The Origin and Evolution of Mammals - Moodle

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Procynosuchus (d) Procynosuchus (a) EVOLUTION OF MAMMAL-LIKE REPTILES 61 (b) Dvinia Figure 3.19 (a) Skull of Procynosuchus delaharpaea in four views. Skull length approx. 11 cm (Kemp 1979). (b). Skull of Dvinia (Tatarivov 1968). (c) Action of postcanine teeth of Procynosuchus dismembering an insect. (d) Postcranial skeleton of Procynosuchus delaharpaea. Presacral length approx. 33 cm (Kemp 1980c). (c)
62 THE ORIGIN AND EVOLUTION OF MAMMALS have a more complex form. There is a single large, main cusp, at the inner base of which is a row of small, but very distinct cuspules. These teeth represent the first step towards the complex multicusped, occluding molar teeth that were eventually to play such a fundamental role in the radiation of mammals. At this stage, however, the upper and lower teeth did not even occlude directly, but appear merely to have increased the general tearing effect as they dealt with food such as insect cuticle (Fig. 3.19(c)). Several features of the skull and lower jaw indicate that there had been further elaboration of the jaw musculature beyond the stage found in the therocephalians, although still to a degree well short of advanced cynodonts and mammals. The temporal fenestra had expanded, both medially to the extent that there is now a deeper, vertical-faced sagittal crest, and laterally to create an outwardly bowed zygomatic arch. The latter is nevertheless still a relatively delicate structure. The lower jaw is comparably modified. The coronoid process has become broadened, and bears a depression on its lateral surface that indicates the first stage of the invasion of the lateral surface of the jaw by adductor musculature. The dentary being relatively enlarged in this way, the postdentary bone complex is relatively reduced in size, a trend to be continued right up to the mammals. Other changes in the skull of Procynosuchus include the development of a secondary palate in the roof of the mouth, although at this stage the paired extensions of the maxillae and palatals do not meet in the midline so the osseous secondary palate is incomplete; presumably it was completed by soft tissue. Despite these considerable modifications to the skull, the postcranial skeleton of Procynosuchus has progressed little beyond a basic therapsid condition (Fig. 3.19(d)). There is certainly very clear differentiation of the vertebral column into thoracic and lumbar regions, but the limb girdles illustrate the cynodont characteristics to only a small degree. In fact, the Zambian specimen (Kemp 1980c) shows unexpected specialisations indicating a semiaquatic, perhaps otter-like mode of life. The zygapophyses of the lumbar region of the vertebral column are extraordinarily broad and horizontally oriented. Uniquely among therapsids, they must have permitted very extensive lateral undulation of the hind region of the vertebral column. The tail is relatively long, with uniquely expanded haemal arches that suggest a laterally operated swimming organ. The limbs themselves are relatively short and the individual bones stout. The hind foot is not preserved, but the forefoot is broad and the individual bones flattened and poorly ossified. The only other postcranial skeleton attributed to Procynosuchus was described rather superficially by Broom (1948, as the genus Leavachia). This specimen lacks these highly distinctive specialisations of Procynosuchus and may actually belong to a different genus, one that was adapted for a fully terrestrial existence. Dvinia The only other cynodont of the same primitive grade as Procynosuchus is Dvinia (Fig. 3.19(b)) from the Russian Late Permian (Tatarinov 1968), for it also has a relatively small coronoid process and adductor fossa of the dentary, and relatively large postdentary bones. Indeed, it is even more primitive than Procynosuchus in certain details of its braincase such as a very limited contact between the prootic and the epipterygoid bones and a large post-temporal fossa (Hopson and Barghusen 1986). At the same time, however, Dvinia has much more elaborate molariform teeth. In both upper and lower jaws, there is a series of small, simple premolariform teeth, followed by the molariform teeth, each of which is expanded across the jaw so that the crown surface is roughly circular, and bears a complete ring of cuspules. Dvinia was similar in size to Procynosuchus and its diet can only be speculated upon. Perhaps it was an early cynodont herbivore, although certainly unrelated to the advanced herbivorous members of the group. Basal epicynodontia—middle-grade cynodonts All other cynodonts have progressed beyond the procynosuchian grade by enlargement of the coronoid process, and development of a more robust, and dorsally bowed zygomatic arch. There is a further reduction in the size of the quadrate, and the number of incisor teeth is reduced to four uppers and three lowers. The most distinctive feature of the postcranial skeleton is the presence of overlapping costal plates on the dorsal ribs.
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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
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 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 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 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
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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
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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
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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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