VIII.—Variation in Shape of Shell with Respect to Ecological Station. A Review dealing with Recent Unionidæ and Certain Species of the Anthracosiidæ in Upper Carboniferous Times

Abstract

Studies in the variation of the Anthracosiidæ (= Carbonicolidæ) in the South Wales Coalfield by Davies and Trueman (1927) and in the Scottish Coalfields by Leitch (1936, 1940, 1941) have suggested that environmental influence on shell form is confined to changes in thickness of shell and in obesity. Davies and Trueman quoted H. R. Wakefield, who remarked that to-day among the Unionidæ these characters appear to vary according to the station of the shells in a single lake. Leitch referred to the work of Ortmann (1920) on the relation between obesity and distribution of river mussels in a large drainage basin in the U.S.A. The writer, in the course of very detailed work on the most highly variable faunas of the Anthracosiidæ known in the British Coal Measures, found evidence suggesting that certain other changes in shell shape and dimensions may also accompany environmental changes, as far as past environments may be reflected in the lithology of the rocks containing the shells.

Shape variation in the Australian freshwater mussel Alathyria jacksoni Iredale (Bivalvia, Hyriidae)

“…Eagar (1948) drew attention to this, and to similar variation shown by fossil anthracosiid bivalves. He later ventured an explanation for the adaptive significance of the variation (Eagar, 1978), incorporating earlier work by Trueman (1966Trueman ( , 1968.…”

Punctuated equilibria, morphological stasis and the palaeontological documentation of speciation: a biological appraisal of a case history in an African lake

“…In a still earlier review, Eagar (1948), discusses variation in shell form among both fossil and living freshwater bivalves in relation to ecological conditions. Similar reservations must be expressed with regard to gastropods.…”

Middle Jurassic unionids (non-marine Bivalvia) from the Shiwandashan Basin, southern China, with special emphasis onCuneopsisSimpson

“…0.5) and the umbo is situated in the anterior part (Table 1). Thus, based on such morphological features, we conclude that these bivalves probably lived in a large river (Table 2, Ball 1922;Eagar 1953;Scholz 2003;Good 2004). …”