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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.

2

Ontogeny and variability in ribbing of Late Valanginian lamellaptychi (Ammonitina)

Vašíček Z., Klein J., Janssen N. M .M.

Annales Societatis Geologorum Poloniae

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2016

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Vol. 86, No. 1

17--28

EN

Late Valanginian (Early Cretaceous) lamellaptychi of the genus Mortilletilamellaptychus were collected from seven ammonite-controlled sections in south-eastern France demonstrate distinct changes in ribbing during growth. Simpler juvenile ribbing, which is essentially uniform for all of the specimens studied, differs distinctly from the complicated arrangement of the adult ribs. Changes in ribbing morphology were observed in the five species studied, two of which were identified as new (i.e. Mortilletilamellaptychus heterocostatus sp. nov. and M. bicostatus sp. nov.).

3

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.

4

Growth in early species of the conodont Ancyrodella and implications for correlation of the Middle-Upper Devonian boundary

Miller C.G.

Geological Quarterly

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2007

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Vol. 51, No 4

443-452

EN

The first occurrence of the conodont Ancyrodella rotundiloba has been used extensively for correlating the Middle-Up per Devonian (Givetian-Frasnian) boundary in sections worldwide despite many arguments as to its precise taxonomic definition. These arguments are summarised herein and three ontogenetic series illustrated from three samples across the Givetian-Frasnian boundary within the Vorota Formation of the Kozhym River section, Sub-Polar Urals, Russia. General trends within the three ontogenetic series suggest that the ratio of basal pit width to platform width in Ancyrodella pristina, and Ancyrodella recta in creases through ontogeny but the morphology of lateral secondary keel extensions to the basal pit remains constant and is a useful taxonomic feature. Folds and collars on the basal surface occur only in the later stages of development. The out line of the platform within species is variable and controlled by the formation of incipient nodes in juveniles; gerontic specimens can also have very variable platform out lines. Measure ments of platform width to basal pit width ratios and platform shape out lines may not therefore be a good way to compare between species. The three ontogenetic series provide typical late Givetian and early Frasnian examples and increase the potential for correlation of the Middle-Upper Devonian boundary particularly using juvenile Ancyrodella specimens.