Unique bid auctions: Equilibrium solutions and experimental evidence

Two types of auction were introduced on the Internet a few years ago and have rapidly been gaining widespread popularity. In both auctions, players compete for an exogenously determined prize by independently choosing an integer in some finite and common strategy space specified by the auctioneer. In the unique lowest (highest) bid auction, the winner of the prize is the player who submits the lowest (highest) bid, provided that it is unique. We construct the symmetric mixed-strategy equilibrium solutions to the two auctions, and then test them in a sequence of experiments that vary the number of bidders and size of the strategy space. Our results show that the aggregate bids, but only a minority of the individual bidders, are accounted for quite accurately by the equilibrium solutions.

Unique bid auctions: Equilibrium solutions and experimental evidence

Two types of auction were introduced on the Internet a few years ago and have rapidly been gaining widespread popularity. In both auctions, players compete for an exogenously determined prize by independently choosing an integer in some finite and common strategy space specified by the auctioneer. In the unique lowest (highest) bid auction, the winner of the prize is the player who submits the lowest (highest) bid, provided that it is unique. We construct the symmetric mixed-strategy equilibrium solutions to the two auctions, and then test them in a sequence of experiments that vary the number of bidders and size of the strategy space. Our results show that the aggregate bids, but only a minority of the individual bidders, are accounted for quite accurately by the equilibrium solutions.unique bid auctions; equilibrium analysis; experiment

Bostonia Perplexa Gen. Et Sp. Nov., A Calamopityan Axis From The New Albany Shale Of Kentucky

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141922/1/ajb206093.pd

Phylogenetic analysis and fossil plants

This paper presents a perspective on the relationship between cladistic methods and the study of fossil plants. Paleobotany has been slow in evaluating the potential of these and other explicit methods compared to other branches of systematics. However, the unique or particularly difficult problems paleobotanists face make more interesting, rather than prohibit, their application. A model of a cladistic approach to phylogenetic analysis is introduced in order to evaluate what role fossils, including fossil plants, should play in phylogenetic analysis. Major elements of the model include sets of hypotheses about useful systematic comparison, phylogenetic relationship, evolutionary pattern and process, and age, linked by recursive directional arguments. Arguments at one level only, those linking characters with the cladogram, are viewed as being strictly deductive. Character hypotheses at the highest level are distinguished by the term "cladistic character". When cladistic characters are compatible, estimates of phylogeny suggested by each may be readily combined into a summary result. However, character conflict is common and represents a major challenge to the ultimate success of cladistic methods. The main advantage of cladistic characters lies in the attempt to separate out portions of complex phylogenetic hypotheses for independent scrutiny and debate. Under the model of phylogenetic analysis presented here, it is argued that fossils provide morphological information, not obtainable by other means of inquiry, which may have a profound effect on our view of characters and relationship. Fossils also provide estimates of age useful in two distinct ways. The first involves using age estimates of states, combined with external criteria such as out-group analysis, in providing defensible proximity and polarity proposals for cladistic characters. The second involves using age estimates of entire taxa to judge historical plausibility of a set of phylogenetic hypotheses generated from a cladogram. Incompatible characters may also be analyzed in this way, allowing evaluation of the plausibility of alternative character formulations. The use of fossils in phylogenetic analysis tends to emphasize the necessity of coming to terms explicitly with the ancestor-descendant relationship in cladistic methods. It is proposed that, when properly formulated, the relationship is similar in structure to other phylogenetic hypotheses and at least partly addressed by the hypothetico-deductive format.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26812/1/0000370.pd

New Iridopteridalean from the Devonian of Venezuela

The first permineralized Devonian plant fossil is reported here from the Middle or lowermost Upper Devonian of western Venezuela. Two orders of branching plus dichotomous ultimate appendages are known from compressions. A branch of the first order contains a mesarch actinostele with six primary xylem ribs, each with a protoxylem strand near the rib tip (peripheral edge). Compressions of first‐order branches demonstrate three equally spaced lateral organs (higher‐order branches and dichotomous ultimate appendages) attached in whorls, with every other whorl displaying laterals placed in identical orientations and intermediate whorls with laterals offset exactly halfway between. The permineralized specimen partly confirms the presence of whorls and indicates that vascular traces are derived from every other primary xylem rib in each whorl, with intervening ribs producing traces in whorls above and below. Second‐order branches have only ultimate appendages that are attached in a nonwhorled, three‐dimensional, or alternate arrangement. Sterile ultimate appendages dichotomize up to six times and terminate in recurved tips. Fertile ultimate appendages have paired sporangia distally; these sporangia are often upright but are otherwise similar to sterile examples. The stelar anatomy demonstrates an iridopteridalean affinity for these plants, resembling Arachnoxylon kopfii Read in arrangement and number of xylem ribs although it is smaller in size. Among iridopteridaleans, the branching pattern and mode of trace departure is unique, and we therefore name the plant Compsocradus laevigatus gen. et sp. nov

New information on Bostonia perplexa--an unusual member of the calamopityaceae from North America

