Integrative Zoology 2014; 9: 107–110
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doi: 10.1111/1749-4877.12088
EDITORIAL
Paleontology and evolution–part I Evolution is one of the central unifying concepts of natural history and modern science. Although it is well documented by many lines of evidence from a number of scientific disciplines (e.g. genetics, molecular biology, comparative anatomy, biogeography), its major support indeed comes from the fossil record, where the history of life can be seen unravelling through geological deep time. Organisms have modified their characteristics over time, and new taxa have incessantly appeared. Which mechanisms and causal factors have been shaping this multifaceted evolutionary history? These issues have long been addressed almost exclusively by biological science, where Paleontology played the fairly marginal role of witness of the truth of Evolution (Simpson 1944), although fossils contributed substantially to Darwin’s conceiving of his theory (Eldredge 2008) Paleontology, indeed, provides hints for deciphering the dynamic processes of evolution. Studies aimed at disclosing evidence from extinct organisms are now acknowledged to be of central significance to a better understanding of various evolutionary mechanisms. This is the reason why Paleontology, Biology and Evolution are now considered closely related and mutually dependent. Despite our knowledge of the Earth’s History has significantly progressed over the last decades, many intriguing and fascinating questions about the evolutionary history of the Biosphere still remain unaddressed. The theory of Evolution must keep pace with our improving knowledge about life’s history, in a never-ending cognitive process where Paleontology looks at the Present for a better understanding of ecosystem dynamics, and Biology looks at the Past for deciphering the pathways leading to Present ecosystems. In so doing, Integrative Zoology, a journal especially devoted to delve into neontological themes, dedicates this special issue to evolutionary aspects in a deep time perspective and related paleontological issues such as paleobiogeography and paleoecology as well as taxonomic principles. Intriguing is the target of the pa-
per authored by Buckeridge et al. (2014) which analyze some enigmatic calcareous conical fossils with no living equivalents, ascribed to the genus Waiparaconus. The problematic remains were first recorded from marine Paleocene–Eocene sequences of New Zealand in the early 1870s and then interpreted as cirripedes, anellids, rudists, or even inorganic structures, reflecting the difficulty to find morphologic traits of undisputable taxonomic significance. Such an example faces us with the problem of forcing problematic fossil remains into the pigeonholes of established classifications or rather accommodating them in a not better defined insertae sedis category. Buckeridge et al. (2014) chose the first option and finally classified Waiparaconus as a pennatulacean. Though based on sound data, such a decision might anyhow be questionable. Taxonomy is indeed central to both Paleontology and Biology. It is the indispensable foundation for any bioscientific study, as well as for paleobiogeographic reconstructions (Wilson 2004). The multifaceted analysis of the paleobiogeographic patterns of brachiopod faunas in South China before and during the first radiations of the Great Ordovician Biodiversification Event (GOBE) required the detailed preliminary analysis of key stratigraphic sections, as well as of their brachiopod fossil record (Zhan & Jin 2014). The study described the brachiopod faunal dynamics, together with tempo and mode of their radiation and dispersal. In particular, the paper drew attention to the role of tectonics in driving both onshore and offshore dispersal routes. The results obtained clearly indicate that in South China the paleogeographic dispersal of brachiopods was likely related to the evolution of the Qianzhong Arch, which could have “provided a diverse paleobatymetric gradient in the central part of the Upper Yangtze Platform” by possibly supplementing new niches (Zhan & Jin 2014, p. 135). The evolution of Qianzhong Arch, and the consequent perturbation of ecosystems, probably played a key role in the macroevolution of south Chinese marine taxa during the GOBE. The GOBE was a long period of strong increase
© 2014 International Society of Zoological Sciences, Institute of Zoology/ Chinese Academy of Sciences and Wiley Publishing Asia Pty Ltd
