The Origin and Evolution of Mammals - Moodle

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ol.b (a) (b) cer.hem gorgonopsian th. Probainognathus (e) 1 cm hyp Triconodon ol.b cer.hem. op.l. cerb. fl. ol.b pin pit cer.hem. cerb. cerb. fl. (c) ol.b. EVOLUTION OF MAMMALIAN BIOLOGY 119 pit pin. cer. hem. cerb. III IV VIII V VI VII IX XII X Procynosuchus (f) Kennalestes Figure 4.11 Brain reconstructions. (a) Kemp’s (1969b) reconstruction of a gorgonopsian brain in lateral view. (b) Quiroga’s (1980) reconstruction of the brain of the eucynodont Probainognathus. (c) Kemp’s (1979) reconstruction of the brain of the basal cynodont Probainognathus in dorsal view. (d) The same in lateral view, and in situ in the skull. (e) Simpson’s (1927) recnstruction of the brain of the Jurassic mammal Triconodon. (f) Kielan-Jaworowska’s (1986) reconstruction of the brain of the Cretaceous placental mammal Kennalestes in dorsal and lateral views. cerb, cerebellum; cer.hem, cerebral hemisphere; fl, flocculus; hyp, hypothalamus; ol.b, olfactory bulb; op.l, optic lobe; pin, pineal; pit, pituitary; th, thalamus. op.l. fl. (d)
120 THE ORIGIN AND EVOLUTION OF MAMMALS comparable-sized modern reptiles, and with no indication of the beginning of the enlargement of the forebrain that was later to dominate mammalian brains. Quiroga (1980) described the cranial cast of the Middle Triassic eucynodont Probainognathus (Fig. 4.11(b)). According to his interpretation, there actually was some expansion of the cerebrum and the beginning of the development of the neocortex. Even more extreme, Kemp (1979) reconstructed a much larger brain in the basal cynodont Procynosuchus, based on an acid-prepared skull (Fig. 4.11(c) and (d)). His interpretation starts with a confident reconstruction of the cerebellum, because the markings on the internal walls of the hind part of the braincase indicate that the cerebellum filled the cavity completely. Given that in all vertebrates the cerebrum is larger than the cerebellum, this gives a minimum size for the cerebrum that is substantially greater than Hopson’s and other’s tubular structure. Therefore the forebrain, although still relatively narrow as indicated by the impression of its dorsal surface, but must have been considerably deeper than other authors allow. At the maximum estimate possible, the brain volume would have been at the lower end of the size range for mammals. There is, however, little consensus about the evolution of the brain within the cynodonts, important a topic as it is. Kielan-Jaworowska (1986) inclined to the view that it was still very small compared to mammals, although accepting Quiroga’s (1980, 1984) interpretation that some enlargement had occurred within the group. Rowe (1996) also believed that little brain enlargement had occurred in cynodonts, and indeed that the neocortex did not develop significantly until much later, in the common ancestor of modern mammal groups. On the other hand, Allman (1999) accepted Kemp’s reconstruction of a considerably larger, and especially deeper brain for the group. What is beyond dispute, however, is that the earliest mammals themselves did have significantly enlarged brains. As shown by a famous endocast (Fig. 4.11(e)) of the Jurassic Triconodon (Simpson 1927), and by the reconstruction of the Morganucon brain by Kermack et al. (1981), and those of Cretaceous multituberculates (Fig. 5.12) and placentals (Fig. 4.11(f)) by Kielan-Jaworowska (1986), brain size in Mesozoic mammals lay within the lower part of the size range of the brains of living mammals. This represents an overall increase of some four or more times the volume of basal amniote brains, and presumably involved the evolution of the neocortex, the complex, six-layered surface of the cerebral hemispheres that is one of the most striking of all mammalian characters (Kielan- Jaworowska 1986; Allman 1999). Growth and development The ancestral pattern of growth of amniotes is described as indeterminate, because it is continuous throughout life and there is no absolute adult size. It is associated with polyphyodont tooth replacement, in which there are several to many successive replacements of each tooth. This process provides the necessary increasing size of teeth and length of tooth row as growth proceeds. In mammals, the growth is determinate, with a rapid phase of juvenile growth ending in adult size, after which no further growth takes place. This is associated with diphyodont tooth replacement, in which there is a single juvenile, deciduous, milk dentition, followed by a permanent adult dentition (e.g. Luckett 1993; Kielan-Jaworowska et al. 2004). The mammalian growth pattern is only possible with an extremely high rate of parental provision of nutrition to the young, in their case by lactation, although by comparison with the similar growth pattern found in birds, direct provision of foraged food can achieve the same end. Many direct studies of size ranges of specimens have revealed an indeterminate growth pattern in all non-mammalian synapsid groups (e.g. Abdala and Giannini 2000, 2002). The pattern of tooth replacement corresponds to this, for in all there is polyphyodonty, although a specialised version is present in the diademodontoid eucynodonts (Fig. 4.12(a)) in which the rate of replacement was reduced, and the anterior postcanines were not replaced as they were shed. The total tooth number was maintained by the addition of new teeth at the posterior end of the tooth row (Hopson 1971). However, this is related to the specialised form of the gomphodont teeth, which are designed for true, accurate occlusion between specific uppers and lowers, rather than reflecting the evolution of lactation or mammalian growth pattern.
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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
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collected from the Lystrosaurus Ass
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(a) (d) (c) (b) Leontocephalus V PA
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(a) (c) Lycosuchus Oliveria (d) EVO
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separate families. Lycosuchidae (Fi
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consist of a large labial cusp and
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Procynosuchus (d) Procynosuchus (a)
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They constitute the monophyletic gr
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Although there is no mammal-like co
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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
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 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
Page 162 and 163: adjacent lower molars. A small exte
Page 164 and 165: (a) (b) (d) P4 P4 Plagiaulax P4 Pau
Page 166 and 167: American Morrison Formation genus C
Page 168 and 169: a self-sharpening property. As the
Page 170 and 171: near parasagittal gait (Fig. 5.11(e
Page 172 and 173: pass through the birth canal. Relat
Page 174 and 175: (a) 1 (b) (d) me (c) me.d 3 styl st
Page 176 and 177: (a) (c) Henkelotherium Crusafontia
Page 178 and 179: 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
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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