Ikaria Wariootia: The earliest known animal ancestor on the planet has been discovered from South Australia

Time of India

22-05-2025

Scientists have identified
Ikaria wariootia
, a tiny, wormlike creature that lived over 555 million years ago, as the
earliest known bilaterian
— an animal with a front, back, and symmetrical sides. Detailed in the journal
Proceedings of the National Academy of Sciences
, this discovery from South Australia provides crucial evidence for a major evolutionary leap during the Ediacaran period: the origin of bilateral body structure, a key feature of nearly all animals today, including humans.
Ikaria Wariootia: A peek into the first bilaterian animals
Bilaterians are animals that exhibit bilateral symmetry, meaning their bodies have two symmetrical halves, each mirroring the other. This structure includes distinct head, tail, back, and belly, facilitating controlled movement and internal complexity. Scientists had long hypothesized that the earliest bilaterians would be simple, small, and possess basic sensory organs, but no fossil evidence had confirmed this—until the discovery of
Ikaria wariootia
. Measuring just 2 to 7 millimeters, this creature is about the size of a grain of rice.
Dr. Scott Evans from the University of California, Riverside, explained, 'While we believed such animals existed during this time, we didn't expect them to be easy to identify. When we saw the 3D scans, we knew we had found something significant.' Using advanced 3D laser scanning, the team uncovered the fossil's cylindrical body, clear bilateral symmetry, and signs of musculature, marking a pivotal discovery in understanding early bilaterian life.
Insights into ediacaran lie and the evolution of animals
This discovery also changes how scientists perceive other Ediacaran organisms. While large, iconic species like
Dickinsonia
were previously considered evolutionary dead ends without any living descendants, smaller and simpler creatures like
Ikaria
may represent the earliest ancestors of bilaterians, the group that gave rise to most modern animals.
"While
Dickinsonia
and similar large creatures were likely evolutionary dead ends, we also had many smaller organisms and suspected they might be the early bilaterians we were searching for," said Professor Droser. The identification of
Ikaria wariootia
bridges the gap between genetic theories and fossil records, confirming that early bilaterians had the body structure and abilities necessary for complex behaviors like directed movement and burrowing.
Fossilized burrows provide evidence of purposeful movement in Ikaria Wariootia
The discovery is linked to fossilized burrows known as
Helminthoidichnites
, found in the same geological layers in Nilpena, South Australia. For over 15 years, paleontologists speculated these burrows were created by bilaterians, but the exact organism remained unclear. The size and shape of
Ikaria wariootia
match these burrows, reinforcing the idea that the creature actively burrowed into oxygen-rich ocean-floor sand in search of organic matter.
"Burrows of
Ikaria wariootia
are found deeper than any other, making it the oldest fossil with this level of complexity," said Professor Mary Droser. The fossil also shows V-shaped ridges in the burrows, indicating that
Ikaria
used peristaltic locomotion, contracting its muscles like modern worms. This type of movement suggests an advanced level of coordination and sensory input previously unknown in such early animals.
Significance of this discovery by Proceedings of the National Academy of Sciences
The discovery of
Ikaria wariootia
significantly reshapes our understanding of early animal evolution. Dating back 555 million years to the Ediacaran period, it is the earliest known bilaterian fossil, showing bilateral symmetry, a key feature of most modern animals. This discovery bridges the gap between genetic predictions and fossil evidence, supporting the idea that early bilaterians were small, simple creatures with complex capabilities, such as purposeful movement and burrowing. The fossil's association with Helminthoidichnites burrows suggests that
Ikaria
actively tunneled through oxygenated ocean-floor sand, indicating coordination and sensory input. This finding challenges prior assumptions about the pace of evolution, demonstrating that complex behaviors and body plans could have evolved much earlier than previously thought.
Ikaria wariootia
provides a crucial insight into the origins of animal complexity, marking a significant milestone in our understanding of the pre-Cambrian evolution of life on Earth.
Fossil characteristics of Ikaria Wariootia
The
Ikaria wariootia
fossil exhibits several key characteristics that make it a groundbreaking discovery in the study of early animal evolution. These characteristics are:
Bilateral Symmetry
The fossil shows clear evidence of bilateral symmetry, meaning it has a defined left and right side that mirror each other. This symmetry is a key trait of bilaterians, the group from which most modern animals, including humans, evolved.
Small Size
Ikaria wariootia
measures just 2 to 7 millimeters long, roughly the size of a grain of rice. Its small size is consistent with its position as an early, simple bilaterian.
