Original paper

Sillakkudirhynchia gen. nov. (Rhynchonellida, Brachiopoda) from the Upper Cretaceous (Campanian) of the Cauvery Basin, southern India: Taxonomy, palaeoecology and palaeobiogeography

Radulović, Barbara V.; Ayoub-Hannaa, Wagih; Radulović, Vladan J.; Banjac, Nenad J.

Abstract

A new rhynchonellide genus Sillakkudirhynchia, with type species “Rhynchonella” plicatiloides Stoliczka, 1872, from the Campanian of the Cauvery Basin, southern India, is established. The specimens were collected from the calcareous sandstone beds of the Campanian Sillakkudi Formation (ammonite K. karapadense Zone) of the Ariyalur Group. Sillakkudirhynchia is distinguished by a subcircular to transversely oval shell, medium size, moderately dorsibiconvex valves, very small suberect beak, small and circular mesothyridid foramen, fine costellation, a broadly uniplicate arcuate to trapezoidal anterior commissure, slightly developed sulcus and fold, and very thick shell wall with serrated lateral ends. Internally, it is characterized by having disjunct deltidial plates, thin and slightly divergent dental plates, reduced subhorizontal hinge plates, small crescent-like inwardly concave crural bases, strong median septum, and raduliform crura. The shell structure of Sillakkudirhynchia plicatiloides is shown to be of typical fine fibrous (i.e. leptinoid) pattern. The raduliform crura of the type species are associated with fine fibrous (i.e. leptinoid) shell microstructure and confirm the attribution to the superfamily Hemithiridoidea. Sillakkudirhynchia gen. nov. was attached to hard substrate in a shallow-water, high-energy near-shore environment. The Upper Cretaceous brachiopod fauna from Gondwanaland shows at the generic level relatively moderate affinity to the fauna of the Northern Hemisphere.

Keywords

sillakkudirhynchiasillakkudi formationcampanianrhynchonellidasouthern indiabrachiopodacauvery basin