A low oxygen tolerant East Pacific flat clam (Posidonotis semiplicata) from the lower Jurassic of the Canadian Cordillera

M. Aberhan, J. Pálfy

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Flat clams represent a loosely defined group of thin-shelled, flat-valved bivalves. Their distribution and high concentration in some, especially Mesozoic, rocks have attracted interest, and several contrasting paleoecologic interpretations have been proposed to explain their occurrence. We present a comprehensive study of Posidonotis semiplicata (Hyatt), an Early Jurassic flat clam common in western North and South America. Posidonotis symmetrica (Hyatt), Posidonotis balteata (Crickmay), and Posidonotis cancellala (Leanza) are interpreted as subjective junior synonyms. In North America, P. semiplicata occurs in the upper Sinemurian to lower Toarcian of several Cordilleran allochthonous terranes. The South American record is restricted to upper Pliensbachian to lower Toarcian occurrences, suggesting that the species originated in the northeast Pacific in late Sinemurian time and spread to the southeast Pacific by the late Pliensbachian. The closely related Posidonotis dainellii (Losacco), sporadically known from the Tethys, is likely derived from P. semiplicata via migration through the Hispanic Corridor and subsequent geographic isolation. The functional morphology of P. semiplicata suggests an early ontogenic byssal attachment followed by a reclining mode of life with adaptation to soft substrates. The species is commonly found forming shell pavements in dark mudrocks with no, or very few, other benthic organisms. It provides an example of an epibenthic bivalve that favoured low-energy, dysaerobic environments, a niche preferentially exploited by flat clams.

Original languageEnglish
Pages (from-to)993-1006
Number of pages14
JournalCanadian Journal of Earth Sciences
Volume33
Issue number7
Publication statusPublished - Jul 1996

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Sinemurian
Pliensbachian
Toarcian
cordillera
bivalve
Jurassic
functional morphology
oxygen
Tethys
pavement
mudstone
terrane
niche
shell
substrate
rock
energy
North America
distribution
corridor

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

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title = "A low oxygen tolerant East Pacific flat clam (Posidonotis semiplicata) from the lower Jurassic of the Canadian Cordillera",
abstract = "Flat clams represent a loosely defined group of thin-shelled, flat-valved bivalves. Their distribution and high concentration in some, especially Mesozoic, rocks have attracted interest, and several contrasting paleoecologic interpretations have been proposed to explain their occurrence. We present a comprehensive study of Posidonotis semiplicata (Hyatt), an Early Jurassic flat clam common in western North and South America. Posidonotis symmetrica (Hyatt), Posidonotis balteata (Crickmay), and Posidonotis cancellala (Leanza) are interpreted as subjective junior synonyms. In North America, P. semiplicata occurs in the upper Sinemurian to lower Toarcian of several Cordilleran allochthonous terranes. The South American record is restricted to upper Pliensbachian to lower Toarcian occurrences, suggesting that the species originated in the northeast Pacific in late Sinemurian time and spread to the southeast Pacific by the late Pliensbachian. The closely related Posidonotis dainellii (Losacco), sporadically known from the Tethys, is likely derived from P. semiplicata via migration through the Hispanic Corridor and subsequent geographic isolation. The functional morphology of P. semiplicata suggests an early ontogenic byssal attachment followed by a reclining mode of life with adaptation to soft substrates. The species is commonly found forming shell pavements in dark mudrocks with no, or very few, other benthic organisms. It provides an example of an epibenthic bivalve that favoured low-energy, dysaerobic environments, a niche preferentially exploited by flat clams.",
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N2 - Flat clams represent a loosely defined group of thin-shelled, flat-valved bivalves. Their distribution and high concentration in some, especially Mesozoic, rocks have attracted interest, and several contrasting paleoecologic interpretations have been proposed to explain their occurrence. We present a comprehensive study of Posidonotis semiplicata (Hyatt), an Early Jurassic flat clam common in western North and South America. Posidonotis symmetrica (Hyatt), Posidonotis balteata (Crickmay), and Posidonotis cancellala (Leanza) are interpreted as subjective junior synonyms. In North America, P. semiplicata occurs in the upper Sinemurian to lower Toarcian of several Cordilleran allochthonous terranes. The South American record is restricted to upper Pliensbachian to lower Toarcian occurrences, suggesting that the species originated in the northeast Pacific in late Sinemurian time and spread to the southeast Pacific by the late Pliensbachian. The closely related Posidonotis dainellii (Losacco), sporadically known from the Tethys, is likely derived from P. semiplicata via migration through the Hispanic Corridor and subsequent geographic isolation. The functional morphology of P. semiplicata suggests an early ontogenic byssal attachment followed by a reclining mode of life with adaptation to soft substrates. The species is commonly found forming shell pavements in dark mudrocks with no, or very few, other benthic organisms. It provides an example of an epibenthic bivalve that favoured low-energy, dysaerobic environments, a niche preferentially exploited by flat clams.

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