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in marine biodiversity worldwide. It was possibly triggered by the synergetic action of several geological and biological processes, whose positive feedbacks deeply affected the ecological structures of all marine ecosystems (e.g. Servais et al. 2010). The evolution of marine communities can be analyzed under 2 perspectives: the deep time dimension of the paleoecological modifications, as that involved by the GOBE, and the changes of their structure over short time scale. This approach was followed by Lirer et al. (2014) to monitor the climatic changes that occurred during the last 2000 years. With a high-resolution, integrated study of a super-expanded marine record from the SE Tyrrhenian Sea, the authors identify 5 major environmental changes (transition from the Roman period to the Dark Age, the Dark Age to the Medieval Classic Anomaly, the Medieval Classic Anomaly to the Little Ice Age, and the Maunder event and the period at ca. 1950–170 AD) marked by changes in the relative frequency of herbivorous vs carnivorous and opportunistic vs generalist planktonic foraminifera. Notable are 4 evident δ18O oscillations of Globigerinoides ruber (i.e. alternations of warm/wet and cold/dry events related to the Roman Period, the Dark Age, the Medieval Classic Anomaly, the Little Ice Age, and the Modern warm period), which match the 4 minima of solar activity known as Wolf, Sporer, Maunder and Dalton events. This issue also includes a number of papers devoted to taxa that lived on islands, from very large (Australia, Worthy et al. 2014) to small ones (Mallorca, Bover et al. 2014). Islands have long been recognized as laboratories for biological studies, as well as a precious source to the understanding of time and mode of Evolution and of the processes that determine global biotic diversity. The evolutionary modifications of endemic settlers are of great interest for evolutionary biologists, paleontologists, ecologists and biogeographers. Nonetheless there is heated debate about the general patterns, but also the causal mechanisms driving the evolution of island biota (see e.g. inter alios Benton et al. 2010; Köhler 2010; Millien 2011; Raia & Meiri 2011; Montgomery 2013). Most studies have focused on living species, whereas only a few added the historical information disclosed from the fossil record, even though the combined analysis of fossil and living species could evidence, at least in the case of mammals, how various processes operate together in an integrated fashion to shape the peculiar insular biota. Although insular mammals generally evolve inde-
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pendently from one another, some general patterns have nonetheless been described. The actual significance of parallel patterns and trends in functional structures in extinct insular mammals is discussed by van der Geer (2014), who analyzes body size trends, cranial and neurological changes, as well as changes in dentition and in postcranial elements over a large spectrum of Miocene to the Early Holocene insular species worldwide. Of particular interest the discussion on how distinguishing between apomorphies and plesiomorphies in endemic species when the mainland ancestral species is difficult to ascertain. Mistaking one for another can significantly complicate phylogenetical and taxonomical conclusions and obscure the evolutionary processes undergone by insular taxa. Parallel patterns and trends, which have been reckoned as ‘adaptations’ of insular mammals to ecologically similar environments (van der Geer 2014), have been frequently observed in phylogenetically related mammalian taxa. Artiodactyls offer notable examples. They include quite common and well-studied island settlers, though only few insular bovids have been the subject of much research. Despite the family Bovidae includes a large number of extinct and living species on islands located in different ecozones, a comprehensive overview of the evolutionary patterns of these insular ungulates was thus far missing. The study presented by Rozzi and Palombo (2014) suggests the possible existence of parallel evolutionary trends among insular Bovidae and adds support to the ‘island rule’. In particular, body size of fossil and extant insular bovids seems to be influenced by the insular community structure, the nature of available niches and the dynamics of ecological interactions. However, these factors operate in different ways on different islands, based on the characteristics of each island, the modes of dispersal and the timing of isolation of the island settlers. Because of the emphasis that the island rule puts on the body size modifications of insular mammals, the body size estimates of extinct species need to be most accurate. Moncunill-Solé et al. (2014) used regression equations devised for extant rodents to estimate the body masses of extinct species from Mediterranean and Canary Islands. The results of this study reveal the nature of the ecological pressures that drive the evolution of body size in insular rodents. Moncunill-Solé et al. (2014) suggest that resource availability, i.e. island area, is a key factor in determining rodent size in the absence of predators (e.g. Canariomys lineage on Canary
