A huge discovery, shelved and forgotten for almost 100 years. The remarkable story of the early chordate Pikaia Gracilens starts in 1911 when famous Burgess Shale discoverer, Charles Doolittle Walcott finds a strange-looking “worm/eel-like” fossil in the Canadian Rockies.
It’s tiny – just 5cm long – and nowhere near as exciting as the massive Cambrian arthropod monsters he’d found thus far. So Walcott marks the fossil as a worm and shelves it.
And it takes mankind until the 1970s to find it, re-examine it and realise that Walcott’s “worm” was no worm at all.
It’s the then-first-known Cambrian chordate, the ancient precursor to vertebrates – all creatures with a backbone, from Dunkleosteus to Velociraptor to ground sloths and all the way to mammals and us humans.
Turns out Pikaia Gracilens was a super-special fossil discovery.
What is so Special About Pikaia?
Pikaia is celebrated as one of the earliest known and most primitive members of the chordate family. Its discovery is pivotal because it provides crucial evidence of the early stages of evolution leading to vertebrates, including humans.
See, throughout the 1900s, and even still today, the Cambrian is a hotly debated topic because it appears as if complex life suddenly appeared on the planet overnight – where the term “Cambrian Explosion” comes from.
(Although today we know it’s simply fossil bias because biomineralisation really took off in the Cambrian.)
Finding an early chordate in the Cambrian was a big deal because it shows just how complex life had already gotten by this stage. Turns out our earliest vertebrate ancestors were already in the seas of the Cambrian.
The most distinctive feature of Pikaia is its notochord, a flexible rod-like structure that runs along its back, which is a key characteristic of chordates. This notochord is thought to have been used for swimming, supporting the body, and as a precursor to the vertebral column in later vertebrates.
Discover: Did humans evolve from Pikaia?
When did Pikaia First Appear?
Funny story: We only have evidence of Pikaia in one slice of time – the Middle Cambrian period, specifically around 505 million years ago, a time when life in Earth’s oceans was becoming more diverse and complex.
We haven’t found any other evidence (fossils) of Pikaia in any previous or subsequent rock layers. So we have to assume it lived and went extinct in the Cambrian.
Why did Pikaia Go Extinct?
The extinction of Pikaia, like many species from the Cambrian period, is attributed to natural selection and environmental changes that rendered its survival challenging.
Over millions of years, evolutionary pressures and changing ecosystems likely led to the emergence of more advanced forms of life, outcompeting Pikaia and leading to its eventual disappearance from the fossil record.
The specifics of its extinction remain a topic of scientific investigation.
Discover more: When did Pikaia go extinct?
What did Pikaia evolve from?
Scientists think Pikaia must have evolved from simpler, non-chordate ancestors. These precursors were likely similar to other early multicellular organisms found in earlier strata, such as the Ediacaran, and they probably lacked the defining characteristics of chordates, such as a notochord and a dorsal nerve cord.
The transition from these simple forms to more complex organisms like Pikaia marks a significant step in the evolution of life on Earth.
Learn more: Did Pikaia have bones?
Where did Pikaia Live?
Pikaia gracilens lived in the ancient seas of the Cambrian period, specifically in what is now known as the Burgess Shale in British Columbia, Canada.
Scientists have found that the Burgess Shale community was a deep-sea one, situated at least 100 metres below sea level, at the foot of a large continental shelf. Nutrients washing down from the eroding landmass nearby would have created a rich and productive marine environment, supporting the development of diverse marine life (Briggs et al. 1994).
What did Pikaia eat?
While we don’t know the exact diet of Pikaia, scientists speculate that it was a filter feeder or scavenger, consuming small particles of food or organic matter suspended in the water.
You can get an idea of its potential feeding habits by looking at its closest living modern relative, the cephalochordates (lancelets), who are filter feeders.
The structure of its body, including the presence of a notochord and segmented muscles, suggests it was capable of swimming and thus could have actively pursued its food or scavenged along the ocean floor.
Discover All about what Pikaia ate.
Is Pikaia a fish?
