Deuterostomes are all bilaterians, and thus eumetazoan animals, who fall into the superphylum of Deuterostomia (meaning “second mouth”), characterised by the mouth forming after the anus in embryonic development as well as pharyngeal gill slits.
This includes all animals on the echinoderm line, as well as all chordates – important because chordates are what become vertebrates, which includes everything from fish to amphibians, reptiles, dinosaurs, birds and mammals like us!
But when did our Deuterostome ancestors first show up on Earth and where can you go to see their fossils?
About Deuterostomes
Scientific Classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Infrakingdom: Bilateria
Superphylum: Deuterostomia
Time Frames
Molecular Clock: Most say Cryogenian, 670 million years ago (Ayala et al. 1998) but some contend it may have been earlier: circa 900 million years ago (Blair et al. 2005)
First Body Fossils: Cambrian, Haikouichthys Ercaicunensis, Myllokunmingia and Zhongjianichthys, from the Myllokunmingiidae family, 518 million years ago; Pikaia Gracilens and Metaspriggina Walcotti, 505 million years ago.
Characteristics (Synapomorphies)
1. Deuterostomes are unified by their unique embryonic development; unlike other animals, their anus forms from the first opening in the embryo, and the mouth develops later. This hallmark is accompanied by a complex nervous system, a skeletal structure (in chordates), and a water vascular system (in echinoderms), among other features.
2. Deuterostomes also have pharyngeal gill slits – a series of openings on the pharynx (throat) during embryonic development (yes, dinosaurs and human embryos have gills!), and oftentimes during their entire lifetime, like fish who turn them into gills.
What are Deuterostomes Exactly?
Deuterostomia is not something observable in the fossil record per se, but rather a set of traits that biologists observed by studying the embryonic development of modern animals.
As early as the 1800s, scientists looking at the developing embryos of a range of animals noticed that bilaterians (who have bilateral symmetry as embryos) develop in two easily distinguishable ways.
In Deuterostomes (meaning “second mouth”) the cells that will one day become the intestinal tract form, and then two openings at either end – the first opening that forms is the anus. Deuterostomes’ mouths form second, thus “second mouth”.
Deutorestomes also have pharyngeal gill slits as embryos. Fish, who are chordates and vertebrates, for example, turn those into their mouths and gills. But all vertebrates – crocodiles, T Rex, velociraptors and us mammals also have these gill slits as embryos, we just reappropriate them to become jaws and ears etc. after birth.
All creatures on the echinoderm line and all chordates – including vertebrates such as fish, birds, crocodiles dinosaurs and us mammals – are deuterostomes.
Are Humans a Deuterostomes?
Yes, humans are most certainly deuterostomes. All vertebrates are deuterostomes, and since we’re vertebrates (we have a backbone), so are we.
Bet you never thought you’re more closely related to a starfish and sea urchin than an octopus, did you?
How are Protostomes different to Deuterostomes?
Protostomes (meaning “first mouth” are kind of the flipside to deuterostomes – also bilaterians, but in embryonic development, protostomes develop their mouth before the anus. Thus: “first mouth”.
All the other bilaterian animals, from mollusks like octopuses and cuttlefish to worms, brachiopods and arthropods – crustaceans, insects etc. – are protostomes.
What are the First Deuterostome Fossils?
Today we know Metaspriggina Walcotti (Morris 2008) and Pikaia Gacilens (Morris 2013) are both 505-million-year-old Cambrian chordates from the famous Burgess Shale and can be considered the second oldest deutorestome fossils.
There’s a bit of a history, though, since both species were discovered in the early 1900s already but misinterpreted and misdescribed for decades. It was really only after the much more recent discovery of older 518-million-year-old chordates like Haikouichthys, Zhongjianichthys and Myllokunmingia (Shu et al. 2003) in China that anyone seriously considered chordates could have been around since the Cambrian.
That prompted Western scientists to go back and reinterpret the 100-year-old Metaspriggina and Pikai fossils as chordates (and thus deuterostomes), too.
Also see: Is Pikaia a fish? And: Did humans evolve from Pikaia? Also: What did Pikaia Eat?
2 Major Animal Groups that are Deuterostomes
1. Chordates
Chordates encompass a broad range of animals, including lancelets, tunicates, and all vertebrates (fish, amphibians, reptiles, dinosaurs, birds, and mammals like you!).
This group is characterised by having a notochord at some stage in their development. Vertebrates, a subset of chordates, are particularly notable for their complex nervous systems and adaptive capabilities, which have allowed them to inhabit nearly every ecosystem on Earth, from deep oceans to high mountains.
Chordates are deuterostomes that first show up in the fossil record in the Cambrian time. Discover some of the earliest known chordates.
2. Echinoderms
Echinoderms, such as starfish, sea urchins, and sea cucumbers, are unique for their radial symmetry (later in life, as embryos they have bilateral symmetry like the rest of us) and remarkable regenerative abilities.
Starfish, for instance, can regrow lost arms; in some cases, a single arm can regenerate into an entirely new starfish. This group plays a pivotal role in the ocean’s ecosystems, often acting as keystone species that significantly influence the ecological balance.
Echinoderms first show up in the fossil record in the Cambrian.
Fossil locations: Where can you Go to See Early Deuterostome 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 Deutoretomes
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. 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.
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. 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.
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