WFS News: Arctostrea Oyster fossils found in India

Arctostrea fossil from dalmiapuram,India.( Photo Courtesy: (C)World Fossil Society.Photo by Riffin T Sajeev ,Russel T Sajeev

Arctostrea fossil from dalmiapuram,India.( Photo Courtesy: (C)World Fossil Society.Photo by Riffin T Sajeev ,Russel T Sajeev

The fossil of Arcostrea from Dalmiapuram formation has a well defined high zigzag commissure. The problem of oxygen and food supply is particularly important to the development of oysters. Passive mode of life on the basin floors of muddy and often turbid waters and gregarious occurrence did not create good living conditions. In response to difficult environmental regime the oysters have developed highly advanced functional adaptations which are reflected first of all in structural peculiarities of the shell. These are: arcuate shape, zigzag commissure, lobe-like enlarged posterior edge of umbo, promyal chamber and also marginal denticles and pedal retractor muscle scar .

Part of Arctostrea fossil from dalmiapuram,India.( Photo Courtesy: (C)World Fossil Society.Photo by Riffin T Sajeev ,Russel T Sajeev

Arctostrea fossil from dalmiapuram,India.( Photo Courtesy: (C)World Fossil Society.Photo by Riffin T Sajeev ,Russel T Sajeev

Pervinquiere (1910) proposed to separate from Alectryonia new genus, Arctostrea, with type species Ostrea carinata Lamarck, comprising strongly elongated, slender, arcuate forms with high zigzag commissure. These genera differ in a number of features in external and inner structures, but some representatives of genus Alectryonia (e.g., AL rastellaris or AL gregarea) are rather elongated and arched. Probably the Arctostrea originated from such forms.

Arctostrea fossil from dalmiapuram,India.( Photo Courtesy: (C)World Fossil Society.Photo by Riffin T Sajeev ,Russel T Sajeev

Arctostrea fossil from dalmiapuram,India.( Photo Courtesy: (C)World Fossil Society.Photo by Riffin T Sajeev ,Russel T Sajeev

Arctostrea fossil from dalmiapuram,India.Commisures are visible( Photo Courtesy: (C)World Fossil Society.Photo by Riffin T Sajeev ,Russel T Sajeev

I proposed The Rastellum (Arcostrea) genus in cavery basin geological area may have originated in late Jurassic with adaptive modifications like high toothed commissure. The reason for such adaptation is the existence of high energy environment with heavy sedimentation. Hence the possibility of various adaptations on the alectryonia cannot be ruled out. The functional importance of high toothed commissure was broadly discussed by Carter (1968) on the Cretaceous representatives of Arctostrea.

Arctostrea fossil from dalmiapuram,India.( Photo Courtesy: (C)World Fossil Society.Photo by Riffin T Sajeev ,Russel T Sajeev