Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Kalyanbrata Daitai ¹, Debasish Bhaumik ², Sudipta K. Jana ², Subhendu Bardhan ²

Affiliations
1 Oil and Natural Gas Commission, Ankleshwar-393 010, IN
2 Department of Geological Sciences, Jadavpur University, Calcutta-700 032, IN

Abstract

Macrocephalites triangularis Spath is the oldest macrocephalitid species in Kutch. Judging from the associated taxa and comparison of similar macrocephalitids and other forms between Kutch and other parts of the world, a Late Bathonian age for M. triangularis is reaffirmed. Previous systematic description was based on only two specimens. A fair number of well preserved specimens has enabled us to trace the ontogenetic development and decipher sexual dimorphism. The importance of this species in the evolution of later rnacrocephalitids of Kutch is explored.

Keywords

Macroceplullites (Ammonoidea), Bathonian, Palaeontology, Kutch, Gujarat.

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Debasish Bhaumik ¹, Kalyanbrata Datta ², Sudipta Kumar Jana ¹, Subhendu Bardhan ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta 700 032, IN
2 Oil & Natural Gas Commission, Ankleshwar 393 020, IN

Abstract

Macrocephalites Zittel, 1884, an important genus in Kutch biostratigraphy, shows considerable diversity at species level. Macrocephalites formosus (Sowerby) is one species which shows a wide range of variability of different morphological characters. A detailed statistical analysis of the principal biocharacters of 140 individuals collected from different localities of Kutch was made to assess quantitatively the range of variation of the species.  "Macrocephalites chariensis (Waagen)", which was previously designated as a separate species, is demonstrated here to be a variant of Macrocephalites formosus and is incorporated into the latter species. An attempt is made to delineate the generic characters of Macrocephaliles and describe the diagnostic characters of the species M. formosus in detail. The variability of the species has no obvious adaptive significance.

Keywords

Ammonoidea, Jurassic, Kutch, Palaeontology.

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