The Origin and Evolution of Mammals - Moodle

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(a) (b) (c) humerus radius aquatic tetrapod would not be expected to lose its gills even if living in low-oxygen waters, because of the effectiveness of gills in nitrogen and carbon dioxide excretion. On this argument, only gill-less tetrapods would be expected to have been in the habit of spending at least periods of their life completely out of the water. ulna EVOLUTION OF MAMMAL-LIKE REPTILES 15 Acanthostega Ichthyostega stapes gill bars Figure 3.1 Early tetrapods. (a) Skull of Acanthostega gunnari in dorsal, ventral and lateral views, and lateral view showing position of branchial arches. Skull length up to 20 cm (Clack 2002) (b) Reconstruction of the skeleton, and the bones of the forelimb of Acanthostega gunnari (Coates 1996). (c) Skeleton of Ichthyostega. Length approx. 1 m (Coates and Clack 1995). Once into the Carboniferous, a substantial radiation of tetrapods commenced and there were lineages showing a wide range of respective degrees of terrestrial adaptation (Clack 2002). Many had secondarily reduced or even lost the limbs and developed streamlined bodies, while the great majority retained lateral lines. Although only
16 THE ORIGIN AND EVOLUTION OF MAMMALS demonstrable in the few cases where larval forms are known, presumably they mostly retained the anamniotic egg laid in water and hatching into a gilled, fully aquatic larval form. Evolutionary speculations concerning the origin of tetrapods, as for other major new kinds of organisms, have been dominated by the idea of preadaptation. This is defined as the process whereby a structure of an organism that is adapted for a particular function in a particular habitat, becomes co-opted for a different function in a different habit. In fact, this is not a very helpful concept, because characters such as limbs and lungs in pre-tetrapods evidently did not change their function on attaining land. Rather, they were adaptations for aspects of the environment that were common to both the shallow water and to the muddy bank alongside. It is more plausible to view the origin of tetrapods as a transition along an ecological gradient in which there are no abrupt barriers. To be adapted to shallow, lowoxygen water a vertebrate requires the capacity for substrate locomotion and air breathing, a feeding mechanism suitable for small terrestrial organisms falling in, and aerial sense organs. These same adaptations must exist in a vertebrate adapted to life on the muddy bank adjacent to the water. Even such apparently radical differences between the two habitats as loss of buoyancy, increased dryness, and exposure to heat are in effect gradual across the boundary insofar as an organism can ameliorate them by temporarily returning to the protection of the water. From this perspective, the radiation of early tetrapods consists of lineages adapted to various points along the water to land gradient. Within the context of the Carboniferous radiation of tetrapods, the lineage that evolved the most extreme terrestrial adaptations, to the extent that its members were eventually completely independent of free-standing water were the Amniota, represented today by the reptiles, birds, and mammals. The modern reptiles, lizards, snakes, crocodiles, and turtles, possess internal fertilisation and the cleidoic egg, greatly reduced skin permeability, a water-reabsorbing cloaca, and use of solid uric acid for excretion. Such physiological characters as these cannot normally be demonstrated in fossils, but fortunately the modern forms also possess a number of osteological characters that do permit a diagnosis of the group Amniota, so that exclusively fossil groups can be added. Laurin and Reisz (1995) list nine skeletal synapomorphies, including for instance the entry of the frontal bone of the skull into the orbital margin, a row of large teeth on the transverse flange of the pterygoid, absence of enamel infolding of the teeth, two coracoid bones in the shoulder girdle, and the presence of a single astragalus bone formed from fusion of three of the ankle bones. The earliest known possible amniote is Casineria (Paton et al. 1999), which comes from the Middle Carboniferous of Scotland. Unfortunately, only a partial postcranial skeleton is preserved, so its correct taxonomic attribution remains dubious. The earliest certain amniote fossils occur in the Upper Carboniferous (Middle Pennsylvanian) of South Joggins, Nova Scotia. Hylonomus and Paleothyris are found preserved in a remarkable way, entombed within approximately 315 Ma petrified lycopod tree stumps (Carroll 