characters (synapomorphies) (Mayr and Ashlock 1991; Brooks and McLennan 1991). Sister groups are derived from the same common ancestor. A major goal of cladistic analysis is the recognition of synapomorphies, the derived (homologous) characters. Convergent evolution can result in organisms possessing structurally analogous but not evolutionarily related characters (termed homoplasies). Cladograms should be considered as hypotheses of evolutionary relationships. Support for cladistic hypotheses increases with the number of synapomorphies used in a study (i.e., studies based on few characters can be misleading), and by the number of studies, based on different characters, that come to the same or similar conclusions.
Age information from fossils or calibrated molecular phylogenies is available for 27 families of North American freshwater fishes (Figure 2.3). One family, the lampreys (Petromyzontidae), likely dates to the Paleozoic, and 5 groups (bowfins, Amiidae; pikes, Esocidae; sturgeons, Acipenseridae; paddlefishes, Polyodontidae; and gars, Lepisosteidae) have been present since the Cretaceous Period of the late Mesozoic. The remaining 21 families all date within the Cenozoic. Although 6 of the 27 families (22%) were represented prior to the Cenozoic, considering the current number of species per family, the ancestors of only 1.8% of the North American fish fauna occurred earlier than the Cenozoic. Within the Tertiary Period of the Cenozoic, 11 families are represented in the Paleogene Period (Paleocene to Oligocene epochs), and the remaining 10 families are represented in the Neogene Period (Miocene to Pliocene epochs).
Paleogene families include the ictalurids, percopsids, clupeids, salmonids, moronids, hiodontids, catostomids, centrarchids, aphredoderids, umbrids, and cyprinids. Neogene families are represented by the goodeids, poeciliids, percids, cichlids, fundulids, cyprinodontids, cottids, gasterosteids, atherinopsids, and sciaenids. Although the second most speciose family of North American freshwater fishes, the Percidae, is known from fossils only from the Pleistocene, calibrated molecular phylogenies suggest a much earlier occurrence. The separation of darters from nondarter percids dates to 19.8 mya (Carlson et al. 2009) and within the darter genus Nothonotus, the age of the most recent common ancestor dates to 18.5 mya (Near and Keck 2005). Consequently, percids likely occurred in North America at least by the early Miocene (approximately 23 mya). Seventy-eight percent of the 27 major families were present in North America by the early Miocene (23–16 mya) and were thus affected by numerous geologic and climatic events of the late Tertiary.
FIGURE 2.3. The earliest representation of major fish families in North America based on the first occurrence of fossils or from calibrated molecular phylogenies. Because the earliest fossils represent a minimal age of origin, families could be much older. Within the Cenozoic, geologic ages refer to epochs; within the Mesozoic and Paleozoic, ages refer to periods. Numbers at the top of each column are the beginning age (mya) of each geologic age or period. Numbers after families indicate sources; gaps in fossil record are not shown.
SOURCES: 1. Carlson et al. (2009), 2. Cavender (1986), 3. Cavender (1991), 4. Grande (1982), 5. Grande (1984), 6. Grande (1999), 7. Grande and Bemis (1991), 8. Grande and Bemis (1996), 9. Grande et al. (2002), 10. Mateos et al. (2002), 11. Meyer and Lydeard (1993), 12. Miller (1981), 13. Murray (2001a), 14. Murray and Wilson (1996), 15. Myers (1966), 16. Near and Keck (2005), 17. Near et al. (2005), 18. Nelson (2006), 19. Webb et al. (2004), 20. Wilson and Williams (1992).
