Aretz et al_2011.pdf - ORBi - Université de Liège

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Kölner Forum Geol. Paläont., 19 (2011)
M. ARETZ, S. DELCULÉE, J. DENAYER & E. POTY (Eds.)
Abstracts, 11th Symposium on Fossil Cnidaria and Sponges, Liège, August 19-29, 2011
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ARCHAEOCYATHA: Computer-aided identification of genera
Adeline KERNER 1 & Françoise DEBRENNE 2
1 CNRS, UMR 7207, Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements, Laboratoire
Informatique et Systématique, MNHN, Département Histoire de la Terre, Bâtiment de Géologie, CP48, 57
rue Cuvier, 75005 Paris, France; kerner@mnhn.fr
2 13 rue du long foin, 91700 Sainte Geneviève des bois, France; francoise.debrenne@gmail.com
Archaeocyatha are a key-group in different fields of Life and Earth History. Assigned to various phyla,
they are now recognized as a class within the Phylum Porifera. The discovery of living aspiculate sponges
with a calcified skeleton by scuba divers in sub-marine caves of the Caribbeans in the late seventies, has
renewed interest in the biology, phylogeny and ecology of related fossils with previously problematic
status, such as Archaeocyatha. Morphological structures shows a great similarity in growth pattern,
immune reactions, and types of asexual reproduction (intercalicular budding) in both groups. Presently,
the class consists of 6 orders, 120 families and 307 genera.
They are an important group of marine sessile organisms almost entirely Early Cambrian, with some
relicts persisting into the Middle and Late Cambrian. Due to counter-clockwise rotation of Gondwana, the
only archaeocyaths species of post-Early Cambrian age are found in Antarctica which alone remained in
low latitudes.
They provide reliable basis for biozonation in key regions. The first stage subdivision based on
Archaeocyatha was established on Siberian Platform. Morocco, Western Europe, Australia, China and
Laurentia have provided regional scales.
Reef dwellers, they are necessary substrate for calcified cyanobacteria and cement but they seldom
produced a true framework to reefs. The Cambrian system is generally characterized by the absence of any
climate indicators useable as constraints for tectonic reconstructions. Then the distribution of Early
Cambrian reefs may provide suitable constraints to settle tropical paleolatitudes. Early Cambrian provinces
and realms are delimited using an exhaustive compendium of archaeocyathan genera.
Since Archaeocyatha are important Cambrian organisms, it is necessary for scientists dealing with
Paleozoic rocks to identify those fossils. But keys, easy to use and adapted even to incomplete specimens,
are lacking. Up to now, a knowledge-database in English, carried out with the software XPER², is now
available online free: http://www.infosyslab.fr/archaeocyatha
It comprises the 307 valid genera described with 120 descriptors (85 morphological and ontogenetic, 8
stratigraphic and geographic and 27 taxonomic).
This site comprises information about Archaeocyatha (morphology, bibliography…), detailed
descriptive cards with figures of type-specimens and eventually additional figures to illustrate
morphological details. Information of the database is used to build an identification unit as an interactive
key with free access.
Results of this study allow the standardization of currently used descriptors, the definition of a revised
terminology and the possibility to identify synonyms. The need of establishing new characters and/or
states of characters may appear during the work.
Fig. 1 is an example for the identification module. The interface is composed of three parts: on the left,
the list of descriptors to be chosen by the user, at the center, information about the descriptors (definitions,
figures) and on the right, the lists of remaining and discarded taxa. Identification consists of the repetition
of successive steps: firstly, the choice of a descriptor, secondly, the choice of one or several states of the
descriptors and finally a confirmation with the submit button. At each validation, lists of remaining and
discarded taxa and list of possible descriptors are updated. Descriptors can be sorted to facilitate
identification.
With this interactive key, different lists (i.e. all Australian genera during Atdabanian…) may be rapidly
established. Another possibility is to bring into light similarities and differences (i.e. between genera of the
same family).
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