36
Y. Kumazawa et al.
gence of African and neotropical cichlids at the time of continental breakup,
actinopterygian vs. sarcopterygian divergence, and bony fish vs. chondrichthyan
divergence. An alternative but unlikely assumption of the cichlid divergence in the
Cenozoic caused clear inconsistency with the latter calibration points. All pairwise
distances among the examined perciform families exceeded those between African
and neotropical cichlids and diversification of the perciforms was estimated to be
substantially older than that deducible from the first occurrence evidence of the
corresponding fossil records. Thus, the explosive radiation of perciform families in
the early Cenozoic was not supported by the mitochondrial sequence data. Molecular methods are expected to provide new insights into macroevolutionary history of
vertebrates which has been established on the basis of fossil evidence.
1 Introduction
Teleosts are a modern group of fishes with well over 22000 living species which
are classified into 40 orders (Nelson 1994). They are characterized by various morphological characteristics with regard to the feeding and locomotor apparatus
(Gosline 1971; Carroll 1988; Benton 1997). Osteoglossomorphs (arowanas and
their relatives), Elopomorphs (eels, tarpons, and notacanths), Clupeomorphs (herrings and anchovies), and Euteleostei (the remaining teleosts) were recognized to
be four basal teleost groups (Nelson 1994). Paleontological records suggest that the
first teleosts (pholidophorids and ichthyokentemids) occurred in the early Late Triassic approximately 230 million years ago (MY A), and that various orders of
Tcleostei were diversified during Jurassic and Cretaceous times (Goody 1969; Benton
1993, 1997). Fossil records for euteleost orders start to occur only from the beginning of the Cretaceous (Benton 1993).
The predominant euteleostean order Perciformes, which contains 18 suborders,
148 families, and the largest number (>9000) of species of any vertebrate orders,
shows the greatest amount of morphological diversity (Nelson 1994). Perciforms
currently dominate in vertebrate ocean life and are the dominant fish group in
(sub )tropical freshwaters. Paleontological records suggest that perciforms originated in the early Late Cretaceous (approximately 90 MYA) and that many of
perciform families rapidly radiated in the Paleocene or early Eocene after the Cretaceousn'ertiary boundary (KIT boundary) at 65 MY A (Benton 1993; Carroll 1997).
These diversified perciforms contained a number of genera which look very much
like extant forms now dominating the marine vertebrate fauna (Carroll 1988). This
radiation appeared so explosive that it was occasionally compared to the apparently
explosive radiation of mammals at about the same time with a speculation that the
perciform radiation may have been related to global changes in climate or ecosystems that led to the extinction of most archaic actinopterygian groups that flourished throughout the Mesozoic (Carroll 1988).
In this study, molecular phylogenetic analyses were conducted in order to evaluate
the fossil-based history of perciform radiation in the early Cenozoic. We did not
Y. Kumazawa et al.
gence of African and neotropical cichlids at the time of continental breakup,
actinopterygian vs. sarcopterygian divergence, and bony fish vs. chondrichthyan
divergence. An alternative but unlikely assumption of the cichlid divergence in the
Cenozoic caused clear inconsistency with the latter calibration points. All pairwise
distances among the examined perciform families exceeded those between African
and neotropical cichlids and diversification of the perciforms was estimated to be
substantially older than that deducible from the first occurrence evidence of the
corresponding fossil records. Thus, the explosive radiation of perciform families in
the early Cenozoic was not supported by the mitochondrial sequence data. Molecular methods are expected to provide new insights into macroevolutionary history of
vertebrates which has been established on the basis of fossil evidence.
1 Introduction
Teleosts are a modern group of fishes with well over 22000 living species which
are classified into 40 orders (Nelson 1994). They are characterized by various morphological characteristics with regard to the feeding and locomotor apparatus
(Gosline 1971; Carroll 1988; Benton 1997). Osteoglossomorphs (arowanas and
their relatives), Elopomorphs (eels, tarpons, and notacanths), Clupeomorphs (herrings and anchovies), and Euteleostei (the remaining teleosts) were recognized to
be four basal teleost groups (Nelson 1994). Paleontological records suggest that the
first teleosts (pholidophorids and ichthyokentemids) occurred in the early Late Triassic approximately 230 million years ago (MY A), and that various orders of
Tcleostei were diversified during Jurassic and Cretaceous times (Goody 1969; Benton
1993, 1997). Fossil records for euteleost orders start to occur only from the beginning of the Cretaceous (Benton 1993).
The predominant euteleostean order Perciformes, which contains 18 suborders,
148 families, and the largest number (>9000) of species of any vertebrate orders,
shows the greatest amount of morphological diversity (Nelson 1994). Perciforms
currently dominate in vertebrate ocean life and are the dominant fish group in
(sub )tropical freshwaters. Paleontological records suggest that perciforms originated in the early Late Cretaceous (approximately 90 MYA) and that many of
perciform families rapidly radiated in the Paleocene or early Eocene after the Cretaceousn'ertiary boundary (KIT boundary) at 65 MY A (Benton 1993; Carroll 1997).
These diversified perciforms contained a number of genera which look very much
like extant forms now dominating the marine vertebrate fauna (Carroll 1988). This
radiation appeared so explosive that it was occasionally compared to the apparently
explosive radiation of mammals at about the same time with a speculation that the
perciform radiation may have been related to global changes in climate or ecosystems that led to the extinction of most archaic actinopterygian groups that flourished throughout the Mesozoic (Carroll 1988).
In this study, molecular phylogenetic analyses were conducted in order to evaluate
the fossil-based history of perciform radiation in the early Cenozoic. We did not