Dinocochlea: a Solution to the Mysterious Giant Snail

Dinocochlea: a Solution to the Mysterious Giant Snail
Left: Apical whorl of the large dextral specimen of Dinocochlea. Right: A model of Dinocochlea with Natural History Museum research scientist Paul Taylor as a scale.

Found in 1921 in the Wealden area of Sussex in England during construction of an arterial road, Dinocochlea was originally presumed to be a fossilised gastropod shell. As such, it was given a Latin name that translates to "giant terrible snail" using the "dino-" prefix in a nod to Dinosaur ("terrible lizard") and refers to the nearby, paleontologically significant, quarry that featured many dinosaur fossils, the "Iguanodon Necropolis".

The history of the find is pretty interesting since the hypotheses that have been given for its identity include (in order of their proposal):
  1. It is a fossil of a FREAKISHLY big snail!
  2. It is a coprolite, a.k.a the remnant of a giant turd (most likely from an Iguanodon).
  3. It is a concretion fossil formed from the indents left underground by a spiraling path of a very small burrowing most likely worm-like organism.
The specimen didn't look quite right to be a gastropod, since the contours of proper fossils usually exhibited certain biological nuances (as well as traces of materials from the shell). As well, the direction of the spiral was also odd - it seemed as if these Dinocochlea specimen could spiral either way, which is actually quite odd for gastropods.

While being convinced that it was not a snail, Cox was unable to reach a firm conclusion about the true identity of Dinocochlea. However, he did entertain  alternative hypothese. That it is an enormous coprolite, perhaps the fossil excrement of the dinosaur, Iguanodon, the bones and teeth of which had been collected at the nearby Hollington Quarry. Spiral coprolites are known as fossils, mostly excreted by sharks with spiral valves in their lower intestines, but none come remotely close in size to Dinocochlea. Neither does Dinocochlea contain any of the expected remains of partly ingested food.

The last hypothesis involved a fossil type known as a concretion. Essentially what might have happened here, is that long long ago, there was a remnant of a thin spiral path left in the dirt by some burrowing creature. This would have left small but physically present shifts in the grains of sand, minerals, and rock around that path, which in turn provide potential spaces for mineral cements to seep into during the process of sedimentation. Over the years, these would become squeezed into what might look like a mini spiral fossil - similar in structure to a really thin spiral drinking straw.

However, these hard concretions inevitably shift the sedimentary rock that they are in, potentially creating other spaces for more mineral cement to come in. The net effect is that if the conditions are right, and if you wait long enough, concretion specimens will act like nuclei and will get "fatter." In other words, if you imagine the dimensions of a drinking straw getting wider, it might eventually look like our Dinocochlea specimen!

Dinocochlea was featured in the final episode of the 2010 BBC series Museum of Life which documented the work of the Natural History Museum.

See also:  The Largest Insect Ever Existed Was a Giant "Dragonfly"
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