The Origin and Evolution of Mammals - Moodle

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Pachygenelus (e) (a) (c) Therioherpeton (b) Riograndia Diarthrognathus Brasilodon Brasilitherium Figure 3.24 Tritheledontans. (a) Pachygenelus skull (Bonaparte et al. 2003, from Hopson, in prep). (b) Riograndia guaibensis skull in lateral view and lower jaw in medial view. Length of lower jaw approx. 3 cm (Bonaparte et al. 2001). (c) Skull as preserved of Therioherpeton cargnini in dorsal and lateral views. Skull length approx. 3 cm (Bonaparte and Barbarena 2001). (d) Lower jaw of Diarthrognathus in medial view. Jaw length approx. 5 cm (Crompton 1963). (e) Skull in lateral view, and upper dentition in lateral and occlusal views of Brasilodon quadangularis. Skull length approx. 2.2 cm (Bonaparte et al. 2003). (f) Brasilitherium riograndensis skull and lower jaw in lateral view, upper dentition in lateral view, and lower dentition in internal view. Estimated skull length approx. 2.4 cm (Bonaparte et al. 2003). (f) (d)
74 THE ORIGIN AND EVOLUTION OF MAMMALS reported. Gow (2001) has described some isolated bones of Pachygenelus, showing that the anterior edge of the scapula blade has everted and shifted posteriorly to a sufficient degree as to regard it as a true, mammalian scapula spine. The humerus and femur are very similar indeed to those of the basal mammal Morganucodon. The main character diagnosing the family Tritheledontidae is the dentition, which is quite specialised in some respects. It is best known in Pachygenelus (Gow 1980; Shubin et al 1991), where only two incisors are present in the upper and lower jaws (Fig. 3.24(a)). The canines are unique amongst non-mammalian cynodonts in that the lower one works against the antero-lateral rather than the inner side of the upper, a feature that is typical of mammals. There are seven postcanine teeth in both upper and lower jaws, with incipiently divided roots. The uppers are circular in crown view and have a single, dominant main cusp. An anterior and a posterior accessory cusp are present, offset to the inner side of the main cusp and connected by an internal cingulum. The lower teeth are slightly larger, laterally compressed, and the anteriorly positioned main cusp is followed by up to three accessory cusps along the line of the jaw. These also have an internal cingulum. One unexpected feature concerns the relative thickness of the enamel. In the occluding regions of the teeth it is thin and soon wears away, leaving the thicker enamel edges that surround the crown exposed as sharp cutting edges. The postcanine teeth of Diarthrognathus are essentially similar to those of Pachygenelus though differing in detail (Gow 1980). Chaliminia (Bonaparte 1980) is a poorly known form from the Upper Triassic of the Rio Grande do Sul in Brazil, but has upper postcanine teeth sufficiently similar to those of Pachygenelus for it to be regarded as a member of the Tritheledontidae. Riograndia (Bonaparte et al. 2001) is represented by several specimens of a very small form of skull from the same locality (Fig. 3.24(b)). It has a very peculiar dentition, but which is comparable to Pachygenelus in several respects. There are only three, procumbent upper incisors, of which the second is the largest, and also three lowers, but here the first one is much larger than the other two. The canines are small. Both the upper and lower postcanines are blade-like and bear up to nine cuspules arranged in line. Each tooth is then set at an angle to the line of the tooth row, a condition seen to a small extent in Pachygenelus but taken to extremes here. Presumably Riograndia is a specialised tritheledontid, perhaps adapted for a diet of softer invertebrates than insects. In addition to members of Tritheledontidae as diagnosed by the reduced incisors and the postcanine tooth structure, there are several small, superficially tritheledontid-like specimens from the Rio Grande do Sul, Brazil that have been described by Jose Bonaparte and his colleagues. Prozostrodon (Bonaparte and Barberena 2001) is a slightly larger form that is represented at present by the anterior half of a 7 cm long skull, with the lower jaw and a few fragments of the postcranial skeleton. It is primitive compared to all other tritheledontans in some respects, notably retention of small prefrontal and postorbital bones, although the postorbital bar is absent and the frontal bone does form the orbital margin as in tritheledontids. The lower jaw has a well-developed articular process of the dentary, but it is unknown whether contact between this bone and the squamosal occurred. The dentition of Prozostrodon lacks the derived characters of the members of the family Tritheledontidae. There are five upper and four lower simple incisors, followed by well-developed canines. The seven upper postcanines have up to four linearly arranged cusps and lack a cingulum. There are 10 lower postcanines, of which the more complex posterior ones have a small anterior accessory cusp, the main cusp, and two posterior accessory cusps all in line, and also a welldeveloped internal cingulum. They have a similar appearance to the postcanine teeth of Thrinaxodon and to the basal mammal Morganucodon. Bonaparte and Barberena (1975, 2001) described a very small, poorly preserved Rio Grande do Sul skull as Therioherpeton (Fig. 3.24(c)), which they regard as a member of a separate family Therioherpetontidae. Again the postorbital bar is lacking, but as in tritheledontids the postfrontal and postorbital bones have been lost completely and the zygomatic arch has the same very slender construction. The differences from tritheledontids are that the anterior orbital and interorbital region of the skull is more completely ossified by meeting of the frontal,
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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
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 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 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 130 and 131: ol.b (a) (b) cer.hem gorgonopsian t
Page 132 and 133: (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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The Origin and Evolution of Mammals - Moodle

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