Ecology of North American Freshwater Fishes. Stephen T. Ross Ph. D.
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mobile terrestrial and freshwater organisms from pole to pole and east to west (A. G. Smith et al. 1994; Scotese 2002). During this time, tetrapod vertebrates were essentially cosmopolitan with no evidence of latitudinal variation (Briggs 1995).
MESOZOIC, LATE JURASSIC (161 MYA) The northern and southern supercontinents of Laurasia and Gondwana separated from each other as the young central Atlantic Ocean began to increase in size (Figure 2.5B). The southern landmasses were still grouped within Gondwana, but the components of Laurasia had begun to drift apart. Western and eastern North America were joined along the southern margin, although A. G. Smith et al. (1994) portrayed the northern elements as separated by a large, north-to-south-oriented inland sea (not shown by Scotese 2002). Greenland was part of eastern North America, whereas Europe had “recently” (e.g., approximately 20 million years earlier) separated from eastern North America and was also separated from northern Asia by the Obik Sea to the north, and by the Turgai Straits to the south (A. G. Smith et al. 1994; Zwick 2000; Scotese 2002).
MESOZOIC, LATE CRETACEOUS (70 MYA) High sea levels, resulting in shallow epicontinental seas, separated western and eastern North America as well as northern and southern sections of eastern North America (A. G. Smith et al. 1994) (Figure 2.5C). A large landmass comprising northern Asia, Beringia, and western North America dominated the Northern Hemisphere. Greenland was apparently close to, but perhaps separated from, eastern North America. There is disagreement about whether eastern North America, Greenland, and Europe were connected. Briggs (1986, 1995) and Rage and Rocek (2003) supported a connection, whereas other recent authors (e.g., A. G. Smith et al. 1994; Scotese 2002) show separations between these landmasses (as I have done in Figure 2.5C). Europe was separated from Asia by the Obik Sea to the north and the Turgai Straits to the south (the combined water body is the Uralian Sea [Rage and Rocek 2003]). There is also disagreement about the connection of North and South America during this period. Briggs (1995) and Rage and Rocek (2003) indicate a connection via Central America, whereas A. G. Smith et al. (1994) and Scotese (2002) do not.
CENOZOIC, EARLY TERTIARY
PALEOCENE (60 MYA) The Northern Hemisphere was largely ringed by a single landmass comprising Asia, Beringia, North America, Greenland, and Europe (Figure 2.5D). Asia was linked to western North America via Siberia and Beringia, the large inland sea separating eastern and western North America had partially receded, and eastern North America was connected to Europe via Greenland. Europe continued to be totally (Rage and Rocek 2003) or partially (A. G. Smith et al. 1994) separated from northern Asia, and North and South America were not connected.
CENOZOIC, EARLY TERTIARY
MIDDLE EOCENE (45 MYA) The Northern Hemisphere was dominated by a landmass comprising northern Asia, Beringia, and North America (Figure 2.5E). There were possible northern connections between Greenland and North America, and Greenland and northern Europe (A. G. Smith et al. 1994; Briggs 1995), although more recent data seem to cast doubt on this since Torsvik et al. (2001) showed Greenland separated from North America by the Labrador Sea in the early Tertiary (54 mya) and also separated from northern Europe; this is reflected in Figure 2.5E. The Turgai Straits had reopened from the south and, along with the Obik Sea to the north, separated Europe from northern Asia. South America was separate from North America, with Central America existing as island archipelagos (A. G. Smith et al. 1994; Briggs 1995; Scotese 2002). Although less critical for understanding the North American fauna, the position of India during the Eocene is uncertain—Briggs (1989) argued, based on faunal evidence, that India must have already contacted the Asian continent by the early Eocene, whereas other studies based on geophysical evidence indicate that it did not make contact until the Miocene (e.g., A. G. Smith et al. 1994; Scotese 2002).
CENOZOIC, LATE TERTIARY, MIDDLE MIOCENE (10–15 MYA) The large, Northern Hemisphere landmass of northern Asia, Beringia, and North America not only continued to persist but had expanded with the closure of the Uralian Sea (Turgai Straits and Obik Sea) and the union of Europe with northern Asia (Figure 2.5F). South America was still separate, but Central America was joined with North America. By the early Miocene, Africa had contacted Asia along the Arabian Peninsula, allowing potential interchange of freshwater fishes and resulting in the formation of the Mediterranean Sea (A. G. Smith et al. 1994; Briggs 1995; Scotese 2002; Rage and Rocek 2003). The present configuration of landmasses differs from the middle Miocene by the submergence of Beringia, the expansion of the Atlantic and Pacific oceans, and the union of South and Central America (Figure 2.5G).
Ages and Origins of Major Fish Families
PETROMYZONTIDAE (21 SPECIES) Lampreys represent one of the two surviving groups of jawless fishes, the other being the strictly marine hagfishes (Myxini). All lampreys have a prolonged larval stage (termed ammocoetes) during which they burrow into soft sediments of streams and feed on small organisms at the sediment-water interface. Some 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