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PROGRAMME‐EVOLUTION IN THE GRAPTOLITES
Author(s) -
BULMAN O. M. B.
Publication year - 1933
Publication title -
biological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.993
H-Index - 165
eISSN - 1469-185X
pISSN - 1464-7931
DOI - 10.1111/j.1469-185x.1933.tb01091.x
Subject(s) - series (stratigraphy) , range (aeronautics) , paleontology , interpretation (philosophy) , line (geometry) , relative species abundance , race (biology) , abundance (ecology) , biology , evolutionary biology , ecology , geology , mathematics , philosophy , geometry , linguistics , materials science , composite material
Summary. 1. As an illustration of the occurrence of programme‐evolution among the graptolites, some of the series included within the “isolate” line of thecal elaboration in the monograptids have been selected. 2. These are represented in the Lower Silurian (Valentian) rocks of Sweden, Britain, Germany and Bohemia. When the species constituting these series in any one area are compared with those of another, as is attempted here for the British and German forms, they are found often to exhibit slight differences in form (although occupying the same relative positions in precisely comparable evolutionary series), and possibly also in time‐range. It is suggested that this local aspect is probably to be attributed largely to direct environmental influence. 3. Against the view that the thecal elaboration is adaptive, it is pointed out that several distinct progressive and regressive lines of development, not only in the isolate line, but also in the hooked and lobate lines, occur simultaneously (while simple unmodified thecal types also persist), and all these are represented by species which, as far as can be ascertained at present, lived under the same environmental conditions. 4. There is evidence of certain definite periods of evolutionary activity (represented by a marked abundance of species and particularly of new species), again suggesting the operation of what may be referred to as some “internal” factor in the evolution of the race. None of the explanations which has been advanced in the interpretation of similar series in other groups of animals seems applicable here, but no alternative is offered.