Porambonites, PANDER, 1830

Mergl, Michal, 2013, Porambonites Havliceki Sp. Nov., A New Brachiopod From The Šárka Formation (Darriwilian) From Bohemia And Its Contribution To Early History Of The Porambonitidae, Acta Musei Nationalis Pragae Series B 69 (1 - 2), pp. 87-92 : 90

Porambonites in the Prague Basin

Porambonites havliceki sp. nov. occurs within a deeper-water faunal fossil association of the Šárka Formation (Darriwilian), by Havlíček and Vaněk (1990) named Euorthisina – Placoparia Community. This “community” is characterised by invertebrates adapted to soft muddy bottom: trilobites, hyolithids, nuculid bivalves, gastropods, ostracods, asteroids, ophiouroids, mitrates, cystoids, and machaeridians. Planktonic and nektonic biota are common in the fossil assemblage, represented by graptoloids, cephalopods and cyclopygid trilobites. Sessile brachiopods are less common, with orthids Eodalmanella and Euorthisina (often forming monospecific clusters), and minute, likely infaunal obolids. Composition and preservation indicate a deeper-water environment of the outer shelf type, with more taxa, especially among the trilobites, common with the contemporaneous deeper-water associations of Avalonia and Iberia ( Fatka and Mergl 2009).

Rarity and deeper-water origin of Porambonites havliceki in this fossils association indicates, that several tens up to a few hundred metres deep sea was generally a hostile environment for the porambonitids. Enviroment was much deep, cold, with muddy sea floor and possible weak oxygen deficiecy. There may be also other explanations of the Porambonites rarity in the Šárka Formation. A small porambonitid population originated by a peripatric speciation from the distant Baltic source occupied for a short time the shallower shelves of the Perunica. The unique find simply represents a unique example of the specimen transported from presently unpreserved shallower shelf. Notwithstanding the rarity of P. havliceki , the presence of a porambonitid in the Prague Basin indicates, that barrier of the Rheic Ocean between Perunica and Baltica could be over-crossed in the Darriwilian.