Sunday, 27 April 2014

A Circulatory System From The Pompeii Of The Invertebrate World

The dinosaur Amphicoelias is know from this single vertebra
Some creatures can be enigmatic. Yet due to the more complete nature of related organisms, we can reconstruct anatomies to a greater degree than fossils alone would allow.

With other species we can but guess at their general form. Many invertebrates end up being preserved as two dimensional, while translating the coloured splotches of organs and shells into a 3D form can be difficult. For years, creatures unknown as conodonts, were thought to be tubular creatures covered in spines and scales. Better preserved fossils showed them to be snake-like organisms with complex tooth-lined jaws.

For many creatures the general form is challenging enough, let alone the internal organs. Yet in some exceptional cases we know almost as much about the lifestyle and physiology of some extinct organisms as we do about living species. An example of this are the specimens of Marella splendens from the Burgess Shale which have been collected in literally the tens of thousands. Within this massive study sample we can see specimens preserved in a variety of orientations and degrees of degradation. This has allowed the accurate reconstruction of its anatomy. 

A reconstruction of the 520 million year old arthropod Fuxianhuia
showing the gun in green, the nervous system in blue and
the circulatory system in red
Fuxianhuia protensa, from the 520 million year old Chengjiang fossil beds, a locality which has been described as the Burgess Shale of the East, used a plethora of imaging techniques to map the eyes, brain and nervous system of this three inch long shrimp-like creature.

Now an international team of palaeontologists have found evidence of a circulatory system in Fuxianhuia. A circulatory system which is not only complex but has helped shed light on just how closely related the internal anatomy of these ancient Cambrian organisms is to their living relatives.

'This is the first preserved vascular system that we know of,' said Nicholas Strausfeld from the University of Arizona's Department of Neuroscience. 'Fuxianhuia is relatively abundant, but only extremely few specimens provide evidence of even a small part of an organ system, not even to speak of an entire organ system. The animal looks simple, but its internal organization is quite elaborate.' Indeed many aspects of its circulatory physiology proved to be more complex than versions seen in living creatures.

A fossil of Fuxianhuia protensa
Using a method of analysis which allows different parts of the fossil to be selectively viewed based in their chemical composition, Strausfeld's team identified the carbonaceous remains of a system of arteries and veins spanning the body and the heart which originally pumped blood through them.

'It appears to be the ground pattern from which others have evolved,' added Strausfeld. 'Different groups of crustaceans have vascular systems that have evolved into a variety of arrangements but they all refer back to what we see in Fuxianhuia. Over the course of evolution, certain segments of the animal's body became specialized for certain things.' 

Having obtained good reconstructions of its circulatory and nervous system the team were able to make some deductions about the lifestyle it might have lived. With its large brain supplied by an extensive arterial network, complex nervous system controlling a number of appendages, two antennae and powerful eyes, it is likely that this creature was active and capable of making a variety of behavioural decisions. The Cambrian was a time of great biological innovation. Yet only recently that we have been able to understand the physiological as well as the morphological aspects of the Cambrian Explosion.