Vertebral elements, possible tripartite brain and defined skull. Haikouichthys Ercaicunensis was more than a mere early chordate – recent evidence shows it was in fact a stem vertebrate.
But how does Haikouichthys fit into the tree of life and especially the story of vertebrate evolution? How and when did it live? And what major impact would it have on the history of Planet Earth?
Let’s discover…
About Haikouichthys
Haikouichthys Class & Scientific Classification
Domain: Eukaryota
Kingdom: Animalia (Metazoa)
Subkingdom: Eumetazoa
Infrakingdom: Bilateria
Superphylum: Deuterostomia
Phylum: Chordata
Paleo Classification: Stem Vertebrate
Order: Myllokunmingiida
Family: Myllokunmingiidae
Genus: Haikouichthys
Species: Haikouichthys Ercaicunensis (H. ercaicunensis)
Haikouichthys Ercaicunensis is part of the Myllokunmingiidae family, a group that diverged from chordates right before the emergence of crown-group vertebrates.
Haikouichthys Time-Frame: When it Appears on Earth
Stem vertebrate Haikouichthys Ercaicunensis appears in the fossil record during the Middle Cambrian at 518 million years ago. It was found in China and first described by Shu et al. in 1999.
Its relative Myllokunmingia was found in the same rock layers in the same place, so they were contemporaries.
Haikouichthys Characteristics (Synapomorphies)
It was always known from the 1999 holotype fossil that Haikouichthys was a chordate, but a subsequent find of more fossils revealed more previously unseen characteristics (Shu et al. 2003) that suggest it was more derived, possessing potential vertebrate characteristics:
- Vertebral elements hint at the possible evolution of bony structures around the notochord.
- A lobe-like extension in the brain, with eyes, possible nasal sacks and possible otic (hearing) capsule, suggests that Haikouichthys might have had a primitive tri-partite brain.
- A clearly defined skull.
Those are all vertebrate characteristics, placing Haikouichthys as a transitional form between chordates and vertebrates. It’s considered a stem-vertebrate, falling just outside of the crown group of Vertebrata because it’s not part of any living lineage and the body characteristics are inferred, not directly observed.
What is Haikouichthys?
Haikouichthys is an extinct genus of Cambrian chordate and a stem vertebrate of the Myllokunmingiidae family, including Myllokunmingia and Zhongjianichthys, often heralded as one of the earliest known vertebrates from China, some 518 million years ago.
It’s been proposed as a transitional form from chordates to vertebrates – the ancestors of all backboned animals, from Dimetrodon to T Rex, Mammoths and us humans.
What’s exceptionally interesting about Haikouichthys is that it lived 518 million years ago, 13 million years BEFORE the first chordate fossil we know of, Pikaia. This is absolutely fascinating because it would mean that there must have been more chordates long before Pikaia, we just haven’t found them yet.
We only know one species, Haikouichthys Ercaicunensis, from Chengjiang in Yunnan, China. But there are numerous fossils, indicating Haikouichthys – although it has no direct modern descendants – as something of a pivotal point in the evolution of vertebrates.
Is Haikouichthys the First Fish?
Well, that depends very much on how you define “fish”.
See, when it was first found Haikouichthys was touted by the media to be the “first fish” because it was just so very close to what we would expect to see in early chordate-to-vertebrate evolution. And it certainly is very fish-like: a streamlined body, primitive fins, an aquatic lifestyle – it’s even an actual vertebrate (well, stem vertebrate, falling just outside the crown group of Vertebrata).
So, in the sense of it being an early fish, yes, definitely.
But note: Haikouichthys does not have all the features you would ascribe to a fish today – it is very primitive. And, if you want to be very technical, you could argue that, since it’s a stem vertebrate and not part of the crown group of Vertebrata (which is what includes all extinct and living groups of true fish), it’s not the direct ancestor of what we might call the first true fish.
In fact, it’s probably more correct to say that Haikouichthys shared a common ancestor with fish. But, as we said, that’s a very technical approach.
About Agnathan Fishes
If you like getting technical about these kinds of things, consider this: Haikouichthys is commonly touted in the media as an early “agnathan” (jawless fish), which you could argue is wrong because:
- Haikouichthys and in fact all of the Myllokunmingiidae family (Myllokunmingia) had no descendants. They could not be directly linked to anything within the vertebrate crown group (where fishes are), meaning they went extinct without leaving any descendants whatsoever, so they couldn’t possibly even be fish ancestors, let alone fish themselves. They merely shared a common ancestor with true fish.
