The Origin and Evolution of Mammals - Moodle

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(c) (a) M 1 M 1 M 2 Steropodon M 2 M 3 M 3 (b) pa.d Obdurodon (e) me.d pr.d THE MESOZOIC MAMMALS 177 hyl.d hp.d (d) Monotrematum Teinolophos Figure 5.21 Fossil monotremes. Skull of Obdurodon dicksoni in (a) dorsal, ventral and lateral views. Skull length approx. 5.2. cm (after Musser and Archer 1998). (b) Lower molar in occlusal and lingual views. (c) Jaw fragment and molars 1–3 of Steropodon in occlusal lingual, and lateral view. Length of fragment approx. 2.9 cm (d) Fragment of lower jaw and occlusal view of molar tooth of Teinolophos trussleri. Max. length of fragment 3.6 cm (Rich et al. 2001. (e) Upper and lower molars in occlusal view, as preserved, of Monotrematum sudamericanum. (Pascual et al. 2002).
178 THE ORIGIN AND EVOLUTION OF MAMMALS of the tribosphenic molar tooth has agreed with simple evolutionary expectations, from the Middle Jurassic Amphitherium, through the Late Jurassic Peramus, to the Early Cretaceous aegialodontids and the fully expressed version in the various younger Cretaceous lineages. While not to be read literally as a sequence of ancestor-descendants, these forms do illustrate an approximate morphocline. Even the monotremes fit in well, with the Albian age of the earliest member, Steropodon, compatible with the derivation of the group from a basal tribosphenidan ancestor. This simple picture was seriously upset when Flynn et al. (1999) described Ambondro mahabo from the Middle Jurassic (Bathonian) of Madagascar (Fig. 5.22(a)). The single specimen consists of three teeth in a fragment of the dentary, which the authors interpret as the last premolar and the first two molars. The molars are remarkable for possessing a very large talonid, virtually the same size as the trigonid, in which respect they resemble even more than do aegialodontids the fully expressed tribosphenic molars of advanced members of the Tribosphenida, apart from one primitive respect: there are only two rather then three fully developed cusps on the otherwise completely basined talonid. Ambondro extends backwards the known temporal range of the tribosphenic tooth by some 25 Ma, which is equivalent to about 20% of its previous known history. Indeed, such a discovery seemed sufficiently improbable for there to be some doubt about the correctness of the dating, despite the apparently reliable correlation with fossils of undisputed Middle Jurassic age. Ambondro was also extremely unusual in being a Gondwanan Mesozoic mammal. Indeed, at the time of its description only two others were known. One was the monotreme Steropodon already mentioned. The other was Ausktribosphenos (Fig. 5.22(b)), an Early Cretaceous, Aptian age specimen consisting of a fragment of lower jaw bearing the posteriormost four postcanine. Rich et al. (1997) believed these to represent the last premolar and all three molars and therefore, despite several unusual characters of the teeth, they tentatively proposed that it was a placental mammal. This conclusion was promptly challenged by Kielan-Jaworowska et al. (1998) because of the primitive jaw structure, and unique feature of the molars. Rich et al. (1999) then went so far as to suggest that it was specifically an erinaceid placental. These three Cretaceous Gondwana mammals taken together are anomalous. As well as the surprisingly, and in the case of Ambondro almost absurdly early dates, the structure of the molar teeth does not conform as closely as might be expected to that of the Laurasian tribosphenidan forms. Luo et al. (2001a) addressed the issue by a detailed comparison of the three and pointed out that they share certain unique characters of the molar teeth (Fig. 5.22(d)). The last premolar is triangular but lacks a talonid, there is a cingulum wrapping around the anterior base of the molar, and the trigonid part of the cusp is relatively low. There are also certain minor characteristics of the lower jaw. On the basis of these admittedly quite limited characteristics, and also the Middle Jurassic age of Ambondro, they made the radical proposal that the tribosphenic type of molar tooth evolved on two independent occasions. One occurred in a lineage restricted to the southern continents of Gondwana, that they termed the Australosphenida, and it is represented today by the monotremes. The other occurred in a lineage restricted during the Mesozoic to the northern, Laurasian continents, is represented today by the marsupials and placentals, and is referred to by them as the Boreosphenida, although removal of a few fossil jaws plus the monotremes from the rest of the Tribosphenida does not really warrant a change of name for this taxon. The hypothesis of a dual origin of the tribosphenic tooth requires that at least one, and preferably both of the proposed convergent groups can be demonstrated to be related to known pre-tribosphenic mammals. The cladogram of Luo et al. (2001a, 2002; Kielan-Jaworowska et al. 2004) indicates that both the ‘Eutriconodonta’ and the basal therian group ‘Eupantotheria’ are related to the Tribosphenida. Regarding the Australosphenida, Luo et al. (2002) argued that the peculiar Chinese Shuotherium (Fig. 5.13(e) to (g)), with its pseudotalonid at the front of the lower molar teeth, is related to them. The characters supporting the proposal consist of little more than the form of what may or may not be the last premolar, and Averianov (2002) has strongly criticised it. It might be more convincing if Shuotherium was at least from a Gondwanan continent.
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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
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(e) (f) Figure 3.22 (continued). Ma
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(c) (d) (a) (b) Kayentatherium EVOL
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Pachygenelus (e) (a) (c) Therioherp
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palatal, and orbitosphenoid bones,
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Wible and Hopson 1993). The interor
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published a cladogram based on rece
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310-320 Ma. By this time, the great
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are forms such as Casea itself, var
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lakes and swamps in the low-lying l
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urrowing and subsisting on a diet o
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Eothyris Haptodus sphenacodontine B
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z (a) (c) a.pt.m. M B PO P P SQ P M
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(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
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
Page 180 and 181: Cretaceous, (Aptian or Albian) of M
Page 182 and 183: eautifully preserved placentals fro
Page 184 and 185: subsequent specimens revealed that
Page 186 and 187: Minimal divergence of tribosphenida
Page 190 and 191: (b) (a) (c) pa.d pr.d me.d Ambondro
Page 192 and 193: crown-group therians) is accepted b
Page 194 and 195: form of the tooth, must reflect sub
Page 196 and 197: of feasibility that a taxon of endo
Page 198 and 199: mammals, by creating environmental
Page 200 and 201: the 11 species of marsupial, of whi
Page 202 and 203: (d) (a) pa A Dasyuromorphia B C pr
Page 204 and 205: earing two huge claws on digits thr
Page 206 and 207: that contains the independent ances
Page 208 and 209: (b) (d) (a) Glasbius Alphadon (c) D
Page 210 and 211: elieved to be Late Cretaceous in ag
Page 212 and 213: (Fig. 6.5(c)). The dentition exhibi
Page 214 and 215: (d) Figure 6.6 (continued). Thylaco
Page 216 and 217: (a) (c) Caroloameghina and Procarol
Page 218 and 219: (a) (e) (d) Proargyrolagus Groeberi
Page 220 and 221: (a) (b) Djarthia Thylacotinga (c) (
Page 222 and 223: LIVING AND FOSSIL MARSUPIALS 211 M
Page 224 and 225: Extinct Notoryctemorphia At present
Page 226 and 227: (f) (g) Wakaleo Diprotodon optatum
Page 228 and 229: fossil mammals, which might help cl
Page 230 and 231: 30 40 50 60 Figure 6.13 Southern Go
Page 232 and 233: the Diprotodontia also included gen
Page 234 and 235: 1. Placentalia 2. Edentata 3. Epith
Page 236 and 237: 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
Page 318 and 319:
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
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
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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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