- Email: [email protected]
The elephant shall lie down with the elephant-shrew
Update
300
TRENDS in Ecology and Evolution
Vol.19 No.6 June 2004
The elephant shall lie down with the elephant-shrew Placental Mammals: Origins and Relationships of the Major Clades edited by Kenneth D. Rose and J. David Archibald. John Hopkins University Press, 2005. US$95.00 hbk (272 pages) ISBN 0 8018 8022 X
Adrian Friday University Museum of Zoology, Downing Street, Cambridge, UK, CB2 3EJ
For many years, the main groups of placental mammals (the orders, in formal terms) were each well known, but there was a lack of consensus about where the orders fitted in relationship to one another [1,2]. Biological colleagues outside the immediate field tended to assume that, partly perhaps because we are ourselves placental mammals, those relationships had long ago been worked out and were a stable component of received knowledge, no longer contended and, therefore, no longer exciting as a research area. That is not so, and I read through this large collection of chapters on the individual orders and their interrelationships with an increasing sense of optimism. Although it has mostly been there in the recent primary literature, being brought up against the collected evidence is exhilarating. Much recent progress has occurred as a result of comparative molecular analyses [3–5], although these have not been unanimous [6]. Placental Mammals achieves a balance between molecular work, on the one hand, and anatomical and palaeontological work, on the other. Influential figures of 20th-century studies of placental mammalian phylogenetics are fulsomely acknowledged, particularly W.K. Gregory and G.G. Simpson. It is indeed impressive just how much the pre-cladistic, pre-molecular figures of Gregory (a major contribution of his was published in 1910) and Simpson (a major contribution published in 1945) were able to contribute. Nevertheless, only during the past eight years or so has a fuller picture of the interrelationships of the orders of placental mammals come into focus. The previous multi-author volume [7] to consider a similar subject area was published (as the editors note in their introductory chapter to this new volume) in 1993. Perhaps there are those who would be more grudging about the progress made since then, but it does seem that this timely volume somehow represents that biological cliche´: a new synthesis. What are the reasons for the excitement and optimism? Well, first, the recent comparative molecular studies have partly confirmed and consolidated groupings of placental orders previously suspected on anatomical and palaeontological grounds. However, there have been surprises. I know of at least three doctoral students who began their projects under the convenient view that the order Insectivora (or Lipotyphla) was, as only quite recently constituted, monophyletic, and were galvanized to learn of Corresponding author: Adrian Friday ([email protected]). www.sciencedirect.com
a challenge to this assumption halfway through their work. Two families of lipotyphlans, the tenrecs of Madagascar and the golden moles of mainland Africa, were (delightfully) found to unite with a collection of superficially improbable bedfellows (aardvark, sirenians, hyraxes, elephants and elephant-shrews) in a grouping that has come to be known as the Afrotheria. The second major contribution of the recent molecular work was the support for a few superordinal bundlings of placental orders, with the reassignment of several individual orders to superorders that were different from the ones to which they had previously been tentatively assigned. For example, the bats (Chiroptera) had long been members of the Superorder Archonta, along with Primates, Dermoptera (flying lemurs) and Scandentia (tree shrews). A series of molecular studies, however, agreed in transferring the bats to a different collection of orders, together now named the Laurasiatheria. Four superordinal groupings have emerged: Xenarthra, Afrotheria, Laurasiatheria and Euarchontaglires. Only the Xenathra could really be described as ‘traditional’. One of the encouraging features of these groupings is that they also begin to make some zoogeographical sense [8]. Placental Mammals emerged as a result of a symposium that was part of the 2002 meeting of the Society of Vertebrate Paleontology. That such a complete treatment of uniformly high quality has emerged so swiftly is a tribute to the vision and dynamism of the editors, and a vindication of their choice of contributors. Each of what the editors refer to as ‘the standard 18 anatomically based orders of placental mammals’ is represented in the volume, either by a dedicated single chapter or in a chapter dealing with another, or several, orders to which it is related. Tensions are still palpable between the new molecular synthesis described here and the necessarily narrower, order-based, interests of several contributors. For example, in her chapter about the bats, Nancy Simmons notes the 17 morphological evolutionary innovations that appear to unite bats with flying lemurs, as a grouping within the Archonta, but she acknowledges that ‘Regardless, there is no molecular support for placing bats within Archonta’. Adjustment to the new ideas is going to involve simultaneous pain and pleasure for most of those involved. References 1 Benton, M.J. (1988) The relationships of the major group of mammals: new approaches. Trends Ecol. Evol. 3, 40 – 45 2 Novacek, M.J. et al. (1988) The major groups of eutherian mammals. In The Phylogeny and Classification of the Tetrapods, vol. 2: Mammals (Benton, M.J., ed.), pp. 31 – 71, Clarendon Press
