Biomedical subjects

N N Iordanskiĭ

Publications and source records attributed to N N Iordanskiĭ.

3 recordsLinked to original sources

PubMedDate not supplied

Cranial kinesis in the amphibia: a review.

All extant orders of amphibians are characterized by kinetic skulls. Main type of intracranial movability in amphibians is pleurokinetism, that is supplemented in different amphibian groups by various types of rhyncho- and prokinetism. The most primitive pattern of cranial kinesis is revealed in the stegocrotaphic gymnophions. More paedomorphic species retain general cranial flexibility that is characteristic of larval skull. That is unfavourable for evolution of well-regulated (adult) cranial kinesis and related feeding adaptations. Kinetism is also reduced in the species with heavily ossified skulls. Adaptive role and evolution of cranial kinesis in amphibians are discussed.

Amphibians↗

PubMedDate not supplied

[Macroevolution: macrogenesis and typogenesis].

One can distinguish two levels (and stages) of macroevolutionary processes: the lower (macrogenesis) and higher (typogenesis) ones. The macrogenesis represents macroevolutionary alterations of separate structures; the typogenesis is the forming of general Bauplan (type of organization) of a new macrotaxon on a base of initial macrogenesis. Discrete (or quantum) character of many macroevolutionary transformations is caused by various mechanisms, which are based on properties of integrated organismic systems and are characterized by threshold effect of their action. Initial macrogenesis can be resulted from the morphofunctional preadaptations; the pattern (or regime) transformations of morphofunctional organismic systems; emerging of dichotomy of morphogenetic programs and their following switching; the ontogenetic heterochronies (in particular, paedomorphosis); the allometric structural changes (and possibly some other mechanisms). The initial macrogenesis forms a base for qualitatively new adaptation and essentially influences on other systems in whole organism. That changes the selection vectors significantly. All these alterations trigger the typogenesis. The latter represents a complex of organismic systems transformations, integrated by selection and interconnections of various systems in whole organism. The important role in typogenesis belongs to the key alterations of some limiting organismic system that trigger and direct evolutionary changes of depended organismic systems. In course of typogenesis evolution, new macrotaxon occupies new adaptive zone.

Adaptation, Physiological↗

PubMedDate not supplied

[Evolutionary saltations and evolution].

The term saltation is a composite notion covering different categories of supposed saltational evolutionary changes. One can distinguish interspecies, macroevolutionary and morphofunctional saltations corresponding to saltational arising of a new species, of general Bauplans of new macrotaxons, and of large-scale morphofunctional alterations (irrelevant to any taxonomic aspects). Current data confirm the possibility of interspecies and mophofunctional saltations as relatively rare modes of evolutionary changes. Morphofunctional saltations result in the arising of macromorphoses that can sometimes stimulate the beginning of macroevolutionary typogenesis. Saltationism extremely exaggerates the evolutionary role of saltations, considering these to be the main factor of speciation and macroevolution. However, saltations are only peculiar and relatively rare form of hereditary variability representing elementary evolutionary material. Natural selection is the principal evolutionary mechanism that produces new adaptations and integrates different systems of the organism in the process of typogenesis. The arising of general Bauplans of new macrotax by means of macroevolutionary saltations seems to be improbable.

Animals↗