| Name | Pikaia | Diet | Carnivorous |
| Name Meaning | Named after the Pikaia Mountain in Canada | Length | 3.8–5 centimeters (1.5–2 inches) |
| Pronunciation | Pik-ay-ah | Weight | N/A |
| Era | Paleozoic — Cambrian | Location | Canada (North America) |
| Classification | Chordata, Pikaiidae, & Pikaia |
Pikaia Pictures
The Pikaia
What looks like a worm but isn’t really a worm?
That’s the Pikaia—a primitive chordate that lived during the Middle Cambrian Period.
When scientists discovered this 500-million-year-old animal with an elongated body and no defined head, they assumed it was a worm.
This was back in 1911, and the discovery was made by Paleontologist Charles Walcott in the Burgess Shale of British Columbia.
The newly identified organism was named Pikaia, after Pikaia Peak, a mountain in Alberta, Canada.
Subsequent studies in the 1970s showed that the Pikaia was misidentified all along as a worm, and other speculations that it was the oldest fish were wrong as well.
Instead, this ancient organism was actually found to be a primitive chordate, a close relative of the ancestors of modern vertebrates.
So far, more than a hundred specimens have been discovered, providing more insights into the life of this prehistoric animal and clearing up misconceptions about its identity.
In this article, we’ll explore the different aspects of Pikaia’s life, including what it looked like and how it lived.
Physical Characteristics
Pikaia was a small, worm-like creature with a slender, elongated body similar to that of a lancelet.
However, both animals are not directly related.
The Pikaia’s body was laterally flattened.
It tapered at both ends but did not have a well-defined head.
The total length of the Pikaia’s body was about 3.8 to 5 centimeters (1.5–2 inches).
The head region had a pair of antenna-like tentacles that resembled the antenna of snails.
In addition to these tentacles, there were a series of short appendages on either side of this animal’s head, but their exact function isn’t well-known.
The tail end was laterally compressed, forming a sort of leaf-shaped tail fin.
A key distinctive feature of the Pikaia was its primitive notochord.
This flexible, rod-like structure runs along the length of its body from the head to the tail.
The notochord is a defining characteristic of chordates (vertebrates, tunicates, hagfish, and lancelets) and is considered an early precursor to the vertebrate spine.
In addition to this, the Pikaia had faint V-shaped markings on its body that resemble the muscle bundles (myomeres) of chordate animals.
The body may have been covered almost entirely by cuticles.
This is a hard proteinous layer commonly found in the exoskeleton of invertebrates like arthropods, mollusks, and nematodes.
But the Pikaia didn’t have an exoskeleton, and the cuticle in this animal was different from that of other hard-bodied organisms.
Habitat and Distribution
Pikaia lived during the Middle Cambrian Period and was alive between 513 and 501 million years ago.
Fossils of this ancient chordate have been recovered from the Burgess Shale, a fossil-rich deposit located in the Canadian Rockies in British Columbia, Canada.
The Burgess Shale is renowned for its exceptional preservation of soft-bodied organisms, especially those around during the Cambrian Period.
The formation’s assemblage of fossils provides valuable insights into the diversity and complexity of life during the Cambrian explosion.
Due to limited fossil records, the exact geographic range of Pikaia is not entirely clear.
However, it may have inhabited shallow marine environments along the western margin of the ancient continent called Laurentia.
Pikaia lived in the waters near the coast, possibly in areas with a seabed made up of soft sediments.
It was alive during the Middle Cambrian Period, a significant period in Earth’s history.
It was one of the soft-bodied animals that evolved during the “Cambrian explosion.”
This was a biological event that took place over a few million years and was characterized by a quick diversification and proliferation of multicellular life forms.
The Burgess Shale, where fossils of the Pikaia were discovered, provides an exceptional snapshot of the burst of evolutionary innovation during this period.
The climate during the Middle Cambrian was generally warmer than today.
Conditions were relatively stable, promoting the proliferation of life in the oceans.
Behavior and Diet
Although it is often described as a worm-like organism, Pikaia was an active free swimmer.
It moved in the water column by throwing its body in a series of S-shaped, zigzag curves similar to how eels move.
Experts think present-day fish inherited this type of swimming movement from primitive chordates like this, but they’re less flexible due to their stiff backbone.
Pikaia couldn’t swim very fast either.
That’s because it lacked the fast-twitch fibers present in modern chordates, which made them capable of swimming rapidly.
Since it was a slow swimmer, the Pikaia would be incapable of escaping quickly from predators in its ecosystem.
Based on this, experts think it survived by avoiding these predators entirely.
This would mean not swimming actively high in the water column or near the surface.
Instead, it was probably a bottom-feeder that cruised inconspicuously near the sea bottom.
This ancient chordate was likely a filter feeder.
It browsed on benthic detritus and small microorganisms that were a part of the microbial mat at the bottom of the sea.
Pikaia had a small circular mouth that may have been useful for filtering particles out of the water.
However, because the mouth is too tiny, it is difficult to determine if it had any additional appendages or teeth for grinding food materials.
As a result, there’s little diet evidence of how this primitive animal fed and what exactly it ate.
Given the size of its mouth, Pikaia would have been unable to take in large amounts of water when feeding like typical suspension feeders.
