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 Paläontologie und Historische Geologie
Letzte Änderung
11.03.2009
 

The genus Myriapora. Pathways of evolution.

Schäfer, P., Bader, B., Nikulina, E.


Myriapora is an evolutionary young cheilostome bryozoan genus restricted to the Northern hemisphere. It is known with at least six species from mid Tertiary to recent times. Earliest, unproved reports of the type species M. truncata are from the eocene of Rumania, followed by the Oligocene of Germany, the Miocene (Tortonian) of the Paratethys (Vienna basin) and the Guadalquivir basin (SW Spain) and NW Marocco, and from the lower Pliocene of Netherlands. Today, M. truncata is an exclusively Mediterranean species. It is distinguished from the fossil populations by its distinctly ssed and bilamellar).


M. fungiformis was found in Oligocene (Rupelian), near-coast sediments of epicontinetal Europe, M. bugei has its distribution around the oceanic islands of the Central Atlantic (Azores, Great Meteor Bank). Fossil occurrences are restricted to the Miocene (Upper Tortonian, Messinian) of NW Marocco).


In contrast to the former species, M. coaractata, M. orientalis, M. subgracilis and M. subgracilis variabilis are restricted to cold-temperate to polar shelves of the N Atlantic, Siberian Sea and N Pacific.


Based on their different wall ultrastructures (apomorphies), two phylogenetic lineages are considered as sister groups. According to this hypothesis, the taxon Myriapora Blainville is based on the types species Millepora truncata Pallas; adelphotaxon is Leieschara M. Sars based on the types species L. coarctata Sars. Thus, the formerly revised taxon Leieschara M. Sars should be re-established.


The hypothetical phylogeneic tree is confirmed by the biogeographic distribution of the two clades. Myriapora is a mediterranean(Central Atlantic, warm-temperate taxon, while Leieschara is restricted to polar/subpolar provinces.


This hypothetical phylogenetic tree is based exclusively on morphologic characters. As a next step, the attempt is undertaken to test the tree by molecular genetics.