Cylindrical Body Shape
The fossil's cylindrical body, observed through 3D scanning, suggests a simple yet functional body plan, capable of basic movement and burrowing.
Musculature Evidence
The fossil displays signs of musculature, which support the idea that
Ikaria
could move in a coordinated manner, likely using peristaltic locomotion similar to modern worms.
Burrow Association
The fossil is linked to Helminthoidichnites burrows, which are V-shaped and indicative of active tunneling behavior. These burrows suggest that
Ikaria
moved purposefully through oxygenated ocean-floor sand, searching for organic matter.
Complex Locomotion
The presence of V-shaped ridges in the burrows indicates
Ikaria
used a form of peristaltic movement, contracting muscles across its body, highlighting an early form of coordinated, complex movement.
Importance of discovery of Ikara wariootia
The discovery of
Ikaria wariootia
provides valuable insights into early animal behavior, particularly in terms of its locomotion and environmental interactions. Here are some key behavioral implications:
Purposeful Movement
The presence of
Ikaria wariootia
in association with Helminthoidichnites burrows suggests that it actively tunneled through the ocean-floor sand. This implies that
Ikaria
was capable of purposeful movement, likely searching for organic matter. Such behavior indicates a level of coordination and sensory input, much like modern worms, which use their muscles to move in a controlled manner.
Peristaltic Locomotion
The V-shaped ridges observed in the burrows suggest that
Ikaria
used peristaltic movement—contracting muscles along its body to propel itself forward. This form of locomotion is still seen in modern worms and other simple animals, demonstrating that early bilaterians had complex movement abilities, likely enabling them to explore their environment more effectively.
Environmental Interaction
The burrowing behavior highlights
Ikaria's
interaction with its environment, particularly its use of oxygenated sand for shelter and feeding. This shows that early bilaterians were capable of modifying their surroundings, a trait that would evolve in later species to allow more complex forms of behavior, such as constructing shelters or hunting.
Sensory and Nervous System Development
The ability to move purposefully and burrow suggests that
Ikaria
had a developed nervous system that allowed it to respond to its environment and carry out coordinated actions. The presence of muscles, coupled with coordinated movement, implies the evolution of basic sensory input and motor control, essential for more complex behaviors in future animals.
Adaptation to the Environment
Ikaria's
ability to move through oxygenated sand in search of food suggests early adaptations for survival, allowing it to exploit available resources efficiently. This reflects a fundamental aspect of animal behavior—the need to adapt to and interact with the environment to find food, shelter, and mates.
Impact of Ikara wariootia on study of early life
The discovery of
Ikaria wariootia
provides valuable insights into early animal behavior, particularly in terms of its locomotion and environmental interactions. Here are some key behavioral implications:
Purposeful Movement
The presence of
Ikaria wariootia
in association with Helminthoidichnites burrows suggests that it actively tunneled through the ocean-floor sand. This implies that
Ikaria
was capable of purposeful movement, likely searching for organic matter. Such behavior indicates a level of coordination and sensory input, much like modern worms, which use their muscles to move in a controlled manner.
Peristaltic Locomotion
The V-shaped ridges observed in the burrows suggest that
Ikaria
used peristaltic movement—contracting muscles along its body to propel itself forward. This form of locomotion is still seen in modern worms and other simple animals, demonstrating that early bilaterians had complex movement abilities, likely enabling them to explore their environment more effectively.
Environmental Interaction
The burrowing behavior highlights
Ikaria's
interaction with its environment, particularly its use of oxygenated sand for shelter and feeding. This shows that early bilaterians were capable of modifying their surroundings, a trait that would evolve in later species to allow more complex forms of behavior, such as constructing shelters or hunting.
Sensory and Nervous System Development
The ability to move purposefully and burrow suggests that
Ikaria
had a developed nervous system that allowed it to respond to its environment and carry out coordinated actions. The presence of muscles, coupled with coordinated movement, implies the evolution of basic sensory input and motor control, essential for more complex behaviors in future animals.
Adaptation to the Environment
Ikaria's
ability to move through oxygenated sand in search of food suggests early adaptations for survival, allowing it to exploit available resources efficiently. This reflects a fundamental aspect of animal behavior—the need to adapt to and interact with the environment to find food, shelter, and mates.
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