Life Cycle
Considering how long ago it lived and the nature of the fossils preserved, it’s difficult to tell how exactly the PIkaia reproduced.
Since it is considered a chordate, reproduction was likely sexual. This involves a fusion of male and female gametes to produce offspring.
It’s difficult to determine how this animal reproduced or if it exhibited specific mating behavior.
Fertilization was likely external in the water column.
Pikaia juveniles probably started their life as a larva after hatching from an egg.
This larval stage might have been a free-swimming form, allowing it to disperse and explore new areas before settling into a more sedentary, bottom-dwelling lifestyle.
As it grew and matured, Pikaia juveniles would have metamorphosed several times until they transformed into adult forms.
This would have involved changes in their overall body proportions and the development of specific features to adapt to their environment.
Evolution and History
The evolutionary history of the Pikaia is particularly significant because the animal is considered one of the earliest known chordates that offer valuable insights into the early years of vertebrate evolution.
Interestingly, the Pikaia wasn’t the first primitive chordate in the fossil record.
Scientists have found fossils of chordates in rocks of the Chengjiang Fossil Site in China.
These were found to be at least ten years older than the Pikaia.
This confirms that chordates have been around since the Early Cambrian Period, at the very least.
Pikaia did evolve some unique features that set it apart from other primitive chordates.
One of these is the development of a distinct head region.
Although the Pikaia did not have a head separated from its body, it was one of the first chordates to develop some form of cephalization.
The head structure of this chordate, complete with its tentacles, was a result of its long shape and its swimming habit.
Over time, a mouth developed at the end of its body to aid in its search for food.
Experts think this search for food and the need to test and identify things that were in front of the body laid the groundwork for the development of sensory features in this primitive animal, such as sight and the ability to smell and feel things.
While the Pikaia didn’t have these features in well-defined forms, its evolution may have laid the groundwork for these fixtures.
Interactions With Other Species
Pikaia evolved during the Cambrian explosion, a time when the marine ecosystem was starting to burst with new life forms.
Soft-bodied organisms dominated Earth’s oceans during this period, but a few of them also developed hard shells and exoskeletons.
The largest of these hard-shelled organisms were the top predators of the Cambrian seas.
Pikaia likely had some of these predators in its ecosystem.
Some of them, like the Anomalocaris, preferred soft-bodied organisms like Pikaia and may have hunted them for food.
Pikaia’s lack of defensive structures or adaptations for quick movement may have made it an easy target for these predators, and the only way to survive was to avoid them as much as possible.
Since it was a filter feeder, the Pikaia’s prey would have included small particles of plankton, organic detritus, or other suspended matter in the water.
It likely played a role in controlling the abundance of these underwater detritus and also consuming primary producers in its ecosystem.
Cultural Significance
Soft-bodied animals are quite abundant in the fossil record.
Even in the Burgess Shale, where the Pikaia was found, there are many others like it.
However, it has received more attention than many of these other soft-bodied creatures because of its possible link to the chordates.
Although first discovered in the early 1900s, it wasn’t till 1979 that scientists could explain this animal’s evolutionary importance.
The discovery of the Pikaia as a possible chordate completely changed everything scientists thought they knew about how this group of advanced animals evolved.
Initially, scientists believed the first chordates to have ever evolved came on the scene during the Ordovician Period (484–443 million years ago).
By confirming the Pikaia as a chordate, scientists were forced to revise the existing knowledge about evolution and ecology.
It is worth noting that it is still commonly mislabelled to the general public as the ancestor of all vertebrates, the oldest fish, or even the ancestor of humans.
These labels are not accurate.
Although it shows fish-like attributes, it was not a fish.
It is also related to the ancestors of modern vertebrates but cannot be considered the ancestor of all vertebrates or humans.
Considering how important this primitive animal is, it is commonly referenced in documentaries, books, museum exhibits, and other educational materials.
Conclusion
Pikaia was a primitive chordate that lived during the Middle Cambrian Period.
It is one of the soft-bodied creatures whose fossils have been recovered from the famous Burgess Shale in Columbia.
The unique anatomy of this animal has made it particularly interesting to scientists.
It was initially classified as an annelid worm, but later studies found it to be a relative of modern chordates.
Its body shows evidence of a primitive notochord as well as segmented blocks of skeletal muscles known as myomeres.
Pikaia moved like an eel in its benthic home.
It was a filter feeder that fed on organic detritus at the bottom of the water column.
The discovery of this prehistoric chordate has played a crucial role in redefining our understanding of vertebrate evolution and the origins of life in general.
FAQs
Does Pikaia still exist?
No, Pikaia went extinct during the Cambrian Period.
However, there are primitive chordates that are still alive today, such as the Lancelet.
Was Pikaia the first fish?
No, it wasn’t.
Although commonly described as the oldest fish, Pikaia is not a direct ancestor of fish.
It was a basal chordate, which means it was a close relative of the first vertebrates that eventually gave rise to fish and other vertebrates.
Sources
- https://evodevojournal.biomedcentral.com/articles/10.1186/2041-9139-3-12
- https://en.wikipedia.org/wiki/Pikaia
- https://evolution.berkeley.edu/the-arthropod-story/meet-the-cambrian-critters/pikaia/is-pikaia-an-arthropod/pikaia-a-chordate/
- https://www.cam.ac.uk/research/news/humans-oldest-ancestor-found
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