Ontogeny and heterochrony in the ostracode Cavellina Coryell from Lower Permian rocks in Kansas

Abstract

Animals evolve by changing their form and by changing the rate at which they develop. Since evolution of development through time may be directly related to the adaptation of their life histories, study of ontogeny in fossils may yield information about the ecology of extinct animals. We need to know how to measure animals' ontogeny and at what taxonomic level structural differences overshadow differences in development. Two closely related species of the Permian ostracode Cavellina were compared to determine how much of the morphological difference between them is due to differences in their ontogenies. Most of the difference is not related to ontogeny. They also differ in a way that could be explained by heterochrony, although this difference is secondary in importance to the structural difference. These findings suggest that ecological adaptation might best be studied by examining the changes in development that occur within species through time and space.

The importance of lithographic limestones for revealing ontogenies in fossil crustaceans

“…Developmental data of fossils have been successfully used in various non-arthropod taxa (e.g., Sevastopulo 2005;Nützel et al 2006;Schoch and Fröbisch 2006;Bandel 2007;Sumrall and Wray 2007). For fossil arthropods, dorsal hard parts of trilobites or ostracod shields have mainly been used for ontogenetic studies (e.g., Gramm 1973;Schweitzer et al 1986;Smith 2000;Hughes et al 2006 and references therein). Ontogenetic stages of trilobites have been recognised since the work of Barrande (1887).…”

“…Based on morphometrics and shell structures, ontogenetic sequences have been reconstructed for a number of such species (e.g., Gramm 1973;Schweitzer et al 1986). Preservation of ventral morphology for such fossils is rather rare, and only three occurrences yield developmental information of such structures: Weitschat (1983) described Triadocypris spitzbergensis WEITSCHAT 1983 from the Triassic of Spitzbergen, not only based on adults, but also specimens of a sub-adult stage are briefly mentioned.…”

Morphotypes of the lacustrine ostracod Limnocythere rionegroensis Cusminsky & Whatley from Patagonia, Argentina, shaped by aquatic environments

“…Outline analysis is a more appropriate geometric morphometric method applied to nonmarine ostracods, because it usually needs few landmarks for the characterization of their morphology (Baltanás et al, 2003). Many studies have been carried out using outline analysis, including, for example, the pioneering work of Kaesler & Waters, (1972), Kaesler & Maddocks (1984), Schweitzer et al (1986), and Maness & Kaesler (1987), among others.…”

Ontogenetic changes in the ostracod <i>Cytherella</i> cf. <i>ovata</i> Roemer, from the Cenomanian of Algeria

“…Between group variation is subsequently determined by an additional eigenshape analysis of the firsteigenshape of each growth stage. Most of the shape change between the different categories is shown by the second and third eigenshapes of this final eigenshape analysis (Lohmann, 1983;Schweitzer et a/., 1986;Maness & Kaesler, 1987).…”

“…Schweitzer et al, 1986;Maness & Kaesler, 1987). The first eigenshape of this analysis represents the general or shared shape and accounts for 96% of the total variation, a high value that indicates aclose agreement in shape among the instars.…”