lampreys have a parasitic adult stage where they feed on body fluids of other fishes, whereas others do not feed after their metamorphosis to adults (Hardisty and Potter 1971). Petromyzontid lampreys likely represent the oldest living group of North American freshwater fishes, although there are no North American fossils that can be conclusively placed within the family (Cavender 1986). Lamprey fossils, described as Mayomyzon pieckoensis, were from Pennsylvanian marine shale deposits in Illinois, dating to approximately 310 mya (Bardack and Zangerl 1968), and another species, Hardistiella montanensis, was described from lower Carboniferous (ca. 350 mya) marine formations from what is now Montana (Janvier and Lund 1983). Although both were initially placed within the Petromyzontidae, Mayomyzon is now recognized as being the sole described species in the extinct family Mayomyzontidae, whereas the family relationship of Hardistiella is uncertain (Nelson 2006). A third fossil species, Pipiscius, also dates from Paleozoic formations in North America (Janvier 1997a). Of these extinct lampreys, Mayomyzon is most similar in body form to modern petromyzontids and certainly demonstrates that the lamprey body plan, and most likely mode of life, has been around since the Paleozoic. Recent work on lamprey phylogeny supports the notion that the fossil family Mayomyzontidae is as old or older than any extant families and that the North American Petromyzontidae are monophyletic (Gill et al. 2003). Freshwater lampreys are likely derived from marine ancestors (Gilbert 1976) and the Petromyzontidae probably originated in Pangean North America (Figure 2.2) in the Paleozoic (Cavender 1986).
ESOCIDAE (4 SPECIES) The pike and pickerel are one of the five North American families dating from the Mesozoic, a group that includes two subclasses: Chondrostei (sturgeon, paddlefish) and Neopterygii (bowfins, gars, and pickerels) (Nelson 2006). Fossil and living pikes and pickerels are found only in the Northern Hemisphere, including North America, Europe, and Asia (Grande 1999; Berra 2001). The family includes major recreational species such as Muskellunge (Esox masquinongy) and Northern Pike (E. lucius). The earliest known North American fossils are from late Cretaceous deposits of the Green River Formation (Grande 1999), when western North America was separated from eastern North America by the Late Cretaceous Seaway but linked with eastern Asia via Beringia (Figure 2.5C). The oldest species, Esox tiemani, was described from Paleocene lake and river deposits in Alberta and Saskatchewan (Wilson and Williams 1992). The discovery of this fossil species demonstrated the highly conserved body plan of esocids. The family perhaps originated in Laurasian North America, although data remain inconclusive about possible origins in northern Europe or Asia (Patterson 1981; Grande 1999; Wilson and Williams 1992).
ACIPENSERIDAE (8 SPECIES) Sturgeons are also an ancient group with fossils from Asia, Europe, and North America. The family is, and has been, essentially limited to temperate regions (Bemis and Kynard 1997). The order Acipenseriformes, containing sturgeons and paddlefishes, originated during the Triassic in Western Europe at a time when Laurasian elements were beginning to separate (Figure 2.5A, B) and sturgeons likely had their earliest diversification in Central Asia (Bemis and Kynard 1997). North America fossils date from the Paleogene and Upper Cretaceous deposits in areas that are now Montana and Alberta (Cavender 1986; Bemis and Kynard 1997). There is also a Miocene fossil from Virginia (Bemis and Kynard 1997). Sturgeon have a Laurasian/Pangean origin (Grande and Bemis 1996), although whether ancestral forms were present in Laurasian North America, or whether Sturgeon arrived via Beringia or from Western Europe is uncertain. Sturgeon body form is highly conserved, having changed little since the Mesozoic (G. R. Smith 1981; Sulak and Randall 2002). The family includes both freshwater and anadromous species, has a Holarctic distribution, and includes some of the largest and longest-lived species of freshwater fishes (Berra 2001). In fact, the Beluga Sturgeon (Huso huso) of the Black and Caspian seas reaches 9 m and 1300 kg and may live for nearly 100 years (Berra 2001). North American sturgeons in the genus Acipenser also reach large sizes (> 2m TL) and may live 100 years or more (Sulak and Randall 2002). Anadromous North American forms (all in the genus Acipenser) are derived from freshwater forms and were one of the first groups of fishes to solve the physiological challenges of moving from fresh to salt water (Bemis and Kynard 1997; Sulak and Randall 2002).
