Die Faunenwende Perm/Trias

Zusammenfassung

Aufgrund der Diversitätsverteilung der Invertebraten im Phanerozoikum wird folgende These aufgestellt: Die Faunenwende Perm/Trias war kein katastrophales Aussterben sondern es entstanden weniger neue Arten. Dies wird durch einige Fallstudien untermauert, welche Aussterben und Neuauftreten im oberen Paläozoikum untersuchen. Ursache des verminderten Neuauftretens ist die mit dem Zusammendriften der Kontinente einhergehende Abnahme der Isolationsmöglichkeit neuer Arten. Die Wechselwirkungen verschiedener Umweltparameter sowie die Wechselwirkung Organismen — Umwelt werden zunächst allgemein und schließlich in spezieller Anwendung auf die Ereignisse im oberen Paläozoikum und in der Trias dargestellt. Für die geringe Faunendiversität an der Perm-Trias Grenze zeichnen allein Mutation und natürliche Selektion verantwortlich. Jedoch verminderten im oberen Paläozoikum die Umweltverhältnisse über die natürliche Selektion die Möglichkeit zur Neuentstehung von Arten und höheren Taxa.

Abstract

Considering the diversity distribution of invertebrates throughout Phanerozoic time one can see clearly: Extinction rates in the Permian are not higher than at other times (tab. 1, fig. 3). But the origination of new forms is extremly low (tab. 1, fig. 4). So the low diversity at the Permian-Triassic boundary is not the result of a catastrophic event, but merely the result of reduced rates of origination. This is indicated by a more detailed look at the Trilobites (fig. 5, 6, 7), the Ammonites (fig. 8, 9, 10), the Blastoids (fig. 11, 12, 13) and the Fusulinids (fig. 14). Faunal diversity was reduced over millions of years during the Upper Palaezoic by lower rates of origination.

The second part of this paper is concerned with the reasons for these low rates of originations. At first the environment through time is examined. Fig. 15 shows the shifting environment through time, which is altered by input from the mantle, the cosmos and biologic factors. If life lineages, that only could evolve within that environment are going to collide with the boundaries of that environment then they become extinct. This extinction may be very slow, it can be established not only by desasters but also by reduced rates of origination. Because so many different organisms in different environments were affected by the faunal change from Permian to Triassic, it seems to be appropriate to look for reasons that act in the upper levels of the ecologic hierarchy (see fig. 16).

The formation of Pangea during Upper Paleozoic times was a process that could have affected several faunal provinces covering a considerable part of the biosphere. So we have to look for a possible relationship between continental convergence and reduced rates of origination. Fig. 17 shows how mantle and cosmic input act on the environment and how some essential factors of the environment interact with themselves and with organisms. Environmental change by the formation of Pangea is geologically well documented for the Upper Paleozoic, so we should deduce the possible implications. Fig. 18 shows the physical implications of continental convergence. Origination of new species is predomninantly correlated with the possibility of isolation (allopatric speciation). Isolation is correlated with the presence of barriers. The most important barriers are morphology and climate. In Fig. 20 the possible barriers for different environments are listed. If we look at Fig. 18 we can see that continental convergence is a well-known process that can destroy the barriers cited in Fig. 20. Taking in mind the importance of allopatric speciation, we must clearly deduce from theory the same thing, that really happened in the Upper Paleozic: lowering of rates of species origination and higher taxa. Because Triassic was a time of beginning continent dispersal, the opposite effects are to be expected: higher origination rates and increased diversity. This is well documented by the geologic record.

Résumé

La distribution de la diversité des invertébrés au Phanérozoique permet d'élaborer la thèse suivante: le changement des faunes du Permien au Trias ne fut pas une extinction provoquée par une catastrophe, mais il se formait moins de genres nouveaux. Cecit est appuyé par quelques examples d'extinction et de naissance dans le Paléozoique supérieur. La raison de la diminution des naissances nouvelles est la réduction de la possibilité d'isolation de genres nouveaux liée au charriage convergent des continents. Les effets d'alternance des paramètres d'environnement ainsi que les effets d'alternance des organismes environnement sont présentés d'abord d'une façon générale et ensuite comme une application particulière en ce qui concerne les événements au Paléozoique supérieur et au Trias. Pour la faible diversité des faunes à la limite Permien — Trias sont responsables seulement, comme toujours, les deux causes antagonistes de taute évolution des organismes, la mutation et la sélection naturelle. Les circonstances d'environnement au Paléozoique supérieur ont pourtant réduit la possibilité de naissance de genres nouveaux et de taxa plus élevés par la voie de la séléction naturelle.

Краткое содержание

На основании изучени я распространения ра зличных видов беспозвоночны х в фанерозое предлага ется следующая гипот еза: На рубеже перм/триас вым ирание видов шло he интенсивне е, чем в другие периоды. Но новые виды появлялись значител ьно реже. Причины этом у следует искать в дрифте матер иков, что приводило к пониж ению инсоляции. Рассм атривается взаимодействие различных параметро в окружающей среды, а т акже взаимодействие организм-среда вообщ е и в позднем палеозое и триасе в частности. За незначительное по явление новых видов и подвидов в указанный отрезок времени отвестствен ны только мутации и ес тествнный отбор. Условия среды в позднем палеозое по низили возможность возникновения новых видов и высших таксономичес ких групп путем естес твенного отбора.