1969). They are relatively small forms with a body length of about 10 cm, and are members of a group Protorothyrididae (Fig. 3.2(b) and (e)), which is related to the diapsid and testudine reptiles (Carroll 1972; Laurin and Reisz 1995; Berman et al. 1997). Surprisingly perhaps, a second distinct group of amniotes appears at about the same time, characterised most significantly by the presence of a single opening low down in the cheek region of the skull. This is the synapsid version of temporal fenestration and is the most prominent, unambiguous hallmark of the Synapsida, the mammal-like reptiles and mammals (Fig. 3.2(c)). Carroll (1964) attributed some fragmentary remains from the same locality as Hylonomus to the synapsids, naming them Protoclepsydrops, although in his monograph on the pelycosaurs, Reisz (1986) was unable positively to confirm this conclusion. Be that as it may, there are indisputable pelycosaur synapsids (Fig. 3.2(f)) only very slightly younger than Hylonomus, namely Archaeothyris (Reisz 1972). There is no serious questioning of the monophyly of the amniotes, including both protorothyridids and synapsids, but the relationships of the group to other Carboniferous tetrapod taxa is presently a matter of intense debate and disagreement. Amongst proposed stem-group amniotes, the earliest and most basal is the poorly known Late Devonian
Page 2 and 3: The Origin and Evolution of Mammals
Page 4 and 5: The Origin and Evolution of Mammals
Page 6 and 7: Preface This book arose from twin a
Page 8 and 9: For Mal /gosia with love and thanks
Page 10 and 11: Contents 1 Introduction The definit
Page 12 and 13: CHAPTER 1 Introduction There are ab
Page 14 and 15: transversely occluding molar teeth
Page 16 and 17: 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 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 72 and 73: Procynosuchus (d) Procynosuchus (a)
Page 74 and 75: 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
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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
Page 150 and 151:
(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
Page 162 and 163:
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
Page 168 and 169:
a self-sharpening property. As the
Page 170 and 171:
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
Page 212 and 213:
(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
Page 242 and 243:
(a) Leptictidium Palaeoryctidans we
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(a) Purgatorius (c) are part of the
Page 246 and 247:
(a) (d) (e) (g) Protoungulatum Meso
Page 248 and 249:
(a) (f) (e) Hyopsodus Phenacodus (d
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Titanoides (pantodont) (a) (c) (b)
Page 252 and 253:
(a) (b) (d) Trogosus (tillodont) Es
Page 254 and 255:
Mioclaenus Paulacoutoia (didolodont
Page 256 and 257:
their presence. The five orders may
Page 258 and 259:
Xenungulata. Only two Late Palaeoce
Page 260 and 261:
(a) (b) (d) (c) Oxyaena Patriofelis
Page 262 and 263:
continuously growing, and form a gr
Page 264 and 265:
navicular facet, 19 or more thoraci
Page 266 and 267:
(a) (c) Phosphatherium Numidotheriu
Page 268 and 269:
coexist with other characters that
Page 270 and 271:
The salient feature of Widanelfasia
Page 272 and 273:
1 (a) 1. Perissodactyla 2. Titanoth
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(a) (b) BUNODONTIA or SUIFORMES SUI
Page 276 and 277:
time, which suggests that it was on
Page 278 and 279:
condition. This particular combinat
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etween Primates, Dermoptera (colugo
Page 282 and 283:
have postcranial adaptations for ar
Page 284 and 285:
undoubtedly related at a supraordin
Page 286 and 287:
indisputably to occur prior to the
Page 288 and 289:
The Late Cretaceous mammal record i
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interordinal divergences in the Lat
Page 292 and 293:
diversity on Earth (Janis 1993). Fu
Page 294 and 295:
effect of the surrounding sea. Trop
Page 296 and 297:
was high. It lasted from 5 to 3 Ma
Page 298 and 299:
and thus remain in their preferred
Page 300 and 301:
agreement about exactly when within
Page 302 and 303:
References Abdala, F. Redescription
Page 304 and 305:
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
Page 322 and 323:
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
Page 336 and 337:
Index Note: Page numbers in italics
Page 338 and 339:
Equoidea 262 Equus 262 Erethizon 28
Page 340 and 341:
Overkill hypothesis 289, 290 Oxyaen
Page 342:
Tulerpeton 14, 18 Tylopoda 264 Ukha
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