http://onlinelibrary.wiley.com/doi/10.1111/j.1472-4642.2001.00106.x/abstract
[justify]
Há evidências de registros fósseis que sugerem que gradientes latitudinais na diversidade taxonômica podem ser características invariantes no tempo , embora quase certamente não na mesma escala como o observado nos dias de hoje . É evidente agora que ambos os gradientes de latitude e longitude aumentaram dramaticamente na força através da era Cenozóica (ou seja, nos últimos 65 mio ) para se tornar mais pronunciada hoje do que em qualquer momento no passado geológico. Atuais gradientes de diversidade taxonômicas , tanto marinhos e em reinos terrestres , são sustentados pelas radiações tropicais de um número relativamente pequeno de clades ricos em espécies . O porquê de estas taxas especiais terem proliferadas durante o Cenozóico é incerto, mas pode ser que pelo menos parte da explicação envolve o fenômeno da escalada evolutiva. Esta é , em essência, uma teoria da diversificação biológica através de mecanismos de feedback evolutivas entre predadores e presas ; primeiro desenvolve uma vantagem adaptativa , e , em seguida, a outra . No entanto, também pode ter sido alguma forma de controle extrínseco no processo de diversificação tropical, e isso provavelmente foi centrada sobre o fenômeno da mudança climática global. Isso é especialmente verdade nos últimos 15 mio de anos. Vários eventos tardios no Cenozóico ( Neógeno ) vicariantes efetivamente dividiram os trópicos em uma série de centros de alta diversidade, ou focos . Tem sido sugerido que, na maior delas no reino marinho ( centro do Indo- Pacífico Ocidental ou IWP ) , padrões críticos de ilhas agiram como um modelo para especiação rápida durante os ciclos do nível do mar glacioeustatico . O mesmo processo ocorreu no Atlântico , Caribe e leste do Pacífico ( ACEP ) Centro , embora em menor escala . Diversidade terrestre Tropical também pode ter sido promovida por expansões e contrações rápidas alcancadas em conjunto com os ciclos glaciais (hipótese refúgio modificado ) . Estamos começando a perceber isso em uma seqüência integrada de eventos tectônicos de neugene e eventos climáticos de grande influência na formação de padrões de diversidade taxonômicas contemporâneos
INTRODUCTION
Inherent biases in the fossil record notwithstand-ing, there is now widespread agreement that global biodiversity has increased dramatically over the last 100 million years (my) (Fig. 1; Bambach, 1977; Valentine et al., 1978; Sepkoski et al., 1981; Vermeij, 1987; Signor, 1990; Benton, 1995, 1999). From approximately the mid-Cretaceous period onwards, the numbers of marine invertebrates, vascular land plants, insects, marine and non-marine vertebrates rose steeply to peak values at, or very close to, the present day. Following the K-T mass extinction event, there were particularly steep rises in each of these major taxonomic groups through the Cenozoic era (i.e. the last 65 my) (Benton, 1999). Although we still have much to learn about the biogeography of this dramatic latest Mesozoic and Cenozoic diversity increase, some important evidence has come to light recently to suggest that a disproportionate amount took place in tropical and low-latitude regions. This comes from a com-bination of studies on the fossil and living records and is such as to suggest that taxonomic diversity gradients must have steepened substantially over the same period of time. Not only may we be close to the maximum number of organisms that have ever lived on earth at the present day, but we may Molluscs comprise one of the largest groups of living marine invertebrate organisms, and both bivalves and gastropods have been instrumental in developing our concept of latitudinal diversity gradients on a global scale. Major regional syn-theses of bivalve gradients, incorporating data from both the northern and southern hemispheres, include those of Stehli et al. (1967), Flessa & Jablonski (1995, 1996) and Crame (2000a; 2000b); more detailed examinations of bivalve and gast-ropod gradients in both the Eastern Pacific and North Atlantic oceans have been presented by Taylor & Taylor (1977), Taylor et al. (1980) and Roy et al. (1994, 1995, 1996, 1998; 2000). In all
Fig. 2 Latitudinal diversity gradients in the northern hemisphere through geological time. Latitudinal/ palaeolatitudinal range is from the equator to 80N; gradients plotted are for numbers of genera. Data points and sources are as follows: Tournaisian (~360 Ma) brachiopods from Raymond et al., 1989, Fig. 4; Visean (~345 Ma) brachiopods from Raymond et al., 1989, Fig. 4; Tithonian (~150 Ma) bivalves from Crame, 2001; Maastrichtian (~74 Ma) bivalves from Raup & Jablonski, 1993, Fig. 1. Recent bivalves from database held by the author. N.B. Low equatorial values recorded for certain localities in both the Tithonian and Maastrichtian stages could have been influenced by both collection failure and poor preservation of fossils (Raup & Jablonski, 1993; Morris & Taylor, 2000; Crame, 2001).