© 2014 International Society of Zoological Sciences, Institute of Zoology/ Chinese Academy of Sciences and Wiley Publishing Asia Pty Ltd
Editorial
Islands). In contrast, body sizes change less in the presence of specialized predators, as shown by the Balearic Hypnomys that evolved under the pressure of birds of prey (Aquila chrysaetos, A. dalberti, Haliaeetus albicilla, etc.), and especially of its direct natural enemy Tyto balearica. The ancestor of Hypnomys arrived on the Balearic islands during a second phase of sweepstake faunal dispersal that started at the Messinian Salinity Crisis, between 5.6 and 5.32 Ma ago. The lineage spread during the Plio–Pleistocene (Bover et al. 2014). Recent discoveries from Pliocene deposits in Mallorca and Menorca have been shedding new light on the structure and evolution of the Balearic paleofauna. In particular, the terrestrial vertebrates from the Mallorcan Early Pliocene deposits are morphologically relatively archaic and therefore at the beginning of their evolution in an isolated environment. Moreover, the presence of a remarkable number of reptiles in the Messinian–Early Pliocene fossil record of the Balearic Islands indicates subtropical climate conditions (Bover et al. 2014). Reptiles are a common component in a number of balanced to strongly impoverished insular faunas. Although the increase in size of insular reptiles is not actually follow a rule, ecological release, low predation and competition pressures in highly disharmonic assemblages could explain the gigantism of most endemic insular reptiles. The ‘gigantism’ of the crocodylian specimen collected by Dubois at Kali Gedeh (latest Early Pleistocene of Java, Indonesia) and described by Delfino and de Vos (2014) – who tentatively referred it to the genus Crocodylus – requires a different explanation. The specimen is part of the Trinil H.K. fauna, which is the second of the 4 successive faunal complexes of the Early to Middle Pleistocene Stegodon–Homo erectus Fauna. Because at that time Java was likely part of the mainland (e.g. van den Bergh et al. 2001) the large size of Kali Gedeh crocodilian cannot be the product of ‘insularity’ and related effects. Besides, it is worth noting that another extinct ‘giant’ crocodilian was the continental Crocodylus thorbjarnarsoni recorded from the Plio–Pleistocene deposits of Turkana Basin (Kenya). It was probably up to 7.5 m long and the largest Crocodylus known thus far (Brochu & Storrs 2012). Ontogenetic growth and adult size may be affected by environmental temperature. Nonetheless, although an intraspecific thermal cline in body size consistent with the Bergman rule has been documented in a variety of organisms some clear exceptions exist. Therefore, biologists are far
from reaching a consensus about the nature and mechanisms at the basis of the relationships between organismal growth and adult body size on one hand, and environmental temperature on the other. In particular, it is not clear whether or not the so-called ‘temperature-size rule’ (decreasing temperature increases final size, particularly in ectotherms), which is a property of some reptiles (e.g. Angilletta & Dunham 2003; Arendt 2011) also applies to fossil crocodylians. Delfino and de Vos (2014) wonder if the past reactions of crocodylians and other terrestrial ectothermic animals to the temperature changes would provide evidence to better quantify the impact of current climate change on the size and evolution of modern counterparts. The effects of climate and environmental change on faunal evolution is a topic that provokes the most heated debate in paleobiology and paleoecology. Ecologists and evolutionists have hotly disputed, for instance, the actual role of physical-environmental perturbations in evolutionary processes. The study on the phylogenetic relationships of the Australian Oligo–Middle Miocene Casuaridae Emuarius gidju (Worthy et al. 2014) may add hints to the debate. The paper provides a detailed analysis and description of the fossil record of the genus Emuarius from the Riversleigh deposits, which potentially span a period of about 10 million years. The research by Worthy et al. (2014) includes an analysis of the variation in the size of the specimens from the Riversleigh deposits, which is not correlated with site age but may be a very plastic character, driven by the variations in habitat and food availability. The most notable outcome of the study, however, results from the phylogenetic analysis that strongly supports a monophyly of casuariids inclusive of Emuarius. The phylogenetic analysis of the morphological data indicates that E. gidju is the sister taxon of Dromaius, and that Emuarius and Dromaius form a clade that is sister to Casuarius. Moreover, the small eyes and poorly-developed cursorial ability suggest that Emuarius was adapted to a habitat with dense vegetation. It was quite similar to the extant C. casarius than to D. novaehollandiae. After the evolutionary divergence of the emu-cassowary lineages, Dromaius evolved towards enhanced cursorality, although this was likely not the driving mechanism of the divergence (Worthy et al. 2014). All in all, the variety of papers included in the present volume highlights the complex interplay of palaegeography, climatic and environmental changes, and biotic interactions in shaping the multifaceted and intricate evolutionary history of organisms that led to the present day biodiversity and biogeographical setting. Paleontol-