A calamopityacean axis exhibiting multiple segments of primary xylem surrounded by secondary vascular tissue is analyzed here for its morphological and systematic significance. The plant is fundamentally protostelic with a deeply three-ribbed column of primary xylem. Each rib consists of a semi-discrete bundle of tracheids at the tip, intermittently connected to the stelar center by an extensive primary xylem parenchyma. The appearance of separate vascular segments at some levels is associated with departure of paired leaf traces. Between levels of trace departure, the three-ribbed protostele is reconstituted with primary xylem ribs following a helical course through the stem and supplying a regular Fibonacci phyllotaxis. Attached petiole bases are broadly of the Kalymma-type but exhibit a distinctly three-ribbed medial petiole bundle. The new specimen is assigned to Bostonia perplexa requiring an expanded concept of the taxon. A restricted cladistic analysis of stelar architecture and nodal anatomy within the Calamopityaceae produces two phylogenetic hypotheses. One is preferred on morphological grounds but necessitates viewing at least some protostelic calamopityaceans as exhibiting a derived condition within the group. The redefinition of Bostonia proposed here, a protostelic calamopityacean with medullosan-like vascular segments, reinforces long-standing views of a calamopityacean origin of Medullosales. Cladistic interpretation of stelar form and petiole anatomy in members of these groups, however, reveals character incompatibility hinging upon whether Quaestora (a protostelic medullosan) or Bostonia (a calamopityacean with medullosan-like dissected vascular system) should be preferred as a candidate for medullosan ancestor.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30042/1/0000410.pd

A reinvestigation of Diichnia Read from the New Albany Shale of Kentucky

The type material of Diichnia Read, supplemented by several additional specimens, has been restudied and a lectotype designated. Special attention has been paid to the nature of the primary vascular system, the pattern of leaf-trace divergence, branching of the leaf traces to form the petiolar vascular supply, and the zone of parenchyma just outside the secondary phloem. Generic and species diagnoses are emended and a new species, D. readii, is established.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29689/1/0000016.pd

Unique bid auctions: Equilibrium solutions and experimental evidence

Two types of auction were introduced on the Internet a few years ago and have rapidly been gaining widespread popularity. In both auctions, players compete for an exogenously determined prize by independently choosing an integer in some finite and common strategy space specified by the auctioneer. In the unique lowest (highest) bid auction, the winner of the prize is the player who submits the lowest (highest) bid, provided that it is unique. We construct the symmetric mixed-strategy equilibrium solutions to the two auctions, and then test them in a sequence of experiments that vary the number of bidders and size of the strategy space. Our results show that the aggregate bids, but only a minority of the individual bidders, are accounted for quite accurately by the equilibrium solutions

Techniques for preparation of pyrite and limonite permineralizations

Procedures are presented for the preparation of fine-polished surfaces of pyrite permineralizations, and demineralized thin-sections of limonite permineralizations. A major new feature in both procedures involves the re-embedding in plastic of individual cut sections in order to promote stability of the often crumbly material during further preparation. Pyrite sections are kept flat during polymerization of the plastic by means of a binder clip press. The technique for limonite permineralizations is characterized by the use of plastic not only for re-embedding individual sections but also for adhesion of sections to glass slides. Following this, sections are ground thin and demineralized with hydrochloric acid. We strongly recommend use of the thin-section technique for all studies utilizing limonite permineralizations because this method permits a much greater resolution of detail than is possible with other methods.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24068/1/0000320.pd

Environmental influences on the stable carbon isotopic composition of Devonian and Early Carboniferous land plants

Systematic analysis of the stable carbon isotopic composition of fossil land plants (δ13Cp) has the potential to offer new insights regarding paleoclimate variation and plant-environment interactions in early terrestrial ecosystems. δ13Cp was measured for 190 fossil plant specimens belonging to 10 genera of Early to Late Devonian age (Archaeopteris, Drepanophycus, Haskinsia, Leclercqia, Pertica, Psilophyton, Rhacophyton, Sawdonia, Tetraxylopteris, and Wattieza) and 2 genera of Early Carboniferous age (Genselia and Rhodeopteridium) collected from sites located mainly in the Appalachian Basin (22–30°S paleolatitude). For the full carbon-isotopic dataset (n = 309), δ13Cp ranges from −20.3‰ to −30.5‰ with a mean of −25.5‰, similar to values for modern C3 land plants. In addition to a secular trend, δ13Cp exhibits both intra- and intergeneric variation. Intrageneric variation is expressed as a small (mean 0.45‰) 13C-enrichment of leaves and spines relative to stems that may reflect differential compound-specific compositions. Intergeneric variation is expressed as a much larger (to ~5‰) spread in the mean δ13Cp values of coeval plant genera that was probably controlled by taxon-specific habitat preferences and local environmental humidity. Among Early Devonian taxa, Sawdonia yielded the most 13C-depleted values (−27.1 ± 1.7‰), reflecting lower water-use efficiency that was probably related to growth in wetter habitats, and Leclercqia, Haskinsia, and Psilophyton yielded the most 13C-enriched values (−23.0 ± 1.6‰, −22.3 ± 1.3‰, and −24.8 ± 1.6‰, respectively), reflecting higher water-use efficiency probably related to growth in drier habitats