cases these studies have detected very pronounced gradients of decreasing taxonomic diversity with increasing latitude. Northern hemisphere gradients are characterized by a very steep fall in values at the edge of the tropics, and thereafter a much gentler rate of decline (see below, Fig. 2). There is some evidence to suggest that southern hemi-sphere gradients may be subtly different in form (Flessa & Jablonski, 1995, fig. 1; Crame, 2000a, fig. 3a), although they are currently based on a substantially smaller database. In his taxonomic analysis of latitudinal gradi-ents, Crame (2000a) split the bivalve fauna into seven component clades (i.e. protobranchs, arcoids, mytiloids, pteriomorphs, lucinoids, heteroconchs and anomalodesmatans) (Fig. 3). When this is done, it is readily apparent that by far the steepest gradients occur in the geologically youngest (and largest) clade, the heteroconchs. The age of this clade (65 my) is derived from the median age of extremely rapidly at this time. These include two of the largest known bivalve families at the present day, the Veneridae (~500 living species) and the Tellinidae (~350 living species) (Crame, 2000a). Steep, equatorial–polar diversity gradients are also characteristic of marine gastropods (Fischer, 1960; Taylor & Taylor, 1977; Taylor et al., 1980; Roy et al., 1994, 1998). From an approximate total of 18 000–20 000 marine gastropod species, about 3000 can be assigned to the Archaeogastropoda clade (i.e. sensu Ponder & Lindberg, 1997) and 15 000 to the Caenogastropoda clade (i.e. Meso-gastropoda + Architaenioglossa + Neogastrapoda) (Boss, 1982). Both the Archaeogastropoda and Mesogastropoda (approx. 10 000 living species) have lower Palaeozoic origins (Signor, 1985), but the Neogastropoda (approx. 5000 living species) is very substantially younger and concentrated in tropical and low-latitude regions. Neogastropods show very strong latitudinal gradients at the present day and there is evidence to suggest that these are such as to heavily underpin those shown by gastropods as a whole (Taylor & Taylor, 1977; Taylor et al., 1980; Morris & Taylor, 2000). From probable Lower Cretaceous (Aptian; 124 my) origins, the neogastropods radiated extens-ively through the Late Cretaceous and Early Cenozoic. There is some evidence to suggest that this radiation commenced in extra-tropical regions, and by the Campanian–Maastrichtian there were slight reverse gradients, with more neogastropod taxa in the mid-latitudes (30–45) than lowest latitude regions (Taylor et al., 1980; Sohl, 1987). Nevertheless, by the Eocene more normal gradi-ents were established, and these were progressively strengthened through the Cenozoic era. Neogas-tropod taxa that are particularly common in the tropics at the present day include: Muricoidea (? ~500 species; Albian/Cenomanian origins, 97 my);
Mitridae (~400 species; Cenomanian- period (Crane & Lidgard, 1989, fig. 2). It must Turonian, ~90 my); Nassariidae (319 species; have gone on doing so throughout the Cenozoic Coniacian, 88 my); Coninae (~500 species, Thanetian, to produce the very strong latitudinal gradients 60 my); Terebridae (~300 species; Ypresian, in flowering plant diversity seen at the present 56 my); Volutidae (estimated 325–500 species, Cenomanian, 97 my) (Boss, 1982; Kohn, 1990; Tracey et al., 1993; Taylor, 1998)
An even more dramatic mid-Cretaceous–Cenozoic evolutionary radiation was that of the flowering plants, or angiosperms, in the terrest-rial realm. From an Early Cretaceous origin, angiosperms arose to become by far the most dominant plant group at the present day (Fig. 4a); with an estimated 230 000 species they comprise approximately 88% of all living plant taxa (Crane et al., 1995) and over 99% of extant seed plants (Magallón et al., 1999). A combination of macro-and micropalaeontological evidence indicates that this massive radiation in the northern hemisphere began in tropical and low-latitude regions, and then spread progressively northwards through the Albian–Maastrichtian stages of the Cretaceous period (Crane & Lidgard, 1989; Lidgard & Crane, 1990). This rise to dominance coincided with a modest reduction in the non-conifer gymnosperms (cycads, Bennettitales, seed ferns, etc.) and a much more dramatic decline in the free-sporing plants
[justify]
