The Origin and Evolution of Mammals - Moodle

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the dentary bone above the level of the rest of the jaw, for increasing the attachment area of this newly enlarged temporalis muscle. The masseter muscle is the lateral component of the adductor mandibuli found in later evolutionary stages, where it takes its origin from an expanded zygomatic arch bounding the temporal fenestra laterally. It is possible that there was an incipient masseter muscle in therocephalians, but it would have been restricted to the posterior root of the zygomatic arch, and have inserted on part of the reflected lamina of the angular (Kemp 1972a). Even if it did exist, it could not have had an important functional role at this stage. A consequence of the very considerable increase in the size of the medial and posterior parts of the jaw-closing musculature is that there was a corresponding increase in the postero-medially directed component of its net force, that required a remarkable specialisation of the jaw articulation with farreaching consequences (Kemp 1972a, 1982). The articular bone of the lower jaw faces postero-medially and articulates with an antero-laterally facing condyle of the quadrate (Fig. 4.3(c)). This geometry resists to the tendency of the back of the jaw to be disarticulated by the postero-medial component of the jaw-closing force pulling it inwards. But to achieve this effect, the axis of the hinge joint has to be aligned obliquely to the transverse axis of the skull. As the right and left lower jaws are firmly attached at the symphysis, it would be impossible for the jaws to open without disarticulation between articulars and quadrates unless the latter were capable of adjusting their orientation. The nature of the attachment between the quadrate and the squamosal bone against which it lies allows exactly this to happen. The two are not sutured and the contacting surfaces are smooth and covered with cartilage in life, forming a mobile joint. The quadrate could rotate about a longitudinal axis which allowed the necessary adjustments during jaw opening and closing for the articulating surfaces of the articular and quadrate to remain fully in contact. Improbable as such a mechanism might seem at first sight, not only is it an intelligible mechanical adaptation for a therapsid whose jaw adductor musculature is concentrated internal and posterior to its insertion on the jaw, but it also helps to explain the extraordinary history of the jaw articulation EVOLUTION OF MAMMALIAN BIOLOGY 95 that was to follow from this stage. It was, indeed, this evolution of quadrate mobility that permitted the eventual evolution of the mammalian jaw and hearing mechanisms. Procynosuchian grade Within the cynodont grades that follow, all the mammalian features of the feeding mechanism reach their full expression step by step, some as further development of the incipient characters seen so far, others as innovations. The procynosuchian grade was a significant advance in a number of features. The dentition achieved the mammalian pattern of heterodonty (Fig. 3.19(a)). Simple incisors are followed by canines as in earlier stages. However the postcanine dentition has become the main region for food manipulation, with around a dozen teeth, divided into a series of simpler premolariform teeth with little more than a swelling around the base of the main cusp, and a series of more complex molariform teeth behind. In the latter there is a large main cusp and a lingual cingulum of small, but distinct accessory cusps around the base; for the first time, incipiently multicusped teeth had evolved, teeth that ultimately were to evolve into the array of highly elaborate, precisely occluding teeth that characterise the mammalian radiation. At this stage, there was no direct, precise occlusion between upper and lower postcanines, although the nature of the wear facets indicates that there was general, abrading contact. The function of the incisors and canines was to seize and ingest insects and other small prey. The postcanines, particularly the molariforms, masticated the food prior to swallowing. The effect of the accessory cuspules of the molariform teeth would have been particularly important when dealing with tough insect cuticle (Fig. 3.19(c)). As opposing teeth entered the material, they would become anchored by the cingulum, after which further relative movement between opposing teeth would tend to cause tearing of the stiff cuticle (Kemp 1979). Use of a dentition in this way requires a larger bite force than does crude disablement and tearing of prey with the anterior teeth, and it was provided by further increase in the size and effectiveness of the adductor musculature (Fig. 4.4(a)). The medial expansion of the temporal fenestra characteristic of
96 THE ORIGIN AND EVOLUTION OF MAMMALS mass (d) (a) (b) (c) temp. int add. temp.m M Chiniquodon mass.m T B R T B Procynosuchus Thrinaxodon o x mass.m sag int.add.m y M R M temp.m mass.m mass.m temp.m T temp.m zyg temp. Luangwa s.mass.m temp.m d.mass.m Figure 4.4 The jaw musculature of cynodonts. (a) Lateral and dorsal views of the skull and jaw musculature of Procynosuchus. (b) the same for Thrinaxodon. (c) the same for Chiniquodon (Probelesodon), with a coronal section through the temporal region. (d) Lateral view of the jaw musculature of Luangwa, with outline of the lower jaw showing the vectors of the masseter muscle (M), temporalis muscle (T), and reaction force generated at the teeth (B). The triangular of forces of these three is shown, and at the left, the balance in a transverse direction achieved by the temporalis muscle (temp) plus internal adductor muscle (int.add) acting medially and the masseter (mass) muscle acting laterally. (Kemp 1980a; 1982). d.mass.m, deep masseter muscle; int.add.m, internal adductor muscle; mass.m, masseter muscle; sag, sagittal crest; s.mass. m, superficial masseter muscle; zyg, zygomatic arch.
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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
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
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 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
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
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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
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
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cladogenesis in dasyurid marsupials
Page 320 and 321:
(eds) Evolution of Tertiary mammals
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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
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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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