Mark V. H. Wilson

Biological determinants of species diversity

We consider four categories of biological mechanisms of deter- minants which cause and maintain species diversity: niche relations, habitat diver- sity, mass effects and ecological equivalency. Two of these determinants are origi- nal to this paper: mass effect, the establishment of species in sites where they cannot be self-maintaining; and ecological equivalency, the coexistence of species with effectively identical niche and habitat requirements. The mode of action and ecological implications of each biological determinant are discussed using a schematic method for measuring alpha (community), beta (differentiation), and gamma (regional) diversities. The importance of mass effects and ecological equivalency to species richness is documented with several types of field data from Israel and California, U.S.A. Floristic richness and, in particular, the richness of floristic transitions, are discussed and interpreted by use of the biological determinants of diversity. Contact transitions between distinct floras are rich predominantly because of mass effects. Transitions induced by marked environmental changes are rich because of the combined influences of habitat diversity and mass effects. The rate at which species richness increases with sample area is related to the combined effects of all four biological determinants. This complexity explains the failures of simple species-area models. The relative intensity of each determinant is related to area: niche relations are most important at within-community scales, habitat diversity most important at both within-community and land- scape scales, and ecological equivalency most important at regional scales. We suggest that understanding patterns of species diversity will be enhanced by the partitioning of total species richness into the richness caused by each of the four ecologically distinct determinants of diversity.

Eocene lake environments: Depth and distance-from-shore variation in fish, insect, and plant assemblages

Abstract Eocene lake environments of British Columbia, Canada, and Washington State, U.S.A., are reconstructed using assemblages of fishes, fish bones, scales, and coprolites. Assemblages of terrestrial insects and terrestrial plant organs corroborate and help explain those based on fishes. For each fossil type, a major deep-water, off-shore/shallow-water, near-shore component of variation is apparent. This variation appears between stratigraphic intervals at one site, and between sites representing various Eocene lakes and formations. Deep/off-shore assemblages are more uniform and taxonomically less diverse than shallow/ near-shore assemblages. For terrestrial fossils, a near-shore/off-shore sorting by flying ability, wind, or floating is suggested. Fish assemblages are distinguished by taxa present and by degree of disarticulation. Shallow-water/near-shore assemblages have more amiids, percopsids, disarticulated fish, bibionids, incomplete insects, evergreen needles, and taxodiaceous leafy shoots. A moderately deep/near-shore assemblages has abundant salmonids and hiodontids. Deep-water/off-shore assemblages are dominated by articulated catostomid skeletons, catostomid scales, complete insects, dicot leaves, and wood.

Devonian Fishes and Plants of Miguasha, Quebec, Canada

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Reconstruction of ancient lake environments using both autochthonous and allochthonous fossils

Abstract Eocene lacustrine paleoenvironments in western North America have been reconstructed using evidence from assemblages of autochthonous and allochthonous fossils. Seasonal variation is recorded in varved sediments that contain fossil assemblages indicative of deep-water, off-shore deposition. Stratigraphic variation at one locality records a transgression from a coal swamp, through near-shore lacustrine environments, to more off-shore lacustrine environments. Fish assemblages preserved in this section change in the taxa represented, and in the taphonomic characteristics of their preservation. Terrestrial fossils (insects and plants) change in abundance concomitantly. A large proportion of the taxonomic and taphonomic variation between fish assemblages from other formations and localities is directly correlated with the near-shore to off-shore variation. Insect and plant assemblages also differ greatly between near-shore and off-shore depositional environments. If ones goal is to reconstruct ancient lacustrine communities, sampling programs must be designed to compensate for these biases.

Sudan black B as a nerve stain for whole cleared fishes

JORDAN, D. S., B. W. EVERMANN AND H. W. CLARK. 1930. Check list of the fishes and fishlike vertebrates of North and Middle America north of the northern boundary of Venezuela and Columbia. US Bureau of Fisheries Report, 1928, 2. LACEPEDE, B. G. E. 1797. Memoire sur le polyodon feuille. Bulletin des Sciences, Societe Philomathique, Paris 1(2):49. . 1798. Histoire naturelle des poissons. Plassan, Paris. Vol. I. (Vol. 32 of Buffons Histoire naturelle, 1749-1804.) LE PAGE DU PRATZ, A. S. 1947. The history of Louisiana, from the T. Beckett, London, ed. of 1774. Notes by S. C. Arthur. J. W. W. Harmanson, New Orleans.

New Paleocene genus and species of smelt (Teleostei: Osmeridae) from freshwater deposits of the Paskapoo Formation, Alberta, Canada, and comments on osmerid phylogeny

ABSTRACT Articulated specimens of fish recovered from the Paskapoo Formation, of Tiffanian (Paleocene) age, near Red Deer, Alberta, are described as a new genus and species of smelt (Family Osmeridae). The new smelt is characterized by a long, toothed mandible and premaxilla and a slender, toothless maxilla, in combination with the virtual absence of teeth inside the mouth and a distinct second ural centrum. Cladistic analysis of osteological features of osmerids and several outgroups indicates that the new genus is most closely related to Plecoglossus, a Recent genus not always included in the family. These two in turn are more closely related to a derived clade of osmerid genera (Allosmerus, Osmerus, Spirinchus, Thaleichthys) than they are to primitive osmerids (Hypomesus and Mallotus). Anal fins of the new fish are sexually dimorphic, and several presumed males probably have breeding tubercles. Possibly the fish became stranded after attempting to spawn during a high-water stage. Anadromous life histor...

