Fossils of Spriggina floundersi from South Australia may provide the oldest known evidence of population-wide “handedness” in the animal kingdom, according to a study published in Scientific Reports. Researchers found that these 550-million-year-old organisms exhibited a statistically significant preference for turning in one direction over the other, suggesting a complex nervous system existed long before the Cambrian explosion.
How Spriggina floundersi Demonstrated Behavioral Lateralization
The research team analyzed 75 fossils from the Ediacara Member, supplemented by additional specimens from the South Australia Museum in Adelaide and Nilpena Ediacara National Park. They discovered that approximately 70 percent of the specimens were bent along the body axis, with angles ranging from 5 to 81 degrees.
Crucially, the data showed a consistent bias in direction. Because these fossils are mirror-image impressions, a leftward bend in the rock indicates the animal actually bent to the right in life. The study reported a p-value of 0.0017, confirming the directional preference wasn’t random.
Active Movement vs. Passive Water Currents
A primary goal for the researchers was determining if these bends were caused by the animal’s own will or by external forces like ocean currents. The team argued for active movement based on two key observations:
- Inconsistent Orientation: Neighboring fossils on the same bedding planes showed different body orientations and different bend directions.
- Lack of Current Correlation: The direction of Spriggina’s bends did not match other signs of current direction.
Scott Evans, lead author of the study and assistant curator of invertebrate paleontology at the American Museum of Natural History, noted that this suggests an animal without hands or feet had its own version of handedness over 500 million years ago.
Implications for Ancient Nervous Systems
The discovery suggests that Spriggina possessed a nervous system capable of coordinated, asymmetric activity. Coauthor Mary Droser, a paleontologist at the University of California, Riverside, stated that the findings serve as a reminder that traits taken for granted today have incredibly ancient origins.
According to Evans, the presence of this behavioral bias is significant because modern animals with similar traits—such as mammals and birds—possess complex sensory abilities. This implies Spriggina’s nervous system was relatively complex and more similar to those of animals that we know today.
Physical Characteristics of the Organism
The creature featured an elongated body with a broad, undivided front and a narrower rear. While it appeared segmented due to repeated units running off a central midline, the researchers stopped short of claiming clear membership in any modern animal group. The study suggests the organism may have been “nektobenthic,” occasionally lifting off the seafloor.
The Classification Struggle of Ediacaran Biota
Spriggina remains one of the better-known members of the Ediacara biota, which existed between 635 and 538 million years ago. Over the years, various researchers have compared it to different groups:
| Proposed Classification | Key Evidence/Reasoning |
|---|---|
| Annelids/Arthropods | Comparison by researchers. |
| Flatworms | Comparison by researchers. |
| Unknown/Sessile | The study argues against it being a sessile form anchored to the seafloor. |
This latest study argues the creature was a free-living, actively motile organism that may have crawled or glided. If the repeated body units are confirmed as an early form of segmentation, it would push that biological trait very deep into animal history.
Frequently Asked Questions
What is the Ediacaran Period?
It is the period of geologic time from about 635 to 538 million years ago, during which multicellular organisms became larger and more complex.
Does “handedness” in fossils mean the animal had hands?
No. In this context, handedness refers to “behavioral lateralization,” or a population-level bias in movement.
Where were these fossils found?
The specimens were collected from the Flinders Ranges and surrounding region of South Australia, including Nilpena Ediacara National Park.
Why is the p-value of 0.0017 important?
The preference for one direction was statistically significant, with a reported p-value of 0.0017.
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