Perhaps radiodonts were crucial in the Cambrian Explosion

Pahvantia hastasta fossils (Image courtesy Stephen Pates / Rudy Lerosey-Aubril)
Pahvantia hastasta fossils (Image courtesy Stephen Pates / Rudy Lerosey-Aubril)

An article published in the journal “Nature Communications” describes a study on Pahvantia hastasta, a relative of today’s arthropods that lived about half a billion years ago, in the Cambrian period. Stephen Pates of the British University of Oxford and Rudy Lerosey-Aubril of the Australian New England University examined fossils discovered many years ago in the mountains of today’s Utah, USA, after extensive preparatory work. They believe that this species belonged to the group of radiodonts, that it fed on microplankton and that this type of aquatic animal contributed to kickstart the diversification of life forms on the seabed in the Cambrian Explosion.

The animals of the radiodont (Radiodonta) group include some of the first predators known such as Anomalocaris canadensis. Their study is important to try to reconstruct the phases that led to the diversification of the first animals in the phyla existing today. Pahvantia hastasta was smaller than others belonging to that group with a length of less than 25 cm and its identification was complex since initially four specimens were assigned to two different arthropods since one of them was first considered a part of an arthropod called Proboscicaris agnosta and then of another radiodont of the genus Hurdia.

The new study showed the characteristics that convinced the researchers that Pahvantia hastasta was really part of the group of radiodonts and some interesting aspects that led them to believe that it’s an important species in the Cambrian Explosion, the period of maximum diversification of living species in the history of life on Earth. The causes of that event are the subject of arguments, partly due to the limited amount of fossils and geological evidence.

The researchers pointed out that Pahvantia hastasta had a fine mesh structure that allowed it to capture plankton much smaller than any other known sea animal among those capable of swimming and of similar size. This may seem not very significant, instead it could be a determining factor for the success of that type of animal because it ensured an efficiency in eating higher to its competitors.

The reasoning is that at that time there were various types of plankton, also microscopic, and the ability to collect a considerable amount, also from sources not accessible by other species, provided a lot of nourishment and therefore a lot of energy. An animal such as Pahvantia hastasta could be very successful with a population increase. This in turn meant an increase in their feces and carcasses that sank down to the seabeds providing nourishment for other organisms.

Other species in the radiodont group may have had similar roles in their ecosystems. According to the researchers, they gave important contributions to the marine ecosystems of the Cambrian, which had a development that led to the great explosion of that period, which changed the history of life on Earth forever.

Various researches are showing how just a few species can be crucial for the prosperity or for the collapse of an ecosystem. Pahvantia hastasta and other radiodonts could be an extreme case of species that developed at a crucial moment in the animals’ history. There were probably also other environmental factors that determined that result. Certainly the discussions will continue but this research offers an interesting interpretation of those events.

Pahvantia hastasta reconstruction (Image courtesy Masato Hattori)
Pahvantia hastasta reconstruction (Image courtesy Masato Hattori)


  1. It’s wonderful and incredible, I’m from Mexico and here there are strange exotic animals but that specimen if it seems to be taken from a story of aliens, thanks for sharing the knowledge


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