Dinocochlea: a solution to the mysterious spiral of Hastings

Last week, we introduced Dinocochlea ingens, a gigantic spiral fossil from the Lower Cretaceous Wadhurst Clay Formation of Hastings, Sussex. Discovered in 1921 during the extension of St Helens Road near Old Roar Glen, this fossil immediately excited local and, indeed, national interest. The specimens were despatched to the British Museum (Natural History) where BB Woodward, a mollusc specialist who had recently retired as chief librarian, formally described the fossil as the new genus and new species – Dinocochlea ingens. The clue to Woodward’s interpretation of the fossil is in the name Dinocochlea, meaning ‘terrible snail’. Woodward (1922) considered Dinocochlea to be the largest snail that had ever lived. By piecing together the fragments found by the workmen building the road, he was able to reconstruct the supposed snail as a monster over 7 feet tall, 14 inches wide and with 23 spiral whorls (Fig. 1).

Dinocochlea Fig1Fig. 1. Plaster reconstruction of Dinocochlea, measuring more than 2m in length.

Not a snail

For a short time, Dinocochlea achieved celebrity status and was exhibited in the public galleries of the BM(NH) between the wars. However, its identity as a colossal snail was soon to be challenged. One of Woodward’s colleagues, the eminent fossil mollusc researcher LR Cox, was the main critic. Cox (1929, 1935) pointed to the variability in the tightness of spiral coiling between specimens of Dinocochlea and the fact that both left and right-handed varieties existed, which would be very unusual for a true snail. Furthermore, the shell itself was not preserved, nor was there was a space between the spiral whorls that would be expected had the shell dissolved, as is so often the case in fossil molluscs. The fatal blow to the snail theory was the structure of the initial whorl. Even in large snails, this begins with a tiny larval shell – the protoconch – a millimetre or less in diameter. In contrast, the final whorl of Dinocochlea is a bulbous structure, measuring 30 to 40mm in diameter, hardly consistent with the tiny free-swimming larva of a snail.

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