Há evidências de registros fósseis que sugerem que gradientes latitudinais na diversidade taxonômica podem ser características invariantes no tempo , embora quase certamente não na mesma escala como o observado nos dias de hoje . É evidente agora que ambos os gradientes de latitude e longitude aumentaram dramaticamente na força através da era Cenozóica (ou seja, nos últimos 65 mio ) para se tornar mais pronunciada hoje do que em qualquer momento no passado geológico. Atuais gradientes de diversidade taxonômicas , tanto marinhos e em reinos terrestres , são sustentados pelas radiações tropicais de um número relativamente pequeno de clades ricos em espécies . O porquê de estas taxas especiais terem proliferadas durante o Cenozóico é incerto, mas pode ser que pelo menos parte da explicação envolve o fenômeno da escalada evolutiva. Esta é , em essência, uma teoria da diversificação biológica através de mecanismos de feedback evolutivas entre predadores e presas ; primeiro desenvolve uma vantagem adaptativa , e , em seguida, a outra . No entanto, também pode ter sido alguma forma de controle extrínseco no processo de diversificação tropical, e isso provavelmente foi centrada sobre o fenômeno da mudança climática global. Isso é especialmente verdade nos últimos 15 mio de anos. Vários eventos tardios no Cenozóico ( Neógeno ) vicariantes efetivamente dividiram os trópicos em uma série de centros de alta diversidade, ou focos . Tem sido sugerido que, na maior delas no reino marinho ( centro do Indo- Pacífico Ocidental ou IWP ) , padrões críticos de ilhas agiram como um modelo para especiação rápida durante os ciclos do nível do mar glacioeustatico . O mesmo processo ocorreu no Atlântico , Caribe e leste do Pacífico ( ACEP ) Centro , embora em menor escala . Diversidade terrestre Tropical também pode ter sido promovida por expansões e contrações rápidas alcancadas em conjunto com os ciclos glaciais (hipótese refúgio modificado ) . Estamos começando a perceber isso em uma seqüência integrada de eventos tectônicos de neugene e eventos climáticos de grande influência na formação de padrões de diversidade taxonômicas contemporâneos
INTRODUCTION
Inherent biases in the fossil record notwithstand-ing, there is now widespread agreement that global biodiversity has increased dramatically over the last 100 million years (my) (Fig. 1; Bambach, 1977; Valentine et al., 1978; Sepkoski et al., 1981; Vermeij, 1987; Signor, 1990; Benton, 1995, 1999). From approximately the mid-Cretaceous period onwards, the numbers of marine invertebrates, vascular land plants, insects, marine and non-marine vertebrates rose steeply to peak values at, or very close to, the present day. Following the K-T mass extinction event, there were particularly steep rises in each of these major taxonomic groups through the Cenozoic era (i.e. the last 65 my) (Benton, 1999). Although we still have much to learn about the biogeography of this dramatic latest Mesozoic and Cenozoic diversity increase, some important evidence has come to light recently to suggest that a disproportionate amount took place in tropical and low-latitude regions. This comes from a com-bination of studies on the fossil and living records and is such as to suggest that taxonomic diversity gradients must have steepened substantially over the same period of time. Not only may we be close to the maximum number of organisms that have ever lived on earth at the present day, but we may Molluscs comprise one of the largest groups of living marine invertebrate organisms, and both bivalves and gastropods have been instrumental in developing our concept of latitudinal diversity gradients on a global scale. Major regional syn-theses of bivalve gradients, incorporating data from both the northern and southern hemispheres, include those of Stehli et al. (1967), Flessa & Jablonski (1995, 1996) and Crame (2000a; 2000b); more detailed examinations of bivalve and gast-ropod gradients in both the Eastern Pacific and North Atlantic oceans have been presented by Taylor & Taylor (1977), Taylor et al. (1980) and Roy et al. (1994, 1995, 1996, 1998; 2000). In all
Fig. 2 Latitudinal diversity gradients in the northern hemisphere through geological time. Latitudinal/ palaeolatitudinal range is from the equator to 80N; gradients plotted are for numbers of genera. Data points and sources are as follows: Tournaisian (~360 Ma) brachiopods from Raymond et al., 1989, Fig. 4; Visean (~345 Ma) brachiopods from Raymond et al., 1989, Fig. 4; Tithonian (~150 Ma) bivalves from Crame, 2001; Maastrichtian (~74 Ma) bivalves from Raup & Jablonski, 1993, Fig. 1. Recent bivalves from database held by the author. N.B. Low equatorial values recorded for certain localities in both the Tithonian and Maastrichtian stages could have been influenced by both collection failure and poor preservation of fossils (Raup & Jablonski, 1993; Morris & Taylor, 2000; Crame, 2001).
