Taxonomy and phylogeny of cementing Triassic bivalves (families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae)

Abstract

ABSTRACT. Based on new material from the Upper Triassic Nayband Formation of east-central Iran and on type material from the Alpine Triassic, the taxonomy of the cementing bivalve families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae is examined and their phylogenetic relations are discussed. The Prospondylidae are characterized by the presence of an early pectiniform stage in their Palaeozoic genera which disappeared in most later forms due to ontogenetic pre-displacement of cementation. The Plicatulidae probably evolved from an ancestor within the Prospondylidae by the formation of strong crura, which allowed the reduction of the lateral part of the ligament. Their hinge was later modi®ed by shifting resilifer and crura in a ventral direction and by forming a secondary ligament dorsally. The emended genera Eoplicatula and Pseudoplacunopsis represent different early stages of this development. The species Eoplicatula parvadehensis sp. nov. and Pseudoplacunopsis asymmetrica sp. nov. from the Nayband Formation are described. The shell of some early Ostreidae is characterized by the lack of structural chambers and by the presence of an originally aragonitic inner shell layer. For such forms, the new genus Umbrostrea is proposed, and the new species Umbrostrea emamii and Umbrostrea iranica are described. The available data on shell microstructure as well as most conchological characters do not support a close relationship between Ostreidae, Plicatulidae and Dimyidae.

Ichthyosaurs from the French Rhaetian indicate a severe turnover across the Triassic–Jurassic boundary

“…Hallam and Wignall 1997;Wignall and Bond 2008;Smith et al 2014). But other groups such as plesiosaurs and neoichthyosaurians radiated immediately after (Benson et al 2012;Fischer et al 2013), implying a Rhaetian or older divergence of lineages.…”

The oyster enigma variations: a hypothesis of microbial calcification

“…This condition is best exemplified by Late Triassic to Recent oysters (Ostreoidea) (Harry 1985;Chinzei 1986Chinzei , 1995Chinzei , 2013Malchus 1990;Chinzei and Seilacher 1993;Carriker 1996;Hautmann 2001;Kirby 2001).…”

Treatise Online no. 45: Part N, Revised, Volume 1, Chapter 21: Cementing Bivalvia

“…Among extant Pteriomorphia, cementation has been recorded in members of Ostreoidea, Plicatuloidea, Dimyoidea, and Pectinoidea (within the Spondylidae and sporadically within the Pectinidae, e.g., Hinnites dEfrancE, 1821; Eopecten douVillé, 1897; Prohinnites gillEt, 1922; Crassadoma bErnard, 1986). Additionally, there are a number of extinct cementing pteriomorph taxa (Terquemiidae, Lithiotidae, Chondrontontidae, a few genera of Pseudomonotidae) (rEiS, 1903;frEnEix & lEfèVrE, 1967;nEwEll & boYd, 1970;hautMann, 2001). Most members of the pectinoid superfamily Anomioidea fix themselves permanently to hard substrata by a massive calcified byssus (YongE, 1977), but this cannot be properly referred to as cementation.…”

“…A particular problem has been to establish the origin of oysters and their relationships to some of the rather problematic extinct early Mesozoic cementers, such as terquemiids. This topic has provoked a rather lively debate (e.g., nEwEll & boYd, 1970;cartEr, 1990, p. 220, 250;hautMann, 2001hautMann, , 2006MárquEz-aliaga & others, 2005;chEca & others, 2006;MalchuS, 2008), although the paleontological, anatomical, and molecular data now clearly indicates that oysters were derived from pterioids, rather than from pectinoids (cartEr, 1990, p. 220, 250;caMpbEll, 2000;StEinEr & haMMEr, 2000;giribEt & whEElEr, 2002;giribEt & diStEl, 2003). It has also been debated whether the extant chamids were descended from the extinct rudists (odhnEr, 1919;YongE, 1967).…”