Small but mighty, chordates are evolutionary giants. These bilaterian eumetazoan animals are the first deuterostome organisms to develop the structures we recognise as the primitive beginnings of a backbone.
Though chordates are not quite vertebrates (backboned animals) just yet, they do have a notochord and dorsal nerve chord, which will eventually become the backbone that all vertebrates, from Dunkleosteus and T Rex to Smilodon all the way down to us humans, share.
But when did the first chordates (chordata) first show up? Which prehistoric creatures are chordates? And where can you go to see their fossils?
About Chordates (Chordata)
Scientific Classification of Chordates
Domain: Eukaryota
Kingdom: Animalia (Metazoa)
Subkingdom: Eumetazoa
Infrakingdom: Bilateria
Superphylum: Deuterostomia
Phylum: Chordata
Chordate Time Frame: When did they First Appear on Earth?
When we infer chordates’ first appearance through DNA, the molecular clock estimates the first chordates might have appeared between the Proterozoic, 1 billion years ago and the Ediacaran’s Vendian, 544 million years ago (Ayala et al. 1998).
However, the first body fossils are from the Cambrian: Haikouichthys Ercaicunensis, Myllokunmingia and Zhongjianichthys, 518 million years ago; Pikaia Gracilens and Metaspriggina Walcotti, 505 million years ago.
Characteristics (Synapomorphies) of Chordates
- All chordates inherited the pharyngeal gill slits of deuterostomes.
- But also have a notochord – a rod made of cartilage that’s considered to be the precursor to our backbones.
- As well as a dorsal nerve chord, running along the notochord in their back (another primitive part of our vertebrate backbones).
- A post-anal tail, meaning a tail that extends further back on the body than the anus (non-chordates don’t have this, their anus [if they have one separate from their mouths] often extends all the way to the “tail”, or it sits somewhere else on the body entirely).
What are Chordates Exactly?
Chordata is one of the 9 best-known main animal phyla. But chordates are more than just a fancy taxonomic group. They represent a major turning point in the story of life on Earth.
Chordates are the first creatures to develop the structures that would eventually become the backbone shared by all of the most amazing prehistoric and living creatures you love – from Dimetrodon to Velociraptor to Mammoths and all the vertebrate animals alive today, all the way down to you.
While most other animal groups built exoskeletons (arthropods, mollusks etc.) or no “hard parts” at all (echinoderms, jellyfish etc.), chordates developed a stiff rod in their backs and anchored powerful muscles off it, to power themselves through the water – a structure that later would work well on land, too.
They might be super small and seemingly harmless compared to the big arthropod predators back in the Cambrian and Ordovician. But make no mistake, one family line of these little guys’ descendants will go on to one day rule the world – can you guess which?
What are the First Chordates Fossils?
Technically, Pikaia Gacilens (Morris 2013) is the oldest-known specifically chordate fossil. It’s a small worm/fish-like creature that lived 505 million years ago, first discovered in Canada’s famous Burgess Shale middle-Cambrian lagerstätte back in 1911 by none other than palaeontologist Charles Doolittle Walcott himself.
But, there’s a bit of a funny edge to this story.
See, Walcott also found another somewhat similar creature, Metaspriggina Walcotti (Morris 2008), which is also 505 million years old. And, many years later, in China, Haikouichthys and Myllokunmingia as well as Zhongjianichthys (Shu et al. 2003) were found – but even older at 518 million years old.
Now, all 3 of these had notochords and all of the characteristics of chordates. So for some time, the race was on to discover which of the 3 was the true first chordate (because they’re all technically chordates).
But then something magical happened, scientists found out that Metaspriggina, Haikouichthys and Myllokunmingia were actually even more developed than Pikaia – they weren’t just chordates, they were stem vertebrates (almost vertebrates)!
This means, if you want to be technical, Pikaia is still the “first” primitive chordate, and Metaspriggina, Myllokunmingia, Haikouichthys and Zhongjianichthys are already vertebrates. And they lived side-by-side(ish) – insane!
Plus Find out: Did Pikaia have bones? And: Is Pikaia a fish? Also: When did Pikaia go extinct? And: What did Pikaia eat?
6 Animals and Groups that are Chordates
1. Pikaia Gacilens
Officially one of the oldest fossils we have of a truly primitive Cambrian chordate. Pikaia Gacilens was a 3.8cm chordate with a “lancelet-like” body (almost like a worm with tiny fins) found in 1911 by Charles Doolittle Walcott in Canada’s Burgess Shale.
Originally thought to be a type of annelid (worm) by Walcott, Pikaia was redescribed as a chordate in 1979. Plus Find out: Did Pikaia have bones? And did humans evolve from Pikaia? Also discover: Pikaia size.
2. Metaspriggina Walcotti
Another amazing Cambrian find by Walcott himself, Metaspriggina is an eel-like specimen slightly larger than Pikaia at 7cm. And, though Walcott didn’t know where to place it, it was in 1979 considered to be a descendant of the Ediacaran fossil Spriggina.
But after more specimens were found in 2001, it was reinterpreted (Caron and Morris 2014) as not only a chordate but a primitive (stem) vertebrate, and thus a kind of early fish.
Learn more about the fascinating Metaspriggina.
3. The Myllokunmingiidae Family
In recent years, an entire family of Cambrian chordate stem vertebrates were discovered in China, which includes the family of Myllokunmingiidae and genera Haikouichthys Ercaicunensis (Shu et al. 2003), Myllokunmingia Fengjiaoa (Morris et al. 2014) and Zhongjianichthys Rostratus (Shu et al. 2003).
4. All Vertebrates
Oh-ho, now it gets interesting: All vertebrates, meaning every creature with a backbone, are descendants of chordates. Starting from super-primitive members in the Cambrian to insane Ordovician-Devonian fish diversity to tetrapods first crawling on land in the Carboniferous to synapsid, dinosaurs, mammals like lions, tigers and elephants, all the way to you – all us vertebrates come from chordates.
5. Cephalochordates (Lancelets)
Still alive today, Lancelets are small fish-like filter-feeding creatures that generally sit half-buried in the sands of tropical coastal marine shelves and filter feed. They are a bit of an enigma since they retain what seems to be primitive chordate features – notochord, nerve chord and post-anal tail – yet they do not use their gills for breathing, only feeding. What’s more, we don’t have great fossils for them, so whether this is the ancestral chordate condition remains a mystery.
That said, they are still one of our closest “invertebrate” chordate relatives.
6. Weird and Wonderful Tunicates
Another “invertebrate” chordate, tunicates are still alive today. And you would never have guessed that this is your closest “invertebrate” relative, because adult tunicates are beyond weird: Adults are sessile filter feeders – sometimes loners who resemble tube-like organs sitting and filter-feeding at the bottom of the ocean floor.
But they can also form great colonies of tube-like structures that resemble sponges or corals, floating freely in the ocean.
The trick to recognising them as chordates lies in observing their larva. The weird adult stage is preceded by a larval stage which you’d recognise – tunicate larvas look and swim like little fish, with notochords and post-anal tail etc. It’s only when they get older that they anchor themselves and become something way different.
Fossil locations: 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 and deuterostomes, 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.
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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