Half-billion-year-old fossils offer new clues to how life exploded on the sea floor

September 14, 2018, University of Oxford
Artist reconstruction of Pahvantia hastasta. Credit: Masato Hattori

Stephen Pates, a researcher from Oxford University's Department of Zoology, has uncovered secrets from the ancient oceans.

With Dr. Rudy Lerosey-Aubril from New England University (Australia), he meticulously re-examined fossil material collected over 25 years ago from the mountains of Utah, USA. The research, published in a new study in Nature Communications, reveals further evidence of the great complexity of the oldest animal ecosystems.

Twenty hours of work with a needle on the specimen while submerged underwater exposed numerous, delicate microscopic hair-like structures known as setae. This revelation of a frontal appendage with fine filtering setae has allowed researchers to confidently identify it as a radiodont – an extinct group of stem arthropods and distant relatives of modern crabs, insects and spiders.

"Our new study describes Pahvantia hastasta, a long-extinct relative of modern , which fed on microscopic organisms near the ocean's surface," says Stephen Pates. "We discovered that it used a fine mesh to capture much smaller plankton than any other known swimming animal of comparable size from the Cambrian period. This shows that large free-swimming animals helped to kick-start the diversification of life on the over half a billion years ago."

Causes of the Cambrian Explosion—the rapid appearance in the fossil record of a diverse animal fauna around 540-500 million years ago—remain hotly debated. Although it probably included a combination of environmental and ecological factors, the establishment of a system to transfer energy from the area of primary production (the surface ocean) to that of highest diversity (the sea floor) played a crucial role.

Even though relatively small for a radiodont (FIG), Pahvantia was 10-1000 times larger than any mesoplanktonic primary consumers, and so would have made the transfer of energy from the surface oceans to the deep sea much more efficient. Primary producers such as unicellular algae are so small that once dead they are recycled locally and do not reach the deep ocean. In contrast large animals such as Pahvantia, which fed on them, produce large faecal pellets and carcasses, which sink rapidly and reached the seafloor, where they become food for bottom-dwelling animals.

Amateur enthusiasts provide research gold-dust

The presence of Pahvantia in the Cambrian of Utah has been known for decades thanks to the efforts of local amateur collectors Bob Harris and the legendary Gunther family.

"This work also provides an opportunity to celebrate the exceptional contribution of local and amateur collectors to modern palaeontology," explains Stephen. "Without their tireless efforts, knowledge, and generosity, thousands of specimens representing hundreds of new species, would not be known to science."

Bob Harris is rumoured to have turned down a job offer from the CIA, instead opening up a fossil shop and a number of quarries in the spectacular House Range, Utah. He discovered the first specimens of Pahvantia in the 1970s, and donated them to Richard Robison, a leading expert on Cambrian life from the University of Kansas. The Gunther family are famous for their extensive fossil collecting in Utah and Nevada. Over a dozen species have been named in honour of their contributions to palaeontology, as they have shared thousands of specimens with museums and schools over the years. Among these were specimens of Pahvantia which they uncovered between 1987 and 1997. Donated to the Kansas University Museum of Invertebrate Paleontology (KUMIP), these specimens are described for the first time in our study.

"I visited the KUMIP in the first year of my Ph.D.," says Stephen. "It was awesome, exploring such a fantastic collection of fossils from the Cambrian of Utah and Nevada."

The study has produced the most up-to-date analysis of evolutionary relationships between radiodonts. It shows that filter feeding evolved twice, possibly three times in this group, which otherwise essentially comprised fearsome predators such as Anomalocaris canadensis from the Burgess Shale in Canada.

Pahvantia adds to an ever-growing body of evidence that radiodonts were vital in the structure of Cambrian ecosystems, in this case linking the primary producers of the surface waters to the highly diverse fauna on the sea floor. It also shows the importance of museum collections like the KUMIP, and local collectors, such as Bob Harris and the Gunther family, in uncovering new and exciting findings about early animal life.

Explore further: Scientists describe 'enigmatic' species that lived in Utah some 500 million years ago

More information: Rudy Lerosey-Aubril et al. New suspension-feeding radiodont suggests evolution of microplanktivory in Cambrian macronekton, Nature Communications (2018). DOI: 10.1038/s41467-018-06229-7

Related Stories

Scientists take a closer look at Earth's first animals

August 10, 2018

When did animals originate? In research published in the journal Palaeontology, we show that this question is answered by Cambrian period fossils of a frond-like sea creature called Stromatoveris psygmoglena.

Recommended for you

Matter waves and quantum splinters

March 25, 2019

Physicists in the United States, Austria and Brazil have shown that shaking ultracold Bose-Einstein condensates (BECs) can cause them to either divide into uniform segments or shatter into unpredictable splinters, depending ...

How tree diversity regulates invading forest pests

March 25, 2019

A national-scale study of U.S. forests found strong relationships between the diversity of native tree species and the number of nonnative pests that pose economic and ecological threats to the nation's forests.

