2 results
Going round the twist—an empirical analysis of shell coiling in helicospiral gastropods
- Katie S. Collins, Roman Klapaukh, James S. Crampton, Michael F. Gazley, C. Ian Schipper, Anton Maksimenko, Benjamin R. Hines
-
- Journal:
- Paleobiology / Volume 47 / Issue 4 / November 2021
- Published online by Cambridge University Press:
- 23 March 2021, pp. 648-665
-
- Article
- Export citation
-
The logarithmic helicospiral has been the most widely accepted model of regularly coiled molluscan form since it was proposed by Moseley and popularized by Thompson and Raup. It is based on an explicit assumption that shells are isometric and grow exponentially, and an implicit assumption that the external form of the shell follows the internal shape, which implies that the parameters of the spiral could be reconstructed from the external whorl profile. In this contribution, we show that these assumptions fail on all 25 gastropod species we examine. Using a dataset of 176 fossil and modern gastropod shells, we construct an empirical morphospace of coiling using the parameters of whorl expansion rate, translation rate, and rate of increasing distance from coiling axis, plus rate of aperture shape change, from their best-fit models. We present a case study of change in shell form through geologic time in the austral family Struthiolariidae to demonstrate the utility of our approach for evolutionary paleobiology. We fit various functions to the shell-coiling parameters to demonstrate that the best morphological model is not the same for each parameter. We present a set of R routines that will calculate helicospiral parameters from sagittal sections through coiled shells and allow workers to compare models and choose appropriate sets of parameters for their own datasets. Shell-form parameters in the Struthiolariidae highlight a hitherto neglected hypothesis of relationship between Antarctic Perissodonta and the enigmatic Australian genus Tylospira that fits the biogeographic and stratigraphic distribution of both genera.
13 - The Distribution of Wealthy Athenians in the Attic Demes
- Edited by Mirko Canevaro, University of Edinburgh, Andrew Erskine, University of Edinburgh, Benjamin Gray, University of London
- Josiah Ober
-
- Book:
- Ancient Greek History and Contemporary Social Science
- Published by:
- Edinburgh University Press
- Published online:
- 06 May 2021
- Print publication:
- 06 June 2018, pp 376-402
-
- Chapter
- Export citation
-
Summary
INTRODUCTION
This chapter investigates the spread of wealthy citizens across the 139 demes of Attica, the constituent villages and boroughs of the Athenian state. We look primarily at the number of citizens (or councillors, a proxy for the number of citizens), and the number of wealthy citizens, in each of the demes, and see how closely they are correlated. A close correlation would suggest that one sort of economic opportunity was smoothly spread; a man's origins in a particular deme would be a poor way of predicting whether or not he was wealthy. A weak correlation would suggest that some demes did give their citizens a higher chance of being wealthy. We also consider demes with an unexpectedly high number of wealthy citizens, and ask whether these outliers had anything in common.
LITERATURE REVIEW
A number of scholars have anticipated some of our methods and results. Bresson offered a regression analysis of the number of magistrates and wealthy citizens from the demes of Hellenistic Rhodes. Osborne produced a ‘Wealth Index’ for most of the Athenian demes by ‘taking the number of wealthy men attested per deme from Davies’ work and dividing this by the number of bouleutai provided by that deme’. Taylor provided a regression analysis of known officials against liturgists in the demes. How does our analysis add to theirs? In several ways, we hope.
First, we use a slightly improved dataset. In particular, where our predecessors took paired demes such as Upper and Lower Lamptrai together, we treat them as two separate demes.
Second, we offer a more fine-grained analysis. We look at the distribution not only of the total number of wealthy citizens identified by Davies (1971), but also of various subsets of wealthy citizens. We reflect on the differences in the distribution of wealthy citizens from these different categories. We also think a lot about the differences that the data throws up between individual demes. In particular, we will think hard about demes that are statistical outliers. This goes against Osborne's assertion that ‘the figures for individual demes are clearly too subject to the effect of individual chance attestations to be taken too seriously’. We discuss the reliability of individual results on a category-by-category basis.