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Ornamentation of dermal bones of Placodermi from the Lower Devonian of Morocco as a measure of biodiversity

Antczak M., Berkowski B.

Geologos

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2017

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Vol. 23, No. 2

65--73

EN

Dermal bones are formed early during growth and thus constitute an important tool in studies of ontogenetic and evolutionary changes amongst early vertebrates. Ornamentation of dermal bones of terrestrial vertebrates is often used as a taxonomic tool, for instance in Aetosauria, extant lungfishes (Dipnoi) and ray-finned fishes (Actinopterygii), for which it have been proved to be of use in differentiating specimens to species level. However, it has not been utilised to the same extent in placoderms. Several features of the ornamentation of Early Devonian placoderms from Hamar Laghdad (Morocco) were examined using both optical and scanning electron microscopy to determine whether it is possible to distinguish armoured Palaeozoic fishes. Four distinct morphotypes, based on ornamentation of dermal bones, are dif-ferentiated. These distinct types of ornamentation may be the result of either different location of dermal plates on the body or of ontogenetic (intraspecific) and/or interspecific variation.

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Ontogenetic and intraspecific variation in the late Emsian – Eifelian (Devonian) conodonts Polygnathus serotinus and P. bultyncki in the Prague Basin (Czech Republic) and Nevada (western U.S.)

Klapper G., Vodrážková S.

Acta Geologica Polonica

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2013

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Vol. 63, no. 2

153--174

EN

Samples from populations of Polygnathus serotinus Telford 1975 and P. bultyncki Weddige 1977 from the Prague Basin and Nevada display normal variation for Devonian conodont species. A considerable number of previous authors, however, have proposed unnecessary synonyms of these two species, primarily because they have not recognized ontogenetic variation. In contrast, we interpret the variation as ontogenetic as well as intraspecific and present detailed synonymies as a result. A third species, P. praetrigonicus Bardashev 1992, which has been carried in open nomenclature for many years, is an important indicator of the basal costatus Zone in the Prague Basin, New York, and Nevada. We review the stratigraphic distribution of these three species and the conodont zonation across the Emsian-Eifelian (Lower-Middle Devonian) boundary. Polygnathus pseudocostatus sp. nov. (partitus-costatus zones, central Nevada) is described herein. We have observed a decrease in the pit size during ontogeny in P. bultyncki although we have not observed enough specimens to rule out intraspecific versus ontogenetic variation.

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Morphological plasticity of leaves in natural regeneration of Fagus sylvatica L. : effects of direct and diffuse light, ontogeny and shoot type

Jarcuska B.

Polish Journal of Ecology

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2011

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Vol. 59, nr 2

339-353

EN

It is known that the role of accessible light as a growth-determining factor in beech natural regeneration rises in importance with growth of individuals. However, the accompanied changes in leaf traits underlying this shift in light demands are not well known. The aim of this study was to investigate influence of ontogenetic stage (0.5 m high 'seedlings', 2.1 m 'saplings'), shoot type (terminal, lateral long and lateral short) and diffuse and direct light on morphological traits of leaves at spring-shoot-level in naturally regenerated beech individuals - shoot mean leaf area (mLA), shoot mean leaf weight (mLW), leaf mass per area (LMA), leaf area per shoot unit length (LAL), leaf mass per shoot unit length (LWL), number of leaves per shoot unit length (NLL), and ratio of mean-leaf width to its length (LSh). Ontogenetic drift affected the values of these traits; its influence depended on shoot type and component of light. The light explained more trait variability in saplings compared to seedlings (on average 45% vs 32%). The most evident shift was in the case of direct light - while direct light explained on average 18% of traits variability in seedlings, it was about 42% in saplings. The saplings compared with seedlings showed higher values of mLA, mLW, LMA, LAL on short shoots, LWL on lateral long and short shoots, LSh on terminal and lateral long shoots, and lower NLL values on terminal and long lateral shoots. Plastic response to light was higher in saplings than in seedlings (except mLA). Generally, the observed traits showed more plastic response to diffuse than to direct light in seedlings; the response of saplings was similar in both light components. The most plastic trait was LMA, the least LSh. Individuals of saplings displayed higher plasticity in traits close correlating with annual length growth of main axis, which suggests that saplings would benefit from increased light availability more than seedlings.

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A new rissoid gastropod with lecithotrophic development from the Miocene of Paratethys

Anistratenko V.

Acta Geologica Polonica

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2009

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Vol. 59, no. 2

261-267

EN

The results of detailed morphological studies on Rissoa sobieskii from the Badenian of the eastern Central Paratethys are presented. Its paucispiral protoconch with a bulbous embryonic shell indicates it to have had a lecithotrophic (non-planktotrophic) larval development, apparently lacking even a short free-swimming larval stage. This contrasts with all other known Miocene Rissoa species, which have shell features indicating a planktotrophic larval stage. The peculiarity of R. sobieskii is also supported by its characteristic narrowing of the aperture and almost complete lack of teleoconch sculpture. The time coincidence of the appearance of the non-planktotrophic species with distinct changes in salinity of the badenian basin suggests that the alteration (.switching.) of the type of early ontogeny from planktotrophic to non-planktotrophic development could have been an environmentally induced phenomenon.

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Students’ Conception of a Point and its Relation to a Straght Line : A Comparison of Phylogenesis and Ontogenesis

Prokopová M.

Scientific Issues of Jan Długosz University in Częstochowa. Mathematics

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2003

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Vol. 9

179--185

EN

A point and a straight line are fundamental objects of Euclidean geometry which is taught at basic and secondary schools. Philosophers meditated on the nature of a point and a straight line long before Euclid (from the 6th century BC). But it was Euclid (about 325-265 BC) who delimited the concept of a point and a straight line (and others) in the First book of his Elements (Stocheia) by means of a definition. The phylogenesis of a point and its relation to a straight line is marked out by names such as Viéte, Kepler, Leibniz, Newton, Bolzano and Cantor. Students meet the concept of a point before they start to create their geometrical structures. Our analysis will try to show that there is a strong parallel between the ontogenetic and phylogenetic aspects of the conception of a point and its relation to a straight line, a ray and/or a segment.