Kheraiceras Spath (Ammonoidea)-new forms and records from the Middle Jurassic sequence of the Indian Subcontinent

概要

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Kheraiceras Spath reached its peak during the Late Bathonian-Early Callovian and achieved a wide biogeographic distribution during that interval. The genus speciated rapidly and is represented in the fossil record by many species. The present endeavour provides a full taxonomic account of six species, of which five are from Kutch, western India. The sixth, K. noetlingisp. nov., is based on the specimen described as 'Sphaeroceras' cf. bullatum d'Orbigny by Noetling (1896) from Baluchistan, Pakistan. Among the five Kutch species one has also been found in Baluchistan. We know little about specific dimorphism in Kheraiceras. In at least three instances dimorphic pairs have been matched. Of the six species of Kheraiceras described herein three are new and two are new records. They are : Kheraiceras cosmopolitum, K. bullatum, K. cf. hannoveranum, K. spathi sp. nov., K. sp. A, and K. noetlingi sp. nov. Like many other biota, including other ammonites, Kheraiceras speciation is marked by a high degree of endemism in the Kutch Sea, which extended up to Baluchistan. The endemism in this newly opened basin is due to the transgressions resulting from the fragmentation of Gondwanaland.
日本古生物学会の論文
2000-09-29