- The former group of “agnatha” was recently found to be paraphyletic – basically just wrong – and no longer means what people think – we’re not really sure if it should even be recognised as an actual phylogenetic classification.
If you’re interested, the story of “Agnatha” goes: we thought that all jawed fishes (gnathostomes) evolved from jawless fishes. This was convenient because phylogenetically, we could just have an “agnatha” node which diverged neatly into cyclostomes (hagfishes and lampreys) and gnathostomes (all other fishes [jawed]). But it was wrong.
Recently, scientists found that the cyclostome-gnathostome divergence happened much earlier than we thought. The truth is that two biologically distinct lines of early jawless fishes lived at the same time; one is closer to the cyclostome (true jawless fishes) line, and the other leads directly to the gnathostome (jawed fish) line. This means the term agnatha is paraphyletic, which isn’t scientifically sound. And some scientists are trying to change the definition of agnatha to mean something slightly different.
Haikouichthys is certainly very fish-like, a vertebrate, yes, but not the direct ancestor of all fish, as far as we know. It’s as close as we’ve ever gotten to finding that true ancestor, though.
Did Haikouichthys Have Eyes?
Although the original 1999 holotype fossil didn’t show it clearly, the subsequent 2003 additional fossils clearly show that Haikouichthys possessed simple eyes, indicative of an ability to sense its surroundings visually. These eyes, while not complex, mark an essential evolutionary adaptation, facilitating a more interactive engagement with the environment.
New Haikouichthys Fossils
Did Haikouichthys Have a Skull?
While the first specimen of Haikouichthys did not seem to have a skull, the later finding of some 500 specimens shows that it did indeed have a rudimentary skull.
Although not of bone like the skulls we know, Haikouichthtys did have what seems to be a rudimentary perhaps even cartilaginous brain encasing.
What is Haikouichthys’ Size?
The average size among over 500 specimens we have of Haikouichthys is around 2.5cm in length. Though it ranges greatly in size, from just 1cm upwards.
Its diminutive size suggests it occupied a niche low in the prehistoric food chain, potentially feeding on microscopic organisms or scavenging.
What Did Haikouichthys Evolve From?
Haikouichthys likely evolved from earlier, simpler chordates that possessed a notochord but lacked the more advanced features of vertebrates. It would have diverged from the true and as yet undiscovered vertebrate ancestor just before the crown group Vertebrata‘s appearance.
Haikouichthys’s evolution and existence reflect a significant evolutionary transition from invertebrate chordates to more complex vertebrates.
Also discover the slightly larger stem vertebrate, Metaspriggina.
What Did Haikouichthys Evolve Into?
Haikouichthys itself doesn’t seem to have evolved into anything. Or at least, went extinct without leaving any living relatives. As an early stem vertebrate Haikouichthys diverged from the main vertebrate lineage and went extinct without leaving any direct descendants, as far as we can tell.
As an early chordate-vertebrate member, though, It is still a stem-group member of the lineage that would diversify into all modern fish, amphibians, reptiles, birds, and mammals).
An Actual Haikouichthys Fossil
When & Where was the First Haikouichthys Fossil Found?
The first Haikouichthys fossil was discovered in the Maotianshan Shales of Yunnan Province, China and described in 1999. A few years later, over 500 more specimens were found in the same rock layers.
Fossil Locations: Where Are Cambrian Fossils Like Haikouichthys Found?
- Haikouichthys itself is only known from the Chengjiang fossil site in Yunnan Province, China
- Yet other Cambrian sites include the Burgess Shale in British Columbia, Canada
- 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. 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.
2. 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.
3. 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
4. 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.
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 & Vertebrates
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
This chapter in the “Walking With” series is an absolute must for Haikouichthys fans, because it’s the main character in the Cambrian segments, facing off against the mighty Anomalocaris. 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!
You’ll notice it starts off, right after the anchornworm-like ancestor, with a fish-like creature called “Milo”. That stands for Myllokunmingiidae, the family that Haikouichthys belongs to. Or possibly it’s relative, Myllokunmingia.
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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