Gill openings, a nerve chord and a primitive backbone. The Cambrian was a period of rapid evolutionary diversification around 538 to 485 million years ago, introducing a plethora of awesome prehistoric life to Earth’s ancient seas.
Among them, Pikaia gracilens stands out as an enigmatic figure, shedding light on the early evolution of chordates, the ancient precursors to all of us vertebrates.
This leads to an intriguing question about this half-a-billion-year-old creature: Did Pikaia have bones in its body?
Did Pikaia have bones?
No, we have no evidence of bones in the primitive chordate Pikaia. Its body included a notochord, though – a flexible, rod-like structure that is the precursor to the backbone vertebrates like fish, reptiles, dinosaurs and us mammals share.
But it lacked the calcified, bony structures characteristic of more evolved organisms.
The notochord provided structural support, a place to anchor muscles, which likely enabled Pikaia to move more efficiently through the water.
So, Was Pikaia Vertebrate or Invertebrate?
Technically, Pikaia gracilens was still an invertebrate. As an early chordate, it exhibited some of the foundational features that would later be seen in vertebrates, such as a notochord and a dorsal nerve cord, but it did not possess a vertebral column or other skeletal elements that would officially classify it as a vertebrate.
Discover its more evolved relatives, the stem-vertebrates Haikouichthys and Myllokunmingia as well as Zhongjianichthys.
Where Did Pikaia Live?
Pikaia gracilens lived in the Cambrian seas, around 508 million years ago. We know this because its fossil(s) was found in Canada’s famous Burgess Shale in the Rocky Mountains.
This region was part of a shallow sea during the Cambrian, and most of the fossilised creatures (including Pikaia) from this site lived in deeper water on the ocean floor at the foot of a large underwater cliff, at least 100m metres below sea level.
It would have been a thriving underwater community, with many strange-looking creatures filling the ecological niches of an ocean reef community today.
But instead of fish, you would have had large hunting arthropods and such.
Discover more: When did Pikaia go extinct?
Did Pikaia Have a Jaw?
No, Pikaia did not have a jaw. Jaws would not evolve until the much later Ordovician/Silurian – definitely by the Devonian, for sure.
As a primitive chordate, Pikaia’s feeding mechanism likely involved simple oral structures for filter-feeding or perhaps scavenging, rather than the more complex jawed mouth found in later vertebrates.
Did Pikaia Have Eyes?
The fossil records of Pikaia do not clearly show the presence of eyes. It is possible that it had simple, light-sensitive spots that helped it navigate its environment since many creatures of that time developed some form of optical structures.
But Pikaia probably did not have the complex eyes seen in many later organisms, nor do we see any evidence in Pikaia of the brain capacity necessary for eyes like ours.
Primitive light-sensory organs would have been good enough to help an early chordate detect changes in light and shadow, helping it survive in the Cambrian seas.
What Was so Special about Pikaia?
Pikaia is special because it represents one of the earliest known chordates, the evolutionary precursors to us vertebrates.
Finding it in the Burgess Shale was the first proof we humans had that notochord-bearing creatures were alive during the Cambrian time, marking it a crucial point in the evolutionary lineage leading from the first deuterostomes and bilaterians to backboned creatures.
Discover loads more amazing insights into what is so special about Pikaia.
What Did Pikaia Eat?
While it’s almost impossible to know the exact diet of Pikaia, we can speculate that it might have been either a filter-feeder, akin to some of its modern-day relatives like the Cephalochordata or lancelets, whom it somewhat resembles.
Another possibility is that it could have been a scavenger.
Either way, it might very well have spent its time consuming small organic particles or detritus suspended in the water.
Its body structure, including the notochord, suggests it was likely capable of swimming (Morris et al. 2012), which could have aided in its feeding strategy.
Learn more about Pikaia’s diet.
Is Pikaia a Fish?
No, Pikaia is not considered an actual fish. It lacks the definitive features of true fish, such as fins, scales, and a complex skeletal system.
As an early chordate, Pikaia represents a formative stage in the evolution of the chordate lineage, which predates yet would perhaps eventually lead to fish – although Pikaia is also not the direct ancestor to fish, either, but rather a contemporary to some of the first stem vertebrates, such as Zhongjianichthys.
Read the full story on: Is Pikaia a fish?
What Did Pikaia Evolve Into, Then?
Pikaia is an early chordate, part of the family that would eventually become vertebrates, but Pikaia itself is not a direct ancestor of any specific modern animal, as far as we know.
Its closest living relatives are probably primitive chordates like lancelets (Cephalochordata), “invertebrates” that still inhabit shallow, warm seas today.
The fact that we found Pikaia fossils, though, teaches us about the ancestral chordate-vertebrate condition, but the evolutionary path from early chordates like Pikaia to more complex forms involved numerous branches and transitional forms.
So, when people say Pikaia is your ancestor, that’s not quite true – in fact, Pikaia lived alongside other small animals that are much closer related to you.
Also see: Is Pikaia a fish? And: Did humans evolve from Pikaia?
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 period.
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 vertebrates 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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