NDLI: Body plan and evolutionary trends in fossil echinoderms (Homalozoa, Blastoidea, Edrioasteroidea)

Content Provider	Springer Nature Link
Author	Gudo, Michael
Copyright Year	2005
Abstract	Der Körperbau der Echinodermen lässt sich bei konstruktionsmorphologischer Betrachtung als hydraulische Skelettkapsel-Konstruktion verstehen. Diese Konzeption erlaubt es, den Körperbau und die Evolutionsgeschichte einiger nur fossil bekannter Echinodermen zu rekonstruieren. Hierbei wird deutlich, dass es neben den beiden Hauptevolutionslinien der pentaradialsymmetrischen Echinodermen einen weiteren Grundbauplan der Echinodermen gibt, den der Homalozoen i.w.S. Diese Fossilien repräsentieren keine urtümlichen Echinodermen oder gar Chordaten, sondern eine eigene Evolutionslinie. Von allen drei Hauptevolutionslinien gab es mehrfach Differenzierungsmöglichkeiten. Hiervon werden die Körperkonstruktionen der Blastoiden und der Edrioasteroiden genauer betrachtet. Gemeinsam ist diesen beiden Abzweigen, dass sie einen Evolutionstrend repräsentieren, der sich mehrfach in der Echinodermenevolution gezeigt hat: die sphärische Ausformung des Körpers, wobei die Arme mit den Ambulacralfeldern in den Körper einbezogen werden. Dieser Trend ist zudem noch in der Körperkonstruktion der rezenten Echinozoen zu beobachten, und er lässt sich konstruktionell begründen: die sphärische Ausformung des Körpers ist eine mechanische (hydraulische) Notwendigkeit der hydraulischen Skelettkapselkonstruktion der Echinodermen, die sich immer dann einstellt, wenn interne Verspannungselemente aufgelöst oder umorganisiert werden.The basic body plan of echinoderms can be best explained from the functional morphological point of view as a skeleton-capsule construction. This conceptual design explains the body plan of some echinoderms that are known only from fossils, and points up that in addition to the two main evolutionary lines of pentameric radial symmetry one further one exists: that of the homalozoans sensu lato. These fossils represent neither basal echinoderms nor chordates, but rather, a separate evolutionary line. All three lines were sources of radiation, but only the structure of the blastoids and edrioasteroids will be further discussed here. These two branches have a spherical form in common, whereby the arms with their tube feet remain appressed to the body: a tendency seen often in echinoderm evolution. This trend occurs even among Recent echinoderms and can be rationalized biomechanically. The spherical body form is a structural necessity of a hydraulic skeletal-capsule construction in echinoderms, and always occurs when internal support structures are lost or reorganized. Such historical evolutionary explanations make it most plausible that all body structures of the various echinoderm classes most likely represent side branches of the main evolutionary pathway of pentameric echinoderms.
Starting Page	39
Ending Page	62
Page Count	24
File Format	PDF
ISSN	00372110
Journal	Palaeobiodiversity and Palaeoenvironments
Volume Number	85
Issue Number	1
Language	English
Publisher	Springer-Verlag
Publisher Date	2005-01-01
Publisher Place	Berlin, Heidelberg
Access Restriction	Subscribed
Subject Keyword	Soft body reconstruction engineering morphology hydraulic skeletal capsule echinoderms homalozoans blastoids edriosteroids spherical body shape Paleontology Biodiversity Animal Systematics/Taxonomy/Biogeography Plant Systematics/Taxonomy/Biogeography Freshwater & Marine Ecology
Content Type	Text
Resource Type	Article
Subject	Paleontology

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