Rhynchonellida

The Rhynchonellida are an order of brachiopods, also known as lamp shells. These marine invertebrates are characterized by their two-valved shells, which are typically sharply beaked and ridged, with one valve being convex and the other more flattened.1

Brachiopods, in general, resemble mollusks but are a distinct phylum. They have been present since the Cambrian Period, over 542 million years ago, and were once extremely abundant. While most modern brachiopods are small, some fossil forms were quite large. The Rhynchonellida order has been present since the Ordovician Period (approximately 488 to 444 million years ago) and has survived to the present day, though with fewer genera than in the past. They are useful as index fossils for dating geological periods.23