No, we don’t consider Pikaia a fish. While it shares some characteristics with modern fish, such as a notochord and a basic body plan, it lacks other key features that would classify it as a true fish, such as jaws, fins, and a complex skeletal structure.
Get the whole story in our look at: Is Pikaia a fish?
Did Pikaia have eyes?
The fossil evidence of Pikaia does not clearly show any eyes, leading scientists to speculate that it might have had simple light-sensitive spots instead of well-developed eyes. This would have been sufficient for detecting changes in light intensity, helping it navigate the Cambrian seas.
Pikai Gracilens stands as a monumental discovery in understanding the origins of vertebrate life. As research continues, the story of Pikaia and its place in the tree of life will undoubtedly become even more fascinating.
Fossil Locations: Where Are Cambrian Fossils Like Pikaia Found?
- Pikaia itself is only known from the Burgess Shale in British Columbia, Canada
- Yet other Cambrian sites include the Chengjiang fossil site in Yunnan Province, China
- The Wheeler Shale in the House Range of western Utah, USA
- The Sirius Passet site in North Greenland is another critical location for understanding Cambrian life.
Museum Fossils: Where can you Go to See Early Chordate and other Cambrian Fossils?
If you live nearby or can make the trip, there are a few great places to go and see some of the first animals and eumetazoans, including bilaterians, protostomes, deuterostomes and chordates, for yourself…
1. The Burgess Shale
Did you know you can actually go to the Burgess Shale fossil sites in the Canadian Rockies yourself? You can book a guided hike with The Burgess Shale Geoscience Foundation and visit the Walcott quarry, Mt. Stephen – the works.
Phone 1 (250) 343-6006, email info@burgess-shale.bc.ca or visit their website
2. Royal Ontario Museum
The Royal Ontario Museum in Toronto, Canada is famous for its connection to the world-famous Cambrian site, the Burgess Shale. They have both an amazing fossil collection if you visit in-person or even here online and a cool virtual sea odyssey you can experience online right now.
Phone: 416 586 8000 (Canada) | or visit their website
3. Smithsonian National Museum of Natural History
The Smithsonian has quite a large Cambrian fossil collection. And it’s completely free! So, if you’re ever in Washington DC, it’s one of the coolest places to go check out Cambrian fossils.
4. Chengjiang Fossil Site Natural History Museum
Being in China, it’s a bit hard to track down English info. But the Chinese government says there is a Chengjiang Fossil Site Natural History Museum. With over 60’000 fossil specimens at its location in Xincun Road, Chengjiang county, Yuxi City in Yunnan province.
5. The Natural History Museum, London, UK
With a rich collection of fossils and exhibitions that trace the history of life on Earth, the London Natural History Museum’s displays on Cambrian and Precambrian life provide context for the evolution of complex organisms.
Phone +44 (0)20 7942 5000 or visit their website.
6. Field Museum of Natural History, Chicago, USA
Boasting a broad collection of fossils and active in paleontological research, its Evolving Planet exhibition takes visitors through the history of life on Earth, including the Cambrian time.
Phone +1 312 922 9410 or visit their website.
Documentaries Featuring some of the First Chordates
They’re not always 100% accurate because we make new scientific discoveries all the time. But documentaries at least deliver the gist of the information in a fun and engaging way. Just click play, hit full screen and enjoy hours’ worth of awesome documentaries on first animals, right here…
1. Walking with Monsters
BBC, 2005
A bit older now and flashing past early animals a bit too quickly, this one in the “Walking With” series is still pretty cool for its Cambrian bits. It’s also available via Amazon.
2. Mankind Rising
2012
The 2012 TV movie production of Mankind Rising is a single animated journey from the earliest vertebrate ancestors right through to present-day humans. It’s pretty cool, maybe a bit dated, but still a lot of fun!
3. David Attenborough’s Rise of Animals: Triumph of the Vertebrates
BBC, 2013
Although more focused on the evolution of vertebrates, it’s still an awesome documentary to watch. It’s available to purchase from Amazon.
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