Tuesday, 23 October 2012

New Research Suggests That The First Jawed Vertebrates Had A Vicious Bite

On the side of a high mountain in the Rocky Mountains of British Columbia, Canada, lies perhaps the most hallowed locality in all of palaeontology. The Burgess Shale preserves the remains of a biological event known as the Cambrian Explosion in which, the diversity of life increased 1000 fold. The foundations for modern groups of animals were laid down during this point in Earth's history some 510 million years ago.

One of the 16 known fossils of Pikaia, the oldest vertebrate on the planet
The primordial ancestors of everything from the arthropods to the sea urchins can be found within the rocks at the Burgess Shale. However, amongst all the weird and wonderful organisms, the super predators, the five eyed, armored beasts which crawled and swam their way through the oceans of the Cambrian, was one seemingly insignificant creature called Pikaia. Yet despite its rather humble appearance  it is one of the most important fossil organisms from the shale.

Known from just 16 specimens, it was only about 5 centimetres in length with two structures akin to tentacles on its head and fluke running along the length of its tail. Not much to look at, but Pikaia is the oldest creature on Earth with a backbone. Every vertebrate throughout the whole of natural history is descended from this tiny creature. It would give rise to the first ever fish around 30 million years later. Yet these creatures were very different to most kinds of fish today as they did not have jaws.

They fed by using their jawless mouths to siphon nutrients from mud on the sea floor. It was also thought that the first ever vertebrates with jaws were also filter feeders. However analysis of fossils of some earliest jawed vertebrates is changing this long-held view of evolution. Philip Donoghue, a palaeontologist from the University of Bristol, is known for his work on the oldest predator on Earth.

Using a machine called a synchrotron in Switzerland - a particle accelerator which fires electrons around a circular tunnel, close to the speed of light inside a magnetic field, to produce such high energy x rays that solid objects, with internal structures, can be analysed in perfect, microscopic detail - Donoghue was able to reconstruct a tiny worm-like creature called Markuelia from embryos found in China which possessed the first ever teeth on the planet.

A reconstruction of the 370 million year old placoderm
Compagopiscis with its newly discovered teeth
Using the same machine, which is also the most powerful of its kind, he was able to create perfect 3D models of a group of armored fish known as the placoderms which were the first ever vertebrates to evolve jaws. 'The fossils are very rare and so no museum would ever allow anyone to cut them up to study structure,' said Donoghue. The advantage of the synchrotron is that it is non-invasive and can get down to levels of detail impossible to reach using other methods.
The synchrotron image of the teeth and jaw of Compagopiscis 

'We were able to visualize every tissue, cell and growth line within the bony jaws, allowing us to study the development of the jaws,' said researcher Martin R├╝cklin, another palaeontologist from University of Bristol. The 370 million year old fossils in question came from a placoderm called Compagopiscis which is one of the oldest jawed vertebrates on the planet and is now shown to have possessed teeth. A closer look revealed a similar composition to modern teeth with hard, dense, bony tissue forming the bulk to the tooth with a pulpy cavity in the centre and a layer of enamel on the outside.

The discovery suggests that teeth evolved either with or very soon after jaws, as opposed to long after, preceded by a group of jawed vertebrates with sucker mouths. The placoderms would go on to become the most powerful creatures in the sea until they became extinct. Their armour plates made them almost impervious to any attack and their teeth could deliver deadly, crushing blows to their prey. Some were more powerful than the tyrannosaurids or the giant marine reptiles of the age of the dinosaurs.