© 2014 International Society of Zoological Sciences, Institute of Zoology/ Chinese Academy of Sciences and Wiley Publishing Asia Pty Ltd
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ogy and Evolutionary Biology appear mutually interrelated disciplines where the fossil record can both notably constrain the evolutionary history of the biosphere in a deep time perspective, and provide valuable hints to forecasting the direction of future evolutionary scenarios. Maria Rita Palombo Dipartimento di Scienze della Terra Sapienza Università di Roma Rome, Italy
REFERENCES Angilletta MJ Jr, Dunham AE (2003). The temperaturesize rule in ectotherms: simple evolutionary explanations may not be general. The American Naturalist 162, 332–42. Arendt JD (2011). Size-fecundity relationships, growth trajectories and the temperature-size rule for ectotherms. Evolution 65, 43–51. Benton MJ, Csiki Z, Grigorescu D et al. (2010). Dinosaurs and the island rule: the dwarfed dinosaurs from Haţeg Island. Palaeogeography, Palaeoclimatology, Palaeoecology 293, 438–54. Bover P, Rofes J, Bailon S et al. (2014). Late Miocene/ Early Pliocene vertebrate fauna from Mallorca (Balearic Islands, Western Mediterranean): an update. Integrative Zoology 9, 183–96. Brochu CA, Storrs GW (2012). A giant crocodile from the Plio–Pleistocene of Kenya, the phylogenetic relationships of Neogene African crocodylines, and the antiquity of Crocodylus in Africa. Journal of Vertebrate Paleontology 32, 587–602. Buckeridge JS, Campbell HJ, Maurizot P (2014). Unravelling the nature of Waiparaconus, a pennatulacean (Cnidaria: Octocorallia) from the Late Mesozoic–Early Cainozoic of the Southern Hemisphere. Integrative Zoology 9, 111–20. Delfino M, de Vos J (2014). A giant crocodile in the Dubois Collection from the Pleistocene of Kali Gedeh (Java). Integrative Zoology 9, 141–7. Eldredge N (2008). Paleontology and evolution. Evolution 62, 1544–6. Köhler M (2010). Fast or slow? The evolution of life history traits associated with insular dwarfing. In: Pérez-Mellado V, Ramon C, eds. Islands and Evolu-
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tion. Institut Menorquí d’Estudis Menorca, Spain, pp. 261–80. Lirer F, Sprovieri M, Vallefuoco M et al. (2014). Planktonic foraminifera as bio‐indicators for monitoring the climatic changes occurred during the last 2000 years in the SE Tyrrhenian Sea. Integrative Zoology, doi: 10.1111/1749-4877.12083 (in press). Millien V (2011). Mammals evolve faster on smaller islands. Evolution 65, 1935–44. Montgomery SH (2013). Primate brains, the ‘island rule’and the evolution of Homo floresiensis. Journal of Human Evolution 65, 750–60. Moncunill‐Solé B, Jordana X, Marín‐Moratalla N, Moyà‐Solà S, Köhler M (2014). How large are the extinct giant insular rodents? New body mass estimations from teeth and bones. Integrative Zoology 9, 197–212. Raia P, Meiri S (2011). The tempo and mode of evolution: body sizes of island mammals. Evolution 65, 1927–34. Rozzi R, Palombo MR (2014). Lights and shadows in the evolutionary patterns of insular bovids. Integrative Zoology 9, 213–28. Servais T, Owen AW, Harper DA, Kröger B, Munnecke A (2010). The great ordovician biodiversification event (GOBE): the palaeoecological dimension. Palaeogeography, Palaeoclimatology, Palaeoecology 294, 99–119. Simpson GG (1944). Tempo and Mode in Evolution (No. 15). Columbia University Press, New York, USA. van den Bergh GD, de Vos J, Sondaar PY (2001). The Late Quaternary palaeogeography of mammal evolution in the Indonesian Archipelago. Palaeogeography, Palaeoclimatology, Palaeoecology 171, 385– 408. van der Geer AAE (2014). Parallel patterns and trends in functional structures in extinct island mammals. Integrative Zoology 9, 167–82. Wilson EO (2004). Taxonomy as a fundamental discipline. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 359, 739. Worthy TH, Hand SJ, Archer M (2014). Phylogenetic relationships of the Australian Oligo–Miocene ratite Emuarius gidju Casuariidae. Integrative Zoology 9, 148–66. Zhan R, Jin J (2014). Early–Middle Ordovician brachiopod dispersal patterns in South China. Integrative Zoology 9, 121–40.
