(POZNÁMKA K FYLOGENEZI SCYPHOCRINITIDNÍCH KRINOIDŮ)
Rudolf J. Prokop1 - Václav Petr2
Scyphocrinitid crinoids occur almost worldwide in the Siluro-Devonian boundary formations in Europe, Asia, North Africa and North America. They are the only crinoids in the history of the class bearing a special organ for buoyancy, so-called lobolith. This organ was never found in original connection with stem and crown, only with the distal part of stem. Therefore, even the last speculations of PROKOP et PETR (1986, 1987) and of HAUDE (1992) represent nothing but mere possibilities of probable belonging of both lobolith-types to definite species and genera. The situation is complicated with presence of the cirrus-loboliths and plate-loboliths in both uppermost Silurian and lowermost Devonian strata, at least in the Barrandian area of Bohemia. Some conclusions can be made from calculations of relative abundance of lobolith-types and calyces of determined genera and species, but it is also speculative because of separate occurrences of lobolith-accumulations due to capability of the floats to be drifted on large distances by currents after the death of the crinoids and after the disintegration of their stems.
Because of the presence of both lobolith-types in all stratigraphical levels in the Siluro-Devonian boundary beds and, especially, because of the fact that both types are present also in the lowermost levels (there are no "Niveau der Platten-Lobolithen" or "Niveau der Cirren-Lobolithen" in the Barrandian area as is suggested by HAUDE, 1992), the authors are of the opinion that the origin of both lobolith-types can be rather independent. We believe that there is a good reason for such opinion from many points of view.
It seems to be evident that the scyphocrinitid genera Scyphocrinites
ZENKER, 1833, Marhoumacrinus PROKOP et PETR, 1987 and Carolicrinus
WAAGEN et JAHN, 1899 (we disagree with the resurrection of the genus Camarocrinus
HALL, 1879 by HAUDE, 1992, p.176) are closely related. But we are asking
the question: 'How much they are related?'. The answer is impossible without
knowledge of morphological character of the utmost importance for taxonomy.
Such character cannot be quantitative, i.e. number of secundibrachs, presence
of tertibrachs, sculpture of the plates or number of interbrachials. We
must search for a qualitative one, and that is succession of fixed pinnules,
which was competently studied by SPRINGER (1917) and by PROKOP et PETR
(1986, 1987). We cannot accept Haude's suggestion that:
"Die möglichen Unterschiede im Ansatz der proximalen, in die Kelchwand einbezogenen Pinnulae der Sekundibrachia ... wurden hier als Merkmale nicht berücksichtigt, da deren Lokalisierung bei vielen Formen noch völlig unklar ist." (see HAUDE, 1992, p. 162). Such proclamation is very dangerous because we have nothing more important and, in consequences, it cannot lead to correct taxonomic results.
The main sequence of fixed pinnules in Marhoumacrinus and Scyphocrinites
is clear from the study of North American and Bohemian material and is
given in PROKOP et PETR 1987, p.9, text-fig.11. The succession of the first
two pinnules is constant for each genus. Therefore, it is impossible to
exclude Scyphocrinites subornatus Barrande (MS) WAAGEN et JAHN,
1899 from the genus Scyphocrinites ZENKER, 1833 as proposed by HAUDE
(1992, p. 180). Moreover, the difference between the genera Scyphocrinites
and Marhoumacrinus may be deeper than was previously believed by
PROKOP et PETR, 1987 or by HAUDE, 1992. There is no need to postulate convergence,
but parallel evolution is very plausible. If it is so, the diphyletic "family
Scyphocrinitidae" must be divided into the typical family Scyphocrinitidae,
and family Marhoumacrinidae covering the genera Marhoumacrinus and
From this point of view it is possible, that the cirrus-lobolith was restricted to the typical family, while the plate-type to the latter one. And finally, this situation implies, that predecessors of both these families had no floats. It is also probable, as offered by HAUDE (1992, p.157, fig.5), that the ancestors were endowed with articulated and branching cirri, adapted for anchoring on floating matter, especially on algae. After HAUDE, the "excessive branching of cirri eventually produced a cirral ball capable of keeping gaseous ingredients within small spaces". There is but no necessity for transformation of the cirrus-lobolith into plate-lobolith and "optimization of the cirral ball as a buoy by swelling of soap-bubble-like chambers", because of parallel origin of both.
However, the evolution of the floats is unimaginable in the sense of random mutation following by natural selection. Fortunately, such sentence as "All animals are adapted to the environment through natural selection" is now past even among darwinists. New model of evolution, so-called "punctuational model" or "punctuated equilibria", a model of rapid transitions and long persistences of unchanged species, attracted more and more attention of evolutionists through the advocacy of ELDREDGE et GOULD (1972). Species originated fully characterized, persisting with no or very little change for long intervals of time. Structures of an animal are very precisely constructed to the functions which they have to perform and without an internal self-ordering process most so-called "random" mutations must be harmful. The term "random" is seen by many evolutionists to be not merely vague, but positively misleading. At present, the operation of internal factors is widely accepted. Many new schools marked the past three decades of this century by enlivened controversy about tempo, modes and causes of evolution. The evidence, derived by paleontologists from the fossil record conflicts with orthodox neo-Darwinian concepts and, therefore, these have been deeply questioned.