In western North America, a freshwater fauna dominated by teleosts first appeared by the late Paleocene, followed by the expansion of an essentially modern fauna by the Oligocene and Miocene (Minckley et al. 1986). The western fauna during the Eocene (56–34 mya) and Oligocene (34–23 mya) shared forms with an eastern fauna, including paddlefishes, gars, sturgeons, bowfins, salmon and trout, mooneyes, suckers, catfishes, troutperch, and pickerel (Grande 1984; Minckley et al. 1986; Grande and Lundberg 1988; Grande 1999). The Oligocene fauna included elements from the earlier fauna, such as mooneyes, salmon and trout, and pickerel, as well as from more recent groups, such as minnows, atherinopsids, pupfishes, topminnows, sticklebacks, bass and sunfishes, surfperches, and sculpin (Minckley et al. 1986). Of the nonteleosts, sturgeon are represented by extant western forms, but gars, paddlefishes, and bowfin are now absent from the western fauna.
Although ecologists, until recently, have tended to focus more on current faunas and less on historical aspects, knowledge of the varying ages of occupation of fish groups in North America is of paramount importance to our understanding of fish assemblages and the extent and duration of coevolutionary processes. In addition, recent studies have stressed the importance of incorporating information on evolutionary relationships of component species (i.e., phylogeny) into studies of community ecology (Webb et al. 2002).
As is evident from Figure 2.3 and the previous paragraphs, fish groups vary widely in their ages of occupation in North America. Consequently, the forces shaping the evolution of morphology, physiology, and behavior of species making up present-day assemblages are likely not to be found by only looking within the contemporary assemblage. Instead, selective pressures leading to various traits may date to earlier time periods and may not even include the present-day assemblage. As an example, assemblages that have included pike have changed over time since the Paleocene (65–56 mya), when pike would have been part of fish assemblages including osteoglossomorphs, percopsiforms, amiids, gonorynchids, lepisosteids, asineopids (now extinct), osmerids, clupeids, cyprinoids (possibly catostomids), and ictalurids (Wilson and Williams 1992). Although feeding and morphological specializations show little change in pike, the community relationships have since changed a great deal, consequently, and “major adaptations of pike evolved before modern predator-prey systems existed” (Wilson and Williams 1992).
Origins of North American Fish Families
As with differences in ages, North American fish families exhibit a variety of origins, including archaic groups and some more recent groups whose origins can be traced to Pangean and Laurasian faunas (Figure 2.4). Of the 50 North American fish families listed by Burr and Mayden (1992), half show a marine origin. In some groups the radiation from the marine environment into fresh water occurred early, as with the bowfin subfamily Amiinae (family Amiidae) that has occupied freshwater habitats in the Northern Hemisphere since the late Cretaceous, some 90 mya (Grande and Bemis 1999). The second-largest group has a North American origin (including those originating in old landmasses of Pangea or Laurasia), followed by groups originating in Central and South America and Eurasia (Figure 2.4).
FIGURE 2.4. General origins of North American fish families. Phylogenetic and/or fossil information generally does not allow enough resolution to determine modern continental origins listed as arising in Laurasia/Pangea.
SOURCES: 1. Berra (2001), 2. Briggs (1986), 3. Burr and Mayden (1992), 4. Cavender (1986), 5. Cavender (1991), 6. Collette and Banarescu (1977), 7. Echelle and Echelle (1992), 8. S. A. Foster et al. (2003), 9. Gilbert (1976), 10. Grande (1984), 11. Grande (1999), 12. Grande and Bemis (1991), 13. Grande and Bemis (1996), 14. Grande and Bemis (1998), 15. Grande and Bemis (1999), 16. Grande et al. (2002), 17. Hrbek and Larson (1999), 18. Miller and Smith (1986), 19. Moyle and Cech (2004), 20. Parenti (1981), 21. Patterson (1981), 22. G. R. Smith and Stearley (1989), 23. Wiley (1976), 24. Wilson and Williams (1992).
The 15 fish families containing 90% of the modern species have their origins in Eurasia (minnows and suckers); Central America (livebearers and topminnows); North America, including Pangean/Laurasian elements (catfishes, trouts and salmons, goodeids, sunfishes, and perches); the marine environment (New World silversides, pupfishes, sculpins, lampreys, herrings); and South America (cichlids). The histories of these groups are treated in more detail in the following section.
Numerically Dominant Families
Plate Tectonics, Ages, and Origins
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