. The dentary bone is relatively larger, and its coronoid process rises right up into the temporal fenestra; the adductor fossa has expanded to occupy most of the external surface of the dentary behind the tooth row. The temporal fenestra has enlarged considerably compared to Procynosuchus, and the zygomatic arch was much deeper and more robustly built, and bowed dorsally, indicating the presence of a substantial masseter muscle. There are several significant differences in the postcranial skeleton compared to Procynosuchus, most conspicuously the appearance of large costal expansions on the hind, proximal part of the ribs, each of which overlaps the one behind and bears a strong ridge for muscle attachment. There are also accessory articulations between adjacent vertebrae, with a peg below each postzygapophysis fitting into a groove below the prezygapophysis of the next vertebra behind. The functional significance of this arrangement of the axial skeleton is obscure. Jenkins (1971b) believed that it was a method for more effectively applying muscle forces causing lateral bending of the vertebral column; Kemp (1980a), in contrast, proposed that the effect would be quite the opposite by making the column more rigid. At any event, a full set of costal plates is evidently the primitive condition for Triassic cynodonts generally, and they are variously reduced or completely lost by the Middle and Upper Triassic groups. The limbs of Thrinaxodon were probably approaching mammalian in pose, particularly the hindlimb where the knee was evidently turned well forwards. The tail is reduced, indicating the increased reliance on muscles from the ilium and body fascia for the power stroke of the stride. Platycraniellidae There is a third well-established genus of Lystrosaurus Assemblage Zone cynodont, which is Platycraniellus (Abdala unpublished manuscript). It is remarkable for having an extremely short snout and broad temporal fenestrae (Fig. 3.20(d)). In fact, comparatively it has the widest skull of any cynodont. The secondary palate is complete and extends posteriorly as far as the end of the tooth rows, a feature characteristic of later, more advanced forms. Unfortunately, few details of the dentition or the structure of the lower jaw are clear in the one reliably identified specimen. It may be that Platycraniellus is an aberrant basal member of the more advanced cynodont taxon Eucynodontia. Eucynodontia All the remaining cynodonts form a monophyletic group Eucynodontia, in which there has been further evolution of the temporal fenestra, lower jaw, and by inference the jaw musculature. The dentary has increased in relative size to such an extent that the postdentary bones are reduced to a small, vertically oriented compound sheet or rod of bones set into a recess occupying the medial face of the dentary. The coronoid process rises right up to the level of the top of the sagittal crest, there is a large angular process ventrally, and an articular process posteriorly that reaches towards the jaw articulation. The hinge bones, articular bone at the hind end of the postdentary complex, and quadrate held in a recess in the squamosal are relatively minute.
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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
Page 24 and 25: Table 2.3 Classification of marsupi
Page 26 and 27: (a) (b) (c) humerus radius aquatic
Page 28 and 29: (a) Westlothiana Limnoscelis PO Wes
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 76 and 77: Although there is no mammal-like co
Page 78 and 79: Cynognathidae Cynognathus (Fig. 3.2
Page 80 and 81: (e) (f) Figure 3.22 (continued). Ma
Page 82 and 83: (c) (d) (a) (b) Kayentatherium EVOL
Page 84 and 85: Pachygenelus (e) (a) (c) Therioherp
Page 86 and 87: palatal, and orbitosphenoid bones,
Page 88 and 89: Wible and Hopson 1993). The interor
Page 90 and 91: published a cladogram based on rece
Page 92 and 93: 310-320 Ma. By this time, the great
Page 94 and 95: are forms such as Casea itself, var
Page 96 and 97: lakes and swamps in the low-lying l
Page 98 and 99: urrowing and subsisting on a diet o
Page 100 and 101: Eothyris Haptodus sphenacodontine B
Page 102 and 103: z (a) (c) a.pt.m. M B PO P P SQ P M
Page 104 and 105: (b) a.pt.m. temp.m. a.pt.m. temp.m.
Page 106 and 107: the dentary bone above the level of
Page 108 and 109: the therocephalian grade was not on
Page 110 and 111: A balance was also achieved in the
Page 112 and 113: Locomotion Ancestral amniote grade
Page 114 and 115: screw-shaped: the front part faces
Page 116 and 117: For the recovery phase, the relativ
Page 118 and 119: SC PRC p.i.f.i tr.min (c) dp.cr ect
Page 120 and 121: the therocephalian pelvis and hindl
Page 122 and 123: 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
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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
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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
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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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