Discover the 567-Million-Year-Old Animal That Looked Like a Leaf

567 million years ago, the planet looked considerably different from its current form. The little strip of dry land that was available was bare and desolate. Life only existed in the oceans, teeming with numerous multicellular organisms that occasionally formed colonies. However, with time, various life forms began to appear, and multicellular organisms became more commonplace. One of the earliest multicellular organisms that appeared on the prehistoric seafloor of the Precambrian earth was Dickinsonia, a flat soft-bodied animal that looked like a leaf. 

Since the discovery of fossils representing this organism, experts have suggested different possible classifications for it. Some have suggested that it was a fungus or even a unique kingdom of organisms that became extinct over the years. However, more recent discoveries indicate that Dickinsonia was an animal. While the squishy leaf-like organisms look nothing like present-day animals in terms of their anatomy, they represent the first group of multicellular organisms on the planet and are most likely our ancestors. 

Dickinsonia Appearance

The Precambrian ocean, where this organism lived, was devoid of predators or significant threats. Consequently, Dickinsonia did not evolve a solid support structure or skeleton. A soft, squishy body like this means this animal did not leave any hard parts preserved in the fossil record. 

Most of what’s left of this animal for scientists to interpret is in the form of casts and imprints left behind in sandstone beds. Dickinsonia had a flattened body in the shape of an egg. This means it had a round (oval) outline with one end slightly expanded. From the fossils, we can also conclude that it had rib-like segments inclined radially toward the narrow ends. The individual segments grew bigger towards the wide end of the fossils. 

A thin vertical ridge or groove divided Dickinsonia’s body into two halves. Scientists are not exactly sure what the organism’s body would have felt like. However, the prevailing theory is that the segments were liquid-filled chambers providing ambient pressure to support the organism’s body. Some fossils have also been found that seem to preserve some part of their internal anatomy. Studies of these fossils suggest that they might have had a tract to digest food and distribute nutrients throughout their body. 

Paleontologists have found several Dickinsonia fossils to date, and they all vary in size. While some were only a few millimeters long, large fossils, up to 4ft 7 inches also exist. It’s difficult to estimate this animal’s thickness, but experts think they were about a fraction of an inch thick. 

Classification 

Dickinsonia is one of the earliest members of the evolutionary tree. Since it differed considerably from present-day lifeforms, classifying it was a little difficult for scientists. The earliest attempts had classified the organism as a jellyfish, fungi, coral, polychaete worm, or turbellarian. Due to the difficulties in assigning them to a branch, some experts proposed creating a separate kingdom for them. 

However, more recently, studies have been carried out to tell the exact nature of this organism. The latest results have conclusively identified them as animals. To carry out this classification, scientists studied molecular biomarkers known as sterols which exist naturally in every living organism but vary considerably from one group to the other.

Cholesterol is a classic example of a biomarker like this. If there was a way to isolate and identify the type of molecular biomarker present in the Dickinsonia’s body, it would allow us to determine which group of organisms they belonged to once and for all. 

A team of scientists recently set out to use this method to determine the correct classification for this organism. The team collected samples of this organism from the White Sea region of northwest Russia. By studying the molecular composition of the fossil relative to the composition of the sea floor around them, the scientist found that the organism had an abundance of trace biomarkers. These molecules pointed to a closer association with animals than any other kingdom of organisms. 

Dickinsonia is classified in the phylum Proarticulata along with other extinct marine organisms whose origin dates back to the Ediacaran Period. Other members of this group include Cephalonega and Praecambridium.

When and Where Did Dickinsonia Live? 

Fossils of the planet’s oldest animals were first discovered in Bhimbetka Rock Shelters in India. This area is more popularly known for its Paleolithic and Mesolithic cave arts. Also, UNESCO has designated it as a World Heritage Site. The organism’s fossils have also been found in other locations across present-day China, Russia, Ukraine, and Australia. 

Dickinsonia lived during the late Ediacaran Period. This was a 96 million-year period (between 635-538 million years ago). The period is the last of the Proterozoic Eon and precedes the Cambrian Period of the Phanerozoic Eon. 

There are different hypotheses about how this organism lived. However, the prevailing thought is that it was a bottom dweller that spent most of its life anchored to sediment on the ocean floor. They probably attached themselves to the rock surface via a secretion like present-day oysters do or a type of fungus-like attachment which would have consisted of an underground network of roots.

This means this animal looked like a leaf or palm frond on the ocean floor. Despite their ability to anchor themselves to a spot in the sediments, experts think they were not sedentary. Instead, they could move slowly from one resting place to the other. Scientists believe this animal probably grew throughout its life. This means it would have kept growing until it was killed or covered with sediments. 

Considering how old this organism is and the state of fossil preservation, scientists have been unable to identify this organism’s mouth, gut, or anus. The prevailing theory is that it fed by absorbing food using its bottom surface. This is quite similar to the feeding habit of modern placozoans-one of the simplest life forms known to absorb food with their bottom surface. 

Discovery 

Based on how the organism was preserved, their preserved parts were probably made up of a biopolymer structure such as keratin which is often better preserved in fossil records than more brittle minerals like calcite or pyrite. 

Generally, Dickinsonia fossils are found in the form of negative impressions (otherwise known as death masks) on the base of sandstone beds. The impression left by the animal looked like leaf imprints on the rock surface. A negative impression is an imprint formed by the upper sides of an organism on the sand sediment deposited on top of it. A few trace fossils that show evidence of the organism’s feeding activities have been found as well. 

The first fossils of Dickinsonia were discovered in 1946 in the Flinders Ranges of South Australia. Red Sprigg is the original discoverer of the fossil, and he published the first description of the organism, assigning the name Dickinsonia to it. The name is in honor of the Director of Mines for South Australia at the time, Ben Dickinson. 

Was Dickinsonia the First Animal Ever?

Until a few years ago, the spiked and armored organisms that emerged after the Precambrian explosion were our best bet at figuring out what the earliest animals might have looked like. However, the more recent confirmation of organisms like the Dickinsonia as an animal means it is one of the oldest animals found so far. 

While the 567 million-year-old animal that looked like a leaf is definitely one of the oldest animals found so far, it isn’t the only one we know of. For instance, Kimberella, an early mollusk-like animal, is around the same age as Dickinsonia. Animals like this provide great insights into how our animal ancestors might have begun their journey. 

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