The Origin and Evolution of Mammals - Moodle

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To date the postcranial skeleton of Eodicynodon is incompletely known (Rubidge et al. 1994). However, it has been described in some detail for the small, relatively unspecialised dicynodont Robertia (King 1981b), which occurs in the Tapinocephalus Assemblage Zone, immediately overlying the Eodicynodon Assemblage Zone (Fig. 3.12(b)). There is no reason to doubt that Robertia had retained the ancestral form of dicynodont postcranial skeleton, which remained relatively conservative within the group (King 1988). The first strikingly unique feature is the occipital condyle of the skull, which is markedly trefoilshaped, unlike the kidney-shape of other therapsids. Kemp (1969a) showed that in dicynodonts it was part of a complex joint involving the atlas and the axis vertebrae that permitted rotation of the head about a longitudinal and a transverse axis, but by a mechanism sufficiently different in detail from that found in other therapsids, to indicate that it had an independent origin from the pelycosaur state. Robertia has a full-length ribcage, with no tendency to develop reduced, immobile lumbar ribs. The tail is very short. The limbs are short compared to therapsids generally, with humerus and femur longer than the respective lower limb bones. On the other hand, the limb girdles are relatively advanced, in the sense of developing mammal-like characteristics (see Chapter 4). The front edge of the slender scapula blade is everted and there is a very welldeveloped acromion process for attachment of the clavicle. The coracoid plate below the acromion process is reduced so that there is ample space for expansion of the supracoracoideus muscle from its primary site at the front of the coracoid to the anterior part of the internal surface of the scapula. Thus there appears to have been a precocious, independent development of a mammal-like ‘supraspinatus’ muscle. The pelvic girdle has an enlarged and anteriorly extended ilium coupled with reduction of the pubis, indicating that the ilio-femoralis muscle had expanded and was taking over the role of the presumably greatly reduced caudi-femoralis muscle in femoral retraction. Confirmation is offered by the very distinctive form of the femur, which bears a large trochanter major occupying about a third of the shaft behind the head, but lacks any sign of a fourth or internal trochanter. Finally, the feet are EVOLUTION OF MAMMAL-LIKE REPTILES 45 also precociously evolved. They are very short and the phalangeal formula is reduced to the mammalian condition of 2 : 3 : 3 : 3 : 3. Despite these superficially ‘advanced’ features, the mode of locomotion appears to have been relatively primitive. King (1981a, 1988) analysed in detail the locomotory mechanics of the later form Dicynodon trigonocephalus, and concluded that the forelimb could not have operated in anything other than a sprawling mode. The hind limb had a more complex action, with elements of both a sprawling and a more erect gait, but was not capable of the simple parasagittal gait of other progressive therapsids. The few adequately preserved fossil trackways of dicynodonts generally confirm King’s interpretation (Smith 1993; De Klerk 2003). They show a plantigrade foot, with a wide forelimb trackway, but a slightly narrower hindlimb trackway. However, the dicynodont postcranial skeleton can perhaps best be understood as adapted for digging, basically to collect food lying just below the surface of the ground, but in some specialised cases for active burrowing. The dicynodont radiation The anatomy and functioning of the skull as seen in Eodicynodon remained relatively conservative throughout the subsequent evolutionary radiation of the dicynodonts (Fig 3.13) although, as befits a highly successful, diverse, and widespread group, there is much detailed variation, associated with different diets and habitats, in the size and shape of the skull, the extent to which tusks and postcanine teeth were retained or even elaborated, and the form of the horny beak as inferred from the nature of the bony surfaces of the jaws supporting them. Increasing information about the diversity of the postcranial skeleton is accumulating and can be correlated with habitat, particularly in terms of different degrees of digging and burrowing ability (King 1988; Ray and Chinsamy 2003). Biogeographically, the dicynodonts are far and away best known as a consequence of the hundreds of specimens recovered from the Late Permian and Lower Triassic of the Karoo of South Africa and other parts of southern Africa. However, by the Triassic the group had a worldwide distribution, occurring in all continents, including Myosaurus
46 THE ORIGIN AND EVOLUTION OF MAMMALS E P K D Endothiodon Diictodon Pristerodon Aulacephalodon Figure 3.13 Phylogeny of the main groups of Permian dicynodonts, based on King (1988). D-Diictodontoidea; E-Endothiodontoidea; K-Kingorioidea; P-Pristerodontoidea. and Lystrosaurus from Antarctica (Hammer and Cosgriff 1981; Cosgriff et al. 1982) and a couple of fragments of what is probably Lystrosaurus from Australia (King 1983; Thulborn 1983). Eodicynodon Kingoria Cistecephalus Dicynodon Oudenodon The complex phylogenetic interrelationships of the dicynodonts are not well understood. The pioneering work of Gillian King and colleagues (Cluver and King 1983; King 1988, 1990; King and Rubidge 1993)
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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 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 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.
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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
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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
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
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Index Note: Page numbers in italics
Page 338 and 339:
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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