with which it is closely related, Amyzon was a fairly large-bodied fish. More derived species of suckers have tended toward smaller body sizes (G. R. Smith 1992). Catostomids occupied much of western North America and eastern Asia by the late Eocene, a time when the Asian and North America landmasses were connected via Beringia (Figure 2.5E) (Cavender 1986, 1991). Of the modern genera of suckers, Ictiobus occurred by the middle Miocene and Chasmistes by the late Miocene (Cavender 1986). Suckers are thought to have originated in Eurasia and then reached North America via the Pacific connection of Beringia (Figs. 2.4 and 2.5E) (Gilbert 1976; Briggs 1986; Burr and Mayden 1992; Berra 2001).
CENTRARCHIDAE (31 SPECIES) The centrarchids are endemic to North America and likely evolved there (Gilbert 1976; Burr and Mayden 1992). The earliest fossils of this primarily eastern North American family date from the Eocene epoch of northwestern Montana (ca. 45 mya) in drainages that flowed eastward from the continental divide (Cavender 1986). During this time, North America had separated from Europe but was still connected to Asia via Beringia (Figure 2.5E). Based on a fossilcalibrated molecular phylogeny, Near et al. (2005) estimated the age of the most recent common ancestor to the Centrarchidae to be 33.6 million years, providing another line of evidence supporting the Eocene age estimate for the group. Because the earliest fossils have not been linked to species, they could not be used in calibrating the molecular phylogeny. By the Miocene, modern genera including Lepomis, Micropterus, and Pomoxis were well represented and, especially by the early Pleistocene, centrarchids had become a dominant element in the North American freshwater fish fauna (G. R. Smith 1981). Ages of modern species, based on molecular phylogenies, are 8–11 million years for Micropterus, at least 11 million years for Pomoxis, and 14 million years for Lepomis (Near et al. 2003, 2005). Centrarchids also were widespread by the middle Miocene, based on fossils found west of the continental divide and including fossils of the extant western genus Archoplites (Cavender 1986).
CYPRINIDAE (297 SPECIES) The largest family of North American fishes has a Eurasian origin and likely reached North America via Beringia. The earliest fossil evidence in North America is from several Oligocene deposits in the northwestern United States in a region that in the middle Tertiary would have been near the western continental margin (Cavender 1986, 1991). By the late Miocene and Pliocene, cyprinids had taken their place as a major component of the North American fish fauna (Cavender 1986, 1991). In the New World, cyprinids are restricted to North America with no records, past or present, from South America. They are well represented both in lineage and species diversity throughout Europe, Asia, and sub-Saharan Africa (Howes 1991; Berra 2001). Although there are a variety of hypotheses of relationships within the Cyprinidae, there appear to be two main lineages (treated as subfamilies), the Leuciscinae and the Cyprininae (Cavender and Coburn 1992). North American minnows are all within the subfamily Leuciscinae, which is also well represented in Eurasia. Two phyletic groups are recognized within the subfamily Leuciscinae, the Phoxinini and the Leuciscini. The majority of North American minnows are phoxinins, with only the monotypic genus Notemigonus placed in the Leuciscini (Cavender 1991).
Cyprinids likely reached North America via Beringia during periods of lowered sea level that occurred coincident with a period of climatic cooling during the late Eocene to early Oligocene—a cooling event perhaps caused by changes in ocean currents related to the separation of Australia from Antarctica and the opening of a seaway between Greenland and Norway, allowing an exchange between North Atlantic and Arctic waters (Figs. 2.5D, E) (Cavender 1991). By the time that cyprinids reached North America, the Atlantic Ocean had filled the gap between the North American and European plates, precluding movement from eastern North America and western Europe (Figure 2.5E). As a group, the Cyprinidae likely originated in the Oriental region where all major cyprinid groups are represented (Cavender 1991).
From an ecological standpoint, the speciose cyprinids are relatively recent arrivals to North America and were thus a new element incorporated into fish assemblages already composed of older groups such as salmonids, esocids, ictalurids, and others (cf. Figure 2.3). The rapid radiation of minnows was perhaps related to the rise of many insect families such as the dipterans (Cavender 1991).