Study suggests trees are crucial to the future of our cities

March 25, 2019

The shade of a single tree can provide welcome relief from the hot summer sun. But when that single tree is part of a small forest, it creates a profound cooling effect. According to a study published today in the Proceedings ...


Adjust slider to filter visible comments by rank

Display comments: newest first

3 / 5 (2) Sep 14, 2018
The cambrian explosion might be more evidence for the recent Gaia generalisation of natural selection. The evolution spurts comes from life maximizing ecological resources. Or, if a species helps stabilize the environment, the species is selected.
1 / 5 (2) Sep 15, 2018
"Twenty hours of work with a needle on the specimen while submerged underwater exposed numerous, delicate microscopic hair-like structures..." THis is careless writing. Does it mean the scientist himself was submerged for 20 hours? Or that the specimen was under water in a lab tank while the scientist stood (dry) above it?

not rated yet Sep 15, 2018
The cambrian explosion might be more evidence for the recent Gaia generalisation of natural selection.

"Gaia" hypotheses are not connected to population genetics such as selection. And group (species) selection has not been observed, nor is expected to be (since gene selection is primary).
3.5 / 5 (2) Sep 16, 2018
Both E. O. Wilson and D. S. Wilson have demonstrated and observed group selection in the natural world. W. D. Hamilton also demonstrated mathematically the nature of eusociality, or group selection. None of that actually supports the 'Gaia' hypothesis and ultimately both group and sexual selection (see Richard O. Prum) depend on natural selection at the genetic level for the evolution of social systems and sexual reproduction. But both group and sexual selection are very real, fast acting evolutionary processes that are new or emergent evolutionary properties not easily, if at all, reduced to natural selection of individual attributes.
not rated yet Sep 16, 2018
Why would the Cambrian Explosion be evidence for the wishful speculations for Gaia 1 or 2?

More likely that the simplest explanation is more correct. That at the beginning of the Cambrian era, there was a great increase in shallow seas and coastal wetlands. Exposing the preceding species to Solar and Cosmic radiation. The surviving species bred and random selection set off a chain reaction of mutations that radiated in new species.

Nothing mysterious about that process. Just random events and the devil take the hindmost!
5 / 5 (1) Sep 17, 2018
Both E. O. Wilson and D. S. Wilson have demonstrated and observed group selection in the natural world.

No, they have not, which is why you give no references. AFAIK they have published papers of such claims that have been thoroughly rejected by most biologists.

Hamilton's math is good (excellent in fact), but only the most powerful selection - which is directly on the genetic carriers (genes) - have ever been observed. And that is that is taught in the best universities, I know that from experience and discussion.
5 / 5 (1) Sep 17, 2018

"The idea that adaptations in organisms result from "group selection" (selection among groups that differentially bud off subgroups, with those having good "group traits" becoming more numerous), rather than from selection among genes themselves, usually within individuals, has undergone a bit of resurgence in popular culture. This is in stark contrast to the views of most evolutionary biologists, who see group selection as a logical possibility, but one that doesn't easily work in theoretical models and, more important, has explained almost nothing about nature. In contrast, the gene-centered view of evolution worked out by biologists like W. D. Hamilton, Robert Trivers, and John Maynard Smith, and popularized by Richard Dawkins, has been immensely fruitful."

5 / 5 (2) Sep 17, 2018
"I've posted a lot on the intellectual vacuity of group selection, particularly its failure to explain the evolution of traits like human altruism and cooperation (see, for example, here, here, and here). If you want an elegant and easily digestible explanation of the weaknesses of group selection, Steve Pinker has just published a nice essay on John Brockman's Edge website, "The false allure of group selection." If you're interested in seeing three smart biologists take group selection apart, there's an excellent paper by West, Griffin, and Gardner (reference below), which you can download for free here (the paper is not too hard, and the meat extends from pp. 376, beginning at "Error 3: the new", to p. 379, bottom of Table 2)."
5 / 5 (2) Sep 17, 2018
"So if group selection is so intellectually and scientifically unproductive, why do we hear so much about it? I think there are two reasons.

First, its few proponents make a lot of noise. And those proponents include well-known scientists like Martin Nowak, E. O. Wilson, David Sloan Wilson, and Jon Haidt. Nowak, Tarnita, and Wilson published a big (and deeply faulty) paper in Nature ...

Second, people want to believe in group selection. That doesn't just include scientists like D. S. Wilson, who has made it his life's mission to defend the concept, but, more importantly, the general public. ...

So while group selection is moribund among evolutionary biologists and many evolutionary psychologists, the criticisms of the idea are buried in the technical literature while its vocal proponents write best-selling books. Behind much of this is the insidious Templeton Foundation ..."

It is analogous to epigenetic heredity, possibilities but not factual.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.