In a high-tech laboratory in Nashville, Tennessee, a team of paleontologists pores over a virtual simulation. Fascinated, they watch as the computer recreates a process that first took place millions of years ago. Will they finally learn the truth about an organism so strange it defies our understanding of evolution itself?
Ever since the early 19th century, scientists and biologists have used tree-like diagrams to depict the relationships between different forms of life on earth. However, it wasn’t until Charles Darwin published On the Origin of Species in 1859 that the idea really began to gain widespread popularity.
Darwin’s seminal work put forward the concept of a “Tree of Life” – a model used to explain his theory of evolution. In it, he used branches and twigs to illustrate how organisms shared a common ancestry. And although science has changed a lot since Darwin’s time, the concept of the Tree of Life is still used by scientists today.
However, the model is far from perfect. Sometimes, scientists will come across organisms that don’t fit easily into the Tree of Life. In fact, those working with animals that lived long ago often stumble across fossils with features that defy easy categorization.
For example, there are the bizarre rangeomorphs, leaf-like organisms composed of strange fronds. Even odder is Tribrachidium, a hemispherical creature that boasts three branches curving around its outer surface. Although scientists have guessed at their evolutionary origins, the truth remains a mystery.
One of the most interesting of these organisms is Parvancorina, a creature that dates back to the Ediacaran period. Beginning some 635 million years ago and lasting almost 100 million years, this period is thought to have begun with what’s known as a Snowball Earth event.
According to scientists, these events occurred when the surface of the Earth became almost entirely covered in ice. Apparently, the Ediacaran period saw the last of these episodes. Afterwards, the planet entered the prolific evolutionary period known as the Cambrian explosion.
During the Cambrian explosion, animals began to emerge that shared characteristics with those that we recognize today. So a paleontologist studying fossils from this era can guess at their place in the Tree of Life with relative ease. However, for those researching the Ediacaran period, things are not so simple.
For these reasons and more, Parvancorina has proved something of a puzzle. For example, most scientists would use features such as eyes or legs to determine where an organism sits on the Tree of Life. However, Parvancorina has none of these things.
Instead, Parvancorina is a shield-shaped organism, divided into two sub-species. One, P. minchami, was first found in the Flinders Ranges (pictured) in South Australia. The other, P. sagittal, was found thousands of miles away in the Arkhangelsk Region of Russia.
Interestingly, Parvancorina bears little resemblance to what we think of as an animal today. Usually less than an inch in size, it boasts a series of ridges running down one side and a symmetrical shape. Although scientists are unsure exactly how this strange creature lived, they believe that it spent its time fixed to the sea floor.
Because scientists have been unable to determine what – if any – modern creature Parvancorina may be related to, they have struggled to understand it. Instead, they have taken a reverse-engineering approach, hoping to learn the answers to some important questions along the way.
One of the most useful tools to scientists hoping to understand Parvancorina is a technique known as computational fluid dynamics. First developed in the 1920s, this method simulates the effects of fluid flows on virtually modeled surfaces.
Today, scientists are able to learn a lot about organisms by studying how they interact with their environment. And while they cannot observe a living Parvancorina in its ocean habitat, a simulation offers them the next best thing.
In June 2017, Simon Darrach, the Assistant Professor of Earth and Environmental Sciences at Nashville’s Vanderbilt University, and Imran Rahman, a Junior Research Fellow at the University of Oxford, announced the results of their latest experiment with CFD – and their findings could revolutionize our understanding of Parvancorina’s role in the Tree of Life.
The first step in the process was to create a three-dimensional model of Parvancorina, before placing it in a sort of virtual tank. There, the model was subjected to a simulated flow of water, and the effects were closely observed. So what did they learn about how this organism might have lived millions of years ago?
Previously, the lack of limbs or tracks associated with Parvancorina had led scientists to assume that the creature was sessile – one that remains in a fixed place. However, the simulation soon showed that the organism was poorly adapted for this lifestyle.
In fact, it was revealed that Parvancorina would only have been adept at catching food if it came directly towards them, making life as a suspension feeder in a constantly changing current difficult. Additionally, studies revealed that the shape of the organism was vulnerable to drag, and ill-suited to strong currents.
From these two observations, scientists were able to put forward the theory that Parvancorina may in fact have been a mobile organism. And although this may seem like a small development, it could finally provide the clues needed to put the creature on the evolutionary map.
Furthermore, scientists have theorized that if Parvancorina was mobile, many other fossils from that period might have been too. And if scientists are able to prove this, it will transform our understanding of life on earth before the Cambrian explosion – revealing a complex, dynamic and very different world.