GOODEIDAE (45 SPECIES) The distribution of the goodeids includes the western Great Basin of the United States (subfamily Empetrichthyinae) and the Mexican plateau (subfamily Goodeinae) (Berra 2001; Webb et al. 2004). The oldest fossils are Miocene—the subfamily Goodeinae is represented by the extinct genus Tapatia from deposits in the state of Jalisco, Mexico (Cavender 1986), and the subfamily Empetrichthyinae by material of the extant genus Empetrichthys from deposits in Southern California (Webb et al. 2004). A molecular-based phylogeny indicates that the family originated 23 mya, which corresponds well to the Miocene fossils. The two subfamilies diverged between 11.5 and 16.8 mya (Doadrio and Dominguez 2004; Webb et al. 2004).
The family is thought to have originated in North America (Gilbert 1976; Burr and Mayden 1992). Increasing aridity during the Tertiary may have fragmented the once continuous range of the family, resulting in the divergence of the two subfamilies (Parenti 1981; Webb et al. 2004).
POECILIIDAE (69 SPECIES) The livebearers are primarily a Neotropical group with most of the diversity centered in Mexico, Central America, South America, and the West Indies, and with relatively few species in temperate North America (Parenti 1981; Rauchenberger 1988). There are no known fossils of this group in North America and no pre-Quaternary fossils known at all (Hedges 1996). This led Matthews (1998) to suggest a recent (< 1 mya) North American age for the family. However, recent molecular phylogenetic studies of Poeciliopsis, a large genus within the family that occurs on the central Mexican Plateau, indicate that divergence within this genus occurred 6–18 mya (Mateos et al. 2002). As a consequence, the age of the family in North America must be at least Miocene. In further support of this, both morphological (Parenti 1981) and molecular phylogenies (Meyer and Lydeard 1993) show that the clade containing the Poeciliidae and the clade containing the Goodeidae are sister groups (i.e., derived from a common ancestor). Given that a molecular phylogeny (Webb et al. 2004) places the origin of the Goodeidae in the Miocene (ca. 23 mya), a similar age should apply to the Poeciliidae. North American poeciliids are most likely derived from Central American ancestors (Gilbert 1976; Burr and Mayden 1992; Lydeard et al. 1995).
CICHLIDAE (16 SPECIES) This large family has a broad Neotropical distribution occurring in Mexico, Central and South America, and the West Indies, with one species, the Rio Grande Cichlid (Cichlasoma cyanoguttatum), even reaching into the United States. Cichlids are poorly represented in the North American fossil record. In the Paleotropics, cichlids occur in Africa, Madagascar, and parts of southern Asia (India, Sri Lanka, Syria, and Iran) (Murray 2001a). There is a Miocene fossil of the modern genus Cichlasoma that was found in Haiti (Cavender 1986; Hedges 1996; Murray 2001a), and the oldest known cichlid fossil was found in an African deposit and dates from the middle Eocene (Murray 2001b). One view is that the separation between African and South American cichlids may postdate the formation of the Atlantic Ocean and that South American cichlids were derived from marine dispersal of cichlids from Africa, with molecular phylogeny suggesting a divergence time of 58–41 mya (Vences et al. 2001). However, a more recent review supports a vicariance hypothesis and thus requires an older age for divergence of New and Old World cichlids (Chakrabarty 2004).
The family as a whole is thought to have an early Tertiary origin, and movement from South America to Central America perhaps occurred in the late Tertiary (ca. < 20 mya) (Myers 1966; Murray 2001a). Consequently, the origin of cichlids in North America (primarily Mexico) could have occurred as early as the middle Miocene (ca. 12–15 mya).
PERCIDAE (186 SPECIES) Percids are the second most speciose family of North American freshwater fishes. The family occurs in Europe, northern Asia, and eastern North America (Collette and Banarescu 1977; Berra 2001) and seems to represent a Laurasian clade (Wiley 1992; Carney and Dick 2001). The family likely originated in the early Tertiary (Paleocene; ca. 65 mya) when land connections existed between eastern North America and Europe (Figure 2.5D) (Wiley 1992; Carney and Dick 2001). However, fossil remains of percids are only dated to the Miocene (26 mya) (Carney and Dick 2001), and the earliest North