CLUPEIDAE (10 SPECIES) Although this family is primarily marine, there are a number of freshwater species worldwide, all considered to be derived from marine forms. In North America, clupeids first appeared in the fossil record in the middle Paleocene (ca. 60 mya) in what is now Montana and apparently occupied western North America until the middle Eocene (Grande 1982). After the middle Eocene, freshwater clupeid fossils did not show up again in the fossil record for approximately 40 million years until the Pliocene/Pleistocene (Cavender 1986). The Plio/Pleistocene fossil was identifiable as a modern species—the Threadfin Shad (Dorosoma petenense) (Miller 1982).
ICTALURIDAE (46 SPECIES) Ictalurid catfishes date from the Paleogene and are restricted to North America. The earliest North American fossils referable to the Ictaluridae date from the late Paleocene (60 mya) (Cavender 1986; Lundberg 1992). The most complete specimens are of the extinct genus Astephus and are from Eocene lake deposits in the Green River Formation, a large system of lakes located in intermontane basins, in what is now Utah, Colorado, and Wyoming, that were formed by the uplift of the Rocky Mountains in the Tertiary (Grande 1984; Grande and Lundberg 1988). From the Paleocene through the late Eocene, the Green River system comprised one of the world’s largest and longest-lived Great Lakes systems (Grande 2001). Ictalurids likely originated in North America (Gilbert 1976; Burr and Mayden 1992; Lundberg 1992) and, although there were connections with Asia and Europe in the Cretaceous and Paleocene (Figs. 2.5C, D), this group has never been found outside of North America. Of the modern genera, Ictalurus, Ameiurus, and Trogloglanis occurred in the early Oligocene, and Pylodictis fossils are known from the middle Miocene (Lundberg 1992). The genus Noturus (madtom catfishes) is younger, with fossil material dating only from the early Pleistocene (1–2 mya) (Cavender 1986).
SALMONIDAE (38 SPECIES) The oldest fossil salmonids are of the extinct genus Eosalmo, found in Eocene deposits located in what is now British Columbia and northern Washington (Wilson and Williams 1992). Eosalmo apparently occupied Pacific drainages and, based on phylogenetic analysis, was basal to all other members of the Salmonidae (i.e., considered a stem group) (Wilson 1992). Although Gilbert (1976), among many others, considered the Salmonidae to likely have a marine origin, later work on salmonid phylogeny and ecology points to a freshwater origin for the group. All primitive salmonids are restricted to freshwater habitats, whereas derived groups all contain anadromous species (i.e., those spawning in fresh water and then moving to the sea to feed) (Stearley 1992). The fossil species Eosalmo provides additional support for the freshwater origin hypothesis because of the discovery of a large size series of specimens, ranging from young to adult fish, in the same lake deposit (Stearley 1992; Wilson and Williams 1992). The anadromous life cycle shown by some modern members of the family, such as Steelhead (Oncorhynchus mykiss), Pacific salmon species, and Atlantic Salmon (Salmo salar), is thus considered a secondary adaptation. Anadromy may have been triggered by increased seasonality caused by the cooling of the climate in the middle Cenozoic, such that the marine habitat offered greater productivity and more constant temperatures that would have favored increased growth in the marine compared to the freshwater habitats (Gross et al. 1988; Stearley 1992).
Based on the worldwide distribution of the family throughout northern Asia and also Europe (Berra 2001), and the presence of the stem-group fossils in western North America, the family likely evolved in the region of Laurasia that included western North America and perhaps northern Asia (Figure 2.5E). The modern species of Pacific trout (genus Oncorhynchus) likely originated in the Miocene and have had at least six million years of history (Stearley and Smith 1993). The Atlantic basin salmonids (genus Salmo) are primarily a European lineage, and the separation of the eastern Salmo and the western Oncorhynchus lineages likely occurred via a vicariant event across the northern coast of Asia in the Miocene (Stearley 1992).
CATOSTOMIDAE (71 SPECIES) Suckers represent the median in terms of age in North America (Figure 2.3). The oldest North American fossils, of the extinct genus Amyzon, date from the middle Eocene (ca. 49 mya). Amyzon is represented in various western fossil deposits, including the Green River Formation of Wyoming (Grande et al. 1982; Grande 1984; Cavender 1991). The habitat was likely swamp-like and included crocodiles and alligators (Grande et al. 1982). Like the modern subfamily