For the purpose to throw light upon the origin of scyphocrinitid floats there seems to be need for rapid change without transitions and a plausible explanation for the mechanism of it. The only explanation seems to be rooted in series of symbioses with epipelagic algae, in accordance with the theory of endosymbiogenesis of MARGULIS (1981). This theory was originally based on change from cells without a nucleus (prokaryotes) to cells with a nucleus (eukaryotes) and now it has further consequences in relation to the Gaia hypothesis of LOVELOCK (1988). Both these concepts are also of great importance in the evolutionary theory of the "Frankfurter Schule" (see e.g., GUTMANN-EDLINGER 1991a,b).
The recognition of practical ubiquity of the symbiotic state and persistence of most symbioses through time has led Lynn Margulis to reexamination of evolutionary implications of "living together of differently named organisms". After MARGULIS (1981) symbiosis has affected the course of evolution "as profoundly as biparental sex". Most organisms depend directly on others for nutrients and gases. Only photo- and chemoautotrophic bacteria require merely inorganic nutrients, however, even oxygen, carbon dioxide and ammonia are end products of metabolism of other organisms. Although symbiotic relationships are treated in biological literature as exotic, they abound, and many of them affect entire ecosystems. For example, in tropical seas most invertebrates have algal symbionts. After Ferguson-Wood (1967, citation see MARGULIS 1981) these symbiotic algae are quantitatively more important than phytoplankton and free benthic algae on coral reefs and in other shallow waters with calcareous sediments; the productivity of these waters is maintained essentially due to such symbionts.
At present, Lynn Margulis is tend to be of the opinion, that her theory is non-Darwinian regarding the mechanisms of the origin of species. Why not, if it brings about natural explanations for natural phenomena? The fossil record, as mentioned above, is really in many respects not compatible with neo-Darwinian concepts and, therefore, the present authors believe that it is time to escape from misleading dogma within which such concepts envelop us and influence the facts we see.
From this point of view the symbiosis between discussed crinoids and epipelagic algae is very probable. Moreover, such speculation seems to be very useful, because we need no unnatural constructional change through a miraculous random mutation creating a 'hopeful monster' - a crinoid having at its disposal an evolutionary supernovelty unknown in all older and all younger taxa.
|number of basals and radials||character at the superfamily-level|
|sequence of first two fixed pinnules||the most important character
higher than species-level
(herein placed at the family-level)
|type of TBrr and of free arms
(uniserial or biserial)
|important character at genera-level
(in some cases strongly influenced
by ontogenetic stage)
|type of lobolith||probably family-level character
but the most speculative of all
|sculpture of calyx plates||in some cases species-level
but generally extremely variable
|number of SBrr||ontogenetically influenced but in
adult forms very good species-level
|presence of intertertibrachs||in some cases genera-level
sometimes possibly species-level
(dependence on ontogenetic stage)
|number of interbrachials||generally strongly dependent on
the ontogenetic stage
|Sequence of first two fixed pinnules||Type of lobolith||Stratigraphical distribution|
|SBr2 (outer) - SBr4 (inner)||probably cirrus-type||Upper Silurian - Lower Devonian|
|as in the family||as in the family||as in the family|
|Marhoumacrinidae n. fam.||SBr2 (outer) - SBr3 (inner)||probably plate-type||Upper Silurian - Lower Devonian|
PROKOP et PETR, 1987
|as in the family||as in the family||as in the family|
WAAGEN et JAHN, 1899
|as in the family||as in the family||Upper Silurian|
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POZNÁMKA K FYLOGENEZI SCYPHOCRINITIDNÍCH KRINOIDŮ
Rudolf J. Prokop - Václav Petr
V článku je na základě přísného vážení taxonomických znaků navržena nová systematika scyphocrinitidních krinoidů. Autoři polemizují s taxonomickým hodnocením, které podal HAUDE (1992), a ukazují, že nejdůležitější taxonomický znak scyphocrinitidních krinoidů - sled pevných pinulí na sekundibrachiáliích, nelze z hlediska přirozenosti systému opominout. Původní čeleď Scyphocrinitidae je zde proto nově rozdělena na typickou čeleď Scyphocrinitidae (zahrnující jen rod Scyphocrinites) a na čeleď Marhoumacrinitidae (s rody Marhoumacrinites a Carolicrinus). Autoři tím tedy dokumentují difyletický původ "krinoidů s plováky". Vznik plováků (tzv. lobolitů) přitom vysvětlují symbiózou s epipelagickými řasami, která umožnila paralelní evoluci v rámci obou čeledí. Na závěr autoři zdůrazňují význam symbiózy pro nedarwinovské přístupy k evoluční teorii.