Cretaceous Esocoidei (Teleostei); early radiation of the pikes in North American fresh waters

ABsTRAcr-Contrary to ideas that Cretaceous fresh waters contained few teleosts, there were several taxa of Esocoidei (pikes and relatives) in North American Cretaceous rivers. Dentaries and palatines of Campanian to Maastrichtian age all have C-shaped tooth bases and other distinctive features of shape and foramina. The fossils include at least three distinct kinds, two of which are described here as new genera and species in the Esocidae: Estesesoxfoxi n. gen. and sp. and Oldmanesox canadensis n. gen. and sp. These old, diverse, and apparently primitive specimens show that pikes radiated when Eurasia and North America were still joined. Some references in the literature to the Cretaceous fish Platacodon Marsh are based on referred dentaries that are here identified as esocoid fossils. The Esocidae are the first example of a family of Recent North American freshwater teleosts that has been shown to have speciated in Cretaceous fresh waters and survived the terminal Cretaceous extinction.

The Furcacaudiformes: a new order of jawless vertebrates with thelodont scales, based on articulated Silurian and Devonian fossils from northern Canada

ABSTRACT A new order of “fork-tailed” agnathans (jawless vertebrates), the Furcacaudiformes, is described from Wenlockian (Silurian) and Lochkovian (Devonian) fossils from the Northwest Territories of Canada. Six new species are classified in five new genera and two new families. One Silurian species is in the genus Pezopallichthys, family Pezopallichthyidae. One Devonian species is described in each of the genera Cometicercus, Drepanolepis, and Sphenonectris. The Devonian genus Furcacauda includes two species, one new and another that was previously described as Sigurdia heintzae Dineley and Loeffler. Preliminary phylogenetic analysis suggests the following relationships within Furcacaudiformes: (Pezopallichthys (Cometicercus (Drepanolepis (Sphenonectris (Furcacauda)))). Furcacaudiforms resemble some previously described thelodonts in structure of their scales, which are of loganellid and nikoliviid types, but differ in having generally smaller scales, as well as in having laterally compressed, hump-back...

An anoxic event at the Albian-Cenomanian boundary: the Fish Scale Marker Bed, northern Alberta, Canada

Abstract The Fish Scale Marker Bed (FSMB) of the Shaftesbury Formation, which marks the Albian-Cenomanian boundary, is a regional stratigraphic marker in the Western Interior of Canada. At the outcrop studied on the Smoky River in northwestern Alberta, three major shale units can be distinguished in the FSMB and contiguous strata. The lowermost shale (Unit 1) is bioturbated and contains high-diversity dinoflagellate and moderate-diversity foraminiferal assemblages. It has dominantly Type III (terrestrial) organic matter (OM) and low total organic carbon content (TOC). The unit was deposited in an open-marine, neritic environment of normal salinity. The FSMB (Unit 2) represents a zone of condensed bioclastic accumulation composed of abundant fish remains. The dinoflagellate species diversity is drastically reduced in this unit and it lacks benthonic foraminifera and bioturbation. Unit 2 is characterized by mainly Type II (marine) OM and high TOC values. Unit 2A contains rippled sandstone related to either a shallowing or to deeper water currents. A fish-hash conglomerate making up Unit 2B can alternatively be interpreted as a bioclastic, condensed and winnowed deposit or as a transgressive lag. Unit 2C consists of black, platy shale with abundant fish remains and represents a minor marine trangression during the deposition of FSMB, when the bottom waters were dominantly anoxic. Collectively, the features of Unit 2 suggest deposition under a stratified water column with moderate productivity of planktonic and nektonic organisms in the upper oxygenated layers but with anoxic bottom waters. Unit 3, overlying the FSMB, consists of blocky shale with reduced concentration of fish remains. Due to increased rate sedimentation during its deposition, the organic-rich sediment of Unit 3 was progressively diluted by clastic material and there was an increase in the dissolved oxygen content of the bottom waters. The anoxic event at the FSMB is related to a relative rise in sea level and possibly to the mixing of waters different salinities and temperatures from the Arctic Ocean and the Gulf of Mexico in the Western Interior seaway.

Seven centuries of taphonomic variation in Eocene freshwater fishes preserved in varves; paleoenvironments and temporal averaging

Eocene lake beds of Horsefly, British Columbia, are preserved in varves, or discrete year- ly layers representing seasonal changes in the lake. These varves allow study of temporal variation and rates of change in morphological and ecological characters on a very short time scale. One of the most sensitive indicators of the paleoenvironmental conditions on the floor of the lake may be the taphonomic condition of the fishes, which vary between perfectly articulated and completely disarticulated skeletons. Patterns of disarticulation correspond to those produced by scavengers. The taphonomy supports the hypothesis that the lake was warm monomictic, circulating in the winter, at which time scavengers could gain access to the bottom of the lake. Larger-scale environ- mental events (on the order of hundreds of years) are suggested by the fact that the proportion of well-preserved specimens reached two peaks within the seven centuries of deposition, one peak during the second century and another during the fifth and sixth centuries. These results clearly demonstrate two principles: that taphonomy can be a sensitive indicator of paleoenvironmental conditions, and that temporal averaging can affect the taphonomic properties of this fossil site, and presumably of others with equal or lower time resolution.