The Origin and Evolution of Mammals - Moodle

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separate families. Lycosuchidae (Fig. 3.17(a)) is a basal group of short, broad-snouted forms, and the longer snouted Scylacosauridae (Fig. 3.17(b)) are related to the rest of the therocephalians, which he refers to as Eutherocephalia. At any event, this paraphyletic primitive group of ‘pristerognathids’ consists of generally fairly large animals, with skull length of the order of 20–30 cm. As in the gorgonopsians, though to a lesser extent, the dentition is dominated by large upper and lower canine teeth. The number of upper incisor teeth varies from five to seven in different taxa, but there are always only three lower incisors. The postcanine dentition is better developed than in the gorgonopsians, although it does tend to be reduced to as few as five modest teeth in several genera such as Lycosuchus. These primitive therocephalian groups disappeared after the Tapinocephalus Assemblage Zone, coincidentally with the rise of larger sized, superficially very similar gorgonopsians. They were replaced in the later part of the Permian by a mixture of both small, generalised therocephalians, and some highly specialised new kinds. Among the specialists, the whaitsiids, such as the South African Theriognathus (Fig. 3.18(a)) and the Russian Moschowhaitsia, were relatively large animals. They retained well-developed incisors and canines, but the postcanine dentition was greatly reduced or completely absent. The snout is constricted behind the canines, where the palatal exposure of the maxilla forms a broad, heavily ridged and pitted surface that opposes a similarly broad, concave dorsal surface of the dentary bone; the postcanine dentition had evidently been replaced by directly opposing keratinised tooth plates (Watson and Romer 1956; Kemp 1972b). Other unique features of whaitsiids include a partial secondary palate formed by maxillary processes meeting the vomer, partial or complete loss of the paired suborbital fenestrae, closure of the interpterygoid vacuity, and a great broadening of the primitively rod-like epipterygoid connecting the palato-quadrate to the skull roof. All these new characters can be interpreted as devices for strengthening the skull against the action of its own jaw musculature (Kemp 1972b). Whaitsiids were probably highly specialised as hyaena-like scavengers, capable of crushing the bones of abandoned carcasses between nutcracker like jaws. Moscorhinus (Fig. 3.18(c)) was another fairly large form, about 25 cm in skull length. Here, the skull is EVOLUTION OF MAMMAL-LIKE REPTILES 57 very broad and low, with a short, massive snout and extraordinarily expanded vomer in the palate. Like whaitsiids, it too has tended to reduce the number and size of the postcanine teeth (Durand 1991). Euchambersia (Fig. 3.18(e)) may be a close relative, having a similarly broad, short-snouted skull. Uniquely in this genus there is an extraordinary, deep recess on either side of the snout, between the canine and the front of the orbit, the walls of which are covered in fine foramina. The canine tooth has a groove down its outer face indicating that Euchambersia possessed a pair of maxillary poison glands coupled to fangs for delivering venom. The postorbital bars and zygomatic arches are very weakly developed implying that the jaw musculature was poorly developed and the jaws therefore unable to deal with struggling live prey. Altogether, Euchambersia appears to have been a therapsid analogy of snakes. For the rest, therocephalians are small-sized, generalised carnivorous animals. The smallest ones were at one time referred to as ‘scaloposaurs’ (Fig. 3.17(d) and 3.18(b)), but Hopson and Barghusen (1986) abandoned this taxon because many and perhaps all of them were believed to be the juvenile individuals of a variety of genera. They erected in its place the taxon Baurioidea, of which the early Triassic, Lystrosaurus Assemblage Zone Oliveria (Fig.3.17(c)) is a typical, welldescribed example (Mendrez 1972; Kemp 1986). The skull is about 10 cm in length. There are six upper incisors, a modest canine, and a row of ten small postcanine teeth. A partial secondary palate has formed by contact between the maxillae and the vomer towards the front of the palate, which is continued posteriorly by a pair of ridges that presumably indicates the attachment of a soft secondary palate. The intertemporal roof is narrow and incipiently crested, while the zygomatic arches are slender and not flared laterally as occurs in gorgonopsians and cynodonts. The postcranial skeleton of an immature regisaurid (Fig. 3.17(d)) described by Kemp (1986) is that of a very slenderlimbed, agile creature with skeletal proportions comparable to a modern mammal. Several other very similar latest Permian and earliest Triassic baurioids are known that differ from Oliveria only in such details as the degree of development of the secondary palate (Hopson and Barghusen 1986),
58 THE ORIGIN AND EVOLUTION OF MAMMALS Theriognathus Moschorhinus Bauria and whether the postcanine teeth bear small additional cuspules or not. The small animal Bauria (Fig. 3.18(d)) is remarkable because of the convergence in tooth structure (a) (c) (d) (e) with the later herbivorous cynodont therapsids. The postcanine teeth are transversely widened and the uppers and lowers meet in true, direct occlusion. The crowns of both the uppers the lowers (b) Scaloposaurus Euchambersia Figure 3.18 Therocephalian diversity. (a) Skull of the whaitsiid Theriognathus. Skull length approx. 7.5 cm (Brink 1956a). (b) Skull in lateral and dorsal views, and enlarged view of lower post-canines of Scaloposaurus constrictus. Skull length approx. 10.5 cm (Mendrez-Carroll 1979). (c) Skull of Moschorhinus kitchingi in lateral and dorsal views. Skull length approx. 23 cm (Durand 1991). (d) Skull of Bauria cynops. Skull length approx. 12 cm (Brink 1963a). (e) Anterior palate of Euchambersia mirabilis (Mendrez 1975). recess recess
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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
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 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 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.
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
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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
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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
Page 330 and 331:
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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The Origin and Evolution of Mammals - Moodle

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