May 22, 2015

The first 500 million year old grappling hooks in the evolutionary arms race.


A weird group of ancient but surviving carnivorous worms, known as priapulids, which live in burrows on the seabed, evolved a remarkable method of capturing their prey – they can turn their hook-lined throat region inside out through the mouth to form a very effective grappling iron for capturing their prey.
Category: May 2015
Posted by: Sarah

                        
Photo credits:
Fossil of a flattened and carbonized Ottoia with soft parts preserved from the 508 million year old Burgess Shale.  (photo: Martin Smith, Dept. Earth Sciences, University of Cambridge)

Reconstruction of a 508 million year old priapulid worm Ottoia in its seabed burrow during Cambrian times in the Burgess Shale of Canada (reconstruction_by Smokeybjb)

Now, a detailed study by researchers in the Department of Earth Sciences of the University of Cambridge of the fossil remains of 500 million year old priapulids, belonging to the extinct genus Ottoia, shows that these finger-sized worms were much more common and widespread predators in Cambrian times than previously thought.

Now Dr Martin Smith and his colleagues have used high-powered electron-microscopy to detail the internal structure of fossil hooks and spines from some 40 fossil specimens of Ottoia from the Cambrian age Burgess Shale of Western Canada. Here, unusual conditions have preserved remains of both the body tissues and the various sclerotized structures from priapulid fossils. As a result, the researchers can be certain that the hooks and spines they are examining are clearly associated with priapulids. Furthermore, Martin Smith and colleagues have been able to recognize similar characteristics in a variety of other Cambrian microfossils, generally known as SCFs (small carbonaceous fossils) from as far away as Australia and China whose origin has previously puzzled palaeontologists. Some of them were previously thought to be algal spores, which can also carry projecting hook-like structures.Like the more familiar annelid worms, the priapulids were essentially soft-bodied, apart from the tiny but tough organic hook-like and spiny structures, which are used for catching their prey and dragging themselves over the seabed. It is very rare for priapulid soft parts to be preserved, normally it is only the millimetre-sized, sclerotized organic structures which turn up when palaeontologists examine ancient seabed sediments.

Cambrian times saw an explosion in the diversity of marine life with the evolution of many groups of animals, ranging from sponges to the first fish. With so many different kinds of organisms, competition for food was intense. Although they were soft-bodied and therefore vulnerable to predation, the priapulids themselves became remarkably well adapted and successful predators. By burrowing into the seabed sediment they could hide from surface dwelling predators. And by evolving the extraordinary eversible hooked proboscis they became ambush predators that could grab any small unaware creature that wandered too close to a priapulid burrow.

Five hundred million years after they first evolved the priapulids are still around with 16 living species, although they are now restricted to certain inhospitable environments.

The research is published in the journal Palaeontology (May, 2015; http://dx.doi.org/10.1111/pala.12168)

To see some of these remarkable fossil priapulids and other fossil treasures of the Burgess Shale come and see the Sedgwick Museum’s display on the Explosion of Life in Cambrian times.

Douglas Palmer, Sedgwick Museum

Photo credits:

Microscopic close-up of the everted tooth-covered 'throat' of Ottoia, in a fossil from the Burgess Shale. (photo: Martin Smith, Dept. Earth Sciences, University of Cambridge)

A selection of isolated (SCF) microfossils identified as Ottoia teeth. Scale bar represents 50 µm (0.05 mm). (photo: Tom Harvey, Dept. Geology, University of Leicester)