| P number: | P549455 |
|---|---|
| Caption: | Pterotrigonia scabricola, a fossil bivalve. |
| Description: | The trigoniids are a very distinctive family of bivalves that first evolved during the mid Trias and are still found living today. Pterotrigonia, however, is an extinct form which evolved in the late Jurassic (about 140 million years ago) and spread around the world, before disappearing during the late Cretaceous (65-98 million years ago). Pterotrigonia scabricola has inequilateral shaped valves with a wide, flattened area (escutcheon) behind the umbone and separated from the side of the valve by a marked angularity. Very heavy ribs run obliquely over the flank of the valve and make a chevron-like shape at the angularity. Bivalves are molluscs that first evolved over 500 million years ago during the middle of the Cambrian period. They flourished during the Mesozoic (particularly the Jurassic and Cretaceous) and in the Cainozoic eras. They are abundant in the modern seas and dead shells are often found in the beach sands around the world. The early bivalves are associated with marine palaeoenvironments, but they later colonised brackish and fresh waters. As they are so common in modern times, their mode of life can be extrapolated back into the geological past and used in palaeoenvironmental reconstructions. |
| Photographer: | Unknown |
| Copyright statement: | NERC |
| Orientation: | Square |
| Size: | 453.33 KB; 1000 x 1000 pixels; 85 x 85 mm (print at 300 DPI); 265 x 265 mm (screen at 96 DPI); |
| Average Rating: | Not yet rated |
| Categories: | Best of BGS Images/ Fossils |
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