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doi: 10.1111/1749-4877.12088
EDITORIAL
Paleontology and evolution–part I Evolution is one of the central unifying concepts of natural history and modern science. Although it is well documented by many lines of evidence from a number of scientific disciplines (e.g. genetics, molecular biology, comparative anatomy, biogeography), its major support indeed comes from the fossil record, where the history of life can be seen unravelling through geological deep time. Organisms have modified their characteristics over time, and new taxa have incessantly appeared. Which mechanisms and causal factors have been shaping this multifaceted evolutionary history? These issues have long been addressed almost exclusively by biological science, where Paleontology played the fairly marginal role of witness of the truth of Evolution (Simpson 1944), although fossils contributed substantially to Darwin’s conceiving of his theory (Eldredge 2008) Paleontology, indeed, provides hints for deciphering the dynamic processes of evolution. Studies aimed at disclosing evidence from extinct organisms are now acknowledged to be of central significance to a better understanding of various evolutionary mechanisms. This is the reason why Paleontology, Biology and Evolution are now considered closely related and mutually dependent. Despite our knowledge of the Earth’s History has significantly progressed over the last decades, many intriguing and fascinating questions about the evolutionary history of the Biosphere still remain unaddressed. The theory of Evolution must keep pace with our improving knowledge about life’s history, in a never-ending cognitive process where Paleontology looks at the Present for a better understanding of ecosystem dynamics, and Biology looks at the Past for deciphering the pathways leading to Present ecosystems. In so doing, Integrative Zoology, a journal especially devoted to delve into neontological themes, dedicates this special issue to evolutionary aspects in a deep time perspective and related paleontological issues such as paleobiogeography and paleoecology as well as taxonomic principles. Intriguing is the target of the pa-
per authored by Buckeridge et al. (2014) which analyze some enigmatic calcareous conical fossils with no living equivalents, ascribed to the genus Waiparaconus. The problematic remains were first recorded from marine Paleocene–Eocene sequences of New Zealand in the early 1870s and then interpreted as cirripedes, anellids, rudists, or even inorganic structures, reflecting the difficulty to find morphologic traits of undisputable taxonomic significance. Such an example faces us with the problem of forcing problematic fossil remains into the pigeonholes of established classifications or rather accommodating them in a not better defined insertae sedis category. Buckeridge et al. (2014) chose the first option and finally classified Waiparaconus as a pennatulacean. Though based on sound data, such a decision might anyhow be questionable. Taxonomy is indeed central to both Paleontology and Biology. It is the indispensable foundation for any bioscientific study, as well as for paleobiogeographic reconstructions (Wilson 2004). The multifaceted analysis of the paleobiogeographic patterns of brachiopod faunas in South China before and during the first radiations of the Great Ordovician Biodiversification Event (GOBE) required the detailed preliminary analysis of key stratigraphic sections, as well as of their brachiopod fossil record (Zhan & Jin 2014). The study described the brachiopod faunal dynamics, together with tempo and mode of their radiation and dispersal. In particular, the paper drew attention to the role of tectonics in driving both onshore and offshore dispersal routes. The results obtained clearly indicate that in South China the paleogeographic dispersal of brachiopods was likely related to the evolution of the Qianzhong Arch, which could have “provided a diverse paleobatymetric gradient in the central part of the Upper Yangtze Platform” by possibly supplementing new niches (Zhan & Jin 2014, p. 135). The evolution of Qianzhong Arch, and the consequent perturbation of ecosystems, probably played a key role in the macroevolution of south Chinese marine taxa during the GOBE. The GOBE was a long period of strong increase
© 2014 International Society of Zoological Sciences, Institute of Zoology/ Chinese Academy of Sciences and Wiley Publishing Asia Pty Ltd
