Giant file clams: A common fossil as an exciting document of Earth history

Jens Lehmann (Germany) Plagiostoma – a record of about 200 million years Are there any boring fossils out there in the ground? I do not think so and to demonstrate this, an “ordinary” fossil find is focussed on here. We are talking about “just” a mussel, but one that belongs to an extinct group and even this alone makes it exciting. Plagiostoma is a member of the file clam family. This genus is only known from the fossil record and appeared probably in the Permian and certainly by the Mid-Triassic period, about 240 million years ago. This genus became extinct at the Cretaceous-Palaeogene boundary – according to the most recent timescale dated 66 million years ago. At least two dozen of species have been described so far. The shells of Plagiostoma are moderately inflated and can reach the size of a hand, with an oblique oval outline. It is a common fossil, for example, in the Muschelkalk (Middle Triassic) in the Germanic Basin and quite a few continental countries. It is also well known from the Blue Lias of Southern England and stratigraphic equivalents, and can be frequently found at Monmouth Beach in Lyme Regis, a world-famous spot for fossil hunting. The giant Plagiostoma The species frequently encountered at Lyme Regis is Plagiostoma gigantea and the name already suggests that it is a giant amongst the representatives of the genus. The specimens figured here (Fig. 1) are of moderate size, with a total length of each about 8cm, but there … Read More

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