The Origin and Evolution of Mammals - Moodle

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Locomotion Ancestral amniote grade Amniote locomotion is compounded from several separate movements of the limbs and body. Lateral undulation of the vertebral column contributes a significant fraction of the overall stride length: as waves of contraction pass down alternate sides of the body, the limbs are passively protracted and retracted. Added to this, the limbs actively protract and retract relative to the vertebral column, which increases the length of the stride. The transversely oriented humerus and femur also undergo rotation about their long axes, which has the effect of shifting the foot forwards and backwards relative to the body. Finally, the limbs as a whole are extensible struts so the stride can be increased yet further by extension at the joints once the foot is behind the level of the limb girdle. The change from this design to that of mammals involved altering the relative contributions of these four elements of the stride. Lateral undulation and long-axis rotation of the propodials were lost, while active retraction–protraction, and extension of the limbs were retained and developed. Additionally, two new elements were added: movement of the shoulder girdle on the ribcage, and dorso-ventral bending of the lumbar region of the vertebral column. The reconstructions of the hypothetical ancestral stages of mammal-like reptiles illustrate much of how and by inference why this radical remodelling of the locomotor system occurred. No understanding of the functioning of locomotor systems, or the transition from primitive amniote to mammalian is possible without appreciating that in all non-specialised tetrapods the function of the forelimb differs in important respects from the hindlimb, which accounts for several differences in their design. The forelimb is primarily to maintain the front of the animal off the ground during locomotion, and produces virtually no net locomotor force, analogous to the wheel of a wheelbarrow. The humerus has a simple, predetermined stride pattern and there is about the same volume of protractor as retractor musculature. It is the hindlimb that generates the necessary thrust. Therefore, the hindlimb is the larger, movement of the femur is much less constrained, and the retractor musculature is far larger than the protractor musculature. EVOLUTION OF MAMMALIAN BIOLOGY 101 Sphenacodontine grade As reviewed by Kemp (1982), Romer’s (1922) classic reconstruction of the musculature and locomotor mechanism of the pelycosaur Dimetrodon is still the basis for the sphenacodontine-grade ancestor, although subsequent studies, especially of the joints, have added further detail. Vertebral column. A significant modification of the vertebral column towards the eventual mammalian condition occurred, even at this early stage in which otherwise the locomotor apparatus is little modified from the ancestral amniote. The articulating surfaces of the zygapophyses of adjacent vertebrae are no longer horizontal, but oblique in orientation. Even in more primitive pelycosaurs, such as ophiacodontids, the prezygapophyses face inwards at an angle of about 30º from the horizontal, while in Dimetrodon the angle is increased to about 45º. This indicates that the lateral undulation component of locomotion was reduced in pelycosaurs, and probably virtually abolished in the latter genus. The small size of the intercentra, small bones between the ventral margins of adjacent vertebrae, also relates to the reduction of mobility between adjacent vertebrae, and presumably the loss of lateral undulation permitted certain pelycosaurs to evolve hugely long neural spines. Otherwise, the axial skeleton (Fig. 4.5(a)) has changed little from a primitive amniote condition. Moveably attached and ventrally directed ribs occur all the way back to the pelvic region, with no abrupt distinction between dorsal and lumbar regions, indicating that prevention of the body from sagging while walking still depended on the intercostal muscles and tendons between the ribs, rather than on the specialised lumbar musculature that evolved later. Forelimb. The action of the forelimb of pelycosaurs was heavily constrained by the design of the shoulder and elbow joints. The pectoral girdle (Fig. 4.5(b)) is a massive structure. The clavicles and interclavicle together form a U-shaped arch around the thorax that would have prevented any extensive movements of the shoulder girdle relative to the ribcage. The scapula is very broad, and the coracoid plus procoracoid bones together form a broad ventral plate. The glenoid fossa is elongated from front to back and its articulatory surface is described as
102 THE ORIGIN AND EVOLUTION OF MAMMALS (a) (b) (e) (f) CLEI sc.hum.ant delt spc art.h art IC cap delt PRC SC sc.tric sgl.but art.h ent glen uln. art COR sup.cr sc.hum.ant ent U U R (c) (d) sc.hum.ant spc ect cap ol.pr dp cap.art sc.hum.ant spc (g) sbc.sc delt sc.tric sbc.sc H sc.hum.ant sc.tric cor.tric spc.sc lat.dor Figure 4.5 Pelycosaur-grade forelimb. (a) Lateral view of the sphenacodontine pelycosaur Sphenacodon. (b) Lateral view of the shoulder girdle of Dimetrodon. (c) The same with deep shoulder musculature. (d) The same with superficial shoulder musculature. (e) Dorsal, ventral and distal views of the left humerus, and (below) anterior and medial views of the upper part of the left ulna and radius. (g) The position of the humerus at the start and completion of a stride, in postero-lateral view. Kemp 1982, after Romer and Price 1940 and Jenkins 1971b. art, articulating surface; art.h, articular head; cap.art, articulating surface for capitulum of humerus; CLEI, cleithrum; COR, coracoid; cor.tri, coracoid slip of triceps muscle; delt, deltoideus muscle; dp, deltopectoral crest; ect, ectepicondyle; ent, entepicondyle; glen, glenoid fossa; IC, interclavicle; lat.dor, latissimus dorsi muscle; ol.pr, olecranon process; pect, pectoralis muscle; PRC, procoracoid; sbc.sc, subcoraco-scapularis muscle; SC, scapular; sc.hum.ant, scapulo-humeralis anterior muscle; sc.tric, scapular slip of the triceps muscle; sgl.but, supraglenoid buttress; spc, supracoracoideus muscle; sup.cr, supinator crest; uln.art, articulation for the ulna. pect
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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
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
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 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
Page 124 and 125: no significant novelties to what ha
Page 126 and 127: (a) (c) (e) (g) D D ex. au.m C tym
Page 128 and 129: (a) (c) (d) PMX (f) V n.turb mx.tur
Page 130 and 131: ol.b (a) (b) cer.hem gorgonopsian t
Page 132 and 133: (a) (b) (i) (ii) (iii) (iv) (v) a g
Page 134 and 135: cold stress, the part that usually
Page 136 and 137: conducted the experiment of wrappin
Page 138 and 139: mammals themselves that the enlarge
Page 140 and 141: elevation of maximum aerobic activi
Page 142 and 143: a mammal. The difficulty with all s
Page 144 and 145: collection, ingestion, and assimila
Page 146 and 147: were edaphosaurid and caseid pelyco
Page 148 and 149: CHAPTER 5 The Mesozoic mammals The
Page 150 and 151: (a) (d) AL condylar foramina are se
Page 152 and 153: evidence to relate the haramiyidans
Page 154 and 155: postcranial skeleton, and Graybeal
Page 156 and 157: side of the head can be in action a
Page 158 and 159: the lower molars is relatively high
Page 160 and 161: 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
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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
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Simpson, G.G. 1970. The Argyrolagid
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Thewissen, J.G.M. 1990. Evolution o
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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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