cases these studies have detected very pronounced gradients of decreasing taxonomic diversity with increasing latitude. Northern hemisphere gradients are characterized by a very steep fall in values at the edge of the tropics, and thereafter a much gentler rate of decline (see below, Fig. 2). There is some evidence to suggest that southern hemi-sphere gradients may be subtly different in form (Flessa & Jablonski, 1995, fig. 1; Crame, 2000a, fig. 3a), although they are currently based on a substantially smaller database. In his taxonomic analysis of latitudinal gradi-ents, Crame (2000a) split the bivalve fauna into seven component clades (i.e. protobranchs, arcoids, mytiloids, pteriomorphs, lucinoids, heteroconchs and anomalodesmatans) (Fig. 3). When this is done, it is readily apparent that by far the steepest gradients occur in the geologically youngest (and largest) clade, the heteroconchs. The age of this clade (65 my) is derived from the median age of extremely rapidly at this time. These include two of the largest known bivalve families at the present day, the Veneridae (~500 living species) and the Tellinidae (~350 living species) (Crame, 2000a). Steep, equatorial–polar diversity gradients are also characteristic of marine gastropods (Fischer, 1960; Taylor & Taylor, 1977; Taylor et al., 1980; Roy et al., 1994, 1998). From an approximate total of 18 000–20 000 marine gastropod species, about 3000 can be assigned to the Archaeogastropoda clade (i.e. sensu Ponder & Lindberg, 1997) and 15 000 to the Caenogastropoda clade (i.e. Meso-gastropoda + Architaenioglossa + Neogastrapoda) (Boss, 1982). Both the Archaeogastropoda and Mesogastropoda (approx. 10 000 living species) have lower Palaeozoic origins (Signor, 1985), but the Neogastropoda (approx. 5000 living species) is very substantially younger and concentrated in tropical and low-latitude regions. Neogastropods show very strong latitudinal gradients at the present day and there is evidence to suggest that these are such as to heavily underpin those shown by gastropods as a whole (Taylor & Taylor, 1977; Taylor et al., 1980; Morris & Taylor, 2000). From probable Lower Cretaceous (Aptian; 124 my) origins, the neogastropods radiated extens-ively through the Late Cretaceous and Early Cenozoic. There is some evidence to suggest that this radiation commenced in extra-tropical regions, and by the Campanian–Maastrichtian there were slight reverse gradients, with more neogastropod taxa in the mid-latitudes (30–45) than lowest latitude regions (Taylor et al., 1980; Sohl, 1987). Nevertheless, by the Eocene more normal gradi-ents were established, and these were progressively strengthened through the Cenozoic era. Neogas-tropod taxa that are particularly common in the tropics at the present day include: Muricoidea (? ~500 species; Albian/Cenomanian origins, 97 my);
Mitridae (~400 species; Cenomanian- period (Crane & Lidgard, 1989, fig. 2). It must Turonian, ~90 my); Nassariidae (319 species; have gone on doing so throughout the Cenozoic Coniacian, 88 my); Coninae (~500 species, Thanetian, to produce the very strong latitudinal gradients 60 my); Terebridae (~300 species; Ypresian, in flowering plant diversity seen at the present 56 my); Volutidae (estimated 325–500 species, Cenomanian, 97 my) (Boss, 1982; Kohn, 1990; Tracey et al., 1993; Taylor, 1998)
An even more dramatic mid-Cretaceous–Cenozoic evolutionary radiation was that of the flowering plants, or angiosperms, in the terrest-rial realm. From an Early Cretaceous origin, angiosperms arose to become by far the most dominant plant group at the present day (Fig. 4a); with an estimated 230 000 species they comprise approximately 88% of all living plant taxa (Crane et al., 1995) and over 99% of extant seed plants (Magallón et al., 1999). A combination of macro-and micropalaeontological evidence indicates that this massive radiation in the northern hemisphere began in tropical and low-latitude regions, and then spread progressively northwards through the Albian–Maastrichtian stages of the Cretaceous period (Crane & Lidgard, 1989; Lidgard & Crane, 1990). This rise to dominance coincided with a modest reduction in the non-conifer gymnosperms (cycads, Bennettitales, seed ferns, etc.) and a much more dramatic decline in the free-sporing plants