«Happy families are all alike; every unhappy family
is unhappy in its own way.» Anna Karenina LEO TOLSTOY, 1877 |
«The prevalence of convergent evolution in pectinoid bivalves is a major problem for reconstructing their phylogenetic history. The currently available data of shell morphology, shell microstructure, and stratigraphic occurrence suggest that the alivincular-alate ligament evolved independently in the Pernopectinidae–Entolioidesidae–Entoliidae clade and in Pectinidae, and possibly more than once in the latter group. Shell microstructural trends were similar but not synchronous in the Pernopectinidae–Entolioidesidae–Entoliidae and possible Aviculopectinoidea–Pectinidae clades. It appears that different lineages of pectinoids were affected by similar evolutionary trends, perhaps driven by changes in the macroecological regime associated with the Paleozoic–Mesozoic transition. More data on Triassic pectinoids are needed to clarify their phylogenetic relationships and to elaborate the characteristics of their monophyletic groups. However, the available shell microstructural and shell morphological data suggest that Pectinoidea sensu Waller (2006) might be polyphyletic, containing one clade initiated by Pernopectinidae, and another initiated by the Aviculopectinoidea.»
CARTER, J. G. & M. HAUTMANN. 2011. Shell microstructure of the basal pectinid Pleuronectites laevigatus: implications for pectinoid phylogeny (Mollusca: Bivalvia: Pteriomorphia). Journal of Paleontology, 85 (3): 464-467. [p. 467]
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«In spite of substantial systematic revisions of the superfamily Pectinoidea in the 20th century, the old idea of a diphyletic Pectinoidea (Philippi, 1899, 1900) has persisted. Newell (1938: 35) recognized that Pernopecten is the only Palaeozoic genus that has a pectinoidean resilifer. He thought, however, that this genus gave rise only to the ‘modern amussiums’ (Propeamussiidae in modern terms) and not to other modern pectinoids, instead deriving the latter independently from the Aviculopectinoidea probably during the Triassic. As late as 2004, Hautmann (2004: 169) asserted that Newell’s concept of an independent origin of the Pectinidae from an aviculopectinoidean ancestor ‘has been accepted by most later authors ... although the missing link has not yet been found’.
The present study provides ‘the missing link’ between Palaeozoic Pernopecten and Mesozoic Pectinidae. The link is represented by the mainly Triassic Entolioididae, new family, which shares a common shell microstructural plan and filosus structure with the Pernopectinidae and a hinge articulation plan with the Entoliidae. Another link, between the Entolioididae and the Propeamussiidae, is provided by the new Triassic genus Filamussium, which shares a shell microstructural plan, filosus structure, and hinge articulation with the Entolioididae but shares slatlike internal ribs with the Propeamussiidae. Finally, Entolioidid genera such as Filopecten and Entolioides have well-developed multiordered radial costae and commarginal lamellae on their left valves not unlike those present in some of the earliest Pectinidae as represented by Praechlamys. Yet another possibility for the polyphyly of the Pectinoidea is provided by the family Spondylidae, which some authors think evolved a pectinoid resilium independently of other members of the superfamily. However, arguments are presented here that the family originated in the Late Triassic or Early Jurassic from a pectinoidean ancestor. Recent molecular genetic analyses involving the cytochrome oxidase gene lend support to this conclusion in that they indicate that the Spondylidae and Pectinidae are sister groups and that the Propeamussiidae has a more remote origin. If the superfamily Pectinoidea is indeed monophyletic, then clearly the basic adaptation of the group was to swimming facilitated by an enlarged pectinoidean type resilium, an enlarged centralized adductor in which the striated (‘quick muscle’) component became enlarged relative to the nonstriate component, and an amusiiform streamlined shape. All of these features are present in Late Palaeozoic Pernopecten. The inequilateral chlamydoid form, representing adaptation to byssal attachment through most or all of ontogeny, evolved later and repeatedly, as shown by some members of the Entolioididae, some members of the Entoliidae, and in the earliest members of the Pectinidae. This morphological plasticity set the stage for the phenomenal evolutionary radiation of shell form in the Pectinidae that was well underway before the end of the Mesozoic.» WALLER, T. R. 2006. Phylogeny of families in the Pectinoidea (Mollusca: Bivalvia): importance of the fossil record. Zoological Journal of the Linnean Society, 148: 313-342, figs. 1-12. [p. 335]
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