Abstract
The cerithioids are a diverse group of gastropods found globally as fossil and living animals during the Cenozoic Era. Their systematics is riddled with problems stemming from large morphological variability, homoplasy, and wide geographical distribution. Six cerithioid species are described here from the lower Middle Eocene of Kutch, Gujarat, western India. All but two are new species. They are Palmerella kutchensis, Tenagodus? sowerbyi, Potamides archiaci, and Cerithium harudiensis. The rest are new records from Kutch and were known only from Pakistan. A palaeobiogeographical review based on major published records of benthic molluscs from Pakistan reveals strong endemism. The cerithioid faunas from different parts of Pakistan and this report from Kutch also show strong endemism and often quite localized development. It is argued here that unhindered faunal mixing was not possible in this province since these newly evolved basins were restricted in nature in their Lower Cenozoic history.
Highlights
Cerithioids are an extremely diverse and less understood group of gastropods
Allmon [7] erected the genus Palmerella to include American Palaeogene turritellids from the Gulf Coastal Plain with the spiral rib sequence of C1B1A2, growth line with a moderately deep lateral sinus flanked by two inflection points and a moderately deep basal sinus, relatively short protoconch, and basally carinate to rounded whorl profile
The genus Haustator differs from Palmerella in having sculpture formula of C1B2A3, a prominent basal carina and generally a frustrate whorl section with flat whorl side
Summary
Cerithioids are an extremely diverse and less understood group of gastropods. It includes the family Turritellidae with one of the highest specific diversity among gastropods since the Late Cretaceous period. Their taxonomic prodigality does not reflect on morphological disparity. The simple turreted coiling characterizes all cerithioids. Cerithioid species are often defined based on very small and minute differences in characters. Many species, especially geographically widespread ones, have extremely variable morphological features resulting in large overlapping in several attributes with one or another species (e.g., see Houbrick [1] and Reid et al [2]). Morphological convergence is common in higher taxonomic categories, such as families and genera [3]
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