Update
TRENDS in Ecology and Evolution
3 Springer, M.S. et al. (1997) Endemic African mammals shake the phylogenetic tree. Nature 388, 61– 64 4 Madsen, O. et al. (2001) Parallel adaptive radiations in two major clades of placental mammals. Nature 409, 610– 614 5 Murphy, W.J. et al. (2001) Molecular phylogenetics and the origins of placental mammals. Nature 409, 614 – 618 6 Liu, F-G.R. et al. (2001) Molecular and morphological supertrees for eutherian (placental) mammals. Science 291, 1786– 1789
Vol.19 No.6 June 2004
301
7 Szalay, F.S., et al. eds (1993) Mammal Phylogeny: Placentals, SpringerVerlag 8 Eizirik, E. et al. (2001) Molecular dating and biogeography of the early placental mammal radiation. J. Hered. 92, 212 – 219
0169-5347/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tree.2004.03.033
Putting animals in their place Environmental Physiology of Animals (2nd edn) by Pat Willmer, Graham Stone and Ian Johnston. Blackwell Scientific, 2004. US$99.95/£34.95 hbk (816 pages) ISBN 1405107243
Andrew Clarke British Antarctic Survey, High Cross, Madingley Road, Cambridge, UK, CB3 0ET
I can still recall from my undergraduate days a mind-numbing slog through the invertebrates, from coelenterates (as they then were) to hemichordates, which almost put me off biology for life. But then I was exposed to a wonderful little book [1], and suddenly realized why I found invertebrate animals so interesting. Here were animals moving, breathing and sensing their environment and, although each organism did things in its own way, there was also a deeper underlying theme of what today we would call unity in diversity. So, as a direct result of a charismatic text, which incidentally broke the mould that physiology was somehow divorced from ecology, I became a comparative biologist. As a PhD student, I then ventured into comparative physiology, where I encountered the classic texts from the fathers of the field C Ladd Prosser [2] and Knut Schmidt-Nielsen [3], and found that there was more to the way that organisms were built and functioned than Escherichia coli and rat liver. These classic texts have gone through several editions, but a few honourable exceptions apart [4], have tended to remain as the dominant force in comparative physiology for undergraduates. Even classic texts can date, however, and, most recently, the challenge has come from the first edition of Environmental Physiology of Animals. This quickly established itself as a major player, and is now proceeding to its second edition. So how does this new edition differ from the first? The answer is by an updated text, major new sections about excitable tissues and control systems, the addition of colour to the diagrams, and inclusion of a selection of pictures of representative habitats. The book has a tripartite structure. The first section covers some basic principles, including evolution, adaptation and scaling. The authors tackle the difficult question of what constitutes a stressful environment by a classification that depends on how far a given habitat deviates from the cool and stable marine environment that is believed to have harboured the origin of life. These sections Corresponding author: Andrew Clarke ([email protected]). www.sciencedirect.com
also represent a change from the traditional approach in recognizing that all species are not equal in the comparative context: unless phylogenetic history is explicitly included, then erroneous evolutionary conclusions might result. This topic is explored through a brief introduction to phylogenetic trees and outgroup analysis. These preliminary sections also introduce the topic of scaling as a tool in comparative analysis, and explore the role of timescale in understanding the process of physiological adjustment to environmental conditions. These introductory sections give the book a particular flavour, but their success depends on how well these themes have been integrated into the following two sections, which deal with the central issues of physiology and coping with the environment. My feeling is that generally they do so well. Scaling analyses permeate the book, and there is a strong phylogenetic context to most of the discussions and, although there are few formal analyses, this is usually down to the lack of data rather than intent. Given the importance of lizard thermal ecology to the evolution of phylogenetic ideas in physiology. Perhaps the authors missed a trick in not presenting this work in more detail. The sections covering physiology and environment form the main bulk of the book, and these are uniformly excellent. The depth of coverage is exemplary, the style is lucid and the diagrams exceptionally clear. The split into physiology and environment is nice, but it does lead to some duplication and it is not always clear why a particular topic fell into section or the other. Overall, however, I applaud the thought that has clearly gone into the approach, and it is refreshing to read a comparative physiology text that includes taxa such as sipunculids, ascidians and brachiopods. I also enjoyed the brief glimpses into other areas of enquiry, such as geological history, macroecology, life-history theory and the impact of humans. Although none of these are developed, there is indeed no room to do so; they do at least indicate to the thinking student that no field of enquiry is complete in itself. This book is large because it is thorough, and this makes it more of a reference than an introduction, but this second edition confirms its status as the first place I would go for