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in marine biodiversity worldwide. It was possibly triggered by the synergetic action of several geological and biological processes, whose positive feedbacks deeply affected the ecological structures of all marine ecosystems (e.g. Servais et al. 2010). The evolution of marine communities can be analyzed under 2 perspectives: the deep time dimension of the paleoecological modifications, as that involved by the GOBE, and the changes of their structure over short time scale. This approach was followed by Lirer et al. (2014) to monitor the climatic changes that occurred during the last 2000 years. With a high-resolution, integrated study of a super-expanded marine record from the SE Tyrrhenian Sea, the authors identify 5 major environmental changes (transition from the Roman period to the Dark Age, the Dark Age to the Medieval Classic Anomaly, the Medieval Classic Anomaly to the Little Ice Age, and the Maunder event and the period at ca. 1950–170 AD) marked by changes in the relative frequency of herbivorous vs carnivorous and opportunistic vs generalist planktonic foraminifera. Notable are 4 evident δ18O oscillations of Globigerinoides ruber (i.e. alternations of warm/wet and cold/dry events related to the Roman Period, the Dark Age, the Medieval Classic Anomaly, the Little Ice Age, and the Modern warm period), which match the 4 minima of solar activity known as Wolf, Sporer, Maunder and Dalton events. This issue also includes a number of papers devoted to taxa that lived on islands, from very large (Australia, Worthy et al. 2014) to small ones (Mallorca, Bover et al. 2014). Islands have long been recognized as laboratories for biological studies, as well as a precious source to the understanding of time and mode of Evolution and of the processes that determine global biotic diversity. The evolutionary modifications of endemic settlers are of great interest for evolutionary biologists, paleontologists, ecologists and biogeographers. Nonetheless there is heated debate about the general patterns, but also the causal mechanisms driving the evolution of island biota (see e.g. inter alios Benton et al. 2010; Köhler 2010; Millien 2011; Raia & Meiri 2011; Montgomery 2013). Most studies have focused on living species, whereas only a few added the historical information disclosed from the fossil record, even though the combined analysis of fossil and living species could evidence, at least in the case of mammals, how various processes operate together in an integrated fashion to shape the peculiar insular biota. Although insular mammals generally evolve inde-
108
pendently from one another, some general patterns have nonetheless been described. The actual significance of parallel patterns and trends in functional structures in extinct insular mammals is discussed by van der Geer (2014), who analyzes body size trends, cranial and neurological changes, as well as changes in dentition and in postcranial elements over a large spectrum of Miocene to the Early Holocene insular species worldwide. Of particular interest the discussion on how distinguishing between apomorphies and plesiomorphies in endemic species when the mainland ancestral species is difficult to ascertain. Mistaking one for another can significantly complicate phylogenetical and taxonomical conclusions and obscure the evolutionary processes undergone by insular taxa. Parallel patterns and trends, which have been reckoned as ‘adaptations’ of insular mammals to ecologically similar environments (van der Geer 2014), have been frequently observed in phylogenetically related mammalian taxa. Artiodactyls offer notable examples. They include quite common and well-studied island settlers, though only few insular bovids have been the subject of much research. Despite the family Bovidae includes a large number of extinct and living species on islands located in different ecozones, a comprehensive overview of the evolutionary patterns of these insular ungulates was thus far missing. The study presented by Rozzi and Palombo (2014) suggests the possible existence of parallel evolutionary trends among insular Bovidae and adds support to the ‘island rule’. In particular, body size of fossil and extant insular bovids seems to be influenced by the insular community structure, the nature of available niches and the dynamics of ecological interactions. However, these factors operate in different ways on different islands, based on the characteristics of each island, the modes of dispersal and the timing of isolation of the island settlers. Because of the emphasis that the island rule puts on the body size modifications of insular mammals, the body size estimates of extinct species need to be most accurate. Moncunill-Solé et al. (2014) used regression equations devised for extant rodents to estimate the body masses of extinct species from Mediterranean and Canary Islands. The results of this study reveal the nature of the ecological pressures that drive the evolution of body size in insular rodents. Moncunill-Solé et al. (2014) suggest that resource availability, i.e. island area, is a key factor in determining rodent size in the absence of predators (e.g. Canariomys lineage on Canary
© 2014 International Society of Zoological Sciences, Institute of Zoology/ Chinese Academy of Sciences and Wiley Publishing Asia Pty Ltd
Editorial