300
TRENDS in Ecology and Evolution
Vol.19 No.6 June 2004
The elephant shall lie down with the elephant-shrew Placental Mammals: Origins and Relationships of the Major Clades edited by Kenneth D. Rose and J. David Archibald. John Hopkins University Press, 2005. US$95.00 hbk (272 pages) ISBN 0 8018 8022 X
Adrian Friday University Museum of Zoology, Downing Street, Cambridge, UK, CB2 3EJ
For many years, the main groups of placental mammals (the orders, in formal terms) were each well known, but there was a lack of consensus about where the orders fitted in relationship to one another [1,2]. Biological colleagues outside the immediate field tended to assume that, partly perhaps because we are ourselves placental mammals, those relationships had long ago been worked out and were a stable component of received knowledge, no longer contended and, therefore, no longer exciting as a research area. That is not so, and I read through this large collection of chapters on the individual orders and their interrelationships with an increasing sense of optimism. Although it has mostly been there in the recent primary literature, being brought up against the collected evidence is exhilarating. Much recent progress has occurred as a result of comparative molecular analyses [3–5], although these have not been unanimous [6]. Placental Mammals achieves a balance between molecular work, on the one hand, and anatomical and palaeontological work, on the other. Influential figures of 20th-century studies of placental mammalian phylogenetics are fulsomely acknowledged, particularly W.K. Gregory and G.G. Simpson. It is indeed impressive just how much the pre-cladistic, pre-molecular figures of Gregory (a major contribution of his was published in 1910) and Simpson (a major contribution published in 1945) were able to contribute. Nevertheless, only during the past eight years or so has a fuller picture of the interrelationships of the orders of placental mammals come into focus. The previous multi-author volume [7] to consider a similar subject area was published (as the editors note in their introductory chapter to this new volume) in 1993. Perhaps there are those who would be more grudging about the progress made since then, but it does seem that this timely volume somehow represents that biological cliche´: a new synthesis. What are the reasons for the excitement and optimism? Well, first, the recent comparative molecular studies have partly confirmed and consolidated groupings of placental orders previously suspected on anatomical and palaeontological grounds. However, there have been surprises. I know of at least three doctoral students who began their projects under the convenient view that the order Insectivora (or Lipotyphla) was, as only quite recently constituted, monophyletic, and were galvanized to learn of Corresponding author: Adrian Friday ([email protected]). www.sciencedirect.com
a challenge to this assumption halfway through their work. Two families of lipotyphlans, the tenrecs of Madagascar and the golden moles of mainland Africa, were (delightfully) found to unite with a collection of superficially improbable bedfellows (aardvark, sirenians, hyraxes, elephants and elephant-shrews) in a grouping that has come to be known as the Afrotheria. The second major contribution of the recent molecular work was the support for a few superordinal bundlings of placental orders, with the reassignment of several individual orders to superorders that were different from the ones to which they had previously been tentatively assigned. For example, the bats (Chiroptera) had long been members of the Superorder Archonta, along with Primates, Dermoptera (flying lemurs) and Scandentia (tree shrews). A series of molecular studies, however, agreed in transferring the bats to a different collection of orders, together now named the Laurasiatheria. Four superordinal groupings have emerged: Xenarthra, Afrotheria, Laurasiatheria and Euarchontaglires. Only the Xenathra could really be described as ‘traditional’. One of the encouraging features of these groupings is that they also begin to make some zoogeographical sense [8]. Placental Mammals emerged as a result of a symposium that was part of the 2002 meeting of the Society of Vertebrate Paleontology. That such a complete treatment of uniformly high quality has emerged so swiftly is a tribute to the vision and dynamism of the editors, and a vindication of their choice of contributors. Each of what the editors refer to as ‘the standard 18 anatomically based orders of placental mammals’ is represented in the volume, either by a dedicated single chapter or in a chapter dealing with another, or several, orders to which it is related. Tensions are still palpable between the new molecular synthesis described here and the necessarily narrower, order-based, interests of several contributors. For example, in her chapter about the bats, Nancy Simmons notes the 17 morphological evolutionary innovations that appear to unite bats with flying lemurs, as a grouping within the Archonta, but she acknowledges that ‘Regardless, there is no molecular support for placing bats within Archonta’. Adjustment to the new ideas is going to involve simultaneous pain and pleasure for most of those involved. References 1 Benton, M.J. (1988) The relationships of the major group of mammals: new approaches. Trends Ecol. Evol. 3, 40 – 45 2 Novacek, M.J. et al. (1988) The major groups of eutherian mammals. In The Phylogeny and Classification of the Tetrapods, vol. 2: Mammals (Benton, M.J., ed.), pp. 31 – 71, Clarendon Press
Update
TRENDS in Ecology and Evolution
3 Springer, M.S. et al. (1997) Endemic African mammals shake the phylogenetic tree. Nature 388, 61– 64 4 Madsen, O. et al. (2001) Parallel adaptive radiations in two major clades of placental mammals. Nature 409, 610– 614 5 Murphy, W.J. et al. (2001) Molecular phylogenetics and the origins of placental mammals. Nature 409, 614 – 618 6 Liu, F-G.R. et al. (2001) Molecular and morphological supertrees for eutherian (placental) mammals. Science 291, 1786– 1789
Vol.19 No.6 June 2004
301
7 Szalay, F.S., et al. eds (1993) Mammal Phylogeny: Placentals, SpringerVerlag 8 Eizirik, E. et al. (2001) Molecular dating and biogeography of the early placental mammal radiation. J. Hered. 92, 212 – 219
0169-5347/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tree.2004.03.033
Putting animals in their place Environmental Physiology of Animals (2nd edn) by Pat Willmer, Graham Stone and Ian Johnston. Blackwell Scientific, 2004. US$99.95/£34.95 hbk (816 pages) ISBN 1405107243
Andrew Clarke British Antarctic Survey, High Cross, Madingley Road, Cambridge, UK, CB3 0ET
I can still recall from my undergraduate days a mind-numbing slog through the invertebrates, from coelenterates (as they then were) to hemichordates, which almost put me off biology for life. But then I was exposed to a wonderful little book [1], and suddenly realized why I found invertebrate animals so interesting. Here were animals moving, breathing and sensing their environment and, although each organism did things in its own way, there was also a deeper underlying theme of what today we would call unity in diversity. So, as a direct result of a charismatic text, which incidentally broke the mould that physiology was somehow divorced from ecology, I became a comparative biologist. As a PhD student, I then ventured into comparative physiology, where I encountered the classic texts from the fathers of the field C Ladd Prosser [2] and Knut Schmidt-Nielsen [3], and found that there was more to the way that organisms were built and functioned than Escherichia coli and rat liver. These classic texts have gone through several editions, but a few honourable exceptions apart [4], have tended to remain as the dominant force in comparative physiology for undergraduates. Even classic texts can date, however, and, most recently, the challenge has come from the first edition of Environmental Physiology of Animals. This quickly established itself as a major player, and is now proceeding to its second edition. So how does this new edition differ from the first? The answer is by an updated text, major new sections about excitable tissues and control systems, the addition of colour to the diagrams, and inclusion of a selection of pictures of representative habitats. The book has a tripartite structure. The first section covers some basic principles, including evolution, adaptation and scaling. The authors tackle the difficult question of what constitutes a stressful environment by a classification that depends on how far a given habitat deviates from the cool and stable marine environment that is believed to have harboured the origin of life. These sections Corresponding author: Andrew Clarke ([email protected]). www.sciencedirect.com
also represent a change from the traditional approach in recognizing that all species are not equal in the comparative context: unless phylogenetic history is explicitly included, then erroneous evolutionary conclusions might result. This topic is explored through a brief introduction to phylogenetic trees and outgroup analysis. These preliminary sections also introduce the topic of scaling as a tool in comparative analysis, and explore the role of timescale in understanding the process of physiological adjustment to environmental conditions. These introductory sections give the book a particular flavour, but their success depends on how well these themes have been integrated into the following two sections, which deal with the central issues of physiology and coping with the environment. My feeling is that generally they do so well. Scaling analyses permeate the book, and there is a strong phylogenetic context to most of the discussions and, although there are few formal analyses, this is usually down to the lack of data rather than intent. Given the importance of lizard thermal ecology to the evolution of phylogenetic ideas in physiology. Perhaps the authors missed a trick in not presenting this work in more detail. The sections covering physiology and environment form the main bulk of the book, and these are uniformly excellent. The depth of coverage is exemplary, the style is lucid and the diagrams exceptionally clear. The split into physiology and environment is nice, but it does lead to some duplication and it is not always clear why a particular topic fell into section or the other. Overall, however, I applaud the thought that has clearly gone into the approach, and it is refreshing to read a comparative physiology text that includes taxa such as sipunculids, ascidians and brachiopods. I also enjoyed the brief glimpses into other areas of enquiry, such as geological history, macroecology, life-history theory and the impact of humans. Although none of these are developed, there is indeed no room to do so; they do at least indicate to the thinking student that no field of enquiry is complete in itself. This book is large because it is thorough, and this makes it more of a reference than an introduction, but this second edition confirms its status as the first place I would go for