Islands). In contrast, body sizes change less in the presence of specialized predators, as shown by the Balearic Hypnomys that evolved under the pressure of birds of prey (Aquila chrysaetos, A. dalberti, Haliaeetus albicilla, etc.), and especially of its direct natural enemy Tyto balearica. The ancestor of Hypnomys arrived on the Balearic islands during a second phase of sweepstake faunal dispersal that started at the Messinian Salinity Crisis, between 5.6 and 5.32 Ma ago. The lineage spread during the Plio–Pleistocene (Bover et al. 2014). Recent discoveries from Pliocene deposits in Mallorca and Menorca have been shedding new light on the structure and evolution of the Balearic paleofauna. In particular, the terrestrial vertebrates from the Mallorcan Early Pliocene deposits are morphologically relatively archaic and therefore at the beginning of their evolution in an isolated environment. Moreover, the presence of a remarkable number of reptiles in the Messinian–Early Pliocene fossil record of the Balearic Islands indicates subtropical climate conditions (Bover et al. 2014). Reptiles are a common component in a number of balanced to strongly impoverished insular faunas. Although the increase in size of insular reptiles is not actually follow a rule, ecological release, low predation and competition pressures in highly disharmonic assemblages could explain the gigantism of most endemic insular reptiles. The ‘gigantism’ of the crocodylian specimen collected by Dubois at Kali Gedeh (latest Early Pleistocene of Java, Indonesia) and described by Delfino and de Vos (2014) – who tentatively referred it to the genus Crocodylus – requires a different explanation. The specimen is part of the Trinil H.K. fauna, which is the second of the 4 successive faunal complexes of the Early to Middle Pleistocene Stegodon–Homo erectus Fauna. Because at that time Java was likely part of the mainland (e.g. van den Bergh et al. 2001) the large size of Kali Gedeh crocodilian cannot be the product of ‘insularity’ and related effects. Besides, it is worth noting that another extinct ‘giant’ crocodilian was the continental Crocodylus thorbjarnarsoni recorded from the Plio–Pleistocene deposits of Turkana Basin (Kenya). It was probably up to 7.5 m long and the largest Crocodylus known thus far (Brochu & Storrs 2012). Ontogenetic growth and adult size may be affected by environmental temperature. Nonetheless, although an intraspecific thermal cline in body size consistent with the Bergman rule has been documented in a variety of organisms some clear exceptions exist. Therefore, biologists are far
from reaching a consensus about the nature and mechanisms at the basis of the relationships between organismal growth and adult body size on one hand, and environmental temperature on the other. In particular, it is not clear whether or not the so-called ‘temperature-size rule’ (decreasing temperature increases final size, particularly in ectotherms), which is a property of some reptiles (e.g. Angilletta & Dunham 2003; Arendt 2011) also applies to fossil crocodylians. Delfino and de Vos (2014) wonder if the past reactions of crocodylians and other terrestrial ectothermic animals to the temperature changes would provide evidence to better quantify the impact of current climate change on the size and evolution of modern counterparts. The effects of climate and environmental change on faunal evolution is a topic that provokes the most heated debate in paleobiology and paleoecology. Ecologists and evolutionists have hotly disputed, for instance, the actual role of physical-environmental perturbations in evolutionary processes. The study on the phylogenetic relationships of the Australian Oligo–Middle Miocene Casuaridae Emuarius gidju (Worthy et al. 2014) may add hints to the debate. The paper provides a detailed analysis and description of the fossil record of the genus Emuarius from the Riversleigh deposits, which potentially span a period of about 10 million years. The research by Worthy et al. (2014) includes an analysis of the variation in the size of the specimens from the Riversleigh deposits, which is not correlated with site age but may be a very plastic character, driven by the variations in habitat and food availability. The most notable outcome of the study, however, results from the phylogenetic analysis that strongly supports a monophyly of casuariids inclusive of Emuarius. The phylogenetic analysis of the morphological data indicates that E. gidju is the sister taxon of Dromaius, and that Emuarius and Dromaius form a clade that is sister to Casuarius. Moreover, the small eyes and poorly-developed cursorial ability suggest that Emuarius was adapted to a habitat with dense vegetation. It was quite similar to the extant C. casarius than to D. novaehollandiae. After the evolutionary divergence of the emu-cassowary lineages, Dromaius evolved towards enhanced cursorality, although this was likely not the driving mechanism of the divergence (Worthy et al. 2014). All in all, the variety of papers included in the present volume highlights the complex interplay of palaegeography, climatic and environmental changes, and biotic interactions in shaping the multifaceted and intricate evolutionary history of organisms that led to the present day biodiversity and biogeographical setting. Paleontol-
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Editorial
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ogy and Evolutionary Biology appear mutually interrelated disciplines where the fossil record can both notably constrain the evolutionary history of the biosphere in a deep time perspective, and provide valuable hints to forecasting the direction of future evolutionary scenarios. Maria Rita Palombo Dipartimento di Scienze della Terra Sapienza Università di Roma Rome, Italy
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